A folded Sagnac fiber optic acoustic sensor array operates in a manner similar to a Sagnac interferometer but uses a common delay path to reduce distributed pickup in downlead fibers. The fiber optic acoustic sensor array is used to detect acoustic waves in water. By basing the folded Sagnac sensor array on operating principles similar to the Sagnac interferometer rather than basing the array on a Mach-Zehnder interferometer, the sensor array has a stable bias point, has reduced phase noise, and...

A depolarizer 11 is inserted between an optical branch unit 2 and a polarization filter 3, a depolarizer 12 and a polarization filter 14 are inserted between an optical phase modulator 5 and a quarter-wave plate 16, and a depolarizer 13 and a polarization filter 15 are inserted between the other branch end of the optical branch unit 4 and a quarter-wave plate 17. The optical branch unit 2 and the optical phase modulator 5 are formed by single mode optical fibers, and single mode optical fibers a...

Disclosed is a method and apparatus for modulating the phase difference between a pair of optical waves that exit a Sagnac interferometer, and, more particularly, one that is commonly employed as a fiber gyro, and includes a detector responsive to phase difference between the pair of waves that exit the interferometer, and a phase modulator that forms part of two control loops that are instrumental in deriving an accurate measurement of rotation rate. As disclosed herein, phase modulation applie...

A system based on the usage of a Sagnac interferometer operating in a dual sensing mode is described which allows the determination of the location and amplitude of a time varying disturbance on a single fiber.

A system based on the usage of a Sagnac interferometer operating in a dual sensing mode is described which allows the determination of the location and amplitude of a time varying disturbance on a single fiber.

A Sagnac interferometer (19) is defined by four port, 50:50 optical fiber coupler (20), two output ports (38, 40) of which are coupled together by a non-linear semiconductor laser amplifier (3) in series between a pair of optical fibres (22, 24). The coupling losses between the ports (38, 40) and the amplifier (30) are different. An input pulse coupled to port (34) of the coupler (20) is split into two portions which counterpropagate from one of the output ports (38, 40) to the other. The portio...

Wavelength division multiplexed Sagnac distributed sensor systems that allow the determination of the position and amplitude of a frequency dependent environmental effect acting on the optical path of Sagnac loops. The sensor includes two Sagnac interferometers operating at different wavelengths and having optically spaced combining couplers and optical loops which include as portions thereof, the optical path. The outputs of the Sagnac interferometers are summed to determine the relative amplit...

A folded Sagnac fiber optic acoustic sensor array operates in a manner similar to a Sagnac interferometer but uses a common delay path to reduce distributed pickup in downlead fibers. The fiber optic acoustic sensor array is used to detect acoustic waves in water. By basing the folded Sagnac sensor array on operating principles similar to the Sagnac interferometer rather than basing the array on a Mach-Zehnder interferometer, the sensor array has a stable bias point, has reduced phase noise, and...

An optical switch employs a modified sagnac arrangement that includes a sagnac loop and a coupler for injecting a signal into the loop and developing thereby two signals that travel along the loop in opposite directions. The coupler has at least one signal port that is accessible from outside the switch. In addition, a coupler is included to inject a pump signal into the loop to travel through the loop only in one direction. The loop is made of, or comprises, a material that has a controllable p...

A folded Sagnac fiber optic acoustic sensor array operates in a manner similar to a Sagnac interferometer but uses a common delay path to reduce distributed pickup in downlead fibers. The fiber optic acoustic sensor array is used to detect acoustic waves in water. By basing the folded Sagnac sensor array on operating principles similar to the Sagnac interferometer rather than basing the array on a Mach-Zehnder interferometer, the sensor array has a stable bias point, has reduced phase noise, and...