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 （V_πL） 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.