arXiv subjects

Shi-Qiang Li

Publications and source records attributed to Shi-Qiang Li.

6 recordsLinked to original sources

arXiv2021

High resolution multispectral spatial light modulators based on tunable Fabry-Perot nanocavities

Spatial light modulators (SLMs) are the most relevant technology for dynamic wavefront manipulation. They find diverse applications ranging from novel displays to optical and quantum communications. Among commercial SLMs for phase modulation, Liquid Crystal on Silicon (LCoS) offers the smallest pixel size and, thus, the most precise phase mapping and largest field of view (FOV). Further pixel miniaturization, however, is not possible in these devices due to inter-pixel cross-talks, which follow from the high driving voltages needed to modulate the thick liquid crystal (LC) cells that are necessary for full phase control. Newly introduced metasurface-based SLMs provide means for pixel miniaturization by modulating the phase via resonance tuning. These devices, however, are intrinsically monochromatic, limiting their use in applications requiring multi-wavelength operation. Here, we introduce a novel design allowing small pixel and multi-spectral operation. Based on LC-tunable Fabry-Perot nanocavities engineered to support multiple resonances across the visible range (including red, green and blue wavelengths), our design provides continuous 2pi phase modulation with high reflectance at each of the operating wavelengths. Experimentally, we realize a device with 96 pixels (~1μm pitch) that can be individually addressed by electrical biases. Using it, we first demonstrate multi-spectral programmable beam steering with FOV~18 degrees and absolute efficiencies exceeding 40%. Then, we reprogram the device to achieve multi-spectral lensing with tunable focal distance and efficiencies ~27%. Our design paves the way towards a new class of SLM for future applications in displays, optical computing and beyond.

physics.optics↗

arXiv2021

80-degree field-of-view transmissive metasurface-based spatial light modulator

Compact, lightweight and high-performance spatial light modulators (SLMs) are crucial for modern optical technologies. The drive for pixel miniaturization, necessary to improve their performance, has led to a promising alternative, active optical metasurfaces, which enable tunable subwavelength wavefront manipulation. Here, we demonstrate an all-solid-state programmable transmissive SLM device based on Huygens dielectric metasurfaces. The metasurface features electrical tunability, provided by mature liquid crystals (LCs) technology. In contrast to conventional LC SLMs, our device enables high resolution with a pixel size of ~1 um. We demonstrate its performance by realizing programmable beam steering, which exhibits high side mode suppression ratio of ~6 dB. By complementing the device with a 3D printed doublet microlens, fabricated using two-photon polymerization, we enhance the field of view up to ~80 degrees. The developed prototype paves the way to compact, efficient and multifunctional devices for next generation augmented reality displays, light detection and ranging (LiDAR) systems and optical computing.

physics.optics↗

arXiv2019

Phase-only transmissive spatial light modulator based on tunable dielectric metasurface

Rapidly developing augmented reality (AR) and 3D holographic display technologies require spatial light modulators (SLM) with high resolution and viewing angle to be able to satisfy increasing customer demands. Currently available SLMs, as well as their performance, are limited by their large pixel sizes of the order of several micrometres. Further pixel size miniaturization has been stagnant due to the persistent challenge to reduce the inter-pixel crosstalk associated with the liquid crystal (LC) cell thickness, which has to be large enough to accumulate the required 2π phase difference. Here, we propose a concept of tunable dielectric metasurfaces modulated by a liquid crystal environment, which can provide abrupt phase change and uncouple the phase accumulation from the LC cell thickness, ultimately enabling the pixel size miniaturization. We present a proof-of-concept metasurface-based SLM device, configured to generate active beam steering with >35% efficiency and large beam deflection angle of 11°, with LC cell thickness of only 1.5 μm, much smaller than conventional devices. We achieve the pixel size of 1.14 μm corresponding to the image resolution of 877 lp/mm, which is 30 times larger comparing to the presently available commercial SLM devices. High resolution and viewing angle of the metasurface-based SLMs opens up a new path to the next generation of near-eye AR and 3D holographic display technologies.

physics.optics↗

arXiv2018

Origin of the anapole condition as revealed by a simple expansion beyond the toroidal multipole

Toroidal multipoles are a topic of increasing interest in the nanophotonics and metamaterials communities. In this paper, we separate out the toroidal multipole components of multipole expansions in polar coordinates (two- and three-dimensional) by expanding the Bessel or spherical Bessel functions. We discuss the formation of the lowest order of magnetic anapoles from the interaction between the magnetic toroidal dipole and the magnetic dipole. Our method also reveals that there are higher order current configurations other than the electric toroidal multipole that have the same radiation characteristics as the pure electric dipole. Furthermore, we find that the anapole condition requires that there is a perfect cancellation of all higher order current configurations.

physics.app-ph↗

arXiv2015

Broadband resonances in ITO nanorod arrays

In the nanophotonics community, there is an active discussion regarding the origin of the selective absorption/scattering of light by the resonances with nanorod arrays. Here we report a study of the resonances in ordered indium-tin-oxide (ITO) nanorod arrays resulted from the waveguide modes. We discover that with only 2.4% geometrical coverage, the micron-length nanorod arrays strongly interact with light across an extra-wide band from visible to mid-infrared resulting in less than 10% transmission. Simulations show excellent agreement with our experimental observation. Near-field profile obtained from simulation reveals the electric field is mainly localized on the surfaces of the nanorods at all the resonances. Theoretical analysis is then applied to explain the resonances and it was found that the resonances in the visible are different from those in the infrared. When the light arrives at the array, part of the light wave propagates through the free space in between the nanorods and part of the wave is guided inside the nanorods and the phase difference at the ends of the rod interactions forms the basis of the resonances in the visible region; while the resonances in the infrared are Fabry-Perot resonances of the surface guided waves between the two ends of the nanorods. The simple analytical formulae developed predict the spectral positions of these resonances well. This information can be used to design devices like wavelength-selective photodetector, modulators, and nanorod-based solar cells.

physics.optics↗

arXiv2014

Highly tunable ultra-narrow-resonances with optical nano-antenna phased arrays in the infrared

We report our recent development in pursuing high Quality-Factor (high-Q factor) plasmonic resonances, with vertically aligned two dimensional (2-D) periodic nanorod arrays. The 2-D vertically aligned nano-antenna array can have high-Q resonances varying arbitrarily from near infrared to terahertz regime, as the antenna resonances of the nanorod are highly tunable through material properties, the length of the nanorod, and the orthogonal polarization direction with respect to the lattice surface,. The high-Q in combination with the small optical mode volume gives a very high Purcell factor, which could potentially be applied to various enhanced nonlinear photonics or optoelectronic devices. The 'hot spots' around the nanorods can be easily harvested as no index-matching is necessary. The resonances maintain their high-Q factor with the change of the environmental refractive index, which is of great interest for molecular sensing.

physics.optics↗