Evaluating the position of a disturbance
First Claim
1. A method of evaluating the position of a time-varying disturbance on a transmission link, the method comprising:
- copying, at least in part, an output signal from an optical pulse source, such that there is a pair of signal copies by channeling light from the optical source onto first and second paths such that the power of the optical source traveling along each path is shared in a predetermined manner between the signal copies and one signal copy travels along the first path in an outbound direction with the other signal copy traveling along the second path in the outbound direction;
delaying one of the pulse copies relative to the other pulse copy in the outbound direction;
combining light traveling in the outbound direction;
transmitting the combined light of the differentially delayed pair of signal copies onto the transmission link in the outbound direction;
receiving in a return direction from the transmission link return signals comprising backscattered components comprising at least partially returned copies of said signal copies previously transmitted on said transmission link, wherein at least one of said backscattered components has suffered a phase change caused by said time-varying disturbance;
combining the received returned signal copies of a transmitted pair so as to produce a combination signal; and
using a temporal characteristic in the combination signal of received returned signal copies of a transmitted pair which has traveled along the transmission link to beyond the location of the time-varying disturbance to evaluate the position of the time-varying disturbance on the transmission link,wherein the position of the disturbance is determined from the time of return of said phase-modulated backscattered components of said returned signal copies, the phase-modulated backscattered components including backscattered components of a given pair of pulse copies that are phase-modulated by the disturbance on return.
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Accused Products
Abstract
The position of a disturbance on an optical link is evaluated, in particular where the disturbance is a time-varying disturbance. An optical time domain reflectometry technique is used in which a series of low coherence test pulses is launched by means of an optical pulse source into an the optical link, and the backscattered return signal is monitored. The test pulses pass through an unbalanced Mach Zhender interferometer with the result that for each test pulse, a pair of time-displaced pulse copies is launched onto the link. The backscattered return signal is passed through the same interferometer, which causes the pulse copies of each pair to become realigned and to interfere with one another. A time-varying disturbance is likely to affect each pulse copy of a pair differently. As a result, an abnormality such as a step is likely to occur in the backscattered signal. From the time position of an abnormality, the distance of the disturbance responsible is evaluated.
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Citations
27 Claims
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1. A method of evaluating the position of a time-varying disturbance on a transmission link, the method comprising:
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copying, at least in part, an output signal from an optical pulse source, such that there is a pair of signal copies by channeling light from the optical source onto first and second paths such that the power of the optical source traveling along each path is shared in a predetermined manner between the signal copies and one signal copy travels along the first path in an outbound direction with the other signal copy traveling along the second path in the outbound direction; delaying one of the pulse copies relative to the other pulse copy in the outbound direction; combining light traveling in the outbound direction; transmitting the combined light of the differentially delayed pair of signal copies onto the transmission link in the outbound direction; receiving in a return direction from the transmission link return signals comprising backscattered components comprising at least partially returned copies of said signal copies previously transmitted on said transmission link, wherein at least one of said backscattered components has suffered a phase change caused by said time-varying disturbance; combining the received returned signal copies of a transmitted pair so as to produce a combination signal; and using a temporal characteristic in the combination signal of received returned signal copies of a transmitted pair which has traveled along the transmission link to beyond the location of the time-varying disturbance to evaluate the position of the time-varying disturbance on the transmission link, wherein the position of the disturbance is determined from the time of return of said phase-modulated backscattered components of said returned signal copies, the phase-modulated backscattered components including backscattered components of a given pair of pulse copies that are phase-modulated by the disturbance on return. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A monitoring station for monitoring a transmission link, the monitoring station comprising:
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a source for generating optical pulse signals; an interferometer stage for copying at least in part the optical pulse signals from the source such that for each optical pulse signal there is a pair of pulse signal copies, the interferometer stage having a delay stage to differentially delay one copy of each pulse signal relative to the other copy; an output for launching the differentially delayed pulse signal copies onto the transmission link; and a processor circuit; wherein the interferometer stage is arranged to receive pulse signal copies returned by a process of distributed backscattering from the link and to combine the pulse signal copies so as to produce an interference signal, wherein at least one of said backscattered signal copies has suffered a phase change, wherein the processor circuit is arranged to store the interference signal in association with an indication of a temporal characteristic of the return signal, and wherein when said phase change is caused by a time-varying disturbance, said interference signal stored in association with an indication of a temporal characteristic of the return signal copies of a transmitted pair which has traveled along the transmission link to beyond the location of the time-varying disturbance enables the position of the disturbance to be determined from the time of return of phase-modulated backscattered components of said returned pulse signal copies, the phase-modulated backscattered components including backscattered components of a given pair of pulse copies that are phase-modulated by the disturbance on return. - View Dependent Claims (20, 21)
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22. A sensing system for sensing the position of a moving vehicle, the sensing system comprising:
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a guide track for guiding the movement of the vehicle; an optical transmission link extending along the guide track; and monitoring apparatus coupled to the optical transmission link, wherein the optical transmission link is mechanically coupled to the guide track such that movement of the vehicle causes a moving disturbance to be sensed by sensing optical signal pulse signals propagating along the optical transmission link, wherein the monitoring apparatus comprises; a source for generating the sensing optical pulse signals; an interferometer stage for copying at least in part the optical pulse signals from the source such that for each optical pulse signal there is a pair of pulse signal copies, the interferometer stage having a delay stage to differentially delay one copy of each pulse signal relative to the other copy; an output for launching the differentially delayed pulse signal copies onto the transmission link; and a processor circuit; wherein the interferometer stage is arranged to receive pulse signal copies returned by a process of distributed backscattering from the link and to combine the pulse signal copies so as to produce an interference signal, wherein at least one of said backscattered signal copies has suffered a phase change, and wherein the processor circuit is arranged to store the interference signal in association with an indication of a temporal characteristic of the return signal, wherein, when said phase change is caused by a time-varying disturbance, said interference signal stored in association with an indication of a temporal characteristic of the return signal copies of a transmitted pair which has traveled along the transmission link to beyond the location of the time-varying disturbance enables the position of the disturbance to be determined from the time of return of phase-modulated backscattered components of said returned pulse signal copies, the phase-modulated backscattered components including backscattered components of a given pair of pulse copies that are phase-modulated by the disturbance on return, the monitoring apparatus being configured to; (i) detect said sensing optical pulse signal from the optical transmission link, wherein said sensing light signal is indicative of the moving disturbance, (ii) evaluate at least one temporal characteristic of the sensing optical signal, and (iii) in dependence on the evaluated temporal characteristic, determine an indication of the position of the moving disturbance along the transmission link so that the position of the vehicle along the track can be sensed.
