Characterization of Bragg grating pressure sensor using finite element analysis theory and experimental results
- Authors: Van Niekerk, Wynand F.
- Date: 2010-10-04T08:55:31Z
- Subjects: Bragg gratings , Fiber optics , Pressure transducers , Finite element method
- Type: Thesis
- Identifier: uj:6925 , http://hdl.handle.net/10210/3435
- Description: M.Ing. , Optical fibre Bragg gratings are a periodic variation of the refractive index in the core of an optical fibre andmay be formed by exposure to intense UV laser light under specific conditions. Light at a certain wavelength, called the Bragg wavelength, is reflected back when illuminating the grating with a light source. Bragg gratings can relatively easily be employed as strain and temperature sensors, but have small sensitivity for pressure. Special transducers are required to increase the sensitivity. A pressure sensor was manufactured by coating a fibre Bragg grating with a polymer. The polymer coating converts transverse pressure into longitudinal strain through the Poisson effect inside the polymer coating. This thesis investigates the sensitivity of themanufactured Bragg grating pressure sensor, by using the method of finite element analysis. An account of the experimental setup, whereby the Bragg grating is written with a frequency tripled Nd:YAG laser, is given. The process whereby the fibre is coated with the polymer is described. The sensor is characterized through experimental results and a comparison is made between theoretical and experimental results. Uses for this sensor and ways with which the sensitivity may be increased are suggested as future work.
- Full Text:
- Authors: Van Niekerk, Wynand F.
- Date: 2010-10-04T08:55:31Z
- Subjects: Bragg gratings , Fiber optics , Pressure transducers , Finite element method
- Type: Thesis
- Identifier: uj:6925 , http://hdl.handle.net/10210/3435
- Description: M.Ing. , Optical fibre Bragg gratings are a periodic variation of the refractive index in the core of an optical fibre andmay be formed by exposure to intense UV laser light under specific conditions. Light at a certain wavelength, called the Bragg wavelength, is reflected back when illuminating the grating with a light source. Bragg gratings can relatively easily be employed as strain and temperature sensors, but have small sensitivity for pressure. Special transducers are required to increase the sensitivity. A pressure sensor was manufactured by coating a fibre Bragg grating with a polymer. The polymer coating converts transverse pressure into longitudinal strain through the Poisson effect inside the polymer coating. This thesis investigates the sensitivity of themanufactured Bragg grating pressure sensor, by using the method of finite element analysis. An account of the experimental setup, whereby the Bragg grating is written with a frequency tripled Nd:YAG laser, is given. The process whereby the fibre is coated with the polymer is described. The sensor is characterized through experimental results and a comparison is made between theoretical and experimental results. Uses for this sensor and ways with which the sensitivity may be increased are suggested as future work.
- Full Text:
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.
- Full Text:
- 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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Towards the fabrication of polymer optical fibre Bragg gratings at 980 nm
- Terblanche, Johannes Theodorus
- Authors: Terblanche, Johannes Theodorus
- Date: 2012-09-10
- Subjects: Fiber optics , Bragg gratings
- Type: Thesis
- Identifier: uj:9908 , http://hdl.handle.net/10210/7307
- Description: M.Ing. , Bragg gratings written in polymer optical fibres are much more sensitive to temperature and strain measurements than silica fibre with a lower Young's modules and higher temperature coefficient. The good biocompatibility of polymer fibres makes them ideal medical sensors for in vivo strain and temperature measurements as well as excellent chemical sensors that can easily be doped with organic compounds. Most of the Bragg gratings in polymer optical fibres are inscribed around 1550 nm where the attenuation is as large as 1 dB/em. Grating fabrication was investigated at 980 nm where the attenuation was discovered to be optimal (less than 0.1 dB/em). The polymer optical fibre was spliced to silica optical fibre through butt-coupling and affixed with optical adhesive to produce transmission loss of between 7 and 25 dB (at 980 nm). Preliminary results show that it may be possible to create fibre Bragg gratings in polymer optical fibre at 980 nm. Gratings inscribed in fibre with an energy density of between 80 and 150 mJ/cm2 supplied by Paradigm Optics (MORFOP3) had a repeatability of 25%. With the fibres supplied by Prof. Peng (PBzMA- PEMA- PMMA co-polymer) a success rate of more than 90% was achieved when using energy densities around 70 mJ/cm2 • However, these gratings were weak and disappeared within 48 hours. The strength of these gratings varied from grating to grating. The reason of this instability is unknown and should be further investigated. The temperature sensitivity of polymer optical fibre at 976 nm was found to be -100 ±17 pm;oc corresponding with the reported value of -94 pm;oc at 976 nm.
