In this letter, a curvature sensing setup based on a fiber ring laser containing a long-period fiber grating (LPFG) is presented. The LPFG operates as a wavelength selective filter and as a curvature sensing head. The LPFG consists of a periodically tapered fiber section written by a CO2-laser glass processing system. Experimental results show that by increasing the curvature values from 0 to 0.266 m-1, the laser wavelength emission shifts linearly from 1572 to 1560 nm, and a curvature sensitivity of -42.488 nm/m-1 is achieved. Additionally, the laser emission has a linewidth of 0.05 nm, a slope laser efficiency of 0.43single-mode suppression ratio (SMSR) of 60 dB. Finally, this fiber laser offers output power stability at room temperature, compactness, and robustness.

An all-fiber comb-filter using a Mach-Zehnder interferometer based on concatenated tapers is presented. The central wavelength, the amplitude, the period, and the spectral width of the transmission interference pattern can be tailored by varying the diameter and length of the waist, the length of the up- and down-transition of the fiber tapers, and the separation between the two tapers. Depending on the geometrical parameters of the tapers, the central position and span of the spectral interference pattern were tailored in the range of 1200-1650 and 50-300 nm, respectively. By varying the interferometer length, the fringe period and bandwidth were tailored between 3-36 and 2.5-11 nm, respectively. The physical length of the devices fabricated ranges from 15 to 30 mm. The proposed device is simple and suitable for applications in optical communications systems, fiber lasers, and optical fiber sensors for the monitoring of strain and displacement.

A compact, highly sensitive optical fiber displacement and curvature radius sensor is presented. The device consists of an adiabatic bi-conical fused fiber taper spliced to a single-mode fiber (SMF) segment with a flat face end. The bi-conical taper structure acts as a modal coupling device between core and cladding modes for the SMF segment. When the bi-conical taper is bent by an axial displacement, the symmetrical bi-conical shape of the tapered structure is stressed, causing a change in the refractive index profile which becomes asymmetric. As a result, the taper adiabaticity is lost, and interference between modes appears. As the bending increases, a small change in the fringe visibility and a wavelength shift on the periodical reflection spectrum of the in-fiber interferometer is produced. The displacement sensitivity and the spectral periodicity of the device can be adjusted by the proper selection of the SMF length. Sensitivities from around 1.93 to 3.4 nm/mm were obtained for SMF length between 7.5 and 12.5 cm. Both sensor interrogations, wavelength shift and visibility contrast, can be used to measure displacement and curvature radius magnitudes.