Optical waveguides – Optical waveguide sensor – Including physical deformation or movement of waveguide
Reexamination Certificate
1998-07-29
2001-11-20
Spyrou, Cassandra (Department: 2872)
Optical waveguides
Optical waveguide sensor
Including physical deformation or movement of waveguide
C702S141000
Reexamination Certificate
active
06320992
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to measurement of acceleration and particularly to measurement of acceleration by means of an interferometer.
The prior art suffers from several factors. Conventional piezoelectric accelerometer devices require significant mechanical support structure to isolate them from platform self noise. Electronics required near the sensor are a significant reliability issue, especially for marine applications. Telemetry with multiplexed sensors requires yet additional electronics that may need to be located in a hostile environment.
SUMMARY OF THE INVENTION
The present invention measures the amplitude of a wide bandwidth acceleration input by converting the acceleration into a mechanical strain, then into an electrical signal via an optical interferometer that has at least one arm formed to include an integrated optics waveguide. The integrated optics waveguide is formed in an integrated optics substrate. The substrate is preferably formed to comprise silica or silicon, lithium niobate, polymer waveguide structure or other similar material suitable for serving as a substrate for an optical waveguide. The sensor according to the present invention is potentially low cost because it utilizes standard photolithographic and vacuum deposition processes common to the microelectronics and integrated optics industries. Assembly of the device can be very robust, thereby further reducing the cost of manufacture and increasing durability while the device is in use.
An acceleration sensor according to the present invention comprises an integrated optics substrate having a first optical waveguide of a selected length formed on a first side thereof. The optical waveguide is included in a first arm of an interferometer that is arranged to produce an interference pattern. The integrated optics substrate is mounted and arranged such that acceleration of the integrated optics substrate along a selected axis produces a change in the interference pattern. Changes in the interference pattern are monitored and correlated with the acceleration.
The interferometer is preferably formed to include a second optical waveguide in a second arm. The second interferometer may be formed on the side of the substrate opposite the first optical waveguide. Alternatively, the second optical waveguide may be formed on a second integrated optics substrate. The substrates may be mounted together back-to-back.
In a preferred embodiment of the invention, the optical waveguides include reflecting apparatus arranged such that the interferometer is formed in the Michelson configuration.
Optical signals may be introduced into the two optical waveguides by means of optical fibers mounted to the substrates and arranged to be end-to-end with the corresponding optical waveguides. An optical coupler is arranged to couple optical signals between the optical fibers so that part of the light from a light source is coupled from one fiber into the other. The result is that optical signals having a definite phase relationship are coupled into the two arms of the interferometer. Acceleration along the sensing axis then increases the length of one optical waveguide and decreases the length of the other, which changes the phase relationship between light in the two arms of the interferometer.
The interferometer is mounted in a housing. In one embodiment of the invention the interferometer is mounted to a post mounted in the housing, such that the periphery of the integrated optics substrate becomes displaced lengthwise along the longitudinal axis of the post in response to acceleration of the housing along the longitudinal axis of the post. In another embodiment of the invention, the integrated optics substrate has its periphery mounted to the housing such that the central portion of the integrated optics substrate becomes displaced along an axis perpendicular to optical waveguide in response to acceleration of the housing.
An appreciation of the objectives of the present invention and a more complete understanding of its structure and method of operation may be had by studying the following description of the preferred embodiment and by referring to the accompanying drawings.
REFERENCES:
patent: 5317929 (1994-06-01), Brown et al.
patent: 5633960 (1997-05-01), Lagakos et al.
patent: 5680489 (1997-10-01), Kersey
patent: 5903349 (1999-05-01), Vohra et al.
patent: 6018390 (2000-01-01), Youmans et al.
Goldner Eric L.
Hodgson Craig W.
Litton Systems Inc.
Lynn & Lynn
Spyrou Cassandra
Treas Jared
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