- Full Text:
- Authors: Terblanche, Johannes Theodorus
- Date: 2012-09-10
- Subjects: Fiber optics , Bragg gratings
- Type: Thesis
- Identifier: uj:9908 , http://hdl.handle.net/10210/7307
- Description: M.Ing. , Bragg gratings written in polymer optical fibres are much more sensitive to temperature and strain measurements than silica fibre with a lower Young's modules and higher temperature coefficient. The good biocompatibility of polymer fibres makes them ideal medical sensors for in vivo strain and temperature measurements as well as excellent chemical sensors that can easily be doped with organic compounds. Most of the Bragg gratings in polymer optical fibres are inscribed around 1550 nm where the attenuation is as large as 1 dB/em. Grating fabrication was investigated at 980 nm where the attenuation was discovered to be optimal (less than 0.1 dB/em). The polymer optical fibre was spliced to silica optical fibre through butt-coupling and affixed with optical adhesive to produce transmission loss of between 7 and 25 dB (at 980 nm). Preliminary results show that it may be possible to create fibre Bragg gratings in polymer optical fibre at 980 nm. Gratings inscribed in fibre with an energy density of between 80 and 150 mJ/cm2 supplied by Paradigm Optics (MORFOP3) had a repeatability of 25%. With the fibres supplied by Prof. Peng (PBzMA- PEMA- PMMA co-polymer) a success rate of more than 90% was achieved when using energy densities around 70 mJ/cm2 • However, these gratings were weak and disappeared within 48 hours. The strength of these gratings varied from grating to grating. The reason of this instability is unknown and should be further investigated. The temperature sensitivity of polymer optical fibre at 976 nm was found to be -100 ±17 pm;oc corresponding with the reported value of -94 pm;oc at 976 nm.
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An investigation into performance criteria for Fibre Bragg Grating sensors embedded in composite structures
- Authors: Roberson, Craig Valentine
- Date: 2014-09-17
- Subjects: Bragg gratings , Fiber optics , Diffraction gratings
- Type: Thesis
- Identifier: uj:12338 , http://hdl.handle.net/10210/12124
- Description: M.Ing. (Mechanical Engineering) , The dissertation explores the applications and limitations of optic Fibre Bragg Grating (FBG) sensors for the purpose of structural health monitoring of high performance composite aerospace structures. The absence of a set of stringent performance criteria governing the form and function of a sensory system for embedded high performance applications highlights the major hurdle to be overcome before widespread acceptance of these technologies becomes apparent. The dissertation therefore develops through an extensive literature study a basic framework of performance criteria to be met by the sensory system upon which a prototype Structural Health Monitoring (SHM) system can be further developed. The resolution of the performance criteria into categories of mechanical and non-mechanical performance allows independent evaluation of factors that directly affect the performance of the sensor (in terms of strength, embeddability and load carrying ability) as well as its functional performance (in terms of orientation, spatial resolution and measurement philosophy). The literature study uses the non-mechanical performance limitations as a guideline for the selection of Fibre Bragg Grating (FBG) sensors as the sensory mechanism. The mechanical performance limitations of these specific sensors are then called into question and evaluated. Independent experiment campaigns are therefore developed to evaluate the mechanical and non-mechanical performance limitations such that a set of performance criteria can be developed governing the use of embedded sensory systems. Non mechanical performance with particular emphasis on sensor placement and orientation is investigated by simulating a fixed-free Euler Bernoulli cantilever using the Finite Element Method (FEM). The ability of the sensor to identify structural changes by measuring changes in modal response shows good results. Furthermore the inability of modal based monitoring to identify structural changes in the vicinity of modal inflection points is identified as an opportunity to locate structural deficiencies by monitoring multiple modes with known inflection point positions. The method also provides recommendations of sensor placement and orientation (close to the beam fixture and parallel with the neutral axis) such that the effectiveness of strain component measurements from all measurable modes is maximised. Mechanical performance of embedded FBG sensors is evaluated through an extensive fracture testing program which measures the fracture strains of fibre samples subjected to two-point bending. The fracture test program allows the quantification of the effects of the presence of the fibre’s protective polymer coating on fibre embeddability in composites, the consequent effects that the removal of this coating has on the mechanical performance and fracture behaviour of FBG sensors. These effects are qualified and mitigatory measures developed to improve the mechanical performance. A system of crack masking, hydrofluoric acid etching and fibre treatment is developed and statistical data analysis methods are employed and refined such that improvements in the mechanical properties of the FBG sensors can be quantified. An evaluation of the effectiveness of the proposed mechanical performance improvements yields good results culminating in the development of a comprehensive set of mechanical performance criteria to facilitate further development of a reliable SHM system.
