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.

This paper presents an erbium-doped fiber laser temperature sensor, which is based on an intracavity fiber filter immersed in glycerol/water solutions. The sensing element is the intracavity fiber filter, consisting of a two-taper fiber Mach-Zehnder interferometer (MZFI). The high refractive index dispersion of glycerol/water solutions with temperature allowed the modification of the MZFI spectral characteristics and hence determines the lasing wavelength. The sensitivity of 1089 pm/°C and a signal-to-noise ratio of 50 dB make the proposed sensor suitable for real applications.

This paper presents the characterization of the response of CO $_2$ -laser induced LPFGs by using a glass-processing system. The symmetric perturbation induced by the process is a result of the tapering of the fiber cladding and diffusion of the fiber core. The core diameter is increased from 8.4 um to 13.8 um at the waist of the taper as obtained from SEM microscope images of the fiber end. Sensitivity to temperature, strain, and bending was 101.2 pm/°C, -1.05 pm/ue, and -17.74 nm/m $^{-1}$ , respectively. Application to the measurement of glycerol-distilled water and gasoline-alcohol solutions was realized, resulting in the last case, in a sensitivity of 514 pm/percent of gasoline in alcohol. A simulation that accounts for dispersion material, core diffusion, cladding tapering, and stress release closely reproduces the unperturbed transmission spectrum; however, it only can reproduce the response to changes in the external refractive index of LPFGs fabricated and measured under specific conditions explained in the text. The study presented in this work is essential for considerations on the stability that the LPFGs must have in order to be useful for practical applications. Application to the measurement of glycerol-distilled water and gasoline-alcohol solutions was realized, resulting in the last case, in a sensitivity of 514 pm/percent of gasoline in alcohol. A simulation that accounts for dispersion material, core diffusion, cladding tapering and stress release closely reproduces the unperturbed transmission spectrum, however, it only can reproduce the response to changes in the external refractive index of LPFGs fabricated and measured under certain conditions explained in the text. The study presented in this work is important for considerations on the stability that the LPFGs must have in order to be useful for practical applications.

The simultaneous measurement of the numerical aperture (NA) and mode field diameter (MFD) of single-mode fibers was performed on several commercial fibers by means of digital image processing of the output light projected into a screen. In addition, the changes induced by core diffusion in an ultra-high (UH) NA fiber at several heat depositions from a ${\mathrm{CO}}_2$ laser source were measured. The measurement method was demonstrated to be useful to monitor the adiabaticity of this process, by taking the product of the NA and MFD to verify if it remains constant. The method provides a cheap alternative to measure these optical fiber parameters by using simple optomechanical elements and a readily available smartphone camera, and it can be easily implemented in the laboratory.