GB2165118A - OTDR for sensing distortions in optical fibres - Google Patents
OTDR for sensing distortions in optical fibres Download PDFInfo
- Publication number
- GB2165118A GB2165118A GB08424671A GB8424671A GB2165118A GB 2165118 A GB2165118 A GB 2165118A GB 08424671 A GB08424671 A GB 08424671A GB 8424671 A GB8424671 A GB 8424671A GB 2165118 A GB2165118 A GB 2165118A
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- United Kingdom
- Prior art keywords
- fibre
- optical
- pulse
- optical fibre
- along
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Classifications
-
- 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
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
- G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
- G01M11/31—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter and a light receiver being disposed at the same side of a fibre or waveguide end-face, e.g. reflectometers
- G01M11/3109—Reflectometers detecting the back-scattered light in the time-domain, e.g. OTDR
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
- G01S17/06—Systems determining position data of a target
- G01S17/08—Systems determining position data of a target for measuring distance only
- G01S17/10—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/499—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00 using polarisation effects
Abstract
An optical sensing system comprises a highly birefringent optical fibre 5 having two principal polarisation axes. The optical fibre 5 is arranged to be subjected to deforming forces such as acoustic waves. The optical fibre 5 is divided into a plurality of elements by discontinuities 7 to 15 so that a small proportion of coherent light transmitted along either axis of the optical fibre 5 will be reflected back along the fibre 5 at each. The reflected light pulses interfere with each other within either axis of the optical fibre 5, and after leaving the optical fibre 5, they are passed to a photo- detection means 19a, 19b and decoding means 20a, 20b from which signals indicative of changes in optical length of the elements are produced. There is substantially no interaction between light passing along the two axes, and so by transmitting a first pulse train of one polarization along one axis and a second pulse train of a second polarization along the other axis, the bandwidth of the system is effectively doubled. <IMAGE>
Description
SPECIFICATION
Optical systems
This invention relates to optical systems, in particular, optical systems for sensing strain or deformation (e.g. elongation or bending) ofvarious members.
A previously proposed optical sensing system is described in our co-pending Patent Application No.
GB 8220793 (Publication No. 2126820A) in which single coherent light pulse or pairs of coherent light pulse are launched into an optical fibre which is arranged to be subjected to deforming forces such as acoustic waves. The optical fibre is divided into a plurality of discrete fibre elements so that a small proportion of each coherent light pulse transmitted along the fibre will be reflected back along the fibre at the junction between each of the elements.
Reflected light pulses interfere with one another in the optical fibre, and after leaving the optical fibre, they are passed to a photo-detection means and decoding means. In response to receiving the pulses, the photo-detection means produces electrical signals indicative of changes in optical path length of the elements due to the incidence of the deforming forces.
This system suffers from the disadvantage that it is necessary to wait for all reflected pulses to leave the optical fibre before launching a further coherent light pulse or pulse pair down the fibre. As a consequence, the sampling rate of the sensing system is limited by the time taken for all reflected pulses to leave the fibre, and so the maximum frequency acoustic wave which can be sensed is also limited. This problem is particularly troublesome in optical sensing systems having a long optical fibre where the optical "round trip" time is greater than about 50 microseconds.
It is an aim of the present invention to produce an optical sensing system which can sense acoustic waves having a relatively high frequency even if a long optical fibre is employed in the system.
According to the present invention there is provided an optical system comprising a highly birefringent optical fibre having a pair of principal polarisation axes, which optical fibre is arranged to be subjected along its length to fibre deforming forces during operation of the system, and means for producing first train of coherent light pulses for transmission along one of the polarisation axes and a second train of coherent light pulses for transmission along the other polarisation axis, wherein the high birefringence of the optical fibre is such that there is substantially no interaction between the first pulse train and the second pulse train, and the optical fibre is provided with a number of equally spaced discontinuities along its length which effectively divide the fibre into a plurality of discrete fibre elements so that a small proportion of each light pulse being transmitted along the fibre will be reflected back along the fibre from each of the discontinuities whereby, within the pulse train transmitted down either of the polarisation axes, each reflected light pulse after the first interferes with either the previously reflected pulse from the preceding discontinuity or a reference light signal of the same frequency or a frequency with a constant difference frequency to the transmitted pulse train to produce an electrical signal in square law photodetection means of the system, the difference between respective electrical signals corresponding to successive fibre elements being dependent upon the length of the fibre element so that changes in optical path lengths of these elements produced by the incidence of the deforming forces will result in changes in the electrical signals which will be detected.
