GB2096762A - Optical fibre sensor device - Google Patents
Optical fibre sensor device Download PDFInfo
- Publication number
- GB2096762A GB2096762A GB8111250A GB8111250A GB2096762A GB 2096762 A GB2096762 A GB 2096762A GB 8111250 A GB8111250 A GB 8111250A GB 8111250 A GB8111250 A GB 8111250A GB 2096762 A GB2096762 A GB 2096762A
- Authority
- GB
- United Kingdom
- Prior art keywords
- sensor
- optical fibre
- pulses
- optical
- fibre
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
- 239000013307 optical fiber Substances 0.000 title claims abstract description 61
- 230000003287 optical effect Effects 0.000 claims abstract description 40
- 230000010363 phase shift Effects 0.000 claims abstract description 13
- 230000000694 effects Effects 0.000 claims abstract description 11
- 230000005855 radiation Effects 0.000 claims abstract description 9
- 230000001427 coherent effect Effects 0.000 claims abstract description 6
- 239000000835 fiber Substances 0.000 claims description 12
- 230000001934 delay Effects 0.000 claims description 4
- 230000007613 environmental effect Effects 0.000 claims description 4
- 238000001514 detection method Methods 0.000 claims description 3
- 238000005259 measurement Methods 0.000 claims description 3
- 230000001902 propagating effect Effects 0.000 claims description 3
- 235000003625 Acrocomia mexicana Nutrition 0.000 claims description 2
- 244000202285 Acrocomia mexicana Species 0.000 claims description 2
- 230000005540 biological transmission Effects 0.000 claims description 2
- 230000008878 coupling Effects 0.000 claims description 2
- 238000010168 coupling process Methods 0.000 claims description 2
- 238000005859 coupling reaction Methods 0.000 claims description 2
- 238000005562 fading Methods 0.000 claims description 2
- 238000000034 method Methods 0.000 claims description 2
- 230000002706 hydrostatic effect Effects 0.000 description 2
- 230000001133 acceleration Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L11/00—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00
- G01L11/02—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00 by optical means
- G01L11/025—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00 by optical means using a pressure-sensitive optical fibre
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/35303—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using a reference fibre, e.g. interferometric devices
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/35338—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using other arrangements than interferometer arrangements
- G01D5/35341—Sensor working in transmission
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L1/00—Measuring force or stress, in general
- G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
- G01L1/242—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optical Transform (AREA)
Abstract
A sensing arrangement comprises a source of coherent radiation, e.g. a laser (2), and a modulator (10) for forming from it a train of optical pulses carried by an optical fibre lead to a sensor (11), where they pass to the sensor output through two parallel paths one of which includes an optical fibre responsive to a parameter to be measured. The sensor output is connected via another optical fibre lead to a photodetector (7), which also receives the output from e.g. a Bragg cell 6, fed by the laser 2, and feeds a circuit which compares the relative phase shifts of the pulses traveling respectively through the two paths of sensor 11. Since the phase shifts of the optical fibre leads are common to both pulses, their effect is eliminated. <IMAGE>
Description
SPECIFICATION
Optical fibre sensor device
This invention relates to an optical fibre sensor
and to an arrangement including such a sensor.
Work on the development of optical fibres for
long range telecommunications has also resulted
in the same fibres being used as sensing elements for the detection of changes in mechanical strain,
temperature, acceleration and other parameters.
If a short length of single mode optical fibre,
carrying coherent light, is subjected to
longitudinal mechanical strain three effects will occur, namely a change of physical length, a change of fibre diameter and a change of the refractive index of the optical fibre material. Each of these three effects will result in an optical phase shift being imposed on the optical signals propagating within the fibre. In this particular
example the dominant effect will be that due to change of length followed by that due to change of refractive index, the effect of diameter change being very small. The three effects could also be induced by the application of transverse strain upon the fibre (e.g. by imposing hydrostatic pressure on the outside of the fibre).This basic phenomenon can be used to measure mechanical strain or hydrostatic pressure by measuring the resultant change of phase shift and this can be extended to measurements of temperature (by relating strain to thermal expansion) or acoustic signals (by measuring dynamic strain). Also, temperature can be measured by an optical fibre without its undergoing strain since changes in the temperature of an optical fibre will of themselves affect its optical properties.
