Spatial Light Modulator Research Articles

Dynamic geometric phase holography based on in-plane switching liquid crystal

ABSTRACT Liquid crystal geometric phase modulation technology is expected to achieve thin, small and achromatic spatial light modulation, which in turn has the potential to achieve holographic displays with large field angles and high clarity. This article presents a continuous dynamic geometric phase liquid crystal spatial light modulation method based on in-plane switching (IPS) mode. The relationship between geometric phase modulation and driving voltage is calibrated by using interferometry. Two hundred fifty-six phase orders within the phase modulation range of 0~π/2 is achieved. Subsequently, a phase hologram with a modulation range of 0~π/2 was designed by combining the GS (Gerchberg-Saxton) algorithm and single Fourier transform, demonstrating the holographic display capability. This article provides a low-cost approach for dynamic geometric phase holographic display.

NeuroART: Real-Time Analysis and Targeting of Neuronal Population Activity during Calcium Imaging for Informed Closed-Loop Experiments.

Two-photon calcium imaging allows for the activity readout of large populations of neurons at single cell resolution in living organisms, yielding new insights into how the brain processes information. Holographic optogenetics allows us to trigger activity of this population directly, raising the possibility of injecting information into a living brain. Optogenetic triggering of activity that mimics "natural" information, however, requires identification of stimulation targets based on real-time analysis of the functional network. We have developed NeuroART (Neuronal Analysis in Real Time), software that provides real-time readout of neuronal activity integrated with downstream analysis of correlations and synchrony and of sensory metadata. On the example of auditory stimuli, we demonstrate real-time inference of the contribution of each neuron in the field of view to sensory information processing. To avoid the limitations of microscope hardware and enable collaboration of multiple research groups, NeuroART taps into microscope data streams without the need for modification of microscope control software and is compatible with a wide range of microscope platforms. NeuroART also integrates the capability to drive a spatial light modulator (SLM) for holographic photostimulation of optimal stimulation targets, enabling real-time modification of functional networks. Neurons used for photostimulation experiments were extracted from Sprague Dawley rat embryos of both sexes.

Optical characteristics and wavefront control of femtosecond laser pulses and their effect on the performance of diamond graphite electrodes

High purity diamond is an excellent material for making radiation hard detectors suitable for high-energy particle detection, cancer treatment and other fields. Electrodes are formed by the localized graphitization of the diamond bulk, where fine control of the manufacturing process is essential to the performance of the detector. The resistivity of the electrode formed by diamond graphitization significantly affects the performance of the detector. Femtosecond laser pulses interact with the material for a very short time (10-13 s), exhibiting a cold processing. In this paper, we utilize Spatial Light Modulators (SLM) to optimize the optical characteristics of the 800 nm femtosecond laser pulse and control the graphitization process. Our research focuses on the analysis of the influence exerted by the pulse characteristics on the diameter and resistivity of inscribed graphite structures. By examining these parameters, the study aims to refine the graphitization process, thereby optimizing the functional characteristics of the diamond-based detectors.

Spatiotemporal hologram

Spatiotemporal structured light has opened up new avenues for optics and photonics. Current spatiotemporal manipulation of light mostly relies on phase-only devices such as liquid crystal spatial light modulators to generate spatiotemporal optical fields with unique photonic properties. However, simultaneous manipulation of both amplitude and phase of the complex field for the spatiotemporal light is still lacking, limiting the diversity and richness of achievable photonic properties. In this work, a simple and versatile spatiotemporal holographic method that can arbitrarily sculpt the spatiotemporal light is presented. The capabilities of this simple yet powerful method are demonstrated through the generation of fundamental and higher-order spatiotemporal Bessel wavepackets, spatiotemporal crystal-like and quasi-crystal-like structures, and spatiotemporal flat-top wavepackets. Fully customizable spatiotemporal wavepackets will find broader application in investigating the dynamics of spatiotemporal fields and interactions between ultrafast spatiotemporal pulses and matters, unveiling previously hidden light-matter interactions and unlocking breakthroughs in photonics and beyond.

Far-Field Phase-Shifting Structured Light Illumination Enabled by Polarization Multiplexing Metasurface for Super-Resolution Imaging.

The phase-shifting structured light illumination technique is widely used in imaging but often relies on mechanical translation stages or spatial light modulators, leading to system instability, low displacement accuracy, and limited integration feasibility. In response to these challenges, we propose and demonstrate an approach for generating far-field phase-shifting structured light using a polarization multiplexing metasurface. By controlling the polarization states of incident and transmitted light, the metasurface creates a three-step displacement of structured light, eliminating the need to move samples or illumination sources. As a proof of concept, we experimentally demonstrate microscopic imaging using structured light illumination generated by metasurfaces, extracting high-frequency information from objects, and surpassing the diffraction limit. The proposed metasurface platform offers a promising approach for developing compact and robust phase-shifting imaging systems, with broad prospects in quantitative detection, machine vision, and beyond.

Quality improvement of unfiltered holography by optimizing high diffraction orders with fill factor.