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23. A method of sensing the position of a vehicle moving along a guide track, wherein there is provided an optical transmission link extending along the guide track, and monitoring apparatus coupled to the optical transmission link, the optical transmission link being mechanically coupled to guide track such that movement of the vehicle causes a moving disturbance to be sensed by combined differentially delayed copies of a sensing optical pulse signal propagating in an outward direction along the optical transmission link, the method comprising:
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(i) detecting backscattered signal components of said outwardly propagating combined differentially delayed copies of said optical signal from the optical transmission link, said backscattered signal components being indicative of a moving disturbance; (ii) evaluating at least one temporal characteristic of the detected backscattered signal components; (iii) in dependence on the evaluated temporal characteristic, determining an indication of the position of the moving disturbance along the optical transmission link; and (iv) inferring the position of the vehicle from the position of the disturbance along the optical transmission link, wherein the position of the disturbance is determined from the time of return of phase-modulated backscattered components which have traveled along the optical transmission link to beyond the location of the time-varying disturbance, the phase-modulated backscattered components including back-scattered components of a given pair of pulse copies that are phase-modulated by the disturbance on return.
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24. An apparatus for evaluating the position of a time-varying disturbance on a transmission link, the apparatus including:
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means for copying, at least in part, an output signal from an optical pulse source, such that there is a pair of pulse signal copies by channeling light from the optical source onto first and second paths such that the power of said optical source traveling along each path is shared in a predetermined manner between said signal copies and one signal copy travels along said first path in an outbound direction with the other signal copy traveling along the second path in said outbound direction; delay means for delaying one of the pulse copies relative to the other pulse copy in said outbound direction; means for combining light traveling in the outbound direction; means for transmitting the combined light of the differentially delayed pair of signal copies onto the transmission link in an outbound direction; wherein said means for combining provides means for receiving in a return direction from the transmission link return signals comprising backscattered components comprising at least partially returned copies of said signal copies of a transmitted pair which has traveled along the transmission link to beyond the location of the time-varying disturbance previously transmitted on said transmission link, wherein at least one of said backscattered components has suffered a phase change caused by said time-varying disturbance; wherein said means for copying provides means for combining the received returned signal copies of a transmitted pair so as to produce a combination signal; and means for evaluating using a temporal characteristic in the combination signal the position of the time-varying disturbance on the transmission link, whereby the position of the disturbance is determined from the time of return of said phase-modulated backscattered components of said returned signal copies, the phase-modulated backscattered components including backscattered components of a given pair of pulse copies that are phase-modulated by the disturbance on return. - View Dependent Claims (27)
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25. An apparatus for evaluating the position of a time-varying disturbance on a transmission link, the apparatus including:
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an optical pulse source; a first differential power splitter for copying, at least in part, an output signal from said optical pulse source, such that there is a pair of signal copies by channeling light from the optical source onto first and second paths such that the power of said optical source traveling along each path is shared in a predetermined manner between said signal copies and one signal copy travels along said first path in an outbound direction with the other signal copy traveling along the second path in said outbound direction; a delay stage for delaying one of the pulse copies relative to the other pulse copy in said outbound direction; a coupler for combining light traveling in the outbound direction; a transmitter for transmitting the combined light of the differentially delayed pair of signal copies onto the transmission link in an outbound direction; wherein the coupler is arranged to act as a second power splitter for light received in a return direction from the transmission link, wherein the light received in the return direction comprises backscattered components of said combined signal copies of a transmitted pair which has traveled along the transmission link to beyond the location of the time-varying disturbance originally transmitted in said outbound direction, wherein at least one of said backscattered components has suffered a phase change caused by said time-varying disturbance, such that the intensity of the return signals is split with one portion being channeled along the first path, and the other portion being channeled along the second path; wherein said first differential power splitter functions to combine the received returned signal copies of a transmitted pair so as to produce a combination signal; a signal processing system for evaluating using a temporal characteristic in the combination signal the position of the time-varying disturbance on the transmission link, wherein the position of the disturbance is determined from the time of return of said phase-modulated backscattered components of said returned signal copies, the phase-modulated backscattered components including backscattered components of a given pair of pulse copies that are phase-modulated by the disturbance on return. - View Dependent Claims (26)
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Specification