Gain equalization of erbium doped fibre amplifiers with tuneable long-period gratings
- Authors: Nhlapo, Thabiso J.
- Date: 2009-02-26T12:21:27Z
- Subjects: Optical amplifiers , Optical fibers , Optical communications
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/391229 , uj:8171 , http://hdl.handle.net/10210/2176
- Description: M.Ing. , This thesis is about the gain equalization of erbium doped fibre amplifiers (EDFA), which is a key technology for enabling wavelength-division multiplexed (WDM) optical communication systems. In order to flatten dynamically the EDFA gain spectrum, a tuneable long-period grating filter was demonstrated. Long-period gratings were fabricated by using a KrF excimer laser combined with the metal amplitude mask technique. The transmission spectrum characteristic of the long- period grating was simulated theoretically by the coupled-mode theory. The coupling between the core and cladding modes of the long-period grating was investigated both experimentally and theoretically. The EDFA was constructed by using the forward pumping configuration consisting of pump laser source, WDM couplers, an optical isolator, and the erbium-doped fibre. The EDFA was characterized theoretically and experimentally for WDM applications. The tuneable long-period grating filter design is based on the tuneable coupler that uses the Mach-Zehnder interferometer configuration. The tuneable filter was demonstrated by equalizing the EDFA gain spectrum and the amplified spontaneous emission (ASE) source. The main advantage of this filter compared to other optical filters is its tuneability of the attenuation over a wide range of pump power.
- Full Text:
- Authors: Nhlapo, Thabiso J.
- Date: 2009-02-26T12:21:27Z
- Subjects: Optical amplifiers , Optical fibers , Optical communications
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/391229 , uj:8171 , http://hdl.handle.net/10210/2176
- Description: M.Ing. , This thesis is about the gain equalization of erbium doped fibre amplifiers (EDFA), which is a key technology for enabling wavelength-division multiplexed (WDM) optical communication systems. In order to flatten dynamically the EDFA gain spectrum, a tuneable long-period grating filter was demonstrated. Long-period gratings were fabricated by using a KrF excimer laser combined with the metal amplitude mask technique. The transmission spectrum characteristic of the long- period grating was simulated theoretically by the coupled-mode theory. The coupling between the core and cladding modes of the long-period grating was investigated both experimentally and theoretically. The EDFA was constructed by using the forward pumping configuration consisting of pump laser source, WDM couplers, an optical isolator, and the erbium-doped fibre. The EDFA was characterized theoretically and experimentally for WDM applications. The tuneable long-period grating filter design is based on the tuneable coupler that uses the Mach-Zehnder interferometer configuration. The tuneable filter was demonstrated by equalizing the EDFA gain spectrum and the amplified spontaneous emission (ASE) source. The main advantage of this filter compared to other optical filters is its tuneability of the attenuation over a wide range of pump power.
- Full Text:
A simpler approach to distributed sensing with ultra-low reflectivity fibre points
- Sutherland, Harriet Elizabeth
- Authors: Sutherland, Harriet Elizabeth
- Date: 2016
- Subjects: Optical fiber detectors , Optical fibers , Interferometers
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/212850 , uj:21035
- Description: Abstract: Distributed fibre sensors based on the frequency-domain analysis of Rayleigh backscattered light are well established. They exhibit excellent performance in both sensitivity and spatial resolution, but their application can be limited due to their cost and the complexity of the analysis. This work presents a system based on coherent optical frequency-domain reflectometry used in Rayleigh distributed sensors, but with some modifications to the fibre and the implementation of signal-conditioning algorithms that enable the use of more readily available components and simplified analysis. A sensing fibre is prepared by printing uniformly spaced (in this instance), ultra-low reflectivity points. When swept-wavelength light is introduced into the fibre, the reflections from the ultra-low reflectivity points interfere with the reflection from the tip of the fibre. These reflections can be processed with the techniques used in coherent optical frequency-domain reflectometry, providing information about the state of the fibre with regards to a parameter (such as temperature) between the reflective points. The function of the ultra-low reflectivity points is to provide stronger reflections than those produced by Rayleigh backscatter. The ultra-low reflectivity points are fibre Bragg gratings that act as reflectors and not as sensors per se. They are manufactured to reflect the same wavelength and, because of their low reflectivity, they also have a wider reflective spectral range than commonly used high-reflectivity fibre Bragg gratings. This removes the need for specialised detection equipment. Use of a reference interferometer and signal-processing algorithms (linearisation and phase fixing) makes it possible to replace a high-precision linearly tuneable laser with a standard tuneable laser or even a distributed feedback laser diode as the optical source. A novel technique is also presented for identifying the initial phase in the signal, post-acquisition, by means of a fibre Bragg grating in the reference interferometer. In combination with the linearisation and phase fixing algorithms, this locks the phase of the signal prior to analysis, dispensing with the need for precise synchronisation between the optical source and signal acquisition. The best spatial resolution that can be achieved by the system is 0.36 mm, and the best temperature resolution achieved (with a spatial resolution of 60 mm) had a standard deviation of... , M.Ing. (Electrical and Electronic Engineering)
- Full Text:
- Authors: Sutherland, Harriet Elizabeth
- Date: 2016
- Subjects: Optical fiber detectors , Optical fibers , Interferometers
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/212850 , uj:21035
- Description: Abstract: Distributed fibre sensors based on the frequency-domain analysis of Rayleigh backscattered light are well established. They exhibit excellent performance in both sensitivity and spatial resolution, but their application can be limited due to their cost and the complexity of the analysis. This work presents a system based on coherent optical frequency-domain reflectometry used in Rayleigh distributed sensors, but with some modifications to the fibre and the implementation of signal-conditioning algorithms that enable the use of more readily available components and simplified analysis. A sensing fibre is prepared by printing uniformly spaced (in this instance), ultra-low reflectivity points. When swept-wavelength light is introduced into the fibre, the reflections from the ultra-low reflectivity points interfere with the reflection from the tip of the fibre. These reflections can be processed with the techniques used in coherent optical frequency-domain reflectometry, providing information about the state of the fibre with regards to a parameter (such as temperature) between the reflective points. The function of the ultra-low reflectivity points is to provide stronger reflections than those produced by Rayleigh backscatter. The ultra-low reflectivity points are fibre Bragg gratings that act as reflectors and not as sensors per se. They are manufactured to reflect the same wavelength and, because of their low reflectivity, they also have a wider reflective spectral range than commonly used high-reflectivity fibre Bragg gratings. This removes the need for specialised detection equipment. Use of a reference interferometer and signal-processing algorithms (linearisation and phase fixing) makes it possible to replace a high-precision linearly tuneable laser with a standard tuneable laser or even a distributed feedback laser diode as the optical source. A novel technique is also presented for identifying the initial phase in the signal, post-acquisition, by means of a fibre Bragg grating in the reference interferometer. In combination with the linearisation and phase fixing algorithms, this locks the phase of the signal prior to analysis, dispensing with the need for precise synchronisation between the optical source and signal acquisition. The best spatial resolution that can be achieved by the system is 0.36 mm, and the best temperature resolution achieved (with a spatial resolution of 60 mm) had a standard deviation of... , M.Ing. (Electrical and Electronic Engineering)
