Coherent detection of data and timing signals over optical fiber for telescope networks
- Authors: Nfanyana, Ketshabile
- Date: 2020
- Subjects: Fiber optics , Very large array telescopes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/49226 , vital:41612
- Description: Telescope networks are increasingly being developed with networks such as the SKA telescope demanding the use of high-end technology to be incorporated. These networks require accurate clock signals to be transported to antennas as well as massive data to be transported from individual parabolic array antennas to a central computer for data analysis. To achieve this, optical fiber technology forms the backbone of these networks, proving high speed transmission and required bandwidth. For a distributed telescope network, coherent detection technology serves as the ideal optical fiber technology candidate for transport of information to a correlator. Use of this technology constitutes too many benefits. Sensitivity of the system is improved, and advanced modulation formats can be employed thereby improving spectral efficiency. Furthermore, coherent detection allows for digital signal processing algorithms to be employed for equalization of transmission impairments such as chromatic dispersion (CD), polarization mode dispersion (PMD), phase noise and nonlinear effects in the electrical domain. CD equalization is performed in the time or frequency domain using digital filters which suppress the fibers dispersion effectively. PMD equalization is usually performed in the time domain through the use of adaptive filters which employ algorithms such as least mean squares (LMS) and constant modulus algorithm (CMA). These algorithms further equalize residual CD. In mitigation of phase noise (carrier phase recovery), feed-forward and feedback carrier phase algorithms are used. Fiber nonlinearities and other impairments are compensated using the digital backpropagation algorithm which solves for the Manakov equation and nonlinear Schrödinger equation (NLSE). Distribution of stable clock signals to individual antennas is an important aspect of telescope networks. Clock signals are used to drive the digitizers and time stamping of received antenna information. These clock signals can be distributed using coherent detection technology by phase modulating the clock so as to provide inherent phase modulation robustness to noise through the fiber. In this thesis, we present coherent detection of non-return-to-zero pseudorandom binary sequence (PRBS-7) using binary phase shift keying (BPSK) through 26.6 km non-zero dispersion shifted fiber (NZDSF) at 10 Gbps. Digital signal processing for equalization of CD and PMD was performed offline using MATLAB software. For residual CD and PMD equalization, the LMS algorithm was used. The performance of the system, bit error rate (BER), was compared with that of an intensity modulated on-off keying (OOK) signal at the same bit rate. Basing on receiver sensitivity performance of OOK at 10-9 bit error rate, BPSK achieved superior performance with receiver sensitivity improvements of 18.37 dB and 13.89 dB attained for back-to-back and transmission over fiber, respectively. Phase modulation transmission of a 4 GHz clock signal was also conducted. Frequency instability, Allan variance and phase noise, of phase modulated clock was compared with that of intensity modulated clock. Moreover, we present an all optical clock generation scheme using frequency heterodyning technique. Allan variance values in the range of 10-10 were attained. The frequency instability of this clock generation scheme was quantified using the spectrum analyzer method. Furthermore, an all-photonic technique for data latency tracking of 5G networks over optical fiber is presented. The technique is spectrally efficient and is able to track latency down to the nano second timescale.
- Full Text:
- Date Issued: 2020
- Authors: Nfanyana, Ketshabile
- Date: 2020
- Subjects: Fiber optics , Very large array telescopes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/49226 , vital:41612
- Description: Telescope networks are increasingly being developed with networks such as the SKA telescope demanding the use of high-end technology to be incorporated. These networks require accurate clock signals to be transported to antennas as well as massive data to be transported from individual parabolic array antennas to a central computer for data analysis. To achieve this, optical fiber technology forms the backbone of these networks, proving high speed transmission and required bandwidth. For a distributed telescope network, coherent detection technology serves as the ideal optical fiber technology candidate for transport of information to a correlator. Use of this technology constitutes too many benefits. Sensitivity of the system is improved, and advanced modulation formats can be employed thereby improving spectral efficiency. Furthermore, coherent detection allows for digital signal processing algorithms to be employed for equalization of transmission impairments such as chromatic dispersion (CD), polarization mode dispersion (PMD), phase noise and nonlinear effects in the electrical domain. CD equalization is performed in the time or frequency domain using digital filters which suppress the fibers dispersion effectively. PMD equalization is usually performed in the time domain through the use of adaptive filters which employ algorithms such as least mean squares (LMS) and constant modulus algorithm (CMA). These algorithms further equalize residual CD. In mitigation of phase noise (carrier phase recovery), feed-forward and feedback carrier phase algorithms are used. Fiber nonlinearities and other impairments are compensated using the digital backpropagation algorithm which solves for the Manakov equation and nonlinear Schrödinger equation (NLSE). Distribution of stable clock signals to individual antennas is an important aspect of telescope networks. Clock signals are used to drive the digitizers and time stamping of received antenna information. These clock signals can be distributed using coherent detection technology by phase modulating the clock so as to provide inherent phase modulation robustness to noise through the fiber. In this thesis, we present coherent detection of non-return-to-zero pseudorandom binary sequence (PRBS-7) using binary phase shift keying (BPSK) through 26.6 km non-zero dispersion shifted fiber (NZDSF) at 10 Gbps. Digital signal processing for equalization of CD and PMD was performed offline using MATLAB software. For residual CD and PMD equalization, the LMS algorithm was used. The performance of the system, bit error rate (BER), was compared with that of an intensity modulated on-off keying (OOK) signal at the same bit rate. Basing on receiver sensitivity performance of OOK at 10-9 bit error rate, BPSK achieved superior performance with receiver sensitivity improvements of 18.37 dB and 13.89 dB attained for back-to-back and transmission over fiber, respectively. Phase modulation transmission of a 4 GHz clock signal was also conducted. Frequency instability, Allan variance and phase noise, of phase modulated clock was compared with that of intensity modulated clock. Moreover, we present an all optical clock generation scheme using frequency heterodyning technique. Allan variance values in the range of 10-10 were attained. The frequency instability of this clock generation scheme was quantified using the spectrum analyzer method. Furthermore, an all-photonic technique for data latency tracking of 5G networks over optical fiber is presented. The technique is spectrally efficient and is able to track latency down to the nano second timescale.
- Full Text:
- Date Issued: 2020
Data transport over optical fibre for ska using advanced modulation flexible spectrum technology
- Authors: Dlamini, Phumla Patience
- Date: 2020
- Subjects: Fiber optics
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/50666 , vital:42329
- Description: Flexible Spectrum Dense Wavelength Division Multiplexed (DWDM) optical fibre networks are next-generation technology for handling extremely high data rates of the kind produced by MeerKAT and SKA.We optimise the flexible spectrum for real-time dynamic channel wavelength assignment, to ensure optimum network performance. We needed to identify and develop novel hardware and dynamic algorithms for these networks to function optimally to perform critical tasks. Such tasks include wavelength assignment, signal routing, network restoration and network protection. The antennas of the Square Kilometre Array (SKA) network connect to the correlator and data processor in a simple point-to-point fixed configuration. The connection of the astronomer users to the data processor, however, requires a more complex network architecture. This is because the network has users scattered around South Africa, Africa and the whole world. This calls for upgrade of the classical fixed wavelength spectrum grids, to flexible spectrum grid that has improved capacity, reliable, simple and cost-effectiveness through sharing of network infrastructure. The exponential growth of data traffic in current optical communication networks requires higher capacity for the bandwidth demands at a reduced cost per bit. All-optical signal processing is a promising technique to improve network resource utilisation and resolve wavelength contention associated with the flexible spectrum. Flexible Spectrum Dense Wavelength Division Multiplexed (DWDM) optical fibre networks are next-generation technology for handling extremely high data rates of the kind produced by MeerKAT and SKA. Each DWDM channel is capable of 10 Gbps transmission rate, which is sliceable into finer flexible grid 12.5 GHz granularity to offer the network elastic spectrum and channel spacing capable of signal routing and wavelength switching for the scalability of aggregate bandwidth. The variable-sized portions of the flexible spectrum assignment to end users at different speeds depend on bandwidth demand, allowing efficient utilisation of the spectrum resources. The entire bandwidth of dynamic optical connections must be contiguously allocated. However, there is an introduction of spectrum fragmentation due to spectrum contiguity related to the optical channels having different width. Thus large traffic demands are likely to experience blocking regardless of available bandwidth. To minimise the congestion and cost-effectively obtain high performance, the optical network must be reconfigurable, achievable by adding wavelength as an extra degree of freedom for effectiveness. This can introduce colourless, directionless and contentionless reconfigurability to route individual wavelengths from fibre to fibre across multiple nodes to avoid wavelength blocking/collisions, increasing the flexibility and capacity of a network. For these networks to function optimally, novel hardware and dynamic algorithms identification and development is a critical task. Such tasks include wavelength assignment, signal routing, network restoration and network protection. In this work, we for the first time to our knowledge proposed a spectrum defragmentation technique through reallocation of the central frequency of the optical transmitter, to increase the probability of finding a sufficient continuous spectrum. This is to improve network resource utilisation, capacity and resolve wavelength contention associated with a flexible spectrum in optical communication networks. The following chapter provides details on a flexible spectrum in optical fibre networks utilising DWDM, optimising transmitter-receivers, advanced modulation formats, coherent detection, reconfigurable optical add and drop multiplexer (ROADM) technology to implement hardware and middleware platforms which address growing bandwidth demands for scalability, flexibility and cost-efficiency. A major attribute is tunable lasers, an essential component for future flexible spectrum with application to wavelength switching, routing, wavelength conversion and ROADM for the multi-node optical network through spectrum flexibility and cost-effective sharing of fibre links, transmitters and receivers. Spectrum slicing into fine granular sub-carriers and assigning several frequency slots to accommodate diverse traffic demands is a viable approach. This work experimentally presents a spectral efficient technique for bandwidth variability, wavelength allocation, routing, defragmentation and wavelength selective switches in the nodes of a network, capable of removing the fixed grid spacing using low cost, high bandwidth, power-efficient and wavelength-tunable vertical-cavity surface-emitting laser (VCSEL) transmitter directly modulated with 10 Gbps data. This to ensure that majority of the spectrum utilisation at finer channel spacing, wastage of the spectrum resource as caused by the wavelength continuity constraint reduction and it improves bandwidth utilisation. The technique is flexible in terms of modulation formats and accommodates various formats with spectrally continuous channels, fulfilling the future bandwidth demands with transmissions beyond 100 Gbps per channel while maintaining spectral efficiency.
