Mid-infrared (MIR) photonic sensors are revolutionizing optical sensing by enabling precise chemical and biological detection through the interrogation of molecules’ unique vibrational modes. This review explores the core principles of MIR photonics, emphasizing the light–matter interactions within the 2–20 µm wavelength range. Additionally, it examines innovative sensor architectures, such as integrated photonic platforms and optical fibers, that enhance sensitivity, specificity, and device miniaturization. The discussion extends to groundbreaking applications in environmental monitoring, medical diagnostics, industrial processes, and security, highlighting the transformative impact of these technologies. This comprehensive overview aims to illuminate the current state-of-the-art while inspiring future developments in MIR photonic sensing.

We present a multicore fiber dedicated for next generation transmission systems. To overcome the issue of multicore fibers' integration with existing transmission systems, the fiber is designed in such a way that the transmission parameters for each core (i.e., chromatic dispersion, attenuation, bending loss, etc.) are in total accordance with the obligatory standards for telecommunication single core fibers (i.e., ITU-T G.652 and G.657). We show the results of numerical investigations and measurements carried out for the fabricated fiber, which confirm low core-to-core crosstalk and compatibility with standard single-core single-mode transmission links making the fiber ready for implementation in the near future.

We present an extensive study of resonant two-dimensional (2D) plasmon excitations in grating-gated quantum well heterostructures, which enable an electrical control of periodic charge carrier density profile. Our study combines theoretical and experimental investigations of nanometer-scale $\mathrm{AlGaN}/\mathrm{GaN}$ grating-gate structures and reveals that all terahertz (THz) plasmonic resonances in these structures can be explained only within the framework of the plasmonic crystal model. We identify two different plasmonic crystal phases. The first is the delocalized phase, where THz radiation is absorbed with the entire grating-gate structure that is realized at a weakly modulated 2D electron gas (2DEG) regime. In the second, the localized phase, THz radiation interacts only with the ungated portions of the structure. This phase is achieved by fully depleting the gated regions, resulting in strong modulation. By gate controlling of the modulation degree, we observe a continuous transition between these phases. We also discover that, unexpectedly, the resonant plasma frequencies of ungated parts (in the localized phase) still depend on the gate voltage. We attribute this phenomenon to the specific depletion of the conductive profile in the ungated region of the 2DEG, the so-called edge gating effect. Although we study a specific case of plasmons in $\mathrm{AlGaN}/\mathrm{GaN}$ grating-gate structures, our results have a general character and are applicable to any other semiconductor-based plasmonic crystal structures. Our work represents the first demonstration of an electrically tunable transition between different phases of THz plasmonic crystals, which is a crucial step toward a deeper understanding of THz plasma physics and the development of all-electrically tunable devices for THz optoelectronics.

In this Letter we present, for the first time to our knowledge, the results of fiber Bragg grating (FBG) inscription in a novel microstructured multicore fiber characterized by seven single-mode isolated cores. A clear Bragg reflection peak can be observed in all of the 7 cores after one inscription process with a KrF nanosecond laser in a Talbot interferometer set up. We furthermore perform a numerical analysis of the effective refractive indices of the particular modes and compare it with the FBG inscription results. An experimental analysis of the strain and temperature sensitivities of all of the Bragg peaks is also included.

Microstructured optical fibers can be precisely tailored for many different applications, out of which sensing has been found to be particularly interesting. However, placing silica optical fiber sensors in harsh environments results in their quick destruction as a result of the hydrolysis process. In this paper, the degradation mechanism of bare and metal-coated optical fibers at high temperatures under longitudinal strain has been determined by detailed analysis of the thermal behavior of silica and metals, like copper and nickel. We furthermore propose a novel method of enhancing the lifetime of optical fibers by the deposition of electroless nickel-phosphorous alloy in a low-temperature chemical process. The best results were obtained for a coating comprising an inner layer of copper and outer layer of low phosphorous nickel. Lifetime values obtained during the annealing experiments were extrapolated to other temperatures by a dedicated model elaborated by the authors. The estimated copper-coated optical fiber lifetime under cycled longitudinal strain reached 31 h at 450 °C.

In optical communication and sensing, silicon nitride (SiN) photonics plays a crucial role. By adeptly guiding and manipulating light on a silicon-based platform, it facilitates the creation of compact and highly efficient photonic devices. This, in turn, propels advancements in high-speed communication systems and enhances the sensitivity of optical sensors. This study presents a comprehensive exploration wherein we both numerically and experimentally display the efficacy of a SiN-based ring resonator designed for refractive index sensing applications. The device’s sensitivity, numerically estimated at approximately 110 nm/RIU, closely aligns with the experimental value of around 112.5 nm/RIU. The RR sensor’s Q factor and limit of detection (LOD) are 1.7154 × 10⁴ and 7.99 × 10⁻⁴ RIU, respectively. These congruent results underscore the reliability of the two-dimensional finite element method (2D-FEM) as a valuable tool for accurately predicting and assessing the device’s performance before fabrication.