The samples this thesis investigated were m-plane nitrides films grown on m-plane sapphire by plasma-assisted molecular beam epitaxy (PAMBE). Scanning electron microscopy (SEM) images revealed the surface morphologies of the films and thicknesses of the films were measured by cross-sectional scanning electron microscopy. Then we used electron back-scattered diffraction (EBSD) and X-ray diffraction (XRD) to check the growth orientation of the films. The m-plane nitrides films have the anisotropic optical properties were due to the growth orientation of the films. The films are under anisotropic stress since they were grown along m-axis and hence change the electron band structure (EBS), which resulted in anisotropic optical property. We studied the polarization properties of the luminescence at 15 K and 300 K by polarization dependent photoluminescence (PL) and calculated the degree of polarization. And then measured the strain of the m-plane nitrides films by micro-Raman spectroscopy, discussed the degree of polarization and stress. The degree of polarization larger as the anisotropic stress of the film increased.

I examine two methods for modeling the temporal dynamics of optical communication networks that rapidly and accurately simulate the statistics of unlikely but physically significant system configurations. First, I implement a fiber emulator based upon a random uniform walk over the Poincaré sphere that reproduces the expected polarization temporal autocorrelation statistics with a small number of emulator sections. While easy to implement numerically, the increased computational efficiency afforded by this approach allow simulations of the PMD temporal dynamics to be preferentially biased towards regions of low probability using standard multicanonical methods for the first time. Then, in a subsequent study, I present a general transition matrix formalism that additionally applies to other time-dependent communication systems. I compare the numerical accuracy of several transition matrix sampling techniques and show that straightforward modifications of the acceptance rule can significantly increase computational efficiency if the numerical parameters are chosen to ensure a small self-transition probability within each discretized histogram bin. The general applicability of the transition matrix method is then demonstrated by calculating the outage dynamics associated with the hinge model of polarization evolution and, separately, fading in wireless communication channels. Further, I develop a Magnus expansion formalism for the rapid and accurate estimation of the frequency dynamics of optical polarization that extends the work of Ref.[94] to systems with PMD and PDL. My approach reproduces the power-series expansion and differential equation solution techniques of previous authors while also preserving the required symmetries of the exact solution in every expansion order. This significantly improves the bandwidth of high estimation accuracy, making this method well-suited to the stochastic analysis of PMD and PDL induced system penalty while also yielding physically realizable operator expansions applicable to the joint compensation of PMD and PDL. Finally, I employ high-speed polarimetery to demonstrate experimentally that low-amplitude mechanical excitations of commercially available dispersion compensation modules can excite high-frequency, > 75,000 rotations/s, polarization transients that are nearly invariant between successive measurements. I extend this procedure to measurements of the transient evolution of PMD.

In this study, we study the polarization dependence, gain property, and amplified spontaneous emission in Cr4+: YAG crystal fibers. Cr4+: YAG crystal has an ultra-wide bandwidth of 300 nm. Cr4+: YAG crystal fibers fabricated through laser heated pedestal growth technique are suitable for the applications of fiber amplifiers, fiber lasers, and broadband light sources. The experiment results showed that the polarization-dependent loss has a severe variation as the optical wavelength change. The maximum polarization-dependent loss was up to 18 dB. The main reason of such a large polarization-dependent loss is the combination of multimode interference and the birefringence induced by the non-uniformity of optical waveguide structure and residue strain in Cr4+: YAG crystal fibers. Thus, the results of polarization-dependent loss can be used as a feedback parameter to improve the fabrication process. In the experiment of gain property, bi-directional pump and double-pass transmission scheme was adopted and a 0.2 dB net gain was obtained for the first time at signal wavelength of 1400 nm, pumping wavelength of 1060 nm, and total pumping power of 2.8 W. It shows that Cr4+: YAG crystal fiber has potential to be developed as a broadband fiber amplifier. In the measurement of amplified spontaneous emission spectrum, a wide bandwidth of amplified spontaneous emission of 300 nm with total power of 50 £gWwas obtained at 0.2W pumping power condition. The coupling efficiencies from amplified spontaneous emission to single mode fibers and multimode fibers were 1.5 % and 9.9 %, respectively. This result reveals that it has potential to be developed as a broadband light source. To improve the optical properties of Cr4+: YAG crystal fiber in the future, improving the uniformity of optical fiber waveguide and reducing the residue strain in Cr4+: YAG crystal fiber may suppress the polarization-dependent loss; increasing the fiber length, decreasing the mode number, and employing a cladding pump technique with a well-distributed pump power in the crystal fiber to alleviate the excited state absorption may raise the gain performance and the amplified spontaneous emission power.