Various sensors have been proposed which fundamentally depend upon the above concepts.
Figure 1 of the accompanying drawings is a schematic diagram of a simple form of such a sensor. Figure 1 shows a sensing element 1 which comprises a short coil of single mode optical fibre. Coherent light from a laser 2 is directed through a beam splitter 3 and thence via an optical coupler into an optical fibre 4 which leads into, and is continuous with, the optical fibre forming the sensing element coils. From the sensing element the optical fibre directs the light via an optical coupler to a second beam splitter 5.
In order to measure the phase shift imposed on the light as it passes through the sensing element, the beam splitter 3 directs a small fraction of the optical power to the beam splitter 5, via a device 6 capable of frequency translating the optical signals by a convenient frequency shift. The device 6 may, for example, be a Bragg cell, and a frequency shift of a few MHz is suitable. The path between the beam splitters 3 and 5 may be an air path, and it is not necessary that the light be guided over this distance by an optical fibre or other means. The beam splitter 5 combines the signal emerging from the optical fibre with the signal emerging from the Bragg cell, and the combined signal passes to a photodetector 7.The output of the photodetector 7 is an electrical signal representing the difference frequency between the signals combined by the beam splitters 5 (i.e. a signal whose frequency is equal to the frequency shift applied by the Bragg cell), with the phase shift produced by the sensing element 1 imposed thereon. This phase shift is measured by a suitable circuit to give a value for the parameter being measured by the sensing element.
Instead of the Bragg cell, some other suitable device could be used, for example an optical single sideband modulator. It will be appreciated that if the Bragg cell, optical single sideband modulator, or equivalent device were omitted, the photodetector would have to handle a signal at optical frequency. However, in that case it would provide a DC output, and since the phase modulation produces no change of amplitude the modulation information would be lost.
A disadvantage of the arrangement shown in
Figure 1 is that the lead portions of the optical fibre 4 are liable to pick up additionai, unwanted effect due to variations in ambient pressure, ambient temperature background vibrations, and other phenomena. This results in super-imposing an erroneous phase shift on the phase shift which it is desired to measure. The object of the present invention is to provide an arrangement in which this problem is eliminated or reduced, and a sensor for use in such an arrangement.
According to the present invention there is provided a sensing arrangement comprising a source of coherent optical radiation; an optical pulse modulator for forming a train of optical pulses from the radiation emitted by the said source; a first optical fibre lead arranged to carry the said train of pulses from the optical pulse modulator; a sensor connected to the first optical fibre lead to receive the said train of pulses; the said sensor having means for directing the train of pulses to an output thereof through two paths in parallel with one another, one path passing through an optical fibre arranged to respond to a parameter to be measured, and the other path bypassing the said optical fibre; and a second optical fibre lead arranged to carry pulses from the sensor to a detecting device.
The invention further provides a sensor having an input for receiving a train of optical pulses, an output for emitting a train of optical pulses, and means for directing pulses from the input to the output through two paths in parallel with one another, one path passing through an optical fibre arranged to respond to a parameter to be measured, and the other path bypassing the said optical fibre.
An embodiment of the invention is shown in
Figure 2 of the accompanying drawings. It will be seen that this is similar to what is shown in Figure 1, except in two respects. Firstly, an optical pulse modulator 10 is provided which gates the output of the laser to form short pulses of duration T. It will be observed that the signal passing along the reference path through the Bragg cell is not subject to pulse gating. The second aspect in which the arrangement of Figure 2 differs from that shown in Figure 1 is that the sensor 1 is replaced by a sensor 1 This sensor includes the sensing element which made up the sensor 1 and also includes a pair of optical T junctions 12.The effect of these T junctions is to produce two light paths in parallel to one another through the sensor, the first passing via the sensing element and the second bypassing the sensing element.
The second path may be very short, and in the limiting case it can be effectively zero.
