arXiv subjects

Shanhui Fan

Publications and source records attributed to Shanhui Fan.

At least 199 records · Page 11Linked to original sources

arXiv2018

Electronically Programmable Photonic Molecule

Physical systems with discrete energy levels are ubiquitous in nature and are fundamental building blocks of quantum technology. Realizing controllable artifcial atom- and molecule-like systems for light would allow for coherent and dynamic control of the frequency, amplitude and phase of photons. In this work, we demonstrate a photonic molecule with two distinct energy-levels and control it by external microwave excitation. We show signature two-level dynamics including microwave induced photonic Autler-Townes splitting, Stark shift, Rabi oscillation and Ramsey interference. Leveraging the coherent control of optical energy, we show on-demand photon storage and retrieval in optical microresonators by reconfguring the photonic molecule into a bright-dark mode pair. These results of dynamic control of light in a programmable and scalable electro-optic platform open doors to applications in microwave photonic signal processing, quantum photonics in the frequency domain, optical computing concepts and simulations of complex physical systems.

physics.optics↗

arXiv2018

Absence of unidirectionally propagating surface plasmon-polaritons in nonreciprocal plasmonics

In the presence of an external magnetic field, the surface plasmon polariton that exists at the metal-dielectric interface is believed to support a unidirectional frequency range near the surface plasmon frequency, where the surface plasmon polariton propagates along one but not the opposite direction. Recent works have pointed to some of the paradoxical consequences of such a unidirectional range, including in particular the violation of the time-bandwidth product constraint that should otherwise apply in general in static systems. Here we show that such a unidirectional frequency range is nonphysical, using both a general thermodynamic argument, and a detailed calculation based on a nonlocal hydrodynamic Drude model for the metal permittivity. Our calculation reveals that the surface plasmon-polariton remains bidirectional for all frequencies. This work overturns a long-held belief in nonreciprocal photonics, and highlights the importance of quantum plasmonic concepts for the understanding of nonreciprocal plasmonic effects.

physics.optics↗

arXiv2018

Synthetic Dimension in Photonics

The physics of a photonic structure is commonly described in terms of its apparent geometric dimensionality. On the other hand, with the concept of synthetic dimension, it is in fact possible to explore physics in a space with a dimensionality that is higher as compared to the apparent geometrical dimensionality of the structures. In this review, we discuss the basic concepts of synthetic dimension in photonics, and highlighting the various approaches towards demonstrating such synthetic dimension for fundamental physics and potential applications.

physics.optics↗

arXiv2018

Implications of exceptional points for few-photon transport in waveguide quantum electrodynamics

We identify a general connection between the physics of exceptional points in non-Hermitian systems and the few-photon bound states in waveguide quantum electrodynamics (QED) systems. We show that, in waveguide QED systems where the local quantum system exhibits an exceptional point, the tightest-bound few-photon bound state occurs at the exceptional point. We illustrate this connection with an explicit computation on a waveguide QED system in which a waveguide is coupled to a Jaynes-Cummings system. Our result provides a quantum signature of the exceptional point physics and indicates that the physics of exceptional point can be used to understand and control the photon-photon interaction.

quant-ph↗

arXiv2018

Laterally confined photonic crystal surface emitting laser based on monolayer tungsten disulfide operating at room temperature

We report a photonic crystal surface emitting laser using monolayer tungsten disulfide as the gain medium. The cavity design utilizes a heterostructure in the photonic crystal lattice to provide lateral confinement for a high quality factor with a compact active region. Room temperature continuous wave lasing is realized after integrating monolayer tungsten disulfide flakes onto the silicon nitride photonic crystal on quartz substrate. Highly directional, near surface normal emission has also been experimentally demonstrated.

physics.optics↗

arXiv2018

First-Principles Threshold Calculation of Photonic Crystal Surface-Emitting Lasers Using Rigorous Coupled Wave Analysis

We show that the threshold of a photonic crystal surface-emitting laser can be calculated from first-principles by the method of rigorous coupled wave analysis (RCWA), which has been widely used to simulate the response spectra of passive periodic structures. Here, the scattering matrix (S-matrix) of a surface-emitting laser structure with added gain is calculated on the complex frequency plane using RCWA, and the lasing threshold is determined by the value of gain for which the pole of the S-matrix reaches the real axis. This approach can be used for surface emitting laser struc tures in general, and is particularly useful for the surface emitting laser systems with complex in-plane structures.

