Apparatus and method for using a counter-propagating signal method for locating events

Abstract

An apparatus and method for using a counter-propagating signal method for locating events is disclosed. The apparatus and method uses a Mach Zehnder interferometer through which counter-propagating signals can be launched. If the sensing zone of the Mach Zehnder interferometer is disturbed, modified counter-propagating signals are produced and the time difference between receipt of those signals is used to determine the location of the event. Polarisation controllers ( 43, 44 ) receive feedback signals so that the polarisation states of the counter-propagating signals can be controlled to match the amplitude and/or phase of the signals. Detectors are provided for detecting the modified signals.

1 . An apparatus for detecting and locating disturbances, comprising: 
 at least one light source;    an optical system with at least one optical waveguide, the optical waveguide having at least one detection zone at which a disturbance can occur and affect optical signals from the light source when traveling through the waveguide, in the detection zone, along counter-propagating optical channels;    at least one beam separator between the light source and the optical system, wherein the beam separator couples at least two beams into the optical waveguide for each of the at least two counter-propagating optical channels;    at least one polarization controller operable to manage optical properties of said counter-propagating optical channels, the polarization controller adjusting optical properties for at least one of the optical signals when propagating toward the detection zone;    at least one detector coupled to the optical waveguide and responsive to the optical signals after traversing the detection zone;    a data processing unit coupled to the detector, the data processing unit being operable to localize a place of the disturbance in the detection zone from a difference between times at which effects of the disturbance appear at the detector; and,    a feedback control coupled to the optical system and to at least one said polarization controller, wherein the feedback control and the polarization controller are configured to maximize a signal-to-noise ratio and to minimize a polarization contribution to said difference between times, by at least one of: seeking a predetermined relationship between polarization phase transformations along the counter-propagating optical channels, maximizing a peak swing in intensity at a point of interference of the beams, and varying an input state of polarization for one of testing and adjusting a balance between said polarization transformations for the counter-propagating channels.    
   
   
       2 . The apparatus of  claim 1 , wherein the light source comprises a laser.  
   
   
       3 . The apparatus of  claim 1 , wherein the light source is wavelength tunable.  
   
   
       4 . The apparatus of  claim 1 , wherein the light source comprises a single beam source coupled to the at least one beam separator, wherein the beam separator couples a portion of light energy from the single beam source separately into each of the counter-propagating optical channels, respectively.  
   
   
       5 . The apparatus of  claim 1 , wherein the light source comprises at least two beam sources that are coupled respectively to said counter-propagating channels.  
   
   
       6 . The apparatus of  claim 1 , wherein the optical waveguide comprises at least one optical fiber in the detection zone, and the counter-propagating beams are passed through said at least one optical fiber in the detection zone.  
   
   
       7 . The apparatus of  claim 6 , wherein the at least one optical fiber in the detection zone comprises a single mode optical fiber.  
   
   
       8 . The apparatus of  claim 1 , wherein the optical waveguide comprises at least two optical fibers that are coextensive at least in the detection zone, and wherein both of said at least two optical fibers are subject to the disturbance in the detection zone.  
   
   
       9 . The apparatus of  claim 1 , wherein optical waveguide comprises at least one optical fiber extending along the detection zone, and wherein said optical fiber is at least one of configured and controlled such that the optical properties are substantially the same for said counter propagating channels with respect to optical phase.  
   
   
       10 . The apparatus of  claim 1 , wherein optical waveguide comprises at least two optical fibers, at least one of which extends along the detection zone, and wherein said two optical fibers are at least one of configured and controlled such that the optical properties are substantially the same for the said counter propagating channels with respect to optical phase.  
   
   
       11 . The apparatus of  claim 1 , wherein said at least one polarization controller is placed between said light source and at least one of the counter-propagating optical channels.  
   
   
       12 . The apparatus of  claim 1 , wherein the said optical waveguide is coupled to define at least one path in an interferometer.  
   
   
       13 . The apparatus of  claim 12 , wherein the said interferometer is configured as a Mach-Zehnder interferometer.  
   
   
       14 . The apparatus of  claim 1 , wherein said beam separator is polarization insensitive.  
   
   
       15 . The apparatus of  claim 1 , wherein said beam separator is polarization sensitive.  
   
   
       16 . The apparatus of  claim 1 , wherein the polarization controller is operable to transform the optical properties of at least one beam of the counter propagating optical channels from a first arbitrary state of polarization to a second arbitrary state of polarization.  
   
   
       17 . The apparatus of  claim 1 , wherein said at least one optical detector is operable to sense at least one aspect of a light signal from said counter propagating channels.  
   