- Full Text:
- Authors: Roberson, Craig Valentine
- Date: 2014-09-17
- Subjects: Bragg gratings , Fiber optics , Diffraction gratings
- Type: Thesis
- Identifier: uj:12338 , http://hdl.handle.net/10210/12124
- Description: M.Ing. (Mechanical Engineering) , The dissertation explores the applications and limitations of optic Fibre Bragg Grating (FBG) sensors for the purpose of structural health monitoring of high performance composite aerospace structures. The absence of a set of stringent performance criteria governing the form and function of a sensory system for embedded high performance applications highlights the major hurdle to be overcome before widespread acceptance of these technologies becomes apparent. The dissertation therefore develops through an extensive literature study a basic framework of performance criteria to be met by the sensory system upon which a prototype Structural Health Monitoring (SHM) system can be further developed. The resolution of the performance criteria into categories of mechanical and non-mechanical performance allows independent evaluation of factors that directly affect the performance of the sensor (in terms of strength, embeddability and load carrying ability) as well as its functional performance (in terms of orientation, spatial resolution and measurement philosophy). The literature study uses the non-mechanical performance limitations as a guideline for the selection of Fibre Bragg Grating (FBG) sensors as the sensory mechanism. The mechanical performance limitations of these specific sensors are then called into question and evaluated. Independent experiment campaigns are therefore developed to evaluate the mechanical and non-mechanical performance limitations such that a set of performance criteria can be developed governing the use of embedded sensory systems. Non mechanical performance with particular emphasis on sensor placement and orientation is investigated by simulating a fixed-free Euler Bernoulli cantilever using the Finite Element Method (FEM). The ability of the sensor to identify structural changes by measuring changes in modal response shows good results. Furthermore the inability of modal based monitoring to identify structural changes in the vicinity of modal inflection points is identified as an opportunity to locate structural deficiencies by monitoring multiple modes with known inflection point positions. The method also provides recommendations of sensor placement and orientation (close to the beam fixture and parallel with the neutral axis) such that the effectiveness of strain component measurements from all measurable modes is maximised. Mechanical performance of embedded FBG sensors is evaluated through an extensive fracture testing program which measures the fracture strains of fibre samples subjected to two-point bending. The fracture test program allows the quantification of the effects of the presence of the fibre’s protective polymer coating on fibre embeddability in composites, the consequent effects that the removal of this coating has on the mechanical performance and fracture behaviour of FBG sensors. These effects are qualified and mitigatory measures developed to improve the mechanical performance. A system of crack masking, hydrofluoric acid etching and fibre treatment is developed and statistical data analysis methods are employed and refined such that improvements in the mechanical properties of the FBG sensors can be quantified. An evaluation of the effectiveness of the proposed mechanical performance improvements yields good results culminating in the development of a comprehensive set of mechanical performance criteria to facilitate further development of a reliable SHM system.
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Numerical modelling of an Erbium-Ytterbium co-doped distributed feedback fiber laser
- Authors: Mpoyo, Justice Sompo
- Date: 2015-06-26
- Subjects: Erbium , Fiber optics , Optical communications , Bragg gratings
- Type: Thesis
- Identifier: uj:13635 , http://hdl.handle.net/10210/13815
- Description: M.Phil. (Electrical and Electronic Engineering) , A numerical model of an Erbium-Ytterbium co-doped distributed feedback (DFB) fiber laser is developed. The DFB fiber laser is a short length fiber laser whose feedback is distributed throughout the cavity. Its main advantage is its single longitudinal mode operation. The amplifying medium of a DFB fiber laser is a few centimetres long rare earth doped fiber. The feedback is obtained by a fibre Bragg grating printed in the core of the rare earth doped fiber. This type of laser emits naturally in two longitudinal modes. To obtain the single longitudinal mode operation, a π phase shift is introduced in the middle of the grating. Erbium doped DFB fiber lasers present the advantage of emitting single frequency light in the 1550 nm region where telecommunication fibers present the minimum loss. However due to the relatively short length of the gain medium, the number of available Erbium ions is small; as a result pump power absorption is low and the efficiency of the fiber laser is strongly reduced. The straightforward solution to this problem could be increasing the concentration of Erbium ions. This solution however has the disadvantage of increasing the Erbium ions interactions, thus leading to detrimental effect like cooperative upconversion and excited state absorption, which in term reduce considerably the laser efficiency. The best solution is to use Ytterbium ions as sensitizers along with Erbium ions to enhance the pump absorption, hence the efficiency of the laser. A model of the DFB fiber laser is an indispensable tool for its design, because it allows one to predict characteristic behaviour that would be both difficult and costly to deduce in laboratory conditions. The model developed in this project is based on rate equations of the Er3+-Yb3+ gain medium and coupled mode equations describing the laser field propagation in the fibre Bragg grating structure. The equations are solved using a quasi-analytical iterative method along with transfer matrix method with appropriate boundary conditions. The quasianalytical method used in this thesis is more robust than numerical solutions because it does not require providing an initial guess on the solution. Furthermore this method is hundreds time faster than the exact numerical solution while giving almost similar results.
