An improved optical branching/coupling unit for an optical fiber gyroscope, and navigation system employing the same

An optical fiber gyroscope having an optical branching/coupling unit in which light from a coherent light source is bifurcated or conjoined in two directions, an optical system which includes an optical fiber loop for propagating bifurcated light beams in terms of reverse rotations, as well as light phase difference bias means for affording a bias to the bifurcated light beams, a signal processing system which converts an optical output of the optical system into an electric signal and processes the electric signal, and detection means for detecting an angular velocity on the basis of a processed result of the signal processing system;

• an optical fiber gyroscope characterized in that said optical branching/coupling unit develops a predetermined light phase difference between transmitted light and branched light, thereby to function also as said means for affording the light phase bias;
• comprising optical phase modulation means interposed between said optical fiber loop and said optical branching/coupling unit, and means for driving said optical phase modulation means and for compensating an intensity fluctuation of interference light by the use of a peak value of the interference light obtained;
• and further comprising buffers which are respectively interposed between the optical phase modulator and mounting portions for said optical phase modulator.

An optical fiber gyroscope having an optical branching/coupling unit in which light from a coherent light source is bifurcated or conjoined in two directions, an optical system which includes an optical fiber loop for propagating bifurcated light beams in terms of reverse rotations, as well as light phase difference bias means for affording a bias to the bifurcated light beams, a signal processing system which converts an optical output of the optical system into an electric signal and processes the electric signal, and detection means for detecting an angular velocity on the basis of a processed result of the signal processing system;

• an optical fiber gyroscope characterized in that said optical branching/coupling unit develops a predetermined light phase difference between transmitted light and branched light, thereby to function also as said means for affording the light phase bias;
• comprising means for bringing said coherent light source into an oscillation suspension state for a moment in a period shorter than a propagation delay time in which the light emergent from said light source is fed back to aid light source after propagating through said optical fiber loop.

An optical fiber gyroscope having an optical branching/coupling unit in which light from a coherent light source is bifurcated or conjoined in two directions, an optical system which includes an optical fiber loop for propagating bifurcated light beams in terms of reverse rotations, as well as light phase difference bias means for affording a bias to the bifurcated light beams, a signal processing system which converts an optical output of the optical system into an electric signal and processes the electric signal, and detection means for detecting an angular velocity on the basis of a processed result of the signal processing system;

• an optical fiber gyroscope characterized in that said optical branching/coupling unit develops a predetermined light phase difference between transmitted light and branched light, thereby to function also as said means for affording the light phase bias;
• comprising memory means for storing as an offset value an output signal of said signal processing system delivered when said coherent light source is temporarily turned "off", and detection means for correcting with the offset value an output signal delivered when said coherent light source is "on".

In a navigation system having a rotational angle sensor which detects a rotational angle of a moving object, a distance sensor which detects a movement distance, an azimuth sensor which detects an absolute direction, a main control device which includes information record means for recording map information, as well as calculation means for evaluation a present position of the moving object on the basis of the outputs of the sensors and the map information, and display means for displaying the present position;

• a navigation system characterized in that said rotational angle sensor is comprised of an optical branching/coupling unit affording a predetermined phase bias, and in that said main control device includes means for judging a state of the moving object and means for issuing an offset cancel command for said optical fiber gyroscope on the basis of a judged result thereof.

In an optical fiber gyroscope having an optical branching/coupling unit in which light from a coherent light source is bifurcated or conjoined in two directions, an optical system which includes an optical fiber loop for propagating bifurcated light beams in terms of reverse rotations, as well as light phase difference bias means for affording a bias to the bifurcated light beams, a signal processing system which converts an optical output of the optical system into an electric signal and processes the electric signal, detection means for detecting an angular velocity on the basis of a processed result of the signal processing system, a thermal buffer box which envelops said optical fiber loop, and a spool for said optical fiber loop, wherein an inner wall of said thermal buffer box and the spool for said optical fiber loop are connected only to a heat insulator.