In this talk, I will present several design concepts for nanolasers based on collective resonances of dielectric nanoantennas. The interference of collective resonances associated with the bound state in the continuum (BIC) or Van Hove singularity will be discussed in detail based on Mie theory analysis. I will show experimentally and theoretically various directional nanolasers made out of GaAs at cryogenic temperature. By using a more efficient gain material such as CdSe/CdxZn1-xS nanoplatelets or InGaP multi-quantum well, room temperature lasing operation is also illustrated. This work presents design guidelines for high-performance in-plane and out-of-plane lasers, which may find broad applications in nanophotonics.
High-refractive index dielectric nanostructures with both electric and magnetic responses to external optical field have recently become a hot topic in nanophotonics. The resonances inside these particles at subwavelength scale are governed by the nanoparticle geometry and can be described by Mie theory. There has been many potential applications based on this concept such as: light beam focusing, bending, hologram generation, etc. Recently, lasing behavior have been realized in these systems by combining these resonance with the bound state in the continuum. In this presentation, we will show how to engineer these resonances and their strong coupling effect to create effective optical cavities for lasing with controlled emission directionality both in-plane and out-of-plane. The coupling of Mie resonances will be discussed in three different cases: 2D arrays, 1D chains and single nanoparticles. In all cases, by carefully designing the geometry and periodicity of these nanoparticles, highly localized states or so-called supercavities can be formed by strong coupling of dipole or multipole resonances of individual nanoparticles. Using GaAs – a common III-V semiconductor- as both dielectric nanoantenna and gain medium, we demonstrate experimentally unprecedented lasing behavior in these systems by optical pumping at cryogenic temperature. Our design concept will provide a guideline for nanolasers with controllable directionality for optoelectronic applications.
A theoretical study is presented on planar micro-optic solar concentrators. These can be inexpensively fabricated using nanoimprinting techniques and can provide indoor illumination. Multiple combinations of lenslet array designs and coupling features are optimized, and full system efficiencies are evaluated by ray-tracing simulations. Concentrator designs are optimized with considerations of suitability to tropical regions. A design capable of near-unity efficiency at up to 18-deg field angles and up to 92.14% collection efficiency within ±30-deg incident angle is reported. A cost analysis is then performed using meteorological data.
We have successfully fabricated and measured our silicon bridge waveguide polarization beam splitter (PBS). Our proposed PBS is based on a bend directional coupler with a bend bridge waveguide and is experimentally realized using silicon waveguide thickness of 220 nm and 250 nm, which are the commonly used silicon thickness for silicon photonics manufacturing. Our experimental results demonstrated high extinction ratio of > 20 dB for the TE-like mode, and > 15 dB for the TM-like mode across a broad bandwidth of 90 nm that covers the entire C-band with a small footprint of ~18×9 μm2. On-chip high performance PBS is important for polarization diversity in integrated photonics, and for communication applications such as dual-polarization quadrature phase-shift keying (DP-QPSK) modulation.
KEYWORDS: Solar concentrators, Prisms, Waveguides, Channel waveguides, Absorption, Interfaces, Energy efficiency, Solar cells, Microlens array, Refractive index
Thin form-factor planar sunlight concentrators fabricated using low-cost materials in conjunction with high-efficiency solar cells may prove economically competitive with silicon photovoltaics. A periodic structure with planar interfaces employing an array of microlenses and coupling structures is amenable to high-volume imprint manufacturing and hence a drastic cost reduction. A numerical study of periodic prismatic void structures aligned with microlenses to efficiently couple incoming light into a constant cross-section channel waveguide is reported. Three different prism-like cut-out structures: a bare prism, a planar connected prism, and a pointed prism are proposed. Numerical results show that the proposed pointed prism design offers a high-efficiency coupling with one-sided output (90.8% and 85.4% peak efficiency at concentration ratios of 320× and 400×, respectively).
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