arXiv subjects

Wing Yim Tam

Publications and source records attributed to Wing Yim Tam.

13 recordsLinked to original sources

arXiv2025

Metalens array for complex-valued optical discrete Fourier transform

Photonic computing has emerged as a promising platform for accelerating computational tasks with high degrees of parallelism, such as image processing and neural network. We present meta-DFT (discrete Fourier transform), a single layer metasurface device, designed to perform optical complex-to-complex DFT with O(N) time complexity. One critical challenge in free-space analog optical computing is to control the measurement error. Our scheme addresses this issue by focusing light on spatially separated focal points and reconstructing the complex phase, which enable error correction. We systematically evaluate the device's performance using input vectors with random complex amplitudes and phases, to demonstrate its robust accuracy. Our findings pave the way towards advancement of metasurface-based computation, offering a robust framework that is readily extensible to an arbitrary complex-valued matrix-vector multiplication (MVM).

physics.optics↗

arXiv2023

Metasurface for programmable quantum algorithms with quantum and classical light

Metasurfaces have recently opened up applications in the quantum regime, including quantum tomography and the generation of quantum entangled states. With their capability to store a vast amount of information by utilizing the various geometric degrees of freedom of nanostructures, metasurfaces are expected to be useful for processing quantum information. In this study, we propose and experimentally demonstrate a programmable metasurface capable of performing quantum algorithms using both classical light and quantum light at the single photon level. Our approach encodes multiple programmable quantum algorithms, such as Grover's algorithm and the quantum Fourier transform, onto the same metalens array on a metasurface. A spatial light modulator selectively excites different sets of metalenses to carry out the quantum algorithms, while the photon arrival data or interference patterns captured by a single photon camera are used to extract information about the output state. Our programmable quantum metasurface approach holds potential as a cost-effective means of miniaturizing components for quantum computing and information processing.

physics.optics↗

arXiv2021

One-sided destructive quantum interference from an exceptional point-enabled metasurface

We propose the concept of one-sided quantum interference based on non-Hermitian metasurfaces.By designing bianisotropic metasurfaces with a non-Hermitian exceptional point, we show that quantum interference can exist only on only one side but not another. This is the quantum inheritance of unidirectional zero reflection in classical optics.The one-side interference can be further manipulated with tailor-made metasurface. With two photons simultaneously entering the metasurface from different sides, the probability for only outputting one photon on the side with reflection can be modified to zero as a one-sided destructive quantum interference while the output on another side is free of interference. We design the required bianisotropic metasurface and numerically demonstrate the proposed effect. The non-Hermitian bianisotropic metasurfaces provide more degrees of freedom in tuning two-photon quantum interference, in parallel to the celebrated Hong-Ou-Mandel effect.

physics.optics↗

arXiv2021

Broadband optical magnetism in chiral metallic nanohole arrays by shadowing vapor deposition

We show that broadband optical magnetism can be achieved through incorporating multi-scaled 3D metallic meta-elements into Z-shaped nanohole arrays. The broadband effect arises from the excitation of multiple magnetic resonances in the meta-elements at different wavelengths. Moreover, the nanohole arrays exhibit a large transmission difference for left- and right-handed circularly polarized incident light due to the chiral arrangement of the meta-elements. More importantly, we have realized experimentally the broadband behavior for the optical range in Ag nanohole arrays fabricated by using a shadowing vapor deposition method. Our study opens up new opportunities for achieving broadband artificial magnetism at visible frequencies which allows possible applications in plasmonic bio-sensors or energy concentrators.

physics.optics↗

arXiv2020

Asymmetric frequency conversion with acoustic non-Hermitian space-time varying metamaterial

Space-time modulated metamaterials support extraordinary rich applications, such as parametric amplification, frequency conversion and non-reciprocal transmission. However, experimental realization of space-time modulation is highly non-trivial, hindering many interesting physics that are theoretically predicted to be experimentally demonstrated. Here, based on the proposed virtualized metamaterials with software-defined impulse response, we experimentally realize non-Hermitian space-time varying metamaterials for efficient and asymmetric frequency conversion by allowing material gain and loss to be tailor-made and balanced in the time domain. In the application of frequency conversion, the combination of space-time varying capability and non-Hermiticity allows us to diminish the main band through gain-loss balance and to increase the efficiency of side band conversion at the same time. In addition, our approach of software-defined metamaterials is flexible to realize the analogy of quantum interference in an acoustic system with design capability. Applying an additional modulation phase delay between different atoms allows to control such interference to get asymmetric amplification in frequency conversion.

physics.app-ph↗

arXiv2018

Angular momentum-dependent topological transport and its experimental realization using a transmission line network

Novel classical wave phenomenon analogs of the quantum spin Hall effect are mostly based on the construction of pseudo-spins. Here we show that the non-trivial topology of a system can also be realized using orbital angular momentum through angular-momentum-orbital coupling. The idea is illustrated with a tight-binding model and experimentally demonstrated with a transmission line network. We show experimentally that even a very small network cluster exhibits one-way topological edge states, and their properties can be described in terms of local Chern numbers. Our work provides a new mechanism to realize counterparts of the quantum spin Hall effect in classical waves and may offer insights for other systems.