Fabry-Pérot (FP) filters are widely used in telecommunications, lasers and spectroscopy to measure the wavelengths of light. The properties of a FP filter depend on the wavelength and incident angle of the light source, the thickness of the etalon and the refractive index of the material between the reflecting surfaces. In previous studies, the nematic liquid crystal (NLC) is employed as the medium of FP filters because of its simple structure and ease of modulation. The directors of the NLC could be rotated by applying an electric field. Due to the birefringence of the NLC, the optical characteristics of the device are polarization dependent. Blue phase liquid crystal (BPLC) is the phase between cholesteric phase and isotropic phase. It¡¦s an optically isotropic material can function as an active index-tuning material adopted in a FP filter, and the characteristics of the BPLC-based FP filter are polarization independent. By applying an electric field, the Kerr effect can be induced due to the local reorientation of liquid crystals in BP structure, leading to the effective index change of BPLC and the transmission peak shifts. Furthermore, the effective index of BPLC approaches the ordinary index of host LCs under increasing electric fields. In addition, the BPLC using polymer network construction can be stabilized in room temperature and improves the convenience of the device. According to the experimental results, the tunability of the BPLC-based FP filter is about 1nm/V. The measured response time of the BPLC-based FP filter is 1ms.

A rigorous power coupling model for three-core optical waveguides is proposed based on a full-wave vector boundary element method (VBEM). In addition to the influence of the state of the polarization (SOP) of the input light on the coupling behavior of the three-core optical waveguides can be simulated, the polarization dependent loss (PDL) of the three-core optical waveguides can also be investigated by combining the Mueller matrix method into the power coupling model. In this dissertation, the power coupling model is applied to investigate two kinds of power splitters. The first power splitters are constructed of step-index single mode fibers called triangular 3 3 fused tapered couplers. The influence of the SOP of the input light on the coupling behavior of the triangular 3 3 fused tapered couplers and the effect of fabricating parameters of the coupler, fusion degree, and heated length on the PDL of the coupler are investigated in this dissertation. The second kind of power splitters are constructed of photonic crystal fibers (PCFs). And, several fundamental coupling properties of three-core photonic crystal fibers (PCFs) with equilateral triangular cores are investigated numerically included coupling length, bandwidth, and polarization dependent loss (PDL). It is found the three-core PCFs are good candidate to be realized as an ultra-compact power splitter. And, for three-core PCFs that chose a proper coupling point can raise the yield and performance stability of the power splitter. In addition to the coupling behavior of the power splitters, two-dimensional photonic crystals (PCs) are also studied in this dissertation based on finite-difference time-domain (FDTD) method. The phase interference phenomenon due to the multiple plane-wave signals as initial conditions of the FDTD method for computing band structure of two-dimensional PCs is studied in this dissertation. It is found some normal modes supposed to exist could be lost if the phase interference is nearly out of phase at eigenfrequency. To overcome this problem, we proposed a new solving procedure based on FDTD algorithm which can avoid mode loss phenomenon and obtain complete normal modes over interested frequency range.

I examine two methods for modeling the temporal dynamics of optical communication networks that rapidly and accurately simulate the statistics of unlikely but physically significant system configurations. First, I implement a fiber emulator based upon a random uniform walk over the Poincaré sphere that reproduces the expected polarization temporal autocorrelation statistics with a small number of emulator sections. While easy to implement numerically, the increased computational efficiency afforded by this approach allow simulations of the PMD temporal dynamics to be preferentially biased towards regions of low probability using standard multicanonical methods for the first time. Then, in a subsequent study, I present a general transition matrix formalism that additionally applies to other time-dependent communication systems. I compare the numerical accuracy of several transition matrix sampling techniques and show that straightforward modifications of the acceptance rule can significantly increase computational efficiency if the numerical parameters are chosen to ensure a small self-transition probability within each discretized histogram bin. The general applicability of the transition matrix method is then demonstrated by calculating the outage dynamics associated with the hinge model of polarization evolution and, separately, fading in wireless communication channels. Further, I develop a Magnus expansion formalism for the rapid and accurate estimation of the frequency dynamics of optical polarization that extends the work of Ref.[94] to systems with PMD and PDL. My approach reproduces the power-series expansion and differential equation solution techniques of previous authors while also preserving the required symmetries of the exact solution in every expansion order. This significantly improves the bandwidth of high estimation accuracy, making this method well-suited to the stochastic analysis of PMD and PDL induced system penalty while also yielding physically realizable operator expansions applicable to the joint compensation of PMD and PDL. Finally, I employ high-speed polarimetery to demonstrate experimentally that low-amplitude mechanical excitations of commercially available dispersion compensation modules can excite high-frequency, > 75,000 rotations/s, polarization transients that are nearly invariant between successive measurements. I extend this procedure to measurements of the transient evolution of PMD.

