This paper introduces an innovative Multifunction Integrated Optic Circuit (MIOC) design utilizing thin-film lithium niobate, surpassing traditional bulk waveguide-based MIOCs in terms of size, half-wave voltage requirements, and integration capabilities. By implementing a sub-wavelength grating structure, we achieve a Polarization Extinction Ratio (PER) exceeding 29 dB. Furthermore, our electrode design facilitates a voltage-length product (VπL) below 2 V·cm, while a double-tapered coupling structure significantly reduces insertion loss. This advancement provides a pivotal direction for the miniaturization and integration of optical gyroscopes, marking a substantial contribution to the field.