GB2239944A - An optical fibre coupled sensor system - Google Patents
An optical fibre coupled sensor system Download PDFInfo
- Publication number
- GB2239944A GB2239944A GB9000377A GB9000377A GB2239944A GB 2239944 A GB2239944 A GB 2239944A GB 9000377 A GB9000377 A GB 9000377A GB 9000377 A GB9000377 A GB 9000377A GB 2239944 A GB2239944 A GB 2239944A
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- United Kingdom
- Prior art keywords
- optical
- sensor
- optical fibre
- sensor system
- sensor heads
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- 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
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- 239000013307 optical fiber Substances 0.000 title claims abstract description 33
- 230000003287 optical effect Effects 0.000 claims abstract description 51
- 238000001228 spectrum Methods 0.000 claims abstract description 15
- 230000004044 response Effects 0.000 claims abstract description 12
- 230000008859 change Effects 0.000 claims abstract description 3
- 238000000255 optical extinction spectrum Methods 0.000 claims abstract description 3
- 230000003595 spectral effect Effects 0.000 claims description 17
- 230000005540 biological transmission Effects 0.000 claims description 15
- 238000001914 filtration Methods 0.000 claims description 12
- 239000000835 fiber Substances 0.000 claims description 6
- 238000000034 method Methods 0.000 claims description 5
- 230000008569 process Effects 0.000 claims description 4
- 238000011084 recovery Methods 0.000 claims description 4
- 230000003466 anti-cipated effect Effects 0.000 claims description 2
- 230000035945 sensitivity Effects 0.000 claims description 2
- 239000000126 substance Substances 0.000 description 3
- 230000002452 interceptive effect Effects 0.000 description 2
- 239000006096 absorbing agent Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- 239000010937 tungsten Substances 0.000 description 1
Classifications
-
- 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
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Investigating Or Analysing Materials By Optical Means (AREA)
- Optical Transform (AREA)
Abstract
An optical fibre coupled sensor system (2) comprising at least two sensor heads (4) connected in an optical fibre network between a broadband optical source unit (8) and an optical spectrum analyser means (10), the sensor heads (4) being such that the response to at least one parameter to be measured is a change in the variation of the optical transmission spectrum as a function of optical frequency or wavelength. The sensor system (2) is such that the data output from the optical spectrum analyser means (10) is subjected to mathematical analysis (12) in order to recover information on the state of the individual sensor heads (4) and hence to derive information regarding the value of desired parameters in a region (6) in which the sensor heads are situated. <IMAGE>
Description
AN OPTICAL FIBRE COUPLED SENSOR SYSTEM
This invention relates to an optical fibre coupled sensor system and, more especially, this invention relates to the multiplexed interrogation of spectrallyencoded optical sensors.
It is well known to measure the spectral variations of the optical transmission of an optical fibre (intrinsic) sensor element or of an optical fibre remoted optical head (extrinsic) sensor, in order to sense physical or chemical variables. It is also well known to use a variety of types of optical interferometers, for example the Mach-Zehnder,
Fabry-Perot, Michelson or polarimetric optical interferometers in the form of a fibre remoted measurement head, where the interferometers themselves may be configured either in optical fibre form (where all the interfering beams in the sensor head are guided by the fibre and directed, split or combined where necessary, by optical fibre couplers) or in a bulk optics form (using suitable fibre-compatible beam splitters or combiners in the sensor head to form more conventional optical interferometer arrangements) in conjunction with optical fibre leads to link the sensor head to a light source and to a spectral interrogation receiver unit.
The present invention relates to an optical fibre coupled sensor system using more than one sensor head.
Accordingly, the present invention provides an optical fibre coupled sensor system comprising at least two sensor heads connected in an optical fibre network between a broadband optical source unit and an optical spectrum analyser means, the sensor heads being such that the response to at least one parameter to be measured is a change in the variation of the optical transmission spectrum as a function of optical frequency or wavelength, and the sensor system being such that the data output from the optical spectrum analyser means is subjected to mathematical analysis in order to recover information on the state of the individual sensor heads and hence to derive information regarding the value of desired parameters in a region in which the sensor heads are situated.
