The diploma thesis deals with the influence of magnetic and electromagnetic fields on signals transmitted by optical fibers. Subsequently, the results of individual measured values are evaluated and analyzed, which were measured using an interferometer and a polarimeter. The first part deals with the theoretical analysis of the principles of interference and polarization of light. It further explains the basic operation of the above-mentioned devices as well as the immunity of the optical fiber to EMI. The second part of the work presents selected devices and technologies that were used as a source of electromagnetic or magnetic radiation. Subsequently, individual phenomena are plotted both in the course of time and with the help of a spectrogram or Poincaré sphere. From the measured results we can conclude that the commonly available technologies, which were selected for the diploma thesis, will not cause greater negative problems to the signal on measured frequencies in optical fibre, that could degrade the transmitted signal.

One of two project reports. Part B can be found at: / No abstract was provided. / Thesis / Master of Engineering (ME)

One of two project reports. Part B can be found at: / No abstract was provided. / Thesis / Master of Engineering (ME)

One of two project reports. Part A can be found at: http://hdl.handle.net/11375/18452 / No abstract was provided. / Thesis / Master of Engineering (ME)

This thesis describes the development of optical wavelength converters with an integrated coupling structure, fabricated on periodically poled MgO doped lithium niobate (MgO:LN) for optical fiber communication and other all-optical signal processing applications. Wavelength converter is an integral part of any broadband communication system. The ability to transfer information between carrier wavelengths allows for efficient use of the available bandwidth in a transmission medium. Wavelength converters based on PPLN waveguides are among the most efficient nonlinear optical devices available today, due to highspeed operation, low noise, parallel operation on multiple wavelength channels and preservation of information carried in the optical domain. However, low conversion efficiency is an issue for wavelength converter based on PPLN waveguide. Compared to pure LN, MgO doped LN decrease restriction in optical damage and increase conversion efficiency. Integrated coupling structure demonstrates a solution to mode-coupling of the input wave to the fundamental mode of DFG device and increase the conversion efficiency. Therefore, a periodically poled MgO doped lithium niobate (MgO:LN) waveguides with integrated coupling structure is fabricated. The components of integrated coupling structure are compatible with lithium nobate waveguides, including directional couplers, small radius bends, adiabatic taper, and mode filter. The integrated coupling structure combines the pump and signal waves into the DFG conversion section, and makes the single mode conversion of the pump from input waveguide to conversion section. Theoretical models and simulations are provided in this thesis, and performances of the device with this structure are also presented. / Thesis / Master of Applied Science (MASc)

Drawing of standard telecommunication-type optical fibres has been optimised in terms of optical and physical properties. Specialty fibres, however, typically have more complex dopant profiles. Designs with high dopant concentrations and multidoping are common, making control of the fabrication process particularly important. In photonic crystal fibres (PCF) the inclusion of air-structures imposes a new challenge for the drawing process. The aim of this study is to gain profound insight into the behaviour of complex optical fibre structures during the final fabrication step, fibre drawing. Two types of optical fibre, namely conventional silica fibres and PCFs, were studied. Germanium and fluorine diffusion during drawing was studied experimentally and a numerical analysis was performed of the effects of drawing parameters on diffusion. An experimental study of geometry control of PCFs during drawing was conducted with emphasis given to the control of hole size. The effects of the various drawing parameters and their suitability for controlling the air-structure was studied. The effect of air-structures on heat transfer in PCFs was studied using computational fluid dynamics techniques. Both germanium and fluorine were found to diffuse at high temperature and low draw speed. A diffusion coefficent for germanium was determined and simulations showed that most diffusion occurred in the neck-down region. Draw temperature and preform feed rate had a comparable effect on diffusion. The hole size in PCFs was shown to depend on the draw temperature, preform feed rate and the preform internal pressure. Pressure was shown to be the most promising parameter for on-line control of the hole size. Heat transfer simulations showed that the air-structure had a significant effect on the temperature profile of the structure. It was also shown that the preform heating time was either increased or reduced compared to a solid structure and depended on the air-fraction.

Fibre-optic sensors have been the focus of a lot of research, but their associated high cost has stifled their transferral from the laboratory to real world applications. This thesis addresses the issue of multiplexing, a technology that would lower the cost per unit sensor of a sensor system dramatically. An overview of the current state of research of, and the principles behind, multiplexed sensor networks is given. A new scheme of multiplexing, designated W*DM, is developed and implemented for a fibre Bragg grating (FBG) optical fibre sensor network. Using harmonic analysis, multiplexing is performed in the domain dual to that of the wavelength domain of a sensor. This scheme for multiplexing is compatible with the most commonly used existing schemes of WDM and TDM and thus offers an expansion over, and a resultant cost decrease from, the sensor systems currently in use. This research covered a theoretical development of the scheme, a proof of principle, simulated and experimental analysis of the performance of the multiplexed system, investigation into sensor design requirements and related issues, fabrication of the sensors according to the requirements of the scheme and the successful multiplexing of eight devices (thus offering an eightfold increase over current network capacities) using this scheme. Extensions of this scheme to other fibre sensors such as Long Period Gratings (LPGs) and blazed gratings were also investigated. Two LPGs having a moir?? structure were successfully multiplexed and it was shown that a blazed Fabry Perot grating could be used as a tuneable dual strain/refractive index sensor. In performing these tests, it was discovered that moir?? LPGs exhibited a unique thermal switching behaviour, hereto unseen. Finally the application of fibre sensors to the civil engineering field was investigated. The skill of embedding optical fibre in concrete was painstakingly developed and the thermal properties of concrete were investigated using these sensors. Field tests for the structural health monitoring of a road bridge made from a novel concrete material were performed. The phenomenon of shrinkage, creep and cracking in concrete was investigated showing the potential for optical fibre sensors to be used as a viable research tool for the civil engineer.

