Waveguide Base Anti-reflection Structure Andits Application To The Polarization Independent Semiconductor Optical Amplifier

Integration has become a major tendency of the modern optoelectronic devices. The silicon platform is regarded as a most promising solution of integrated optics for it offers many advantages such as high index contrast, low cost and compatible with the COMS fabrication technology. Various passive devices have been successfully realized on the silicon platform. Active devices such as laser diodes and semiconductor optical amplifiers can also be integrated with the silicon platform by taking advantage of the wafer bonding technique. An important problem to be solved is the elimination of the unwanted back reflections to protect the light source.This dissertation presents a waveguide based anti-reflection structure. This structure consists of a polarization beam splitter (PBS), two 45 polarization rotators (PRs) and two 90° phase delay units (PDU). Incident light with arbitrary polarization state will firstly be split into TE and TM polarization and be guided to different ports. Then the two mutually orthogonal linearly polarization beams are converted into circularly polarized by the combination of PR and PDU, respectively. Therefore, the output light is circularly polarized. Upon reflection from an ideal mirror, the polarization state of circularly polarized light changes, for example, from right circularly polarized to left circularly polarized and vice versa. After passing through the combination of PR and PDU again in the contra-direction, the reflected beam converts itself back into the linearly polarized state, but with its polarization angle rotated by 90° relative to the incident beam. The returned light is therefore directed to a standalone port of the PBS. Simulation results show that the total device length can be made as short as 10.4um, and an isolation of 44.2dB can be achieved at central wavelength of 1.55?m. The bandwidth is 100nm for an isolation beyond 20dB.Another property of the proposed anti-reflection structure is that the reflected light is collected and guided to a separate port with its polarization angle rotated by 90° compared with the incident light. By utilizing this property, this structure has potential application for building the polarization diversity circuit to eliminate the polarization dependence of optoelectronic devices. A hybrid integrated polarization independent semiconductor optical amplifier is then proposed. Simulation results show that the polarization dependent gain is effectively suppressed and the device has a broad working band of 60nm for a PDG below 0.5dB.The simulations of semiconductor optical amplifier are performed using the one dimensional traveling wave model. The direct convolution traveling wave model and wavelength slicing traveling wave model are introduced for the simulation of broadband semiconductor optoelectronic devices. To efficiently solve the convolution term of the direct convolution traveling wave model, a digital filter based algorithm is proposed. Numerical simulation results show the direct convolution traveling wave model agrees well with narrowband traveling wave model in the case which the narrowband model can handle. Besides, the direct convolution traveling wave model can handle the devices with broad working band, where the narrowband model can't. Newly designed digital filter approach based algorithm provides the computation burden of the direct convolution traveling wave model is only about two times that of the narrow band traveling wave model.