Made available in DSpace on 2016-03-15T19:37:40Z (GMT). No. of bitstreams: 1 Suzanne Baruh Susskind.pdf: 1627296 bytes, checksum: 5e0a86235d0abcb7084c0b28f0c7c21d (MD5) Previous issue date: 2006-08-03 / An investigation of Polarization Dependent Loss (PDL) behavior is performed in an Recirculation Loop (RCL) experimental apparatus. The PDL statistical nature turns its accumulated contribution in the RCL different from the sum of each different elements contributions. Theoretical analyses are also performed using the Jones and Mueller matrix approach to represent each element in the loop. Experimental errors are considered in the theoretical results and compared with experimental ones. A 7% depolarization most likely due to optical amplifier amplified spontaneous emission is identified in the experimental apparatus. / O estudo experimental da Perda Dependente da Polarização (Polarization Dependent Loss PDL) é realizado em um Anel de Recirculação Óptico (Recirculating loop - RCL). A PDL por sua natureza estatística tem seu valor acumulado diferente da soma da PDL de cada elemento que constitui o anel. Estudos teóricos são conduzidos utilizando o método da matrix de Jones e Mueller para representar os diferentes elementos ópticos constituintes do anel. Erros experimentais são introduzidos nos resultados teóricos e comparados com os resultados experimentais. Verifica-se que uma despolarização em torno de 7% ocorre no aparato experimental. Essa despolarização tem forte indicação de ser oriunda do amplificador óptico devido a natureza não polarizada da emissão espontânea amplificada.

In the UK, large quantities of intermediate level waste pose complex radiological remediation challenges. Chemical understanding of uranium in these Mg-rich sludges is vital. Previous studies have examined uranium uptake by calcium carbonate minerals (calcite and aragonite) under conditions pertinent to both natural and anthropogenically perturbed systems. However, research on uranyl uptake by magnesium-rich minerals such as magnesite [MgCO3], brucite [Mg(OH)2], nesquehonite [MgCO3·3H2O] and hydromagnesite-[Mg5(CO3)4(OH)2·4H2O] has not, to the best of our knowledge, been previously conducted. Such experiments will improve our understanding of the mobility of uranium and other actinides in natural lithologies such as dolomitic limestones or mafic igneous emplacements, as well as provide key information applicable to nuclear waste repository strategies involving Mg-rich phases. By two EXAFS techniques, we determined: (1) where uranyl (UO22+) is adsorbed, and (2) how uranyl is attached to the mineral surface. Therefore powder experiments of U(VI) were performed with magnesite, brucite, nesquehonite and hydromagnesite. The second experiment (GIXAFS) consisted of single crystals of magnesite (10.4) and brucite (0001). The powders were reacted in solution pH ~8.5 with U(VI)nitrate for 48 hrs. under ambient PCO2 = -3.5. The single crystals were reacted under ambient and reduced PCO2 ~ -4.5 for 48 hrs. with concentrations of U(VI)chlroride above (500; 50 ppm) and below (5 ppm) solubility of schoepite [UO2(OH)2·H2O]. The GIXAFS measurements were made at χ = 0˚ and χ = 90˚ relative to the synchrotron beam polarisation to uequivocally determine the adsorbate structures. Kd values for Mg-carbonate phases were comparable to or exceeded those published for calcium carbonates. GIXAFS results clearly showed polarisation for both ambient and reduced PCO2. XANES results showed uranyl is oriented with the axial oxygens perpendicular to the mineral surface. This implies, using also X-ray reflectivity and diffuse scatter, local hydrated bayleyite [Mg2(UO2)(CO3)3∙18H2O] and possible rutherfordine-like [UO2CO3] regions, which will be useful to predict uranium behaviour in various remediation processes.

