Method of reducing polarization fluctuation inducing drift in resonator fiber optic gyro

A method of reducing the polarization fluctuation inducing drift in a resonator fiber optic gyro, comprising the step of:

• setting ΔL and L3 so that the relationship of ΔL, Δβ and L3 satisfies a formula ΔβΔL=π+2nπ [radian] (n:
• integer) and ΔβL3=mπ [radian] (m:
• integer), or approximately satisfies the formulae to minimize the error induced by the polarization fluctuation where L1 is the distance from said first coupler to the polarization-rotating point, L2 is the distance from the polarization-rotating point to said second coupler, L3 is the distance from said second coupler to said first coupler, ΔL is the difference between L1 and the length (L2+L3) from the polarization-rotating point to said first coupler through said second coupler, and Δβ is the difference in propagation constant of two axes of polarization of the waveguide when the waveguide is divided into three portions by said first coupler, said polarization-rotating point and said second coupler in a method of measuring the non-reciprocal effect such as the rotation in a transmitter ring resonator comprising a sensing loop formed of the waveguide having two axes of polarization to propagate the light wave, a first coupler to guide the light wave from a laser beam source to said sensing loop and a second coupler to emit the light wave in said sensing loop which are inserted in said sensing loop, and having a polarization-rotating point in said sensing loop.