Search for: All records

We present the design and demonstration of polarization insensitive all-dielectric metalenses operating in the mid-wave infrared (MWIR) region at around 4.6µm based on the high refractive index PbSe thin film on the BaF2 substrate. 

Surface-enhanced Raman scattering (SERS) spectroscopy is an ultra-sensitive analytical method with the powerful signal-molecule detection capability. Coupling with the polydimethylsiloxane (PDMS) material, SERS can be enabled on a polymeric substrate for fast-developing bio-compatible sensing applications. However, due to PDMS’s high viscosity, conventional PDMS-SERS substrates are typically thick and stiff, limiting their freedom for engineering flexible micro/nano functioning devices. To address this issue, we propose to adopt a low viscosity decamethylcyclopentasiloxane (D5) solvent as a diluent solution. Via controlling the mixture ratio of D5 and PDMS and the spin-coating speed for deposition, this method resulted in a film of a well-defined thickness from sub-millimeter down to a 100 nm scale. Furthermore, thanks to the unsaturated Si-H chemical bonds in the PDMS curing agent, the PDMS film could effectively reduce the Ag+ ions to Ag nanoparticles (NPs) directly bonding onto the substrate surface uniformly. Via adjusting the size and density of the AgNPs through reaction temperature and time, strong SERS was achieved and verified using R6G with the detection limit down to 0.1 ppm, attributed to the AgNPs’ plasmonic enhancement effect. 

Photonic topological insulators with boundary states present a robust solution to mitigate structure imperfections. By alteration of the virtual boundary between trivial and topological insulators, it is possible to bypass such defects. Coupled resonator optical waveguides (CROWs) have demonstrated their utility in realizing photonic topological insulators, as they exhibit distinct topological phases and band structures. With this characteristic, we designed and experimentally validated a CROW array capable of altering its topological phase by adjusting the coupling strength. This array functions partially as a topological insulator and partially as a topologically trivial array, guiding light along the virtuous boundary between these two regions. By altering the shape of the topological insulator, we can effectively control the optical path. This approach promises practical applications, such as optical switches, dynamic light steering, optical sensing, and optical computing. 

The global trends of urbanization and industrialization have given rise to critical environmental and air pollution issues that often receive insufficient attention. Among the myriad pollution sources, volatile organic compounds (VOCs) stand out as a primary cluster, posing a significant threat to human society. Addressing VOCs emissions requires an effective mitigation action plan, placing technological development, especially in detection, at the forefront. Photonic sensing technologies rooted in the infrared (IR) light and matter interaction mechanism offer nondestructive, fast-response, sensitive, and selective chemical measurements, making them a promising solution for VOC detection. Recent strides in nanofabrication processes have facilitated the development of miniaturized photonic devices and thus sparked growing interest in the creation of low-cost, highly selective, sensitive, and fast-response IR optical sensors for VOC detection. This review work thus serves a timely need to provide the community a comprehensive understanding of the state of the art in this field and illuminate the path forward in addressing the pressing issue of VOC pollution. 

This research studies the impact of the charging effect on the RIE-etched profile of narrow-slot Lead- Selenide (PbSe) gratings. By decreasing the slot width from 4 to 2 𝜇𝑚, we observed the increased irregularity and RIE-lag in etched profiles.We suggest that the charging effect is the main responsible mechanism for this phenomenon. The accumulated charge on the non-conductive photoresist plays a crucial role in forming this effect. Therefore, introducing a conductive layer can neutralize the accumulated charge and significantly improves the profile. To prove this theory, we introduced a thin layer of copper on the gratings. While without any conductive coating, we failed to etch gratings with a slot width of less than 1 𝜇𝑚, by introducing a copper layer, we succeeded etching gratings with 0.7 𝜇𝑚 slot width with the improved sidewall profiles. Hence, this technique enables us to fabricate sub-micron PbSe gratings with applications of mid-infrared (MIR) devices. 

Nanocone-patterned sapphire serves as an excellent dielectric platform for enhanced mid-infrared light–matter interactions, enabling the excitation of multiple phonon polariton and epsilon-near-zero modes in a broad Reststrahlen band. 

Designing a metasurface with appropriate phase correlation between light's linear and circular polarization states is challenging. The focus here is obtaining the geometric phases from different geometric shapes for optimum dielectric metasurface design. 

Following the formulation of cavity quantum-electrodynamical time-dependent density functional theory (cQED-TDDFT) models [Flick et al., ACS Photonics 6, 2757–2778 (2019) and Yang et al., J. Chem. Phys. 155, 064107 (2021)], here, we report the derivation and implementation of the analytic energy gradient for polaritonic states of a single photochrome within the cQED-TDDFT models. Such gradient evaluation is also applicable to a complex of explicitly specified photochromes or, with proper scaling, a set of parallel-oriented, identical-geometry, and non-interacting molecules in the microcavity.