The Interferometric Fiber Optic Gyroscope (IFOG) was first developed at Stanford University in 1981. The Stanford IFOG is more fully described in the Stanford Report No. 3586, June 1983 by Ralph Alan Bergh G. L., of Stanford, C A. The operation of this basic IFOG follows. A light source passes light through the interferometer optics and is split into two beams that propagate in opposite directions around the fiber optic coil. The light is recombined and the resultant intensity at the detector is proportional to the phase difference between the two beams. This phase difference is in turn proportional to an input rotation rate.
The Stanford IFOG research demonstrated the suitability of the IFOG as a rotation sensor for navigation applications. If mass production techniques could be devised for fabricating the sensor, electronic methods employed for error compensation as well as obtaining a linear digital output, and packaging devised for overcoming environmental sensitivities, the gyro could be made practical. Technology developed in the 1980's addressed these issues.
To make the sensor more producible, environmentally stable, and better suited to digital electronics, a Lithium Niobate (LiNbO3) crystal integrated optical chip with waveguides, couplers, and phase modulators was developed. Optical waveguides are devices that guide light waves along a path typically defined by a transparent core and a transparent cladding surrounding the core, with the cladding material generally having a lower index of refraction than the core material. The chip is employed between the input fiber optic coupler and the fiber optic coil of the gyroscope. The highly degenerate mode rejecting true single mode waveguide operation (highly polarizing waveguide), high modal purity, and low polarization cross talk performance of the crystal waveguides enabled navigation application gyro performance. The high modulation bandwidth and linearity possible with the LiNbO3 chip enabled the use of electronic means for error compensation and generating a linear digital output. Additionally, the component plainarization afforded by integrated optic fabrication eliminates some of the intercomponent misalignments which degrade performance. Finally, using the integrated optics chip reduces the parts count, the volume, and the touch labor required to manufacture the gyroscope.
Although the LiNbO3 chip provides a level of integration, the gyro remains as an assembly of discretely packaged components wherein each gyro component has attached fiber optics used to communicate with other components. Further, the redundant packaging adds bulk, cost, and electrical complication from shielding and grounding considerations.
USPTO Backgrounds
USPTO Backgrounds