US 5,397,891 A · Sensor systems employing optical fiber gratings

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 optical filter unaffected by the environmental effect and compared with the spectral envelope of the local optical filter 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 optical filters and those local optical filters 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. In addition, the fiber grating may have multiple gratings at the same location so that different kinds of effects or effects from different directions can be sensed from a single location.

Claims42

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 at least a portion of said first light beam and positioned exposure to the environmental effect, said first fiber grating having:
a first internal grating pattern comprised of:
areas having different indices of refraction whose instantaneous positions relative to each other 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 reflection of the instantaneous positions of said areas having different indices of refraction of said first internal grating pattern;
a first local optical filter positioned for isolation from the environmental effect, said first local optical filter determining a spectrum having a band width overlapping at least some of the frequency spectrum of said second light beam, so that combination thereof 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.

4 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 for separating a first spectral envelope from broadband light, said fiber grating means being exposed to the at least one environmental effect, 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 optical filter means for 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 optical filter 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.

5 more elements

A sensor system to sense at least 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;
fiber grating means exposed to the first and second environmental effects, said first fiber grating means being for 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 for 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 first and second 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

Dependencies are inferred from the claim text.

Sensor systems employing optical fiber gratings

Life of this patent

Sensor systems employing optical fiber gratings

Life of this patent

Abstract

Claims42