Quantum Optoelectronics

Abstract:

The miniaturization and enhanced functionality of LiDAR systems present critical challenges in automotive sensing technologies, particularly in achieving efficient wide-angle beam scanning while maintaining compact form factors. We demonstrate a novel dual-wavelength polarization-selective concave metalens operating at 904 nm and 940 nm wavelengths, the standard operating wavelengths for LiDAR systems. By engineering rectangular TiO2 nanopillars on a quartz substrate, we achieved simultaneous polarization filtering and concave phase profile functionality within a single metasurface layer. The optimized 600 nm × 600 nm unit cell design with 1.7 μm height nanopillars enables full 2π phase coverage while maintaining high transmission efficiency for the desired polarization state. Our fabricated metalens exhibits remarkable polarization extinction ratios (ER) of 124:1 and 102:1 at 904 nm and 940 nm wavelengths, respectively. Angular-resolved measurements demonstrate wide beam divergence angles of 148° and 138° at the respective wavelengths, with 50 % of total power contained within ± 38° and ± 25°.

Abstract:

Achieving efficient optical coupling between the emission from perovskite quantum dots (PQDs) and photonic integrated elements requires ultranarrow linewidths and highly directional emission. These are challenging goals at room temperature due to the broad and isotropic nature of perovskite emission. Here, we demonstrate ultranarrow‐linewidth emission from CsPbBr3 PQDs at room temperature, in both spontaneous and stimulated regimes, by coupling to state‐of‐the‐art open‐access curved dielectric cavities under continuous wave excitation. The emission is confined to a single transverse electromagnetic mode of the cavity, achieving a remarkably narrow linewidth of 0.2 nm, ≈100× narrower than free‐space emission in both the emission regime. Single‐mode lasing from a small number of PQDs is observed, yielding a quality factor of ≈2590, among the highest reported for single‐mode lasing. The open‐access design enables precise tuning of cavity length and selective coupling of emitters in their native state, overcoming the limitations associated with closed and fixed‐length vertical‐cavity surface emitting laser geometries. The geometry's low divergence and tunability provide an efficient route for integrating perovskite emitters with on‐chip photonic circuits, advancing their use in quantum and optoelectronic technologies.

Abstract:

We report the fabrication of nanoscale MoS2 (nMoS2) via laser ablation in liquid and its application in electrochemical sensing. The laser ablation process fragments microscale MoS2 sheets into ~5 nm dots with stable aqueous dispersibility. Electrochemical analysis reveals that nMoS2 possesses multiple reversible redox states, enabling it to participate in redox cycling reactions that can amplify electrochemical signals. When the nMoS2 is embedded in an electrochemically inert matrix, a chitosan layer, and subsequently incorporated within a nanostructured Au electrode, the nMoS2-participating redox cycling reactions are further enhanced by the nanoconfinement effect, leading to synergistic signal amplification. As a model system, this hybrid nMoS2-in-nanoporous Au electrode demonstrates a 9-fold increase in sensitivity for detecting pyocyanin, a biomarker of Pseudomonas aeruginosa infection, compared with a flat electrode without nMoS2 loading. This study not only elucidates the redox characteristics of laser-fabricated zero-dimensional transition metal dichalcogenides but also presents a strategy to integrate semiconducting nanomaterials with metallic nanostructures for high-performance electrochemical sensing.

Abstract:

The accelerating growth of the hydrogen (H2) economy is pivotal for achieving large-scale decarbonization of current energy resources. Ensuring safe and efficient handling of this potentially hazardous resource has led to an increasing demand for fast, selective and reliable H2 sensors. In this work, we report a nanohybrid H2 sensing platform comprising uniformly dispersed AuPd bimetallic nanoparticles (BNPs) embedded in a ZnO-based metal oxide semiconductor (MOS) matrix infiltrated within an anodized porous silicon (PSi) framework. This hybrid design (PSi-MOS#AuPd) synergistically merges the strong chemisorption affinity and rapid desorption kinetics of Pd with the enhanced catalytic activity and electronic modulation imparted by AuPd interactions. Precise control over BNPs thickness (~ 8.6 nm) ensures uniform dispersion and effectively mitigates the inherent volume expansion of Pd during hydrogenation, maintaining structural integrity and catalytic efficiency. The PSi support characterized by high porosity (~1.1 μm) and superhydrophobicity (θ w  = 153.6° ± 0.2°), promotes efficient gas diffusion and enhances humidity resilience. The resulting sensor exhibits remarkable performance, including high sensitivity ~46 %@50ppm, low-operating temperature (~90 °C), rapid response time (~14 s), excellent stability over 60 days and strong selectivity against interfering gases (H2S, NH3, NO2, and CO) under varying humidity conditions (25–85 % RH). This work paves the way for the advancement of H2 sensors and highlights the potential of substrate engineering and bimetallic synergy in enhancing gas sensing technology for safety-critical applications.

Abstract:

Advancements in utilizing low refractive index dielectric particles have implications for sensing, lasing, and strong‐coupling at nano and microscopic scales. These cavities offer benefits like ease of fabrication and biocompatibility, making them promising for a wide range of technologies by utilizing their narrow linewidth modes. However, optical modes sustained in these dispersive systems can show distinct behaviors depending on the detection configuration. This study shows the influence of numerical aperture (NA) of the objective lens on the detection of Mie modes in a dielectric microsphere under far‐field excitation and collection. It is demonstrated experimentally and numerically that Mie modes from microspheres outcouple at different angles, with variations in mode amplitudes contingent on the NA of the objective lens, thus leading to distinct linewidths while probing with different NA objectives. Furthermore, it is shown that metallic substrates can facilitate efficient detection of Mie modes by redirecting scattered modes towards low angles. This enables mode detection with low NA lenses and further preventing the inclusion of incident scattered light from higher angles which otherwise perturb the modes. The results underline the importance of careful detection strategies to fully harness dielectric particles as optical platforms for applications in particle detection and characterization.