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Methodologies used for increasing the output power of an Erbium doped fiber ring laser
- Authors: Le Roux, Josias Johannes
- Date: 2014-09-17
- Subjects: Optical amplifiers , Optical fibers , Lasers , Optical communications
- Type: Thesis
- Identifier: uj:12332 , http://hdl.handle.net/10210/12119
- Description: M.Ing. (Electrical And Electronic Engineering) , Please refer to full text to view abstract
- Full Text:
- Authors: Le Roux, Josias Johannes
- Date: 2014-09-17
- Subjects: Optical amplifiers , Optical fibers , Lasers , Optical communications
- Type: Thesis
- Identifier: uj:12332 , http://hdl.handle.net/10210/12119
- Description: M.Ing. (Electrical And Electronic Engineering) , Please refer to full text to view abstract
- Full Text:
Design and fabrication of long-period fibre gratings and wavelength-selective couplers for wavelength-division multiplexing networks
- Authors: Kritzinger, Ronnie
- Date: 2012-03-12
- Subjects: Optical fibers , Optical fiber detectors , Optical communications , Fiber gratings , Long-period gratings , Wavelength division multiplexing
- Type: Thesis
- Identifier: uj:2156 , http://hdl.handle.net/10210/4527
- Description: D.Ing. , Optical fibre-based devices (e.g. fibre gratings) play an important role in the optical com- munications and sensing industry. One type of fibre grating, the long-period grating (LPG), is becoming more and more popular as a simple and versatile component for a multitude of applications in optical engineering. The sensitivity of LPGs to various external perturbations and their ability to manipulate selectively light propagating in optical fibres make them well- suited to creating fibre-based devices. LPGs can be used in various applications, for example as gain equalisers for erbium-doped fibre amplifiers, as channel routers in optical add-drop multiplexers and as sensors. LPGs are typically fabricated by exposing photosensitive optical fibre to ultraviolet light. However, a variety of other techniques can be used to fabricate LPGs, including exposure to carbon dioxide (CO2) laser light. Over the years, it has become evident that CO2 laser- induced LPGs exhibit unique properties and features that can be harnessed to develop devices for important applications. It is necessary to understand the physical properties and optical characteristics of CO2 laser-induced LPGs to harness, manipulate and enhance their features. Research has been conducted on the development of an automated fabrication system that produces axially symmetric LPGs in single-mode fibre with a CO2 laser. A detailed study was undertaken on the design of uniform and non-uniform LPGs for wavelength-division multiplexing networks, as well as the characterisation of the CO2 laser beam propagating in the LPG fabrication system. These LPGs have been designed, using either analysis or syn- thesis techniques. The polarisation-dependent loss of the LPGs has also been investigated. Wavelength-selective couplers (WSCs) have been constructed using CO2 laser-induced LPGs and it was shown that these couplers were e®ective but not efficient in routing power to the output port of the tapping fibre. The physical properties, optical transmission characteris- tics, applications and other related issues of CO2 laser-induced LPGs have been investigated and satisfactory experimental results have been obtained. Areas for potential future research concerning CO2 laser-induced LPGs have been identified and discussed.
- Full Text:
- Authors: Kritzinger, Ronnie
- Date: 2012-03-12
- Subjects: Optical fibers , Optical fiber detectors , Optical communications , Fiber gratings , Long-period gratings , Wavelength division multiplexing
- Type: Thesis
- Identifier: uj:2156 , http://hdl.handle.net/10210/4527
- Description: D.Ing. , Optical fibre-based devices (e.g. fibre gratings) play an important role in the optical com- munications and sensing industry. One type of fibre grating, the long-period grating (LPG), is becoming more and more popular as a simple and versatile component for a multitude of applications in optical engineering. The sensitivity of LPGs to various external perturbations and their ability to manipulate selectively light propagating in optical fibres make them well- suited to creating fibre-based devices. LPGs can be used in various applications, for example as gain equalisers for erbium-doped fibre amplifiers, as channel routers in optical add-drop multiplexers and as sensors. LPGs are typically fabricated by exposing photosensitive optical fibre to ultraviolet light. However, a variety of other techniques can be used to fabricate LPGs, including exposure to carbon dioxide (CO2) laser light. Over the years, it has become evident that CO2 laser- induced LPGs exhibit unique properties and features that can be harnessed to develop devices for important applications. It is necessary to understand the physical properties and optical characteristics of CO2 laser-induced LPGs to harness, manipulate and enhance their features. Research has been conducted on the development of an automated fabrication system that produces axially symmetric LPGs in single-mode fibre with a CO2 laser. A detailed study was undertaken on the design of uniform and non-uniform LPGs for wavelength-division multiplexing networks, as well as the characterisation of the CO2 laser beam propagating in the LPG fabrication system. These LPGs have been designed, using either analysis or syn- thesis techniques. The polarisation-dependent loss of the LPGs has also been investigated. Wavelength-selective couplers (WSCs) have been constructed using CO2 laser-induced LPGs and it was shown that these couplers were e®ective but not efficient in routing power to the output port of the tapping fibre. The physical properties, optical transmission characteris- tics, applications and other related issues of CO2 laser-induced LPGs have been investigated and satisfactory experimental results have been obtained. Areas for potential future research concerning CO2 laser-induced LPGs have been identified and discussed.
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Experimental study of photosensitivity of optical fibre
- Authors: Joubert, Wietz Louwrens
- Date: 2012-02-06
- Subjects: Optical fibers , Optical fiber detectors , Interferometry
- Type: Thesis
- Identifier: uj:2024 , http://hdl.handle.net/10210/4376
- Description: M.Ing. , Bragg gratings exist due to permanent changes in the refractive index introduced in the fibre through exposure to ultraviolet radiation. Standard telecommunications fibre (SMF-28) is only slightly photosensitive at 248 nm irradiation. A comparative study of different photosensitization techniques is undertaken on the basis of the desired photosensitivity characteristics and efficiency of the technique used. The analytical method is used to determine valuable properties of fibre Bragg gratings. The bandwidth and maximum reflectivity of the fibre Bragg grating is dependant on the change of refractive index and is determined analytically. Obtaining very high reflectivity and bandwidth (~lnm) can only be achieved with highly photosensitive optical fibre where refractive index changes of~ 1 o-3 are possible. The change of the refractive index in the optical fibre is related to the phase change by: A new interferometric measurement technique based on this assumption allows the direct measurement of photosensitivity. This technique is modelled with a modified Layer Peeling algorithm. Standard telecommunications fibre was exposed to high-pressure (26B - 160B) hydrogen for several days. This increased the photosensitivity of the optical fibre significantly. The photosensitivity of the fibre is directly dependent on the hydrogen concentration inside the fibre. Refractive index changes, M ~ 1.3x10-3 were achieved in germanium doped fibre and M ~ 5x10-3 in germanium/boron codoped fibre. The knowledge of the hydrogen concentration inside the fibre is important in studying photosensitivity, transmission losses and the wavelength drift after Bragg grating manufacturing. The diffusion proceeds interstitially with no significant chemical interaction. A hydrogen diffusion model was developed based on the transfer of heat between two objects. Although the photosensitivity phenomenon was discovered in optical fibre more than 20 years ago, no complete physical explanation exist for it at present. We agree that stress relaxation and/or compaction are the main reasons for photosensitivity in optical fibre but also that it is still a complex and multifaceted phenomenon. A study of the thermal decay of fibre Bragg gratings suggests that fibre Bragg gratings written in hydrogen loaded fibre is less thermally stable than gratings written in germanium doped fibre. The analysis of accelerated ageing will predict the thermal stability of the Bragg grating over time.
