We propose a novel photonic crystal fiber refractive index sensor which is based on the selectively resonant coupling between a conventional solid core and a microstructured core. The introduced microstructured core is realized by filling the air-holes in the core with low index analyte. We show that a detection limit (DL) of 2.02 × 10⁻⁶ refractive index unit (RIU) and a sensitivity of 8500 nm/RIU can be achieved for analyte with refractive index of 1.33.

We experimentally demonstrate an automatic arc discharge technology for inscribing high-quality helically twisted long period fiber gratings (H-LPFGs) with greatly improved inscription efficiency for single mode fibers. The proposed technology has been developed by implementing an embedded program in a commercial fusion splicer, which employs an ultraprecision motorized translation stage while the tensioning mass required by conventional inscribing technology is eliminated. More significantly, the arc-induced H-LPFGs have been reported to have potential usage as sensors in temperature, refractive index, twist stress, and strain.

We propose a design for a novel broadband polarization splitter based on an asymmetric dual-core square-lattice photonic-crystal fiber. The fiber is designed such that index-matched coupling between the two cores can be achieved for one polarization state, while only a part of the energy could be coupled for the other polarization state. Numerical results demonstrate that a device length of $5.9\mathrm{mm}$ shows extinction ratios as low as $-20\mathrm{dB}$ with bandwidths as great as $101\mathrm{nm}$.

Surface-enhanced Raman scattering (SERS) technology, leveraging its single-molecule-level detection sensitivity, molecular fingerprint recognition capability, and capacity for rapid, non-destructive analysis, has emerged as a pivotal analytical tool in food science, life sciences, and environmental monitoring. This review systematically summarizes recent advancements in SERS technology, encompassing its enhancement mechanisms (synergistic effects of electromagnetic and chemical enhancement), innovations in high-performance substrates (noble metal nanostructures, non-noble metal substrates based on semiconductors/graphene, and hybrid systems incorporating noble metals with functional materials), and its interdisciplinary applications. In the realm of food safety, SERS has enabled the ultratrace detection of pesticide residues, mycotoxins, and heavy metals, with flexible substrates and intelligent algorithms significantly enhancing on-site detection capabilities. Within biomedicine, the technique has been successfully applied to the rapid identification of pathogenic microorganisms, screening of tumor biomarkers, and viral diagnostics. For environmental monitoring, SERS platforms offer sensitive detection of heavy metals, microplastics, and organic pollutants. Despite challenges such as matrix interference and insufficient substrate reproducibility, future research directions aimed at developing multifunctional composite materials, integrating artificial intelligence algorithms, constructing portable devices, and exploring plasmon-catalysis synergy are poised to advance the practical implementation of SERS technology in precision diagnostics, intelligent regulation, and real-time monitoring.

Numerical investigation on the design of a novel kind of large-mode-area optical fiber is presented. Low bending loss propagation in the fiber is achieved by the introduction of low-index rods with small period and large normalized diameter in one segment of the cladding. Single-mode operation is realized by the introduction of low-index rods with large period and small normalized diameter in another segment of the cladding. When a conventional large-mode-area optical fiber is bent, it will generally experience large bend distortion and the mode area will reduce accordingly. To avoid that, a bend-resistant design by introducing a microstructure into the solid core of the proposed fiber is proposed. In particular, the mode area of one such fiber is always larger than 2000 μ m² when the bending radius is larger than 30 cm at the wavelength of 1.064 μm.