- Full Text:
- Date Issued: 2020
- Authors: Dlamini, Phumla Patience
- Date: 2020
- Subjects: Fiber optics
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/50666 , vital:42329
- Description: Flexible Spectrum Dense Wavelength Division Multiplexed (DWDM) optical fibre networks are next-generation technology for handling extremely high data rates of the kind produced by MeerKAT and SKA.We optimise the flexible spectrum for real-time dynamic channel wavelength assignment, to ensure optimum network performance. We needed to identify and develop novel hardware and dynamic algorithms for these networks to function optimally to perform critical tasks. Such tasks include wavelength assignment, signal routing, network restoration and network protection. The antennas of the Square Kilometre Array (SKA) network connect to the correlator and data processor in a simple point-to-point fixed configuration. The connection of the astronomer users to the data processor, however, requires a more complex network architecture. This is because the network has users scattered around South Africa, Africa and the whole world. This calls for upgrade of the classical fixed wavelength spectrum grids, to flexible spectrum grid that has improved capacity, reliable, simple and cost-effectiveness through sharing of network infrastructure. The exponential growth of data traffic in current optical communication networks requires higher capacity for the bandwidth demands at a reduced cost per bit. All-optical signal processing is a promising technique to improve network resource utilisation and resolve wavelength contention associated with the flexible spectrum. Flexible Spectrum Dense Wavelength Division Multiplexed (DWDM) optical fibre networks are next-generation technology for handling extremely high data rates of the kind produced by MeerKAT and SKA. Each DWDM channel is capable of 10 Gbps transmission rate, which is sliceable into finer flexible grid 12.5 GHz granularity to offer the network elastic spectrum and channel spacing capable of signal routing and wavelength switching for the scalability of aggregate bandwidth. The variable-sized portions of the flexible spectrum assignment to end users at different speeds depend on bandwidth demand, allowing efficient utilisation of the spectrum resources. The entire bandwidth of dynamic optical connections must be contiguously allocated. However, there is an introduction of spectrum fragmentation due to spectrum contiguity related to the optical channels having different width. Thus large traffic demands are likely to experience blocking regardless of available bandwidth. To minimise the congestion and cost-effectively obtain high performance, the optical network must be reconfigurable, achievable by adding wavelength as an extra degree of freedom for effectiveness. This can introduce colourless, directionless and contentionless reconfigurability to route individual wavelengths from fibre to fibre across multiple nodes to avoid wavelength blocking/collisions, increasing the flexibility and capacity of a network. For these networks to function optimally, novel hardware and dynamic algorithms identification and development is a critical task. Such tasks include wavelength assignment, signal routing, network restoration and network protection. In this work, we for the first time to our knowledge proposed a spectrum defragmentation technique through reallocation of the central frequency of the optical transmitter, to increase the probability of finding a sufficient continuous spectrum. This is to improve network resource utilisation, capacity and resolve wavelength contention associated with a flexible spectrum in optical communication networks. The following chapter provides details on a flexible spectrum in optical fibre networks utilising DWDM, optimising transmitter-receivers, advanced modulation formats, coherent detection, reconfigurable optical add and drop multiplexer (ROADM) technology to implement hardware and middleware platforms which address growing bandwidth demands for scalability, flexibility and cost-efficiency. A major attribute is tunable lasers, an essential component for future flexible spectrum with application to wavelength switching, routing, wavelength conversion and ROADM for the multi-node optical network through spectrum flexibility and cost-effective sharing of fibre links, transmitters and receivers. Spectrum slicing into fine granular sub-carriers and assigning several frequency slots to accommodate diverse traffic demands is a viable approach. This work experimentally presents a spectral efficient technique for bandwidth variability, wavelength allocation, routing, defragmentation and wavelength selective switches in the nodes of a network, capable of removing the fixed grid spacing using low cost, high bandwidth, power-efficient and wavelength-tunable vertical-cavity surface-emitting laser (VCSEL) transmitter directly modulated with 10 Gbps data. This to ensure that majority of the spectrum utilisation at finer channel spacing, wastage of the spectrum resource as caused by the wavelength continuity constraint reduction and it improves bandwidth utilisation. The technique is flexible in terms of modulation formats and accommodates various formats with spectrally continuous channels, fulfilling the future bandwidth demands with transmissions beyond 100 Gbps per channel while maintaining spectral efficiency.
- Full Text:
- Date Issued: 2020
Compensation for distribution of timing and reference signals over optical fibre networks for telescope arrays
- Authors: Wassin, Shukree
- Date: 2018
- Subjects: Fiber optics , Optical communications Very large array telescopes Optical fiber detectors
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/36425 , vital:33941
- Description: Significant advancements and developments have been made in optical frequency standards, in recent years. In order to verify the accuracy and preciseness of the disseminated RF signal, it is essential to compare its stability with the standards provided in literature as well as by metrology institutes. However, conventional frequency comparison techniques via satellites have extremely inferior stability qualities. As a result, the need for an alternative ultra-high precision RF transfer method presented itself. Highly accurate and precise frequency dissemination across optical fiber has proved a leading contender and a possible solution. When compared to conventional data transfer media, optical fiber has proven to be more superior and yields lower transmission errors and is immune to radio frequency interference. A further quality of optical fibre is that its transmission distance can be extended to greater degree than the traditional coaxial cable due to its low loss property. This thesis deals with the compensation of phase noise in single mode optical fibre. Phase noise degrades the performance and stability of the RF signal as well as the optical carrier frequency across long-haul optical networks. This work begins by experimentally demonstrating a unique and novel way for measuring the round-trip optical fibre latency times. The technique is based on all optical wavelength conversion using a stable PPS injection signal. The result highlighted the importance for active phase error compensation along a fibre link. Various computer simulations were used to study the influence of temperature fluctuation on the optical fibre. The first ever error signals generated at NMU was experimentally demonstrated. Results illustrated that, by minimizing the error voltage the phase difference between the transmitted and reference signals were reduced to zero. Performance analysis testing of the VCSEL phase correction actuator showed that majority of the dither iterations that induced the phase compensation took approximately 0.15 s. Residual frequency instabilities of 3.39791 x 10-12 at 1 s and 8.14848 x 10-12 at 103 s was measured when the 26 km G.655 fibre link was running freely. Experimental results further showed that the relative frequency stabilities measured at 1 s and 103 s were 4.43902 x 10-12 and 1.62055 x 10-13 during active compensation, respectively. The novel work presented in this thesis is exciting since the VCSEL is used as the optical source as well as the phase correction actuator. The benefits of such a device is that is reduces system costs and complexities.
- Full Text:
- Date Issued: 2018
- Authors: Wassin, Shukree
- Date: 2018
- Subjects: Fiber optics , Optical communications Very large array telescopes Optical fiber detectors
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/36425 , vital:33941
- Description: Significant advancements and developments have been made in optical frequency standards, in recent years. In order to verify the accuracy and preciseness of the disseminated RF signal, it is essential to compare its stability with the standards provided in literature as well as by metrology institutes. However, conventional frequency comparison techniques via satellites have extremely inferior stability qualities. As a result, the need for an alternative ultra-high precision RF transfer method presented itself. Highly accurate and precise frequency dissemination across optical fiber has proved a leading contender and a possible solution. When compared to conventional data transfer media, optical fiber has proven to be more superior and yields lower transmission errors and is immune to radio frequency interference. A further quality of optical fibre is that its transmission distance can be extended to greater degree than the traditional coaxial cable due to its low loss property. This thesis deals with the compensation of phase noise in single mode optical fibre. Phase noise degrades the performance and stability of the RF signal as well as the optical carrier frequency across long-haul optical networks. This work begins by experimentally demonstrating a unique and novel way for measuring the round-trip optical fibre latency times. The technique is based on all optical wavelength conversion using a stable PPS injection signal. The result highlighted the importance for active phase error compensation along a fibre link. Various computer simulations were used to study the influence of temperature fluctuation on the optical fibre. The first ever error signals generated at NMU was experimentally demonstrated. Results illustrated that, by minimizing the error voltage the phase difference between the transmitted and reference signals were reduced to zero. Performance analysis testing of the VCSEL phase correction actuator showed that majority of the dither iterations that induced the phase compensation took approximately 0.15 s. Residual frequency instabilities of 3.39791 x 10-12 at 1 s and 8.14848 x 10-12 at 103 s was measured when the 26 km G.655 fibre link was running freely. Experimental results further showed that the relative frequency stabilities measured at 1 s and 103 s were 4.43902 x 10-12 and 1.62055 x 10-13 during active compensation, respectively. The novel work presented in this thesis is exciting since the VCSEL is used as the optical source as well as the phase correction actuator. The benefits of such a device is that is reduces system costs and complexities.