- Full Text:
- Authors: Joubert, Wietz Louwrens
- Date: 2012-02-06
- Subjects: Optical fibers , Optical fiber detectors , Interferometry
- Type: Thesis
- Identifier: uj:2024 , http://hdl.handle.net/10210/4376
- Description: M.Ing. , Bragg gratings exist due to permanent changes in the refractive index introduced in the fibre through exposure to ultraviolet radiation. Standard telecommunications fibre (SMF-28) is only slightly photosensitive at 248 nm irradiation. A comparative study of different photosensitization techniques is undertaken on the basis of the desired photosensitivity characteristics and efficiency of the technique used. The analytical method is used to determine valuable properties of fibre Bragg gratings. The bandwidth and maximum reflectivity of the fibre Bragg grating is dependant on the change of refractive index and is determined analytically. Obtaining very high reflectivity and bandwidth (~lnm) can only be achieved with highly photosensitive optical fibre where refractive index changes of~ 1 o-3 are possible. The change of the refractive index in the optical fibre is related to the phase change by: A new interferometric measurement technique based on this assumption allows the direct measurement of photosensitivity. This technique is modelled with a modified Layer Peeling algorithm. Standard telecommunications fibre was exposed to high-pressure (26B - 160B) hydrogen for several days. This increased the photosensitivity of the optical fibre significantly. The photosensitivity of the fibre is directly dependent on the hydrogen concentration inside the fibre. Refractive index changes, M ~ 1.3x10-3 were achieved in germanium doped fibre and M ~ 5x10-3 in germanium/boron codoped fibre. The knowledge of the hydrogen concentration inside the fibre is important in studying photosensitivity, transmission losses and the wavelength drift after Bragg grating manufacturing. The diffusion proceeds interstitially with no significant chemical interaction. A hydrogen diffusion model was developed based on the transfer of heat between two objects. Although the photosensitivity phenomenon was discovered in optical fibre more than 20 years ago, no complete physical explanation exist for it at present. We agree that stress relaxation and/or compaction are the main reasons for photosensitivity in optical fibre but also that it is still a complex and multifaceted phenomenon. A study of the thermal decay of fibre Bragg gratings suggests that fibre Bragg gratings written in hydrogen loaded fibre is less thermally stable than gratings written in germanium doped fibre. The analysis of accelerated ageing will predict the thermal stability of the Bragg grating over time.
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Eksperimentele ondersoek na die vervaardiging van enkele stelselkomponente vir 'n hidrofoon in optiese veseltegnologie
- Authors: Spammer, Stephanus Johannes
- Date: 2015-02-25
- Subjects: Fiber optics , Optical fibers , Hydrophone
- Type: Thesis
- Identifier: uj:13348 , http://hdl.handle.net/10210/13362
- Description: M.Ing. , A study was done on optical fibre hydrophones. Integrated optic hydrophone components as well as optical fibre components were investigated. An optical fibre coupler was successfully manufactured with an etch process. The coupling ratio can be varied mechanically or by means of refraction index variation. Experimental procedures and results will be shown. Bending losses excited in an optical fibre coil were investigated as a function of different coil diameters. The results were extrapolated to determine the amount of losses arising in a hydrophone coil.
- Full Text:
- Authors: Spammer, Stephanus Johannes
- Date: 2015-02-25
- Subjects: Fiber optics , Optical fibers , Hydrophone
- Type: Thesis
- Identifier: uj:13348 , http://hdl.handle.net/10210/13362
- Description: M.Ing. , A study was done on optical fibre hydrophones. Integrated optic hydrophone components as well as optical fibre components were investigated. An optical fibre coupler was successfully manufactured with an etch process. The coupling ratio can be varied mechanically or by means of refraction index variation. Experimental procedures and results will be shown. Bending losses excited in an optical fibre coil were investigated as a function of different coil diameters. The results were extrapolated to determine the amount of losses arising in a hydrophone coil.
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Development of a multi-point temperature fiber sensor based on a serial array of optical fiber interferometers
- Authors: Della Tamin, Michelin
- Date: 2015-06-29
- Subjects: Interferometers , Optical fibers , Bragg gratings , Optical fiber detectors
- Type: Thesis
- Identifier: uj:13641 , http://hdl.handle.net/10210/13823
- Description: M.Ing. (Electrical and Electronic Engineering) , An experimental study of a multi-point optic fibre sensor for monitoring temperature changes is presented. The multi-point optic fibre sensor is made of a serial array of weak-reflectivity identical gratings. The weak-reflectivity identical gratings form the interferometric cavities UV printed on the single mode fibre. The ability to measure temperatures changes at different cavities along the serial array is particularly interesting for the monitoring of power transformers, high temperature furnaces and jet engines. Changes in temperature in each respective cavity is measured based on the spectral shift in the phase of the light from each respective cavity. The performance of the multi-point fibre sensor system is evaluated. Further, a theoretical and experimental investigation of a serial array composed of two cavities of different lengths is conducted. This investigation is aimed at measuring the impact of the overlap of the two distinct cavities in their respective frequency domain and determining the accuracy of the measurement. The result found shows that the sensor phase response is no more linear to temperature changes. It is also found that the nonlinear response of the sensor to temperature changes increases with the magnitude of the overlap.