- Full Text:
- Authors: Mpoyo, Justice Sompo
- Date: 2015-06-26
- Subjects: Erbium , Fiber optics , Optical communications , Bragg gratings
- Type: Thesis
- Identifier: uj:13635 , http://hdl.handle.net/10210/13815
- Description: M.Phil. (Electrical and Electronic Engineering) , A numerical model of an Erbium-Ytterbium co-doped distributed feedback (DFB) fiber laser is developed. The DFB fiber laser is a short length fiber laser whose feedback is distributed throughout the cavity. Its main advantage is its single longitudinal mode operation. The amplifying medium of a DFB fiber laser is a few centimetres long rare earth doped fiber. The feedback is obtained by a fibre Bragg grating printed in the core of the rare earth doped fiber. This type of laser emits naturally in two longitudinal modes. To obtain the single longitudinal mode operation, a π phase shift is introduced in the middle of the grating. Erbium doped DFB fiber lasers present the advantage of emitting single frequency light in the 1550 nm region where telecommunication fibers present the minimum loss. However due to the relatively short length of the gain medium, the number of available Erbium ions is small; as a result pump power absorption is low and the efficiency of the fiber laser is strongly reduced. The straightforward solution to this problem could be increasing the concentration of Erbium ions. This solution however has the disadvantage of increasing the Erbium ions interactions, thus leading to detrimental effect like cooperative upconversion and excited state absorption, which in term reduce considerably the laser efficiency. The best solution is to use Ytterbium ions as sensitizers along with Erbium ions to enhance the pump absorption, hence the efficiency of the laser. A model of the DFB fiber laser is an indispensable tool for its design, because it allows one to predict characteristic behaviour that would be both difficult and costly to deduce in laboratory conditions. The model developed in this project is based on rate equations of the Er3+-Yb3+ gain medium and coupled mode equations describing the laser field propagation in the fibre Bragg grating structure. The equations are solved using a quasi-analytical iterative method along with transfer matrix method with appropriate boundary conditions. The quasianalytical method used in this thesis is more robust than numerical solutions because it does not require providing an initial guess on the solution. Furthermore this method is hundreds time faster than the exact numerical solution while giving almost similar results.
- Full Text:
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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An access optimization approach for FFH-OCDMA system’s fiber bragg gratings encoder
- Nlend, Samuel, Swart, Theo G., Twala, Bhekisipho
- Authors: Nlend, Samuel , Swart, Theo G. , Twala, Bhekisipho
- Date: 2017
- Subjects: Bragg gratings , FFH-OCDMA , Multiaccess communication
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/243869 , uj:25211 , Citation: Nlend, S., Swart, T.G. & Twala, B. 2017. An access optimization approach for FFH-OCDMA system’s fiber bragg gratings encoder.
- Description: Abstract: This paper suggests an adaptive 2-D Optical CDMA coding system based on one-coincidence frequency hopping (OCFH) code combined with an optical orthogonal code (OOC) in the format OCFH/OOC, suitable for the fast frequency hopping optical code division multiple access (FFH-OCDMA) channel, encoded by the Bragg gratings encoder with an aim to optimize the access network in terms of number of users and transmitted power. As wavelength hopping (WH) code, the OCFH code is herein adapted to the constraints of the encoder: the Bragg gratings chain put on the optical fiber...
- Full Text:
- Authors: Nlend, Samuel , Swart, Theo G. , Twala, Bhekisipho
- Date: 2017
- Subjects: Bragg gratings , FFH-OCDMA , Multiaccess communication
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/243869 , uj:25211 , Citation: Nlend, S., Swart, T.G. & Twala, B. 2017. An access optimization approach for FFH-OCDMA system’s fiber bragg gratings encoder.