- Full Text:
- Date Issued: 2018
Fibre optic network supporting high speed transmission in the square kilometre array, South Africa
- Authors: Rotich, Enoch Kirwa
- Date: 2015
- Subjects: Optical communications , Fiber optics , Telecommunication systems
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/6552 , vital:21109
- Description: This thesis provides in-depth information on the high speed optical transport requirements for the Square Kilometre Array. The stringent data rates as well as timing and synchronization requirements are dealt with respect to the optical fibre technology. Regarding the data transport, we draw a clear comparison between a typical telecommunication access network and a telescope network. Invoking simulations and experiments on the field and laboratory test bed, we successfully implement a suitable telescope network using vertical cavity surface emitting laser (VCSEL) technology. Polarization effects on the KAT-7 telescope network, an operational prototype for the SKA is studied so as to estimate the expected effect in the MeerKAT telescope with transmission distances _ 12 km. The study further relates the obtained values to the expected impact on the distribution of the time and frequency reference in the MeerKAT array. Clock stability depends on the differential group delay (DGD) and polarization stability. On a 10:25 km link that includes the riser cable a DGD of 62:1 fs was attained. This corresponds to a polarization mode dispersion (PMD) coefficient of 19:4 fs=km1=2. This is a low PMD value considering telecommunication network. The PMD value is within the allowed budget in the telescope network. However, this may not be the case at longer baselines extending to over 1000 km as expected in SKA 2. The fibre's deployment contribution to the DGD is measured by comparing the deployed fibre to the undeployed of equal lengths. On the 10:25 km deployed single mode fibre, the maximum and mean DGDs measured were 217:7 fs and 84:8 fs respectively. The undeployed fibre of similar type and equal length, gave a maximum and minimum DGDs of 58:6 fs and 36:3 fs respectively. The deployment is seen to increase the maximum and minimum DGDs by factors of 3.7 and 2.3 respectively. This implies that fibre deployment is very critical in ensuring the birefringence is minimized. Polarization fluctuation recorded a maximum of 180o during the 15 hour real time astronomer use of the antenna. To ascertain the contribution of the riser cable, state of polarization (SOP) of the buried section of the single mode fibre in the link was established. A maximum SOP change of 14o over 15 hour monitoring was measured. From the stability realized on the buried section of the fibre, the change in polarization is contributed by the riser cable. The fluctuation in polarization can cause the phase of a clock signal to drift between the birefringent axes by an equal amount corresponding to DGD. We experimentally demonstrate how polarization stabilization can be attained using the polarization maintaining fibre. We also demonstrate the applicability of VCSEL technology in the SKA unidirectional data flow especially for shorter baselines < 100 km. The VCSEL is a low cost light source with attractive advantages such as low power consumption, high speed capabilities and wavelength tuneability. This work entails the use of traditional amplitude modulation commonly known as non-return-to-zero (NRZ) on-off keying (OOK) because of its simplicity and cost. For the MeerKAT typical distances, we show that even in a worst case scenario, the use of VCSEL on different fibres in MeerKAT distance is achievable. Using the impairment reduction approach, we successfully manage to achieve transmission distance beyond MeerKAT. Several in-line dispersion compensation mechanisms in telecommunication have been successfully employed. The work focused on the use of negative dispersion fibre to mitigate the chromatic dispersion effects in the optical fibre. The inverse dispersion fibre (IDF) is proposed for compensation in the conventional zero dispersion wavelength fibres, G.652 that are used at the third window. Similarly, the chromatic dispersion compensation of non-zero dispersion shifted fibre (NZDSF) is experimentally demonstrated using negative dispersion submarine reduced slope (SRS), G. 655 (-). With dispersion management, we demonstrate how transmissions beyond MeerKAT baselines can be achieved error free. A systematic investigation of the use of distributed Raman amplification to overcome the attenuation losses is provided. High on-off gains of up to 15 dB, 8 dB and 5 dB for bidirectional, forward and backward pumping respectively is achieved on a 25 km Raman optimized NZDSF-Reach fibre. Combined dispersion mitigation technique and low noise distributed Raman amplification, up to about 80 km transmission was achieved on a 4:25 Gbps modulated VCSEL using a single pump. Using bidirectional pumping, more than 100 km of transmission was achieved error free. The high gains enhance the VCSEL transmission distance. We further suggest a novel way of using the Raman pump to distribute the clock signal while amplifying the data signal streaming the astronomical data from the remote placed telescope receivers. In summary, the work presented in this thesis has demonstrated the potential use of VCSEL technology for data collection in the telescope array. We have studied the optical effects and mitigation so as to improve the clock and data transmission. This work is relevant and valuable in providing SKA with VCSELs, an option for extremely high network performance at reasonable costs.
- Full Text:
- Date Issued: 2015
- Authors: Rotich, Enoch Kirwa
- Date: 2015
- Subjects: Optical communications , Fiber optics , Telecommunication systems
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/6552 , vital:21109
- Description: This thesis provides in-depth information on the high speed optical transport requirements for the Square Kilometre Array. The stringent data rates as well as timing and synchronization requirements are dealt with respect to the optical fibre technology. Regarding the data transport, we draw a clear comparison between a typical telecommunication access network and a telescope network. Invoking simulations and experiments on the field and laboratory test bed, we successfully implement a suitable telescope network using vertical cavity surface emitting laser (VCSEL) technology. Polarization effects on the KAT-7 telescope network, an operational prototype for the SKA is studied so as to estimate the expected effect in the MeerKAT telescope with transmission distances _ 12 km. The study further relates the obtained values to the expected impact on the distribution of the time and frequency reference in the MeerKAT array. Clock stability depends on the differential group delay (DGD) and polarization stability. On a 10:25 km link that includes the riser cable a DGD of 62:1 fs was attained. This corresponds to a polarization mode dispersion (PMD) coefficient of 19:4 fs=km1=2. This is a low PMD value considering telecommunication network. The PMD value is within the allowed budget in the telescope network. However, this may not be the case at longer baselines extending to over 1000 km as expected in SKA 2. The fibre's deployment contribution to the DGD is measured by comparing the deployed fibre to the undeployed of equal lengths. On the 10:25 km deployed single mode fibre, the maximum and mean DGDs measured were 217:7 fs and 84:8 fs respectively. The undeployed fibre of similar type and equal length, gave a maximum and minimum DGDs of 58:6 fs and 36:3 fs respectively. The deployment is seen to increase the maximum and minimum DGDs by factors of 3.7 and 2.3 respectively. This implies that fibre deployment is very critical in ensuring the birefringence is minimized. Polarization fluctuation recorded a maximum of 180o during the 15 hour real time astronomer use of the antenna. To ascertain the contribution of the riser cable, state of polarization (SOP) of the buried section of the single mode fibre in the link was established. A maximum SOP change of 14o over 15 hour monitoring was measured. From the stability realized on the buried section of the fibre, the change in polarization is contributed by the riser cable. The fluctuation in polarization can cause the phase of a clock signal to drift between the birefringent axes by an equal amount corresponding to DGD. We experimentally demonstrate how polarization stabilization can be attained using the polarization maintaining fibre. We also demonstrate the applicability of VCSEL technology in the SKA unidirectional data flow especially for shorter baselines < 100 km. The VCSEL is a low cost light source with attractive advantages such as low power consumption, high speed capabilities and wavelength tuneability. This work entails the use of traditional amplitude modulation commonly known as non-return-to-zero (NRZ) on-off keying (OOK) because of its simplicity and cost. For the MeerKAT typical distances, we show that even in a worst case scenario, the use of VCSEL on different fibres in MeerKAT distance is achievable. Using the impairment reduction approach, we successfully manage to achieve transmission distance beyond MeerKAT. Several in-line dispersion compensation mechanisms in telecommunication have been successfully employed. The work focused on the use of negative dispersion fibre to mitigate the chromatic dispersion effects in the optical fibre. The inverse dispersion fibre (IDF) is proposed for compensation in the conventional zero dispersion wavelength fibres, G.652 that are used at the third window. Similarly, the chromatic dispersion compensation of non-zero dispersion shifted fibre (NZDSF) is experimentally demonstrated using negative dispersion submarine reduced slope (SRS), G. 655 (-). With dispersion management, we demonstrate how transmissions beyond MeerKAT baselines can be achieved error free. A systematic investigation of the use of distributed Raman amplification to overcome the attenuation losses is provided. High on-off gains of up to 15 dB, 8 dB and 5 dB for bidirectional, forward and backward pumping respectively is achieved on a 25 km Raman optimized NZDSF-Reach fibre. Combined dispersion mitigation technique and low noise distributed Raman amplification, up to about 80 km transmission was achieved on a 4:25 Gbps modulated VCSEL using a single pump. Using bidirectional pumping, more than 100 km of transmission was achieved error free. The high gains enhance the VCSEL transmission distance. We further suggest a novel way of using the Raman pump to distribute the clock signal while amplifying the data signal streaming the astronomical data from the remote placed telescope receivers. In summary, the work presented in this thesis has demonstrated the potential use of VCSEL technology for data collection in the telescope array. We have studied the optical effects and mitigation so as to improve the clock and data transmission. This work is relevant and valuable in providing SKA with VCSELs, an option for extremely high network performance at reasonable costs.
