A resonant fiber optic gyro has a tapered polarizer in the ring to produce a single resonant polarization mode. A fused coupler closes the ring and provides inlet and outlet paths, with the entire device fabricated from a single PM fiber, thereby eliminating sources of backscatter and drift. In a preferred embodiment MSR fiber is used, and preferably the fused coupler is fabricated to achieve high finesse and modulation depth with its splitting ratio approximately equal to ring transmission coefficients. Apparatus and methods for forming the polarizer and the coupler are described.