   
       18 . The apparatus of  claim 17 , wherein said optical detector is operable to sense an intensity aspect of the light signal.  
   
   
       19 . The apparatus of  claim 1 , wherein-said at least one optical detector is operable individually to sense at least one aspect of light signals emerging respectively from said counter propagating channels.  
   
   
       20 . The apparatus of  claim 1 , wherein the feedback control to the polarization controller is configured to maintain a signal to noise ratio for a signal resulting from the disturbance.  
   
   
       21 . The apparatus of  claim 1 , wherein the feedback control and the polarization controller are configured to minimize at least one of polarization induced signal fading and polarization induced phase shift.  
   
   
       22 . The apparatus of  claim 21 , wherein the polarization controller is configured at least in one mode substantially to scramble a polarization state of at least one the beams, to obtain a substantially random input state of polarization  
   
   
       23 . The apparatus of  claim 21 , wherein the polarization controller and feedback control are coupled to maximize a peak-to-peak swing of interference intensity of the light signals.  
   
   
       24 . The apparatus of  claim 23 , wherein the polarization controller and feedback control are configured to maximize said peak-to-peak swing of interference intensity at a fixed phase difference between the two beams when caused to interfere.  
   
   
       25 . The apparatus of  claim 23 , wherein the polarization controller and feedback control are configured to maximize said peak-to-peak swing of interference intensity at an arbitrary phase difference between the two beams when caused to interfere.  
   
   
       26 . The apparatus of  claim 23 , wherein the polarization controller and feedback control are configured to maximize said peak-to-peak swing of interference intensity by adjusting a polarization state relation of the beams for one of the counter-propagating light signals while scrambling a polarization state relationship of the beams for another of the counter-propagating light signals.  
   
   
       27 . The apparatus of  claim 1 , wherein the polarization controller is placed between the light source and said optical waveguide, such that the polarization controller simultaneously affects both the counter-propagating optical signals.  
   
   
       28 . The apparatus of  claim 27 , further comprising at least one additional polarization controller, wherein said polarization controllers are operable to vary polarization properties for one of the two optical signals, by varying a polarization transformation for at least one of the counter-propagating optical signals while polarization transformations for both the counter-propagating optical signals are matched, at least relative to one another.  
   
   
       29 . The apparatus of  claim 28 , wherein the said polarization controllers are operable to vary said polarization properties by scrambling the polarization transformation for said at least one of the counter-propagating optical signals.  
   
   
       30 . The apparatus of  claim 1 , wherein the data processing unit is programmed to resolve a location of the disturbance in the detection zone from signals received at the detector.  
   
   
       31 . The apparatus of  claim 30 , wherein the said data processing unit comprises at least one of a programmable gate array and a digital signal processor.  
   
   
       32 . The apparatus of  claim 1 , wherein the at least one polarization controller is operable to hold a balance of polarization states in the counter-propagating optical channels, whereby said polarization states are made more likely to correspond during the disturbance.  
   
   
       33 . The apparatus of  claim 1 , wherein the at least one polarization controller is operable to scramble the polarization in the counter-propagating optical channels.  
   
   
       34 . The apparatus of  claim 1 , wherein the at least one polarization controller is operable to hold a relation in polarization states between the counter-propagating optical channels, for maintaining a state of interference between the optical channels.  
   
   
       35 . The apparatus of  claim 1 , further comprising a data transmission path traversing the optical waveguide, supporting at least one optical data transmission signal.  
   
   
       36 . The apparatus of  claim 35 , wherein an operating wavelength of the counter propagating optical beam is different from an operating wavelength of the optical data transmission signal.  
   
   
       37 . The apparatus of  claim 35 , wherein the optical data transmission signal is carried over at least one same channel as the counter-propagating optical channels.  
   
   
       38 . The apparatus of  claim 1 , further comprising a communication device operable to report information regarding the disturbance.  
   
   
       39 . The apparatus of  claim 38 , wherein the communication device comprises one of a wired and wireless reporting link to a remote location.  
   
   
       40 . A method for detecting and locating disturbances, comprising: 
 establishing an optical system including at least one optical waveguide extending along at least one detection zone at which a disturbance can occur, so as to affect optical signals propagating along counter-propagating optical channels from at least one light source to a detector;    separating from the at least one light source, and coupling into each of the counter-propagating optical channels, at least two beams;    managing optical properties in the counter-propagating optical channels using a polarization controller to vary optical properties for at least one of the optical signals while propagating toward the detection zone;    detecting the optical signals after traversing the detection zone and determining a difference between times at which effects of the disturbance appear in the respective counter-propagating channels after traversing said detection zone;    calculating from said difference between times and localizing in the detection zone a place where the disturbance occurred;    wherein said managing of the optical properties comprises providing a control signal to the polarization controller that maintains a signal-to-noise ratio and minimizes a contribution to said difference between times caused by polarization effects, including at least one of:    seeking a predetermined relationship between polarization phase transformations along the counter-propagating optical channels,    maximizing a peak swing in intensity at a point of interference of the beams, and    varying an input state of polarization for one of testing and adjusting a balance between said polarization transformations for the counter-propagating channels.    
   