- Full Text:
- Date Issued: 2015
Nonlinear effects with a focus on cross phase modulation and its impact on wavelength division multiplexing optical fibre networks
- Gamatham, Romeo Reginald Gunther
- Authors: Gamatham, Romeo Reginald Gunther
- Date: 2013
- Subjects: Wavelength division multiplexing , Optical communications , Fiber optics
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/6302 , vital:21071
- Description: The demand for faster data transmission is ever increasing. Wavelength division multiplexing (WDM) presents as a viable solution to increase the data transmission rate significantly. WDM systems are based on the ability to transmit multiple wavelengths simultaneously down the fibre. Unlike time division multiplexing (TDM) systems, WDM systems do not increase the data transfer by increasing the transmission rate of a single channel. In WDM systems the data rate per channel remains the same, only multiple channels carry data across the link. Dense wavelength division multiplexing (DWDM) promises even more wavelengths packed together in the same fibre. This multiplication of channels increases the bandwidth capacity rapidly. Networks are looking into making use of technology that will ensure no electronic signal regeneration at any point within the DWDM network. Examples are; reconfigurable optical add/drop multiplexers (ROADM) and optical cross connect (OXC) units. These components essentially enable network operators to split, combine and multiplex optical signals carried by optical fibre. WDM allows network operators to increase the capacity of existing networks without expensive re-cabling. This provides networks with the flexibility to be upgraded to larger bandwidths and for reconfiguration of network services. Further, WDM technology opens up an opportunity of marketing flexibility to network operators, where operators not only have the option to rent out cables and fibres but wavelengths as well. Cross phase modulation (XPM) poses a problem to WDM networks. The refractive index experienced by a neighbouring optical signal, not only depends on the signal’s intensity but on the intensity of the co-propagating signal as well. This effect leads to a phase change and is known as XPM. This work investigates the characteristics of XPM. It is shown that, in a two channel WDM network, a probe signal’s SOP can be steered by controlling a high intensity pump signal’s SOP. This effect could be applied to make a wavelength converter. Experimental results show that the degree of polarization (DOP) of a probe signal degrades according to a mathematical model found in literature. The pump and probe signals are shown to experience maximum interaction, for orthogonal probe-pump SOP vector orientations. This may be problematic to polarization mode dispersion compensators. Additionally, experimental results point out that the SOP of a probe signal is much more active in the presence of a high intensity pump, as compared to the single signal transmission scenario.
- Full Text:
- Date Issued: 2013
- Authors: Gamatham, Romeo Reginald Gunther
- Date: 2013
- Subjects: Wavelength division multiplexing , Optical communications , Fiber optics
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/6302 , vital:21071
- Description: The demand for faster data transmission is ever increasing. Wavelength division multiplexing (WDM) presents as a viable solution to increase the data transmission rate significantly. WDM systems are based on the ability to transmit multiple wavelengths simultaneously down the fibre. Unlike time division multiplexing (TDM) systems, WDM systems do not increase the data transfer by increasing the transmission rate of a single channel. In WDM systems the data rate per channel remains the same, only multiple channels carry data across the link. Dense wavelength division multiplexing (DWDM) promises even more wavelengths packed together in the same fibre. This multiplication of channels increases the bandwidth capacity rapidly. Networks are looking into making use of technology that will ensure no electronic signal regeneration at any point within the DWDM network. Examples are; reconfigurable optical add/drop multiplexers (ROADM) and optical cross connect (OXC) units. These components essentially enable network operators to split, combine and multiplex optical signals carried by optical fibre. WDM allows network operators to increase the capacity of existing networks without expensive re-cabling. This provides networks with the flexibility to be upgraded to larger bandwidths and for reconfiguration of network services. Further, WDM technology opens up an opportunity of marketing flexibility to network operators, where operators not only have the option to rent out cables and fibres but wavelengths as well. Cross phase modulation (XPM) poses a problem to WDM networks. The refractive index experienced by a neighbouring optical signal, not only depends on the signal’s intensity but on the intensity of the co-propagating signal as well. This effect leads to a phase change and is known as XPM. This work investigates the characteristics of XPM. It is shown that, in a two channel WDM network, a probe signal’s SOP can be steered by controlling a high intensity pump signal’s SOP. This effect could be applied to make a wavelength converter. Experimental results show that the degree of polarization (DOP) of a probe signal degrades according to a mathematical model found in literature. The pump and probe signals are shown to experience maximum interaction, for orthogonal probe-pump SOP vector orientations. This may be problematic to polarization mode dispersion compensators. Additionally, experimental results point out that the SOP of a probe signal is much more active in the presence of a high intensity pump, as compared to the single signal transmission scenario.
- Full Text:
- Date Issued: 2013
Single-end reflectometric measurements of polarization-mode dispersion in single-mode optical fibres
- Authors: Fosuhene, Samuel Kofi
- Date: 2013
- Subjects: Fiber optics , Polarization (Light) , Optical measurements
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/6280 , vital:21069
- Description: In this thesis two novel single-end methods are applied to measure and characterize polarization mode dispersion in single mode optical fibres. Polarization mode dispersion (PMD) is an important factor negatively affecting the successful implementation of high speed long haul optical fibre networks operating at bit rates of 10Gb/s and above. PMD measurements are thus important for quality control during manufacturing and cabling processes. It is also useful for network operators planning to upgrade bitrates in existing networks to 10Gb/s and beyond. In an optical fibre link, sections with particularly high PMD may act to increase the entire PMD of the link. Identifying and replacing such sections can greatly reduce the PMD of the link. PMD measurements can be forward or single-end. In forward measurements, both ends of the fibre are used for input and detection. In single-end configuration, only one end of the fibre is used. For this reason, single-end measurements are more practical for the field where fibre ends are situated several kilometres apart. Single-end techniques can be implemented with a continuous wave for non-local PMD measurements (by Fresnel reflection). If a pulsed wave is used, local measurements can be achieved (by total power due to Rayleigh scattering). Two single-end schemes, one based on Fresnel reflection and the other due to Rayleigh scattering have been applied to measure non-local and local PMD of standard single mode optical fibres. For the non-local PMD measurements, the general interferometric technique (GINTY) was modified to operate in a round-trip configuration. In this configuration, the fibre was treated as a concatenation of two identical fibre segments. Three different sets of fibres were investigated, each set representing a particular mode coupling regime. For polarization maintaining fibres, (PMFs), with no mode coupling, a factor of two was found between forward and single-end measurements. For long single mode fibres in the long length regime, the factor was 1.4. For a combination of PMF and single mode fibres, a factor of 1.6 was obtained. The method which is accurate, repeatable, low cost and robust is very suitable for field applications. The second method is the polarization optical time domain reflectometric (P-OTDR) technique. This technique performs local birefringence measurements by measuring the evolution of the states of polarization (SOP). The birefringence information from such measurements was extracted and analysed to characterise four different fibres. Beat lengths and correlation lengths extracted from the P-OTDR were used to calculate the differential group delay (DGD) of the fibres. Next an expression for the root-mean-square differential group delay was derived and applied to the birefringence measurements to calculate the DGDs at a single wavelength. This method which operates at a single wavelength has a huge advantage. Firstly it is able to measure completely all the fibre characteristic parameters. Secondly it can measure mean DGD, root mean square DGD and instantaneous DGD. A plot of instantaneous DGD vs. length enables one to identify and eliminate sections with particularly high DGD. Finally since the P-OTDR system operates with a single wavelength, real time monitoring of PMD is possible via multiplexing. The results obtained are repeatable, accurate and are in good agreement with the standard Jones Matrix Eigenanalysis (JME) technique.
- Full Text:
- Date Issued: 2013
Single-end reflectometric measurements of polarization-mode dispersion in single-mode optical fibres
- Authors: Fosuhene, Samuel Kofi
- Date: 2013
- Subjects: Fiber optics , Polarization (Light) , Optical measurements
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/6280 , vital:21069
- Description: In this thesis two novel single-end methods are applied to measure and characterize polarization mode dispersion in single mode optical fibres. Polarization mode dispersion (PMD) is an important factor negatively affecting the successful implementation of high speed long haul optical fibre networks operating at bit rates of 10Gb/s and above. PMD measurements are thus important for quality control during manufacturing and cabling processes. It is also useful for network operators planning to upgrade bitrates in existing networks to 10Gb/s and beyond. In an optical fibre link, sections with particularly high PMD may act to increase the entire PMD of the link. Identifying and replacing such sections can greatly reduce the PMD of the link. PMD measurements can be forward or single-end. In forward measurements, both ends of the fibre are used for input and detection. In single-end configuration, only one end of the fibre is used. For this reason, single-end measurements are more practical for the field where fibre ends are situated several kilometres apart. Single-end techniques can be implemented with a continuous wave for non-local PMD measurements (by Fresnel reflection). If a pulsed wave is used, local measurements can be achieved (by total power due to Rayleigh scattering). Two single-end schemes, one based on Fresnel reflection and the other due to Rayleigh scattering have been applied to measure non-local and local PMD of standard single mode optical fibres. For the non-local PMD measurements, the general interferometric technique (GINTY) was modified to operate in a round-trip configuration. In this configuration, the fibre was treated as a concatenation of two identical fibre segments. Three different sets of fibres were investigated, each set representing a particular mode coupling regime. For polarization maintaining fibres, (PMFs), with no mode coupling, a factor of two was found between forward and single-end measurements. For long single mode fibres in the long length regime, the factor was 1.4. For a combination of PMF and single mode fibres, a factor of 1.6 was obtained. The method which is accurate, repeatable, low cost and robust is very suitable for field applications. The second method is the polarization optical time domain reflectometric (P-OTDR) technique. This technique performs local birefringence measurements by measuring the evolution of the states of polarization (SOP). The birefringence information from such measurements was extracted and analysed to characterise four different fibres. Beat lengths and correlation lengths extracted from the P-OTDR were used to calculate the differential group delay (DGD) of the fibres. Next an expression for the root-mean-square differential group delay was derived and applied to the birefringence measurements to calculate the DGDs at a single wavelength. This method which operates at a single wavelength has a huge advantage. Firstly it is able to measure completely all the fibre characteristic parameters. Secondly it can measure mean DGD, root mean square DGD and instantaneous DGD. A plot of instantaneous DGD vs. length enables one to identify and eliminate sections with particularly high DGD. Finally since the P-OTDR system operates with a single wavelength, real time monitoring of PMD is possible via multiplexing. The results obtained are repeatable, accurate and are in good agreement with the standard Jones Matrix Eigenanalysis (JME) technique.