The length of fibre in the sensing element will result in a finite time delay T of any pulse propagating through this coil. It will be assumed that T is very much greater than the corresponding delay through the short parallel optical path between the T junctions. If the pulse duration T is less than T, a pulse entering the sensor 11 will emerge as a pair of pulses, each of duration T but separated in time by T, each pulse having traversed a respective one of the different paths between the T junctions.
It will be apparent that both of these pulses will contain a totai phase change resulting from all the environmental effects arising along the optical fibre leads 4 to and from the sensor. In addition to these effects the second pulse will contain an extra phase shift component associated with the sensing element alone. Accordingly, the phase measurement circuit connected to the photodetector is arranged to compare the relative phase shifts of these pulses in order to detect the phase change due to the sensing element alone.
There is thus provided compensation for any environmental effect in the leads to and from the sensor.
The above description has assumed that the parameter to be investigated is a slowly varying function of time (i.e. a change in temperature, a change in mechanical strain or the like). However, the present invention is also applicable to the detection of vibration or acoustic signals. In this event it is necessary to ensure that the repetition rate of the train of pulses wii adequately sample the variations of the parameter of interest.
The laser used in the present invention can take the form of a conventional gas laser, for example an HeNe laser, and the optical pulse modulator may be an electro-optic modulator.
The optical fibre has been described above as being a single mode fibre, but a multimode fibre may be used in its place. Problems do exist with the use of multimode fibres in this context, as the phase transmission through the multimode fibre is very complex and the resultant signal is subject to severe mode coupling and fading. However, these penalties may be acceptable under some circumstances in order to take advantage of the versatility of multimode systems and the ready availability of components such as Tjunctions for use in multimode systems.
Figure 2 shows only a single sensing element.
However, the principle of the invention can be extended to a plurality of sensing elements served by a single laser and optical fibre lead. The T junctions will then need to be replaced by a more complex form of coupler, for example a star junction or a cascade of T junctions. The output from the sensor will then be formed of groups of more than two pulses. For example, if two sensing elements are used the output from the sensor will consist of pulse triplets, with the first pulse of each triplet representing the reference phase followed by pulses representing the respective delays through the two sensing elements. It will be appreciated that for this technique to be used the different sensing elements must have different delays.
Claims (filed on 7 April 1982)
1. A sensor having an input for receiving a train of optical pulses, an output for emitting a train of optical pulses, and means for directing pulses from the input to the output through two paths in parallel with one another, one path passing through an optical fibre arranged to respond to a parameter to be measured, and the other path bypassing the said optical fibre.
2. A sensor according to claim 1, which comprises first and second T-junctions connected to one another and to the said input and output respectively, the said optical fibre being connected between the first and second Tjunctions.
3. A sensor according to claim 1 or 2, wherein a plurality of parameter-responsive optical fibres are connected to one another between the said input and the said output.
4. A sensor according to any preceding claim, wherein the said optical fibre is a single mode optical fibre.
5. A sensor according to any one of claims 1 to 3, wherein the said optical fibre is a multimode optical fibre.
6. A sensor employing an optical fibre, substantially as herein described with reference to
Figure 2 of the accompanying drawings.
7. A sensing arrangement comprising a source of coherent optical radiation; an optical pulse modulator for forming a train of optical pulses from the radiation emitted by the said source; a first optical fibre lead arranged to carry the said train of pulses from the optical fibre modulator; a sensor connected to the first optical fibre lead to receive the said train of pulses, the said sensor having means for directing the train of pulses to an output thereof through two paths in parallel with one another, one path passing through an optical fibre arranged to respond to a parameter to be measured, and the other path by-passing the said optical fibre; and a second optical fibre lead arranged to carry pulses from the sensor to a detecting device.
8. An arrangement according to claim 7, wherein the sensor is a sensor according to any one of claims 2 to 6.
9. An arrangement according to claim 7 or 8, comprising a first beam splitter interposed between the said source and the optical pulse modulator splitting the said radiation into a first
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (11)
1. A sensor having an input for receiving a train of optical pulses, an output for emitting a train of optical pulses, and means for directing pulses from the input to the output through two paths in parallel with one another, one path passing through an optical fibre arranged to respond to a parameter to be measured, and the other path bypassing the said optical fibre.