- Description: Abstract: This paper suggests an adaptive 2-D Optical CDMA coding system based on one-coincidence frequency hopping (OCFH) code combined with an optical orthogonal code (OOC) in the format OCFH/OOC, suitable for the fast frequency hopping optical code division multiple access (FFH-OCDMA) channel, encoded by the Bragg gratings encoder with an aim to optimize the access network in terms of number of users and transmitted power. As wavelength hopping (WH) code, the OCFH code is herein adapted to the constraints of the encoder: the Bragg gratings chain put on the optical fiber...
- Full Text:
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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The design and development of a side wall wind tunnel balance using fibre optic Bragg grating sensors
- Authors: Vaz, Nuno Figueira
- Date: 2018
- Subjects: Wind tunnel balances , Bragg gratings , Optical fiber detectors , Strain gages
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/284102 , uj:30671
- Description: M.Ing. (Mechanical Engineering) , Abstract: The requirements that a wind tunnel balance needs to satisfy have become increasingly stringent. These requirements, as set out by the wind tunnel testing community at large, include: improved static force accuracy, improved resolution, increased stiffness, temperature compensation and immunity to electromagnetic interference (EMI). In order to satisfy these requirements, wind tunnel balance design philosophy needs to be expanded to include employing alternative strain sensing technologies and alternative manufacturing techniques. This study sets to investigate the design and development of a six component side wall balance using optical fibre Bragg grating sensors (OFBGs). This is done in an attempt to address these stringent requirements by expand on traditional balance design philosophy by determine the viability of using OFBGs in wind tunnel balances. Traditional strain gauge side wall balances (SWB) fundamentally rely on measuring strain, being induced by an applied load, on a balance. For this reasons, the regions of the balance which are intended to be gauged are intentionally made thin. This is done to achieve a high strain gauge output. This however compromises balance stiffness and induces a high level of stress in the balance material at the gauged regions. In order to employ OFBGs on a SWB, the two groove strain sensing method must be employed. The basic working principles of this method is that an optical fibre is spanned between two points across a groove. As a load is applied, the groove deforms. This deformation (displacement) of the groove induces a strain into the optical fibre spanning the groove and a shift in the Bragg grating wavelength. Therefore the design of this SWB is fundamentally based on measuring the displacement between points. Based on these fundamentals, several design iterations were generated and analysed using FEM. The selected design underwent an iterative refinement process, aimed at optimising the design. This balance was manufactured and gauged with OFBGs. The manufactured balance was calibrated at the Counsel for Scientific and Industrial Research (CSIR) wind tunnel testing division in Pretoria, South Africa. The balance was evaluated based on uncertainty, hysteresis and interactions and repeatability...
- Full Text:
- Authors: Vaz, Nuno Figueira
- Date: 2018
- Subjects: Wind tunnel balances , Bragg gratings , Optical fiber detectors , Strain gages
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/284102 , uj:30671
- Description: M.Ing. (Mechanical Engineering) , Abstract: The requirements that a wind tunnel balance needs to satisfy have become increasingly stringent. These requirements, as set out by the wind tunnel testing community at large, include: improved static force accuracy, improved resolution, increased stiffness, temperature compensation and immunity to electromagnetic interference (EMI). In order to satisfy these requirements, wind tunnel balance design philosophy needs to be expanded to include employing alternative strain sensing technologies and alternative manufacturing techniques. This study sets to investigate the design and development of a six component side wall balance using optical fibre Bragg grating sensors (OFBGs). This is done in an attempt to address these stringent requirements by expand on traditional balance design philosophy by determine the viability of using OFBGs in wind tunnel balances. Traditional strain gauge side wall balances (SWB) fundamentally rely on measuring strain, being induced by an applied load, on a balance. For this reasons, the regions of the balance which are intended to be gauged are intentionally made thin. This is done to achieve a high strain gauge output. This however compromises balance stiffness and induces a high level of stress in the balance material at the gauged regions. In order to employ OFBGs on a SWB, the two groove strain sensing method must be employed. The basic working principles of this method is that an optical fibre is spanned between two points across a groove. As a load is applied, the groove deforms. This deformation (displacement) of the groove induces a strain into the optical fibre spanning the groove and a shift in the Bragg grating wavelength. Therefore the design of this SWB is fundamentally based on measuring the displacement between points. Based on these fundamentals, several design iterations were generated and analysed using FEM. The selected design underwent an iterative refinement process, aimed at optimising the design. This balance was manufactured and gauged with OFBGs. The manufactured balance was calibrated at the Counsel for Scientific and Industrial Research (CSIR) wind tunnel testing division in Pretoria, South Africa. The balance was evaluated based on uncertainty, hysteresis and interactions and repeatability...
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