FIBER-OPTIC GYROSCOPE WITH FIBRE POLARIZERS, DEPOLARIZERS AND COUPLING MEANS

摘要

A fibre-optic gyroscope is provided herein for measuring an angular velocity of a fibre coil from a phase difference between a light propagating clockwise and a light propagating counterlockwise in the fibre coil. A light emitting device is provided for emitting a monochromatic light with a definite coherent length. A fibre coil includes a single mode optical fibre wound a plurality of times around a bobbin. A photodetector is provided both for making a light propagating clockwise and a light propagating counterclockwise interfere, thereby producing interference light, and for detecting an intensity of the interference light. A first fibre path is connected to the light emitting device. A fifth fibre path is connected to the photodetector. A third fibre path and a fourth fibre path are each end parts of the fibre coil. A second fibre path is provided, and a first fibre coupler is provided for coupling one end of the second fibre path to both the first fibre path and the fifth fibre path. A second fibre coupler for is provided coupling the other end of the second fibre path to both the third fibre path and the fourth fibre path. A polarizer is located in the second fibre path for polarizing light linearly. A phase modulator is furnished in one of the third fibre path and the fourth fibre path for modulating phases of lights propagating in the fibre path. A first depolarizer, consisting of a single birefringent material, is furnished in the first fibre path for depolarizing lights propagating in the first fibre path by aligning polarization planes of partial lights in all directions so that a probability of one of the partial lights having a given polarization angle is substantially equal to a probability of the one of the partial lights having any other polarization angle. Finally, a second depolarizer is furnished in the third or in the fourth fibre path for depolarizing lights by aligning polarization planes of partial lights in all directions so that a probability of one of the partial lights having a given polarization angle is substantially equal to a probability of the one of the partial lights having any other polarization angle. The light emitted from the light emitting device is transmitted into the polarizer after being depolarized by the first depolarizer.