2. A sensor according to claim 1, which comprises first and second T-junctions connected to one another and to the said input and output respectively, the said optical fibre being connected between the first and second Tjunctions.
3. A sensor according to claim 1 or 2, wherein a plurality of parameter-responsive optical fibres are connected to one another between the said input and the said output.
4. A sensor according to any preceding claim, wherein the said optical fibre is a single mode optical fibre.
5. A sensor according to any one of claims 1 to 3, wherein the said optical fibre is a multimode optical fibre.
6. A sensor employing an optical fibre, substantially as herein described with reference to
Figure 2 of the accompanying drawings.
7. A sensing arrangement comprising a source of coherent optical radiation; an optical pulse modulator for forming a train of optical pulses from the radiation emitted by the said source; a first optical fibre lead arranged to carry the said train of pulses from the optical fibre modulator; a sensor connected to the first optical fibre lead to receive the said train of pulses, the said sensor having means for directing the train of pulses to an output thereof through two paths in parallel with one another, one path passing through an optical fibre arranged to respond to a parameter to be measured, and the other path by-passing the said optical fibre; and a second optical fibre lead arranged to carry pulses from the sensor to a detecting device.
8. An arrangement according to claim 7, wherein the sensor is a sensor according to any one of claims 2 to 6.
9. An arrangement according to claim 7 or 8, comprising a first beam splitter interposed between the said source and the optical pulse modulator splitting the said radiation into a first
beam arranged to pass to the optical pulses modulator and a second beam; a second beam splitter interposed between the end of the second optical fibre lead and the detecting device for receiving and combining pulses from the second optical fibre lead and the said second beam from the first beam splitter; and a frequency shifting device interposed between the first and second beam splitters for shifting the frequency of the said second beam as it passes from the first beam splitter to the second beam splitter.
10. An arrangement according to claim 9, wherein the frequency shifting device is a Bragg cell.
11. A sensing arrangement substantially as herein described with reference to Figure 2 of the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8111250A GB2096762A (en) | 1981-04-09 | 1981-04-09 | Optical fibre sensor device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8111250A GB2096762A (en) | 1981-04-09 | 1981-04-09 | Optical fibre sensor device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB2096762A true GB2096762A (en) | 1982-10-20 |
Family
ID=10521056
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8111250A Withdrawn GB2096762A (en) | 1981-04-09 | 1981-04-09 | Optical fibre sensor device |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2096762A (en) |
Cited By (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2547049A1 (en) * | 1983-06-03 | 1984-12-07 | Sereg Soc | POLARIMETRY TELEMETRY DEVICE |
| EP0165671A2 (en) * | 1984-06-11 | 1985-12-27 | Litton Systems, Inc. | Passive sampling interferometric sensor arrays |
| EP0203682A2 (en) * | 1985-05-28 | 1986-12-03 | Litton Systems, Inc. | Wavelength switched passive interferometric sensor system |
| FR2585849A1 (en) * | 1985-07-30 | 1987-02-06 | Suisse Electro Microtech Centr | FIBER OPTIC DETECTION SYSTEM INCORPORATING AN INTENSITY MODULATION SENSOR |
| US4752132A (en) * | 1986-10-24 | 1988-06-21 | Litton Systems, Inc. | Low power control interferometric sensor with wide dynamic range |
| US4753529A (en) * | 1986-06-23 | 1988-06-28 | Litton Systems, Inc. | Apparatus and method for precision adjustment of interferometer pathlength difference |
