Engineering topics
Fan, Shanhui
Publications and source records attributed to Fan, Shanhui.
Relation between photon thermal Hall effect and persistent heat current in nonreciprocal radiative heat transfer
In this work, we study the photon thermal Hall effect and the persistent heat current in radiative heat transfer. We show that the photon thermal Hall effect is not a uniquely nonreciprocal effect; it can arise in some reciprocal systems with broken-mirror symmetry. This is in contrast with the persistent heat current, which is a uniquely nonreciprocal effect that cannot exist in any reciprocal system. Nevertheless, for a specific class of systems with C 4 rotational symmetry, we note that the photon thermal Hall effect is uniquely nonreciprocal, and moreover there is a direct connection between the persistent heat current and the photon thermal Hall effect. In the near-equilibrium regime, the magnitude of the photon thermal Hall effect is proportional to the temperature derivative of the persistent heat current in such systems. Therefore, the persistent heat current as predicted for the equilibrium situation can be probed by the photon thermal Hall effect away from equilibrium.
Near-complete violation of Kirchhoff’s law of thermal radiation with a 03 T magnetic field
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Wave optics light-trapping theory: mathematical justification and ultimate limit on enhancement
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Accelerating adjoint variable method based photonic optimization with Schur complement domain decomposition
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High-Temperature Polarization-Free III-Nitride Solar Cells with Self-Cooling Effects
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Reconfigurable Photonic Circuit for Controlled Power Delivery to Laser-Driven Accelerators on a Chip
Dielectric laser acceleration (DLA) represents a promising approach to building miniature particle accelerators on a chip. However, similar to conventional RF accelerators, an automatic and reconfigurable control mechanism is needed to scale DLA technology towards high energy gains and practical applications. We present a system providing control of the laser coupling to DLA using integrated optics and introduce a novel component for power distribution using a reconfigurable mesh of Mach-Zehnder interferometers. We show how such a mesh may be sequentially and effciently tuned to optimize power distribution in the circuit and find that this strategy has favorable scaling properties with respect to size of the mesh.
Self-sustaining thermophotonic circuits
Photons represent one of the most important heat carriers. The ability to convert photon heat flow to electricity is therefore of substantial importance for renewable energy applications. However, photon-based systems that convert heat to electricity, including thermophotovoltaic systems where photons are generated from passive thermal emitters, have long been limited by low power density. This limitation persists even with near-field enhancement techniques. Thermophotonic systems, which utilize active photon emitters such as light-emitting diodes, have the potential to significantly further enhance the power density. However, this potential has not been realized in practice, due in part to the fundamental difficulty in thermodynamics of designing a self-sustaining circuit that enables steady-state power generation. Here, we overcome such difficulty by introducing a configuration where the light-emitting diodes are connected in series, and thus multiple photons can be generated from a single injected electron. As a result we propose a self-sustaining thermophotonic circuit where the steady-state power density can exceed thermophotovoltaic systems by many orders of magnitude. This work points to possibilities for constructing heat engines with light as the working medium. The flexibility of controlling the relations between electron and photon flux, as we show in our design, may also be of general importance for optoelectronics-based energy technology.
Experimental demonstration of energy harvesting from the sky using the negative illumination effect of a semiconductor photodiode
We experimentally demonstrate electric power generation from the coldness of the universe directly, using the negative illumination effect when an infrared semiconductor diode faces the sky. Our theoretical model, accounting for the experimental results, indicates that the performance of such a power generation scheme is strongly influenced by the degree of matching between the responsivity spectrum and the atmospheric transparency window, as well as the quantum efficiency of the diode. A Shockley-Queisser analysis of an ideal optimized diode, taking into consideration the realistic transmissivity spectrum of the atmosphere, indicates the theoretical maximum power density of 3.99 W/m2 with the diode temperature at 293 K. The results here point to a pathway towards night-time power generation.
