In optical fiber sensors, sensor signals obtained differ according to the circumstances of installation, in locations being observed, of optical fibers serving as sensors, and it is difficult to perform accurate measurements; therefore, a sensor signal processing apparatus according to the present invention includes variation calculation means for receiving a sensor signal based on scattered light of a light pulse propagating through an optical fiber, and calculating a variation of the sensor signal from a reference value; and normalization processing means for normalizing the variation within a predetermined time, and calculating a normalized variation.

According to examples, a Brillouin and Rayleigh distributed sensor may include a first laser source to emit a first laser beam, and a second laser source to emit a second laser beam. A photodiode may acquire a beat frequency between the two laser beams. The beat frequency may be used to maintain a predetermined offset frequency shift between the two laser beams. A modulator may modulate the first laser beam. The modulated first laser beam is to be injected into a device under test (DUT). A coherent receiver may acquire a backscattered signal from the DUT. The backscattered signal results from the modulated first laser beam injected into the DUT. The coherent receiver may use the second laser beam as a local oscillator to determine Brillouin and Rayleigh traces with respect to the DUT based on the predetermined offset frequency shift.

In some examples, fiber optic cable location may include transmitting a coherent laser pulse into a device under test (DUT). Based on an analysis of reflected light resulting from the transmitted coherent laser pulse, changes in intensity of the reflected light caused by a plurality of signals directed towards the DUT may be determined. Further, based on the changes in intensity of the reflected light, a location of the DUT may be determined.

An optical sensing fiber includes multiple reference reflectors spaced along a length of the fiber. Each of the multiple reference reflectors producing a reference scattering event having a known scattering profile including an elevated amplitude relative to scattering detected for neighboring segments of the optical fiber. Each of the segments is a length of contiguous fiber that is useable to initialize and perform a distributed Optical Frequency Domain Reflectometry (OFDR) sensing operation. An OFDR interrogation system is disclosed that measures a parameter using the optical sensing fiber.

A method of distributed fiber optic sensing is described in which an optical fiber (104) is interrogated with electromagnetic radiation; back-scattered radiation is detected; and the returns are processed to provide a measurement signal (310) for each of a plurality of longitudinal sensing portions of the optical fiber. The method comprises analyzing the measurement signals of a first subset of longitudinal sensing portions to provide a first zone (306a) having a first sensing function and analyzing the measurement signals of at least a second subset of longitudinal sensing portions to provide at least a second zone (306b) having a second, different, sensing function. The different sensing functions may include detecting different events of interest. In some embodiments the geometry of the fiber may provide different sensing zones (406a, 406b).

A computer-implemented event statistic generation method for intrusion detection comprises processing a plurality of return signals from a coherent optical time domain reflectometer into time domain signals for each of a plurality of sensor bins, the plurality of return signals corresponding to a plurality of stimulation pulses injected into an optical sensor fiber during a time period. For each sensor bin, the method comprises transforming the respective time-domain signal into a corresponding frequency-domain signal, calculating, from the respective frequency-domain signal, a first signal power area of a first frequency band expected to contain system noise, calculating, from the respective frequency-domain signal, a second signal power area of a second frequency band expected to contain any energy related to at least a first event; and generating an event statistic proportional to the ratio of the second signal power area to the first signal power area at least in part by dividing the second signal power area by the first signal power area.

A method and device for monitoring oil field operations with a fiber optic distributed acoustic sensor (DAS) that uses a continuous wave laser light source and modulates the continuous wave output of the laser light source with pseudo-random binary sequence codes.

A distributed optical detection system comprising: a broadband optical source; and a phase and amplitude receiver for measuring phases and amplitudes of distributed backscattered signals from a sensing medium. Methods of quantitatively sensing optical path length changes along a sensing medium in a distributed manner are also disclosed.

Aspects of the present disclosure describe systems, methods. and structures for vibration detection using phase recovered from an optical transponder with coherent detection. Advantageously, our systems, methods, and structures leverage contemporary digital coherent receiver architecture in which various adaptive DSP operations performed to recover transmitted data track optical phase. The phase is extracted at low overhead cost, allowing a digital coherent transponder to perform vibration detection/monitoring as an auxiliary function to data transmission. Demonstration of vibration detection and localization based on the extraction of optical phase from payload-carrying telecommunications signal using a coherent receiver in a bidirectional WDM transmission system is shown and described.

An advance in the art is made according to aspects of the present disclosure directed to the detection and localization of a substantially static weight situated on aerial telecommunications fiber optic cable through the effect of phase-distributed acoustic sensing (ϕ-DAS) and signal analysis of ambient data. In sharp contrast to the prior art, our inventive method does not require a special optical fiber arrangement or type of fiber nor is it susceptible to range limitations that plague the prior art.