GB2207236A - Sensing temperature or pressure distribution - Google Patents
Sensing temperature or pressure distribution Download PDFInfo
- Publication number
- GB2207236A GB2207236A GB08717155A GB8717155A GB2207236A GB 2207236 A GB2207236 A GB 2207236A GB 08717155 A GB08717155 A GB 08717155A GB 8717155 A GB8717155 A GB 8717155A GB 2207236 A GB2207236 A GB 2207236A
- Authority
- GB
- United Kingdom
- Prior art keywords
- optical fibre
- measurement
- along
- interferometer
- optical
- 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.)
- Granted
Links
- 239000013307 optical fiber Substances 0.000 claims abstract description 68
- 238000005259 measurement Methods 0.000 claims abstract description 43
- 230000003287 optical effect Effects 0.000 claims abstract description 29
- 230000001427 coherent effect Effects 0.000 claims abstract description 4
- 230000001052 transient effect Effects 0.000 claims abstract description 4
- 239000000835 fiber Substances 0.000 claims description 29
- 230000001902 propagating effect Effects 0.000 claims description 14
- 230000005374 Kerr effect Effects 0.000 claims description 5
- 230000001419 dependent effect Effects 0.000 claims description 4
- 238000010521 absorption reaction Methods 0.000 claims description 2
- 230000031700 light absorption Effects 0.000 claims description 2
- 230000035945 sensitivity Effects 0.000 description 3
- 238000000034 method Methods 0.000 description 2
- 238000000253 optical time-domain reflectometry Methods 0.000 description 2
- 238000012935 Averaging Methods 0.000 description 1
- 238000001069 Raman spectroscopy Methods 0.000 description 1
- 230000003321 amplification Effects 0.000 description 1
- 239000002019 doping agent Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 238000003199 nucleic acid amplification method Methods 0.000 description 1
- 230000010363 phase shift Effects 0.000 description 1
Classifications
-
- 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
- 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
- G01D5/35383—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 multiple sensor devices using multiplexing techniques
-
- 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
Abstract
An optical fibre sensing arrangement comprises an optical interferometer having measurement 1 and reference paths, the measurement path comprising an optical fibre extending over the path along which distributed temperature or pressure is to the measured. Coherent continuous light from source 5 propagates in one direction along the measurement and reference paths of the interferometer to detector 10 and light pulses from source 7 propagate along the measurement path only, in the direction opposite to that in which the continuous light propagates to produce transient variations in the propagation constant (or phase change co-efficient) of the optical fibre at points therealong according to the temperature or pressure at said points. The resultant output from the interferometer, varies with respect to time in dependence upon the temperature or pressure at distributed points along the measurement optical fibre path. <IMAGE>
Description
IMPROVEMENTS RELATING TO OPTICAL FIBRE SENSING
ARRANGEMENTS
This invention relates to optical fibre sensing arrangements for measuring or monitoring temperatures or pressures distributed over a predetermined path.
It is known to measure temperature distribution along an optical fibre extending over a predetermined path by the use of so-called optical time domain reflectometry techniques in which an intense pulse of laser light is launched into one end of the fibre and the variations with tint of back-scattered light (or fluorescent light produced by the laser light pulses acting on temperaturedependent fluorescence of dopant contained within the fibre) received at the launch end of the optical fibre are measured for determining the temperature distribution along the fibre.
It is also known in the measurement of temperature distribution along an optical fibre to launch an intense (pump) pulse of light into an optical fibre extending over a predetermined path so that the pulse propagates along the fibre in the opposite direction to that in which a continuous wave optical signal is propagating and to make use of Raman amplification of the intensity of the continuous wave optical signal by the pump light pulse in determining the amplitude variations which occur in the continuous wave signal detected at the far end of the optical fibre and which are dependent on pressure or temperature variations along the optical fibre.
The present invention is based on the realisation that much improved sensitivity of temperature or pressure optical fibre sensing arrangements can be achieved by using an optical fibre sensing system comprising an optical interferometer, having measurement and reference optical paths, the measurement path comprising an optical fibre extending over the path along which distributed temperature or pressure is to measured, continuous wave light generating means for producing coherent continuous wave light which propagates in one direction along the measurement and reference 1paths of the interferometer, pulse light generating means for producing light pulses which propagate along the measurement path only in the direction opposite to that in which the continuous wave light propagates to produce transient variations in the propagation constant (or phase change co-efficient) of the optical fibre at points therealong according to the temperature or pressure at said points, and detector means for detecting the resultant output from the interferometer, which will vary with time in dependence upon the temperature or pressure at distributed points along the measurement optical fibre path.
The interferometer of the optical sensing arrangement may comprise a Mach-Zehnder interferometer with the continuous wave light produced by the continuous wave light generating means propagating in one direction only along parallel measurement and reference paths the outputs from which are combined before being applied to the detector means.