- Full Text:
- Authors: Della Tamin, Michelin
- Date: 2015-06-29
- Subjects: Interferometers , Optical fibers , Bragg gratings , Optical fiber detectors
- Type: Thesis
- Identifier: uj:13641 , http://hdl.handle.net/10210/13823
- Description: M.Ing. (Electrical and Electronic Engineering) , An experimental study of a multi-point optic fibre sensor for monitoring temperature changes is presented. The multi-point optic fibre sensor is made of a serial array of weak-reflectivity identical gratings. The weak-reflectivity identical gratings form the interferometric cavities UV printed on the single mode fibre. The ability to measure temperatures changes at different cavities along the serial array is particularly interesting for the monitoring of power transformers, high temperature furnaces and jet engines. Changes in temperature in each respective cavity is measured based on the spectral shift in the phase of the light from each respective cavity. The performance of the multi-point fibre sensor system is evaluated. Further, a theoretical and experimental investigation of a serial array composed of two cavities of different lengths is conducted. This investigation is aimed at measuring the impact of the overlap of the two distinct cavities in their respective frequency domain and determining the accuracy of the measurement. The result found shows that the sensor phase response is no more linear to temperature changes. It is also found that the nonlinear response of the sensor to temperature changes increases with the magnitude of the overlap.
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Stabilised C-band dual wavelength erbium doped fibre ring laser
- Authors: Mthukwane, Clarence Modise
- Date: 2018
- Subjects: Optical fibers , Lasers - Industrial applications , Optical amplifiers , Bragg gratings , Erbium
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/280397 , uj:30130
- Description: M.Ing. (Electrical Engineering) , Abstract: In this dissertation, the realisation of a dual wavelength erbium doped fibre ring cavity laser configuration is discussed. The power stability and wavelength stability of a dual wavelength erbium doped fibre laser is investigated. The lasing wavelengths of the fibre laser are 1555.12 nm and 1560.32 nm. The laser is based on a ring cavity resonator which employs a 3 dB coupler and fibre Bragg gratings, as the wavelength selective component arrangement. The active medium in the cavity is a 3.2 m long erbium doped fibre with an absorption of 11.38 dB/m at 980 nm. To achieve simultaneous dual wavelength lasing with an erbium doped fibre laser configuration, there is one major challenge that must be overcome. The challenge is to correct the cavity losses on the selected wavelengths to achieve oscillation for all desired channels. In addition, because of the unevenness of the EDF gain profile, the threshold power for individual wavelengths is different. Subsequently, loss control across each of the selected wavelengths is required to balance the power difference between the wavelengths. The power and wavelength stability of the dual lasing wavelengths is investigated using an optical loop mirror with a 1 m length of single-mode fibre, and an unpumped erbium doped fibre of length 0.5 m, 1 m and 1.5 m. Also, the effect of changing the cavity length on the uniformity of the wavelength power increase relative to an increase in pump power together with the power and spectral stability of the lasing wavelengths is investigated. A 1m long Sagnac loop with a 70:30 coupling ratio was used to adjust the threshold power for simultaneous lasing of the two wavelengths. An increase in cavity length led to a good prospect for a stable dual wavelength laser with an output power difference of 0.4 dBm between the dual wavelengths and a power stability of 0.4 dB. The multi-wavelength and narrow spectral width of 0.19 nm and 0.20 nm of the laser can be used for dispersion measurement in wavelength division multiplexed communication links which consist of more than one wavelength. The laser was characterised for simultaneous dual wavelength output power response and power stability. The project presents the characterisation of an erbium doped fibre ring laser. The laser is cost effective and flexible in selecting preferred components for optimal performance in terms of power and wavelength stability, wavelength selectivity and narrow spectral width. Erbium doped fibre ring laser lasers are commercially available and are showing great promise in terms of their formidability and compatibility with current industrial requirements.
- Full Text:
- Authors: Mthukwane, Clarence Modise
- Date: 2018
- Subjects: Optical fibers , Lasers - Industrial applications , Optical amplifiers , Bragg gratings , Erbium
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/280397 , uj:30130
- Description: M.Ing. (Electrical Engineering) , Abstract: In this dissertation, the realisation of a dual wavelength erbium doped fibre ring cavity laser configuration is discussed. The power stability and wavelength stability of a dual wavelength erbium doped fibre laser is investigated. The lasing wavelengths of the fibre laser are 1555.12 nm and 1560.32 nm. The laser is based on a ring cavity resonator which employs a 3 dB coupler and fibre Bragg gratings, as the wavelength selective component arrangement. The active medium in the cavity is a 3.2 m long erbium doped fibre with an absorption of 11.38 dB/m at 980 nm. To achieve simultaneous dual wavelength lasing with an erbium doped fibre laser configuration, there is one major challenge that must be overcome. The challenge is to correct the cavity losses on the selected wavelengths to achieve oscillation for all desired channels. In addition, because of the unevenness of the EDF gain profile, the threshold power for individual wavelengths is different. Subsequently, loss control across each of the selected wavelengths is required to balance the power difference between the wavelengths. The power and wavelength stability of the dual lasing wavelengths is investigated using an optical loop mirror with a 1 m length of single-mode fibre, and an unpumped erbium doped fibre of length 0.5 m, 1 m and 1.5 m. Also, the effect of changing the cavity length on the uniformity of the wavelength power increase relative to an increase in pump power together with the power and spectral stability of the lasing wavelengths is investigated. A 1m long Sagnac loop with a 70:30 coupling ratio was used to adjust the threshold power for simultaneous lasing of the two wavelengths. An increase in cavity length led to a good prospect for a stable dual wavelength laser with an output power difference of 0.4 dBm between the dual wavelengths and a power stability of 0.4 dB. The multi-wavelength and narrow spectral width of 0.19 nm and 0.20 nm of the laser can be used for dispersion measurement in wavelength division multiplexed communication links which consist of more than one wavelength. The laser was characterised for simultaneous dual wavelength output power response and power stability. The project presents the characterisation of an erbium doped fibre ring laser. The laser is cost effective and flexible in selecting preferred components for optimal performance in terms of power and wavelength stability, wavelength selectivity and narrow spectral width. Erbium doped fibre ring laser lasers are commercially available and are showing great promise in terms of their formidability and compatibility with current industrial requirements.
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Manufacturing of fibre bragg gratings for dispersion compensation
- Authors: De Bruyn, Louis
- Date: 2011-11-30
- Subjects: Optical fibers , Diffraction gratings , Fibre bragg gratings
- Type: Thesis
- Identifier: uj:1751 , http://hdl.handle.net/10210/4106
- Description: M.Ing. , Fibre Bragg gratings (FBGs) have been manufactured for the first time in South Africa by means of the phase mask method. It is possible to manufacture not only uniform FBGs, but also chirped FBGs. The optical fibre that is used for imprinting the FBGs can also be hydrogen loaded locally. FBGs with a reflectivity of 99.7% and higher can be written by making use of the experimental setup presented in this thesis. It is possible to manufacture a FBG with a centre wavelength that has any value between the Bragg wavelength and approximately 6 nm lower than the Bragg wavelength. This is done by stretching the optical fibre prior to the writing process. FBGs have been simulated in MATLAB to get an idea of what one may expect during the manufacturing process. The program makes it possible to simulate the effects of changes in grating length, index modulation, pressure, temperature and strain on the centre wavelength of an FBG. Dispersion is explained in detail. Chromatic dispersion, which is part of dispersion as a whole, can be cancelled by making use of an FBG. The different techniques for the measurement of chromatic dispersion is explained. Some insight is given on dispersion (the pulse broadening in the time domain due to the different velocities of different wavelengths from the source's finite optical bandwidth) compensation. An FBG that was manufactured locally has been tested as a dispersion compensator. It was found that an FBG is effective in performing this function.
