Optical waveguides – With optical coupler
Reexamination Certificate
1998-05-29
2001-03-20
Chang, Audrey (Department: 2872)
Optical waveguides
With optical coupler
C385S012000, C385S024000
Reexamination Certificate
active
06205265
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to fiber optic rotation sensors and particularly to reducing sensitivity of such sensors to radiation environments. Still more particularly, this invention relates to photobleaching the sense coil of a fiber optic rotation sensor system to reduce sensitivity to radiation.
A typical fiber optic gyro uses a long length of polarization maintaining (PM) fiber as a sense element for rotation. It has been shown that this type of fiber is sensitive to radiation environments. When exposed to ionizing radiation, the fiber develops color centers that attenuate light propagating through the sense coil. If enough attenuation occurs, the random walk of the gyroscope will increase significantly. When the attenuation is extremely high due to large doses of ionizing radiation, the gyroscope will lose all signals.
SUMMARY OF THE INVENTION
The present invention minimizes the effects of radiation induced attenuation by photobleaching the sense coil. This is accomplished by injecting enough light at a frequency selected to remove the induced color centers. Since this light is at a different frequency from the light the gyroscope typically uses to sense rotation it must be introduced and removed from the gyroscope optical circuit without effecting the gyro signal.
Apparatus according to the present invention for photobleaching a fiber optic sense coil in a fiber optic rotation sensor system, comprises a photobleach light source and an optical fiber arranged to guide the photobleach light. A wavelength division multiplexing apparatus is connected to the optical fiber and arranged to introduce photobleach light into the fiber optic sense coil to anneal out color centers therein. The invention further includes apparatus arranged for removing the photobleach light from the fiber optic rotation sensor system.
The apparatus for removing the photobleach light from the fiber optic rotation sensor system includes a second wavelength division multiplexing optical coupler. The wavelength division multiplexing couplers may be formed to include the fiber optic leads of the sensing coil. Alternatively, the wavelength division multiplexing couplers may be formed to include the fiber optic sense coil.
The apparatus according to the present invention preferably further includes apparatus for dispersing the photobleach light that has been coupled out of the gyro.
REFERENCES:
patent: 4915503 (1990-04-01), Pavlath
patent: 4997282 (1991-03-01), Pavlath
patent: 5037205 (1991-08-01), Pavlath
patent: 5119229 (1992-06-01), Grasso et al.
patent: 5231465 (1993-07-01), Huang et al.
patent: 5537671 (1996-07-01), Toyama et al.
patent: 5774217 (1998-06-01), Lee et al.
patent: 5848205 (1998-12-01), Bigo
patent: 2252841 (1992-08-01), None
“Photobleaching Effects in Optical Fiber Waveguides” Freibele & Gingrich Applied Optics vol. 20 Oct. 1981 pp. 3448-3352.
“Laser Induced Photobleaching at Low Temperature in Co-60 Irridiated Fibers” Barnes IEEE Annual Conf. Jul. 20, 1982 pp. 1479-1483.
Michal Ronald J.
Rozelle David M.
Chang Audrey
Litton Systems Inc.
Lynn & Lynn
Winstedt Jennifer
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