Fiber optic gyro

Claim 1

In a fiber optic gyro of the type wherein light from a light source is split by optical splitter/coupler means and is coupled, as right-handed light and left-handed light, into both ends of a single-mode optical fiber coil, said right-handed light and said left-handed light having propagated through said optical fiber coil are caused by said optical splitter/coupler means to interfere with each other, said interference light is branched by an optical coupler to a photodetector and is thereby converted to an electric signal corresponding to said branched interference light, an angular rate applied to said optical fiber coil around its axis is detected from said electric signal, and a depolarizer is inserted in series in a loop through which said light from said optical splitter/coupler means propagates thereto, the improvement wherein said depolarizer is so constructed that the difference between the difference in propagation time between perpendicularly intersecting polarized light components in said depolarizer and the difference in propagation time between perpendicularly intersecting polarized light components in said optical fiber coil is greater than a coherence time of light passing through said loop, said depolarizer being composed of first and second tandem-connected birefringent optical fibers with lengths L 1 and 2L 1 , principal axes of said first and second birefringent optical fibers being displaced 45 degrees apart, and letting the birefringence per unit length of said first and second birefringent optical fibers be represented by Δβ, the wavelength and coherence length of light used be represented by λ and l c , respectively, and the length and birefringence per unit length of an optical fiber forming said optical fiber coil be represented by L 0 and Δβ', respectively, the following condition is satisfied: ##EQU5##