[pt] Este trabalho apresenta um método teórico e experimental para medir Perda Dependente de Polarização (PDL) em sistemas ópticos. Este método basea-se na forma como duas componentes de polarização ortogonais da luz moduladas em amplitude por duas frequências distintas são acopladas no detector após a transmissão pelo dispositivo sob caracterização. No presente trabalho é realizado um estudo acerca das propriedades da luz e das técnicas tradicionais utlizadas para medir PDL. Antes da caracterização das medidas de PDL, foi realizado o alinhamento do dispositivo de teste (DUT), ou seja, do sistema que vai emular a PDL, a fim de garantir que o mesmo estivesse com as perdas ópticas minimizadas. Em seguida, conectou-se o DUT à configuração montada no laboratório, sendo realizado os ajustes de polarização e supressão das portadoras ópticas. Neste método é possível calcular o valor da PDL e da na orientação na Esfera de Poincaré. / [en] This work presents a theoretic and experimental method for Polarization Dependent Loss (PDL) measurement in optical systems. This method is based on how two orthogonal polarization components both modulated in amplitude by two different frequency are coupled in the detector. In this present work a study is performed about light properties and traditional techniques used to peform PDL measurement. Before the characterization of PDL measures the alignment of the device under test (DUT) was performed to make sure that optical losses were minimized in the system which will emulate the PDL. Then, the DUT was connected to the experimental setup to optical carriers suppression and polarization alignment. In this method is possible to calculate the PDL value and its orientation on the Poincaré sphere.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-10-02T19:31:50Z No. of bitstreams: 1 felipedesouzadelgado.pdf: 2621698 bytes, checksum: f2d2c40acc8fdf80a70c9f39aabc0cc9 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-10-09T19:46:37Z (GMT) No. of bitstreams: 1 felipedesouzadelgado.pdf: 2621698 bytes, checksum: f2d2c40acc8fdf80a70c9f39aabc0cc9 (MD5) / Made available in DSpace on 2017-10-09T19:46:37Z (GMT). No. of bitstreams: 1 felipedesouzadelgado.pdf: 2621698 bytes, checksum: f2d2c40acc8fdf80a70c9f39aabc0cc9 (MD5) Previous issue date: 2017-08-24 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Esta dissertação apresenta a produção de redes de período longo em fibras ópticas por descargas de arcos elétricos e o seu uso em aplicações de sensoriamento de corrente em veículos aéreos não tripulados. Os aspectos teóricos fundamentais para o entendimento das redes de período longo são apresentados. Além disso, discutiu-se os diferentes tipos de acoplamentos de energia que podem ocorrer em uma rede de período longo e também, os mecanismos responsáveis pela formação dessas redes produzidas por descargas de arco elétrico. A fabricação de redes de período longo utilizando a técnica de arco elétrico foi descrita e o comportamento da perda dependente da polarização das redes produzidas foi investigado. Além disso, é apresentado um novo método para a produção de redes de período longo com perda dependente da polarização reduzida. Constatou-se que por meio de alterações no ângulo de incidência das descargas elétricas na fibra óptica em relação à um ponto de referência, é possível promediar os efeitos induzidos pontualmente por cada descarga de arco elétrico e assim, reduzir a perda dependente da polarização intrínseca dessas redes. Por fim, é apresentada a aplicação de uma rede produzida por arco elétrico combinada a um ímã de neodímio, compondo um novo dispositivo de sensoriamento para medir a corrente elétrica exigida pelos motores elétricos de um veículo aéreo não tripulado. / This dissertation presents the fabrication of long-period fiber gratings through electric arc discharges and their application in current sensing in unmanned aerial vehicles. The theoretical aspects of long-period gratings are presented. Besides, we discussed the different types of coupling that could occur in a long-period fiber grating, as well as the mechanisms responsible for the formation of the gratings produced by electric arc discharges. The manufacture process of the long-period gratings using the electric arc technique was described and the behavior of the polarization dependent loss of these gratings was investigated. In addition, a new method for the production of long period gratings with reduced polarization dependent loss is introduced. It has been found that by changing the incidence angle of the electric discharges in the optical fiber in relation to a reference point, it is possible to average the effects induced by each electric arc discharge and, therefore, reducing the intrinsic polarization dependent loss of these gratings. Finally, the application of a grating produced by electric arc combined with a neodymium permanent magnet is presented. This combination allows us to measure the electric current required by a motor of an unmanned aerial vehicle.