A bending measurement apparatus includes a first multimode fiber, a wavefront input apparatus, a first wavefront measurement device, and a processor. The wavefront input apparatus inputs a first wavefront to the first multimode fiber as an input wavefront. The first wavefront measurement device measures an output wavefront outputted from the first multimode fiber as a measured wavefront. The processor select correspondence information which corresponds to the measured wavefront. The correspondence information shows a correspondence relationship between the input wavefront and the output wavefront. The processor sets the bending amount corresponding to the selected correspondence information as a current bending amount of the first multimode fiber.

Various examples and systems are provided for enhancing optical fibers for sensing temperature and/or strain at low temperatures (e.g., 1.8K to 77K or lower). An enhanced optical fiber for distributed sensing can comprise a core, a cladding surrounding the core, and a coating surrounding the cladding. A coefficient of thermal expansion (CTE) of the coating is greater than a CTE of silica and/or a Young's modulus (E) of the coating is greater than an E of silica.

This application relates to methods and apparatus for distributed fibre optic sensing that can provide an indication of the absolute value of pressure acting on a sensing portion of a fibre optic cable. A sensor apparatus (600) has a first fibre optic cable structure (102) comprising a first optical fibre (101) and an interrogator (103) configured to perform distributed acoustic sensing on the first optical fibre (101) to provide a measurement signal from at least one sensing portion of the first optical fibre. The first fibre optic cable structure (102) is configured such that a sensitivity of a sensing portion (603, 604) to an incident pressure stimulus (P1, P2) depends on the ambient pressure (AP1, AP2) at the location of the respective sensing portion. A processor (104) is configured to process the measurement signal in response to an incident pressure stimulus (P1, P2) based on a predetermined sensitivity profile (504, 701) to determine an indication of the ambient pressure at the respective sensing portion.

An optical fiber includes multiple optical cores configured in the fiber including a set of primary cores and an auxiliary core. An interferometric measurement system uses measurements from the multiple primary cores to predict a response from the auxiliary core. The predicted auxiliary core response is compared with the actual auxiliary core response to determine if they differ by more than a predetermined amount, in which case the measurements from the multiple primary cores may be deemed unreliable.

Example embodiments add an optical amplifier to an multi-channel, continuously swept OFDR measurement system, adjust amplified swept laser output power between rising and falling laser sweeps, and/or utilize portions of a laser sweep in which OFDR measurements are not typically performed to enhance the integrity of the OFDR measurement system, improve the performance and quality of OFDR measurements, and perform additional measurements and tests.

The high sensitivity provided by an enhanced DAS system comprising a DAS interrogator and a high reflectivity fiber allows for the deployment of such a high reflectivity fiber as part of a wireline intervention cable which can be temporarily lowered into a well, thus avoiding the need to permanently cement such a high reflectivity optical fiber cable into the well. Instead, such a wireline cable incorporating the high reflectivity optical fiber has been found to be sensitive enough to detect micro-seismic activity and low frequency strain with many more measurement points and channels than conventional wireline deployed geophones and tiltmeters. Additionally, the cable requires no clamping and can be easily and quickly removed from one well and placed in another well.

A fiber optic cable assembly includes an elongate housing, a signal fiber placed inside the housing and extending longitudinally, and a plurality of sensing fibers placed inside the housing and extending longitudinally. The plurality of sensing fibers is placed around the signal fiber. Each of the plurality of sensing fibers carries a respective laser signal of a distinct frequency. The signal fiber carries one or more evanescent coupling signals responsive to the laser signals in the plurality of sensing fibers.

A novel system and method for detecting a quench of a superconducting conductor and detecting abnormal behavior of a superconducting conductor using acoustic sensor technology in the coolant of a superconducting cable and/or magnet is disclosed. This system and method is not only limited to use for superconductors, but also may be used for any device disposed in liquid and gas. Acoustic sensors are installed along a coolant space of a superconducting conductor and monitor coolant conditions. By monitoring acoustic changes, temperature changes or coolant flow disruption can be detected very quickly by an acoustic sensor array. By disposition of the acoustic sensor array in a coolant flow channel, the acoustic sensor system can quickly detect a local condition, such as the thermal status (temperature) of a superconducting cable and magnet with precise spatial resolution.

This application relates to a fibre optic cable (104, 300) suitable for use with a distributed fibre optic sensor apparatus (106). The fibre optic cable includes at least one optical fibre (301) and a force transformer (304) mechanically coupled to the at least one optical fibre. The cable may also include at least one cladding later (302) and/or a compliant material (303). The cable may be surrounded by a jacket layer (306). The force transformer (304) is configured to transform transverse forces due to dimension changes of the cable arising from a temperature variation of the cable into longitudinal forces to counteract the longitudinal component of said dimension change over a tuned temperature range. In this way optical path length changes due to a change of temperature can be reduced or eliminated providing a cable which is insensitive to temperature.

A fiber optic cable assembly includes an elongate housing, a signal fiber placed inside the housing and extending longitudinally, and a plurality of sensing fibers placed inside the housing and extending longitudinally. The plurality of sensing fibers is placed around the signal fiber. Each of the plurality of sensing fibers carries a respective laser signal of a distinct frequency. The signal fiber carries one or more evanescent coupling signals responsive to the laser signals in the plurality of sensing fibers.