{"id":4718,"date":"2023-10-13T11:14:58","date_gmt":"2023-10-13T09:14:58","guid":{"rendered":"https:\/\/www.institut-foton.eu\/?p=4718"},"modified":"2026-05-04T13:46:33","modified_gmt":"2026-05-04T11:46:33","slug":"capteurs-a-fibre","status":"publish","type":"post","link":"https:\/\/www.institut-foton.eu\/en\/capteurs-a-fibre\/","title":{"rendered":"Fiber sensors"},"content":{"rendered":"<\/p>\n\n\n\n\n\n\n

Presentation<\/h2>\n\n\n\n

Fiber optics offers a multitude of possibilities in terms of sensors. Indeed, the implementation of very long optical paths allows high measurement sensitivity. Furthermore, the fiber itself is a very sensitive sensor to different physical parameters (temperature, mechanical or chemical constraints, etc.). In the DOP team, we develop original fiber architectures allowing us to measure very weak effects.<\/p>\n\n\n\n

Fiber Sagnac interferometer<\/h3>\n\n\n\n

The fibered Sagnac interferometer is an instrument allowing access to the measurement of non-reciprocal effects, i.e. a dependence of the optical index with the direction of travel of the light in the sample. This passive 2-wave fiber interferometer is inspired by the fiber gyroscope used to measure the Sagnac effect. Our instrument thus makes it possible to measure small or poorly understood physical effects.<\/p>\n\n\n\n

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Fig.1 Sketch of a depolarizaied Sagnac interfereometer.<\/figcaption><\/figure>\n\n\n\n

Measurement of magnetochiral birefringence<\/h3>\n\n\n\n

The magnetochiral interaction results, in the optical domain, in a difference in absorption coefficients and refractive indices associated with two counter-propagating waves in a chiral medium subjected to a longitudinal magnetic field. Observations of magnetochirality in optics are rare, the effect being small. The contribution to absorption, called magnetochiral dichroism, was observed for the first time in 1998. We have developed fibered and depolarized Sagnac interferometers at 1.5\u00b5m and 0.8\u00b5m, presenting a detection floor below 500 nrad.Hz-\u00bd, for the detection of the magnetochiral index of molecules in solution.<\/p>\n\n\n\n

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Fig.2 Experimental setup for the detection of magnetochiral birefringence. <\/figcaption><\/figure>\n<\/div>\n\n\n\n
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Test molecule : Helicene mono-Fe(II).<\/figcaption><\/figure>\n<\/div>\n<\/div>\n\n\n\n

Distributed acoustic sensing (DAS)<\/h3>\n\n\n\n

We have implemented a fiber interrogator, capable of measuring in real time the index profile along a fiber with sub-cm resolution. The system is based on the principle of multi-heterodyne or dual-comb interferometry. The dual-comb source is a bi-directional frequency-shifting loop, which delivers several hundred mutually coherent teeth. The spatial and temporal resolutions of the technique are respectively a few mm and a few tens of \u00b5s. This interrogator should make it possible to measure the wall pressure in aero or hydrodynamic flows around moving solids.<\/p>\n\n\n\n

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Fig.3 Architecture of the fiber interrogator allowing distributed measurements of the refractive index along the test fiber. Two mutually coherent frequency combs are produced in a bi-directional frequency-shifting loop. The recombination of the two combs on the detector provides the index profile along the test fiber.<\/figcaption><\/figure>\n\n\n\n

Financial support<\/h2>\n\n\n\n