GB2209211A - Optical fibre sensors - Google Patents
Optical fibre sensors Download PDFInfo
- Publication number
- GB2209211A GB2209211A GB8720525A GB8720525A GB2209211A GB 2209211 A GB2209211 A GB 2209211A GB 8720525 A GB8720525 A GB 8720525A GB 8720525 A GB8720525 A GB 8720525A GB 2209211 A GB2209211 A GB 2209211A
- Authority
- GB
- United Kingdom
- Prior art keywords
- optical fibre
- light
- sensor
- along
- propagating
- 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 title claims abstract description 65
- 230000001902 propagating effect Effects 0.000 claims abstract description 24
- 230000003287 optical effect Effects 0.000 claims abstract description 6
- 230000005540 biological transmission Effects 0.000 claims abstract description 3
- 238000009792 diffusion process Methods 0.000 claims description 3
- 239000000835 fiber Substances 0.000 description 16
- 239000000463 material Substances 0.000 description 5
- 238000010276 construction Methods 0.000 description 4
- 238000005253 cladding Methods 0.000 description 2
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 238000004134 energy conservation Methods 0.000 description 1
- 238000002310 reflectometry Methods 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
- G01D5/268—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 using optical fibres
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
- G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optical Couplings Of Light Guides (AREA)
Abstract
An optical fibre sensor for use in optical fibre sensing arrangements (e.g. pressure or temperature sensing arrangements), in which the optical fibre sensor has optical discontinuities spaced along its length to serve as partial reflectors to light propagating along the sensor, in which each of the discontinuities comprises light reflecting means which extends transversely into the path of light propagating along the sensor, in which each of the discontinuities comprises light reflecting means which extends transversely into the path of light propagating in at least one direction along the optical fibre whereby some of the propagating light travels along the optical fibre unimpeded by the reflecting means whereas the remainder of the propagating light is reflected by impingement on said light reflecting means and in which the angle of reflection of the light propagating in one direction is such that the reflected light travels back along the optical fibre whilst the angle of reflection of light, if any, propagating from the other direction is such that the reflected light is lost by transmission through the wall of the optical fibre.
Description
IMPROVEMENTS RELATING TO OPTICAL FIBRE SENSORS @his invention relates to optical fibre sensors for flee in optical sensing systems such as for the detection of acoustic pressure waves (i.e.
hydrophone applications) or temperatureRfor example.
Nore specifically, the invention relates to optical fibre sensors comprising an optical fibre effectively divided into a plurality of sensor elements by partially reflective splices or discontinuities. An optical sensing system embodying optical fibre sensors of this construction fora the subject of our Patent Bo. 2126820B to which attention is hereby directed.
One of the problems experienoed with such optical fibre sensors is the tendency for multiple reflections to occur within the optical fibre sensor causing cross-talk between the sensing elements of the sensor.
The present invention is directed to minimizing cross-talk within an optical fibre sensor of the form described.
According to the present invention there is provided an optical fibre sensor for use in optical fibre sensing arrangements (e.g. pressure or temperature sensing arrangements), in vhich the optical fibre sensor has optical discontinuities spaced along its length to serve as partial reflectors to light propagating along the sensor, in which each of the disconttnnities comprises light reflecting means which extends transversely into the path of light propagating
o be w- ln 4 r direction along the optical fibre whereby some of the propagating light travels along the optical fibre
unimpeded by the reflecting Deans whereas the remainder of the propagating light is reflected by impingement on said light reflecting means and in which the angle of reflection of the light propagating in one direction is such that the reflected light travels back along the optical fibre whilst the angle of reflection of
ropaga ting from the other direction is such that the reflected light is lost by transmission through the vall of the optical fibre.
It will be appreciated that optical fibre sensors constructed in accordance with the present invention prevent the occurrence of the previously mentioned multiple reflections since that part of light travelling in one direction along the sensor which is reflected will be reflected in its entirety out through the vall of the optical fibre.
The reflection means My comprise separate reflectors (e.g. plates or suitably shaped blocks) which extend radially into the optical fibre path at respective splices there3along. Ib the case where reflector plates are used the spliced ends of the optical fibre may be slightly displaced transversely relative to one another to provide the requisite directional reflective characteristics of the discontinuity.