The principal polarisation axes of the optical fibre may be orthogonal with respect to each other.
The optical system may be a multiplexed optical system in which a plurality of pulse trains are transmitted along each one of the polarisation axes.
A multiplexed optical sensing system is described in our co-pending UK Patent Application No. 84.24670.
Embodiments of the present invention have the advantage that, since there is virtually no interaction (less than 45dB isolation over a short length, for example 10 metres) between the first and second pulse trains travelling along respective principal polarisation axes of the highly birefringent optical fibre, the bandwidth of the optical sensing system is effectively doubled thereby allowing acoustic waves impinging on the optical fibre to be sampled at a higher rate.
The means for producing the first and second pulse trains may comprise a laser coupled to an optical frequency shift means. The optical frequency shift means may comprise an integrated optic phase modulator or a Bragg cell, and may be coupled to a driving means which drives the optical frequency shift means thus enabling it to produce the first and second trains of coherent light pulses.
The pulse trains may be launched into the polarisation axes of the optical fibre by means of a polarisation rotater which, for example, orientates the polarisation axes of the first and second pulse trains so that they are transmitted along respective polarisation axes of the optical fibre.
A polarisation splitter may be provided to separate pulses of the first pulse train from pulses of the second pulse train afterthe pulses have been reflected from the optical fibre. Reflected first and second pulse trains are then fed to respective photo-detection means.
Alternatively, the first and second pulse trains of coherent light may be produced by different lasers.
In this case, the lasers may be polarised at 90 with respect to one another, thereby eliminating the need for the polarisation rotator.
In carrying out the present invention a heterodyne system may be used in which the first and second pulse trains each comprise two-pulse signals having two pulses of slightly different frequencies Fn and Fn + A Fn of predetermined duration and time relationship. The two pulses of the first and second pulse trains are transmitted along respective polarisation axes of the highly birefringent optical fibre, small proportions of the pulses being reflected back at each fibre discontinuity.For each pulse train, the pulse reflected from the second fibre discontinuity is caused to interfere with that reflected from the first discontinuity (i.e. the pulse of frequency Fn of the second reflected pulse is heterodyned with the pulse of frequency Fn + A Fn of the first reflected pulse).
This heterodnyning produces a detectable electrical beat frequency signal the modulation of which will vary with the changes in the optical path length of the first optical fibre element between the first and second optical fibre discontinuities. It will be appreciated that pulses reflected from the third, fourth and fifth and last discontinuities will similarly interfere with those pulses reflected from the preceding discontinuity.
By separating the electrical beat frequency signals of respective pulse trains and measuring phase modulation of the electrical beat signals corresponding to the respective optical fibre elements between discontinuities for each pulse train, any changes in optical path length of such elements due to them being stressed can be determined.
Reflected pulses emerging from the optical fibre may be fed into photo-detection means where the electrical beat frequency signals are produced, and these signals may then be fed into a decoding means which decodes the signals and provides signals indicative of any changes in optical path length of the fibre elements.
As will be fully appreciated from the foregoing the optical sensing system according to the present invention is especially applicable to optical beamforming acoustic wave sensors in which the elements of the optical fibre defines an acoustic wave sensor array for use in hydrophones for sonar purposes.
The present invention has many different applications, and because of the non-conductive nature of the optical fibre sensor it would be of particular advantage in explosive gas or vapour environments, such as coal mines, petrol and chemical plants.
The present invention will now be further described by way of example with reference to the accompanying drawings in which:
Figure 7 shows a schematic diagram of a heterodyne optical sensing system embodying the present invention;
Figure 2 shows a schematic diagram of a second embodiment of the present invention; and
Figure 3 shows a pulse diagram which will be used to illustrate operation of the embodiments shown in
Figures 1 and 2.