physics.optics↗

arXiv2018

Few-photon scattering and emission from open quantum systems

We show how to use the input-output formalism compute the propagator for an open quantum system, i.e. quantum networks with a low dimensional quantum system coupled to one or more loss channels. The total propagator is expressed entirely in terms of the Green's functions of the low dimensional quantum system, and it is shown that these Green's functions can be computed entirely from the evolution of the low-dimensional system with an effective non-hermitian Hamiltonian. Our formalism generalizes the previous works that have focused on time independent Hamiltonians to systems with time dependent Hamiltonians, making it a suitable computational tool for the analysis of a number of experimentally interesting quantum systems. We illustrate our formalism by applying it to analyze photon emission and scattering from driven and undriven two-level system and three- level lambda system.

quant-ph↗

arXiv2018

Direction-Dependent Parity-Time Phase Transition and Non-Reciprocal Directional Amplification with Dynamic Gain-Loss Modulation

We show that a dynamic gain-loss modulation in an optical structure can lead to a direction-dependent parity-time (PT) phase transition. The phase transition can be made thresholdless in the forward direction, and yet remains with a non-zero threshold in the backward direction. As a result, non-reciprocal directional amplification can be realized.

physics.optics↗

arXiv2018

Training of photonic neural networks through in situ backpropagation

Recently, integrated optics has gained interest as a hardware platform for implementing machine learning algorithms. Of particular interest are artificial neural networks, since matrix-vector multi- plications, which are used heavily in artificial neural networks, can be done efficiently in photonic circuits. The training of an artificial neural network is a crucial step in its application. However, currently on the integrated photonics platform there is no efficient protocol for the training of these networks. In this work, we introduce a method that enables highly efficient, in situ training of a photonic neural network. We use adjoint variable methods to derive the photonic analogue of the backpropagation algorithm, which is the standard method for computing gradients of conventional neural networks. We further show how these gradients may be obtained exactly by performing intensity measurements within the device. As an application, we demonstrate the training of a numerically simulated photonic artificial neural network. Beyond the training of photonic machine learning implementations, our method may also be of broad interest to experimental sensitivity analysis of photonic systems and the optimization of reconfigurable optics platforms.

physics.optics↗

arXiv2018

Unidirectional light transport in dynamically modulated waveguides

One-way edge states at the surface of photonic topological insulators are of significant interest for communications, nonlinear and quantum optics. Moreover, when reciprocity is broken in a photonic topological insulator, these states provide protection against disorder, which is of particular importance for slow light applications. Achieving such a one-way edge state, however, requires the construction of a two-dimensional structure. Here, we show how unidiriectional Floquet bands can arise in purely one-dimensional, adiabatically-modulated dynamic systems, in contrasts with the higher dimensionality needed in topological insulators. We also show that, using realistic experimental parameters, the concept can be implemented using both a coupled-resonator optical waveguide and a photonic crystal waveguide. Furthermore, we illustrate the associated protection against disorder, and find it to be of a novel nature when compared to Floquet topological insulators.

physics.optics↗

arXiv2018

Localization and time-reversal of light through dynamic modulation

We study the dynamics of a waveguide made of coupled resonators with a sinusoidal modulation of the resonance frequencies. We present a modulation scheme that achieves complete dynamic localization and is experimentally suitable for optical cavities. Furthermore, we highlight the importance of the way the modulation is turned on and off. One striking consequence is that, while a state returns to its starting amplitude at the end of every cycle, it can also be fully time-reversed if the modulation is turned off mid-cycle. Finally, we show that localization is always achieved when the modulation envelope is adiabatic with respect to the oscillation frequency. The results are experimentally feasible using existing integrated photonic technologies, and are relevant to applications like tunable delay lines, dispersion compensation, and imaging.

physics.optics↗

arXiv2018

Constructing three-dimensional photonic topological insulator using two-dimensional ring resonator lattice with a synthetic frequency dimension