AlternativelyZthe reflection means nay comprise suitably profiled sections of the optical fibre which may remain nnsevered along its length or a suitably reflective medium may be introduced into the optical fibre core by diffusion at suitable points along the optical fibre sensor and shaped to provide the requisite reflective characteristics of the discontinuity.
By t of example the present invention will now be described with reference to the accompanying drawings in which:
Figure 1 illustrates the occurrence of multiple reflections in a conventionally spliced optical fibre sensor; and,
Figures 2 to 6 are diagrams of parts of an optical fibre sensor having a partial reflective discont@@uity in accordance with the present invention.
Referring to Figure 1 of the drawings an optical fibre sensor 1 is provided along its length vith a plurality of partially reflective splices two of which are shown at 2 and 3.
As depicted in the drawing some of the light
propagate along the fibre in the direction I vill be directed back along the fibre froi the splice 2 whereas eome light will pass through the splice 2 and will be reflected by the splice 3 but instead of passing back through the splice 2 it vill be reflected back again to splice 3 where it is reflected so that it finally passes through the splice 2. 8uch multiple reflections cause unwanted cross-talk or cros-coupling between optical fibre sensor elements 4, 5 and 6 defined by the sections of optical fibre between discontinuities.
Referring now to Figures 2 (a) and 2 (b) these show a splice for of discontinuity @ for providing partial reflection of light in both directions along a monomode or multimode optical fibre 7. As can be seen, a tapered reflective block 8 is interposed between the spliced ends of the optical fibre so that the block extends transversely by a short distance
into the path of light travelling along the core of the optical fibre.
The remaining space between the ends of the fibre is filled with material 9 vhich is index matched to the optical fibre 7.
In operation of the optical fibre sensor some of the light propagating along the sensor 7 in the direction B will be reflected back along the fibre as shown by the vertical surface 10 of the block 8. The remainder of the light vill pass through the index matched splice to the next discontinuity (not shown) along the optical fibre sensor. Most of the light reflected back along the optical fibre in direction C from the next and any succeeding discontinuities will pass straight through the index matched splice material 9 but some will impinge on the inclined reflective surface 11 of the block 8 and will be reflected through the wall of the optical fibre to prevent the occurrence of unwanted multiple reflections which would give rise to cross-conpling between sensor leienti.
In the figure 3 (a) and 3(b)
arrangement a plate reflector 12 is introduced into a spliced connection between the ends 13 and 14 of an optical fibre with an inder/matched filling material 15 being provided. As can best be seen in Figure 3 (b) the fibre ends 13 and 14 are slightly displaced relative to one another in the transverse direction so that a segmental section 16 of the reflector 12 is exposed to light propagating along the fibre in direction D to enable a proportion of light to be reflected back along the fibre but any light propagating in the direction S due to reflection from the next or any succeeding discontinuities will pass straight through the inder#matched material without being reflected and causing mltiple reflections. Only a small proportion of the reflected light vill be lost due to the transverse displacement of the fibre ends indicated by the segment 17 in Figure 3 (b).
Referring to Figures 4, 5 and 6, in these constructions the respective discontinuities 18, 19 and 20 are provided in the optical fibre 21 without the need to sever the fibre.
In Figure 4 the core 22 of the optical fibre is etched away as shown to provide a vertical reflection surface 23 and a tapered reflection surface 24. s small proportion of light propagating in the direction F will be reflected back along the optical fibre 21 whereas a small proportion of any light reflected from the next or any succeeding discontinuities along the fibre will be reflected out of the fibre by the tapered reflecting surface 24.
In the Figure 5 construction the refractive index of a region 25 of the fibre core is changed by diffusion of material into the core so that propagating light impinging on the region from direction G will be reflected back along the fibre as shown whereas light reflected from the next or succeeding discontinuities along the fibre and impinging on the region 25 will be reflected out of the fibre as indicated thereby avoiding the problem of multiple reflections.
