GB2165118A
Expired / Lapsed
GB
⏱️ 0.0 years remaining
OTDR for sensing distortions in optical fibres
Assignee: GE Healthcare UK Ltd
•
Filing: 1984-09-29
•
Granted: —
•
Expires: 2004-09-29
Abstract
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>
Inventors
- 👤 Shane Thornton
Bibliographic Details
Application Number
—
Jurisdiction
GB
Data Source
google_patents
Last Synchronized
2026-10-23 01:52
CPC Classifications
G; G01; G01H; G01H9/00; G01H9/004; G01M; G01M11/00; G01M11/30; G01M11/31; G01M11/3109; G01S; G01S17/00; G01S17/02; G01S17/06; G01S17/08; G01S17/10; G01S7/00; G01S7/48; G01S7/499
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
264 words
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.
Claim 2
Dependent Claim
264 words
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.
Claim 3
Dependent Claim
23 words
An optical system according to claim 1, wherein the principal polarisation axes of the optical fibre are orthogonal with respect to one another.
Claim 4
Dependent Claim
34 words
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.
Claim 5
Dependent Claim
44 words
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.
Claim 6
Dependent Claim
32 words
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.
Claim 7
Dependent Claim
42 words
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.
Claim 8
Dependent Claim
23 words
An optical system substantially as herein described with reference to Figures 1 and 3 or
Figures 2 and 3 of the accompanying drawings.
Claim 9
Dependent Claim
23 words
An optical system substantially as herein described with reference to Figures 1 and 3 or
Figures 2 and 3 of the accompanying drawings.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
Maintenance schedule is calculated for granted US utility patents.