In this study, we present a novel surface-enhanced Raman scattering (SERS) substrate based on porous silicon microcavities (PSiMCs) decorated with silver nanoparticles (AgNPs) for ultra-sensitive molecule detection. This substrate utilizes a dual enhancement mechanism: the localized surface plasmon resonance (LSPR) of AgNPs and the optical resonance of the PSiMC structure, which together create intense electromagnetic hot spots and prolong photon–molecule interactions. The porous architecture provides a large surface area for uniform nanoparticle distribution and efficient analyte adsorption. The AgNP/PSiMC substrate demonstrates an impressive detection limit of 1.0 × 10⁻¹³ M for rhodamine101 and 1.0 × 10⁻¹⁰ M for methyl parathion, outperforming many previously reported SERS platforms. Furthermore, the substrate exhibits excellent signal uniformity (RSD ≈ 6.14%) and long-term stability, retaining over 50% signal intensity after 28 days. These results underscore the potential of AgNP/PSiMCs as highly efficient, reproducible, and scalable SERS platforms for trace-level chemical and environmental sensing applications.

Slotted photonic crystal (SPC) cavities provide strong evanescent fields, high quality factors, and small mode volumes. Hence, SPC cavities have been identified as promising candidates for the implementation of high-performance sensors and the development of hybrid devices combining silicon with other active materials. Nevertheless, most state-of-the-art demonstrations rely on electron beam lithography and operate in the telecommunications band near the 1550 nm wavelength. Here, we report the experimental demonstration of SPC cavities operating in the datacom O-band, near 1340 nm wavelength, fabricated using deep-ultraviolet (DUV) lithography. The O-band provides very interesting properties for sensing, communications, and hybrid integration: namely, lower optical absorption of water, lower dispersion in standard optical fibers, and the emission of active materials like carbon nanotubes. On the other hand, DUV fabrication opens interesting opportunities for large volume production. The proposed cavities exhibit a high quality factor exceeding 20,000 and a small mode volume of 0.023 ( λ / n ) 3 . These results open interesting perspectives to exploit enhanced light–matter interaction in SPC cavities harnessing industrial-like fabrication processes.

In this study, we present the experimental evidence demonstrating the utility of electrical double layer (EDL)-induced ion accumulation, using sodium (Na+) ion in water as model substances, on a negatively charged nanostructured surface, specifically thermally grown silicon dioxide (SiO2). This novel approach, termed Ion Surface Accumulation (ISA), aims to enhance the performance of nanostructured porous silicon (PSi) interferometers in optical refractometric applications. The experimental results show that the electrical double layer-induced ion surface accumulation (EDL-ISA) on oxidized PSi interferometers enables remarkable amplification of the interferometer output signal (the spectral interferogram), even when the bulk refractive index variation is below 10-3 RIU. This substantial signal enhancement translates into an increase in sensitivity of up to two orders of magnitude, facilitating the reliable measurement of refractive index variations with both a detection limit (DL) and resolution (R) as low as 10-4 RIU. This achievement elevates the performance of PSi interferometers in photonics and plasmonics-based refractive index platforms.

In this paper, we report a new type of refractometer based on a D-shaped fiber Bragg grating (FBG) integrated in a loop-mirror optical fiber laser. This proposed sensor is used in wavelength interrogation method, in which the D-shaped FBG is applied as a refractive index (RI) sensing probe and a mirror to select mode of laser. The D-shaped FBG is prepared by the removal of a portion of the fiber cladding covering the FBG by means of side-polishing technique. The D-shaped FBG sensing probe integrated in a loop-mirror optical fiber laser with saturated pump technique, the characteristics of sensing signals have been improved to obtain stable intensity, narrower bandwidth and higher optical signal-to-noise ratio compare to normal reflection configuration. The limit of detection (LOD) of this sensor can be achieved to 2.95 x 10^-4 RIU in the refractive index (RI) range of 1.42-1.44. Accordingly, we believe that the proposed refractometer has a huge potential for applications in biochemical-sensing technique.

This work reports the optical properties of surface plasmon resonance (SPR) based on the metal-insulator-metal (MIM) structure towards a refractive index sensor. The MIM-SPR structure operating near infrared region consists of lateral periodicity of subwavelength gold patterns placed on a stack of thin silica spacer and silver film (acting as a reflector) on a silicon substrate. The reflection spectra and the electric field distributions of MIM-SPR structures can be tuned by modifying the geometrical properties and have been numerically investigated by using Lumerical’s finite-difference time-domain (FDTD) solutions. The square lattice configuration of 1200 nm to 1400 nm pitch of gold micro-disks of thickness from 80 nm to 120 nm have been conducted. The size of these considered gold patterns, i.e., the diameter of the micro-disks is in the range of 900 nm to 1000 nm. The proposed MIM-SPR structure possessing sensitivity of 370 nm per refractive index unit (RIU), can be applicable for a wide variety of plasmonic sensing, in particular for refractometric biosensors.