Finally, in the Figure 6 construction the optical fibre core and cladding is profiled as ahown whereby a small proportion of light propagating in direction H is reflected by the
vtc-e a e r --Li reflecting surface 26 whereas some of the light reflected by the next or any succeeding discontinuities is deflected and trana:itted through the tapered surfaces 27 and 28 of the core and cladding to prevent multiple reflectinni occurring.
As vill be observed from the foregoing description of various embodiments of the invention the reflecting means utilised at each of the discontinuities have different reflectivities in different directions and although this would appear to suggest reciprocity or energy conservation this is not necessarily the case if the reflection is either diffuse, energy is absorbed or the unwanted signal is simply side-tracked onto an irrelevant path. In an optical fibre this is particularly easy to accomplish and can provide the basis for reflectors which suppress reflections in one direction within the fibre.
Claims (1)
1. An optical flbre sensor for use in optical fibre sensing affangements, in which the optical fibre sensor has optical discontinuities spaced along its length to serve as partial reflectors to light propagating along the sensor in which each of the discontinuities comprises light reflecting means which extends tfansversely into the path of light propagating in at least one direction along the optical fibre whereby some of the propagating light travels along the optical fibre unimpeded by the reflecting means whereas the remainder 4 the propagating light. as reflected by impingement on said light feflecting means and in which the angle of reflection of the light propagating in one direction is such that the: reflected light travels back along the optical fibre whilst the angle of reflection of light, if any, propagating from the other direction is such that the reflected light 18 lost by transmission through the wall of the optical fibre.
An optical fibre sensor as claimed in claim 1, in which the: reflection means comprises separate ref lectors (eg plates or suitably shaped blocks) which extend radially into the optical fibre path at respective sp@ces therealong
An optical fibre sensor as claimed in claim 2, in which the reflection means compprise reflector plates and in which the spliced ends of the optical fibre are slightly displaced transversely relative to one aiother to provide the requisite directional reflective characteristics of the discontinuity.
4. An optical fibre sensor as claimed in claim 1, in which the reflection means comprises s suitably profiled sections of the optical fibre which remains unsevered along its length.
5 - An optical fibre sensor as claimed in claim 1, in which the reflection means comprises a suitably reflective medium introduced into the optical fibre core by diffusion at suitable points along the optical fibre sensor and shaped to pfovirle the requisite reflective. characteristics of the discontinuity.
6. An optical fibre sensor substantially as hereinbefore described with reference to the accompanying drawings.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8720525A GB2209211B (en) | 1987-09-01 | 1987-09-01 | Improvements relating to optical fibre sensors |
| PCT/GB1988/000677 WO1989002063A1 (en) | 1987-09-01 | 1988-08-17 | Improvements relating to optical fibre sensors |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8720525A GB2209211B (en) | 1987-09-01 | 1987-09-01 | Improvements relating to optical fibre sensors |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8720525D0 GB8720525D0 (en) | 1987-10-07 |
| GB2209211A true GB2209211A (en) | 1989-05-04 |
| GB2209211B GB2209211B (en) | 1991-10-30 |
Family
ID=10623099
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8720525A Expired - Lifetime GB2209211B (en) | 1987-09-01 | 1987-09-01 | Improvements relating to optical fibre sensors |
Country Status (2)
| Country | Link |
|---|---|
| GB (1) | GB2209211B (en) |
| WO (1) | WO1989002063A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19935439A1 (en) * | 1999-07-28 | 2001-02-15 | Siemens Ag | Sensor cable |
| DE102018117979A1 (en) * | 2018-07-25 | 2020-01-30 | Brugg Rohr Ag Holding | Double-walled conduit and an optical fiber for such a conduit |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE435967B (en) * | 1982-04-01 | 1984-10-29 | Asea Ab | FIBEROPTICAL LUMINISCENSMETON |
-
1987
- 1987-09-01 GB GB8720525A patent/GB2209211B/en not_active Expired - Lifetime
-
1988
- 1988-08-17 WO PCT/GB1988/000677 patent/WO1989002063A1/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| GB2209211B (en) | 1991-10-30 |
| GB8720525D0 (en) | 1987-10-07 |
| WO1989002063A1 (en) | 1989-03-09 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19930901 |