- Full Text:
- Date Issued: 2013
Effects of polarization in a distributed raman fibre amplifier
- Authors: Muguro, Kennedy Mwaura
- Date: 2011
- Subjects: Fiber optics , Polarization (Light) , Optical communications , Optical amplifiers , Raman effect
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10544 , http://hdl.handle.net/10948/d1014621
- Description: The need to exploit the large fibre bandwidth and increase the reach has seen the application of the Raman fibre amplifier (RFA) become indispensable in modern light wave systems. The success and resilience of RFAs in optical communication is deeply rooted in their unique optical properties and new technologies which have allowed the amplifier to come of age. However, the full potential of RFAs in optical communication and other applications are yet to be realized. More so are its polarization properties which still remain largely unexploited and have not been fully understood. In this work, fundamental issues regarding distributed RFA have been investigated with the aim of acquiring a better understanding of the amplifier polarization characteristics which have potential applications. In particular the effects of polarization mode dispersion (PMD) and polarization dependent loss (PDL) have been demonstrated both by simulation and experiment. The possibility of Raman polarization pulling in single mode fibres (SMFs) has also been addressed. Polarization sensitivity of RFA has been known for a long time but the clear manifestation of it has become evident in the advent of modern low PMD fibre. Unlike EDFAs which make use of special doped fibre, RFAs require no special fibre for operation. Besides, RFA uses a very long length of fibre and as such the fibre polarization characteristics come into play during amplification. In the demonstrations presented in this thesis a fibre of PMD coefficient < 0.05 pskm-1/2 was regarded as low PMD fibre while one having coefficient ≥ 0.05 pskm-1/2 was categorized to have high PMD unless otherwise stated. Several experiments were performed to evaluate the RFA gain characteristics with respect to fibre PMD and the system performance in the presence of noise emanating from amplified spontaneous emission (ASE). Analysis of Raman gain statistics was done for fibres of low and high PMD coefficients. The statistics of PDG and on-off gain were eventually used to demonstrate the extraction of PMD coefficients of fibres between 0.01- 0.1 pskm-1/2 using a forward pumping configuration. It was found that, at increasing pump power a linear relationship exists between forward and backward signal gain on a dB scale. The interaction of PDL and Raman PDG in the presence of PMD were observed at very fundamental level. It was found the presence of PDL serves to reduce the available on-off gain. It was also established that the presence of PMD mediates the interaction between PDG/PDL. When PMD is high it reduces PDG but the presence of PDL introduces a wavelength dependent gain tilting for WDM channels. Further analysis revealed that signal polarization is influenced by the pump SOP due to the pulling effect which is present even at moderate pump power.
- Full Text:
- Date Issued: 2011
- Authors: Muguro, Kennedy Mwaura
- Date: 2011
- Subjects: Fiber optics , Polarization (Light) , Optical communications , Optical amplifiers , Raman effect
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10544 , http://hdl.handle.net/10948/d1014621
- Description: The need to exploit the large fibre bandwidth and increase the reach has seen the application of the Raman fibre amplifier (RFA) become indispensable in modern light wave systems. The success and resilience of RFAs in optical communication is deeply rooted in their unique optical properties and new technologies which have allowed the amplifier to come of age. However, the full potential of RFAs in optical communication and other applications are yet to be realized. More so are its polarization properties which still remain largely unexploited and have not been fully understood. In this work, fundamental issues regarding distributed RFA have been investigated with the aim of acquiring a better understanding of the amplifier polarization characteristics which have potential applications. In particular the effects of polarization mode dispersion (PMD) and polarization dependent loss (PDL) have been demonstrated both by simulation and experiment. The possibility of Raman polarization pulling in single mode fibres (SMFs) has also been addressed. Polarization sensitivity of RFA has been known for a long time but the clear manifestation of it has become evident in the advent of modern low PMD fibre. Unlike EDFAs which make use of special doped fibre, RFAs require no special fibre for operation. Besides, RFA uses a very long length of fibre and as such the fibre polarization characteristics come into play during amplification. In the demonstrations presented in this thesis a fibre of PMD coefficient < 0.05 pskm-1/2 was regarded as low PMD fibre while one having coefficient ≥ 0.05 pskm-1/2 was categorized to have high PMD unless otherwise stated. Several experiments were performed to evaluate the RFA gain characteristics with respect to fibre PMD and the system performance in the presence of noise emanating from amplified spontaneous emission (ASE). Analysis of Raman gain statistics was done for fibres of low and high PMD coefficients. The statistics of PDG and on-off gain were eventually used to demonstrate the extraction of PMD coefficients of fibres between 0.01- 0.1 pskm-1/2 using a forward pumping configuration. It was found that, at increasing pump power a linear relationship exists between forward and backward signal gain on a dB scale. The interaction of PDL and Raman PDG in the presence of PMD were observed at very fundamental level. It was found the presence of PDL serves to reduce the available on-off gain. It was also established that the presence of PMD mediates the interaction between PDG/PDL. When PMD is high it reduces PDG but the presence of PDL introduces a wavelength dependent gain tilting for WDM channels. Further analysis revealed that signal polarization is influenced by the pump SOP due to the pulling effect which is present even at moderate pump power.
- Full Text:
- Date Issued: 2011
Aerial optical fibres in telecommunication systems : SOP and PMD monitoring, and tolerance of modulation formats
- Authors: Ireeta, Winston Tumps
- Date: 2010
- Subjects: Optical communications , Fiber optics
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10542 , http://hdl.handle.net/10948/1478 , http://hdl.handle.net/10948/d1012894 , Optical communications , Fiber optics
- Description: The topic of this thesis is aerial optical fibres in telecommunication systems: state of polarization (SOP) and polarization mode dispersion (PMD) monitoring and tolerance of modulation formats. Errors in optical fibre telecommunication systems are introduced when these polarization effects (SOP and PMD) change. These changes are so intense especially in aerial optical fibres. Part of the backbone of South Africa’s national grid includes long distances of aerial optical fibre between transmission exchange stations. The work in this thesis can be divided into three parts which all deal with the major aspects of PMD in deployed aerial optical fibres: characterization, environmental effects plus other perturbations, and tolerance of different modulation formats. In our work, SOP and PMD field measurements revealed that they both fluctuate more rapidly in deployed aerial optical fibres especially on windy and hot days. The SOP and PMD changes in the aerial optical fibres showed a significant correlation with these environmental parameters. SOP and PMD are stochastic in nature due to changes in the properties of the optical fibres and its positions because of both intrinsic and extrinsic perturbations. In our work, with only 184 PMD values measured and obtained by use of the FTB-5700 single-ended dispersion analyzer, the predicted theoretical Gaussian fit was obtained with a mean of 0.47 ps and standard deviation of 0.08 ps. This small standard deviation was justification for its robustness and accuracy. The statistical distributions for first-order polarization mode dispersion (FO-PMD) and second-order polarization mode dispersion (SO-PMD) for the first time were experimentally confirmed when measured using the FTB-5700 single-ended dispersion analyzer instrument for deployed aerial optical fibres. We were also able to determine the time scale over which to compensate FO-PMD in deployed aerial fibres using the directional time drift autocorrelation function method. It is slightly higher than 390 s for SOP measurements made on a particular windy and hot day. This is due to the fact that the changes of the PMD vector are known to be slower than the SOP changes. vi We also investigated the theoretical statistical distribution that corresponds to output SOP variations. The SOP variations can either be with wavelength (for buried fibre) or with time (for aerial fibre). Our results showed that the statistics of the relative SOP changes approached the distribution proposed by Foschini et al. (2000). Advanced optical modulation formats have become a key ingredient in the design of modern state-of-the-art wavelength-division-multiplexed (WDM) optical transmission systems. In our work, we investigated which of these advanced modulation formats is best suited for the South African network especially on systems that have links of aerial optical fibres. Keywords: aerial optical fibre, polarization mode dispersion (PMD), principal states of polarization (PSP), state of polarization (SOP), first-order PMD, second-order PMD.
- Full Text:
- Date Issued: 2010
- Authors: Ireeta, Winston Tumps
- Date: 2010
- Subjects: Optical communications , Fiber optics
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10542 , http://hdl.handle.net/10948/1478 , http://hdl.handle.net/10948/d1012894 , Optical communications , Fiber optics
- Description: The topic of this thesis is aerial optical fibres in telecommunication systems: state of polarization (SOP) and polarization mode dispersion (PMD) monitoring and tolerance of modulation formats. Errors in optical fibre telecommunication systems are introduced when these polarization effects (SOP and PMD) change. These changes are so intense especially in aerial optical fibres. Part of the backbone of South Africa’s national grid includes long distances of aerial optical fibre between transmission exchange stations. The work in this thesis can be divided into three parts which all deal with the major aspects of PMD in deployed aerial optical fibres: characterization, environmental effects plus other perturbations, and tolerance of different modulation formats. In our work, SOP and PMD field measurements revealed that they both fluctuate more rapidly in deployed aerial optical fibres especially on windy and hot days. The SOP and PMD changes in the aerial optical fibres showed a significant correlation with these environmental parameters. SOP and PMD are stochastic in nature due to changes in the properties of the optical fibres and its positions because of both intrinsic and extrinsic perturbations. In our work, with only 184 PMD values measured and obtained by use of the FTB-5700 single-ended dispersion analyzer, the predicted theoretical Gaussian fit was obtained with a mean of 0.47 ps and standard deviation of 0.08 ps. This small standard deviation was justification for its robustness and accuracy. The statistical distributions for first-order polarization mode dispersion (FO-PMD) and second-order polarization mode dispersion (SO-PMD) for the first time were experimentally confirmed when measured using the FTB-5700 single-ended dispersion analyzer instrument for deployed aerial optical fibres. We were also able to determine the time scale over which to compensate FO-PMD in deployed aerial fibres using the directional time drift autocorrelation function method. It is slightly higher than 390 s for SOP measurements made on a particular windy and hot day. This is due to the fact that the changes of the PMD vector are known to be slower than the SOP changes. vi We also investigated the theoretical statistical distribution that corresponds to output SOP variations. The SOP variations can either be with wavelength (for buried fibre) or with time (for aerial fibre). Our results showed that the statistics of the relative SOP changes approached the distribution proposed by Foschini et al. (2000). Advanced optical modulation formats have become a key ingredient in the design of modern state-of-the-art wavelength-division-multiplexed (WDM) optical transmission systems. In our work, we investigated which of these advanced modulation formats is best suited for the South African network especially on systems that have links of aerial optical fibres. Keywords: aerial optical fibre, polarization mode dispersion (PMD), principal states of polarization (PSP), state of polarization (SOP), first-order PMD, second-order PMD.
