The novel long-period fiber grating (LPFG) film sensor is composed of the long-period grating coated with solgel-derived sensitive films. The characteristics of the transmissivity of the LPFG film sensor are studied. By analyzing the relation among the sensitivity Sn, the thin film optical parameters, and the fiber grating parameters, the optimal design parameters of the LPFG film sensor are obtained. Data simulation shows that the resolution of the refractive index of this LPFG film sensor is predicted to be 10(-8). Experimentally, a LPFG film sensor for detection of C(2)H(5)OH was fabricated, and a preliminary gas-sensing test was performed.
The design of a novel scheme long-period fiber grating (LPFG) film sensor is presented. The sensor is composed of a long-period grating coated with sol–gel derived films, which are sensitive to the surrounding medium (gases). Based on the coupled-mode theory, a four-layered numerical model has been developed to study the characteristics of the transmissivity of the LPFG film sensor. By analyzing the relationship between the sensitivity Sn and the thin film optical parameters (thickness h3 and refractive index n3) and the fiber grating parameters (the grating period Λ, the core index change σ and the grating length L), the optimal design parameters of the LPFG film sensor can be obtained. Data simulation shows that the resolution of the refractive index of this LPFG film sensor is predicted to be 10−8. Experimentally, a long-period fiber grating film sensor for the detection of C2H5OH was fabricated, and a preliminary gas-sensing test was performed. The results indicate that a novel optical film sensor scheme with structure optimization has higher sensitivity.
We report on interferometric noise limitation of fiber-optic gas sensors with highly coherent lasers and wavelength modulation spectroscopy. Interference between signal wave and reflected waves causes signal fluctuation in the output, which limits the performance of the sensing system. Sensor resolution limited by interferometric noise is calculated for a fiber-optic gas sensor with the Q͑6͒ absorption line of methane gas at approximately 1650 nm. The results are useful for system designers of this particular type of gas sensor.
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