In this study, the phase grating was investigated by using electro-optical characteristics of blue phase liquid crystals(BPLCs) such as fast-response and optically isotropic etc. The BPLC units was affected by distribution of periodically electric field and then changed the cubic structure into others, when applying voltage in etched electrode of grating pattern. A linearly polarized light is incident upon the sample and experience the periodic difference of index, and diffraction effect was generated. In order to find out the best conditions of these liquid crystals device, we discussed different factor such as angle of linearly polarized light, operating temperature of grating, cooling rate and electrode structure.

Arsenic trisulfide (As₂S₃) waveguide devices on lithium niobate substrates (LiNbO₃) provide a set of compact and versatile means for guiding and manipulating optical modes in infrared integrated optical circuits, including the integrated trace gas detection system. As a member of the chalcogenide glass family, As₂S₃ has many properties superior to other materials, such as high transparency up to 10 [mu]m, large refractive index and high nonlinear coefficient. At the wavelength of 4.8[mu]m, low-loss As₂S₃ waveguides are achieved: The propagation loss is 0.33 dB/cm; the coupling efficiency is estimated to be 81 %; and less than 3 dB loss is measured for a 90-degree bent waveguide of 250 [mu]m bending radius. They offer an ideal solution to the optical interconnection -- the fundamental element of an optical circuit. LiNbO₃ is a birefringent crystal that has long been studied as the substrate material. Titanium diffused waveguides in lithium niobate substrate (Ti: LiNbO₃) have excellent electro-optical properties, based on which, on-chip polarization converters are demonstrated. New benefits can be obtained by integrating As₂S₃ and Ti: LiNbO₃ to form a hybrid waveguide, which benefits from the high index contrast of As₂S₃ and the electro-optical properties of Ti: LiNbO₃ as well as its easy connection with commercial single mode fibers. For hybrid waveguides, the mode coupling is key. A taper coupler is preferred owing to its simplicity in design and fabrication. Although preliminary experiments have shown the feasibility of such integration, the underlying mechanism is not well understood and guidelines for design are lacking. Therefore, a simulation method is first developed and then applied to the taper coupler design. Devices based on taper couplers are then fabricated and characterized. The study reveals that in the presence of mode beating, it is not necessarily the longer taper that is the better coupling. There exists an optimum length for a taper with fixed width variation. A two-stage taper design can largely reduce the total length, e. g. by 64%, while keeping the coupling efficiency above 90%. According to the frequency domain analysis, these practical taper couplers work for a wavelength range instead of a single wavelength.

This research investigated the characteristics of single-mode optical pulses generated with orthogonal-polarization optical feedback (OPF) in Fabry-Perot type semiconductor lasers. Single-mode pulse trains with a pulse frequency of 470 MHz and 3.76 GHz were observed. A modified model was proposed to solve the inconsistency between the experimental results and the computer simulations of Otsuka and Chern¡¦s model. These results also solve the problem of a round-trip feedback distance that is too short to enable the feedback system to be implemented, making this technology accomplishable in currently working systems. Furthermore, this investigation recovered and maintained a stable oscillation of every missing longitudinal mode in a hysteresis type mode-hopping gap of a semiconductor laser. A special feature of this method is that both the laser power and spectral purity are preserved during mode recovery and mode switching. The experimental results also reveal that the OPF effectively suppressed mode-hopping in semiconductor lasers and drove the laser into a stable single-mode state. Finally, this research employed OPF to suppress the intensity noise stimulated by coherent optical feedback in a semiconductor laser. At a coherent-feedback level as strong as ¡V14 dB, an OPF ratio of ¡V29 dB could return the laser to its primitive single mode from the multimode, yielding a spectral purity and relative intensity noise (RIN) even better than the solitary values. These discoveries constitute an important contribution to our understanding of applications of semiconductor lasers.

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.

The specific heat Cp has been showed at various temperatures in the literature, which shows a sharp increase labeled as the lambda-transition at the critical temperature. This transition has been observed previously among the phases of solid-nematic-isotropic liquid in p-azoxyanisole (PAA) and anisaldazine (AAD), and among the phases of solid-smectic-cholesteric-isotropic liquid in cholesteryl myristate (CM). In this thesis work, we analyze the experimental data for the temperature dependence of Cp and the thermal expansion alpha_p and also pressure dependence of alpha_p by a power-law formula. From the analysis of pressure dependence of alpha_p, we calculate the temperature dependencies of specific heat Cp and of the isothermal compressibility kappa_T for the phase transitions considered in PAA, AAD and CM. Our calculations for the temperature dependence of the p and kappa_T can be compared with the experimental data when available in the literature. Polarization, tilt angle and the dielectric constant have been reported in the literature at various temperatures close to the solid-smectic C*-smectic A-isotropic liquid transition in the ferroelectric liquid crystals of A7 and C7. The mean field model with the free energy expanded in terms of the order parameters (polarization and tilt angle) has been reported in the literature previously. In this thesis work, we apply the mean field model first time by fitting the expressions derived for the temperature dependence of the polarization, tilt angle and the dielectric constant to the experimental data for A7 and C7 from the literature. Since the mean field model studied here describes adequately the observed behaviour of A7 and C7, the expressions for the temperature dependence of the polarization, tilt angle and the dielectric constant which we derive, can also be applied to some other ferroelectric liquid crystals to explain their observed behaviour.

