Abstract: A fiber-optic sensor can have a Michelson sensor portion and a Mach-Zehnder sensor portion. A first splitter-coupler can be configured to split incoming light between a first fiber portion and a second fiber portion. A first polarization-phase conjugation device can be configured to conjugate a polarization phase of incident light corresponding to the first fiber portion, and a second polarization-phase conjugation device can be configured to conjugate a polarization phase of incident light corresponding to the second fiber portion. Each of the first and second polarization-phase conjugation devices can be configured to reflect light toward a detector and through the respective first and second fiber portions. A coupler can be configured to join light in the first fiber portion with light in the second fiber portion, and a third fiber portion can be configured to receive light from the coupler and to illuminate a second detector.

Abstract: A fiber-optic sensor can have a Michelson sensor portion and a Mach-Zehnder sensor portion. A first splitter-coupler can be configured to split incoming light between a first fiber portion and a second fiber portion. A first polarization-phase conjugation device can be configured to conjugate a polarization phase of incident light corresponding to the first fiber portion, and a second polarization-phase conjugation device can be configured to conjugate a polarization phase of incident light corresponding to the second fiber portion. Each of the first and second polarization-phase conjugation devices can be configured to reflect light toward a detector and through the respective first and second fiber portions. A coupler can be configured to join light in the first fiber portion with light in the second fiber portion, and a third fiber portion can be configured to receive light from the coupler and to illuminate a second detector.

Abstract: A fiber-optic sensor can have a Michelson sensor portion and a Mach-Zehnder sensor portion. A first splitter-coupler can be configured to split incoming light between a first fiber portion and a second fiber portion. A first polarization-phase conjugation device can be configured to conjugate a polarization phase of incident light corresponding to the first fiber portion, and a second polarization-phase conjugation device can be configured to conjugate a polarization phase of incident light corresponding to the second fiber portion. Each of the first and second polarization-phase conjugation devices can be configured to reflect light toward a detector and through the respective first and second fiber portions. A coupler can be configured to join light in the first fiber portion with light in the second fiber portion, and a third fiber portion can be configured to receive light from the coupler and to illuminate a second detector.

Abstract: Variable Sensitivity optical sensors can have a respective actual sensitivity of one or more portions of the sensor corresponding, at least in part, to a selected environment of each respective sensor portion. Some disclosed sensors have a plurality of optical conduits extending longitudinally of the sensors. At least one of the optical conduits can have at least one longitudinally extending segment having one or more optical and/or mechanical properties that differs from the optical properties of an adjacent longitudinally extending segment, providing the conduit with longitudinally varying signal propagation characteristics. An optical sensor having such optical conduits can exhibit a longitudinally varying actual sensitivity. Nonetheless, such a sensor can exhibit a substantially constant apparent sensitivity, e.g., when each respective portion of the sensor exhibits an actual sensitivity corresponding to a selected environment.

Abstract: A fiber-optic sensor can have a Michelson sensor portion and a Mach-Zehnder sensor portion. A first splitter-coupler can be configured to split incoming light between a first fiber portion and a second fiber portion. A first polarization-phase conjugation device can be configured to conjugate a polarization phase of incident light corresponding to the first fiber portion, and a second polarization-phase conjugation device can be configured to conjugate a polarization phase of incident light corresponding to the second fiber portion. Each of the first and second polarization-phase conjugation devices can be configured to reflect light toward a detector and through the respective first and second fiber portions. A coupler can be configured to join light in the first fiber portion with light in the second fiber portion, and a third fiber portion can be configured to receive light from the coupler and to illuminate a second detector.

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 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.