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
Enhancing the accountability of ward councillors through public participation in Buffalo City Metropolitan Municipality
- Authors: Ngeni, Siphiwo Christopher
- Date: 2013
- Subjects: Local government -- South Africa -- Buffalo City -- Citizen participation , Municipal government -- South Africa -- Eastern Cape , Municipal officials and employees -- South Africa -- Eastern Cape , Political participation -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:8292 , http://hdl.handle.net/10948/d10186906
- Description: In terms of section 152(1)(a) of the Constitution of the Republic of South Africa, 1996 local government should provide a democratic and accountable service to local communities. Therefore, elected representatives and municipal officials must be accountable for their actions. This study investigates the influence of public participation in enhancing the accountability of ward councillors in the Buffalo City Metropolitan Municipality (BCMM). For the purpose of the study, the hypothesis was formulated that accountability of ward councillors is hampered by improper public participation mechanisms in Buffalo City Metropolitan Municipality (BCMM). In order to achieve the goal of this study and to test the hypothesis, it was essential to review literature on the accountability of ward councillors and public participation in local government. Primary data was obtained by interviewing ward committees and ward councillors from Buffalo City Metropolitan Municipality. Interviews were conducted with ward councillors and ward committees in wards 13 and 14 of BCMM. The major findings of the study, inter alia, are that ward councillors give feedback to their constituencies. Ward committees are instrumental in encouraging members of the public to attending these meetings. The most popular forum for public participation is the Independent Development Planning (IDP). It was established that approachability, accessibility and visibility of both ward councillors and ward committees in the community enhance public participation. The study concludes with recommendations that will assist the BCMM to enhance the accountability of ward councillors through public participation.
- Full Text:
- Date Issued: 2013
- Authors: Ngeni, Siphiwo Christopher
- Date: 2013
- Subjects: Local government -- South Africa -- Buffalo City -- Citizen participation , Municipal government -- South Africa -- Eastern Cape , Municipal officials and employees -- South Africa -- Eastern Cape , Political participation -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:8292 , http://hdl.handle.net/10948/d10186906
- Description: In terms of section 152(1)(a) of the Constitution of the Republic of South Africa, 1996 local government should provide a democratic and accountable service to local communities. Therefore, elected representatives and municipal officials must be accountable for their actions. This study investigates the influence of public participation in enhancing the accountability of ward councillors in the Buffalo City Metropolitan Municipality (BCMM). For the purpose of the study, the hypothesis was formulated that accountability of ward councillors is hampered by improper public participation mechanisms in Buffalo City Metropolitan Municipality (BCMM). In order to achieve the goal of this study and to test the hypothesis, it was essential to review literature on the accountability of ward councillors and public participation in local government. Primary data was obtained by interviewing ward committees and ward councillors from Buffalo City Metropolitan Municipality. Interviews were conducted with ward councillors and ward committees in wards 13 and 14 of BCMM. The major findings of the study, inter alia, are that ward councillors give feedback to their constituencies. Ward committees are instrumental in encouraging members of the public to attending these meetings. The most popular forum for public participation is the Independent Development Planning (IDP). It was established that approachability, accessibility and visibility of both ward councillors and ward committees in the community enhance public participation. The study concludes with recommendations that will assist the BCMM to enhance the accountability of ward councillors through public participation.
- Full Text:
- Date Issued: 2013
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