Referring to Figure 1 of the drawings, a pulsed laser 1 produces output pulses of coherent light of frequency Fn which are fed into a broadband optical frequency shifter 2 which may be in the form of an integrated optic phase modulatorora Bragg cell. In the case where the shifter 2 is in the form of an integrated optic phase modulator, the pulses passing therethrough can be shifted in frequency by application of a varying voltage signal to the modulator from a driving means 3. In this case, the shifter 2 is driven to produce a first pulse train having two-pulse signals of frequencies (F1, F1 + A F1) and a second pulse train having two-pulses signals of frequencies (F1, F1 + A F2).The pulses of coherent light then pass through a polarisation splitter 4 which orientates the polarisation axes of the first and second pulse trains so that they are at 90 with respect to one another and so that the first pulse train is aligned with one principal polarisation axis of an optical fibre 5, having suitably high birefringence and the second pulse train is aligned with the other principal polarisation axis of the fibre 5. Respective pulse trains are then launched into respective polarisation axes of the fibre 5 after passing through a beam splitter 6, which splitter 6 may be in the form of a polarisation maintaining fibre coupler.
An optical fibre having suitably high birefringence is one in which there is virtually no interaction (i.e.
less than 45 decibels) between signals travelling along respective principal polarisation axes of the fibre, that is, a fibre which is polarisation maintaining with, for example, a beat length of less than 2mm. Such a fibre is manufactured by York Ventures
Special Optical Products, reference number HB600/2 or HB800/2 or HB1200/2.
Equi-spaced discontinuities 7 to 15 are provided along the optical fibre 5 and these discontinuities except for the last may, for example, be formed by suitable joints in the optical fibre. The fibre is effectively divided by these discontinuities into eight sensing elements and variations in the lengths of these fibre elements such as due to the impingement thereon of acoustic waves, can be detected and measured in a manner which will be described with reference to Figure 3 below.
When a two-pulse signal of the first pulse train is transmitted along one of the principal axes of the optical fibre, a small proportion of the signal is reflected, at the discontinuity 7 back along the fibre 5 to the beam splitter 6 which directs the signal to a polarisation splitter 18. The remaining part of the signal travels on to a discontinuity 8 at which a further small proportion thereof is reflected back along the optical fibre 5 to the beam splitter 6. This procedure continues until that part of the signal remaining reaches the last of the optical fibre discontinuities 15 and a small proportion of this signal is again reflected back along the optical fibre 5 to the beam splitter 6.A two-phase pulse signal of the second pulse train, which comprises pulses of frequencies (F1, F1 + A F2), is launched into the other principal polarisation axis of the optical fibre 5 before the two-pulse signal of the first pulse train has left the optical fibre 5 after reflection from the discontinuity 15. However, since the second pulse train is transmitted along a different polarisation axis of the optical fibre 5 from the first pulse train, there is virtually no interference between the two pulse trains.
Reflected signals (of the first and second pulse trains) from the respective discontinuities, except the first, are caused to interfere with signals reflected from the preceding discontinuities to produce amplitude modulated electrical signals in dependence upon the optical path lengths of the optical fibre elements.
Signals reflected from the optical fibre 5 are directed, by the beam splitter 6, to the polarisation splitter 18. The polarisation splitter 18 separates pulses of the first and the second pulse trains and directs them to respective square-law photodetectors 19a and 19b where electrical beatfrequen- cy signals, indicative of changes in optical path length of the optical fibre elements, are produced.
The signals are then fed into respective decoding means 20a and 20b which decode the signals to provide signals indicative of any changes in the optical path length of the optical fibre elements.