- Full Text:
- Authors: De Bruyn, Louis
- Date: 2011-11-30
- Subjects: Optical fibers , Diffraction gratings , Fibre bragg gratings
- Type: Thesis
- Identifier: uj:1751 , http://hdl.handle.net/10210/4106
- Description: M.Ing. , Fibre Bragg gratings (FBGs) have been manufactured for the first time in South Africa by means of the phase mask method. It is possible to manufacture not only uniform FBGs, but also chirped FBGs. The optical fibre that is used for imprinting the FBGs can also be hydrogen loaded locally. FBGs with a reflectivity of 99.7% and higher can be written by making use of the experimental setup presented in this thesis. It is possible to manufacture a FBG with a centre wavelength that has any value between the Bragg wavelength and approximately 6 nm lower than the Bragg wavelength. This is done by stretching the optical fibre prior to the writing process. FBGs have been simulated in MATLAB to get an idea of what one may expect during the manufacturing process. The program makes it possible to simulate the effects of changes in grating length, index modulation, pressure, temperature and strain on the centre wavelength of an FBG. Dispersion is explained in detail. Chromatic dispersion, which is part of dispersion as a whole, can be cancelled by making use of an FBG. The different techniques for the measurement of chromatic dispersion is explained. Some insight is given on dispersion (the pulse broadening in the time domain due to the different velocities of different wavelengths from the source's finite optical bandwidth) compensation. An FBG that was manufactured locally has been tested as a dispersion compensator. It was found that an FBG is effective in performing this function.
- Full Text:
Add-drop multiplexers using fibre bragg gratings and optical couplers
- Authors: Naude, Riaan
- Date: 2009-02-26T12:21:04Z
- Subjects: Diffraction gratings , Optical fibers
- Type: Thesis
- Identifier: uj:8168 , http://hdl.handle.net/10210/2173
- Description: M.Ing. , This thesis, devoted to fibre optics, is primarily concerned with the utilization of fibre Bragg gratings and optical couplers to realize optical add-drop multiplexers (OADMs). A comparative study regarding various OADM configurations is undertaken on the basis of manufacturing and the performance in terms of insertion loss, channel isolation, tuning ranges, stability and cost. The heart of most of the OADMs is fibre Bragg gratings. The Runge-Kutta numerical integration method is used to solve the coupled-mode equations in order to simulate the spectral dependence of Bragg gratings numerically. Properties such as the grating strength, the grating length and the grating index profile governing the spectral dependence of Bragg gratings are investigated. In recent years, there has been an increasing interest in the dispersive properties of Bragg gratings. We investigate methods to limit the amount of dispersion induced by fibre Bragg gratings. The tuning of Bragg gratings for dynamic OADMs is also reviewed. High channel isolation Bragg gratings are theoretically and experimentally investigated. DC-apodized gratings were designed and manufactured by using the phase mask method through the use of a preconditioning technique. Bragg gratings with channel isolations of up to 24.61 dB have been realized by using this technique. The spectral dependence of DC-apodized gratings on the amount of preconditioning and the smoothness of the index envelope is simulated and in agreement with the experimental results. An athermal Bragg grating was designed and manufactured, exhibiting an average wavelength-temperature sensitivity of 2.76 pm/oC. An OADM comprising a DC-apodized Kaiser grating and an optical circulator was realized. The device showed an insertion loss of 1.84 dB and a channel isolation of 22.84 dB. The coupling mechanisms for different types of optical couplers are investigated. The distribution of power was established to be either by evanescent field coupling (etched, polished and weakly fused couplers) or due to the beating phenomenon (strongly fused couplers). The beating phenomenon of the HE11 and HE12 modes in the waist of the tapered-fused coupler is modelled and used to simulate different characteristics, such as wavelength, polarization and external refractive index dependence of tapered-fused couplers, in order to realize OADMs.
- Full Text:
- Authors: Naude, Riaan
- Date: 2009-02-26T12:21:04Z
- Subjects: Diffraction gratings , Optical fibers
- Type: Thesis
- Identifier: uj:8168 , http://hdl.handle.net/10210/2173
- Description: M.Ing. , This thesis, devoted to fibre optics, is primarily concerned with the utilization of fibre Bragg gratings and optical couplers to realize optical add-drop multiplexers (OADMs). A comparative study regarding various OADM configurations is undertaken on the basis of manufacturing and the performance in terms of insertion loss, channel isolation, tuning ranges, stability and cost. The heart of most of the OADMs is fibre Bragg gratings. The Runge-Kutta numerical integration method is used to solve the coupled-mode equations in order to simulate the spectral dependence of Bragg gratings numerically. Properties such as the grating strength, the grating length and the grating index profile governing the spectral dependence of Bragg gratings are investigated. In recent years, there has been an increasing interest in the dispersive properties of Bragg gratings. We investigate methods to limit the amount of dispersion induced by fibre Bragg gratings. The tuning of Bragg gratings for dynamic OADMs is also reviewed. High channel isolation Bragg gratings are theoretically and experimentally investigated. DC-apodized gratings were designed and manufactured by using the phase mask method through the use of a preconditioning technique. Bragg gratings with channel isolations of up to 24.61 dB have been realized by using this technique. The spectral dependence of DC-apodized gratings on the amount of preconditioning and the smoothness of the index envelope is simulated and in agreement with the experimental results. An athermal Bragg grating was designed and manufactured, exhibiting an average wavelength-temperature sensitivity of 2.76 pm/oC. An OADM comprising a DC-apodized Kaiser grating and an optical circulator was realized. The device showed an insertion loss of 1.84 dB and a channel isolation of 22.84 dB. The coupling mechanisms for different types of optical couplers are investigated. The distribution of power was established to be either by evanescent field coupling (etched, polished and weakly fused couplers) or due to the beating phenomenon (strongly fused couplers). The beating phenomenon of the HE11 and HE12 modes in the waist of the tapered-fused coupler is modelled and used to simulate different characteristics, such as wavelength, polarization and external refractive index dependence of tapered-fused couplers, in order to realize OADMs.
