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In this paper, a ratiometric approach to sensing temperature variations is shown using specialty fiber optic devices. We analyzed the transmission response of cascaded segments of multicore fibers (MCFs), and dissimilar lengths were found to generate an adequate scheme for ratiometric operation. The perturbation of optical parameters in the MCFs translates to a rich spectral behavior in which some peaks increase their intensity while others decrease their intensity. Thus, by selecting opposite-behavior peaks, highly sensitive ratiometric measurements that provide robustness against spurious fluctuations can be performed. We implemented this approach using seven-core fiber (SCF) segments of 5.8 cm and 9.9 cm. To test the system's response under controlled perturbations, we heated one of the segments from ambient temperature up to 150 °C. We observed defined peaks with opposite behavior as a function of temperature. Two pairs of peaks within the interrogation window were selected to perform ratiometric calculations. Ratiometric measurements exhibited sensitivities 6–14 times higher than single-wavelength measurements. A similar trend with enhanced sensitivity in both peak pairs was obtained. In contrast to conventional interferometric schemes, the proposed approach does not require expensive facilities or micrometric-resolution equipment. Moreover, our approach has the potential to be realized using commercial splicers, detectors, and filters. [ABSTRACT FROM AUTHOR]

In this paper, we propose a highly sensitive temperature sensor based on two cascaded Mach–Zehnder interferometers (MZIs) that work using the Vernier effect. The all-fiber MZIs were assembled by splicing a segment of capillary hollow-core fiber (CHCF) between two sections of multimode fibers (MMFs). This cascaded configuration exhibits a temperature sensitivity of 1.964 nm/°C in a range from 10 to 70 °C, which is ~67.03 times higher than the sensitivity of the single MZI. Moreover, this device exhibits a high-temperature resolution of 0.0153 °C. A numerical analysis was carried out to estimate the devices' temperature sensitivity and calculate the magnification of the sensitivity produced by the Vernier effect. The numerical results have an excellent agreement with the experimental results and provide a better insight into the working principle of the MZI devices. The sensor's performance, small size, and easy fabrication make us believe that it is an attractive candidate for temperature measurement in biological applications. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A ratiometric fiber optic temperature sensor based on a highly coupled seven-core fiber (SCF) is proposed and experimentally demonstrated. A theoretical analysis of the SCF's sinusoidal spectral response in transmission configuration is presented. The proposed sensor comprises two SCF devices exhibiting anti-phase transmission spectra. Simple fabrication of the devices is shown by just splicing a segment of a 2 cm long SCF between two single-mode fibers (SMFs). The sensor proved to be robust against light source fluctuations, as a standard deviation of 0.2% was registered in the ratiometric measurements when the light source varied by 12%. Its low-cost detection system (two photodetectors) and the range of temperature detection (25 °C to 400 °C) make it a very attractive and promising device for real industrial applications. [ABSTRACT FROM AUTHOR]

• Simple fabrication of a MZI using a capillary hollow core fiber. • Low insertions loss and high signal contrast. • Narrow linewidth (around 0.03 nm). • High SMSR (53 dB) and high SNR (66). • The output of the laser exhibits low power fluctuations (0.1379 dB) and practically no wavelength variations (0.0108 nm). In this paper, a narrow spectral linewidth and wavelength-tunable erbium-doped fiber laser based on a Mach-Zehnder interferometer (MZI) as a filter is proposed and experimentally demonstrated. The filter is fabricated by splicing a short length of capillary hollow-core fiber (CHCF) between two small sections of multimode fibers (MMF). The interference pattern generated by the filter has a free spectral range of 10.5 nm and a maximum extinction ratio of 36 dB at 1560 nm. Then, by incorporating the filter inside a ring cavity laser, a single laser emission centered at 1566.46 nm with a spectral width around 0.03 nm and a high SNR of 66 dB (also has a SMSR of 53 dB) is obtained. By changing the temperature of the filter, the wavelength emission of the laser can be tuned from 1566.46 to 1570.09 nm. Considering that the fabrication process of the filter is relatively simple and can be easily implemented in an EDFL, we strongly believe that it can have a great deal of interest in telecom applications. [ABSTRACT FROM AUTHOR]

A surface plasmon resonance-based fiber-optic sensor for simultaneous measurement of refractive index and temperature of liquid samples is proposed and experimentally demonstrated. The sensor consists of a gold-coated MM-SM-MM optical fiber structure, whose sensitive section was partially covered with polydimethylsiloxane (PDMS) to generate two independent SPR resonance dips in the fiber transmission spectrum. One of the dips is generated by the bare gold-coated fiber section whose wavelength resonance is tuned by the refractive index and temperature of the surrounding medium. The other dip that is exclusively used to monitor the temperature variations of the liquid sample, whose central wavelength at 900 nm corresponds to PDMS refractive index at 20 °C, is produced by the polymerized gold-coated fiber section. The high refractive index and temperature sensitivity achieved, 2323.4 nm/RIU and −2.850 nm/°C respectively, the small size, the ease fabrication process, and the bio-compatibility of the proposed device are appealing characteristics that makes it ideal for practical bio-sensing applications. [ABSTRACT FROM AUTHOR]