- Cambridge, United States
John Joannopoulos
Massachusetts Institute of Technology (MIT), Physics, Faculty Member
Bombardment of materials by high-energy particles often leads to light emission in a process known as scintillation. Scintillation has widespread applications in medical imaging, x-ray nondestructive inspection, electron microscopy, and... more
Bombardment of materials by high-energy particles often leads to light emission in a process known as scintillation. Scintillation has widespread applications in medical imaging, x-ray nondestructive inspection, electron microscopy, and high-energy particle detectors. Most research focuses on finding materials with brighter, faster, and more controlled scintillation. We developed a unified theory of nanophotonic scintillators that accounts for the key aspects of scintillation: energy loss by high-energy particles, and light emission by non-equilibrium electrons in nanostructured optical systems. We then devised an approach based on integrating nanophotonic structures into scintillators to enhance their emission, obtaining nearly an order-of-magnitude enhancement in both electron-induced and x-ray–induced scintillation. Our framework should enable the development of a new class of brighter, faster, and higher-resolution scintillators with tailored and optimized performance.
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Charles Roques-Carmes1,‡,∗ Nicholas Rivera2,‡,† Ali Ghorashi, Steven E. Kooi, Yi Yang, Zin Lin, Justin Beroz, Aviram Massuda, Jamison Sloan, Nicolas Romeo, Yang Yu, John D. Joannopoulos, Ido Kaminer, Steven G. Johnson, and Marin Soljačić... more
Charles Roques-Carmes1,‡,∗ Nicholas Rivera2,‡,† Ali Ghorashi, Steven E. Kooi, Yi Yang, Zin Lin, Justin Beroz, Aviram Massuda, Jamison Sloan, Nicolas Romeo, Yang Yu, John D. Joannopoulos, Ido Kaminer, Steven G. Johnson, and Marin Soljačić ‡ denotes equal contribution. 1 Research Laboratory of Electronics, MIT, Cambridge, MA 02139, USA 2 Department of Physics, MIT, Cambridge, MA 02139, USA 3 Institute for Soldier Nanotechnologies, MIT, Cambridge, MA, 02139, USA 4 Department of Mathematics, MIT, Cambridge, MA, 02139, USA 5 Microsystems Technology Laboratories, MIT, Cambridge, MA 02139 USA, 6 Raith America, Inc., USA, and 7 Department of Electrical and Computer Engineering, Technion Haifa 32000, Israel
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The Hofstadter model, well known for its fractal butterfly spectrum, describes two-dimensional electrons under a perpendicular magnetic field, which gives rise to the integer quantum Hall effect. Inspired by the real-space building blocks... more
The Hofstadter model, well known for its fractal butterfly spectrum, describes two-dimensional electrons under a perpendicular magnetic field, which gives rise to the integer quantum Hall effect. Inspired by the real-space building blocks of non-Abelian gauge fields from a recent experiment, we introduce and theoretically study two non-Abelian generalizations of the Hofstadter model. Each model describes two pairs of Hofstadter butterflies that are spin–orbit coupled. In contrast to the original Hofstadter model that can be equivalently studied in the Landau and symmetric gauges, the corresponding non-Abelian generalizations exhibit distinct spectra due to the non-commutativity of the gauge fields. We derive the genuine (necessary and sufficient) non-Abelian condition for the two models from the commutativity of their arbitrary loop operators. At zero energy, the models are gapless and host Weyl and Dirac points protected by internal and crystalline symmetries. Double (8-fold), trip...
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We demonstrate new axisymmetric inverse-design techniques that can solve problems radically different from traditional lenses, including reconfigurable lenses (that shift a multi-frequency focal spot in response to refractive-index... more
We demonstrate new axisymmetric inverse-design techniques that can solve problems radically different from traditional lenses, including reconfigurable lenses (that shift a multi-frequency focal spot in response to refractive-index changes) and widely separated multi-wavelength lenses (λ = 1 µm and 10 µm). We also present experimental validation for an axisymmetric inverse-designed monochrome lens in the near-infrared fabricated via two-photon polymerization. Axisymmetry allows fullwave Maxwell solvers to be scaled up to structures hundreds or even thousands of wavelengths in diameter before requiring domain-decomposition approximations, while multilayer topology optimization with ∼105 degrees of freedom can tackle challenging design problems even when restricted to axisymmetric structures.
