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We present a highly reproducible method of fabricating a tapered intrinsic Fabry-Perot interferometer (IFPI) device with 5~6-m diameter at the taper waist. A femtosecond laser was applied to inscribe an IFPI with 3-cm cavity length in a single-mode fiber. A CO2 laser heated tapering process enabled by digitally controlled mirrors and a precision motorized fiber feed system was used to create a stable heating zone with the desired temperature profile for tapering the fiber IFPI cavity. The well-engineered tapering process produced tapered IFPI devices with insertion loss less than 0.3-dB at 1550-nm. A strong evanescent field exposed by the taper section was explored for refractive index sensing. Using swept optical frequency domination reflectometry, the tapered IFPI fiber sensor achieved a minimal refractive index sensing resolution 210 -5 . This paper demonstrates an integrated laser fabrication technique to produce tapered fiber optic devices for sensing applications.

This paper studies the use of MUltiple SIgnal Classification (MUSIC) as a super-resolution algorithm to improve demodulation results for intrinsic Fabry–Perot interferometer (IFPI) sensor arrays. Through distinction between noise and signal subspaces in an observation matrix, this paper shows that a 38-fold improvement in the full width at half maximum (FWHM) estimation of IFPI optical path differences (OPD) can be achieved using this algorithm. Based on this improved method, this paper demonstrates that a tunable laser with a 1.3-nm tuning range can achieve the same sensor demodulation performance as a tunable laser with a 50-nm tuning range if a conventional Fourier transform-based algorithm is used. This paper presents a new approach to analyzing optical signals produced by multiple multiplexed interferometers with similar OPDs with potential applications for both single-mode and multiple-mode devices.

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This paper presents a technique for measuring gas flow velocity using femtosecond laser-induced active fiber Bragg grating (FBG) sensors. When the in-fiber high-power laser is turned off, a small volume of gas in the flow stream is heated 0.05 °C to 1 °C above the ambient temperature using an electrical pulse heater. The temperature change of the gas is measured by the FBG sensors, allowing for the calculation of flow velocity based on time-of-flight measurements. Conversely, when the high-power laser is activated, the FBG sensors can be significantly heated by 23.5 °C to 281.9 °C above the ambient temperature through an energy conversion coating that converts leaked light into heat. The flow rate can be calculated according to how much the sensors' temperature drops. The experimental results show that Type-II FBG sensors can be used as highly multiplexable active optical sensors for both temperature and flow sensing with better response times than thermocouple devices.