Design of Passive Components in Integrated Optic Chip on SOI Applied in Fiber Optic Gyroscope System

The passive components in the integrated optic chip applied by fiber optic gyroscope are analyzed and designed on silicon-on-insulator (SOI) wafers. These components include a polarizer and a multimode interference (MMI) coupler. The MMI coupler acts as the traditional Y-branch power splitter. The polarizer consists of two 3dB MMI couplers and two straight single mode waveguides between these two MMI couplers. These two straight waveguides have equal length but have different rib width. The mode propagation constants of TE or TM light are not same and the appropriate selection of the length of the straight waveguide will result in the splitting of TE and TM light. The scalar or semivectorial finite difference beam propagation method (FD-BPM) is used to design these photonic components. The mode parameters of straight waveguide with different rib width are analyzed by semivectorial FD-BPM and the reasonable length of straight waveguide was selected. The MMI coupler is designed by scalar FD-BPM and the length of multimode waveguide and the positions of the input or output ports are determined accurately. The curving waveguide is avoided completely, therefore the design is more reliable and the fabrication of the device is much easy.