US 4,429,997 A · Phase-locked loop laser gyroscope system

Abstract

A very high resolution laser gyroscope system having a phased-locked loop operatively coupled to one or more frequency difference outputs from a laser gyroscope cavity. Waves of at least four frequencies propagate around the gyroscope cavity, with output signals being formed having a frequency equal to the difference between the frequencies of wave pairs. In one set of embodiments of the invention, the frequency difference signal for one wave pair is phase-locked to an external reference source. A signal applied to a Faraday rotator bias coil provides the frequency shifting of the wave pairs necessary to achieve phase lock. The amplitude of the signal applied to the Faraday bias coil provides a highly precise measure of the rate of rotation. In another set of embodiments of the invention, one or more of the wave pair frequency difference signals are coupled as inputs to an external phase-locked loop in which a voltage controlled oscillator is followed by a frequency divider of the feedback circuit. In these embodiments, the output of the voltage controlled oscillator provides an output signal which has a frequency in proportion to but many times higher than the frequencies of the wave pair difference signals. In still further embodiments of the invention, the two phase-locked loop techniques may be combined. In all of the disclosed systems, the quantization error normally associated with laser gyroscope output signals is substantially reduced.

Claims16

Dependent claims

In combination:

means for providing a closed-loop path for sustaining propagation of circularly polarized electromagnetic waves of a plurality of frequencies;
means for producing a first signal having a frequency equal to the difference in frequency between two of said waves;
means for producing a second signal having a frequency equal to a predetermined multiple of the frequency of said first signal;
means comprising a phase detector for phase locking said second signal to said first signal;
said second signal being coupled to the input of said phase detector through frequency dividing means;
and
the output of said phase detector being coupled to means for controlling the frequency of said means for producing said second signal.

4 more elements

In combination:

means for providing a closed-loop propagation path for sustaining propagation of electromagnetic waves of at least four frequencies;
means for producing a first difference signal having a frequency equal to the difference in frequency between a first two of said waves;
means for producing a second difference signal having a frequency equal to the difference in frequency between a second two of said waves;
first and second phase-locked loops, said first phase-locked loop being coupled to said means for producing said first difference signal and said second phase-locked loop being coupled to said means for producing said second difference signal, each of said phase-locked loops comprising:
phase detecting means, the corresponding difference signal being coupled to one input of said phase detecting means;
low-pass filter means coupled to the output of said phase detecting means;
amplifying means coupled to the output of said low-pass filter means;
means for producing a control signal having a frequency determined by the value of an input parameter, the input of said control signal producing means being coupled to the output of said amplifying means, the output of said control signal producing means being coupled to a second input of said phase detecting means;
and
means for producing an output signal having a parameter determined by the difference in frequency between the control signals of said first and second phase-locked loops.

7 more elements

Dependencies are inferred from the claim text.

Phase-locked loop laser gyroscope system

Life of this patent

Phase-locked loop laser gyroscope system

Life of this patent

Abstract

Claims16