US 5,380,995 AGranted

Fiber optic grating sensor systems for sensing environmental effects

AssigneeMcDonnell Douglas Corporation

InventorsEric Udd, Timothy E. Clark

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Abstract

One or more optical fiber gratings are used to sense environmental effects that can vary the spacing between the lines of the grating to vary the center frequency of the spectral envelope, either reflected or passed thereby. Light of the sensor grating's spectral envelope is transmitted to a local grating unaffected by the environmental effect and compared with the spectral envelope of the local grating to produce an intensity modulated signal, which is detected to sense the environmental effect. The sensor systems so constructed may have one or more local gratings and those local gratings may be modulated to reduce the effects of noise, broaden the dynamic range, vary the sensitivity or discriminate in a multiplexed embodiment. The system can be operated either open or closed loop.

Claims74

Dependent claims

A sensor system to sense an environmental effect, said system including:

a light source producing a first light beam with a relatively broad band of frequencies therein;
a first fiber grating connected to receive said first light beam and positioned for exposure to the environmental effect, said first fiber grating having:
first periodic variations in its optical properties therealong, the instantaneous location of said first periodic variations being affectable by the environmental effect to instantaneously determine a first relatively narrow band width of frequencies reflected by said first fiber grating, said first fiber grating creating a second light beam from said first light beam whose frequency spectrum depends on the environmental effect;
a first local optical filter connected to receive at least portions of said second light beam and positioned for isolation from the environmental effect, said first local optical filter being capable of reflecting a spectrum having a relatively narrow band width overlapping at least some of the frequency spectrum of said second light beam, so that upon exposure to said second light beam, said first local optical filter creates a third light beam whose intensity is representative of the environmental effect;
and
first detector means positioned to receive said third light beam and to produce therefrom a first electrical output representative of the environmental effect.

3 more elements

A sensor system to sense at least one environmental effect, said system including:

a light source producing a first light beam with a relatively broad band of frequencies therein;
at least one first fiber grating having a first reflective spectral envelope, said at least one first fiber grating being connected to receive said first light beam and to reflect any portion of said first light beam included within said first reflective spectral envelope thereby creating a second light beam;
at least one second fiber grating having a second reflective spectral envelope, said at least one second fiber grating being connected to receive said second light beam, whereby said at least one second fiber grating reflects any portion of said second light beam within said second reflective spectral envelope thereby creating a third light beam, whereby one of said fiber gratings is exposed to the at least one environmental effect;
and
first detector means positioned to receive said third light beam and produce therefrom an electrical output representative of the at least one environmental effect when at least one of said fiber gratings is exposed to the at least one environmental effect.

2 more elements

A sensor system to sense at least one environmental effect, said system including:

light source means producing light with a relatively broad band of frequencies therein;
fiber grating means exposed to the at least one environmental effect, said fiber grating means being capable of separating a first spectral envelope from broadband light, said first spectral envelope having:
a first center wavelength that is determined at least in part by the at least one environmental effect and varies therewith;
controlled means being capable of separating a second spectral envelope from broadband light, said second spectral envelope having:
a second center wavelength controlled thereby;
means conducting light from said light source means to said fiber grating means and to said controlled means so that said first and second spectral envelopes are mixed to produce at least one output light beam whose intensity varies with the at least one environmental effect;
and
first detector means positioned to receive said at least one output light beam and produce therefrom an output representative of the at least one environmental effect when said fiber grating means are being exposed to the at least one environmental effect.

5 more elements

A sensor system to sense first and second environmental effects that occur at a single location, said system including:

light source means producing light with first and second bands of frequencies therein;
first fiber grating means exposed to the first and second environmental effects, said first fiber grating means being capable of separating:
a first spectral envelope from said first band of light frequencies having:
a first center wavelength that is determined in part by the first environmental effect and in part by said second environmental effect;
and
a second spectral envelope from said second band of light frequencies having:
a second center wavelength that is determined in part by the first environmental effect and in part by said second environmental effect;
optical filter means being capable of separating:
a third spectral envelope from said first band of light frequencies, said third spectral envelope overlapping at least a portion of said first spectral envelope and having:
a third center wavelength;
and
a fourth spectral envelope from said second band of light frequencies, said fourth spectral envelope overlapping at least a portion of said second spectral envelope and having:
a fourth center wavelength;
means conducting light from said light source means to said first fiber grating means and to said optical filter means so that said first and third, and second and fourth spectral envelopes are mixed to produce first and second output light beams whose intensity varies differently with the two environmental effects;
and
detector means positioned to receive said first and second output light beams and to produce therefrom a first output representative of the first environmental effect and a second output representative of the second environmental effect.

13 more elements

A system for sensing at least one environmental effect, said system including:

first fiber means positioned for exposed to the at least one environmental effect, said first fiber means having:
a length;
and
first periodic variation in optical properties along said length thereof, said first periodic variation in optical properties being affectable by the at least one environmental effect, so said first fiber means can reflect a first spectrum of a relatively narrow group of frequencies that depends on said first periodic variation in optical properties and the at least one environmental effect, and can pass a second spectrum of a first relatively large number of frequencies from which said first spectrum is removed;
a first local optical filter isolated from direct action by the at least one environmental effect, said first local optical filter being capable of separating a third spectrum of a relatively narrow group of frequencies from a fourth spectrum of a second relatively large number of frequencies, said third spectrum overlapping at least some of said first spectrum;
and
first comparison means capable of comparing at least one of said first and second spectra with at least one of said third and fourth spectra, and capable of producing therefrom at least a first output representative of the at least one environmental effect.

4 more elements

Dependencies are inferred from the claim text.