The sensor system may be one in which the mathematical analysis is performed on the electrical output of the spectrum analyser means using an electronic computer means.
The sensor heads may be spectral-filtering sensor heads.
The sensor system may be one in which the spectralfiltering sensor heads each comprise an optical filtering device, based on the interference of light beams which undergo in the sensing region transmission through different length optical paths, in which the difference between such optical paths is a function of at least one parameter to be measured in the region of the sensor head, and in which, as a result of the nature of the interferometric process, the spectral transmission of each of the sensor heads varies essentially cyclically with the optical wavelength transmitted and where the optical-frequencyperiod of such spectral variation of transmission is a function of one or more of the parameters to be measured.
The parameter or parameters to be measured may be physical or chemical parameters, The spectral-filtering sensors may be Mach-Zehnder, Fabry-Perot, Michelson or polarimetric spectral-filtering sensors.
The sensor system may be one in which the analysis for the recovery of the information on the state of the individual sensor heads is a mathematical algorithm which involves the use of Fourier analysis in the spectral transmission, as a function of optical frequency or wavelength of the transmitted (or reflected) light.
Alternatively, the sensor system may be one in which the mathematical analysis for the recovery of the information on the state of the individual sensor heads is a process of mathematical correlation with one or more anticipated spectral responses for each sensor head.
The sensor system may be one in which the individual sensor heads are closely located together in space in at least one group, in which each member of the group of the sensors is designed to have a different magnitude of response to each of a plurality of parameters to be monitored, and in which the respective sensor outputs of each sensor head within the group are separated by a processor using a mathematical algorithm essentially involving the solution of a series of simultaneous equations to eliminate cross sensitivity to undesirable parameters in each of the recovered outputs from each sensor head in the group, each final output so obtained corresponding to the value of a desired parameter in the region occupied by the group or groups of sensor heads.
The broadband optical source unit may be a luminescent or superluminescent light emitting diode source or a fluorescent or superfluorescent optical fibre source, or may be an incandescent broadband optical source unit. The latter may be, for example, a tungsten broadband optical source unit or a high pressure arc lamp.
The sensor heads may be remoted via a common fibre optic lead, å pair of leads, or a more complex fibre network of leads, in such a manner that they are able to be separately interrogated. The sensor heads may be fibrecompatible spectral filtering means such for example as a prism or diffraction grating monochromator, or a similar dispersive arrangement with multiple output ports. The fibre-compatible spectral filtering means may also be, for example, an arrangement of optical transmission filters.
In the remote sensor head region, the sensor heads are preferably arranged in à parallel form of interconnection network, such that the intensities of optical signals transmitted by the separate sensor heads combine in a linear manner.
The sensor heads may be fed with light from the broadband optical source unit via an optical fibre downlead. A separate optical fibre, or the same one as the downlead, may then be arranged to guide light back to the spectrum analyser means.
The interconnection sequence of certain of the optical parts of the sensor system of the present invention may by well known principles of light transmission theory be changed. Thus, for example, if the optical spectrum analyser means comprises a wavelength-tunable monochromator, then this element may be also placed at the light source end of the sensor system, instead of being placed immediately before the detection arrangement, without changing the response of the system in a significant manner.
Although a parallel interconnection arrangement of the sensor heads is preferred on theoretical grounds, due to the simple linear addition of signals being simpler to decode, it may in some cases be preferred serially to connect the sensor heads, when their transmission functions will multiply. In this latter case, partial decoding is still possible if the spectral responses are distinctly different.
It will be appreciated from the above that the sensor system of the present invention effects decoding of the spectral response by the mathematical processing of the measured transmission curve. This is in contrast to relying on some form of optical processor or optical matched filter to achieve separate sensor outputs, on distinctly separate detectors.
