Fiber laser sensors have been present for almost four decades as versatile sensing devices with a simple demodulation process, high sensitivity, and competitive resolution. This work discusses the most representative fiber laser sensor configurations employed for detecting critical parameters such as temperature, refractive index, and strain. However, essential information about other interesting parameters that have been measured is considered in this manuscript. Concurrently, the sensing elements and principle operation are described. Furthermore, these configurations are analyzed in terms of their principle of operation, sensitivity, gain medium, and wavelength operation range. According to the literature reviewed, fiber laser sensors offer the possibility of new interrogation techniques and simultaneous, independent detection. Considering interferometric fiber sensors, the fiber laser sensors offer high brightness, good output power, and high resolution. As a result, it is demonstrated that fiber laser sensors are a robust alternative for multiple sensing applications.

This research presents an experimental study focused on measuring temperature at the tool flank during the up-milling process at high cutting speed. The proposed system deals with emissivity compensation through a two-photodetector system and during calibration. A ratio pyrometer composed of two photodetectors and a multimode fiber-optic coupler is employed to capture the radiation emitted by the cutting insert. The pyrometer is calibrated using an innovative calibration system that addresses theoretical discrepancies arising from various factors affecting the measurement of cutting temperature. This calibration system replicates the milling process to generate a calibration curve. Experimentally, AISI 4140 steel is machined with coated tungsten carbide inserts, using cutting speeds of 300 and 400 m/min, and feed rates of 0.08 and 0.16 mm/tooth. The results reveal a maximum recorded cutting temperature of 518 °C and a minimum of 304 °C. The cutting temperature tends to increase with higher cutting speeds and feed rates, with cutting speed being the more influential factor in this increase. Both the pyrometer calibration and experimental outcomes yield satisfactory results. Finally, the results showed that the process and the device prove to be a convenient, effective, and precise method of measuring cutting temperature in machine processes.

We experimentally demonstrate a highly temperature-sensitive external Fabry-Perot cavity. The interferometric structure is composed of an air-microcavity; its fabrication uses a microcapillary and UV polymer. A temperature sensitivity close to 5.7 nm/ºC is achieved with suitable linearity (0.9896) and minimal hysteresis; a phase analysis technique is proposed and applied to overcome the trade-off between sensitivity and range of operation. This technique provides a competitive sensitivity (0.84 rad/ºC), good linearity (0.9934), and a range of operation from 25 °C to 41 °C.

This work shows a study of pressure gas sensing using an optical fiber interferometer inside a gas cell; here, a thin-core fiber modal interferometer (TCFMI) is fabricated using two distinct types of fiber, a single-mode fiber (SMF model 1060XP) and thin-core fiber (TCF model 460 HP). This interferometric structure is set into a ring fiber laser with an ytterbium-doped fiber (YDF) pumped with a 980 nm laser diode. The TCFMI interference spectrum shows wavelength shifting and amplitude variations as the chamber pressure is altered in the range of 5 to 40 PSI; these changes control the ring fiber laser cavity response linearly and lead to good stability in its wavelength operation in a range of 30 nm. The proposed interferometer operates as a wavelength-selective filter in the fiber ring laser cavity. The single laser emission shows a side mode suppression ratio of 34.17 dB. The fiber ring laser is a reliable alternative for air pressure sensing applications.

This work presents the sensitive modal analysis of a long reflective multimode optical fiber device for angle and temperature. The reflective multimode interference optical fiber device was fabricated by splicing ~40 cm of multimode optical fiber (50/125). This structure provides a random interference reflection spectrum; the wavelength sensitivity analysis indicates that estimating the angle detection is impossible due to the several modes involved. However, by the phase analysis of the Fourier components, it was possible to detect slight angle deflection. Here, three spectral Fourier components were analyzed, and the maximal sensitivity achieved was 1.52 rad/°; the maximal angle variation of the multimode fiber was 3.4°. In addition, the thermal analysis indicates minimal temperature affectation (0.0065 rad/°C). Moreover, it was demonstrated that there is a strong dependence between the sensitivity and the m-order of the modes involved. Considering the fiber optic sensor dimensions and signal analysis, this device is attractive for numerous applications where slight angle detection is needed.