Glasswing-Butterfly-Inspired Multifunctional Scleral Lens and Smartphone Raman Spectrometer for Point-of-Care Tear Biomarker Analysis.

Augmenting contact lenses with sensing capabilities requires incorporating multiple functionalities within a diminutive device. Inspired by multifunctional biophotonic nanostructures of glasswing butterflies, a nanostructured scleral lens with enhanced optical, bactericidal, and sensing capabilities is reported. When used in conjunction with a smartphone-integrated Raman spectrometer, the feasibility of point-of-care applications is demonstrated.

Compact meta-spectral image sensor for mobile applications.

We have demonstrated a compact and efficient metasurface-based spectral imager for use in the near-infrared range. The spectral imager was created by fabricating dielectric multilayer filters directly on top of the CMOS image sensor. The transmission wavelength for each spectral channel was selected by embedding a Si nanopost array of appropriate dimensions within the multilayers on the corresponding pixels, and this greatly simplified the fabrication process by avoiding the variation of the multilayer-film thicknesses.

High sensitivity bolometers based on metal nanoantenna dimers with a nanogap filled with vanadium dioxide.

One critical factor for bolometer sensitivity is efficient electromagnetic heating of thermistor materials, which plasmonic nanogap structures can provide through the electric field enhancement. In this report, using finite element method simulation, electromagnetic heating of nanorod dimer antennas with a nanogap filled with vanadium dioxide (VO) was studied for long-wavelength infrared detection. Because VO is a thermistor material, the electrical resistance between the two dimer ends depends on the dimer's temperature.

Tunable colloidal quantum dot distributed feedback lasers integrated on a continuously chirped surface grating.

We report a colloidal quantum dot (CQD) distributed feedback (DFB) laser structure containing a chirped grating. The device exhibits single-mode DFB lasing, of which the wavelength is spatially dispersed in a single chip. A period-chirped surface grating is fabricated using a modified Lloyd-type laser interference lithography setup, where a flat Lloyd's mirror is replaced with a concave one.

Coherent anti-Stokes Raman scattering under frequency comb excitation.

We study the efficiency of coherent anti-Stokes Raman scattering (CARS) under frequency comb excitation. We calculate the power density of the anti-Stokes signal for two major cases: (1) molecular excitation by frequency comb and cw probe and, (2) both excitation and probing by frequency combs. In the first case, average CARS power varies as an inverse third degree of frequency combs free spectral range (FSR); in the second case, it varies as FSR.

Metasurface electrode light emitting diodes with planar light control.

The ability of metasurfaces to manipulate light at the subwavelength scale offers unprecedented functionalities for passive and active lasing devices. However, applications of metasurfaces to optical devices are rare due to fabrication difficulties. Here, we present quantum dot light emitting diodes (QDLEDs) with a metasurface-integrated metal electrode and demonstrate microscopically controlled LED emission.

Ultrathin Colloidal Quantum Dot Films for Optical Amplification: The Role of Modal Confinement and Heat Dissipation.

We demonstrate optical pumping lasers based on colloidal quantum dots, with a very thin geometry consisting of a ≈20 nm thick film. Obstacles in ultrasmall laser devices come from the limitation of gain materials and the size of cavities for lasing modes, which requires a minimum thickness of the gain media (typically greater than 50-100 nm). Here we introduce dielectric waveguide structures with a high refractive index, in order to reduce the thickness of quantum dot gain media as well as their threshold energy (≈39 % compared to the original gain medium).

A colloidal quantum dot photonic crystal phosphor: nanostructural engineering of the phosphor for enhanced color conversion.

Phosphors, long-known color-converting photonic agents, are gaining increasing attention owing to the interest in white LEDs and related applications. Conventional material-based approaches to phosphors focus on obtaining the desired absorption/emission wavelengths and/or improving quantum efficiency. Here, we report a novel approach for enhancing the performance of phosphors: structural modification of phosphors.

Optical Gain in MoS2 via Coupling with Nanostructured Substrate: Fabry-Perot Interference and Plasmonic Excitation.

Despite the direct band gap of monolayer transition metal dichalcogenides (TMDs), their optical gain remains limited because of the poor light absorption in atomically thin, layered materials. Most approaches to improve the optical gain of TMDs mainly involve modulation of the active materials or multilayer stacking. Here, we report a method to enhance the optical absorption and emission in MoS2 simply through the design of a nanostructured substrate.

Modulation of the Dirac point voltage of graphene by ion-gel dielectrics and its application to soft electronic devices.

We investigated systematic modulation of the Dirac point voltage of graphene transistors by changing the type of ionic liquid used as a main gate dielectric component. Ion gels were formed from ionic liquids and a non-triblock-copolymer-based binder involving UV irradiation. With a fixed cation (anion), the Dirac point voltage shifted to a higher voltage as the size of anion (cation) increased.

Babinet-inverted optical Yagi-Uda antenna for unidirectional radiation to free space.

Nanophotonics capable of directing radiation or enhancing quantum-emitter transition rates rely on plasmonic nanoantennas. We present here a novel Babinet-inverted magnetic-dipole-fed multislot optical Yagi-Uda antenna that exhibits highly unidirectional radiation to free space, achieved by engineering the relative phase of the interacting surface plasmon polaritons between the slot elements. The unique features of this nanoantenna can be harnessed for realizing energy transfer from one waveguide to another by working as a future "optical via".

Ultrahigh-Q one-dimensional photonic crystal nanocavities with modulated mode-gap barriers on SiO2 claddings and on air claddings.

We report designs for a silicon-on-insulator (SOI) one-dimensional (1D) photonic crystal (PhC) nanocavity with modulated mode-gap barriers based on the lowest dielectric band. These cavities have an ultrahigh theoretical quality factor (Q) of 10(7)-10(8) while maintaining a very small modal volume of 0.6-2.

Photonic crystal alloys: a new twist in controlling photonic band structure properties.

We identified new photonic structures and phenomenon that are analogous to alloy crystals and the associated electronic bandgap engineering. From a set of diamond-lattice microwave photonic crystals of randomly mixed silica and alumina spheres but with a well defined mixing composition, we observed that both bandedges of the L-point bandgap monotonically shifted with very little bowing as the composition was varied. The observed results were in excellent agreement with the virtual crystal approximation theory originally developed for electronic properties of alloy crystals.