Loss Research On Rib Waveguide

SOI(Silicon-On-Insulator) rib waveguides with excellent optical and electrical properties, have been become the important component of Integrated Optical Circuit. It will play an important role in the optical interconnect and optical computing. However, the waveguide's loss problem is always the main obstacle on its way of being commercial. A systematical work about loss problem has been done in this paper, which includes the design, preparation and characterization of SOI waveguide as well. The main work can be listed as follows:1. The SOI rib waveguide mode propagation and loss characteristics were analyzed through the theoretical methods. Single-mode SOI rib waveguide transmission conditions with the different sizes were obtained by using effective index method to analyze the SOI rib waveguides mode properties. Finite difference beam propagation (FD-BPM) simulation method was utilized to obtain the transverse field of rib waveguides with different size.The semi-TE and semi-TM results of the waveguide with the same size mismatch indicated that semi-TE suffer from more serious scatterring loss because of its susceptivity to the roughness of waveguide sidewall. The structural simulation provided theoretical basis for optimizing waveguide and analyzing its relative loss.2. We simulated the preparation processes of SOI rib waveguides and PIN junction, the impurity distribution and junction depth of SiO2 latex diffusion doping by the two module Dios and MDraw of ISE-CAD software. The reference interval of the two doping width and process parameters of the PIN structure were obtained as a result of the simulation; The electrical properties of PN and PIN junction under forward and reverse bias were simulated to obtain their own built-in electric field distribution and the distribution of free carriers in the intrinsic region with semiconductor laser simulation software Sim Windows on the thermal equilibrium. When the light intensity was proposed, the restrictive relationship between the composite rate and light intensity has been figured out. The PIN simulation results under the reverse bias provided a strong theoretical basis and data support to achieve carrier absorption loss control program by use of PIN structure.3. The approaches to control FCA and scattering loss induced by sidewall roughness were proposed due to the waveguide sidewall roughness on the base of the analysis of main physical mechanism of SOI rib waveguide internal loss. For the scattering loss, we analyzed the two main sources of scattering loss, which involved the standard deviation of roughness and the size of waveguide. Reduction of scattering loss could be achieved by thermal oxidation process for a certain waveguide; FCA was analyzed by use of Comsol software, focusing on the effects of intrinsic region width of SOI rib waveguide, bias voltage and incident light power on the free carrier absorption loss. Finally, we demonstrated that the use of the PIN structure under reverse bias was an effective way to solve the loss problem, noting that this approach was limited in the loss control and the limitations of producing the silicon modulator under the use of forward bias PIN. The simulation results provided important reference data for the establishment of programs related to the experiments of loss control.4. A simple and effective loss measurement method on SOI waveguide was proposed on the ground of Fabry-Perot cavity theory. Through end coupling, the method utilized the information of the reflection power spectrum Fourier transform to achieve the waveguide loss measurement, which was different from the traditional F-P cavity technology using transmission spectrum. In the process of deriving, some result indicated the main reason why the loss index could not be directly solved from the peak and valley values of the F-P peaks of reflection spectrum. The measurement system included a real-time monitoring system for aligning waveguide end, which ensured good measurement accuracy and high reproducibility. The measurement method would be an important tool to study the submicron-size SOI rib waveguide loss. A general loss standard has been established according to the results of loss measurement for the study of waveguide loss under the similar process conditions.5. The doping experiments of silica latex diffusion were carried out by using self-built platform for the semiconductor doping and test. A PIN structure on the SOI rib waveguide was achieved on this platform. The Experimental platform could achieved boron doped and phosphorus doped silicon with control of doping concentration and doping depth. The test platform could be used for testing sheet resistance of the sample with a high doping concentration; The"one step"doping method with a high concentration, high-resolution and shallow junction depth was achieved on the SOI rib waveguide, which would make smaller damage on the silicon substrate lattice structure, be easier to control, cost lower and have higher productivity than the traditional"two-step doping method". The PIN produced by this method has prepared the component for the advanced research on the Free Carriers Absorption of SOI rib waveguides.