Design And Study Of Algorithm For Three Dimension Optical Waveguide And Its Application In Polarization Rotator

Due to the rapid developing of all-optical transmission networks (AON), varioushigh-performance and cost-effective optical devices are demanded. Owing to their smallsize, power consumption, cost-effectiveness and good stability, the integrated opticsdevices play a very important role in the AON. Polarization rotator is the key componentfor the100Gbits/s Multiplexing Quadrature Phase Shift Keying system. It could also beused to realize arbitrary polarization angle rotation to the input light. Based on the III-Vcompound semiconductor, the polarization rotator especially has the advantage of directintegration with optical laser and modulator.Only the simple structure like the one dimension planar optical waveguide could becalculated by analytical method. Many common structures like the rectangle waveguideand the rib waveguide could only be calculated using the numerical methods. So,excellent-performance and high-efficient numerical simulation algorithm is required. Thedissertation proposes a new algorithm form that is used to control the numerical dispersionin the Full Vector Beam Propagation Method (FV-BPM) Simulation in the case of largerefractive index contrast waveguide like the polarization rotator, and rationality of thealgorithm is also given. Only two gradient index layers needed in the simulation, thedispersion can be well controlled. The algorithm has good flexibility, and little disturbanceis done to the exact mode of the waveguide, so the accuracy of the algorithm has also beenguaranteed. Next, the high-efficiency mode solver, imaginary-distance propagationmethod is introduced, and a new transparent boundary condition for the real number modesolver is derived. It only take less than100μm length to get convergent and stable modepattern and refractive index when the mode solver and the new boundary condition areused to calculate the rib waveguide.Vector correction to the scalar wave equation is demonstrated in detail with theauthor’s independent effort, the resulted accurate vector coupled mode equation bring in energy coupling between different polarized components. Compared with the BPM, thevector coupled mode theory need only about one-twelfth of the simulation time to get thecoupling length and period of the polarization rotator, saving a lot of time in designingnew optical device. Coupling coefficients of the asymmetric periodic rib waveguideproposed in this dissertation are calculated, and predictive analysis is made for thehigher-performance polarization rotator.Finally， the asymmetrically loaded periodic polarization rotator is simulated by theFV-BPM and the vector mode coupled theory. Analysis and optimizing of the waveguideis implemented around the coupled length, the periods and the insertion loss of the device.The inaccurate coupled period obtained by the scalar coupled mode theory has decreasedby11by the vector mode coupled theory in this dissertation, and the total length of thewaveguide has decreased by1700μm，compared with the reference. Shorter length andlow insertion loss of the device have been realized by downsizing the width of the load ofrib within limits. It also found that reducing the width of the rib or increasing the loadthickness will further reduce the period but introduce higher insertion loss. The simulationand analysis around the waveguide in the dissertation give the probable solutions anddirection about how to further improve the performance of the device in experiment at thenext step of the whole project.