A5013623888- Plasmonic and Surface Plasmon Research
- Metamaterials and Metasurfaces Applications
- Photonic and Optical Devices
- Photonic Crystals and Applications
- Thermal Radiation and Cooling Technologies
- Near-Field Optical Microscopy
- Optical Coatings and Gratings
- Advanced Fiber Laser Technologies
- Gold and Silver Nanoparticles Synthesis and Applications
- solar cell performance optimization
- Quantum Electrodynamics and Casimir Effect
- Advanced Antenna and Metasurface Technologies
- Orbital Angular Momentum in Optics
- Advanced Thermodynamics and Statistical Mechanics
- Mechanical and Optical Resonators
- Thin-Film Transistor Technologies
- Silicon and Solar Cell Technologies
- Optical properties and cooling technologies in crystalline materials
- Advanced Fiber Optic Sensors
- Random lasers and scattering media
- Semiconductor Lasers and Optical Devices
- Optical Network Technologies
- Advanced Photonic Communication Systems
- Electromagnetic Scattering and Analysis
- Advanced Optical Imaging Technologies
Yale University
2016-2025
Institute for Soldier Nanotechnologies
2014-2018
Massachusetts Institute of Technology
2013-2017
University of California, Berkeley
2010-2015
Lawrence Berkeley National Laboratory
2012-2013
Material Sciences (United States)
2012-2013
University of Virginia
2008
University of Missouri
1973-1977
Absorbed sunlight in a solar cell produces electrons and holes. But, at the open circuit condition, carriers have no place to go. They build up density and, ideally, they emit external fluorescence that exactly balances incoming sunlight. Any additional non-radiative recombination impairs carrier buildup, limiting open-circuit voltage. At open-circuit, efficient is an indicator of low internal optical losses. Thus is, counter-intuitively, necessity for approaching Shockley-Queisser...
We present an adjoint-based optimization for electromagnetic design. It embeds commercial Maxwell solvers within a steepest-descent inverse-design algorithm. The adjoint approach calculates shape derivatives at all points in space, but requires only two "forward" simulations. Geometrical parameterization is by the level set method. Our design applied to Silicon photonics Y-junction splitter that had previously been investigated stochastic methods. Owing speed of calculating method,...
We use inverse design to discover metalens structures that exhibit broadband, achromatic focusing across low, moderate, and high numerical apertures. show standard unit-cell approaches cannot achieve high-efficiency high-NA focusing, even at a single frequency, due the incompleteness of basis, we provide computational upper bounds on their maximum efficiencies. At low NA, our devices highest theoretical efficiencies date. NA—of 0.9 with translation-invariant films 0.99 “freeform”...
Metasurfaces have recently risen to prominence in optical research, providing unique functionalities that can be used for imaging, beam forming, holography, polarimetry, and many more, while keeping device dimensions small. Despite the fact a vast range of basic metasurface designs has already been thoroughly studied literature, number metasurface-related papers is still growing at rapid pace, as research now spreading adjacent fields, including computational augmented virtual reality,...
Numerous modern technologies are reliant on the low-phase noise and exquisite timing stability of microwave signals. Substantial progress has been made in field photonics, whereby low-noise signals generated by down-conversion ultrastable optical references using a frequency comb
We present a general theory of spontaneous emission at exceptional points (EPs)---exotic degeneracies in non-Hermitian systems. Our extends beyond to any light--matter interaction described by the local density states (e.g., absorption, thermal emission, and nonlinear frequency conversion). Whereas traditional spontaneous-emission theories imply infinite enhancement factors EPs, we derive finite bounds on enhancement, proving maximum 4 passive systems with second-order EPs significantly...
At visible and infrared frequencies, metals show tantalizing promise for strong subwavelength resonances, but material loss typically dampens the response.We derive fundamental limits to optical response of absorptive systems, bounding largest enhancements possible given intrinsic losses.Through basic conservation-of-energy principles, we geometry-independent per-volume absorption scattering rates, local-density-of-states that represent power radiated or expended by a dipole near body.We...
Material losses in metals are a central bottleneck plasmonics for many applications. Here we propose and theoretically demonstrate that metal can be successfully mitigated with dielectric particles on metallic films, giving rise to hybrid dielectric--metal resonances. In the far field, they yield strong efficient scattering, beyond even theoretical limits of all-metal all-dielectric structures. near offer high-Purcell-factor (${>}5000$), high-quantum-efficiency (${>}90\%$), highly...
Hybrid nanostructures that couple plasmon and exciton resonances generate hybridized energy states, called plexcitons, which may result in unusual light-matter interactions. We report the formation of a transparency dip visible spectra colloidal suspensions containing silver nanoplatelets cyanine dye, 1,1'-diethyl-2,2'-cyanine iodide (PIC). PIC was electrostatically adsorbed onto surface nanoplatelet core particles, forming an outer J-aggregate shell. This core-shell architecture provided...
Highly directional radiation from photonic structures is important for many applications, including high power crystal surface emitting lasers, grating couplers, and light detection ranging devices. However, previous dielectric, few-layer designs only achieved moderate asymmetry ratios, a fundamental understanding of bounds on asymmetric arbitrary still lacking. Here, we show that breaking the 180$^\circ$ rotational symmetry structure crucial achieving highly radiation. We develop general...