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Conventional computing architectures have no known efficient algorithms for combinatorial optimization tasks such as the Ising problem, which requires finding the ground state spin configuration of an arbitrary Ising graph. Physical Ising... more
Conventional computing architectures have no known efficient algorithms for combinatorial optimization tasks such as the Ising problem, which requires finding the ground state spin configuration of an arbitrary Ising graph. Physical Ising machines have recently been developed as an alternative to conventional exact and heuristic solvers; however, these machines typically suffer from decreased ground state convergence probability or universality for high edge-density graphs or arbitrary graph weights, respectively. We experimentally demonstrate a proof-of-principle integrated nanophotonic recurrent Ising sampler (INPRIS), using a hybrid scheme combining electronics and silicon-on-insulator photonics, that is capable of converging to the ground state of various four-spin graphs with high probability. The INPRIS results indicate that noise may be used as a resource to speed up the ground state search and to explore larger regions of the phase space, thus allowing one to probe noise-dep...
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The inability of conventional electronic architectures to efficiently solve large combinatorial problems motivates the development of novel computational hardware. There has been much effort toward developing application-specific hardware... more
The inability of conventional electronic architectures to efficiently solve large combinatorial problems motivates the development of novel computational hardware. There has been much effort toward developing application-specific hardware across many different fields of engineering, such as integrated circuits, memristors, and photonics. However, unleashing the potential of such architectures requires the development of algorithms which optimally exploit their fundamental properties. Here, we present the Photonic Recurrent Ising Sampler (PRIS), a heuristic method tailored for parallel architectures allowing fast and efficient sampling from distributions of arbitrary Ising problems. Since the PRIS relies on vector-to-fixed matrix multiplications, we suggest the implementation of the PRIS in photonic parallel networks, which realize these operations at an unprecedented speed. The PRIS provides sample solutions to the ground state of Ising models, by converging in probability to their ...
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Extracting light from silicon is a longstanding challenge in modern engineering and physics. While silicon has underpinned the past 70 years of electronics advancement, a facile tunable and efficient silicon-based light source remains... more
Extracting light from silicon is a longstanding challenge in modern engineering and physics. While silicon has underpinned the past 70 years of electronics advancement, a facile tunable and efficient silicon-based light source remains elusive. Here, we experimentally demonstrate the generation of tunable radiation from a one-dimensional, all-silicon nanograting. Light is generated by the spontaneous emission from the interaction of these nanogratings with low-energy free electrons (2–20 keV) and is recorded in the wavelength range of 800–1600 nm, which includes the silicon transparency window. Tunable free-electron-based light generation from nanoscale silicon gratings with efficiencies approaching those from metallic gratings is demonstrated. We theoretically investigate the feasibility of a scalable, compact, all-silicon tunable light source comprised of a silicon Field Emitter Array integrated with a silicon nanograting that emits at telecommunication wavelengths. Our results rev...
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The increasing power demands of portable electronics and micro robotics has driven recent interest in millimeter-scale microgenerators. Many technologies (fuel cells, Stirling, thermoelectric, etc.) that potentially enable a portable... more
The increasing power demands of portable electronics and micro robotics has driven recent interest in millimeter-scale microgenerators. Many technologies (fuel cells, Stirling, thermoelectric, etc.) that potentially enable a portable hydrocarbon microgenerator are under active investigation. Hydrocarbon fuels have specific energies fifty times those of batteries, thus even a relatively inefficient generator can exceed the specific energy of batteries. We proposed, designed, and demonstrated a first-of-a-kind millimeter-scale thermophotovoltaic (TPV) system with a photonic crystal emitter. In a TPV system, combustion heats an emitter to incandescence and the resulting thermal radiation is converted to electricity by photovoltaic cells. Our approach uses a moderate temperature (1000–1200°C) metallic microburner coupled to a high emissivity, high selectivity photonic crystal selective emitter and low bandgap PV cells. This approach is predicted to be capable of up to 30% efficient fuel...
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Thick sputtered tantalum (Ta) coatings on polished Inconel were investigated as a potential replacement for bulk refractory metal substrates used for high-temperature emitters and absorbers in thermophotovoltaic energy conversion... more
Thick sputtered tantalum (Ta) coatings on polished Inconel were investigated as a potential replacement for bulk refractory metal substrates used for high-temperature emitters and absorbers in thermophotovoltaic energy conversion applications. In these applications, high-temperature stability and high reflectance of the surface in the infrared wavelength range are critical in order to sustain operational temperatures and reduce losses due to waste heat. The reflectance of the coatings (8 and 30 μm) was characterized with a conformal protective hafnia layer as-deposited and after one hour anneals at 700, 900, and 1100 °C. To further understand the high-temperature performance of the coatings, the microstructural evolution was investigated as a function of annealing temperature. X-ray diffraction was used to analyze the texture and residual stress in the coatings at four reflections (220, 310, 222, and 321), as-deposited and after anneal. No significant changes in roughness, reflectan...