For a typical interferometer type of spectralfiltering sensor head, the spectral response versus optical frequency may show a cyclical variation with the frequency.
The pitch of this variation depends upon the optical path length difference between interfering optical paths, within the sensor. head. If two or more such sensor heads are multiplexed on to the same spectrometer system then the spectral responses of each will add, in the case of parallel connection of the heads, to give two superimposed cyclical variations. These variations may then be separated in a similar manner to methods used to separate individual components of different electrical frequency in an electrical signal. Thus, for example, mathematical
Fourier analysis may be performed on the spectra. The analysis is effected as a function ofoptical frequency, rather than as a function of time as is the case for
Fourier analysis of electrical signals.
Embodiments of the invention 'will now be described solely by way of example and with reference to the accompanying drawings in which:
Figure 1 shows a first two channel multiplexed sensor interrogation system; and
Figure 2 shows a second two channel multiplexed sensor interrogation system.
Referring to Figure 1, there is shown a two channel multiplexed sensor interrogation system 2 comprising two parallel Mach-Zehnder transmission sensor heads 4 positioned in a sensor head region 6. The sensor system 2 further comprises a broadband optical source unit which is shown in
Figure 1 as a light source 8. The sensor system 2 still further comprises an optical spectrum analyser means in the form of an optical spectrum analyser'l0. The optical spectrum analyser 10 is linked as shown to a data processor 12.Thus the data output from the optical spectrum analyser 10 is able to bemathematicallyanalysed by the data processor 12 in order to recover information on the state of the individual sensor heads 4 and hence to derive information regarding the value of desired parameters, for example physical or chemical parameters, in the sensor head region 6 in which the sensor heads 4 are situated.
Referring now to Figure 2, similar parts as in
Figure 1 have been given the same reference numerals and their precise construction and operation will not again be given. In Figure 2, the sensor system 2 is a reflective version of the sensor system 2 shown in Figure 1.
The sensor system 2 shown in Figure 2 permits the use of a single lead 14 which, as illustrated, is a long lead which extends to the sensor heads 4 as shown. In the sensor head region 6, a pair of mirrors 16, 18 are provided in order to obtain the required reflection. Couplers 20, 22 are employed as shown.
In Figure 2, the sensor system 2 also comprises a light absorber 24 to absorb light from the unused coupler port.
It is to be appreciated that the embodiments of the invention described above with reference to the accompanying drawings have been given by way of example only and that modifications may be effected. Thus, for example, alternative sensor heads 4 may be employed such for example as Fabry-Perot, Michelson or polarimetric sensor heads. Also, the illustrated interconnection sequence of the various optical parts may be changed using well known principles of light transmission theory.
Claims (14)
1. An optical fibre coupled sensor system comprising at least two sensor heads connected in an optical fibre network between a broadband optical source unit and an optical spectrum analyser means, the sensor heads being such that the response to at least one parameter to be measured is a change in the variation of the optical transmission spectrum as a function of optical frequency or wavelength, and the sensor system being such that the data output from the optical spectrum analyser means is subjected to mathematical analysis in order to recover information on the state of the individual sensor heads and hence to derive information regarding the value of desired parameters in a region in which the sensor heads are situated.
2. An optical fibre coupled sensor system according to claim 1 in which the mathematical analysis is performed on the electrical output of the spectrum analyser means using an electronic computer means.
3. An optical fibre coupled sensor system according to claim 1 in which the sensor heads are spectral-filtering sensor heads.
4. An optical fibre coupled sensor system according to claim 3 in which the spectral-filtering sensor heads each comprise a optical filtering device, based on the interference of light beams which undergo in the sensing region transmission through different length optical paths, in which the difference between such optical paths is a function of at least one parameter to be measured in the region of the sensor heads, and in which, as a result of the nature of the interferometric process, the spectral transmission of each of the sensor heads varies essentially cyclically with the optical frequency transmitted and where the optical-frequency-period of such spectral variation of transmission is a function of one or more of the parameters to be measured.