Tunable metasurfaces have demonstrated the potential for dramatically enhanced functionality applications including sensing, ranging and imaging. Liquid crystals (LCs) fast switching speeds, low cost, mature technological development, offering a versatile platform electrical tunability. However, to date, electrically tunable are typically designed at single operational state using physical intuition, without controlling alternate states thus leading limited efficiencies (<30%) small angular...
The emerging field of free-electron quantum optics enables electron-photon entanglement and holds the potential for generating nontrivial photon states information processing. Although recent experimental studies have entered regime, rapid theoretical developments predict that qualitatively unique phenomena only emerge beyond a certain interaction strength. It is thus pertinent to identify maximal strength materials, geometries, particle energies enable one approach it. We derive an upper...
We show that the near-field functionality of hyperbolic metamaterials (HMM), typically proposed for increasing photonic local density states (LDOS), can be achieved with thin metal films. Although HMMs have an infinite internally propagating plane-wave states, external coupling to nearby emitters is severely restricted. analytically properly designed films, thicknesses comparable size a metamaterial, yield LDOS as high (if not higher than) HMMs. illustrate these ideas by performing exact...
We derive shape-independent limits to the spectral radiative heat transfer rate between two closely spaced bodies, generalizing concept of a blackbody case near-field energy transfer. Through conservation and reciprocity, we show that each body susceptibility χ can emit absorb radiation at enhanced rates bounded by |χ|2/Im χ, optimally mediated photon proportional 1/d2 across separation distance d. Dipole-dipole dipole-plate structures approach restricted versions limit, but common...
We show that there are shape-independent upper bounds to the extinction cross section per unit volume of randomly oriented nanoparticles, given only material permittivity. Underlying limits restrictive sum rules constrain distribution quasistatic eigenvalues. Surprisingly, optimally-designed spheroids, with a single degree freedom, reach for four permittivity values. Away from these permittivities, we demonstrate computationally-optimized structures surpass spheroids and approach fundamental limits.
Light trapping in solar cells allows for increased current and voltage, as well reduced materials cost. It is known that geometrical optics, a maximum 4n^2 absorption enhancement factor can be achieved by randomly texturing the surface of cell, where n material refractive index. This ray-optics limit only holds when thickness cell much greater than optical wavelength. In sub-wavelength thin films, fundamental questions remain unanswered: (1) what (2) texture realizes this optimal...
We theoretically demonstrate a near-field radiative thermal switch based on thermally excited surface plasmons in graphene resonators. The high tunability of enables substantial modulation heat transfer, which, when combined with the use resonant structures, overcomes intrinsically broadband nature radiation. In canonical geometries, we nonlinear optimization to show that stacked sheets offer improved conductance contrast between "ON" and "OFF" switching states >10× higher is achieved...
Photonic innovation is becoming ever more important in the modern world. Optical systems are dominating shorter and communications distances, LED's rapidly emerging for a variety of applications, solar cells show potential to be mainstream technology energy space. The need novel, energy-efficient photonic optoelectronic devices will only increase. This work unites fundamental physics novel computational inverse design approach towards such innovation. first half dissertation devoted...
Increasing the refractive index available for optical and nanophotonic systems opens new vistas design, applications ranging from broadband metalenses to ultrathin photovoltaics high-quality-factor resonators. In this work, fundamental limits of any material are derived, given only underlying electron density either maximum allowable dispersion or minimum bandwidth interest. realm small modest dispersion, bounds closely approached not surpassed by a wide range natural materials, showing that...
The internal physics of a solar cell changes as it approaches the fundamental Shockley-Queisser limit. Photonic considerations overtake electronic ones, an intense and external luminescence requires careful photon management. Counter-intuitively, maximizing light extraction increases voltage therefore efficiency. Until 2010 one-sun, single-junction efficiency record was set by GaAs with 26.4% open-circuit V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML"...
Abstract There has been a significant effort to design nanophotonic structures that process images at the speed of light. A prototypical example is in edge detection, where photonic-crystal-, metasurface-, and plasmon-based designs have proposed some cases experimentally demonstrated. In this work, we show multilayer optical interference coatings can achieve visible-frequency detection transmission with high numerical aperture, two-dimensional image formation, straightforward fabrication...
Near-field radiative heat transfer (NFRHT) arises between objects separated by nanoscale gaps and leads to dramatic enhancements in rates compared the far-field. Recent experiments have provided first insights into these enhancements, especially using silicon dioxide (SiO2) surfaces, which support surface phonon polaritons (SPhP). Yet, theoretical analysis suggests that SPhPs SiO2 occur at frequencies far higher than optimal. Here, we show theoretically SPhP-mediated NFRHT, room temperature,...
In this work, we present a reproducible suite of test problems for large-scale optimization (“inverse design” and “topology optimization”) in photonics, where the prevalence irregular, non-intuitive geometries can otherwise make it challenging to be confident that new algorithms software are functioning as claimed. We include exercise wide array physical mathematical features—far-field metalenses, 2d 3d mode converters, resonant emission focusing, dispersion/eigenvalue engineering—and...
2D materials provide a platform for strong light--matter interactions, creating wide-ranging design opportunities via new-material discoveries and new methods geometrical structuring. We derive general upper bounds to the strength of such given only optical conductivity material, including spatial nonlocality, otherwise independent shape configuration. Our material figure merit shows that highly doped graphene is an optimal at infrared frequencies, whereas single-atomic-layer silver in...