Heterodyne interferometry to eliminate the polarization effect in a fiber optic gyro

In practical application, the polarization-maintaining fibers (PMFs) are usually used in the interferometric fiber optic gyroscope. It will lower the manufacturing cost if we use single-mode fibers (SMFs) instead of PMFs. However, SMF is wound as a sensing coil in gyroscope will induce elliptical birefringence. To reduce this effect, a heterodyne interferometric fiber optic gyroscope is proposed that the elliptically birefringent effect can be completely eliminated hence the absolute Sagnac phase with full dynamic range could be exactly obtained in the proposed setup.