In the development of topological photonics, achieving three dimensional topological insulators is of significant interest since it enables the exploration of new topological physics with photons, and promises novel photonic devices that are robust against disorders in three dimensions. Previous theoretical proposals towards three dimensional topological insulators utilize complex geometries that are challenging to implement. Here, based on the concept of synthetic dimension, we show that a two-dimensional array of ring resonators, which was previously demonstrated to exhibit a two-dimensional topological insulator phase, in fact automatically becomes a three-dimensional topological insulator, when the frequency dimension is taken into account. Moreover, by modulating a few of the resonators, a screw dislocation along the frequency axis can be created, which provides robust transport of photons along the frequency axis. Demonstrating the physics of screw dislocation in a topological system has been a significant challenge in solid state systems. Our work indicates that the physics of three-dimensional topological insulator can be explored in standard integrated photonics platforms, leading to opportunities for novel devices that control the frequency of light.

physics.optics↗

arXiv2017

Effects of non-Hermitian perturbations on Weyl Hamiltonians with arbitrary topological charges

We provide a systematic study of non-Hermitian topologically charged systems. Starting from a Hermitian Hamiltonian supporting Weyl points with arbitrary topological charge, adding a non-Hermitian perturbation transforms the Weyl points to one-dimensional exceptional contours. We analytical prove that the topological charge is preserved on the exceptional contours. In contrast to Hermitian systems, the addition of gain and loss allows for a new class of topological phase transition: when two oppositely charged exceptional contours touch, the topological charge can dissipate without opening a gap. These effects can be demonstrated in realistic photonics and acoustics systems.

cond-mat.mes-hall↗

arXiv2017

A Photonic Crystal Slab Laplace Differentiator

We introduce an implementation of a Laplace differentiator based on a photonic crystal slab that operates at transmission mode. We show that the Laplace differentiator can be implemented provided that the guided resonances near the $Γ$ point exhibit an isotropic band structure. Such a device may facilitate nanophotonics-based optical analog computing for image processing.

physics.optics↗

arXiv2017

Generate tensor network state by sequential single-photon scattering in waveguide QED systems

We propose a scheme to generate photonic tensor network states by sequential scattering of photons in waveguide QED systems. We show that sequential scatterings can convert a series of unentangled photons into any type of matrix product states. We also demonstrate the possibility of generating projected entangled pair states with arbitrary network representation by photon re-scattering.

quant-ph↗

arXiv2017

Enhanced High-Harmonic Generation from an All-Dielectric Metasurface

The recent observation of high-harmonic generation from solids creates a new possibility for engineering fundamental strong-field processes by patterning the solid target with subwavelength nanostructures. All-dielectric metasurfaces exhibit high damage thresholds and strong enhancement of the driving field, making them attractive platforms to control high-harmonics and other high-field processes at nanoscales. Here we report enhanced non-perturbative high-harmonic emission from a Si metasurface that possesses a sharp Fano resonance resulting from a classical analogue of electromagnetically induced transparency. Harmonic emission is enhanced by more than two orders of magnitude compared to unpatterned samples. The enhanced high harmonics are highly anisotropic with excitation polarization and are selective to excitation wavelength due to its resonant feature. By combining nanofabrication technology and ultrafast strong-field physics, our work paves the way for designing new compact ultrafast photonic devices that operate under high intensities and short wavelengths.

physics.optics↗

arXiv2017

Thermodynamic Limits of Energy Harvesting from Outgoing Thermal Radiation

We derive the thermodynamic limits of harvesting power from the outgoing thermal radiation from the ambient to the cold outer space. The derivations are based on a duality relation between thermal engines that harvest solar radiation and those that harvest outgoing thermal radiation. In particular, we derive the ultimate limit for harvesting outgoing thermal radiation, which is analogous to the Landersberg limit for solar energy harvesting, and show that the ultimate limit far exceeds what was previously thought to be possible. As an extension of our work, we also derive the ultimate limit of efficiency of thermophotovoltatic systems.

physics.optics↗

arXiv2017

Synthetic space with arbitrary dimensions in a few rings undergoing dynamic modulation

We show that a single ring resonator undergoing dynamic modulation can be used to create a synthetic space with an arbitrary dimension. In such a system the phases of the modulation can be used to create a photonic gauge potential in high dimensions. As an illustration of the implication of this concept, we show that the Haldane model, which exhibits non-trivial topology in two dimensions, can be implemented in the synthetic space using three rings. Our results point to a route towards exploring higher-dimensional topological physics in low-dimensional physical structures. The dynamics of photons in such synthetic spaces also provides a mechanism to control the spectrum of light.

physics.optics↗