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A process for femtosecond laser-based manufacturing was proposed to fabricate a long-period fiber grating (LPFG) with a screw shape. The screw-shaped LPFG was continuously inscribed by single laser scanning, which results in the improvement of fabrication time. For the single laser scanning, an optical fiber was traveled along fiber axis and rotated about the fiber axis. The 44.65-mm-long LPFG with a screw shape and the period of 450 μm was fabricated about 17 min, and its sensitivity was 48 ~ 51 nm/RIU for the glycerin solutions. The proposed process enables us to produce the screw-shaped LPFGs with fast manufacturing time and reliable performance compared with the process with multi-path scanning. [ABSTRACT FROM PUBLISHER]

Miniaturized Mach–Zehnder interferometer (MZI) is constructed using sharply tapered photonic crystal fiber (PCF) for highly sensitive ambient refractive index (RI) measurement. The sensor is fabricated by fusion splicing a small stub of PCF between standard single-mode fibers with fully collapsed air holes of the PCF in a splicing region. The influence of sharp tapering of the PCF is then studied using two different hydrogen flame diameters of 1 and 3.5 mm at the tip. Tiny flame geometry enables the sharp tapering of the PCF for a short fiber length and provides higher RI sensitivity. It appears that sharp tapering has a greater impact on RI sensitivity enhancement compared with decrease in taper waist diameter. The MZI with the taper waist diameter of 65~\mu \textm and the length of 3.8 mm offers an RI sensitivity of 334.03, 673.91, and 1426.70 nm/RIU within the RI range of 1.3327–1.3634, 1.3634–1.3917, and 1.3917–1.4204, respectively. [ABSTRACT FROM PUBLISHER]

Fiber Bragg grating (FBG) embedded in a microfiber Mach–Zehnder interferometer (MZI) is presented for sensing multiparameters, such as temperature and refractive index. The MZI is constructed by splicing a short length of 40- \mu \textm -diameter microfiber between standard single mode fibers. A millimeter long FBG is then written in the microfiber using direct point-by-point ultrafast laser inscription method. The microfiber MZI shows moderate sensitivity to ambient refractive index and temperature changes. In contrast, the microfiber FBG is insensitive to ambient refractive index change while it exhibits typical sensitivity to temperature variation. These distinct characteristics of the FBG and MZI sensors enable the simultaneous measurement of refractive index and temperature, and temperature compensation in ambient refractive index measurement. [ABSTRACT FROM PUBLISHER]