Design And Study Of Highly Efficient Photonic Crystal Beam Splitters

Photonic crystal, proposed simultaneously by E.Yablonovitch and S.John in 1987, is an artificial "band gap" material in which the dielectric constant is arranged periodically. The propagation of electromagnetic wave is highly prohibited in the photonic band gap. Additional, photonic crystals can be used as the conductor of photon to produce various optical devices. Compared with optical waveguide devices, photonic crystal devices have small volume and compact structure, and have tremendous application in optical integration chips and optical communication network. Related research have attracted wide attention and become the research forefront of optical communication.The main research contents of this dissertation are as follows:1. Firstly, It is shown that the new properties, which are related to practical devices using the CMT analysis to ring resonator, is obtained.They are the location, size,coupling characteristics and quality factor of the factors of Influencing performance index in photonic crystal ring resonator,and the efficiency of transmission and beam in the optical devices based on ring resonator. Secondly, the transmission and coupling characteristics of the light wave between the wave guide and ring resonators is studied using finite difference time domain (FDTD) method and research. By adjusting the various parameters in the ring resonator, the transmission characteristic of the light wave for every parameter are researched and analysed. If we choose different rods or change the refractive index of dielectric rods, can make the light field redistributed in the coupling interaction regions, so as to realize uniform or free distribution.2. Photonic crystal ring resonator can be constructed by putting the ring resonators and the waveguides next together. The spectra transmittance and propagation of the optical field entering this system was analyzed numerically using the plane wave expansion (PWE) method and finite-difference time-domain (FDTD) method. On the basis of this structure, ultracompact multiway beam splitter was designed and the ones with three and four output channels were discussed in details as examples. By simply tuning the radii of coupling dielectric rods for beam splitter with rectangular lattice ring resonators; and by adjusting refractive index of the dielectric rods in some regions for beam splitter with triangular lattice ring resonators,both of them inducing the redistribution of the power of the optical field, uniform or free splitting can be achieved. Compared with the results of normal waveguides having been reported, the most important aspect is that a large separating angle can be obtained in this structure.3. The design and simulation of a new and high efficiency beam splitter has been presented based on the coupling characteristics between the waveguide and cavity resonator in two dimensional photonic crystals. The splitting properties of the beam splitter have been numerically studied using the finite difference time domain(FDTD) method. Then in order to minimize backward reflections and to obtain equal or free distribution of power, we placed a cavity resonator consists of some additional rods in photonic crystals waveguides to optimize the devices. It was shown that a small dimension, a large separating angle, a high beam rate, and has been extended to have more light output channels in the beam splitter at optical communication wavelength. These excellent features, including small size, make it a promising candidate prospect in the future of optical communications application.4. We present the design and simulation of an ultracompact high efficiency polarization beam splitter(PBS) based on propagation properties of the light waves in straight waveguide and composite structure photonic crystals. The splitting properties of the PBS have been numerically simulated and analyzed using the Plane Wave Expansion (PWE)method Finite Difference Time Domain(FDTD) method. It consists of three parts, namely, input waveguide, beam structure and output waveguide. It is shown that a high efficiency, a large separating angle for TE mode and TM mode can be achieved. These excellent features, including small size, high rate, make it a promising candidate prospect in the future of photonic integrated circuit.