- Full Text:
- Date Issued: 2010
Compensation for polarization mode dispersion and nonlinear birefringence in a multichannel optical fibre system
- Authors: Waswa, David Wafula
- Date: 2009
- Subjects: Fiber optics , Nonlinear optics , Polarization (Light)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10375 , http://hdl.handle.net/10948/885 , Fiber optics , Nonlinear optics , Polarization (Light)
- Description: Polarization mode dispersion (PMD) is stochastic in nature and continues evolving in an unpredictable manner according to the changing environment. Nonlinear birefringence in multichannel systems alters the polarization states of the bits, so that they vary from one bit to the next in a way that is difficult to predict. These are the two major signal-impairment effects that are inherent in optical fibre transmission links which can seriously degrade network performance. It is therefore extremely challenging to compensate for both linear and nonlinear birefringence in multichannel systems. The purpose of this thesis is to investigate the interaction between PMD and nonlinear induced birefringence in a fibre with consideration of mode coupling. A sound knowledge of this interaction is necessary in designing a linear and nonlinear polarization mode dispersion compensator for WDM systems, as was successfully carried out in this study. The investigation shows that the effect of nonlinear birefringence alone depolarizes the signal, while in high PMD links where polarization mode coupling is high, the nonlinear birefringence effect couples with second-order PMD such that it may reduce the penalty and improve the signal DOP. Further investigation shows that when nonlinear birefringence becomes significant, asymmetry arises between the two principal axes of the fibre, such that it is only one axis which experiences the effect of nonlinear birefringence. It is found out that along this vii axis, there exists a critical point in pump power where the nonlinear birefringence cancels PMD in the link and improves the signal. An adaptive compensator to cancel PMD and nonlinear birefringence was designed based on feedforward DOP-monitoring signal. The compensator was tested both at laboratory level and on the Telkom buried fibre link and found to be functioning as intended. It was able to adaptively track and compensate PMD in the link in less than a second. The compensator was able to cancel PMD in the link up to a maximum of 30 ps. The compensator improved the DOP of the worst signal by more than 100 percent.
- Full Text:
- Date Issued: 2009
- Authors: Waswa, David Wafula
- Date: 2009
- Subjects: Fiber optics , Nonlinear optics , Polarization (Light)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10375 , http://hdl.handle.net/10948/885 , Fiber optics , Nonlinear optics , Polarization (Light)
- Description: Polarization mode dispersion (PMD) is stochastic in nature and continues evolving in an unpredictable manner according to the changing environment. Nonlinear birefringence in multichannel systems alters the polarization states of the bits, so that they vary from one bit to the next in a way that is difficult to predict. These are the two major signal-impairment effects that are inherent in optical fibre transmission links which can seriously degrade network performance. It is therefore extremely challenging to compensate for both linear and nonlinear birefringence in multichannel systems. The purpose of this thesis is to investigate the interaction between PMD and nonlinear induced birefringence in a fibre with consideration of mode coupling. A sound knowledge of this interaction is necessary in designing a linear and nonlinear polarization mode dispersion compensator for WDM systems, as was successfully carried out in this study. The investigation shows that the effect of nonlinear birefringence alone depolarizes the signal, while in high PMD links where polarization mode coupling is high, the nonlinear birefringence effect couples with second-order PMD such that it may reduce the penalty and improve the signal DOP. Further investigation shows that when nonlinear birefringence becomes significant, asymmetry arises between the two principal axes of the fibre, such that it is only one axis which experiences the effect of nonlinear birefringence. It is found out that along this vii axis, there exists a critical point in pump power where the nonlinear birefringence cancels PMD in the link and improves the signal. An adaptive compensator to cancel PMD and nonlinear birefringence was designed based on feedforward DOP-monitoring signal. The compensator was tested both at laboratory level and on the Telkom buried fibre link and found to be functioning as intended. It was able to adaptively track and compensate PMD in the link in less than a second. The compensator was able to cancel PMD in the link up to a maximum of 30 ps. The compensator improved the DOP of the worst signal by more than 100 percent.
- Full Text:
- Date Issued: 2009
Polarization mode dispersion emulation and the impact of high first-order PMD segments in optical telecommunication systems
- Authors: Musara, Vitalis
- Date: 2009
- Subjects: Optical communications , Fiber optics , Polarization (Light)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10519 , http://hdl.handle.net/10948/1138 , Optical communications , Fiber optics , Polarization (Light)
- Description: In this study, focus is centred on the measurement and emulation of first-order (FO-) and second-order (SO-) polarization mode dispersion (PMD). PMD has deleterious effects on the performance of high speed optical transmission network systems from 10 Gb/s and above. The first step was characterising deployed fibres for PMD and monitoring the state of polarization (SOP) light experiences as it propagates through the fibre. The PMD and SOP changes in deployed fibres were stochastic due to varying intrinsic and extrinsic perturbation changes. To fully understand the PMD phenomenon in terms of measurement accuracy, its complex behaviour, its implications, mitigation and compensation, PMD emulation is crucial. This thesis presents emulator designs which fall into different emulator categories. The key to these designs were the PMD equations and background on the PMD phenomenon. The cross product from the concatenation equation was applied in order to determine the coupling angle β (between 0o and 180o) that results in the SO-PMD of the emulator designs to be either adjustable or fixed. The digital delay line (DDL) or single polarization maintaining fibre (PMF) section was used to give a certain amount of FO-PMD but negligible SO-PMD. PMF sections (birefringent sections) were concatenated together to ensure FO- and SO-PMD coexist, emulating deployed fibres. FO- and SO-PMD can be controlled by altering mode coupling (coupling angles) and birefringence distribution. Emulators with PMD statistics approaching the theoretical distributions had high random coupling and several numbers of randomly distributed PMF sections. In addition, the lengths of their PMF sections lie within 20% standard deviation of the mean emulator length. Those emulators with PMD statistics that did not approach the theoretical distributions had limited numbers of randomly distributed PMF sections and mode coupling. Results also show that even when an emulator has high random mode coupling and several numbers of randomly distributed PMFs, its PMD statistics deviates away from expected theoretical distributions in the presence of polarization dependent loss (PDL). The emulators showed that the background autocorrelation function (BACF) approaches zero with increasing number of randomly mode coupled fibre sections. A zero BACF signifies that an emulator has large numbers of randomly distributed PMF sections and its presence means the opposite. The availability of SO-PMD in the emulators made the autocorrelation function (ACF) x asymmetric. In the absence of SO-PMD the ACF for a PMD emulator is symmetric. SO-PMD has no effect on the BACF. Polarization-optical time domain reflectometry (P-OTDR) measurements have shown that certain fibre sections along fibre link lengths have higher FO-PMD (HiFO-PMD) than other sections. This study investigates the impact of a HiFO-PMD section on the overall FO- and SO-PMD, the output state of polarization (SOP) and system performance on deployed fibres (through emulation). Results show that when the wavelength-independent FO-PMD vector of the HiFO-PMD section is greater than the FO-PMD contributions from the rest of the fibre link, the mean FO-PMD of the entire link is biased towards that of the HiFO-PMD section and the SO-PMD increases (β ≠ 0o or 180o) or remains fixed (β = 0o or 180o) depending on the coupling angle β between the HiFO-PMD section and the rest of the fibre link. In addition, the FO-PMD statistics deviates away from the theoretical Maxwellian distribution. However, experimental results show that the HiFO-PMD section has negligible influence on the SOPMD statistical distribution. An increase in the amount of FO-PMD on a HiFO-PMD section reduces the output SOP spread to a given minimum, in this study the minimum was reached when the HiFO-PMD ≥ 35 ps. However, the outcome of the output SOP spread depends on the location of the HiFO-PMD section along the fibre link length. It was found that when the HiFO-PMD section introduces SO-PMD, the bit error rate (BER) is much higher compared to when it does not introduce SO-PMD.
