arXiv subjects

Jack Hu

Publications and source records attributed to Jack Hu.

5 recordsLinked to original sources

arXiv2025

GHz-speed wavefront shaping metasurface modulators enabled by resonant electro-optic nanoantennas

Electrically tunable metasurfaces that control the amplitude and phase of light through biasing of nanoscale antennas present a route to compact, sub-micron thick modulator devices. However, most platforms face limitations in bandwidth, absolute optical efficiency, and tuning response. Here, we present electro-optically tunable metasurfaces capable of both GHz amplitude modulation and transmissive wavefront shaping in the telecom range. Our resonant electro-optic nanoantenna design consists of a silicon nanobar atop thin-film lithium niobate, with gold electrodes. The silicon nanobar is a periodically perturbed optical waveguide that supports high quality factor (Q $>$ 1000) guided mode resonances excited with free space light. Applying a voltage bias to the lithium niobate tunes its refractive index, modulating the resonant behavior of the silicon nanobar through evanescent mode overlap. We demonstrate an absolute transmittance modulation of 7.1% with $\pm$5 V applied voltage, and show the dependence of this modulation behavior on the resonance quality factor. We additionally study the electrode limitations on modulation bandwidth, demonstrating bandwidths exceeding 800 MHz. Finally, we show how this resonant antenna platform can be used to design wavefront shaping metasurfaces. We demonstrate a beamsplitting metasurface device, whose diffraction efficiency can be modulated with a bandwidth of 1.03 GHz. The high-speed modulation and wavefront control capabilities of this platform provide a foundation for compact, high bandwidth free space communications and sensing devices.

physics.optics↗

arXiv2023

Very-Large-Scale-Integrated High-$Q$ Nanoantenna Pixels (VINPix)

Metasurfaces provide a versatile and compact approach to free-space optical manipulation and wavefront shaping. Comprised of arrays of judiciously-arranged dipolar resonators, metasurfaces precisely control the amplitude, polarization, and phase of light, with applications spanning imaging, sensing, modulation, and computing. Three crucial performance metrics of metasurfaces and their constituent resonators are the quality factor ($Q$-factor), mode-volume ($V_m$), and the ability to control far-field radiation. Often, resonators face a trade-off between these parameters: a reduction in $V_m$ leads to an equivalent reduction in $Q$, albeit with more control over radiation. Here, we demonstrate that this perceived compromise is not inevitable $-$ high-$Q$, subwavelength $V_m$, and controlled dipole-like radiation can be achieved, simultaneously. We design high-$Q$, very-large-scale integrated silicon nanoantenna pixels $-$ VINPix $-$ that combine guided mode resonance waveguides with photonic crystal cavities. With optimized nanoantennas, we achieve $Q$-factors exceeding 1500 with $V_m$ less than 0.1 $(\lambda/n_{\text{air}})^3$. Each nanoantenna is individually addressable by free-space light, and exhibits dipole-like scattering to the far-field. Resonator densities exceeding a million nanoantennas per $\text{cm}^2$ can be achieved, as demonstrated by our fabrication of an 8 mm x 8 mm VINPix array. As a proof-of-concept application, we demonstrate spectrometer-free, spatially localized, refractive-index sensing utilizing a VINPix array. Our platform provides a foundation for compact, densely multiplexed devices such as spatial light modulators, computational spectrometers, and in-situ environmental sensors.

physics.optics↗

arXiv2022

Achiral dielectric metasurfaces for spectral and polarization control of valley specific light emission from monolayer MoS2

Excitons in two-dimensional transition metal dichalcogenides have a valley degree of freedom that can be optically accessed and manipulated for quantum information processing. Here, we integrate MoS2 with achiral silicon disk array metasurfaces to enhance and control valley-specific absorption and emission. Through the coupling to the metasurface Mie modes, the intensity and lifetime of the emission of neutral excitons, trions and defect bound excitons can be enhanced, while the spectral shape can be modified. Additionally, we demonstrate the symmetric enhancement of the degree-of-polarization (DOP) of neutral exciton and trions via valley-resolved PL measurements, and find that the DOP can be as high as 24% for exciton emission and 34% for trion emission at 100K. These results can be understood by analyzing the near-field impact of metasurface resonators on both the chiral absorption of MoS2 emitters as well as the enhanced emission from the Purcell effect. Combining Si-compatible photonic design with large-scale (mm-scale) 2D materials integration, our work makes an important step towards on-chip valleytronic applications approaching room-temperature operation.

physics.optics↗

arXiv2021

Rapid genetic screening with high quality factor metasurfaces

Genetic analysis methods are foundational to advancing personalized and preventative medicine, accelerating disease diagnostics, and monitoring the health of organisms and ecosystems. Current nucleic acid technologies such as polymerase chain reaction (PCR), next-generation sequencing (NGS), and DNA microarrays rely on fluorescence and absorbance, necessitating sample amplification or replication and leading to increased processing time and cost. Here, we introduce a label-free genetic screening platform based on high quality (high-Q) factor silicon nanoantennas functionalized with monolayers of nucleic acid fragments. Each nanoantenna exhibits substantial electromagnetic field enhancements with sufficiently localized fields to ensure isolation from neighboring resonators, enabling dense biosensor integration. We quantitatively detect complementary target sequences using DNA hybridization simultaneously for arrays of sensing elements patterned at densities of 160,000 pixels per cm$^2$. In physiological buffer, our nanoantennas exhibit average resonant quality factors of 2,200, allowing detection of two gene fragments, SARS-CoV-2 envelope (E) and open reading frame 1b (ORF1b), down to femtomolar concentrations. We also demonstrate high specificity sensing in clinical nasopharyngeal eluates within 5 minutes of sample introduction. Combined with advances in biomarker isolation from complex samples (e.g., mucus, blood, wastewater), our work provides a foundation for rapid, compact, amplification-free and high throughput multiplexed genetic screening assays spanning medical diagnostics to environmental monitoring.

physics.optics↗

arXiv2020

Fluorescence-Detected Circular Dichroism of a Chiral Molecular Monolayer with Dielectric Metasurfaces

Strong enhancement of molecular circular dichroism has the potential to enable efficient asymmetric photolysis, a method of chiral separation that has conventionally been impeded by insufficient yield and low enantiomeric excess. Here, we study experimentally how predicted enhancements in optical chirality density near resonant silicon nanodisks boost circular dichroism. We use fluorescence-detected circular dichroism spectroscopy to measure indirectly the differential absorption of circularly polarized light by a monolayer of optically active molecules functionalized to silicon nanodisk arrays. Importantly, the molecules and nanodisk antennas have spectrally-coincident resonances, and our fluorescence technique allows us to deconvolute absorption in the nanodisks from the molecules. We find that enhanced fluorescence-detected circular dichroism signals depend on nanophotonic resonances in good agreement with simulated differential absorption and optical chirality density, while no signal is detected from molecules adsorbed on featureless silicon surfaces. These results verify the potential of nanophotonic platforms to be used for asymmetric photolysis with lower energy requirements

physics.optics↗