Study On Silicon-on-insulator Integrated Optical Waveguide Devices

The development and application of optoelectronic devices continues to driveprogress in high speed and large capacity optical communication system. Silicon-on-insulator (SOI) waveguide technology is highly promising for future low-cost photonic integrated circuits due to excellent optical and electronic properties and true compatibility with silicon CMOS integrated circui: technology. Optical coupler and variable optical attenuator are the important components for the implementation of dense wavelength division multiplexed (DWDM) systems In this thesis, bend waveguides, optical couplers and electrooptical variable optical attenuators that based on SOI single-mode rib waveguides with large cross- section are studied and fabricated.The SOI single-mode waveguides with large cross-section can be realized by rib structure. A single-mode condition for SOI rib waveguides is obtained by the effective index method (EIM). It is found the results are in a good agreement with the published experimental data. In order to minimize the modes mismatch losses between SOI rib waveguides and single-mode fibers, the effects of waveguide rib etch depth and width on the coupling losses have been analyzed by the finite difference methodBend waveguides is essential in photonic integrated circuits for altering the direction of light propagation. The loss characteristics of SOI curved rib waveguides and S-bend structures are studied by the finite difference beam propagation method (FD-BPM). The finite difference time domain (FDTD) is applied to .analyze and optimize the parameters involved in the designing low- loss SOI 90-bend waveguides with large rib cross-section, which exploit total internal reflection at the integrated waveguide mirrors. The optimized SOI 90-bend structure of 0.52dB bend loss has been demonstrated by reactive ion etchingtechnology.The Y-branch couplers and symmetric interference (SI) multimode interference (MMI) couplers in SOI technology are studied by FD-BPM. The properties such as field propagation process, wavelength bandwidth and fabrication tolerance are analyzed. The Y-branch couplers and SI-MMI couplers are designed and fabricated with SIMOX (Separation by IMplanted Oxygen) SOI wafers and uniform output are obtained. The systemic FDTD simulation results of SOI T-branch waveguides with large rib cross-section are presented to optimize the design. The T-branch couplers possess excellent properties such as compact size, large bandwidth, large fabrication tolerance and large output spacing. This device is designed and fabricated with SIMOX SOI wafers and realized the function of the coupler. The uniformity of the coupler is less than 0.63dB and the excess loss is 1.61dB.The prototype device of SOI-based electrooptical variable optical attenuator is designed and fabricated by common silicon CMOS processing technique. The device is functionally based on free carriers absorption to achieve attenuation. The PIN structures are integrated into the SOI single-mode rib waveguides for implementation of free carriers injection. The attenuation of 1.55 H m light for each array element is about 13.9dB, and the power consumption is 355mW.