Optical resonant cavity with high polarization extinction ratio

The invention discloses an optical resonant cavity with a high polarization extinction ratio. The optical resonant cavity comprises a first PM (Phase Modulation) optical fiber coupler and a first 90-degree fusing point, wherein the first optical fiber coupler comprises a first PM tail optical fiber, a second PM tail optical fiber, a third PM tail optical fiber and a fourth PM tail optical fiber; a first inclined photoetched grating is etched on the first PM tail optical fiber; and an optical fiber loop consists of the first PM tail optical fiber, the first 90-degree fusing point and the second PM tail optical fiber. According to the optical resonant cavity, the defects of large losses of polarizing devices such as a single polarization fiber, non-matching with the fusing loss of an optical fiber resonant cavity and mode diameter, and the like are overcome, and the noise of polarization fluctuation is suppressed; and moreover, the optical resonant cavity has high resolution, important scientific role and application value, and can be applied to resonant optical fibers, optical waveguide gyroscopes or other sensing fields.