arXiv subjects

Xinan Liang

Publications and source records attributed to Xinan Liang.

7 recordsLinked to original sources

arXiv2025

Spin Correlations in Recirculating Multipass Alkali Cells for Advancing Quantum Magnetometry

Multipass cells enable long optical path lengths in compact volumes and are central to quantum technologies such as atomic magnetometers and optical quantum memories. In optical magnetometry, multipass geometries enhance sensitivity by increasing optical depth, reducing photon shot noise, and enabling quantum non-demolition detection. However, in conventional cylindrical multipass cells, Lissajous beam trajectories lead to repeated revisiting and incomplete mirror coverage, limiting effective volume utilization. Here we present a recirculating multipass alkali cell that overcomes these limitations by increasing the active-to-cell volume ratio and minimizing beam spot overlap. We develop an analytical ABCD-matrix model to predict beam trajectories, spot sizes, and astigmatism, validated by Zemax simulations. We further introduce a general analytical framework for spin correlation noise that incorporates astigmatism and spatial intensity distributions. By deriving the spin-noise time-correlation function and spectrum, we show how beam intensity profiles influence spin diffusion noise. Our results demonstrate improved beam coverage, reduced spot overlap, and enhanced spin correlation, particularly for concave mirrors with long focal lengths, while showing that avoiding tightly-focused regions significantly suppresses spin diffusion noise. These findings establish recirculating multipass cells as a practical, high-performance platform for precision atomic sensing and other multipass-cavity-based quantum devices.

quant-ph↗

arXiv2023

Electrically Tunable Reflective Metasurfaces with Continuous and Full Phase Modulation for High-efficiency Wavefront Control at Visible Frequencies

All-dielectric optical metasurfaces can locally control the amplitude and phase of light at the nanoscale, enabling arbitrary wavefront shaping. However, lack of post-fabrication tunability has limited the true potential of metasurfaces for many applications. Here, we utilize a thin liquid crystal (LC) layer as a tunable medium surrounding the metasurface to achieve a phase-only spatial light modulator (SLM) with high reflection in the visible frequency, exhibiting an active and continuous resonance tuning with associated 2pi phase control and uncoupled amplitude. Dynamic wavefront shaping is demonstrated by programming 96 individually addressable electrodes with a small pixel pitch of ~1 um. The small pixel size is facilitated by the reduced LC thickness, strongly suppressing crosstalk among pixels. This device is used to demonstrate dynamic beam steering with wide field-of-view and high absolute diffraction efficiencies. We believe that our demonstration may pave the way towards realizing next generation, high-resolution SLMs, with wide applications in dynamic holography, tunable optics and light detection and ranging (LiDAR), to mention a few.

physics.optics↗

arXiv2022

Tunable wavefront control in the visible spectrum using low-loss chalcogenide phase change metasurfaces

All-dielectric metasurfaces provide unique solutions for advanced wavefront manipulation of light with complete control of amplitude and phase at sub-wavelength scales. One limitation, however, for most of these devices is the lack of any post-fabrication tunability of their response. To break this limit, a promising approach is employing phase-change-materials (PCM), which provide a fast, low energy and non-volatile means to endow metasurfaces with a switching mechanism. In this regard, great advancements have been done in the mid infrared and near infrared spectrum using different chalcogenides. In the visible spectral range, however, very few devices have demonstrated full phase manipulation, high efficiencies, and reversible switching. Here, we experimentally demonstrate a tunable all-dielectric Huygens metasurface made of antimony sulfide (Sb2S3) PCM, a low loss and high-index material in the visible spectral range with a large contrast (nearly 0.5) between its amorphous and crystalline states. We show close to 2pi phase modulation with high associated transmittance and use it to create switchable beam steering and holographic display devices. These novel chalcogenide PCM metasurfaces have the potential to emerge as a platform for next generation spatial light modulators and to impact application areas such as tunable and adaptive flat optics, LiDAR, and many more.

physics.optics↗

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↗

arXiv2020

Large-scale Huygens metasurfaces for holographic 3D near-eye displays

Novel display technologies aim at providing the users with increasingly immersive experiences. In this regard, it is a long-sought dream to generate three-dimensional (3D) scenes with high resolution and continuous depth, which can be overlaid with the real world. Current attempts to do so, however, fail in providing either truly 3D information, or a large viewing area and angle, strongly limiting the user immersion. Here, we report a proof-of-concept solution for this problem, and realize a compact holographic 3D near-eye display with a large exit pupil of 10mm x 8.66mm. The 3D image is generated from a highly transparent Huygens metasurface hologram with large (>10^8) pixel count and subwavelength pixels, fabricated via deep-ultraviolet immersion photolithography on 300 mm glass wafers. We experimentally demonstrate high quality virtual 3D scenes with ~50k active data points and continuous depth ranging from 0.5m to 2m, overlaid with the real world and easily viewed by naked eye. To do so, we introduce a new design method for holographic near-eye displays that, inherently, is able to provide both parallax and accommodation cues, fundamentally solving the vergence-accommodation conflict that exists in current commercial 3D displays.

physics.optics↗

arXiv2019

Control of LED Emission with Functional Dielectric Metasurfaces

The improvement of light-emitting diodes (LEDs) is one of the major goals of optoelectronics and photonics research. While emission rate enhancement is certainly one of the targets, in this regard, for LED integration to complex photonic devices, one would require to have, additionally, precise control of the wavefront of the emitted light. Metasurfaces are spatial arrangements of engineered scatters that may enable this light manipulation capability with unprecedented resolution. Most of these devices, however, are only able to function properly under irradiation of light with a large spatial coherence, typically normally incident lasers. LEDs, on the other hand, have angularly broad, Lambertian-like emission patterns characterized by a low spatial coherence, which makes the integration of metasurface devices on LED architectures extremely challenging. A novel concept for metasurface integration on LED is proposed, using a cavity to increase the LED spatial coherence through an angular collimation. Due to the resonant character of the cavity, extending the spatial coherence of the emitted light does not come at the price of any reduction in the total emitted power. The experimental demonstration of the proposed concept is implemented on a GaP LED architecture including a hybrid metallic-Bragg cavity. By integrating a silicon metasurface on top we demonstrate two different functionalities of these compact devices: directional LED emission at a desired angle and LED emission of a vortex beam with an orbital angular momentum. The presented concept is general, being applicable to other incoherent light sources and enabling metasurfaces designed for plane waves to work with incoherent light emitters.

physics.optics↗

arXiv2018

A Metalens with Near-Unity Numerical Aperture

The numerical aperture (NA) of a lens determines its ability to focus light and its resolving capability. Having a large NA is a very desirable quality for applications requiring small light-matter interaction volumes or large angular collections. Traditionally, a large NA lens based on light refraction requires precision bulk optics that ends up being expensive and is thus also a specialty item. In contrast, metasurfaces allow the lens designer to circumvent those issues producing high NA lenses in an ultra-flat fashion. However, so far, these have been limited to numerical apertures on the same order of traditional optical components, with experimentally reported values of NA <0.9. Here we demonstrate, both numerically and experimentally, a new approach that results in a diffraction limited flat lens with a near-unity numerical aperture (NA>0.99) and sub-wavelength thickness (~λ/3), operating with unpolarized light at 715 nm. To demonstrate its imaging capability, the designed lens is applied in a confocal configuration to map color centers in sub-diffractive diamond nanocrystals. This work, based on diffractive elements able to efficiently bend light at angles as large as 82°, represents a step beyond traditional optical elements and existing flat optics, circumventing the efficiency drop associated to the standard, phase mapping approach.

physics.optics↗