Eloisa Gallegos-Arellano

The design of a temperature sensor employing the Mach–Zehnder configuration with an offset in the fiber core represents a novel methodology that leverages the distinctive attributes of optical fibers to attain enhanced sensitivity and precision in temperature measurement. Ambient temperature measurement is enabled by aluminum-doped zinc oxide (AZO) thin films deposited via sputtering onto optical fiber structures for sensing applications in the 1540–1555 nm wavelength range. This work explores the potential of this interferometer to measure the effective temperature variation within the core offset of an optical fiber in a cost-effective manner.

The implementation of a spectroscopic system for the detection and real time monitoring of methane (CH ₄ ) and acetylene (C ₂ H ₂ ) is presented, using an all-fiber supercontinuum source generated by noise-like pulses (NLP) tunable by polarization. The generated spectrum ranges from 1500 nm to 1680 nm and has an output power of ∼3.4 mW. Experimental results show that the registered absorption peaks of C ₂ H ₂ have a maximal depth of approximately 30.8 dB , and 32 intense lines in the R and P branches, whereas the CH ₄ peaks have a maximum depth of approximately 14.5 dB , and 18 intense lines. Besides, it is shown that small adjustments in the system polarization state significantly modify the SC spectral profile, affecting the visibility of the absorption signals, and allowing for adjusting the system sensitivity. Finally, the experimental spectra were validated through their comparison with the HITRAN database simulations. To the best of our knowledge, this is the first experimental demonstration of a system for real-time monitoring of two gases based on an SC source generated by NLPs. The proposed configuration represents a robust and simple solution for the practical detection of multiple gaseous species in environmental or industrial environments.

This paper presents a system for the measurement of chlorides in drinking and wastewater, based on an electrochemical process using a selective electrode as a transducer, which was developed by this group. The measurement for the concentration is carried out by introducing the implemented electrode (considered as reference) in the sample that will be analyzed; then a current is passed producing a potential difference in the system. Different aqueous solutions of sodium chloride (NaCl) were used, ranging between 35 and 3546 µg of chloride ions (Cl⁻). As a data acquisition and monitoring system for the analysis, an ATmega 328P microcontroller was used as the main capture element for subsequent interpretation through graphics. The experimental results show that it was possible to detect a potential difference in the electrochemical measurement system that corresponded to 35 µg of chloride ions (Cl⁻), making clear the detection process and the selectivity of chloride ions. It is important to mention that with this measurement system and the applied methodology, results are obtained in real time using a small sample volume and without generate ng extra liquid waste, compared to the application of the traditional analytical titrimetric method. Finally, this chloride measurement system is inexpensive and can be used in drinking and wastewater measurements.

A moisture sensor based on a composite resonator is used to measure different honey samples, which include imitation honey. The sensor changes its frequency response in accordance with the dielectric permittivity that it detects in the measured samples. Although reflectometry sensors have been used to measure the percentage of moisture in honey for almost a century, counterfeiters have achieved that their apocryphal product is capable of deceiving these kinds of sensors. Metamaterial features of the composite resonators are expected to improve their response when detecting lossy samples such as organic samples. It is also sought that these sensors manage to detect small differences not only in the real parts of the dielectric permitivities of samples but also in their imaginary parts, and, thus, the sensors are able to discern between real honey and slightly altered honey. Effectively, not only was it possible to improve the response of the sensors by using lossy samples but it was also possible to identify counterfeit honey.

In this paper, a gas sensing system based on a conventional absorption technique using a single-mode-fiber supercontinuum source (SMF-SC) is presented. The SC source was implemented by channeling pulses from a microchip laser into a one kilometer long single-mode fiber (SMF), obtaining a flat high-spectrum with a bandwidth of up to 350 nm in the region from 1350 to 1700 nm, and high stability in power and wavelength. The supercontinuum radiation was used for simultaneously sensing water vapor and acetylene gas in the regions from 1350 to 1420 nm and 1510 to 1540 nm, respectively. The experimental results show that the absorption peaks of acetylene have a maximum depth of approximately 30 dB and contain about 60 strong lines in the R and P branches, demonstrating a high sensitivity of the sensing setup to acetylene. Finally, to verify the experimental results, the experimental spectra are compared to simulations obtained from the Hitran database. This shows that the implemented system can be used to develop sensors for applications in broadband absorption spectroscopy and as a low-cost absorption spectrophotometer of multiple gases.

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.