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Towards an integrated optic tuneable gain equalizer for erbium-doped fibre amplifiers
- Authors: Botha, Roelene
- Date: 2009-02-26T12:16:33Z
- Subjects: Optical amplifiers , Optical fibers , Optical communications
- Type: Thesis
- Identifier: uj:8146 , http://hdl.handle.net/10210/2153
- Description: M.Ing. , Long distance optical communication systems experience a large degree of attenuation due to fibre losses, necessitating signal amplification. Erbium Doped Fibre Amplifiers (EDFAs) have found widespread use as all-fibre optical amplifiers, but exhibit unequal amplification of different wavelengths. Since the gain spectrum is signal-power and pump-power dependent, each EDFA spectrum may differ considerably, and a tuneable gain equalizer is required. A tuneable long-period grating (LPG) can be implemented as a gain equalizer for EDFAs. This dissertation deals with the design of an integrated optic version of the tuneable equalizing filter. The various components of which the device comprises, including optical couplers, Mach-Zehnder interferometers and an LPG, are investigated. The integrated optics designs of these components are then done using the BeamPROP software package. The use and optical properties of germania-doped silica as photosensitive waveguide material is studied. The production of the films for the gain equalizer, using electron-cyclotron resonance plasma-enhanced chemical vapour deposition, is discussed. Characterization of these films was carried out using spectroscopic ellipsometry and infrared spectroscopy. The optical constants, thickness, germania content and hydroxyl absorption was calculated using these measurements.
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- Authors: Botha, Roelene
- Date: 2009-02-26T12:16:33Z
- Subjects: Optical amplifiers , Optical fibers , Optical communications
- Type: Thesis
- Identifier: uj:8146 , http://hdl.handle.net/10210/2153
- Description: M.Ing. , Long distance optical communication systems experience a large degree of attenuation due to fibre losses, necessitating signal amplification. Erbium Doped Fibre Amplifiers (EDFAs) have found widespread use as all-fibre optical amplifiers, but exhibit unequal amplification of different wavelengths. Since the gain spectrum is signal-power and pump-power dependent, each EDFA spectrum may differ considerably, and a tuneable gain equalizer is required. A tuneable long-period grating (LPG) can be implemented as a gain equalizer for EDFAs. This dissertation deals with the design of an integrated optic version of the tuneable equalizing filter. The various components of which the device comprises, including optical couplers, Mach-Zehnder interferometers and an LPG, are investigated. The integrated optics designs of these components are then done using the BeamPROP software package. The use and optical properties of germania-doped silica as photosensitive waveguide material is studied. The production of the films for the gain equalizer, using electron-cyclotron resonance plasma-enhanced chemical vapour deposition, is discussed. Characterization of these films was carried out using spectroscopic ellipsometry and infrared spectroscopy. The optical constants, thickness, germania content and hydroxyl absorption was calculated using these measurements.
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Instembare erbiumgedoteerde optiesevesellasers met nou lynwydtes
- Badenhorst, Christiaan Gerhardus
- Authors: Badenhorst, Christiaan Gerhardus
- Date: 2015-02-16
- Subjects: Lasers , Data communication , Erbium , Optical fibers
- Type: Thesis
- Identifier: uj:13340 , http://hdl.handle.net/10210/13354
- Description: M.Ing. , Please refer to full text to view abstract
- Full Text:
- Authors: Badenhorst, Christiaan Gerhardus
- Date: 2015-02-16
- Subjects: Lasers , Data communication , Erbium , Optical fibers
- Type: Thesis
- Identifier: uj:13340 , http://hdl.handle.net/10210/13354
- Description: M.Ing. , Please refer to full text to view abstract
- Full Text:
Realization of chirped fibre Bragg gratings by strain gradients and their applications for fibre dispersing compensation
- Authors: Zhu, Yinian
- Date: 2012-09-05
- Subjects: Optical fibers , Optical detectors , Diffraction gratings
- Type: Thesis
- Identifier: uj:9621 , http://hdl.handle.net/10210/7040
- Description: M.Phil. , Linearly chirped fibre Bragg gratings can be used to compensate dispersions in a fibre transmission system. Various methods have been developed to chirp fibre gratings. It is proposed that a uniform period grating can be chirped by applying an axially linear strain gradient. In this project, we shall demonstate a novel method for making chirped fibre Bragg gratings, which involves bonding an unchirped fibre Bragg grating of 5cm length to the surface of a tapered stainless steel plate which is strained by bending or dilating. This allows a strain gradient to be formed along the grating length through the transferring of strains from the plate to the fibre. The profiles of tapered stainless steel plates have been determined by means of the finite element method and computer simulations to establish the strain gradient during loading. Ten conventional resistive strain gauges are also bonded on the other surface for strain measurements. Because of the strain gradient, the local Bragg wavelength is a function of the position along the length of the fibre grating so that the grating chirp is an automatic consequence of the strain gradient. This method provides the dynamic control of Bragg wavelength shift, peak reflectivity and spectral bandwidth, and its tunability is also suitable for optimising pulse compression and optical fibre dispersion compensation. Using couple-mode equations, we have also calculated the reflection response of a chirped fibre grating. It is shown that the close agreement between the theoretical and the experimental results suggests that the strain gradient technique provides good control of the Bragg grating chirp and the center wavelength of a chirped fibre Bragg grating.
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- Authors: Zhu, Yinian
- Date: 2012-09-05
- Subjects: Optical fibers , Optical detectors , Diffraction gratings
- Type: Thesis
- Identifier: uj:9621 , http://hdl.handle.net/10210/7040
- Description: M.Phil. , Linearly chirped fibre Bragg gratings can be used to compensate dispersions in a fibre transmission system. Various methods have been developed to chirp fibre gratings. It is proposed that a uniform period grating can be chirped by applying an axially linear strain gradient. In this project, we shall demonstate a novel method for making chirped fibre Bragg gratings, which involves bonding an unchirped fibre Bragg grating of 5cm length to the surface of a tapered stainless steel plate which is strained by bending or dilating. This allows a strain gradient to be formed along the grating length through the transferring of strains from the plate to the fibre. The profiles of tapered stainless steel plates have been determined by means of the finite element method and computer simulations to establish the strain gradient during loading. Ten conventional resistive strain gauges are also bonded on the other surface for strain measurements. Because of the strain gradient, the local Bragg wavelength is a function of the position along the length of the fibre grating so that the grating chirp is an automatic consequence of the strain gradient. This method provides the dynamic control of Bragg wavelength shift, peak reflectivity and spectral bandwidth, and its tunability is also suitable for optimising pulse compression and optical fibre dispersion compensation. Using couple-mode equations, we have also calculated the reflection response of a chirped fibre grating. It is shown that the close agreement between the theoretical and the experimental results suggests that the strain gradient technique provides good control of the Bragg grating chirp and the center wavelength of a chirped fibre Bragg grating.