5. An optical fibre coupled sensor system according to claim 3 or claim 4 in which the spectral-filtering sensors are Mach-Zehnder, Fabry-Perot Michelson or polarimetric spectral-filtering sensors.
6. An optical fibre coupled sensor system according to any one of claims I - 5 in which the analysis for the recovery of the information on the state of the individual sensor heads is a mathematical algorithm which involves the use of Fourier analysis in the spectral transmission, as a function of optical frequency or wavelength of the transmitted ( or reflected) light.
7. An optical fibre coupled sensor system according to any one of claims 1 - 5 in which the mathematical analysis for the recovery of the information on the state of the individual sensor heads is a process of mathematical correlation with one or more anticipated spectral responses for each sensor head.
8. An optical fibre coupled sensor system according to any one of the preceding claims in which the individual sensor heads are closely located together in space in at least one group, in which each member of the group of the sensors is designed to have a different magnitude of response to each of a plurality of parameters to be monitored, and in which the respective sensor outputs of each sensor head within the group are separated by a processor using a mathematical algorithm essentially involving the solution of a series of simultaneous equations to eliminate cross sensitivity to undesirable parameters in each of the recovered outputs from each sensor head in the group, each final output so obtained corresponding to the value of a desired parameter in the region occupied by the group or groups of sensor heads.
9. An optical fibre coupled sensor system according to any one of the preceding claims in which the broadband optical source unit is a luminescent or superluminescent light emitting diode source or a fluorescent or saper- fluorescent optical fibre source, or an incandescent broadband optical source unit.
10. An optical fibre coupled sensor system according to any one of the preceding claims in which the sensor heads are remoted via a common fibre optic lead, a pair of leads, or a more complex fibre network of leads, in such a manner that they are able to be separately interrogated.
11. An optical fibre coupled sensor system according to claim 10 in which the sensor heads are fibre-compatible spectral filtering means.
12. An optical fibre coupled sensor system according to any one of the preceding claims in which the sensor heads are arranged in a parallel form of interconnection network, such that the intensities of optical signals transmitted by the separate sensor heads combine in a linear manner.
13. An optical fibre coupled sensor system according to any one of the preceding claims in which the sensor heads are fed with light from the broadband optical source unit via an optical fibre downlead.
14. An optical fibre coupled sensor system substantially as herein described with reference to the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9000377A GB2239944B (en) | 1990-01-08 | 1990-01-08 | An optical fibre coupled sensor system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9000377A GB2239944B (en) | 1990-01-08 | 1990-01-08 | An optical fibre coupled sensor system |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9000377D0 GB9000377D0 (en) | 1990-03-07 |
| GB2239944A true GB2239944A (en) | 1991-07-17 |
| GB2239944B GB2239944B (en) | 1993-12-08 |
Family
ID=10668968
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9000377A Expired - Fee Related GB2239944B (en) | 1990-01-08 | 1990-01-08 | An optical fibre coupled sensor system |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2239944B (en) |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0248111A2 (en) * | 1986-04-08 | 1987-12-09 | CV Technology, Incorporated | Spectroscopic method and apparatus for optically measuring temperature |
| US4814604A (en) * | 1986-03-13 | 1989-03-21 | Bertin & Cie, B.P. | Opto-electronic method and system for remote detection of physical magnitudes |
-
1990
- 1990-01-08 GB GB9000377A patent/GB2239944B/en not_active Expired - Fee Related
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4814604A (en) * | 1986-03-13 | 1989-03-21 | Bertin & Cie, B.P. | Opto-electronic method and system for remote detection of physical magnitudes |
| EP0248111A2 (en) * | 1986-04-08 | 1987-12-09 | CV Technology, Incorporated | Spectroscopic method and apparatus for optically measuring temperature |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9000377D0 (en) | 1990-03-07 |
| GB2239944B (en) | 1993-12-08 |
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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: 19970108 |