Laser Induced Breakdown Spectroscopy (LIBS) which is used to determine the elemental content of various samples, inspects the emission spectroscopy of samples of interest for searching certain elements or identifying the unknown content. In this study, spectroscopic analyses of various kinds of metals, namely, Cu, Fe, Mo, Ti, W, some compounds such as CuBe, ZnSe, ZnS, GaSe, some semimetals like Si, Ge and even gases were investigated by means of a compact-commercial portable LIBS system and an independently constructed experimental set-up consisting of a single pulse system and various kinds of double pulse configurations using Nd:YAG lasers. The contributions of this thesis to the LIBS community can be classified into two main groups- which are experimental and code development. One of the experimental contributions was the investigation of the different crystal surfaces of silicon in which dangling bond density were taken into account for a more precise comparison of atomic emissions. The second experimental contribution was the polarization experiments by which polarization dependency, to some extent, was demonstrated. The third and final one was the orthogonal double pulse configuration with a 45 o incidence angle for both lasers in opposite directions by which it was shown that the positioning becomes straightforward yielding the desired reproducible results. The second major contribution was to develop a basic code for analyzing the experimental data more accurately. In conclusion, by means of the different experimental approaches, factors relating to the enhancement in intensity were investigated and as a result of developing the code, flexibility in upgrading the constraints of element searching was obtained and the updating of the database was accomplished.

Novel broadband designs of patch antennas with an air substrate have been proposed in this dissertation. In the dual-frequency design, the study of single-fed dual-frequency microstrip antenna with a V-shaped slot has been first presented. As for the broadband patch antenna design, antennas with a U-shaped slot or a pair of wide slits can have an operating bandwidth more than 2.0 times that of a conventional one at a given operating frequency. The antenna bandwidth of then can be enhanced about 25%. In the designs of reducing cross-polarization, by using dual capacitive feeds with equal input powers, but with a 180¢X-phase shift, The cross-polarization radiation can be reduce about 10 to 15dB in the H-plane. Finally, A broadband shorted patch antenna fed by an aperture-coupled feed with an H-shaped coupling slot is proposed. By using an air substrate of thickness about 0.07 free-space wavelength of the center operating frequency, the proposed antenna can have an impedance bandwidth of about 26.2%. And the antenna design reduced the antenna size to be 40%~50%of the simple case.

Novel designs of planar antennas including the feed network for improving the antenna performance improvement (CP axial-ratio bandwidth, XPL, port decoupling for dual-polarized operation, and harmonic control) or achieving dual-band operation are presented. This thesis, comprises five sections. Firstly, for obtaining broadband CP designs, the Wilkinson power divider and branch-line coupler are used. The 3-dB axial ratio CP bandwidths of all proposed antennas are larger than 30%. Secondly, the dual broadband patch antennas including a stopband network are proposed. Thirdly, the dual-polarized patch antenna with high XPL and isolation between two ports by using a Wilkinson power divider with a 180¢X phase shift between its two ports is proposed. Fourthly, the dual-band and dual-polarized patch antenna suitable for base-station antenna applications for mobile communications systems is studied. Finally, the harmonic control study of a square microstrip antenna is presented.

Several broadband dual-polarized patch antenna designs are presented and studied. Good isolation (< ¡V30 dB) between the two feeding ports of the proposed broadband dual-polarized patch antenna has been obtained. This dissertation reports four different innovative designs. Firstly, a new design of the aperture-coupled patch antenna with modified H-shaped coupling slots for achieving dual-polarized radiation with high isolation over a wide bandwidth is studied. Secondly, Optimized feeding of the dual-polarized aperture-coupled patch antenna with H-shaped coupling slots for achieving highly decoupled feeding ports is experimentally investigated. Thirdly, an aperture-coupled patch antenna with a cross slot for compact dual-polarized operation in the 1800-MHz band suitable for applications in personal communication system is presented. Finally, new designs of the broadband dual-polarized patch antenna with hybrid feeds suitable for DCS base-station application are proposed.

A single-mode fused biconical 2¡Ñ2 coupler for polarization beamsplitting is fabricated in this thesis. We use simple fused and tapered method to fabricate the polarization beamsplitter(PBS) stably, and then we can get polarization maintaining in the output fibers. Without changing the manufacturing process, we design the device with special combination of fabrication parameters. We have achieved an extinction ratio of 25.78dB at the throughput port and 27.16dB at the coupled port. A usable spectral window as broad as 37nm and 27nm with an extinction ratio larger than 15dB for both ports is obtained. The excess loss is about 0.3dB. Based on a full-wave numerical approach, the performance of the PBS can be well modeled. We get good agreement between the measured and simulated results.