A Fiber-optic Interferometric Seismometer
Author
Gardner, D.L.
Hofler, T.
Baker, S.R.
Yarber, R.K.
Garrett, S.L.
Date
1987-07Metadata
Show full item recordAbstract
A fiber-optic interferometric sensor has been developed
which consists of a seismic mass of 520 gm supported by two rubber
mandrels, each wound with a single layer of single-mode optical fiber
6.5 m long. One end of each fiber is cleaved to enhance reflection. The
other ends are interconnected via a fiber-to-fiber 3-dB coupler, forming
a Michelson interferometer. When the case of the sensor is displaced,
the fiber around one mandrel extends in length while the other
contracts. The resulting â push-pullâ mechanical operation of the sensor
allows both legs of the interferometer to be active, providing good
common mode rejection of spurious effects, as a reference leg is not
required. This, together with the fact that the light traverses each leg
of a Michelson interferometer twice due to reflection, provides the sensor
with four times the sensitivity of a conventionally constructed interferometric
sensor. sensitivities of 8500 rad of optical phase shift per
micrometer of case displacement have been measured above the massspring
resonance, where the sensor operates as a seismometer. Below
resonance the sensor operates as an accelerometer with a measured
sensitivity of 10 500 rad/g, the highest reported to date. Including both
thermodynamic and demodulator noise sources, below
resonance the sensor has a detection threshold of l ng/JHz, a 20-
dB improvement over the best existing conventional noise vibration
sensors.
Rights
This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.Collections
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