FBG-based interferometer senses the tiniest of acoustic signals

A different type of fiber Bragg grating (FBG)-based sensor has 1000X more sensitivity than standard FBG sensors.

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Fiber-Bragg-grating (FBG)-based optical sensors are typically used to measure distributed stress, strain, and temperature over a wide area. But a different type of FBG-based sensor from Optics11 (Amsterdam, Netherlands) has 1000X more sensitivity than standard FBG sensors, and is around 100X faster compared to Rayleigh-scattering technology.

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Rather than detecting the reflected signals from individual FBGs along a length of fiber, the ZonaSens system is instead an interferometer that measures an optical phase change defined as a variation of displacement or refractive index between FBGs. By measuring the phase of light reflected, for example, from four physically separate FBGs labeled A1, A2, A3, and A4, ZonaSens can define simultaneous signals (“zones”) A43 and A21, which are equal to the optical path difference between given FBGs. The total amount of simultaneous zones in one fiber can be up to 80—however, by combining multiple fibers, this number can reach a few hundred. And there is no optical time-domain reflectometer (OTDR), optical Fourier-domain reflectometer (OFDR), or spectral processing involved. Because the resolution of the measurement is on a subnanometer scale, the system can monitor extremely tiny changes in strain at rapid speeds up to 1 MHz and acquire an acoustic signal from the fiber (and associated object or system) under test.

Applications include analysis of ultrasound signals for structural health monitoring (for instance, bearings at around 200–300 kHz) that are traditionally limited to around 10 kHz for standard technologies. Other applications include monitoring of train wheels, pumps/drills and similar mechanical equipment, and hydrophone-related systems that require high speed and high sensitivity. Reference: http://optics11.com/products/zona-sens.

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