Referring now to Figure 2, this shows a second embodiment of the present invention which comprises two pulsed lasers 20 and 21. The lasers 20 and 21 each generate coherent light, the light from one laser being polarised at with respect of the light from the other. Pulsed Light from each laser then passes through a respective frequency shifter 22 and 23 operative to generate the two-pulse signals F1 and F1 + A F1, and F2 and F2 + A F2 of the first and second pulse trains respectively. The pulse trains are then launched into the optical fibre 5 via respective beam splitters 24 and 25. The signals are transmitted into and reflected by the optical fibre 5 in the manner as described with reference to Figure 1.In this case however, signals of respective pulse trains reflected from the optical fibre 5 are detected and decoded in respective detectors 26 and 27 where signals indicative of any changes in the optical path length of the optical fibre elements are provided.
Referring now to Figure 3 of the drawings, this shows by way of example, reflections of the twopulse signals from the discontinuities 7,8 and 9 for each of the first and second pulse trains in the heterodyne system shown in Figures 1 and 2. As can be seen from the drawing, reflection from the second discontinuity 8 in the present example is delayed with respect to the reflection from the first discontinuity 7 by time T1 and T2 for respective pulse trains, where:
T = 2L where L = to the length of each optical fibre CG element and CG = velocity if light in the optical fibre.
By appropriate choice of length Lthe delay between the reflections is such that there is total coincidence or at least some overlap between the reflected pulse of frequency Fn (where n = 1 or 2) of a later reflected pulse with the pulse of frequency Fn +
A Fn of the preceding reflected signal. Hence, the pulse reflected from the second fibre discontinuity 8 is caused to interfere with that reflected from the first discontinuity (i.e. the pulse of frequency Fn of the second reflected signal is heterodyned with the pulse of frequency Fn + A Fn of the first reflected pulse).This heterodyning produces a detectable electrical beat frequency signal the modulation of which will vary with changes in optical path length of the first optical fibre element between the first and second optical fibre discontinuity.
Although the embodiments of the present inventions have been described with reference to the heterodyne optical sensing systems illustrated in
Figures 1 and 2, the scope of the invention is not limited to these particular optical sensing systems.
For example, an alternative heterodyne system as described in our co-pending Patent Application No.
GB 8220793 is envisaged in which the first and second pulse trains each comprise single-pulse signals of frequency Fn where n=lor2 respectively which are transmitted down the optical fibre 5 for reflection from the fibre discontinuities 7to15 whilst a two-pulse signal comprising consecutive pulses of frequencies Fn and Fn + A Fn, respectively, is used as a continuous reference at the photo-detectors 19a and 19b to beat with the reflected signals of frequency F,. In this case, however, it is necessary to make comparison between the difference frequencies arising from consecutive reflections and this will require some means of electronically delaying or storing the information from the preceding reflection in order to compare electrical phase relationships.
As an alternative system to the heterodyne systems, reflected signals from the optical fibre dicontinuities 7to15 may be homodyned by arranging that one or two light pulses in predetermined time relationship and of the same frequency are transmitted along the optical fibre 5 and reflected signals from the respective discontinuities except the first are caused to interfere with the signals reflected from the preceding discontinuities to produce amplitude modulated electrical signals in dependence upon the optical path lengths of the optical fibre elements. The detection means will detect and/or measure any changes in modulation due to deformation of the fibre elements.
Claims (7)
1. An optical system comprising a highly birefringent optical fibre having a pair of principal polarisation axes, which optical fibre is arranged to be subjected along its length to fibre deforming forces during operation of the system, and means for producing a first train of coherent light pulses for transmission along one of the polarisation axes and a second train of coherent light pulses for transmission along the other polarisation axes, wherein the high birefringence of the optical fibre is such that there is substantially no interaction between the first pulse train and the second pulse train, and the optical fibre is provided with a number of equally spaced discontinuities along its length which effectively divide the fibre into a plurality of discrete fibre elements so that a small proportion of each light pulse being transmitted along the fibre will be reflected back along the fibre from each of the discontinuities whereby, within the pulse train transmitted down either of the polarisation axes each reflected light pulse after the first interferes with either the previously reflected pulse from the preceding discontinuity or a reference light signal ofthe same frequency or a frequency with a constant difference frequency to the transmitted pulse train to produce an electrical signal in square law photodetection means of the system, the difference between respective electrical signals corresponding to successive fibre elements being dependent upon the length of the fibre element so that changes in optical path lengths of these elements produced by the incidence of the deforming forces will result in changes in the electrical signals which will be detected.
