The present invention relates to an optical fibre for use in a system for detection of one or more compounds in a fluid. The optical fibre (100, 101, 202) comprising at least two binding portions (102, 104, 118, 210, 211, 212) separated from each other along the longitudinal direction (106) of the optical fibre (100, 101, 202), wherein each of the at least two binding portions (102, 104, 118, 210, 211, 212) comprises a plasmonic structure (120) and/or a SERS structure (121), and a binding material (126) for binding of one or more compounds, wherein at least two binding portions (102, 104, 118, 210, 211, 212) are arranged for binding the same compound or compounds, wherein the optical fibre (100, 101, 202) is arranged for receiving light and transmitting light to each of the at least two binding portions, wherein each of the at least two binding portions (102, 104, 118, 210, 211, 212) is arranged such that light transmitted through that binding portion (102, 104, 118, 210, 211, 212) without bound compound is different compared to light transmitted through that binding portion (102, 104, 118, 210, 211, 212) with bound compound, or light reflected back from that binding portion (102, 104, 118, 210, 211, 212) without bound compound is different compared to light reflected back from that binding portion (102, 104, 118, 210, 211, 212) with bound compound. The present invention further relates to a system (200) for detection of one or more compounds in a fluid (103) and an optical fibre (100, 101, 202) for use in such a system (200) and a method (400) using the system (200).

Systems and methods for distributed acoustic sensing based on coherent Rayleigh scattering are disclosed herein. A system comprises a pulse generator, an interferometer, a photo detector assembly, and an information handling system. The interferometer comprises a first and second optical switch each comprising a plurality of ports. The information handling system activates one port on each of the first and second optical switches so as to vary the optical path length of the interferometer. A method comprises splitting backscattered light from an optical pulse into a first portion and a second portion, activating one port of a first optical switch and one port of a second optical switch, sending the first portion into a first arm of an interferometer, sending the second portion into a second arm of the interferometer, combining the first and second portions to form an interferometric signal, and receiving the interferometric signal at a photodetector assembly.

The present invention provides a gas measuring method based on photothermal effect in hollow-core optical fiber comprising: filling a target gas into the core of a hollow-core optical fiber; coupling a probe light and a periodically modulated pump light into the hollow-core optical fiber; absorbing the pump light by the target gas resulting in the periodic modulation of the phase of the probe light; demodulating the phase modulation information of the probe light to obtain the concentration of the target gas, wherein the pump laser is wavelength and/or amplitude modulated. In the present invention, two lasers including a pump laser and a probe laser are used for the measurement, this approach is simple and practical. Also, the use of the hollow-core optical fiber with extremely-small core area greatly increases the optical power density, thus enhances the strength of the detected photothermal signal; this method allows ppb level gas measurement with high selectivity, and is universally suitable for the detection of gases with absorption in near-infrared.

A system and method for determining a partial pressure of hydrogen in a volume. A response is measured of a section of an optical fiber disposed in the volume to a parameter of the volume. A partial pressure of hydrogen in the volume is determined from the response of the optical fiber to the parameter. The presence of hydrogen in the volume is determined from the partial pressure of hydrogen.