   
       41 . The method of  claim 40 , further comprising tuning a wavelength of the light source.  
   
   
       42 . The method of  claim 40 , wherein said separating comprises dividing a portion of light energy from a single beam source separately into each of the counter-propagating optical channels, respectively.  
   
   
       43 . The method of  claim 40 , wherein the counter-propagating channels are established through at least one optical fiber extending through the detection zone.  
   
   
       44 . The method of  claim 40 , wherein the counter-propagating channels are established through at least two optical fibers extending through the detection zone.  
   
   
       45 . The method of  claim 40 , comprising managing said optical properties to obtain substantially equal optical phase transformations through said counter propagating channels.  
   
   
       46 . The method of  claim 40 , wherein said detection zone defines a portion of an interferometer and further comprising developing said intensity signal at a point of interference of said beams.  
   
   
       47 . The method of  claim 40 , comprising applying the polarization controller to transform the optical properties of at least one beam of the counter propagating optical channels from a first arbitrary state of polarization to a second arbitrary state of polarization.  
   
   
       48 . The method of  claim 40 , wherein varying the input state of polarization comprises producing a substantially random input state of polarization.  
   
   
       49 . The method of  claim 48 , further comprising successively varying said input state.  
   
   
       50 . The method of  claim 40 , comprising adjusting a polarization state relation of the beams for one of the counter-propagating light signals while scrambling a polarization state relationship of the beams for another of the counter-propagating light signals.  
   
   
       51 . The method of  claim 40 , comprising placing at least one said polarization controller between the light source and said optical waveguide, such that the polarization controller simultaneously affects both the counter-propagating optical signals.  
   
   
       52 . The method of  claim 51 , further comprising placing at least one additional said polarization controller so as to vary polarization properties for one of the two optical signals.  
   
   
       53 . The method of  claim 40 , comprising varying a polarization transformation for at least one of the counter-propagating optical signals while polarization transformations for both the counter-propagating optical signals are matched, at least relative to one another.  
   
   
       54 . An improved method for detecting and locating disturbances affecting an optical system including at least one optical waveguide extending along at least one detection zone at which a disturbance can occur, thereby affecting optical signals propagating along counter-propagating optical channels from at least one light source to a detector, wherein at least two beams are separated from the at least one light source and coupled into each of the counter-propagating optical channels, and an effect of the disturbance is detected after the beams have traversed the detection zone and a time difference is determined for calculating a location of the disturbance in the detection zone, wherein the improvement comprises: 
 managing optical properties in the counter-propagating optical channels using a polarization controller to vary optical properties for at least one of the optical signals while propagating toward the detection zone, wherein said managing includes providing a control signal to the polarization controller that maintains a signal-to-noise ratio and minimizes a contribution to said difference between times caused by polarization effects, and comprises at least one of    seeking a predetermined relationship between polarization phase transformations along the counter-propagating optical channels,    maximizing a peak swing in intensity at a point of interference of the beams, and    varying an input state of polarization for one of testing and adjusting a balance between said polarization transformations for the counter-propagating channels.    
   
   
       55 . An apparatus for locating the position of an event, comprising: 
 a light source;    a waveguide for receiving light from the light source so that the light is caused to propagate in both directions along the waveguide to thereby provide counter-propagating optical signals in the waveguide, the waveguide being capable of having the counter-propagating optical signals or some characteristic of the signals modified or affected by an external parameter caused by or indicative of the event to provide modified counter-propagating optical signals which continue to propagate along the waveguide;    detector means for detecting the modified counter-propagating optical signals affected by the parameter and for determining the time difference between the receipt of the modified counter-propagating optical signals in order to determine the location of the event;    a controller for controlling polarisation states of the counter-propagating optical signals so that the signals are amplitude and phase matched; and    wherein the waveguide comprises a first arm for receiving the counter-propagating signals, and a second arm for receiving the counter-propagating signals, the first and second arms forming a Mach Zehnder interferometer.    
   
   
       56 . The apparatus of  claim 55  wherein the input polarisation states of the counter-propagating signals are controlled to achieve maximum output fringes. However, in other embodiments, polarisation states which lead to amplitude and phase matched outputs, but with sub-maximum fringe visibilities can also be utilised.  
   
