Joaquim Ferreira Martins Filho

Climacteric fruit respiration generates carbon dioxide (CO2), making its real-time monitoring crucial for optimizing storage and transport conditions, minimizing economic losses and waste. This work demonstrates the application of Wavelength Modulation Spectroscopy (WMS) for the development of a sensor capable of measuring CO2 concentration in real time with high precision and reproducibility. For the technique, a Distributed-Feedback diode laser was used, tuned to the 1572.3 nm CO2 absorption line. The temporal evolution of CO2 concentration released by tomato and banana at different ripening stages was measured. The sensor exhibited a detection limit for CO2 variations ranging from 122 to 488 parts per million (ppm). The results demonstrate the applicability of WMS for monitoring fruit respiration. The normalization technique second harmonic/first harmonic (2f/1f) proved essential for mitigating thermal effects, as the 1f signal corrects for laser power and non-absorption losses, thus enhancing data reliability. Analysis of CO2 evolution curves suggests the potential to study gas diffusion phenomena within fruits, evidenced by the sigmoidal profile. This sensor has potential for future applications in modified atmosphere packaging (MAP) and quality control.

The increasing demand for bandwidth in modern communication networks has highlighted the need for efficient and dynamic resource allocation. Elastic Optical Networks address this challenge by enabling flexible spectrum and power assignment. This paper proposes an advanced resource allocation technique based on multi-objective optimization (MOO) to jointly optimize spectrum and power, mitigating nonlinear impairments and enhancing network performance. When a connection request arrives at the Call Admission Control, all possible frequency slot demands are generated by combining the requested bit rate with the available modulation formats. The Min Slot Continuity Capacity Loss (MSCL) heuristic selects routes and slot sets to minimize allocation capacity loss for each modulation level. From this process, a matrix of frequency slot combinations is built and subsequently explored by the MOO framework. The proposed method integrates the MSCL heuristic with power assignment to reduce spectrum fragmentation and select optimal power levels, thereby improving the optical signal-to-noise ratio. By jointly considering spectrum positioning, channel powers, amplified spontaneous emission noise, and nonlinear effects, the approach achieves significant performance gains. Simulation results demonstrate that the proposed method outperforms the Power and MSCL (P-MSCL) algorithm, achieving an approximately 11% reduction in blocking probability under a 180 Erlang load in the NSFNET topology with identical parameters.

This manuscript presents the feasibility of designing a digital Lock-In Amplifier (LIA) for measuring experimental sys-tems through optical measurement techniques, from 32-bit micro-controller platforms, derived from the technology coming from the Internet of Things (IoT). As a proof of concept, the STM32F446RE microcontroller was used, in which the resident program uses the Direct Digital Synthesis (DDS) and synchronous detection tech-nique to promote lock-in processing from harmonic signals gener-ated in 2f. The digital LIA was tested to detect C2H2 (Acetylene) concentrations in a spectrometric cell by Wavelength Modulation Spectroscopy (WMS). The experimental setup also included a DFB laser and other optical components. The comparative analysis with the Signal Recovery® DSP7265 benchtop LIA showed that both systems effectively measured up to 54 ppm of C2H2. A strong Pearson correlation (r>0.8) was observed for all measurements performed. This confirms its potential for applications in situ nonlinear optical spectroscopy, especially WMS.

This paper presents an experimental evaluation of a hetero-core MNM fiber-optic sensor designed for monitoring electrolyte density in lead-acid batteries. The study focuses on two key aspects that affect sensor performance: electrolyte contamination and temperature variation. Spectral analysis reveals that although the sensor's sensitivity slightly decreases with contamination, it remains effective and suitable for long-term applications. Furthermore, experiments were conducted to assess how temperature influences the optical response at low (1100 g/L) and high (1290 g/L) electrolyte concentrations. Results indicate that electrolyte density is temperature-dependent, and significant shifts in optical response were observed with thermal variation. Therefore, incorporating temperature monitoring and compensation is essential to ensure accurate and reliable density measurements. These findings support the feasibility of the proposed sensor for real-time applications, provided proper temperature correction is implemented.

This paper presents the characterization of a heterocore fiber optic refractive index (RI) sensor for discrete interrogation as a function of wavelength. The structure consists of a single-mode, no-core fiber, single-mode fiber (SNS) configuration, demonstrated both experimentally and through simulations. The sensor, with a no-core fiber section of 14.4 mm, achieved a sensitivity of 226.2 dB/RIU in the RI range of 1.3154 to 1.4237 at 1550 nm.

This work investigates the influence of curvature radius on the response of plastic optical fiber (POF) sensors. Using polymethyl methacrylate (PMMA) fibers, sensors with different bending radii were fabricated through a controlled heating and cooling process. Their sensitivity was evaluated by immersing the curved fibers in sodium chloride solutions of varying concentrations and measuring the transmitted optical signal using a 650 nm LED and a photodetector. Results indicate a near-linear relationship between refractive index and output voltage for intermediate radii, with a maximum sensitivity of 13.613 V/RIU observed at a 4 mm curvature. Smaller radii enhance sensitivity due to increased signal interaction with the external medium, though at the cost of greater optical losses. Larger radii exhibit reduced sensitivity and narrower detection ranges. These findings underscore the importance of curvature optimization in designing refractive index sensors and provide valuable insights for selecting appropriate radii based on specific application requirements.