In this paper, we propose and experimentally demonstrate a simple technique to enhance the curvature sensitivity of a bending fiber optic sensor based on anti-resonant reflecting optical waveguide (ARROW) guidance. The sensing structure is assembled by splicing a segment of capillary hollow-core fiber (CHCF) between two single-mode fibers (SMF), and the device is set on a steel sheet for measuring different curvatures. Without any surface treatment, the ARROW sensor exhibits a curvature sensitivity of 1.6 dB/m⁻¹ in a curvature range from 0 to 2.14 m⁻¹. By carefully coating half of the CHCF length with polydimethylsiloxane (PDMS), the curvature sensitivity of the ARROW sensor is enhanced to −5.62 dB/m⁻¹, as well as an increment in the curvature range (from 0 to 2.68 m⁻¹). Moreover, the covered device exhibits a low-temperature sensitivity (0.038 dB/°C), meaning that temperature fluctuations do not compromise the bending fiber optic sensor operation. The ARROW sensor fabricated with this technique has high sensitivity and a wide range for curvature measurements, with the advantage that the technique is cost-effective and easy to implement. All these features make this technique appealing for real sensing applications, such as structural health monitoring.

We propose the implementation of fiber Bragg gratings in tapered few-mode and multimode fibers to accomplish single-mode operation by reducing the core diameter, while preserving the core-cladding structure. The gratings present a single reflection band, and the device shows low insertion losses after the taper fabrication and the fiber Bragg gratings inscription. The excitation of high-order odd modes in the core of the fiber has been identified as the main loss mechanism; it can be prevented by means of symmetric illumination of the fibers. We also demonstrate the excitation of high-order cladding modes (cladding-air modes) along the taper transitions; these modes can be removed without a significant increment of the insertion loss.

We propose an all-fiber-optic multimode interferometer for measuring liquid refractive index. The interferometer was manufactured by using arc splice technique between standard single mode fiber and optical microfiber. A maximum refractive index sensitivity of 112dB/RIU is experimentally demonstrated. In addition, thermal effects exhibit low phase modulation (12pm/°C) with minimal intensity variations (-10.7*10-3dB/°C), as a result, cross-sensitivity around 0.05*10-6 RIU/ °C and 0.9 *10-6 RIU/ °C are obtained for intensity and phase modulation. The stability analysis shows minimal wavelength and power variations, 0.01nm and 0.27dB respectively, for constant temperature and refractive index. Spatial frequency analysis was explored as an alternative method to measure liquid refractive index avoiding thermal effects.

A compact, magnetic field sensor system based on a short, bi-tapered optical fiber (BTOF) span lying on a magnetic tape was designed, fabricated, and characterized. We monitored the transmission spectrum from a broadband light source, which displayed a strong interference signal. After data collection, we applied a phase analysis of the interference optical spectrum. We here report the results on two fabricated, BTOFs with different interference spectrum characteristics; we analyzed the signal based on the interference between a high-order modal component and the core fiber mode. The sensor exhibited a linear response for magnetic field increments, and we achieved a phase sensitivity of around 0.28 rad/mT. The sensing setup presented remote sensing operation and low-cost transducer magnetic material.

A tunable multi-wavelength fiber laser is proposed and demonstrated based on two main elements: an erbium-doped fiber ring cavity and compact intermodal fiber structure. The modal fiber interferometer is fabricated using the cost-effective arc splice technique between conventional single-mode fiber and microfiber. This optical fiber structure acts as a wavelength filter, operated in reflection mode. When the refractive index and temperature variations are applied over the fiber filter, the ring laser cavity provides several quad-wavelength laser spectra. The multi-wavelength spectra are tuned into the C-band with a resolution of 0.05 nm. In addition, the spectra are symmetric with minimal power difference between the lasing modes involved, and the average of the side mode suppression ratio is close to 37 dB. This laser offers low-cost implementation, low wavelength drift, and high power stability, as well as an effect of easy controllability regarding tuned multi-wavelength.

A stable, single, and dual-wavelength erbium-doped fiber laser (EDFL), based on two Mach–Zehnder interferometers (MZIs), arranged in a cascade configuration, was proposed for experimental purposes. Both MZIs were assembled by splicing a capillary hollow-core fiber (CHCF) section between two multimode fibers (MMFs) segments. The novelty of this single and dual-wavelength EDFL is that the switchable operation of the laser is achieved by thermally tuning the interference pattern of one MZI and not by adjusting the polarization state inside the fiber ring cavity. The maximum measured value of SNR was 58.9 dB for the single and dual-wavelength laser emissions. Moreover, the stable output power exhibited by this EDFL, in terms of minimal power and wavelength fluctuations, at 0.05 dB and 10 pm, was detected during the single and dual-wavelength operation. It is worth noticing that switching is achieved at exact wavelength locations with a separation of 1.8 nm and not randomly, as reported by other works. These features make this switchable EDFL an appealing candidate for application in optical fiber communication systems and fiber sensing.