arXiv subjects

Sahil Dagli

Publications and source records attributed to Sahil Dagli.

8 recordsLinked to original sources

arXiv2026

$Q$ Factors Exceeding $10^{4}$ in Wavelength-to-Subwavelength-Scale Free-Space Resonators

Free-space-addressable optical resonators that combine long photon lifetimes (high $Q$ factors) with strong spatial localization of optical fields (small mode volumes, $V_m$) enhance light-matter interactions with facile far-field excitation. The Purcell factor governing spontaneous emission enhancement scales as $Q\,V_m^{-1}$. Periodically asymmetric resonators, in which perturbations convert bound modes into radiating modes, offer a route to free-space resonances, with the radiative $Q$ factor tuned by the geometric and optical strength of the asymmetry-inducing perturbations. However, free-space resonators that simultaneously achieve high $Q$ and small $V_m$ have remained rare. This limitation arises in part because existing designs do not tailor geometric and optical asymmetries concurrently, thus limiting access to high-$Q$ regimes. Here, we show that jointly tuning geometric and optical asymmetries unlocks a biaxial radiative landscape with iso-$Q$ contours that connect disparate perturbations with equivalent $Q$ factors. We demonstrate this framework with very-large-scale-integrated single-crystalline Si nanoantenna pixels (VINPix) with out-of-plane perturbations of 35-150 nm amorphous Si, SiN$_x$, and SiO$_2$. We experimentally establish biaxial $Q$ factor control in air and achieve $Q$ factors up to $76,000$ at wavelength-scale mode volumes ($V_m \sim 1.7\,\lambda_0^3\,n_{\mathrm{eff}}^{-3}$) in simultaneously imaged arrays of $>80$ resonators in water. Furthermore, we computationally demonstrate 50-nm-wide slotted VINPix that reach $Q$ factors of $10^6$ at subwavelength mode volumes ($V_m \sim 0.2\,\lambda_0^3\,n_{\mathrm{eff}}^{-3}$) with 20 nm SiO$_2$ perturbations, yielding Purcell factors as high as $5 \times 10^5$ in an all-dielectric free-space resonator.

physics.optics↗

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↗

arXiv2024

High-throughput antibody screening with high-quality factor nanophotonics and bioprinting

Empirical investigation of the quintillion-scale, functionally diverse antibody repertoires that can be generated synthetically or naturally is critical for identifying potential biotherapeutic leads, yet remains burdensome. We present high-throughput nanophotonics- and bioprinter-enabled screening (HT-NaBS), a multiplexed assay for large-scale, sample-efficient, and rapid characterization of antibody libraries. Our platform is built upon independently addressable pixelated nanoantennas exhibiting wavelength-scale mode volumes, high-quality factors (high-Q) exceeding 5000, and pattern densities exceeding one million sensors per square centimeter. Our custom-built acoustic bioprinter enables individual sensor functionalization via the deposition of picoliter droplets from a library of capture antigens at rates up to 25,000 droplets per second. We detect subtle differentiation in the target binding signature through spatially-resolved spectral imaging of hundreds of resonators simultaneously, elucidating antigen-antibody binding kinetic rates, affinity constant, and specificity. We demonstrate HT-NaBS on a panel of antibodies targeting SARS-CoV-2, Influenza A, and Influenza B antigens, with a sub-picomolar limit of detection within 30 minutes. Furthermore, through epitope binning analysis, we demonstrate the competence and diversity of a library of native antibodies targeting functional epitopes on a priority pathogen (H5N1 bird flu) and on glycosylated therapeutic Cetuximab antibodies against epidermal growth factor receptor. With a roadmap to image tens of thousands of sensors simultaneously, this high-throughput, resource-efficient, and label-free platform can rapidly screen for high-affinity and broad epitope coverage, accelerating biotherapeutic discovery and de novo protein design.

physics.optics↗

arXiv2024

Room-temperature valley-selective emission in Si-MoSe2 heterostructures enabled by high-quality-factor chiroptical cavities

Transition metal dichalcogenides possess valley pseudospin, enabling coupling between photon spin and electron spin for classical and quantum information processing. However, rapid valley-dephasing processes have impeded the development of scalable, high-performance valleytronic devices operating at room temperature. Here we demonstrate that a chiral resonant metasurface can enable room-temperature valley-selective emission in MoSe2 monolayers independent of excitation polarization. This platform provides circular eigen-polarization states with a high quality factor (Q-factor) and strong chiral near-field enhancement. The fabricated Si chiral metasurfaces exhibit chiroptical resonances with Q-factors up to 450 at visible wavelengths. We reveal degrees of circular polarization (DOP) reaching a record high of 0.5 at room temperature. Our measurements show that the high DOP can be attributed to the significantly increased chiroptical local density of states, which enhances valley-specific radiative transition rates by a factor of ~13. Our work could facilitate the development of ultracompact chiral classical and quantum light sources.

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

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↗

arXiv2022

High quality factor silicon-on-lithium niobate metasurfaces for electro-optically reconfigurable wavefront shaping

Dynamically reconfigurable metasurfaces promise compact and lightweight spatial light modulation for many applications, including LiDAR, AR/VR, and LiFi systems. Here, we design and computationally investigate high quality factor silicon-on-lithium niobate metasurfaces with electrically-driven, independent control of its constituent nanobars for full phase tunability with high tuning efficiency. Free-space light couples to guided modes within each nanobar via periodic perturbations, generating quality factors exceeding 30,000, while maintaining bar spacing <$λ$/1.5. We achieve nearly 2$π$ phase variation with an applied bias not exceeding $\pm$ 25 V, maintaining reflection efficiency above 91%. Using full-field simulations, we demonstrate a high angle, 51°, switchable beamsplitter with a diffracted efficiency of 93%, and an angle-tunable beamsteerer, spanning 18-31°, with up to 86% efficiency, all using the same metasurface device. Our platform provides a foundation for highly efficient wavefront shaping devices with a wide dynamic tuning range capable of generating nearly any transfer function.

physics.optics↗

arXiv2019

Thermal conductivity of AlN, GaN, and Al$_x$Ga$_{1-x}$N alloys as a function of composition, temperature, crystallographic direction, and isotope disorder from first principles

Ultra-wide-band-gap group-III nitrides are of interest for applications in deep-ultraviolet optoelectronics and power electronics. Such devices must be able to efficiently dissipate heat generated from their operation, making the thermal conductivity of the constituent materials an important parameter for high-power applications. We have investigated the phonon-limited thermal conductivity of AlN, GaN, and Al$_x$Ga$_{1-x}$N using first-principles calculations, with a focus on the effects of compositional and isotopic disorder. Our Boltzmann-transport-equation calculations show that the maximum thermal conductivity for AlN (GaN) is 348 W m$^{-1}$ K$^{-1}$ (235 W m$^{-1}$ K$^{-1}$) for with pure $^{14}$N, and 292 W m$^{-1}$ K$^{-1}$ for GaN with pure $^{71}$Ga. Al$_x$Ga$_{1-x}$N alloys reach a minimum thermal conductivity at Al mole fractions of x = 0.60 to 0.71 over the 100-1000K temperature range. Our results provide understanding on the effects of isotope disorder on the thermal conductivity of AlN and GaN. We also present an analytical model for the evaluation of the thermal conductivity of Al$_x$Ga$_{1-x}$N alloys for arbitrary composition and temperature, which can be applied for the thermal design of AlGaN-based electronic and optoelectronic devices.

cond-mat.mtrl-sci↗