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Ontwikkeling van 'n veseloptiese stelsel vir video- en datatransmissie
- Authors: Lombard, Hermanus Stephanus
- Date: 2015-03-02
- Subjects: Data transmission systems , Optical fibers , Telecommunication lines
- Type: Thesis
- Identifier: uj:13377 , http://hdl.handle.net/10210/13389
- Description: M.Ing. , Please refer to full text to view abstract
- Full Text:
- Authors: Lombard, Hermanus Stephanus
- Date: 2015-03-02
- Subjects: Data transmission systems , Optical fibers , Telecommunication lines
- Type: Thesis
- Identifier: uj:13377 , http://hdl.handle.net/10210/13389
- Description: M.Ing. , Please refer to full text to view abstract
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Versatile interferometer system for inscription of fiber Bragg gratings
- Authors: Du Toit, Ruan W.
- Date: 2012-06-06
- Subjects: Bragg gratings , Optical fibers , Interferometry , Interferometers
- Type: Thesis
- Identifier: uj:2503 , http://hdl.handle.net/10210/4956
- Description: M.Ing. , Bragg gratings are important components for sensing and for wavelength-division multiplexed optical communication systems. These gratings are manufactured by either side-writing of the fiber with a high intensity UV light through a phase mask, or by exposing the fiber to interference fringes through an interferometer arrangement. With one phase mask, only a small range of grating wavelengths is possible. This is achieved by pre-straining the fiber during the writing process. The limitation arises from the break strength of the fi ber, allowing a maximum range of Bragg wavelengths of only approximately 10 nm. The interferometric technique uses a beam splitter to divide a single input UV beam into two and intersecting them at the fiber. The angle at which the beams intersect will determine the period of the interference fringes and thus the Bragg grating written in the optical fiber. The Argon-ion laser is used with a 1060 nm phase mask (used to split beam) to write Bragg gratings with reflections from 1012 to 1600 nm. Three accurate- translation and rotation stages are used to keep the fiber at the beam intersection. Alignment, mechanical stability and coherence of laser are critical.
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- Authors: Du Toit, Ruan W.
- Date: 2012-06-06
- Subjects: Bragg gratings , Optical fibers , Interferometry , Interferometers
- Type: Thesis
- Identifier: uj:2503 , http://hdl.handle.net/10210/4956
- Description: M.Ing. , Bragg gratings are important components for sensing and for wavelength-division multiplexed optical communication systems. These gratings are manufactured by either side-writing of the fiber with a high intensity UV light through a phase mask, or by exposing the fiber to interference fringes through an interferometer arrangement. With one phase mask, only a small range of grating wavelengths is possible. This is achieved by pre-straining the fiber during the writing process. The limitation arises from the break strength of the fi ber, allowing a maximum range of Bragg wavelengths of only approximately 10 nm. The interferometric technique uses a beam splitter to divide a single input UV beam into two and intersecting them at the fiber. The angle at which the beams intersect will determine the period of the interference fringes and thus the Bragg grating written in the optical fiber. The Argon-ion laser is used with a 1060 nm phase mask (used to split beam) to write Bragg gratings with reflections from 1012 to 1600 nm. Three accurate- translation and rotation stages are used to keep the fiber at the beam intersection. Alignment, mechanical stability and coherence of laser are critical.
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'n Erbiumgedoteerde vesellasersensor met Braggroosterspieëls
- Authors: Burger, Johan Petrus
- Date: 2014-02-11
- Subjects: Optical fibers , Optical detectors
- Type: Thesis
- Identifier: uj:3805 , http://hdl.handle.net/10210/9178
- Description:
M.Eng. (Electrical and Electronic Engineering)
, An in-fibre Bragg grating is a period perturbation of the refractive index of the core of an optical fibre, where the length of the grating is much longer than the period of the grating. These gratings reflect light in a narrow band around a certain optical frequency. This narrow band is shifted in wavelength when the element is strained and is an absolute measure of the strain state of the grating. One way to interrogate this type of sensor is by using it as a mirror of an optical fibre laser, therefby forcing the laser emission band to coincide with the resonant frequency of the grating. In this thesis a theoretical model was developed to describe the operation of optically pumped Er+-doped optical fibre lasers. An explicit expression for the ouput power for a Fabry Perot fibre laser, was derived for the first time. The intracavity power propagation was also solved numerically. An optical fibre laser consisting out of an Er+-doped optical fibre optically pumped at 980nm, was built. A multilayer dielectric stack mirror was deposited on the one fibre endpoint of the laser. The other reflector is an in-fibre Bragg grating with a peak reflectance of 94% at 1548.5nm and a bandwith of
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- Authors: Burger, Johan Petrus
- Date: 2014-02-11
- Subjects: Optical fibers , Optical detectors
- Type: Thesis
- Identifier: uj:3805 , http://hdl.handle.net/10210/9178
- Description:
M.Eng. (Electrical and Electronic Engineering)
, An in-fibre Bragg grating is a period perturbation of the refractive index of the core of an optical fibre, where the length of the grating is much longer than the period of the grating. These gratings reflect light in a narrow band around a certain optical frequency. This narrow band is shifted in wavelength when the element is strained and is an absolute measure of the strain state of the grating. One way to interrogate this type of sensor is by using it as a mirror of an optical fibre laser, therefby forcing the laser emission band to coincide with the resonant frequency of the grating. In this thesis a theoretical model was developed to describe the operation of optically pumped Er+-doped optical fibre lasers. An explicit expression for the ouput power for a Fabry Perot fibre laser, was derived for the first time. The intracavity power propagation was also solved numerically. An optical fibre laser consisting out of an Er+-doped optical fibre optically pumped at 980nm, was built. A multilayer dielectric stack mirror was deposited on the one fibre endpoint of the laser. The other reflector is an in-fibre Bragg grating with a peak reflectance of 94% at 1548.5nm and a bandwith of
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Numerical modelling of a Raman-Rayleigh distributed temperature fiber sensor implementing correlation techniques
- Authors: Shimaponda, Mulundumina
- Date: 2015-06-29
- Subjects: Optical fiber detectors , Optical fibers , Interferometers
- Type: Thesis
- Identifier: uj:13647 , http://hdl.handle.net/10210/13831
- Description: M.Ing. (Electrical and Electronic Engineering) , A distributed temperature fiber sensor based on the ratio of the Raman anti-Stokes to Rayleigh backscattered light components is studied. The aim of the study is to propose a method of quantifying the noise exhibited in the Rayleigh backscattered signal and further propose correlation coding techniques to reduce the noise in the Rayleigh and Raman backscattered signals. The noise in the Rayleigh backscattered signal is referred to as “interferometric noise”. When Rayleigh scattering along the length of an optical fiber occurs, some of the scattered light travels in a direction opposite to the direction of propagation, and is called backscattered light. When the coherence length of the optical source permits interactions between the Rayleigh backscattered light, there is a possibility for the interacting backscattered light, within a distance that is half the coherence length, to interfere with each other. Furthermore, when the sensing optical fiber is greater than the coherence length of the optical source, there will be several interference sections along the length of the sensing fiber causing the intensity of the Rayleigh backscattered light at the photo-detectors to vary randomly. The intensity variation gives the Rayleigh backscattered signal a jagged appearance indicating the presence of interferometric noise. The longer the coherence length of the optical sources, the larger the intensity variations in the backscattered light, that is, the more the interferometric noise exhibited. The more the interferometric noise in the Rayleigh backscattered signal, the poorer the temperature accuracy of the distributed temperature sensor based on the ratio of the Raman anti Stokes to Rayleigh backscattered components. To quantify the interferometric noise affecting the Rayleigh backscattered signal, a mathematical model based on well-known scattering and interferometry theories is developed. Using the developed mathematical noise model, noise powers of approximately -52dBm and -40dBm for coherence lengths of 4m and 24m are respectively obtained...