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Research Interests: Engineering, Mathematics, Applied Mathematics, Computer Science, Physics, and 15 moreModeling, Algorithm, DIELECTRIC, Dielectric Function, Dielectrics, Discretization, Interfaces, Photonic Band Gap Materials, Numerical Analysis and Computational Mathematics, Dielectric Materials, Finite Difference Time Domain, Perturbation Theory, Pixel, Photonic Band Gap, and Finite Difference Time Domain Method
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Research Interests: Materials Engineering, Materials Science, Nanotechnology, Medicine, Multidisciplinary, and 15 moreNature, Imaging Techniques, Electromagnetic Field, Information Analysis, Light field, Geometric Approach to Stability, Large Scale, Atoms, Optical Fibers, Nature Materials, Field of View, Amplitude, Optical Density, Field Measurement, and Beam Splitter
This article details microfabrication of two-dimensional tungsten photonic crystals (2D W PhCs) for high-temperature applications such as selective thermal emitters for thermophotovoltaic energy conversion. In particular, interference... more
This article details microfabrication of two-dimensional tungsten photonic crystals (2D W PhCs) for high-temperature applications such as selective thermal emitters for thermophotovoltaic energy conversion. In particular, interference lithography and reactive ion etching are used to produce large area single crystal tungsten 2D PhCs. For this investigation, we fabricated a 2D W PhC sample consisting of an array of cylindrical cavities with 800 nm diameter, 1.2 μm depth, and 1.2 μm period. Extensive characterization and calibration of all microfabrication steps are presented. Experimentally obtained thermal emissivity spectrum is shown to match well with numerical simulations.
Research Interests: Materials Engineering, Aerospace Engineering, Physics, Materials Science, Solid State Physics, and 14 moreChemistry, Nanotechnology, Optoelectronics, Atmospheric sciences, Microfabrication, Nanoscience, Photonic Crystal, Fabrication, Lithography, High Temperature, Tungsten, Reactive ion etching, Emissivity, and Vacuum Science and Technology
We demonstrate tantalum-tungsten (Ta-W) solid solution alloy photonic crystals (PhCs) as spectrally selective components for high temperature energy conversion. The thermo-mechanical properties of the alloy are tuned by the Ta-W ratio. A... more
We demonstrate tantalum-tungsten (Ta-W) solid solution alloy photonic crystals (PhCs) as spectrally selective components for high temperature energy conversion. The thermo-mechanical properties of the alloy are tuned by the Ta-W ratio. A 2D PhC was designed as a selective emitter, fabricated on a Ta3%W substrate, and optical properties and thermal stability were characterized. A thin layer of HfO2 was deposited for thermal stability. The PhCs show outstanding emittance selectivity, well preserved after annealing for 24h at 1200 °C. The structure is preserved as shown in cross-sectional images, demonstrating that the coating effectively prevents degradation due to surface diffusion at high temperatures.
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Research Interests: Information Technology, Materials Science, Optics, Photonics, Medicine, and 14 moreMultidisciplinary, Nature, Optoelectronics, Photonic Crystal, Fabrication, Band Gap, Three Dimensional, Gallium Arsenide, Indexation, Boundary Effect, Light Attenuation, optoelectronic device, Low loss, and three-dimensions
The routing and interconnection of optical signals through narrow channels and around sharp corners are important for large-scale all-optical circuit applications. A recent computational result suggests that photonic crystals may offer a... more
The routing and interconnection of optical signals through narrow channels and around sharp corners are important for large-scale all-optical circuit applications. A recent computational result suggests that photonic crystals may offer a novel way of achieving this goal by providing a mechanism for guiding light that is fundamentally different from traditional index guiding. Waveguiding in a photonic crystal and near 100 percent transmission of electromagnetic waves around sharp 90 degree corners were observed experimentally. Bending radii were made smaller than one wavelength.
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Photonic band-gap monorail and air-bridge waveguide microcavities, operating at the wavelength regime of 1550 nm, are fabricated using GaAs-based compound semiconductors. The fabrication process involves gas-source molecular beam epitaxy,... more
Photonic band-gap monorail and air-bridge waveguide microcavities, operating at the wavelength regime of 1550 nm, are fabricated using GaAs-based compound semiconductors. The fabrication process involves gas-source molecular beam epitaxy, electron-beam lithography, reactive ion etching, and thermal wet oxidation of Al0.93Ga0.07As. The fabrication of the air-bridge microcavity, in particular, also entails the sacrificial wet etch of AlxOy to suspend the micromechanical structure. The monorail and air-bridge microcavities have been optically characterized and the transmission spectra exhibit resonances in the 1550 nm wavelength regime. Tunability of the resonant wavelength is demonstrated through changing the defect size in the one-dimensional photonic crystal. The quality factors (Q) of the microcavities are about 140 for the monorail and 230 for the air bridge, respectively.