Fiber optic rate sensor
 In a fiber optic rate sensor employing a Sagnac ring circuit wherein an ocal source launches an optical signal which is divided into two equals signals which are coupled in opposite directions through a multi-turn fiber optic coil to provide two counter-propagating optical signals. The two counter-propagating optical signals are coupled to a photodetector after passing through the multiturn fiber coil. The signals detected at the photodetector have traversed identical optical paths between said source and said photodetector and have undergone a Sagnac phase shift directly related to the rate of rotation of the fiber coil about its axis in inertial space. The two counterpropagating signals are phase modulated by a phase modulator at one end of the fiber optic coil and the output of the photodetector undergoes signal processing in a signal processor to produce a rate output directly related to the rate of rotation of the fiber coil. The improvement being an improved phase modulation and signal processor which comprises a crystal-controlled oscillator providing a sine wave reference signal means for coupling the crystal of the crystal-controlled oscillator to the optical fiber at one end of the coil to produce a non-reciprocal phase modulation of the counter-propagating optical signals, means for multiplying the sine wave reference signal and the output from the photodetector to produce a product output, and means for integrating the product output over a whole number of complete reference cycles to produce the rate output, the sine wave reference signal being coupled to means for integrating to control the integration period of the means for integrating. 
The United States of America as represented by the Secretary of the Navy
G G
G01C G02F
inventional inventional
Donald Hiroshi
Ensley Satake