- Full Text:
- Date Issued: 2009
- Authors: Musara, Vitalis
- Date: 2009
- Subjects: Optical communications , Fiber optics , Polarization (Light)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10519 , http://hdl.handle.net/10948/1138 , Optical communications , Fiber optics , Polarization (Light)
- Description: In this study, focus is centred on the measurement and emulation of first-order (FO-) and second-order (SO-) polarization mode dispersion (PMD). PMD has deleterious effects on the performance of high speed optical transmission network systems from 10 Gb/s and above. The first step was characterising deployed fibres for PMD and monitoring the state of polarization (SOP) light experiences as it propagates through the fibre. The PMD and SOP changes in deployed fibres were stochastic due to varying intrinsic and extrinsic perturbation changes. To fully understand the PMD phenomenon in terms of measurement accuracy, its complex behaviour, its implications, mitigation and compensation, PMD emulation is crucial. This thesis presents emulator designs which fall into different emulator categories. The key to these designs were the PMD equations and background on the PMD phenomenon. The cross product from the concatenation equation was applied in order to determine the coupling angle β (between 0o and 180o) that results in the SO-PMD of the emulator designs to be either adjustable or fixed. The digital delay line (DDL) or single polarization maintaining fibre (PMF) section was used to give a certain amount of FO-PMD but negligible SO-PMD. PMF sections (birefringent sections) were concatenated together to ensure FO- and SO-PMD coexist, emulating deployed fibres. FO- and SO-PMD can be controlled by altering mode coupling (coupling angles) and birefringence distribution. Emulators with PMD statistics approaching the theoretical distributions had high random coupling and several numbers of randomly distributed PMF sections. In addition, the lengths of their PMF sections lie within 20% standard deviation of the mean emulator length. Those emulators with PMD statistics that did not approach the theoretical distributions had limited numbers of randomly distributed PMF sections and mode coupling. Results also show that even when an emulator has high random mode coupling and several numbers of randomly distributed PMFs, its PMD statistics deviates away from expected theoretical distributions in the presence of polarization dependent loss (PDL). The emulators showed that the background autocorrelation function (BACF) approaches zero with increasing number of randomly mode coupled fibre sections. A zero BACF signifies that an emulator has large numbers of randomly distributed PMF sections and its presence means the opposite. The availability of SO-PMD in the emulators made the autocorrelation function (ACF) x asymmetric. In the absence of SO-PMD the ACF for a PMD emulator is symmetric. SO-PMD has no effect on the BACF. Polarization-optical time domain reflectometry (P-OTDR) measurements have shown that certain fibre sections along fibre link lengths have higher FO-PMD (HiFO-PMD) than other sections. This study investigates the impact of a HiFO-PMD section on the overall FO- and SO-PMD, the output state of polarization (SOP) and system performance on deployed fibres (through emulation). Results show that when the wavelength-independent FO-PMD vector of the HiFO-PMD section is greater than the FO-PMD contributions from the rest of the fibre link, the mean FO-PMD of the entire link is biased towards that of the HiFO-PMD section and the SO-PMD increases (β ≠ 0o or 180o) or remains fixed (β = 0o or 180o) depending on the coupling angle β between the HiFO-PMD section and the rest of the fibre link. In addition, the FO-PMD statistics deviates away from the theoretical Maxwellian distribution. However, experimental results show that the HiFO-PMD section has negligible influence on the SOPMD statistical distribution. An increase in the amount of FO-PMD on a HiFO-PMD section reduces the output SOP spread to a given minimum, in this study the minimum was reached when the HiFO-PMD ≥ 35 ps. However, the outcome of the output SOP spread depends on the location of the HiFO-PMD section along the fibre link length. It was found that when the HiFO-PMD section introduces SO-PMD, the bit error rate (BER) is much higher compared to when it does not introduce SO-PMD.
- Full Text:
- Date Issued: 2009
Characterization of polarization dependent loss in optical fibres and optical components in the presence of polarization mode dispersion
- Authors: Pelaelo, Gaoboelwe
- Date: 2008
- Subjects: Fiber optics , Polarization (Light)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10528 , http://hdl.handle.net/10948/695 , Fiber optics , Polarization (Light)
- Description: In this study, the Jones matrix eigenanalysis (JME), optical spectrum analyzer (OSA) and polarization scrambling methods were used to investigate polarization dependent loss (PDL) in the presence of polarization mode dispersion (PMD) in optical components and fibres. The PDL measurements were conducted both in the laboratory and in the field. For field measurements, a buried link (28.8 km) and an aerial fibre (7.1 km) were extensively studied. The findings obtained from these studies are very important for network operators who must assess the impact of PDL on the network reliability. The three different PDL measurement methods (JME, OSA and polarization scrambling) were compared and their PDL values were found to agree very well at the selected wavelength of 1550 nm. Concatenation of PDL components showed that as expected, PDL increase as the number of PDL components were added. The interactions between PMD and PDL measurements were analyzed. A PMD/PDL emulator was constructed. We observed that PMD decreased while PDL increased. The PMD decrease was a result of the PMD vector cancellation enhanced by the randomly distributed mode coupling angles while PDL increase was a result of each PM fibre segments contributing to the overall global PDL. It was observed that the presence of PMD in a link containing PDL, results in PDL being wavelength dependent and this resulted in the extraction of the PMD information from the PDL data. PDL was found to be Maxwellian distributed when considering low values of PMD. High PMD values resulted in the PDL distribution deviating from Maxwellian. Long-term PDL and PMD (average DGD) measurements indicated that the PDL and PMD varied slowly with time and wavelength for both the laboratory and field measurements. It was observed that the BER increase as both PDL and PMD increased for simulated optical link.
- Full Text:
- Date Issued: 2008
- Authors: Pelaelo, Gaoboelwe
- Date: 2008
- Subjects: Fiber optics , Polarization (Light)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10528 , http://hdl.handle.net/10948/695 , Fiber optics , Polarization (Light)
- Description: In this study, the Jones matrix eigenanalysis (JME), optical spectrum analyzer (OSA) and polarization scrambling methods were used to investigate polarization dependent loss (PDL) in the presence of polarization mode dispersion (PMD) in optical components and fibres. The PDL measurements were conducted both in the laboratory and in the field. For field measurements, a buried link (28.8 km) and an aerial fibre (7.1 km) were extensively studied. The findings obtained from these studies are very important for network operators who must assess the impact of PDL on the network reliability. The three different PDL measurement methods (JME, OSA and polarization scrambling) were compared and their PDL values were found to agree very well at the selected wavelength of 1550 nm. Concatenation of PDL components showed that as expected, PDL increase as the number of PDL components were added. The interactions between PMD and PDL measurements were analyzed. A PMD/PDL emulator was constructed. We observed that PMD decreased while PDL increased. The PMD decrease was a result of the PMD vector cancellation enhanced by the randomly distributed mode coupling angles while PDL increase was a result of each PM fibre segments contributing to the overall global PDL. It was observed that the presence of PMD in a link containing PDL, results in PDL being wavelength dependent and this resulted in the extraction of the PMD information from the PDL data. PDL was found to be Maxwellian distributed when considering low values of PMD. High PMD values resulted in the PDL distribution deviating from Maxwellian. Long-term PDL and PMD (average DGD) measurements indicated that the PDL and PMD varied slowly with time and wavelength for both the laboratory and field measurements. It was observed that the BER increase as both PDL and PMD increased for simulated optical link.
- Full Text:
- Date Issued: 2008
Characterization of polarization effects on deployed aerial optical fibre in South Africa
- Authors: Mudau, Azwitamisi Eric
- Date: 2008
- Subjects: Polarization (Light) , Fiber optics
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10521 , http://hdl.handle.net/10948/1060 , Polarization (Light) , Fiber optics
- Description: In this study, two polarization effects, namely the state of polarization (SOP) and polarization mode dispersion (PMD) in optical fibre cable are investigated. The change in polarization effects introduces errors in optical fibre communication system. We find that the SOP drifts slowly in buried cables, and rapidly in aerial cables. This is because buried cables are located in a static environment, whereas aerial cables are exposed directly to a dynamic environment. The SOP change in aerial cable shows significant correlation with its environment (the global radiation, temperature and wind). The autocorrelation function (ACF) was not performed in buried cable, since they do not satisfy the ACF assumption, whereas in aerial cable it is found that the ACF of the SOP decorrelates quite quickly during the day. The 50 percent decorrelation time during the day and night are 9.6 and 30.4 minutes, respectively. During the day the properties of the optical fibre change rapidly as a result of the rapidly changing environmental conditions, whereas at night the environmental conditions change relatively slowly. Fast Fourier Transform (FFT) of the SOP fluctuations show discrete peaks, which corresponds to the wind induced vibrational frequency of the cable. The PMD fluctuations for undeployed and deployed aerial optical fibre cable are monitored using the generalized interferometric technique (GINTY). It is found that the PMD measured with polarization scrambling is more scattered but more reliable than the PMD measured without polarization scrambling. This is because the PMD obtained with polarization scrambling is averaged over different input and output (I/O) SOP pairs. For deployed aerial cable, it is found that the PMD measured without polarization scrambling fluctuates rapidly during high wind speed conditions. Furthermore, there is a correlation between the measured PMD and the change in temperature. It is found that the change in temperature has a stronger influence than the wind on the PMD of the optical fibre link.