2. An optical system according to claim 1, wherein the principal polarisation axes of the optical fibre are orthogonal with respect to one another.
3. An optical system according to claim 1 or claim 2, wherein the system is a multiplexed optical system in which a plurality of pulse trains are transmitted along each one of the polarisation axes.
4. An optical system according to claim 1 or claim 2, wherein the means for producing the first and second pulse trains comprises a laser coupled to an optical frequency shift means, which shift means comprises an integrated optic phase modulator or a
Bragg cell.
5. An optical system according to claim 1, claim 2 or claim 3, wherein respective pulse trains are launched into respective polarisation axes of the optical fibre by means of a polarisation rotator.
6. An optical system according to any one of the preceding claims, wherein a polarisation splitter is provided to separate pulses of the first pulse train from pulses of the second pulse train after the pulses have been reflected from the optical fibre.
7. An optical system substantially as herein described with reference to Figures 1 and 3 or
Figures 2 and 3 of the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08424671A GB2165118B (en) | 1984-09-29 | 1984-09-29 | Otdr for sensing distortions in optical fibres |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08424671A GB2165118B (en) | 1984-09-29 | 1984-09-29 | Otdr for sensing distortions in optical fibres |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2165118A true GB2165118A (en) | 1986-04-03 |
| GB2165118B GB2165118B (en) | 1988-01-20 |
Family
ID=10567482
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08424671A Expired GB2165118B (en) | 1984-09-29 | 1984-09-29 | Otdr for sensing distortions in optical fibres |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2165118B (en) |
Cited By (18)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2189880A (en) * | 1986-04-30 | 1987-11-04 | Plessey Co Plc | Optical sensor system |
| EP0249923A2 (en) * | 1986-06-17 | 1987-12-23 | CSELT Centro Studi e Laboratori Telecomunicazioni S.p.A. | Method of and apparatus for measuring polarization beat-length in highly-birefringent single-mode optical fibres |
| GB2202046A (en) * | 1987-03-11 | 1988-09-14 | Plessey Co Plc | Optical fibre sensor arrangement |
| GB2238112A (en) * | 1986-11-11 | 1991-05-22 | British Aerospace | Measurement of distortion |
| US5038618A (en) * | 1986-11-11 | 1991-08-13 | British Aerospace Public Limited Company | Measurement of distortion |
| GB2243907A (en) * | 1990-04-04 | 1991-11-13 | Smiths Industries Plc | Optical multiplexing |
| GB2248990A (en) * | 1990-09-28 | 1992-04-22 | Ando Electric | Testing optical fiber using optical heterodyne technique |
| EP0484913A2 (en) * | 1990-11-07 | 1992-05-13 | Hewlett-Packard Company | Polarization independent optical coherence-domain reflectometry |
| US5189299A (en) * | 1988-06-20 | 1993-02-23 | Virginia Polytechnic Institute & State University | Method and apparatus for sensing strain in a waveguide |
| US5202745A (en) * | 1990-11-07 | 1993-04-13 | Hewlett-Packard Company | Polarization independent optical coherence-domain reflectometry |
| US5557400A (en) * | 1995-02-15 | 1996-09-17 | Hewlett-Packard Company | Multiplexed sensing using optical coherence reflectrometry |
| US5638165A (en) * | 1994-04-28 | 1997-06-10 | British Aerospace Public Limited Company | Crack detection system |
| US6366348B1 (en) * | 1999-04-22 | 2002-04-02 | Ando Electric Co., Ltd. | Optical fiber distortion measuring apparatus and optical fiber distortion measuring method |