Alternatively, the interferometer may be a Michelson reflective interferometer with the continuous wave light propagating along the measurement and reference paths being reflected back along said paths before the reflected outputs from the paths are combined and applied to the detector means.
In carrying out the present invention the so-called propagation constant (or phase change co-efficient) of the optical fibre may be caused to vary in dependence upon temperature or pressure at points along the fibre by the choice of a suitable optical fibre composition and optical wavelength of the light pulses propagating along the measurement optical fibre path. According to one sensing arrangement envisaged use may be made of the so-called optical Kerr Effect. Due to the optical Kerr Effect the refractive index of the optical fibre at points therealong encountered by the continuous wave propagating along the fibre will be varied by the light pulses as they reach said points from the opposite direction in accordance with -the temperature of the fibre at said points.Since the optical Kerr Effect is temperature dependent, the detected changes in the output signal from the interferometer as a
function of time will proviae an indication of the
temperature distribution along the optical fibre.
According to another sensing arrangement envisaged the measurement optical fibre may be doped to provide a
temperature-dependent absorption co-efficient, whereby variations in the absorption of light along the fibre due
to different temperatures give rise to changes in refractive index of the fibre as the light pulses travel therealong, these changes in refractive index producing changes in the detected output from the interferometer.
When the optical fibre sensing arrangement according to the invention is to be used to measure pressures at points along the optical fibre, pressure-responsive refractive index changes to the fibre will be provided for
in response to the propagation of the light pulses along the optical fibre.
The reference path of the interferometer preferably comprises an optical fibre separate from the measurement optical fibre, but it should be understood that the reference fibre could be provided by the same optical fibre as the measurement fibre by using a separate mode of propagation for the reference path. For example, the measurement and reference paths could be provided by using separate polarisation modes in the same fibre.
Alternatively, the reference path could be a free-space path.
By way of example the present invention will now be described with reference to the accompanying drawings in which:
Figure 1 shows one form of optical fibre temperature sensing arrangement according to the invention;
Figure 2 shows different waveforms appertaining to the sensing arrangement of Figure 1; and Figure 3 shows another form of optical fibre sensing arrangement according to the invention
Referring to Figure 1 the optical temperature sensing arrangement depicted comprises a simple homodyne
Mach-Zehnder interferometer, comprising a measurement optical fibre 1 having connected in parallel therewith a reference optical fibre 2. Suitable optical couplers (3 and 4) will be provided where the two paths 1 and 2 diverge and are combined at the two ends of the interferometer.
A continuous wave signal source 5 is provided for generating coherent continuous wave optical signals 6 which will propagate in parallel along the measurement and optical fibres 1 and 2. A pulsed (pump) laser light source 7 is provided for producing light pulses 8, which are launched into the measurement optical fibre 1 through a suitable optical coupler 9, so that they propagate along the fibre in the opposite direction to that in which the continuous wave optical signals 6 are propagating. The wavelength of the light pulses 8 and the composition of the measurement optical fibre 1 are such that, due to the optical Kerr Effect, the light pulses 8 transmitted along the fibre modify the refractive index of the fibre to varying degrees, according to the temperature of the optical fibre at points therealong.
The output from the interferometer representing the resultant of the optical signals propagating along the fibre 1 which may be subjected to variable temperatures throughout its length and the reference fibre 2 which will be maintained at a substantially constant temperature throughout its length, is applied to a detector 10 which will detect variations in the interferometer output due to phase shifts occurring in the continuous wave signal resulting from variations in refractive index of the fibre 1 along its length.
Referring to Figure 2 of the drawings, this shows at (a) the optical power waveform of the pulses 8 from the laser (pump) light source 7 of Figure 1 and at (b) and (c), respectively, the detected phase difference produced in the interferometer when the measurement fibre is at a constant temperature and when the measurement fibre is at variable temperatures along its length.
In practice, some means of maintaining phase quadrature between the two optical signals in the reference and measurement fibres 1 and 2 will generally be necessary before the light pulses 8 from the source 7 are launched in order to set the arrangement to the point of maximum sensitivty. In addition, an optical amplitude reference will normally be required in order to prevent sensitivity to undesired variations in the continuous wave light source intensity. A simple addition to the interferometer would be to connect a second detector, such as that shown at 11 in Figure 1, into the system by using a suitable optical fibre directional coupler of the output to the interferometer and to monitor the ratio of the outputs of the two detectors 10 and 11.
The use of polarisation-maintaining fibres for the measurement and reference fibres 1 and 2 and couplers will reduce any variations in the system of Figure 1 due to changes in the polarisation state in the optical fibres.
Referring now to Figure 3 of the drawings this shows an optical fibre temperature or pressure sensing arrangement which utilises a Michelson interferometer.
