Digital synthetic serrodyne for fiber optic gyroscope

A digital synthetic serrodyne phase difference controller for a rotation sensor capable of sensing rotation about an axis of a coiled optical fiber based on having a pair of electromagnetic waves propagating through said optical fiber in opposite directions to both impinge on a photodetector with a phase difference relationship therebetween. said digital synthetic serrodyne phase difference controller comprising:

• a phase detector means having an input electrically connected to said photodetector to receive an output signal therefrom representative of phase differences occurring in pairs of electromagnetic waves impinging thereon, said phase detector means being capable of providing an output signal on an output thereof representative of both magnitude and direction of said phase differences indicated by said photodetector output signal;
• a dual output generator means having an input electrically connected to said phase detector means output to receive said phase detector means output signal, said dual output generator means having first and second pluralities of outputs and being capable of providing a first plurality of digit output signals each at a corresponding one of said first plurality of outputs which signals together represent a succession of amplitude values and a second plurality of digit output signals each at a corresponding one of said second plurality of outputs which signals together represent a succession of amplitude values, said first plurality of digit output signals together having a basic set of successive amplitude values repeated at selected frequencies with said basic repetition set consisting of a relatively large fraction of said succession of amplitude values therein having substantially increasing magnitudes followed by a much smaller fraction thereof having substantially decreasing magnitudes, said second plurality of digit output signals together having a basic set of successive amplitude values repeated at selected frequencies with said basic repetition set consisting of a relatively large fraction of said succession of amplitude values having substantially decreasing magnitudes followed by a much smaller fraction thereof having substantially increasing magnitudes, said frequencies of repetition of said basic repetition sets in said first and second pluralities of output signals being determined by said phase detector means output signal;
• a combination means having a plurality of inputs and a plurality of outputs and comprising a first digital adder means having a plurality of outputs on which corresponding ones of a plurality of digit output signals are provided thereby that can be a basis for a plurality of digit output signals provided at said combination means outputs, a first plurality of inputs serving as a portion of said combination means inputs each electrically connected to a corresponding one of said first plurality of outputs of said dual output generator means to receive said first plurality of digit output signals therefrom, and a second plurality of inputs serving as a portion of said combination means inputs each electrically connected to a corresponding one of said second plurality of outputs of said dual output generator means to receive said second plurality of digit output signals therefrom, said first digital adder means being capable of providing said plurality of digit output signals together representing a succession of amplitude values each having a magnitude representative of magnitudes of amplitude values in said dual output generator means first and second pluralities of digit output signals algebraically combined;
• a digital-to-analog converter means having an output and a plurality of inputs each electrically connected to a corresponding one of said combination means plurality of outputs to receive said combination means plurality of digit output signals together representing a succession of amplitude values based at least in part on said first digital adder means plurality of digit output signals, said converter means providing an analog output signal at said output thereof representative of said succession of amplitude values in said combination plurality of digit output signals received;
• and
• a frequency translation means electrically connected to said digital-to-analog converter means output, said frequency translation means being positioned in a corresponding optical path portion selected from among those optical path portions taken by electromagnetic waves to reach or leave said coiled optical fiber enroute on an optical path to said photodetector in said rotation sensor to be capable of providing a frequency translation of any such electromagnetic wave passing therethrough in propagating along said optical path.