| US4775216A (en) * | 1987-02-02 | 1988-10-04 | Litton Systems, Inc. | Fiber optic sensor array and method |
| US4778239A (en) * | 1987-02-02 | 1988-10-18 | Litton Systems, Inc. | Feed-backward lattice architecture and method |
| US4784453A (en) * | 1987-02-02 | 1988-11-15 | Litton Systems, Inc. | Backward-flow ladder architecture and method |
| US4799752A (en) * | 1987-09-21 | 1989-01-24 | Litton Systems, Inc. | Fiber optic gradient hydrophone and method of using same |
| US4848906A (en) * | 1987-02-02 | 1989-07-18 | Litton Systems, Inc. | Multiplexed fiber optic sensor |
| US5039221A (en) * | 1989-07-03 | 1991-08-13 | Litton Systems, Inc. | Interferometer calibration for fiber optic sensor arrays |
| US5155548A (en) * | 1990-05-22 | 1992-10-13 | Litton Systems, Inc. | Passive fiber optic sensor with omnidirectional acoustic sensor and accelerometer |
| US5475216A (en) * | 1990-05-22 | 1995-12-12 | Danver; Bruce A. | Fiber optic sensor having mandrel wound reference and sensing arms |
-
1981
- 1981-04-09 GB GB8111250A patent/GB2096762A/en not_active Withdrawn
Cited By (20)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0152706A1 (en) * | 1983-06-03 | 1985-08-28 | Sereg S.A. | Apparatus for telemetry using polarisation |
| FR2547049A1 (en) * | 1983-06-03 | 1984-12-07 | Sereg Soc | POLARIMETRY TELEMETRY DEVICE |
| EP0165671A2 (en) * | 1984-06-11 | 1985-12-27 | Litton Systems, Inc. | Passive sampling interferometric sensor arrays |
| EP0165671A3 (en) * | 1984-06-11 | 1987-05-20 | Litton Systems, Inc. | Passive sampling interferometric sensor arrays |
| US4789240A (en) * | 1985-05-28 | 1988-12-06 | Litton Systems, Inc. | Wavelength switched passive interferometric sensor system |
| EP0203682A2 (en) * | 1985-05-28 | 1986-12-03 | Litton Systems, Inc. | Wavelength switched passive interferometric sensor system |
| EP0203682A3 (en) * | 1985-05-28 | 1989-06-07 | Litton Systems, Inc. | Wavelength switched passive interferometric sensor system |
| FR2585849A1 (en) * | 1985-07-30 | 1987-02-06 | Suisse Electro Microtech Centr | FIBER OPTIC DETECTION SYSTEM INCORPORATING AN INTENSITY MODULATION SENSOR |
| EP0211804A1 (en) * | 1985-07-30 | 1987-02-25 | Centre Suisse D'electronique Et De Microtechnique S.A. | Fibre-optical detection system incorporating an intensity modulation sensor |
| US4887901A (en) * | 1985-07-30 | 1989-12-19 | Centre Suisse D'electronique Et De Microtechnique S.A. | Optical fiber detection system using an intensity-modulating sensor |
| US4753529A (en) * | 1986-06-23 | 1988-06-28 | Litton Systems, Inc. | Apparatus and method for precision adjustment of interferometer pathlength difference |
| US4752132A (en) * | 1986-10-24 | 1988-06-21 | Litton Systems, Inc. | Low power control interferometric sensor with wide dynamic range |
| US4778239A (en) * | 1987-02-02 | 1988-10-18 | Litton Systems, Inc. | Feed-backward lattice architecture and method |
| US4784453A (en) * | 1987-02-02 | 1988-11-15 | Litton Systems, Inc. | Backward-flow ladder architecture and method |
| US4848906A (en) * | 1987-02-02 | 1989-07-18 | Litton Systems, Inc. | Multiplexed fiber optic sensor |
| US4775216A (en) * | 1987-02-02 | 1988-10-04 | Litton Systems, Inc. | Fiber optic sensor array and method |
| US4799752A (en) * | 1987-09-21 | 1989-01-24 | Litton Systems, Inc. | Fiber optic gradient hydrophone and method of using same |
| US5039221A (en) * | 1989-07-03 | 1991-08-13 | Litton Systems, Inc. | Interferometer calibration for fiber optic sensor arrays |
| US5155548A (en) * | 1990-05-22 | 1992-10-13 | Litton Systems, Inc. | Passive fiber optic sensor with omnidirectional acoustic sensor and accelerometer |
| US5475216A (en) * | 1990-05-22 | 1995-12-12 | Danver; Bruce A. | Fiber optic sensor having mandrel wound reference and sensing arms |
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