The arrangement comprises a continuous wave signal source 12 which produces continuous wave signals 13 which propagate along measurement and reference optical fibres 14 and 15 after passing through a directional optical coupler 16. A pulsed (pump) laser light source 17 produces light pulses 18 which are launched into the measurement optical fibre 15 though an optical coupler 19.
These light pulses propagate along the measurement optical fibre 14 in a direction opposite to that in which the continuous wave light is propagating.
As in the Figure 1 arrangement the wavelength of the light pulses 18 and the composition of the measurement optical fibre 14 may be such that the pulses modify the refraction index of the optical fibre to varying degrees according to the temperature of the optical fibre at points therealong. These variations in refractive index produce transient variations in the propagation contant or phase change coeficient of the optical fibre at points therealong. Thus phase changes with respect to time will be produced in the continuous wave signals propagating along the measurement fibre 14 according to the distributed temperature along the fibre 14.
In this embodiment the continuous wave signals propagating along the optical fibres 14 and 15 are reflected back along the fibres from the ends of the latter and the reflected signals are combined by means of the directional coupler 16 before being applied to a detector 20. The detector 20 serves to detect time-displaced phase changes in the reflected continuous wave signals due to variations in the refractive index of the optical fibre 14 along its length due to changes in temperature of the fibre. The reference fibre 15 will be maintained at a constant temperature throughout its length and the reflected signal therein will serve as a reference signal for the detector 20 in measuring the temperature distribution along the measurement fibre 14. It may here be mentioned that the main advantage of the present invention over the previously referred to known optical time domain reflectometry techniques is the substantial increase in sensitivity. Consequently, such interferometric sensing arrangements enable variations due to effects with only weak temperature or pressure dependence to be monitored, or, more especially, the use of complex electronics for signal averaging of the otherwise weak detected signals may be avoided.
Claims (10)
1. An optical fibre sensing arrangement comprising an optical interferometer having measurement and reference paths, the measurement path comprising an optical fibre extending over the path along which deistributed temperature or pressure is to be measured, continuous wave light generating means for producing coherent continuous wave light which propagates in one direction along the measurement and reference paths of the interferometer, pulse light generating means for producing light pulses which propagate along the measurement path only in the direction opposite to that in which the continuous wave light propagates to produce transient variations in the propagation constant (or phase change co-efficient) of the optical fibre at points therealong according to the temperature or pressure at said points, and detector means for detecting the resultant output from the interferometer, which will vary with respect to time in dependence upon the temperature or pressure at distributed points along the measurement optical fibre path.
2. An optical fibre sensing arrangement as claimed in claim 1, in which the interferometer comprises a Mach
Zehnder interferometer with the continuous wave light produced by the continuous wave light generating means propagating in one direction only along parallel measurement and reference paths the outputs from which are combined before being applied to the detector means.
3. An optical fibre sensing arrangement as claimed in claim 1, comprising a Michelson interferometer with the continuous wave light propagating along the measurement and reference paths being reflected back along said paths before the reflected outputs from the paths are combined and applied to the detector means.
4. An optical fibre sensing arrangement as claimed in any proceeding claim, in which the propagation constant (or phase change coefficient) of the optical fibre is caused to vary in dependence upon temperature or pressure at points along the fibre by the choice of a suitable optical fibre composition and optical wavelength of the light pulses propagating along the measurement optical fibre path.
5. An optical fibre sensing arrangement as claimed in claim 4, in which use is made of the optical Kerr Effect which causes the refractive index of the optical fibre at points therealong encountered by the continuous wave propagating along the optical fibre to be varied by the light pulses as they reach said points from the opposite direction in accordance with the temperature of the fibre at said points, the detected changes in the output signal from the interferometer as a function of time providing an indication of the temperature distribution along the optical fibre.
6. An optical fibre sensing arrangement as claimed in any of claims 1 to 3, in which the measurement path optical fibre is doped to provide a temperature-dependent absorption co-efficient whereby variations in the absorption of light along the fibre due to different temperatures give rise to changes in the refractive index producing changes in the detected output from the interferometer.
7. An optical fibre sensing arrangement as claimed in any preceding claim, in which the reference path of the interferometer comprises an optical fibre separate from the measurement optical fibre.
8. An optical fibre sensing arrangement as claimed in any of claims 1 to 6, in which the measurement and reference paths are provided by using separate polarisation modes in the same optical fibre.