| WO2004102840A1 (en) * | 2003-05-16 | 2004-11-25 | University Of Southampton | Optic communication or transmission media sensing |
| EP1912050A1 (en) | 2006-10-13 | 2008-04-16 | AT&T Corp. | Method and apparatus for acoustic sensing using multiple optical pulses |
| EP1912049A1 (en) | 2006-10-13 | 2008-04-16 | AT&T Corp. | Method and apparatus for acoustic sensing using multiple optical pulses |
| CN102426363A (en) * | 2011-08-31 | 2012-04-25 | 桂林聚联科技有限公司 | Method for improving event distance accuracy based on phase shift technology in OTDR (Optical Time Domain Reflectometry) design |
| CN107369281A (en) * | 2017-08-14 | 2017-11-21 | 桂林聚联科技有限公司 | A kind of deformation formula fiber fence device |
-
1984
- 1984-09-29 GB GB08424671A patent/GB2165118B/en not_active Expired
Cited By (42)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2189880A (en) * | 1986-04-30 | 1987-11-04 | Plessey Co Plc | Optical sensor system |
| GB2189880B (en) * | 1986-04-30 | 1989-12-28 | Plessey Co Plc | Optical sensor system |
| EP0249923A2 (en) * | 1986-06-17 | 1987-12-23 | CSELT Centro Studi e Laboratori Telecomunicazioni S.p.A. | Method of and apparatus for measuring polarization beat-length in highly-birefringent single-mode optical fibres |
| EP0249923A3 (en) * | 1986-06-17 | 1988-05-11 | Cselt Centro Studi E Laboratori Telecomunicazioni S.P.A. | Method of and apparatus for measuring polarization beat-method of and apparatus for measuring polarization beat-length in highly-birefringent single-mode optical fibreslength in highly-birefringent single-mode optical fibres |
| GB2238112A (en) * | 1986-11-11 | 1991-05-22 | British Aerospace | Measurement of distortion |
| US5038618A (en) * | 1986-11-11 | 1991-08-13 | British Aerospace Public Limited Company | Measurement of distortion |
| GB2238112B (en) * | 1986-11-11 | 1991-10-09 | British Aerospace | Measurement of distortion |
| GB2202046A (en) * | 1987-03-11 | 1988-09-14 | Plessey Co Plc | Optical fibre sensor arrangement |
| US5189299A (en) * | 1988-06-20 | 1993-02-23 | Virginia Polytechnic Institute & State University | Method and apparatus for sensing strain in a waveguide |
| US5113458A (en) * | 1990-04-04 | 1992-05-12 | Smiths Industries Public Limited Company | Optical multiplexing |
| GB2243907A (en) * | 1990-04-04 | 1991-11-13 | Smiths Industries Plc | Optical multiplexing |
| GB2243907B (en) * | 1990-04-04 | 1993-12-15 | Smiths Industries Plc | Optical multiplexing |
| GB2248990A (en) * | 1990-09-28 | 1992-04-22 | Ando Electric | Testing optical fiber using optical heterodyne technique |
| GB2248990B (en) * | 1990-09-28 | 1994-08-31 | Ando Electric | Apparatus for testing optical fiber by using optical heterodyne technique |
| EP0484913A2 (en) * | 1990-11-07 | 1992-05-13 | Hewlett-Packard Company | Polarization independent optical coherence-domain reflectometry |
| EP0484913A3 (en) * | 1990-11-07 | 1992-10-28 | Hewlett-Packard Company | Polarization independent optical coherence-domain reflectometry |
| US5202745A (en) * | 1990-11-07 | 1993-04-13 | Hewlett-Packard Company | Polarization independent optical coherence-domain reflectometry |
| US5638165A (en) * | 1994-04-28 | 1997-06-10 | British Aerospace Public Limited Company | Crack detection system |
| US5557400A (en) * | 1995-02-15 | 1996-09-17 | Hewlett-Packard Company | Multiplexed sensing using optical coherence reflectrometry |
| US6366348B1 (en) * | 1999-04-22 | 2002-04-02 | Ando Electric Co., Ltd. | Optical fiber distortion measuring apparatus and optical fiber distortion measuring method |
| WO2004102840A1 (en) * | 2003-05-16 | 2004-11-25 | University Of Southampton | Optic communication or transmission media sensing |
