US 4,440,498 AGranted

Optical fiber gyroscope with (3.times.3) directional coupler

AssigneeThe United States of America as represented by the Secretary of the Navy

InventorSang K. Sheem

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Abstract

A Sagnac rotation sensing interferometer disposed on a rotating platform for use as a gyrsocope comprising a closed optical light path and a beam splitter for splitting an input light beam into two beams directed to transverse the closed optical path in opposite directions wherein the beam splitter is composed of a directional coupler with three input ports and three output ports. The first of the three input ports receives optical input and the second and third of the input ports are disposed symmetrically with respect to the first input port. Optical output from two output ports corresponding to the second and third input ports are directed to both ends of the closed optical fiber light path. A gyroscope according to this arrangement provides light output from the beam splitter which operates automatically near quadrature without a nonreciprocal .pi./2 phase bias applied in the fiber loop as required in conventional optical fiber gyroscopes.

Claims9

Dependent claims

In an optical fiber gyroscope wherein light is introduced into an optical fiber waveguide formed in a loop for propagating therearound in mutually opposite directions to emerge therefrom for relative phase shift detection induced by rotation of the loop, the improvement residing in a directional coupler for carrying light to and from the loop comprising:

a first elongate optical waveguide adapted to have laser light launched into one end thereof and carry that light therethrough;
second and third optical waveguides including elongate portions thereof coextensively disposed with a length of the first optical waveguide at close distances therefrom and from each other whereby the laser light is coupled thereinto and directed into the loop for propagating therethrough in mutually opposite directions;
said second and third optical waveguides receiving the oppositel propagated light from the loop and mixing it for mutual interference by coupling from one to the other across the distance therebetween;
said second and third waveguides directing their respective mixed lights to detection means where their powers are compared;
whereby relative changes in light powers provides an indication of loop rotation.

2 more elements

Dependencies are inferred from the claim text.