arXiv subjects

Shanhui Fan

Publications and source records attributed to Shanhui Fan.

At least 217 records · Page 12Linked to original sources

arXiv2017

Creating anyons from photons using a nonlinear resonator lattice subject to dynamic modulation

We study a one-dimensional photonic resonator lattice with Kerr nonlinearity under the dynamic modulation. With an appropriate choice of the modulation frequency and phase, we find that this system can be used to create anyons from photons. By coupling the resonators with external waveguides, the anyon characteristics can be explored by measuring the transport property of the photons in the external waveguides.

physics.optics↗

arXiv2017

On-Chip Laser Power Delivery System for Dielectric Laser Accelerators

We propose an on-chip optical power delivery system for dielectric laser accelerators based on a fractal 'tree-branch' dielectric waveguide network. This system replaces experimentally demanding free-space manipulations of the driving laser beam with chip-integrated techniques based on precise nano-fabrication, enabling access to orders of magnitude increases in the interaction length and total energy gain for these miniature accelerators. Based on computational modeling, in the relativistic regime, our laser delivery system is estimated to provide 21 keV of energy gain over an acceleration length of 192 um with a single laser input, corresponding to a 108 MV/m acceleration gradient. The system may achieve 1 MeV of energy gain over a distance less than 1 cm by sequentially illuminating 49 identical structures. These findings are verified by detailed numerical simulation and modeling of the subcomponents and we provide a discussion of the main constraints, challenges, and relevant parameters in regards to on-chip laser coupling for dielectric laser accelerators.

physics.optics↗

arXiv2017

Topologically Charged Nodal Surface

We report the existence of topologically charged nodal surface, a band degeneracy on a two-dimensional surface in momentum space that is topologically charged. We develop a Hamiltonian for such charged nodal surface, and show that such a Hamiltonian can be implemented in a tight-binding model as well as in an acoustic meta-material. We also identify a topological phase transition, through which the charges of the nodal surface changes by absorbing or emitting an integer number of Weyl points. Our result indicates that in the band theory, topologically charged objects are not restrict to zero dimension as in a Weyl point, and thus pointing to previously unexplored opportunities for the design of topological materials.

physics.optics↗

arXiv2017

Photonic Chern insulator through homogenization of an array of particles

We propose a route towards creating a metamaterial that behaves as a photonic Chern insulator, through homogenization of an array of gyromagnetic cylinders. We show that such an array can exhibit non-trivial topological effects, including topologically non-trivial band gaps and one-way edge states, when it can be homogenized to an effective medium model that has the Berry curvature strongly peaked at the wavevector k=0. The non-trivial band topology depends only on the parameters of the cylinders and the cylinders' density, and can be realized in a wide variety of different lattices including periodic, quasi-periodic and random lattices. Our system provides a platform to explore the interplay between disorder and topology and also opens a route towards synthesis of topological meta-materials based on the self-assembly approach.

physics.optics↗

arXiv2017

Near-field heat transfer between graphene/hBN multilayers

We study the radiative heat transfer between multilayer structures made by a periodic repetition of a graphene sheet and a hexagonal boron nitride (hBN) slab. Surface plasmons in a monolayer graphene can couple with a hyperbolic phonon polaritons in a single hBN film to form hybrid polaritons that can assist photon tunneling. For periodic multilayer graphene/hBN structures, the stacked metallic/dielectric array can give rise to a further effective hyperbolic behavior, in addition to the intrinsic natural hyperbolic behavior of hBN. The effective hyperbolicity can enable more hyperbolic polaritons that enhance the photon tunneling and hence the near-field heat transfer. However, the hybrid polaritons on the surface, i.e. surface plasmon-phonon polaritons, dominate the near-field heat transfer between multilayer structures when the topmost layer is graphene. The effective hyperbolic regions can be well predicted by the effective medium theory (EMT), thought EMT fails to capture the hybrid surface polaritons and results in a heat transfer rate much lower compared to the exact calculation. The chemical potential of the graphene sheets can be tuned through electrical gating and results in an additional modulation of the heat transfer. We found that the near-field heat transfer between multilayer structure does not increase monotonously with the number of layer in the stack, which provides a way to control the heat transfer rate by the number of graphene layers in the multilayer structure. The results may benefit the applications of near-field energy harvesting and radiative cooling based on hybrid polaritons in two-dimensional materials.