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- Authors: Shimaponda, Mulundumina
- Date: 2015-06-29
- Subjects: Optical fiber detectors , Optical fibers , Interferometers
- Type: Thesis
- Identifier: uj:13647 , http://hdl.handle.net/10210/13831
- Description: M.Ing. (Electrical and Electronic Engineering) , A distributed temperature fiber sensor based on the ratio of the Raman anti-Stokes to Rayleigh backscattered light components is studied. The aim of the study is to propose a method of quantifying the noise exhibited in the Rayleigh backscattered signal and further propose correlation coding techniques to reduce the noise in the Rayleigh and Raman backscattered signals. The noise in the Rayleigh backscattered signal is referred to as “interferometric noise”. When Rayleigh scattering along the length of an optical fiber occurs, some of the scattered light travels in a direction opposite to the direction of propagation, and is called backscattered light. When the coherence length of the optical source permits interactions between the Rayleigh backscattered light, there is a possibility for the interacting backscattered light, within a distance that is half the coherence length, to interfere with each other. Furthermore, when the sensing optical fiber is greater than the coherence length of the optical source, there will be several interference sections along the length of the sensing fiber causing the intensity of the Rayleigh backscattered light at the photo-detectors to vary randomly. The intensity variation gives the Rayleigh backscattered signal a jagged appearance indicating the presence of interferometric noise. The longer the coherence length of the optical sources, the larger the intensity variations in the backscattered light, that is, the more the interferometric noise exhibited. The more the interferometric noise in the Rayleigh backscattered signal, the poorer the temperature accuracy of the distributed temperature sensor based on the ratio of the Raman anti Stokes to Rayleigh backscattered components. To quantify the interferometric noise affecting the Rayleigh backscattered signal, a mathematical model based on well-known scattering and interferometry theories is developed. Using the developed mathematical noise model, noise powers of approximately -52dBm and -40dBm for coherence lengths of 4m and 24m are respectively obtained...
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Dispersion compensation in wavelength-division multiplexed optical fibre links
- Authors: Saleh, Kawaya Shako
- Date: 2009-02-26T12:22:18Z
- Subjects: Optical fibers , Wavelength division multiplexing , Dispersion
- Type: Thesis
- Identifier: uj:8177 , http://hdl.handle.net/10210/2181
- Description: M.Ing. , Lightwave systems used in the core transport network of telecommunication systems operate in the second transmission window. The 1550 nm wavelength region exhibits the lowest attenuation coefficient, thus expanding the repeater distance in the network. However, the influence of the large dispersion coefficient associated with the second transmission window limits the operating speed of the network to 2.5 Gbit/s or less. In order for the network to operate at higher bit-rate, a dispersion management scheme is needed. In this research, the performance of negative dispersion fibre used as a dispersion compensating module is investigated. The negative dispersion fibre used in this study was the AVANEX PureForm DCM. The dispersion coefficient of the DCM measured at 1525 nm, 1545 nm and 1565 nm were given as -918 , -987 and -1047 respectively. The optimal operating condition of the DCM was obtained by considering various dispersion management configurations i.e. post-compensation, pre-compensation and symmetric compensation. The DCM was tested on a single span, single channel system operating at a speed of 10 Gbit/s with the transmitting wavelength of 1551.2 nm, over 60 km of convention single mode fibre. Furthermore, the performance of the system at 55 km and 65 km were also used to examine the results for the over- and under compensation links respectively. The results obtained for 100% dispersion cancellation for the pre-, post- and symmetric configuration showed an increase in the extinction ratio of 2.09 dB, 2.72 dB and 2.37 dB respectively. Similarly, the Q-factor was estimated to equal 13.67, 11.296 and 13.167 respectively. The results indicate similar performance for all the configurations considered, analysis of the eye-diagrams reveals that the post-compensation configuration would ultimately yield the best results. This is due to the fact that eye diagram recovered from this setup has minimal deformation. The experiments for an extremely over-compensated link, i.e. 40 km, showed an increase from 9.49, obtained with no compensation, to 10.63. However, for the extremely under-compensated link i.e. 80 km, the extinction ratio only manages to improve from 4.88 dB to 8.63 dB.
- Full Text:
- Authors: Saleh, Kawaya Shako
- Date: 2009-02-26T12:22:18Z
- Subjects: Optical fibers , Wavelength division multiplexing , Dispersion
- Type: Thesis
- Identifier: uj:8177 , http://hdl.handle.net/10210/2181
- Description: M.Ing. , Lightwave systems used in the core transport network of telecommunication systems operate in the second transmission window. The 1550 nm wavelength region exhibits the lowest attenuation coefficient, thus expanding the repeater distance in the network. However, the influence of the large dispersion coefficient associated with the second transmission window limits the operating speed of the network to 2.5 Gbit/s or less. In order for the network to operate at higher bit-rate, a dispersion management scheme is needed. In this research, the performance of negative dispersion fibre used as a dispersion compensating module is investigated. The negative dispersion fibre used in this study was the AVANEX PureForm DCM. The dispersion coefficient of the DCM measured at 1525 nm, 1545 nm and 1565 nm were given as -918 , -987 and -1047 respectively. The optimal operating condition of the DCM was obtained by considering various dispersion management configurations i.e. post-compensation, pre-compensation and symmetric compensation. The DCM was tested on a single span, single channel system operating at a speed of 10 Gbit/s with the transmitting wavelength of 1551.2 nm, over 60 km of convention single mode fibre. Furthermore, the performance of the system at 55 km and 65 km were also used to examine the results for the over- and under compensation links respectively. The results obtained for 100% dispersion cancellation for the pre-, post- and symmetric configuration showed an increase in the extinction ratio of 2.09 dB, 2.72 dB and 2.37 dB respectively. Similarly, the Q-factor was estimated to equal 13.67, 11.296 and 13.167 respectively. The results indicate similar performance for all the configurations considered, analysis of the eye-diagrams reveals that the post-compensation configuration would ultimately yield the best results. This is due to the fact that eye diagram recovered from this setup has minimal deformation. The experiments for an extremely over-compensated link, i.e. 40 km, showed an increase from 9.49, obtained with no compensation, to 10.63. However, for the extremely under-compensated link i.e. 80 km, the extinction ratio only manages to improve from 4.88 dB to 8.63 dB.
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