cond-mat.mes-hall↗

arXiv2016

Controlling Interface States in 1D Photonic Crystals by tuning Bulk Geometric Phases

Interface states in photonic crystals usually require defects or surface/interface decorations. We show here that one can control interface states in 1D photonic crystals through the engineering of geometrical phase such that interface states can be guaranteed in even or odd, or in all photonic bandgaps. We verify experimentally the designed interface states in 1D multilayered photonic crystals fabricated by electron beam vapor deposition. We also obtain the geometrical phases by measuring the reflection phases at the bandgaps of the PCs and achieve good agreement with the theory. Our approach could provide a platform for the design of using interface states in photonic crystals for nonlinear optic, sensing, and lasing applications

physics.optics↗

arXiv2014

Plasmonic ultra-broadband polarizers based on Ag nano wire-slit arrays

We propose ultra-broadband reflective and absorptive polarizers in the visible range using multi-scaled Ag nano wire-slit arrays. The nano arrays can be tuned from reflective to absorptive by incorporating Ag wires/strips with different lengths/widths. The ultra-broadband nature of the absorptive array, with averaged absorption as high as ~80%, is due to the collective excitations of plasmonic resonances in the Ag wires/strips with different length scales. The Ag nano wire-slit arrays are realized experimentally by using a simple two-times shadowing vapor deposition method. They exhibit broadband transmission difference, in good agreement with simulations. The multi-scaled Ag nano wire-slit array has potential applications as broadband linear polarizers and anti-reflective materials in both optics and photovoltaics.

physics.optics↗

arXiv2007

Icosahedral quasicrystals for visible wavelengths by optical interference holography

Quasicrystals, realized in metal alloys, are a class of lattices exhibiting symmetries that fall outside the usual classification for periodic crystals. They do not have translational symmetry and yet the lattice points are well ordered. Furthermore, they exhibit higher rotational symmetry than periodic crystals. Because of the higher symmetry (more spherical), they are more optimal than periodic crystals in achieving complete photonic bandgaps in a new class of materials called photonic crystals in which the propagation of light in certain frequency ranges is forbidden. The potential of quasicrystals has been demonstrated in two dimensions for the infrared range and, recently, in three-dimensional icosahedral quasicrystals fabricated using a stereo lithography method for the microwave range. Here, we report the fabrication and optical characterization of icosahedral quasicrystals using a holographic lithography method for the visible range. The icosahedral pattern, generated using a novel 7-beam optical interference holography, is recorded on photoresists and holographic plates. Electron micrographs of the photoresist samples show clearly the symmetry of the icosahedral quasicrytals in the submicron range, while the holographic plate samples exhibit bandgaps in the angular-dependent transmission spectra in the visible range. Calculations of the bandgaps due to reflection planes inside the icosahedral quasicrystal show good agreement with the experimental results.

physics.optics↗

arXiv2006

Icosahedral quasicrystals by optical interference holography

Optical interference holography has been proved to be a useful technique in fabricating periodic photonic crystals in which electromagnetic waves are forbidden in certain frequency bandgaps. Compared to periodic crystals quasicrystals, having higher point group symmetry, are more favourable in achieving complete bandgaps. In this report, we propose two seven-beam optical interference configurations based on the reciprocal vector space representations for quasicrystals to fabricate icosahedral quasicrystals. Interference simulations for the quasicrystals exhibit the full symmetry of an icosahedron. The result paves the path for the fabrication of photonic quasicrystals using holographic lithography.

physics.optics↗

arXiv2006

Woodpile and diamond structures by optical interference holography

We report the use of an optical interference holographic setup with a five-beam configuration, consisting of four side beams and one central beam from the same half space, to fabricate woodpile and diamond structures for the use as photonic bandgap materials in which electromagnetic waves are forbidden in the bandgap. By exploiting the advantage of the binarization of the interference pattern, using intensity cut-off, either linear or circular central beam can be used. More importantly, the beam configurations can be easily implemented experimentally as compared to other configurations in which the interfering beams are counter-propagating from both half spaces.

physics.optics↗

arXiv2006

Realization of Woodpile Structure Using Optical Interference Holography

We report the use of a (4+1)-beam optical interference holography technique to fabricate woodpile structures in photo-resists. The configuration consists of 4 linear polarized side beams arranged symmetrically around a circular polarized central beam with all the beams from the same half space, making it easily accessible experimentally. The fabricated woodpile structures are in good agreement with model simulations. Furthermore, woodpiles with the diamond symmetry are also obtained by exploiting the deformations of the photo-resists. Directional bandgaps in the visible range are also observed for the samples with and without the correct stacking of the woodpile structures.

physics.optics↗

arXiv2005

Chiral microstructures (spirals) fabrication by holographic lithography

We present an optical interference model to create chiral microstructures (spirals) and its realization in photoresist using holographic lithography. The model is based on the interference of six equally-spaced circumpolar linear polarized side beams and a circular polarized central beam. The pitch and separation of the spirals can be varied by changing the angle between the side beams and the central beam. The realization of the model is carried out using the 325 nm line of a He-Cd laser and spirals of sub-micron size are fabricated in photoresist.

physics.optics↗