physics.optics↗

arXiv2017

Method for Computationally Efficient Design of Dielectric Laser Accelerators

Dielectric microstructures have generated much interest in recent years as a means of accelerating charged particles when powered by solid state lasers. The acceleration gradient (or particle energy gain per unit length) is an important figure of merit. To design structures with high acceleration gradients, we explore the adjoint variable method, a highly efficient technique used to compute the sensitivity of an objective with respect to a large number of parameters. With this formalism, the sensitivity of the acceleration gradient of a dielectric structure with respect to its entire spatial permittivity distribution is calculated by the use of only two full-field electromagnetic simulations, the original and adjoint. The adjoint simulation corresponds physically to the reciprocal situation of a point charge moving through the accelerator gap and radiating. Using this formalism, we perform numerical optimizations aimed at maximizing acceleration gradients, which generate fabricable structures of greatly improved performance in comparison to previously examined geometries.

physics.optics↗

arXiv2017

Complete photonic bandgaps in supercell photonic crystals

We develop a class of supercell photonic crystals supporting complete photonic bandgaps based on breaking spatial symmetries of the underlying primitive photonic crystal. One member of this class based on a two-dimensional honeycomb structure supports a complete bandgap for an index-contrast ratio as low as $n_{high}/n_{low} = 2.1$, making this the first such 2D photonic crystal to support a complete bandgap in lossless materials at visible frequencies. The complete bandgaps found in such supercell photonic crystals do not necessarily monotonically increase as the index-contrast in the system is increased, disproving a long-held conjecture of complete bandgaps in photonic crystals.

physics.optics↗

arXiv2017

Non-reciprocal geometric phase in nonlinear frequency conversion

We describe analytically and numerically the geometric phase arising from nonlinear frequency conversion and show that such a phase can be made non-reciprocal by momentum-dependent photonic transition. Such non-reciprocity is immune to the shortcomings imposed by dynamic reciprocity in Kerr and Kerr-like devices. We propose a simple and practical implementation, requiring only a single waveguide and one pump, while the geometric phase is controllable by the pump and promises robustness against fabrication errors.

physics.optics↗

arXiv2017

Exact solution to the steady-state dynamics of a periodically-modulated resonator

We provide an analytic solution to the coupled-mode equations describing the steady-state of a single periodically-modulated optical resonator driven by a monochromatic input. The phenomenology of this system was qualitatively understood only in the adiabatic limit, i.e. for low modulation speed. However, both in and out of this regime, we find highly non-trivial effects for specific parameters of the modulation. For example, we show complete suppression of the transmission even with zero detuning between the input and the static resonator frequency. We also demonstrate the possibility for complete, lossless frequency conversion of the input into the side-band frequencies, as well as for optimizing the transmitted signal towards a given target temporal waveform. The analytic results are validated by first-principle simulations.

physics.optics↗

arXiv2017

Achieving arbitrary polarization control using complex birefringent meta-materials

We demonstrate that the key to realizing arbitrary control over pairs of polarization states of light, i.e. transforming an arbitrarily polarized pair of input states to an arbitrarily polarized pair of output states, is the ability to generate pairs of states with orthogonal polarizations from non-orthogonal pairs of initial states. We then develop a new class of non-Hermitian meta-materials, termed complex birefringent meta-materials, which are able to do exactly this. Such materials could facilitate the detection of small polarization changes in scattering experiments, as well as enable new polarization multiplexing schemes in communications networks.

physics.optics↗

arXiv2017

Enhancing Near-Field Radiative Heat Transfer with Si-based Metasurfaces

We demonstrate in this work that the use of metasurfaces provides a viable strategy to largely tune and enhance near-field radiative heat transfer between extended structures. In particular, using a rigorous coupled wave analysis, we predict that Si-based metasurfaces featuring two-dimensional periodic arrays of holes can exhibit a room-temperature near-field radiative heat conductance much larger than any unstructured material to date. We show that this enhancement, which takes place in a broad range of separations, relies on the possibility to largely tune the properties of the surface plasmon polaritons that dominate the radiative heat transfer in the near-field regime.

physics.optics↗

arXiv2016

Synthetic gauge potential and effective magnetic field in a Raman medium undergoing molecular modulation