- Full Text:
- Date Issued: 2008
- Authors: Mudau, Azwitamisi Eric
- Date: 2008
- Subjects: Polarization (Light) , Fiber optics
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10521 , http://hdl.handle.net/10948/1060 , Polarization (Light) , Fiber optics
- Description: In this study, two polarization effects, namely the state of polarization (SOP) and polarization mode dispersion (PMD) in optical fibre cable are investigated. The change in polarization effects introduces errors in optical fibre communication system. We find that the SOP drifts slowly in buried cables, and rapidly in aerial cables. This is because buried cables are located in a static environment, whereas aerial cables are exposed directly to a dynamic environment. The SOP change in aerial cable shows significant correlation with its environment (the global radiation, temperature and wind). The autocorrelation function (ACF) was not performed in buried cable, since they do not satisfy the ACF assumption, whereas in aerial cable it is found that the ACF of the SOP decorrelates quite quickly during the day. The 50 percent decorrelation time during the day and night are 9.6 and 30.4 minutes, respectively. During the day the properties of the optical fibre change rapidly as a result of the rapidly changing environmental conditions, whereas at night the environmental conditions change relatively slowly. Fast Fourier Transform (FFT) of the SOP fluctuations show discrete peaks, which corresponds to the wind induced vibrational frequency of the cable. The PMD fluctuations for undeployed and deployed aerial optical fibre cable are monitored using the generalized interferometric technique (GINTY). It is found that the PMD measured with polarization scrambling is more scattered but more reliable than the PMD measured without polarization scrambling. This is because the PMD obtained with polarization scrambling is averaged over different input and output (I/O) SOP pairs. For deployed aerial cable, it is found that the PMD measured without polarization scrambling fluctuates rapidly during high wind speed conditions. Furthermore, there is a correlation between the measured PMD and the change in temperature. It is found that the change in temperature has a stronger influence than the wind on the PMD of the optical fibre link.
- Full Text:
- Date Issued: 2008
Constructing confidence intervals for polarization mode dispersion
- Authors: Erlank, Warrick
- Date: 2008
- Subjects: Fiber optics , Polarization (Light)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10571 , http://hdl.handle.net/10948/951 , Fiber optics , Polarization (Light)
- Description: Polarization mode dispersion (PMD) causes significant impairment in high bit-rate optical telecommunications systems. Knowledge of a fibre’s PMD mean value, and the relevant confidence interval, is essential for determining a fibre’s maximum allowable bit-rate. Various methods of confidence interval construction for time series data were tested in this dissertation using simulation. These included the autocovariance-matrix methods as suggested by Box and Jenkins, as well as the more practical and simpler batch means methods. Some of these methods were shown to be significantly better than the standard method of calculating confidence intervals for non time series data. The best of the tested methods were used on actual PMD data. The effect of using polarization scramblers was also tested.
- Full Text:
- Date Issued: 2008
- Authors: Erlank, Warrick
- Date: 2008
- Subjects: Fiber optics , Polarization (Light)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10571 , http://hdl.handle.net/10948/951 , Fiber optics , Polarization (Light)
- Description: Polarization mode dispersion (PMD) causes significant impairment in high bit-rate optical telecommunications systems. Knowledge of a fibre’s PMD mean value, and the relevant confidence interval, is essential for determining a fibre’s maximum allowable bit-rate. Various methods of confidence interval construction for time series data were tested in this dissertation using simulation. These included the autocovariance-matrix methods as suggested by Box and Jenkins, as well as the more practical and simpler batch means methods. Some of these methods were shown to be significantly better than the standard method of calculating confidence intervals for non time series data. The best of the tested methods were used on actual PMD data. The effect of using polarization scramblers was also tested.
- Full Text:
- Date Issued: 2008
Investigation of polarization mode dispersion measurement perfomance in optical fibre with a focus on the fixed analyzer technique
- Gamatham, Romeo Reginald Gunther
- Authors: Gamatham, Romeo Reginald Gunther
- Date: 2008
- Subjects: Fiber optics , Polarization (Light)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10524 , http://hdl.handle.net/10948/957 , Fiber optics , Polarization (Light)
- Description: The work presented in this dissertation is a comparative study of polarization mode dispersion (PMD) measurement performance where the fixed analyzer (FA) technique was built and tested for the first time in South Africa. Techniques involved in the study are: the Jones matrix eigenanalysis (JME), generalised interferometric technique (GINTY) and the FA technique, with a particular focus on the FA technique. The FA PMD measurement technique determines the average differential group delay (DGD) from the transmitted intensity spectrum through a polarizer and has three analysis methods (extrema counting, mean level crossing and Fourier analysis) which were all evaluated. PMD measurements were performed in the laboratory on several different fibre types and in the field on buried deployed Telkom fibre links (28.8 km). The techniques showed good agreement in the measured PMD value, both in the laboratory and field measurements. In particular very good agreement was found between the JME average DGD and the extrema counting analysis PMD value. The GINTY and FA Fourier analysis method also gave very similar PMD values. It was found that the fibre birefringence and the mode coupling manifest in different ways on the intensity spectrum. By using the FA ratio method, the length regimes of the different fibre types were determined. Three characteristics of the FA technique were investigated, namely: wavelength window variation, sampling and input SOP scrambling. It was found that the wavelength window and the PMD are inversely proportional. Correct sampling plays a significant role in determining the correct measured PMD value. Lastly an average PMD value over the PMD values for different input SOPs serves as a better representation of the true PMD value. An additional study showed that the FA technique and a developed Poincaré sphere analysis method agree very well regarding the PMD value.
- Full Text:
- Date Issued: 2008
- Authors: Gamatham, Romeo Reginald Gunther
- Date: 2008
- Subjects: Fiber optics , Polarization (Light)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10524 , http://hdl.handle.net/10948/957 , Fiber optics , Polarization (Light)
- Description: The work presented in this dissertation is a comparative study of polarization mode dispersion (PMD) measurement performance where the fixed analyzer (FA) technique was built and tested for the first time in South Africa. Techniques involved in the study are: the Jones matrix eigenanalysis (JME), generalised interferometric technique (GINTY) and the FA technique, with a particular focus on the FA technique. The FA PMD measurement technique determines the average differential group delay (DGD) from the transmitted intensity spectrum through a polarizer and has three analysis methods (extrema counting, mean level crossing and Fourier analysis) which were all evaluated. PMD measurements were performed in the laboratory on several different fibre types and in the field on buried deployed Telkom fibre links (28.8 km). The techniques showed good agreement in the measured PMD value, both in the laboratory and field measurements. In particular very good agreement was found between the JME average DGD and the extrema counting analysis PMD value. The GINTY and FA Fourier analysis method also gave very similar PMD values. It was found that the fibre birefringence and the mode coupling manifest in different ways on the intensity spectrum. By using the FA ratio method, the length regimes of the different fibre types were determined. Three characteristics of the FA technique were investigated, namely: wavelength window variation, sampling and input SOP scrambling. It was found that the wavelength window and the PMD are inversely proportional. Correct sampling plays a significant role in determining the correct measured PMD value. Lastly an average PMD value over the PMD values for different input SOPs serves as a better representation of the true PMD value. An additional study showed that the FA technique and a developed Poincaré sphere analysis method agree very well regarding the PMD value.
- Full Text:
- Date Issued: 2008
Field and laboratory measurements of PMD using interferometric techniques
- Authors: Mankga, Maphuti Comfort
- Date: 2007
- Subjects: Fiber optics , Polarization (Light)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10531 , http://hdl.handle.net/10948/557 , Fiber optics , Polarization (Light)
- Description: In this study, the generalized and traditional interferometric techniques (GINTY and TINTY) are used to investigate some of the important aspects of Polarization Mode Dispersion (PMD) phenomenon in optical fibres. Measurements of PMD and chromatic dispersion (CD) are performed on buried optical fibre cable in the Pretoria Telkom’s metropolitan network. The upgradeability of this network was investigated, and it was observed that just over a half of the fibres are upgradeable to 10 Gb.s-1 transmissions. Long-haul aerial network in the Northern Cape was also tested for upgradeability to 10 Gb.s-1. It was found that 41 percent of the fibres tested are upgradeable to 10 Gb.s-1. Long-term monitoring showed that PMD varies rapidly in aerial fibres and, on the other hand, it is relatively stable in buried cables. Investigations on the accuracy of the techniques showed that polarization scrambling is essential for the reduction of the measurements uncertainties. Furthermore, it was observed that TINTY underestimates the single scan PMD distributions. The study on the effect of the change in mode coupling on various fibre configurations was performed, and fibres showed a reduction in PMD after the introduction of mode coupling. Measurements of PMD conducted in the laboratory on cabled fibre with low PMD showed the floor sensitivity of TINTY. Comparison between GINTY and Jones Matrix Eigeanalysis (JME) PMD measurements methods were performed on an emulator, and the results showed a good agreement in the measured PMD.
- Full Text:
- Date Issued: 2007
- Authors: Mankga, Maphuti Comfort
- Date: 2007
- Subjects: Fiber optics , Polarization (Light)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10531 , http://hdl.handle.net/10948/557 , Fiber optics , Polarization (Light)
- Description: In this study, the generalized and traditional interferometric techniques (GINTY and TINTY) are used to investigate some of the important aspects of Polarization Mode Dispersion (PMD) phenomenon in optical fibres. Measurements of PMD and chromatic dispersion (CD) are performed on buried optical fibre cable in the Pretoria Telkom’s metropolitan network. The upgradeability of this network was investigated, and it was observed that just over a half of the fibres are upgradeable to 10 Gb.s-1 transmissions. Long-haul aerial network in the Northern Cape was also tested for upgradeability to 10 Gb.s-1. It was found that 41 percent of the fibres tested are upgradeable to 10 Gb.s-1. Long-term monitoring showed that PMD varies rapidly in aerial fibres and, on the other hand, it is relatively stable in buried cables. Investigations on the accuracy of the techniques showed that polarization scrambling is essential for the reduction of the measurements uncertainties. Furthermore, it was observed that TINTY underestimates the single scan PMD distributions. The study on the effect of the change in mode coupling on various fibre configurations was performed, and fibres showed a reduction in PMD after the introduction of mode coupling. Measurements of PMD conducted in the laboratory on cabled fibre with low PMD showed the floor sensitivity of TINTY. Comparison between GINTY and Jones Matrix Eigeanalysis (JME) PMD measurements methods were performed on an emulator, and the results showed a good agreement in the measured PMD.
- Full Text:
- Date Issued: 2007
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