Abstract
Topological photonics, leveraging concepts from condensed matter physics, offers transformative potential in the design of robust optical systems. This study investigates the integration of topologically protected edge states into plasmonic nanostructures for enhanced optical sensing. We propose a toy model comprising two chains of metallic filaments forming a one-dimensional plasmonic crystal with diatomic-like unit cells, positioned on a waveguide. The system exhibits edge states localized at the boundaries and a central defect, supported by the Su-Schrieffer-Heeger (SSH) model. These edge states, characterized by significant electric field enhancement and topological robustness, are shown to overcome key limitations in traditional plasmonic sensors, including sensitivity to noise and fabrication inconsistencies. Through coupled mode theory, we demonstrate the potential for strong coupling between plasmonic and guided optical modes, offering pathways for improved interferometric sensing schemes. This work highlights the applicability of topological photonics in advancing optical sensors.

Abstract
This study explores the application of machine learning algorithms to optimize the geometry of the plasmonic layer in a surface plasmon resonance photonic crystal fiber sensor. By leveraging the simplicity of linear regression ( LR) alongside the advanced predictive capabilities of the gradient boosted regression (GBR) algorithm, the proposed approach enables accurate prediction and optimization of the plasmonic layer's configuration to achieve a desired spectral response. The integration of LR and GBR with computational simulations yielded impressive results, with an R-2 exceeding 0.97 across all analyzed variables. Moreover, the predictive accuracy demonstrated a remarkably low margin of error, epsilon < 10(-15). This combination of methods provides a robust and efficient pathway for optimizing sensor design, ensuring enhanced performance and reliability in practical applications.

Abstract
In our study, we conducted a thorough analysis of the spectral characteristics of a D-shaped surface plasmon resonance (SPR) photonic crystal fiber (PCF) refractive index sensor, incorporating a full width at half maximum (FWHM) analysis. We explored four distinct plasmonic materials—silver (Ag), gold (Au), Ga-doped zinc oxide (GZO), and an Ag-nanowire metamaterial—to understand their impact on sensor performance. Our investigation encompassed a comprehensive theoretical modeling and analysis, aiming to unravel the intricate relationship between material composition, sensor geometry, and spectral response. By scrutinizing the sensing properties offered by each material, we laid the groundwork for designing multiplasmonic resonance sensors. Our findings provide valuable insights into how different materials can be harnessed to tailor SPR sensing platforms for diverse applications and environmental conditions, fostering the development of advanced and adaptable detection systems. This research not only advances our understanding of the fundamental principles governing SPR sensor performance but also underscores the potential for leveraging varied plasmonic materials to engineer bespoke sensing solutions optimized for specific requirements and performance metrics. © 2025 SBMO/SBMag.

Abstract
Carbon dioxide (CO2) plays a crucial role in the biosphere, acting as an indicator of anthropogenic activity. Its monitoring is fundamental for controlling air and water quality, preserving the environment and optimizing industrial processes. The preparation of a bright fluorescent scaffold, named rhodol, was optimized by employing microwave heating as an alternative heating source, achieving shorter reaction times and higher yields. Structural characterization was performed by nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRMS-ESI). Its application to produce a fluorescent optical membrane for monitoring CO2 in gas (gCO2) and in water (dCO2) was explored. Two different setups are used for this purpose, and in both, the same optical response is observed: the membrane's fluorescence intensity decreases as the CO2 concentration increases. The sensor's reliability for dCO2 is demonstrated through testing concentrations ranging from 1 ppm to 100 ppm with minimal photobleaching (0.0026 dB) over 7500 data points with an integration time of 200 ms each. The sensor performance for dCO2 evaluation exhibits an experimental error of +/- 1.81 ppm, a response time of 2 min, a limit of detection of 0.6 ppm and a Stokes-shift of 90 nm for concentrations between 1 and 100 ppm. Monitoring of gCO2 using this membrane is hindered by changes in relative humidity (RH), hence the results for concentration between 0.3 % and 100 % of gCO2 were achieved by maintaining a consistent high value of RH. Our findings highlight the effectiveness of the optimized rhodol synthesis and its application in an optical membrane for reliable monitoring of CO2 in various environmental conditions.

Abstract
Optical sensing exploiting plasmonics and other types of surface waves provides exceptional performance for chemical and biological detection due to its high sensitivity and real-time capabilities. This study explores the integration of thin films with plasmonic, specifically leveraging metallic and dielectric nano structures, fabricated through sputtering and colloidal synthesis techniques. Advanced surface wave excitations such as localized surface plasmon resonances (SPR), Tamm Plasmon Polaritons (TPP), Bloch surface waves, and surface plasmon polaritons (SPP) are used to amplify sensor performance. Simulations and experimental data show that these nanostructured coatings significantly enhance electromagnetic field confinement, leading to improved detection limits and sensor robustness, showcasing promising applications in environmental monitoring, gas detection, and biomedical diagnostics.

Abstract

A novel technique based on multiple amplitude wavelength modulation spectroscopy (MA-WMS) for simultaneous measurement of CH4 gas concentration and pressure was developed and validated both through simulation and experiment, showing good agreement. To capture the spectrum broadening caused by increasing pressure and concomitantly obtain the concentration at the sensor’s location, a laser centered at 1650.9 nm was subjected to multiple amplitude modulation depths while the 2fm signal, normalized by the DC component (an invariant quantity under optical loss), was recorded. While the use of a single and fixed modulation can introduce an ambiguity, as different pairs of pressure and concentration can yield the same value, this ambiguity is eliminated by employing multiple amplitude modulations. In this approach, the intersection point of the three level curves can provide the local pressure and concentration. The proposed system was able to measure concentrations from a few percentage points up to 50% and pressure from 0.02 atm up to 2 atm, with a maximum error of 2% in concentration and 0.06 atm in pressure, respectively. The system was also tested for attenuation insensitivity, demonstrating that measurements were not significantly affected for up to 10 dB applied optical loss.