Multiple axis ring laser gyroscopes

Claim 2

A multiple axis ring laser gyroscope in which at least one mirror is shared by beams of different cavities and in which the frequencies of the beams in these different cavities are nominally the same, the frequencies of the beams in those different cavities being caused to be offset one from the other.

Claim 3

A gyroscope according to Claim 1, including path length control means operable for controlling the respective beam path lengths in said different cavities, the path length control means being further operable to maintain a relationship between said respective beam path lengths which produces the offsetting of the beam frequencies in said different cavities.

Claim 4

A gyroscope according to Claim 2, wherein said path length control means comprises servo-means which is operable to sense respective gain signals indicative of the laser beam gains within the different cavities and to derive from the gain signals respective servo signals for controlling the path lengths within the different cavities to maintain said gains within an acceptable range, the control means further including offset signal applying means arranged for affecting the servo signals so as to maintain said laser beam gains at respective different positions within said range.

Claim 5

A gyroscope according to Claim 3, wherein said servo-means comprises perturbation means for producing a periodic variation in the beam path length in each cavity, sensing means for supplying respective intensity signals indicative of the laser beam intensities in the cavities, phase-sensitive detector means connected to said perturbation means and said sensing means and operable for supplying output signals indicative of components of the respective intensity signals at the frequency of said periodic beam path length variation, integrating means for receiving the output signals from the phase sensitive detector means and for integrating said output signals to produce path length control signals for the respective cavities, and offset biassing means for applying offset signals to the integrating means to produce said offsetting of the laser beam frequencies.

Claim 6

A gyroscope according to any preceeding claim, the gyroscope being of the kind which comprises six mirrors positioned at the corners of a notional octahedron and defining between them three planar four-sided optical cavities which are orthogonal one to another, three of the mirrors being coupled to respective displacing devices operable for responding to received displacement control signals to displace the respective mirrors along their respective optical axes, and the gyroscope comprising:- sensor means for supplying respective intensity signals indicative of the laser beam intensities within said cavities, perturbation signal generating means connected to said displacing devices and operable for generating a periodic perturbation signal which produces an oscillatory movement of each of said three mirrors, three phase sensitive detectors each connected to receive said perturbation signal and a respective one of said intensity signals, and each operable to produce a signal indicative of any component of the associated intensity signal of which the frequency equals that of the perturbation signal, three integrators connected to receive and integrate the output signals from respective ones of the phase-sensitive detectors, offset signal supply means connected to apply to the inputs of two of the integrators respective different offset signals, and three summing devices for combining the outputs of said integrators to form respective control signals for controlling said displacement devices.