Arturo Castillo-Guzman

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.

Metal-free polymeric semiconductor graphitic carbon nitride (g-C₃N₄) was synthesized via thermal polycondensation using cyanamide with PVP as a medium, using SiO₂ nanospheres as sacrificial templates to suppress bulk agglomeration. Structural analysis using X-ray diffraction (XRD) confirmed the conservation of the g-C₃N₄ structure, while diffuse reflectance UV-Vis spectroscopy (DRS) showed that there is a slight change in optical absorption, modifying the band gap energy of g-C₃N₄ with the addition of SiO₂. Transmission electron microscopy (TEM) evidenced the formation of interconnected porous architectures, facilitating charge migration. Photocatalytic activity was evaluated under simulated solar irradiation using acetaminophen (ATP) as a model pharmaceutical pollutant. Kinetics experiments demonstrated that the sample containing 7% SiO₂ nanospheres achieved 65% degradation for 180 min. The best photocatalytic performance is attributed to the pore volume, which favors better adsorption, facilitating the degradation of acetaminophen. The participation of different reactive species during the photocatalytic degradation of ATP was determined. Experiments with scavenger agents indicate that the photogenerated holes are the predominant oxidizing reactive species. These results highlight the potential of g-C₃N₄ modified with SiO₂ nanospheres as an efficient photocatalyst for the degradation of emerging contaminants, thus advancing sustainable water treatment technologies.

Microlasers are innovative photonics devices that have recently attracted attention for their unique characteristics, including compactness, broad spectral emission, and low lasing threshold. These properties are beneficial in biophotonics as these lasers can interact with biological materials without causing damage, especially for optical biosensing applications. Among the optical materials recently used as gain media in microlasers are organic dyes, rare-earth ions, fluorescent proteins, and semiconductors, including quantum dots and perovskites. Moreover, different optical cavities and current laser configurations have increased the versatility of microlasers. Recently, digital sensing methods based on novel algorithms, machine learning, and neural networks have been combined with microlaser systems to enhance their accuracy and expand their applications. This work provides a comprehensive review of recent progress in microlasers, covering gain media, microcavity types, and their applications in biophotonics, including conventional spectral-based sensing and new digital approaches for the biomedical field.

This research presents a lens-based light collection system that integrates a handmade glass conical waveguide (GCW) with a single silica multimodal optical fiber (SMMF) and a concentrator Fresnel lens (FL). The GCW functions as a secondary optical element (SOE), effectively expanding the fiber’s receptive area and enabling efficient coupling of concentrated light. Calibrated ray-tracing simulations confirm that the complete FL + GCW + SMMF configuration maintains low transmission losses, thereby validating efficient coupling into the SMMF. Experimental results demonstrated a maximum net optical efficiency of 41% at an FL numerical aperture (NA) of 0.08, with GCW transmission reaching 60% and splice losses to the SMMF around 34%. With a luminous flux input of 155 lumens, the system delivered up to 63 lumens at the fiber output. Importantly, the FL + GCW + SMMF configuration combines reproducible fabrication, straightforward assembly, and reliable characterization, establishing a scalable pathway for daylight harvesting. The major contribution of this work is the demonstration that a simple, manufacturable GCW can substantially expand the effective collection area of multimodal fibers while preserving low optical losses, thereby bridging practical design with efficient energy transfer for sustainable photonics applications.

A relative humidity (RH) fiber optic sensor is demonstrated based on the multimode interference (MMI) phenomenon utilizing a no-core fiber (NCF) coated with polyvinyl alcohol (PVA). The sensor’s structure is simple and consists of a section of NCF spliced between two standard single-mode fibers (SMFs). The fabrication and testing of a tapered version with enhanced sensitivity is also presented. The native MMI sensor showed a sensitivity of 5.6nm/RH%, in the range from 87 RH% to 93 RH%, while the tapered one exhibited an increased sensitivity of 6.6nm/RH%, in the range from 91.5 RH% to 94 RH%. The sensitivity values obtained with these MMI sensors are at least twice as large as the most sensitive fiber optics humidity sensor reported in the literature in a similar RH range.

We review fiber-based multimode interference (MMI) devices with a particular focus on optical fiber-based sensing applications. The present review complements a recently published, extensive review where the sensing of conventional physical variables such as refractive index, temperature, displacement, and strain was covered. This review focuses on MMI fiber sensors for nonconventional physical variables, including mechanical, electromagnetic, chemical, and optical, covering around fifteen years of work in the field. Finally, by the end of this paper, we also review some new trends of MMI-based schemes based on polymer fibers, for wavelength-locking applications, for retrieving the thermo-optic coefficient of liquid samples, and for measuring the dynamics of complex fluids.

This work shows the development of a fiber optic taper machine by applying a controlled melting temperature, which is induced by a 30W CO₂ laser. The laser is made to influence the fiber, heating it and making it malleable. Then the tension axis of the device moves, having three independent axes X, Y and Z on the laser system, it is possible to mark the fiber in order of generate gratings. The device was designed entirely with low-cost materials, which are made for process optimization, such as resources. The software implemented is designed in Arduino for an IOT card that operates with HTML interface, is controlled from a website with which different variables can be handled for the operation of the taper machine, such as distance, speed and time. The device is controlled by means of Wi-Fi, through a website generating accessibility to the free operation of the engines, which can be executed over the same network. The machine has an aluminum base on which are two endless screws, connected each to a step-by-step motor that when turning in opposite directions move each one, a Fiber Holding Blocks on which the fiber is held to be stretched. The electronic circuit is located in a box attached to the motor system.

An experimental study of the switching and tuning of optical fiber ring lasers is presented. The laser wavelength switching and tuning are based on the modifiable wavelength dependent losses of a modal Michelson interferometer, which is composed by a bi-conical fiber taper spliced with a single-mode fiber piece. The wavelength dependent losses of the interferometer are inserted in a ring cavity laser to allow wavelength selection of laser wavelength peaks which induce preferences to generate laser emissions. By altering the interferometer geometrical dimensions, such as the single mode fiber piece length, and the curvature of the interferometer structure, the cavity losses can be adjusted to control the number of output laser wavelength peaks and also to cause wavelength shift of the output laser peaks, respectively. A maxim number of wavelength peaks of 13, and a maximum wavelength tuning by displacement-curvature of ∼2.3 nm mm ⁻¹ were obtained with maximum OSNR values of around 50 dBm.

In the present work, we analyze the influence of the designer’s choice of values for the human metabolic index (met) and insulation by clothing (clo) that can be selected within the ISO 7730 for the calculation of the energy demand of buildings. To this aim, we first numerically modeled, using TRNSYS, two buildings in different countries and climatologies. Then, we consistently validated our simulations by predicting indoor temperatures and comparing them with measured data. After that, the energy demand of both buildings was obtained. Subsequently, the variability of the set-point temperature concerning the choice of clo and met, within limits prescribed in ISO 7730, was analyzed using a Monte Carlo method. This variability of the interior comfort conditions has been finally used in the numerical model previously validated, to calculate the changes in the energy demand of the two buildings. Therefore, this work demonstrated that the diversity of possibilities offered by ISO 7730 for the choice of clo and met results, depending on the values chosen by the designer, in significant differences in indoor comfort conditions, leading to non-negligible changes in the calculations of energy consumption, especially in the case of big buildings.