Abstract: A modalmetric fiber sensor comprising a multimode sensor fiber; a light source for launching light into the multimode sensor fiber to produce a multimode speckle pattern of light at an end of the multimode sensor fiber; a single mode fiber to receive light from the multimode speckle pattern; a detector connected to the single mode fiber to detect the received light from the speckle pattern; and a further multimode fiber disposed between the end of the sensor fiber and the single mode fiber such that the single mode fiber receives light from the speckle pattern by transmission through the further multimode fiber and the received light includes higher order modes regenerated in the further multimode fiber, wherein the further multimode fiber is overfilled with received light from the speckle pattern.

Abstract: A system and method for monitoring a structure and for distinguishing between an alarm condition, and a nuisance event such as rain. An optical fibre sensor (20,22) produces a signal indicative of a disturbance and level crossing rates are determined to distinguish between noise in the signal (nuisance event) and a required event. A FFT technique is also disclosed as well as classification of an event by extracting predetermined features from the signal.

Abstract: A modalmetric fibre sensor comprises a multimode sensor fibre (26), a light source (14) for launching light into the multimode fibre (26) to produce a multimode speckle pattern of light at an end of the fibre (26), a single mode fibre (22) to receive light from the multimode speckle pattern and a detector (18) connected to the single mode fibre (22) to detect the received light from the multimode speckle pattern. A connector (33) connects the ends of the multimode fibre (26) and single mode fibre (22) with the end faces (31,32) of the two fibres disposed at an acute single to one another. The light from source (14) may be transmitted to the multimode fibre (26) through the single mode fibre (22) and the end of multimode fibre (26) remote from single mode fibre (22) may be mirrored to reflect light back along the multimode fibre to the single mode fibre which transmits the received light to the detector (18).

Abstract: A modalmetric fibre sensor comprises a multimode sensor fibre (26) and a light source (14) for launching light into the sensor fibre to produce a multimode speckle pattern at an end of the sensor fibre. A single mode fibre (22) receives light from the multimode speckle pattern for transmission to a detector (18). A further multimode fibre (41) is disposed between the sensor fibre (26) and the single mode fibre (22) so that the single mode fibre (22) receives light from the speckle pattern by transmission through the further multimode fibre (41) and the received light includes higher order modes regenerated in the further multimode fibre (41). The light source may be connected to the single mode fibre (22) so as to launch light through the single mode fibre into the multimode sensor fibre (26) via the further multimode fibre (41) and the remote end (28) of the sensor fibre (26) may be mirrored to reflect light back through the sensor fibre to produce the speckle pattern.

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. A microcontroller receives feedback signals which adjusts polarization controllers so that the polarization states of the counter-propagating signals can be controlled to match the amplitude and/or phase of the output signals. Detectors are provided for detecting the modified signals.

Abstract: A modalmetric fibre sensor comprises a multimode sensor fibre (26), a light source (14) for launching light into the multimode fibre (26) to produce a multimode speckle pattern of light at an end of the fibre (26), a single mode fibre (22) to receive light from the multimode speckle pattern and a detector (18) connected to the single mode fibre (22) to detect the received light from the multimode speckle pattern. A connector (33) connects the ends of the multimode fibre (26) and single mode fibre (22) with the end faces (31,32) of the two fibres disposed at an acute single to one another. The light from source (14) may be transmitted to the multimode fibre (26) through the single mode fibre (22) and the end of multimode fibre (26) remote from single mode fibre (22) may be mirrored to reflect light back along the multimode fibre to the single mode fibre which transmits the received light to the detector (18).

Abstract: A system and method for monitoring a structure and for distinguishing between an alarm condition, and a nuisance event such as rain. An optical fibre sensor (20,22) produces a signal indicative of a disturbance and level crossing rates are determined to distinguish between noise in the signal (nuisance event) and a required event. A FFT technique is also disclosed as well as classification of an event by extracting predetermined features from the signal.

Abstract: A perimeter security system is disclosed which includes a first cable (40) and a second cable (60) buried beneath the ground in a zig-zag pattern. The first cable (40) has a first fibre (44) and a further fibre (42). Second cable (60) has a second fibre (62). The first and second fibres (44) and (62) are connected by a coupler (52) at one end so that light can be launched into the first and second fibres (44) and (62) to propagate in one direction. The further fibre (42) is connected to a coupler (70) which also connects to the other end of the first and second fibres (44) and (62) so light can be launched into the fibres from the other end and travel in the opposite direction.

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 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.

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. A microcontroller receives feedback signals which adjusts polarisation controllers so that the polarisation states of the counter-propagating signals can be controlled to match the amplitude and/or phase of the output signals. Detectors are provided for detecting the modified signals.

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. A Microcontroller receives feedback signals which adjusts polarisation controllers (43, 44) so that the polarisation states of the counter-propagating signals can be controlled to match the amplitude and/or phase of the output signals. Detectors are provided for detecting the modified signals.

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.

Abstract: A perimeter barrier system and method of monitoring a perimeter barrier are disclosed which comprise a perimeter barrier element in the form of a picket or fence panel which is mounted for limited movement by spring loading the barrier element by means of springs. An optical fiber is coupled to the barrier elements so that upon an attempt to breach the perimeter barrier system the barrier element is moved to in turn cause movement of the waveguide. A light source and detector is provided for launching light into the fiber and for detecting light which is passed through the fiber so that when the fiber is moved a parameter of the light is changed and that change in parameter is detected by detector to provide an indication of an attempt to breach the perimeter barrier system.

Abstract: A method and apparatus for monitoring a structure and for locating the position of an event including a light source, a waveguide, and a detector means. The waveguide receives light from the light source so that the light is caused to propagate in counter-propagating optical signals in the waveguide. The waveguide includes the counter-propagating optical signals or some characteristic of the signals modified or effected by an external parameter caused by or indicative of the event to provide modified counter-propagating optical signals. The detector means detects the modified counter-propagating optical signals effected by the parameter and determines the time delay or difference between the modified counter-propagating optical signals in order to determine the location of the event.

Abstract: A method and apparatus for monitoring a structure and for locating the position of an event including a light source, a waveguide, and a detector means. The waveguide receives light from the light source so that the light is caused to propagate in counter-propagating optical signals in the waveguide. The waveguide includes the counter-propagating optical signals or some characteristic of the signals modified or effected by an external parameter caused by or indicative of the event to provide modified counter-propagating optical signals. The detector means detects the modified counter-propagating optical signals effected by the parameter and determines the time delay or difference between the modified counter-propagating optical signals in order to determine the location of the event.

Abstract: A method and apparatus for monitoring a structure and for locating the position of an event including a light source, a waveguide, and a detector means. The waveguide receives light from the light source so that the light is caused to propagate in counter-propagating optical signals in the waveguide. The waveguide includes the counter-propagating optical signals or some characteristic of the signals modified or effected by an external parameter caused by or indicative of the event to provide modified counter-propagating optical signals. The detector means detects the modified counter-propagating optical signals effected by the parameter and determines the time delay or difference between the modified counter-propagating optical signals in order to determine the location of the event.