Papers by Keyword: Birefringence

Abstract: Screw-type dislocations like micropipes (MP) and threading screw dislocations (TSD) are prohibiting the function or at least diminishing the efficiency of electronic devices based on silicon carbide (SiC). Therefore, it is essential to characterize wafers in an efficient and fast manner. Molten potassium hydroxide (KOH) etching or white-beam X-ray topography (SWXRT) are either destructive or not economically viable for an in-depth characterization of every wafer of one SiC crystal. Birefringence microscopy is being utilized as a fast and non-destructive characterization method. Instead of microscopic setups, commercially available flat-bed scanners equipped with crossed polarizer foils can be used for fast large-area scans. This work investigates the feasibility of such a setup regarding the detection rate of MPs and TSDs. The results of a full-wafer mapping are compared with birefringence microscopy and KOH etching. In the investigated sample clusters of MPs caused by a polytype switch in the beginning of the growth could be identified by both birefringence microscopy and the flat-bed scanner setup, as well as small angle grain boundaries and TED arrays. However, the resolution of the scanner was not sufficient to identify TSDs. Nevertheless the setup proves to be an easy-to-setup and cheap characterization method, able to quickly identify defect clusters in 4H-SiC wafers.

Abstract: The paper presents the results of experimental studies of the electro-optical properties of β-Tl_1-xCu_xInS₂ (0 X 0,015) single crystals. It was found that in measurements of the induced birefringence, the transmission of the polarizer - crystal - analyzer (P-C-A) system is nonzero both for the presence of an external electric E = 0 and in its absence, which is apparently associated with the presence of internal fields arising in crystals during their growth ().

Abstract: The kinetic dependence of the photorefractive effect in the congruent lithium niobate crystal is determined in the work. The adequacy of the model for calculating the photoelectric fields from the indicatrix of photoinduced light scattering is shown. Two methods for determining the induced birefringence by interferograms and on the parameters of photoinduced light scattering are compared.

Abstract: In this study, Bismuth-based glasses were prepared and doped with various concentration of potassium chromate. They were melted in an electrical furnace at 1250°C for 4 hours then pressed with fire frame to plate shape and annealed at 500°C for 10 min. Optical spectra were used to analyze color shade of glasses. Homogeneity of glasses was analyzed by birefringence technique. Glasses color was changed from colorless to slightly and opaque green with an increasing amount of potassium dichromate and birefringence result showed that the glasses are non-homogenous.

Abstract: The optical properties of colloidal solutions of nanosized magnetite particles in kerosene were studied by optical methods (birefringence and light scattering). The data on the birefringence kinetics in nonstationary magnetic fields is used to determine the size distribution of magnetite particles and aggregates. It is shown that the particle size distribution essentially depends on the type of magnetic moments of the particles and aggregates. Static and dynamic light scattering experiments confirm the conclusion about the existence of a significant fraction of nanoparticles in the form of aggregates with sizes of several tens of nanometers.

Abstract: A dual-core photonic crystal fiber (PCF) with high birefringence, short coupling length and broadband flat dispersion is proposed in the paper. The symmetry of the original symmetric structure composed of hexagonally distributed air holes is distorted by replacing the innermost 12 air holes with 6 elliptical air holes. The characteristics of the dual-core PCF such as birefringence, coupling length and chromatic dispersion are analyzed by tuning its structural parameters. The results demonstrated that the dual-core PCF exhibits simultaneously a birefringence of up to 10^-2, a coupling length of 68.178 for the x-polarization and 74.825 for the y-polarization, and a broadband flat dispersion ranging from 1.1 to 1.6. The novel dual-core PCF may find applications in polarization-maintaining fibers and fiber-based polarization beam splitters/couplers with broadband flat dispersion.

Abstract: Since the Appearance of Hollow-Core Photonic Bandgap Fiber (HC-PBF), it was Widely Concerned for its Excellent Characteristics. in Order to Study the Characteristics of the HC-PBF that can be Used in Resonator Fiber Optic Gyros (R-Fogs), the Model Structure of a Polarization-Maintaining HC-PBF was Built and its Performance was Simulated by Using the Finite Element Method (FEM). its Mode Field Distribution and Birefringence Characteristics were Obtained. the Influences of the Air Core and Cladding Structures on the Mode Field Distribution and Birefringence were Simulated and Analyzed Further. the Result Showed that there are both Core Mode and Surface Mode in the Structure we Built. by Adding Scattering Points into the Fiber Core, the Surface Mode can be Significantly Suppressed. by Matching the Size of Core and Air Holes around the Core, a Birefringence up to 8*10^-4 were Obtained.

Abstract: Spark plasma sintering enables very rapid fabrication of bulk ceramic materials. Suitability of this technique for preparing of multilayer ceramic discs is up to now relatively seldom reported. Our work is focused on a bi-layered disc consisting of thick Al₂O₃ layer and comparably thick Mg (Ca)TiO₃ (MCT) layer sintered in one run. Al₂O₃ powder was nanometric (less than 40 nm) and composed of the hexagonal α-phase whereas MCT is a solid solution of two orthorombic perovskites. Pre-sintered and crushed MCT powder was coarser than alumina, up to 125 μm. The purpose of this material combination was creating of dielectric sandwich consisting of capacitor MCT material and resistor nanoalumina material. Spark plasma sintering run was done at 1200 °C, using pressure 80 MPa and dwell time only 2 min. Resulting sandwich was subjected to microstructural observations and cross sectional measurement of microhardness. On the border between Al₂O₃ and MCT the microhardness was higher than in MCT but has markedly higher dispersion than in the individual components. The MCT material exhibits birefringence in the polarized light [1]. We attempted to correlate the microhardness of individual MCT grains to their orientation indicated by birefringence.

Abstract: A novel kind of high birefringent terahertz (THz) photonic crystal fibers (PCFs) with material-filled structure is proposed in this paper. Based on the material-filled technology, which different materials are selectively filled into four air holes of the inner first circle near the central core in the designed THz PCFs, high birefringence are obtained from the structural and material-filled induced asymmetry in large frequency ranges near 1THz. Modal birefringence with different structural parameters and diverse refractive indices of the filled materials are investigated by plane wave expansion (PWE) method. The numerical results show that high birefringence up to 10^-3 can be obtained and its structure is simpler than that of the early proposed highly birefringent THz PCFs. It is helpful for PCFs design and real fabrication in the potential THz applications.

Abstract: A novel high-birefringent photonic crystal fiber (PCF) was proposed and analyzed by full-vector finite element method (FEM). The modal field and birefringence properties were investigated. All of air holes in proposed PCF are round, and their diameters are the same. It is greatly reduce the difficulty of fabrication. According to the results of numerical analysis, it can be observed that the mode birefringence of this novel PCF can be easily achieve the order of 10^-3 at 1.55μm. This research provides effective theoretical method for the fabrication, development and construction of high-birefringence photonic crystal fiber.