   
       57 . The apparatus of  claim 55  wherein the control unit comprises the detector means, a polarisation controller for each of the counter-propagating signals and the light source.  
   
   
       58 . The apparatus of  claim 55  wherein the detector means comprises a first detector for one of the counter-propagating signals and a second detector for the other of the counter-propagating signals.  
   
   
       59 . The apparatus of  claim 55  wherein the light source comprises a laser light source having bragg gratings and an adjuster for controlling the bragg gratings and/or laser cavity of the laser light source to thereby alter the wavelength of the light signal output from the laser for producing the counter-propagating signals.  
   
   
       60 . The apparatus of  claim 55  wherein the control unit includes a processor for receiving outputs from the detectors and for processing the outputs to indicate an event and to determine the location of the event.  
   
   
       61 . The apparatus of  claim 55  wherein the processor is coupled to a polarisation control driver and the polarisation control driver is coupled to the polarisation controllers for controlling the controllers to thereby set the polarisation of the signals supplied from the light source to the first and second arms of the Mach Zehnder interferometer to in turn set the polarisation of the counter-propagating signals.  
   
   
       62 . The apparatus of  claim 55  wherein the detectors are connected to a Mach Zehnder output monitor for monitoring the counter-propagating signals detected by the detectors so that when the modified counter-propagating detectors are detected by the detector, the MZ output determines detection of those signals by the detectors for processing by the processor.  
   
   
       63 . The apparatus of  claim 55  wherein invention the first arm of the Mach Zehnder interferometer is of different length than the second arm of the Mach Zehnder interferometer so that the first and second arms have a length mismatch, the control unit further comprising a dither signal producing element for controlling the light source to wavelength dither the output from the light source to produce a dither in the phase difference between the MZ arms, in turn which produces artificial fringes at the drifting output of the MZ.  
   
   
       64 . The apparatus of  claim 63  wherein the dither signal element dithers the phase difference between the MZ arms by at least 360°, to produce artificial fringes, so that the drifting output of the Mach Zehnder's operating point always displays its true fringe visibility.  
   
   
       65 . A method of locating an event comprising the steps of: 
 launching light into a waveguide so that the light is caused to propagate in both directions along the waveguide to thereby provide counter-propagating optical signals in the waveguide, the waveguide being capable of having the counter-propagating optical signals or some characteristic of the signals modified or affected by an external parameter caused by the event, to provide modified counter-propagating optical signals which continue to propagate along the waveguide;    substantially continuously and simultaneously monitoring the modified counter-propagating optical signals, so that when an event occurs, both of the modified counter-propagating optical signals affected by the external parameter are detected;    determining the time difference between the detection of the modified signals in order to determine the location of the event;    forming the waveguide as a Mach Zehnder interferometer having a first arm through which the counter-propagating optical signals travel, and a second arm through which the counter-propagating optical signals travel; and    controlling the polarisation states of the counter-propagating optical signals input into the waveguide to provide amplitude and phase matched counter-propagating signals from the waveguide.    
   
   
       66 . The method of  claim 65  wherein the polarisation states of the counter-propagating signals provide amplitude and phase-matched counter-propagating signals from the waveguide which achieve maximum output fringes. However, in other embodiments, the control of the polarisation states may be such that phase matched sub-maximum fringes are provided.  
   
   
       67 . The method of  claim 65  wherein the step of controlling the polarisation states comprises randomly changing the input polarisation states of the counter-propagating signals whilst monitoring the counter-propagating optical signals output from the Mach Zehnder interferometer to detect a substantially zero state of intensities, or maximum state of intensities of the counter-propagating signals, and selecting the input polarisations which provide the substantially zero or substantially maximum intensities.  
   
   
       68 . The method of  claim 65  wherein fringes for determining the polarisation states are artificially created.  
   
   
       69 . The method of  claim 68  wherein the artificially created fringes are created by dithering or modulating the wavelength of the light source and providing a path length mismatch between the first and second arms of the Mach Zehnder interferometer.  
   
   
       70 . The method of  claim 65  wherein the step of controlling the polarisation states comprises controlling the polarisation controllers to thereby set the input polarisation state of the signals supplied from the light source to each input of the bidirectional Mach Zehnder interferometer to provide phase matched counter-propagating output signals.  
   
   
       71 . The method of  claim 65  wherein the laser source wavelength is dithered by an amount which leads to the dithering of the phase difference between the MZ arms by 360°, to produce artificial fringes, so that with a drifting operating point, the Mach Zehnder's counter-propagating outputs always display their true fringe visibility.