9. An optical fibre sensing arrangement substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.
10. An optical fibre sensing arrangement substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8717155A GB2207236B (en) | 1987-07-21 | 1987-07-21 | Improvements relating to optical fibre sensing arrangements |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8717155A GB2207236B (en) | 1987-07-21 | 1987-07-21 | Improvements relating to optical fibre sensing arrangements |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8717155D0 GB8717155D0 (en) | 1987-08-26 |
| GB2207236A true GB2207236A (en) | 1989-01-25 |
| GB2207236B GB2207236B (en) | 1991-04-24 |
Family
ID=10621001
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8717155A Expired - Lifetime GB2207236B (en) | 1987-07-21 | 1987-07-21 | Improvements relating to optical fibre sensing arrangements |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2207236B (en) |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2651316A1 (en) * | 1989-08-31 | 1991-03-01 | Univ Leland Stanford Junior | APPARATUS FOR DETECTING PHASE DIFFERENCE BETWEEN FIRST AND SECOND OPTICAL SIGNALS AND DETECTION METHOD. |
| EP0585013A1 (en) * | 1992-08-14 | 1994-03-02 | Litton Systems, Inc. | Optic sensor system |
| US5365065A (en) * | 1992-10-14 | 1994-11-15 | Power Joan F | Sensitive interferometric parallel thermal-wave imager |
| WO1995002802A1 (en) * | 1993-07-12 | 1995-01-26 | The Secretary Of State For Defence | Sensor system |
| US5635919A (en) * | 1990-08-06 | 1997-06-03 | Schier; J. Alan | Sensing apparatus |
| CN103733027A (en) * | 2011-04-08 | 2014-04-16 | 光学感应器控股有限公司 | Fibre optic distributed sensing |
| DE102015207165A1 (en) | 2015-04-21 | 2016-10-27 | Robert Bosch Gmbh | A battery system and method for monitoring a temperature of a battery system |
-
1987
- 1987-07-21 GB GB8717155A patent/GB2207236B/en not_active Expired - Lifetime
Cited By (20)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2236030A (en) * | 1989-08-31 | 1991-03-20 | Univ Leland Stanford Junior | Passive quadrature phase detection system for coherent fiber optic systems |
| US5200795A (en) * | 1989-08-31 | 1993-04-06 | The Board Of Trustees Of The Leland Stanford Junior University | Passive quadrature phase detection system for coherent fiber optic systems |
| GB2236030B (en) * | 1989-08-31 | 1994-04-20 | Univ Leland Stanford Junior | Passive quadrature phase detection system for coherent fiber optic systems |
| FR2651316A1 (en) * | 1989-08-31 | 1991-03-01 | Univ Leland Stanford Junior | APPARATUS FOR DETECTING PHASE DIFFERENCE BETWEEN FIRST AND SECOND OPTICAL SIGNALS AND DETECTION METHOD. |
| US5635919A (en) * | 1990-08-06 | 1997-06-03 | Schier; J. Alan | Sensing apparatus |
| US6246469B1 (en) | 1990-08-06 | 2001-06-12 | J. Alan Schier | Sensing apparatus |
| US5764161A (en) * | 1990-08-06 | 1998-06-09 | Schier; J. Alan | Sensing apparatus using frequency changes |
| EP0585013A1 (en) * | 1992-08-14 | 1994-03-02 | Litton Systems, Inc. | Optic sensor system |
| US5365065A (en) * | 1992-10-14 | 1994-11-15 | Power Joan F | Sensitive interferometric parallel thermal-wave imager |
| GB2295010B (en) * | 1993-07-12 | 1997-06-11 | Secr Defence | Sensor system |
| GB2295010A (en) * | 1993-07-12 | 1996-05-15 | Secr Defence | Sensor system |
| WO1995002802A1 (en) * | 1993-07-12 | 1995-01-26 | The Secretary Of State For Defence | Sensor system |
| CN103733027A (en) * | 2011-04-08 | 2014-04-16 | 光学感应器控股有限公司 | Fibre optic distributed sensing |
| US9435668B2 (en) | 2011-04-08 | 2016-09-06 | Optasense Holdings Ltd. | Fibre optic distributed sensing |
| CN103733027B (en) * | 2011-04-08 | 2016-10-19 | 光学感应器控股有限公司 | Fibre optic distributed sensing |
| US9945717B2 (en) | 2011-04-08 | 2018-04-17 | Optasense Holdings Ltd. | Fibre optic distributed sensing |
| DE102015207165A1 (en) | 2015-04-21 | 2016-10-27 | Robert Bosch Gmbh | A battery system and method for monitoring a temperature of a battery system |
| WO2016169702A1 (en) * | 2015-04-21 | 2016-10-27 | Robert Bosch Gmbh | Battery system and method for monitoring a temperature of a battery system |
| CN107534192A (en) * | 2015-04-21 | 2018-01-02 | 罗伯特·博世有限公司 | The method of battery pack system and the temperature for monitoring battery pack system |
| CN107534192B (en) * | 2015-04-21 | 2020-02-21 | 罗伯特·博世有限公司 | Battery pack system and method for monitoring temperature of battery pack system |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2207236B (en) | 1991-04-24 |
| GB8717155D0 (en) | 1987-08-26 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| 732E | Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977) | ||
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19990721 |