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We present a new design of an all-fiber sensor system to enhance the low-temperature sensing performance of cryogenic fuel. Fiber Bragg gratings (FBGs) are inscribed in high attenuation fibers (HAFs), which absorb in-fiber light to raise the local sensor temperature in a cryogenic environment. The heated sensor displays improved sensitivity and response time to measure multiple parameters. Two sensing applications are described in this paper. First, a HAF-FBG sensor coated with palladium is used to detect hydrogen concentration well below the 4% explosion limit at 173 K. Second, an array of three aluminum-coated sensors is capable of measuring the liquid level at 77 K. In addition, through the selection of the length and attenuation coefficient of HAF, numerous FBG sensors can be multiplexed on a single fiber for multipoint sensing using a single fiber feedthrough. © 2010 IOP Publishing Ltd.

A palladium-coated fiber Bragg grating (FBG) inscribed in high attenuation fiber (HAF) capable of measuring hydrogen concentration at -150 °C, well below the 4% explosion limit, is presented. The low-temperature performance of the sensor was improved by heating the gratings as much as 300 K above the ambient temperature with highly attenuated infrared laser light. The sensitivity and response time of the FBG hydrogen sensor were studied as functions of fiber temperature. Through the selection of length and the loss per meter of the HAF, the self-heating scheme demonstrated here enables numerous FBG hydrogen sensors to be multiplexed in a single fiber for multipoint hydrogen sensing using a single fiber feedthrough. © 2009 IEEE.

The use of liquid hydrogen as a fuel requires low-cost multipoint sensing of hydrogen gas for leak detection and location well below the 4% explosion limit of hydrogen. Herein is presented a multipoint in-fiber hydrogen sensor capable of hydrogen detection below 0.5% concentration with a response time of less than 10 s. Our solution entails use of a fiber Bragg grating (FBG) coated with a layer of hydrogen-absorbing palladium which, in turn, induces strain in the FBG in the presence of hydrogen. Infrared power laser light is used to induce heating in the palladium coating which dramatically decreases sensor response time and increases the sensor's sensitivity at low temperatures. This technology promises an inexpensive fiber solution for a multipoint hydrogen detection array with only one fiber feed-through. © 2007 IEEE.

This paper demonstrates, for the first time to our best knowledge, the application of a tunable external-cavity fiber Bragg grating diode laser in spectroscopic chemical sensing. A tunable fiber Bragg grating external-cavity semiconductor laser is demonstrated with over 10 nm of tuning range. A piezoactuator was implemented to stretch the grating for rapid wavelength tuning of the laser. The application of such low-cost tunable FBG lasers in spectroscopic chemical sensing was demonstrated in acetylene gas with a wavelength modulation spectroscopy technique. © 2006 Optical Society of America.

This letter demonstrates an approach for tuning fiber Bragg grating sensors with optical energy carried in the same optical fiber. Optical energy carried in the optical fiber was used to heat in-fiber Bragg gratings in order to alter the grating's optical response to surrounding media. The functional enhancement of optically heated Bragg gratings as sensor devices is demonstrated by a dual-function Bragg grating temperature and level sensing array for liquid at room and cryogenic temperatures. © 2005 American Institute of Physics.

This letter demonstrates functional enhancements of fiber Bragg grating sensors powered by in-fiber light. High-power laser light transmitted in double-clad optical fiber was extracted from the fiber core to heat an on-fiber metal coating. When the power-laser is turned off, the fiber Bragg grating is used as a passive component for temperature sensing. When the laser is turned on, the thermal response of the optically heated grating was used to monitor ambient air pressure. The sensitivity and dynamic range of optically powered fiber sensors can be actively adjusted by in-fiber light to measure vacuum pressures over four orders of magnitude. © 2005 American Institute of Physics.

A deep ultraviolet femtosecond laser was employed to trim phase and birefringence errors in silica planar lightwave circuits. A permanent refractive index change of ∼3.8 × 10-4 and a birefringence change of 1.0 × 10-4 were induced in hydrogen-free Mach-Zehnder planar waveguide circuits. The ultrafast laser enhances the ultraviolet photo-sensitivity response in silica waveguides by two orders of magnitude greater than that of a nanosecond 248 nm KrF excimer laser.