This patent disclosure is based on a silicon, instead of LiNbO3, waveguide chip. The disclosed silicon-based multi-function integrated-optic chip comprises a unique design and fabrication features onto it. A unique polarization-diversity coupler is designed and fabricated to couple the external light into the silicon waveguide structure. A unique two-step (vertical and lateral) taper waveguide region is designed and fabricated to bridge the polarization-diversity coupler output with the input of a multi-mode interferometer (MMI) splitter for power loss reduction. At either end of the Y-junction output, there is a phase modulator to achieve optical phase modulation through various physics mechanisms. With this newly-developed silicon-based multi-function integrated optic chip, the size and cost of fiber sensors including FOG's can be greatly reduced.