Light Material Interactions in Energy Conversion (Final Report)
The scientific vision of the “Light-Material Interactions in Energy Conversion” Energy Frontier Research Center (LMI-EFRC) is embodied in our mission statement: ‘to tailor the morphology, complex dielectric structure, and electronic properties of matter so as to sculpt the flow of sunlight and heat, enabling light conversion to electrical energy with unprecedented efficiency’. Founded in 2009, the LMI-EFRC has become a national resource for fundamental optical principles and phenomena relevant to solar energy conversion, addressing new scientific opportunities that enable efficient utilization of the entire visible and infrared solar resource. The LMI-EFRC is directed by Prof. Ralph Nuzzo and centered at its lead institution, the California Institute of Technology. The Center is an integrated and collaborative partnership of research leaders in photonics and photonic materials, comprising 14 faculty investigators that span six academic departments at five institutions, including Profs. Harry Atwater, Andrei Faraon, Nathan Lewis, and Austin Minnich at Caltech; Profs. Ralph Nuzzo, Paul Braun and John Rogers at the University of Illinois at Urbana-Champaign; Prof. Jennifer Lewis at Harvard University; Profs. Mark Brongersma, Jennifer Dionne, and Shanhui Fan at Stanford University; and Profs. Paul Alivisatos, Eli Yablonovitch, and Xiang Zhang at Lawrence Berkeley National Laboratory. The Center is organized into four research groups (RGs) that address scientific themes related to light-matter interactions, with each team spanning multiple institutional partners and designed to meet our scientific objectives. Notable project outcomes that address the LMI Mission and 2014-2018 goals include: (1) RG1 “New Light Management Mechanisms” demonstrated tunable and active nanostructured patterned surfaces (‘metasurfaces’) for control of light absorption, reflection, and propagation. (2) RG2 “Solar Spectrum Control and Conversion” developed colloidal nanocrystals with designer optical properties for fundamental studies of solar spectrum control and conversion. (3) RG3 “Thermal Photon Harvesting” established photonic design principles to harness and control thermal photons in novel conversion systems. (4) RG4 “Programmable Assembly of Photonic and Electronic Architectures” developed powerful new methods for light- and matter-based additive fabrication of electronic and photonic architectures.
Connection of temporal coupled-mode-theory formalisms for a resonant optical system and its time-reversal conjugate
Temporal coupled-mode theory has been widely used to describe the physics of resonant optical systems. In general, an optical system can be constrained by energy conservation, time-reversal symmetry, and reciprocity. Most previous developments of temporal coupled-mode theory made use of all three constraints. In this paper, we consider separately the implication of each of these constraints on the parameters of temporal coupled-mode theory. For this purpose we made extensive use of the connection between a physical system and its time-reversal conjugate. This connection also indicates some of the nontrivial implications of the relation between the resonant properties of a physical system and its time-reversal conjugate. We validate these implications numerically by direct electromagnetic simulations of a guided resonance system. Furthermore, this work should enable the application of temporal coupled-mode theory to a wider range of resonant systems.
Scattering of electromagnetic waves by cylinder inside uniaxial hyperbolic medium
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Gate-Tunable Near-Field Heat Transfer
Active control over the flow of heat in the near-field holds promise for nanoscale thermal management, with applications in refrigeration, thermophotovoltaics, and thermal circuitry. Analogously to its electronic counterpart, the metal–oxide–semiconductor (MOS) capacitor, we propose a thermal switching mechanism based on accumulation and depletion of charge carriers in an ultrathin plasmonic film, via application of external bias. In our proposed configuration, the plasmonic film is placed on top of a polaritonic dielectric material that provides a surface phonon polariton (SPhP) thermal channel, while also ensuring electrical insulation for application of large electric fields. The variation of carrier density in the plasmonic film enables the control of the surface plasmon polariton (SPP) thermal channel. We show that the interaction of the SPP with the SPhP significantly enhances the net heat transfer. Here, we study SiC as the oxide and explore three classes of gate-tunable plasmonic materials, transparent conductive oxides, doped semiconductors, and graphene, and theoretically predict contrast ratios as high as 225%.