An optical interrogation system, e.g., an OFDR-based system, measures local changes of index of refraction of a sensing light guide subjected to a time-varying disturbance. Interferometric measurement signals detected for a length of the sensing light guide are transformed into the spectral domain. A time varying signal is determined from the transformed interferometric measurement data set. A compensating signal is determined from the time varying signal which is used to compensate the interferometric measurement data set for the time-varying disturbance. The compensation technique may be applied along the length of the light guide.

An optical fiber distributed acoustic sensor system includes weak broadband reflectors inserted periodically along the fiber. The reflectors reflect only a small proportion of the light from the DAS incident thereon back along the fiber, typically in the region of 0.001% to 0.1%, but preferably around 0.01% reflectivity per reflector. In addition, to allow for temperate compensation to ensure that the same reflectivity is obtained if the temperature changes, the reflection bandwidth is relatively broadband. In some embodiments the reflectors are formed from a series of fiber Bragg gratings, each with a different center reflecting frequency, the reflecting frequencies and bandwidths of the gratings being selected to provide the broadband reflection. A chirped grating may also be used to provide the same effect. In preferred embodiments, the reflectors are spaced at half the gauge length i.e. the desired spatial resolution of the optical fiber DAS.

A system (20) for fiber-optic reflectometry includes an optical source (28, 40), a beat detection module (44, 48, 52, 56A, 56B) and a processor (36). The optical source is configured to generate a non-linearly-scanning optical interrogation signal having an instantaneous optical frequency that is a non-linear function of time. The beat detection module is configured to transmit the optical interrogation signal into an optical fiber (24), to receive from the optical fiber an optical backscattering signal in response to the optical interrogation signal, and to mix the optical backscattering signal with a reference replica of the optical interrogation signal, so as to produce a beat signal. The processor is configured (i) to hold a predefined function that is indicative of an expected phase of the beat signal resulting from the non-linearly-scanning optical interrogation signal as a function of position along the optical fiber and time, (ii) to estimate a backscattering profile of the optical fiber by applying the predefined function to the beat signal, and (iii) to sense one or more events affecting the optical fiber by analyzing the backscattering profile.

A displacement sensor including an optical whispering gallery mode (WGM) microresonator and a package encasing at least a portion of the WGM microresonator, the package comprising polydimethylsiloxane (PDMS). The WGM microresonator can be configured as a sensor and used in a displacement detection system that can detect displacement with high quality. Artificial intelligence can be implemented in the displacement detection system for improved sensing of different variables and/or pinpointing the location of perturbations.

A flexible elongate member has at least one optical sensing fiber and is configured to be at least partially submerged or float in waste fluid inside a sewage pipeline or channel for obtaining distributed measurement data along the waste fluid flow. An apparatus is for use in obtaining distributed measurement data from a sewage pipeline or channel. The apparatus has a flexible elongate member in and deployment means for deploying the flexible elongate member in the waste fluid of the sewage pipeline or channel. Furthermore, a method is for obtaining distributed sensor measurements along a sewage pipeline or channel and a method is for deploying a flexible elongate member in a sewage pipeline or channel.

A sensor system for a laminated structure may include a sensor assembly disposed between a first layer and a second layer of the laminated structure. The sensor assembly may include a first anchor member and a second anchor member spaced at a predetermined distance from one another. A sensor chamber is formed between the first and second anchor members. The sensor assembly may also include a sensing line extending through the anchor members and the sensor chamber. The sensing line may include a configuration within the sensor chamber for sensing one of stress forces within the laminated structure, temperature or temperature changes within the laminated structure. A first transport tube may extend from the first anchor member opposite the sensor chamber and a second transport tube may extend from the second anchor member opposite the sensor chamber. The sensing line extends through the first and second transport tubes.

A fiber optic sensor is provided. The fiber optic sensor includes: a fixed portion configured to be secured to a body of interest; a moveable portion; a spring member positioned at least partially between the fixed portion and the moveable portion; an optical fiber wound in contact with the fixed portion and the moveable portion such that the optical fiber spans at least a portion of the spring; and an elastomeric material provided in contact with at least one of the fixed portion, the moveable portion, the spring member, the body of interest, and the optical fiber.

A fiber optic sensor is provided. The fiber optic sensor includes: a fixed portion configured to be secured to a body of interest; a moveable portion; a spring member positioned at least partially between the fixed portion and the moveable portion; an optical fiber wound in contact with the fixed portion and the moveable portion such that the optical fiber spans at least a portion of the spring; and an elastomeric material provided in contact with at least one of the fixed portion, the moveable portion, the spring member, the body of interest, and the optical fiber.

An apparatus for measuring state variables with at least one fiber-optic sensor, containing at least one optical coupler, at least one filter element and at least one photoelectric converter, where the optical coupler, the filter element and the photoelectric converter are integrated on a substrate, and the filter element contains at least one Bragg grating which is designed to supply the light portion reflected by the Bragg grating to the photoelectric converter.

A fiber optic sensor is provided. The fiber optic sensor includes: a fixed portion configured to be secured to a body of interest; a moveable portion; a spring member positioned at least partially between the fixed portion and the moveable portion; an optical fiber wound in contact with the fixed portion and the moveable portion such that the optical fiber spans at least a portion of the spring; and an elastomeric material provided in contact with at least one of the fixed portion, the moveable portion, the spring member, the body of interest, and the optical fiber.