We theoretically demonstrate non-trivial topological effects for a probe field in a Raman medium undergoing molecular modulation processes. The medium is driven by two non-collinear pump beams. We show that the angle between the pumps is related to an effective gauge potential and an effective magnetic field for the probe field in the synthetic space consisting of a synthetic frequency dimension and a spatial dimension. As a result of such effective magnetic field, the probe field can exhibit topologically-protected one-way edge state in the synthetic space, as well as Landau levels which manifests as suppression of both diffraction and sideband generation. Our work identifies a previously unexplored route towards creating topological photonics effects, and highlights an important connection between topological photonics and nonlinear optics.

physics.optics↗

arXiv2016

Fano Interference in Two-Photon Transport

We present a general input-output formalism for the few-photon transport in multiple waveguide channels coupled to a local cavity. Using this formalism, we study the effect of Fano interference in two-photon quantum transport. We show that the physics of Fano interference can manifest as an asymmetric spectral line shape in the frequency dependence of the two-photon correlation function. The two-photon fluorescence spectrum, on the other hand, does not exhibit the physics of Fano interference.

quant-ph↗

arXiv2016

General structure of two-photon S matrix in waveguide quantum electrodynamics systems containing a local quantum system with multiple ground states

We present the general structure of two-photon S matrix for a waveguide coupled to a local quantum system that supports multiple ground states. The presence of the multiple ground states results in a non-commutative aspect of the system with respect to the exchange of the orders of photons. Consequently, the two-photon S matrix significantly differs from the standard form as described by the cluster decomposition principle in the quantum field theory.

quant-ph↗

arXiv2016

Effects of non-uniform distributions of gain and loss in photonic crystals

We present a $\mathbf{k} \cdot \mathbf{p}$ theory of photonic crystals containing gain and loss in which the gain and loss are added to separate primitive cells of the underlying Hermitian system, thereby creating a supercell photonic crystal. We show that the supercell bands of this system can merge outward from the degenerate contour formed from folding the bands of the underlying Hermitian system into the supercell Brillouin zone, but that other accidental degeneracies in the band structure of the underlying Hermitian system do not yield band merging behavior. Finally, we show that the modal coupling matrix in PhCs with balanced gain and loss is trace-less, and thus the imaginary components of the eigenvalues can only move relative to one another as the strength of the gain and loss is varied, without any collective motion.

physics.optics↗

arXiv2016

Persistent Directional Current at Equilibrium in Nonreciprocal Many-Body Near Field Electromagnetic Heat Transfer

We consider the consequence of nonreciprocity in near-field heat transfer by studying systems consisting of magneto-optical nanoparticles.We demonstrate that, in thermal equilibrium, a nonreciprocal many-body system in heat transfer can support a persistent directional heat current, without violating the second law of thermodynamics. Such a persistent directional heat current cannot occur in reciprocal systems, and can only arise in many-body systems in heat transfer. The use of nonreciprocity therefore points to a new regime of near-field heat transfer for the control of heat flow in the nanoscale.

physics.optics↗

arXiv2016

Eigenvalue dynamics in the presence of non-uniform gain and loss

Loss-induced transmission in waveguides, and reversed pump dependence in lasers, are two prominent examples of counter-intuitive effects in non-Hermitian systems with patterned gain and loss. By analyzing the eigenvalue dynamics of complex symmetric matrices when a system parameter is varied, we introduce a general set of theoretical conditions for these two effects. We show that these effects arise in any irreducible system where the gain or loss is added to a subset of the elements of the system, without the need for parity-time symmetry or for the system to be near an exceptional point. These results are confirmed using full-wave numerical simulations. The conditions presented here vastly expand the design space for observing these effects. We also show that a similarly broad class of systems exhibit a loss-induced narrowing of the density of states.

physics.optics↗

arXiv2016

Hyperbolic Weyl point in reciprocal chiral metamaterial

We report the existence of Weyl points in a class of non-central symmetric metamaterials, which has time reversal symmetry, but does not have inversion symmetry due to chiral coupling between electric and magnetic fields. This class of metamaterial exhibits either type-I or type-II Weyl points depending on its non-local response. We also provide a physical realization of such metamaterial consisting of an array of metal wires in the shape of elliptical helixes which exhibits type-II Weyl points.

physics.optics↗