| US9148219B2 (en) | 2006-10-12 | 2015-09-29 | At&T Intellectual Property Ii, L.P. | Method and apparatus for acoustic sensing using multiple optical pulses |
| US9768863B2 (en) | 2006-10-13 | 2017-09-19 | At&T Intellectual Property Ii, L.P. | Method and apparatus for acoustic sensing using multiple optical pulses |
| US10454573B2 (en) | 2006-10-13 | 2019-10-22 | At&T Intellectual Property Ii, L.P. | Method and apparatus for detecting a disturbance in a medium |
| US7764363B2 (en) | 2006-10-13 | 2010-07-27 | At&T Intellectual Property Ii, L.P. | Method and apparatus for acoustic sensing using multiple optical pulses |
| GB2442746B (en) * | 2006-10-13 | 2011-04-06 | At & T Corp | Method and apparatus for acoustic sensing using multiple optical pulses |
| GB2442745B (en) * | 2006-10-13 | 2011-04-06 | At & T Corp | Method and apparatus for acoustic sensing using multiple optical pulses |
| US9154223B2 (en) | 2006-10-13 | 2015-10-06 | At&T Intellectual Property Ii, L.P. | Method and apparatus for acoustic sensing using multiple optical pulses |
| US11431409B2 (en) | 2006-10-13 | 2022-08-30 | At&T Intellectual Property Ii, L.P. | Method and apparatus for detecting a disturbance in a medium based on shifted filtered phase information for a plurality of fixed locations |
| US9787394B2 (en) | 2006-10-13 | 2017-10-10 | At&T Intellectual Property Ii, L.P. | Method and apparatus for acoustic sensing using multiple optical pulses |
| US11438059B2 (en) | 2006-10-13 | 2022-09-06 | At&T Intellectual Property Ii, L.P. | Method and apparatus for detecting a disturbance in a medium based on shifted filtered phase information for a plurality of locations |
| US10972181B2 (en) | 2006-10-13 | 2021-04-06 | At&T Intellectual Property Ii, L.P. | Method and apparatus for detecting a disturbance in a medium |
| EP1912049A1 (en) | 2006-10-13 | 2008-04-16 | AT&T Corp. | Method and apparatus for acoustic sensing using multiple optical pulses |
| EP1912050A1 (en) | 2006-10-13 | 2008-04-16 | AT&T Corp. | Method and apparatus for acoustic sensing using multiple optical pulses |
| US10447388B2 (en) | 2006-10-13 | 2019-10-15 | At&T Intellectual Property Ii, L.P. | Method and apparatus for detecting a disturbance in a medium |
| US7742157B2 (en) | 2006-10-13 | 2010-06-22 | At&T Intellectual Property Ii, L.P. | Method and apparatus for acoustic sensing using multiple optical pulses |
| US10623092B2 (en) | 2006-10-13 | 2020-04-14 | At&T Intellectual Property Ii, L.P. | Method and apparatus for detecting a disturbance in a medium using threshold based detection |
| US10623091B2 (en) | 2006-10-13 | 2020-04-14 | At&T Intellectual Property Ii, L.P. | Method and apparatus for detecting a disturbance in a medium using threshold based detection |
| US10972180B2 (en) | 2006-10-13 | 2021-04-06 | At&T Intellectual Property Ii, L.P. | Method and apparatus for detecting a disturbance in a medium |
| CN102426363B (en) * | 2011-08-31 | 2013-03-20 | 桂林聚联科技有限公司 | Method for improving event distance accuracy based on phase shift technology in OTDR (Optical Time Domain Reflectometry) design |
| CN102426363A (en) * | 2011-08-31 | 2012-04-25 | 桂林聚联科技有限公司 | Method for improving event distance accuracy based on phase shift technology in OTDR (Optical Time Domain Reflectometry) design |
| CN107369281A (en) * | 2017-08-14 | 2017-11-21 | 桂林聚联科技有限公司 | A kind of deformation formula fiber fence device |
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|---|---|
| GB2165118B (en) | 1988-01-20 |
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| 732 | Registration of transactions, instruments or events in the register (sect. 32/1977) | ||
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19920929 |