Fibre-optic sensors have been the focus of a lot of research, but their associated high cost has stifled their transferral from the laboratory to real world applications. This thesis addresses the issue of multiplexing, a technology that would lower the cost per unit sensor of a sensor system dramatically. An overview of the current state of research of, and the principles behind, multiplexed sensor networks is given. A new scheme of multiplexing, designated W*DM, is developed and implemented for a fibre Bragg grating (FBG) optical fibre sensor network. Using harmonic analysis, multiplexing is performed in the domain dual to that of the wavelength domain of a sensor. This scheme for multiplexing is compatible with the most commonly used existing schemes of WDM and TDM and thus offers an expansion over, and a resultant cost decrease from, the sensor systems currently in use. This research covered a theoretical development of the scheme, a proof of principle, simulated and experimental analysis of the performance of the multiplexed system, investigation into sensor design requirements and related issues, fabrication of the sensors according to the requirements of the scheme and the successful multiplexing of eight devices (thus offering an eightfold increase over current network capacities) using this scheme. Extensions of this scheme to other fibre sensors such as Long Period Gratings (LPGs) and blazed gratings were also investigated. Two LPGs having a moir?? structure were successfully multiplexed and it was shown that a blazed Fabry Perot grating could be used as a tuneable dual strain/refractive index sensor. In performing these tests, it was discovered that moir?? LPGs exhibited a unique thermal switching behaviour, hereto unseen. Finally the application of fibre sensors to the civil engineering field was investigated. The skill of embedding optical fibre in concrete was painstakingly developed and the thermal properties of concrete were investigated using these sensors. Field tests for the structural health monitoring of a road bridge made from a novel concrete material were performed. The phenomenon of shrinkage, creep and cracking in concrete was investigated showing the potential for optical fibre sensors to be used as a viable research tool for the civil engineer.

Drawing of standard telecommunication-type optical fibres has been optimised in terms of optical and physical properties. Specialty fibres, however, typically have more complex dopant profiles. Designs with high dopant concentrations and multidoping are common, making control of the fabrication process particularly important. In photonic crystal fibres (PCF) the inclusion of air-structures imposes a new challenge for the drawing process. The aim of this study is to gain profound insight into the behaviour of complex optical fibre structures during the final fabrication step, fibre drawing. Two types of optical fibre, namely conventional silica fibres and PCFs, were studied. Germanium and fluorine diffusion during drawing was studied experimentally and a numerical analysis was performed of the effects of drawing parameters on diffusion. An experimental study of geometry control of PCFs during drawing was conducted with emphasis given to the control of hole size. The effects of the various drawing parameters and their suitability for controlling the air-structure was studied. The effect of air-structures on heat transfer in PCFs was studied using computational fluid dynamics techniques. Both germanium and fluorine were found to diffuse at high temperature and low draw speed. A diffusion coefficent for germanium was determined and simulations showed that most diffusion occurred in the neck-down region. Draw temperature and preform feed rate had a comparable effect on diffusion. The hole size in PCFs was shown to depend on the draw temperature, preform feed rate and the preform internal pressure. Pressure was shown to be the most promising parameter for on-line control of the hole size. Heat transfer simulations showed that the air-structure had a significant effect on the temperature profile of the structure. It was also shown that the preform heating time was either increased or reduced compared to a solid structure and depended on the air-fraction.

The two-photon absorption (TPA) coefficient is measured in indium phosphide (InP) using femtosecond pulses to be 45cm/GW at 1.32μm. Nanosecond pulses are subsequently used to find the free-carrier refractive index cross-section, σ_r, and the free-carrier absorption coefficient, σ_fca. The quantity βσ_r is measured to be -113x10⁻²ºcm⁴/GW at 1.064μm and -84x10⁻²ºcm⁴/GW at 1.534μm. At 1.064μm, with β assumed to be 22cm/GW, the value suggested by theory, σ_r is -5.1x10⁻²ºcm³. Similarly, at 1.534μm, assuming β to be 20cm/GW gives a σ_r value of -4.1x10⁻²ºcm³. Due to refraction affecting the measurements of σ_fca, only an upper limit of 1x10⁻¹⁵cm² can be put on its value. The free-carrier experiments are repeated on two samples of cadmium mercury telluride (CMT) having bandgaps of 0.89eV and 0.82eV. For the first sample, β_σr is measured to be -148x10⁻²ºcm⁴/GW. Assuming β to be 89cm/GW gives a σ_r value of -1.7x10⁻²ºcm³ whilst σ_fca is found to be at most 3x10⁻¹⁵cm². Significant linear absorption occurs in the second sample which generates a large free-carrier population. It is shown that this significantly enhances the nonlinearities. Finally, the results of the work are tested by modelling a nonlinear transmission experiment, and the results found in this work give a closer fit to experimental results than the result of theory. Four-wave mixing (FWM) in a photonic crystal fibre is exploited to create a high output power optical parametric amplifier (OPA). To optimise the OPA conversion efficiency, the fibre length has to be increased to 150m, well beyond the walk-off distance between the pump and signal/idler. In this regime, the Raman process can take over from the FWM process and lead to supercontinuum generation. The OPA exhibits up to 40% conversion efficiency, with the idler (0.9μm) and the signal (1.3μm) having a combined output power of over 1.5W.