Computer-generated holography (CGH) suffers from high diffraction orders (HDOs) due to the pixelated nature of spatial light modulators (SLMs), typically requiring bulky optical filtering systems. To address this issue, a novel unfiltered holography approach known as the high-order gradient descent (HOGD) algorithm was previously introduced to optimize HDOs without optical filtering, enabling compact holographic displays. However, this algorithm overlooks a crucial physical parameter of SLMs-the fill factor-leading to limited optical quality. Here, we introduce a fill factor-based HOGD (FF-HOGD) algorithm, specifically designed to improve the quality of unfiltered holography by incorporating the fill factor into the optimization process. The quality advantage of FF-HOGD is demonstrated through numerical simulations and optical experiments.

Decoupling of Phase and Amplitude Channels with a Terahertz Metasurface Toward High‐Security Image Hiding

AbstractSteganography technology which conceals a message in a carrier to make it invisible is critical for information security. Conventional optical image steganography using diffractive optical components or spatial light modulators suffers from less encoding channel and bulky volume. The emergence of multifunctional metasurface that can manipulate abundant physical dimensions of optical fields allows the multi‐channel image steganography in a compact volume. Here, the image hiding in a metasurface is demonstrated by modulating the amplitude, phase, and polarization states of terahertz (THz) waves completely. Especially, the phase channel can decouple from the amplitude channel based on a Fresnel‐diffraction‐based algorithm. By directly measuring the phase distribution using the homemade THz focal plane imaging system, the number of transmission channels can expand from N to 2N. As a proof of concept, it is shown that the secret images can encode in the phase channel and subsequently extract by using different keys, such as polarization states, detection distances, and its combinations. Moreover, different hiding strategies with different attacker behaviors are also demonstrated. The decoupling of the phase and amplitude channels with a single metasurface may open an avenue toward innovative optoelectronic devices for optical image steganography, data storage, and terahertz communication.

Compact binocular holographic near-eye 3D display system based on a liquid crystal polarization grating

Holographic technology is considered as one of the most ideal 3D display technologies and has significant potential in near-eye display. However, binocular holographic near-eye 3D display still faces challenges such as serious visual fatigue and complex system. Here, we propose a compact binocular holographic near-eye 3D display system based on a liquid crystal polarization grating (LCPG). Based on the LCPG, the reconstructed light can be deflected respectively to left and right viewing areas. The proposed system achieves binocular display with only one phase-only spatial light modulator used to load computer-generated hologram, which makes the binocular display system more compact. Simultaneously, the proposed system reduces mismatches in the images perceived by two eyes, thus achieving a better binocular display effect. Experimental results demonstrate the feasibility of the proposed binocular holographic near-eye 3D display system with dual viewing areas. Additionally, based on the time-division multiplexing method, dynamic binocular holographic near-eye display can be achieved. The proposed system has potential applications in holographic virtual reality and augmented reality display.

Light-field modulation and optimization near metal nanostructures utilizing spatial light modulators

Abstract Plasmonic modes within metal nanostructures play a pivotal role in various nanophotonic applications. However, a significant challenge arises from the fixed shapes of nanostructures post-fabrication, resulting in limited modes under ordinary illumination. A promising solution lies in far-field control facilitated by spatial light modulators (SLMs), which enable on-site, real-time, and non-destructive manipulation of plasmon excitation. Through the robust modulation of the incident light using SLMs, this approach enables the generation, optimization, and dynamic control of surface plasmon polariton (SPP) and localized surface plasmon (LSP) modes. The versatility of this technique introduces a rich array of tunable degrees of freedom to plasmon-enhanced spectroscopy, offering novel approaches for signal optimization and functional expansion in this field. This paper provides a comprehensive review of the generation and modulation of SPP and LSP modes through far-field control with SLMs and highlights the diverse applications of this optical technology in plasmon-enhanced spectroscopy.

Impact of altering phase modulation and geometrical shape of laser beam via a phase-only spatial light modulator on laser-induced fluorescence

This study investigates the impact of modulating and shaping a laser beam via a phase-only spatial light modulator (SLM) on the intensity of the laser-induced fluorescence (LIF) signal. Different phase modulations ranging from 0 to 2π are applied to the SLM window to evaluate the effect of the modulated beam on the emitted LIF signal from extra virgin olive oil EVOO samples. The laser beam is also shaped into circular and square geometries with varying diameters to determine the optimum size for maximizing the LIF signal strength. The results reveal that the highest LIF signal intensity could be obtained after modulating the incident laser beam with phase shifts of 0 and 2π, with an improvement factor of approximately 3 for Avanti olive oil and 1.42 for Al Jouf olive oil. Furthermore, laser beam shaping into a circular aperture with a radius of 2.45 mm or a square aperture with a side length of 2.45 mm yields the highest LIF signal improvement, with enhancement factors of approximately 2.9 for Avanti olive oil and 1.42 for Al Jouf olive oil. This work demonstrates the potential of SLM-based beam shaping techniques to optimize LIF measurements by tailoring the wavefront characteristics of the excitation laser source.

Dynamic deformation measurement with 2-frame phase-shifting speckle interferometry based on speckle statistics and wavefront multiplexing.

Phase-shifting speckle interferometry could achieve full-field deformation measurement of rough surfaces. To meet the dynamic requirement and further improve the accuracy, a two-step synchronous phase-shifting measurement system is established based on the polarization-sensitive phase modulation ability of a liquid crystal spatial light modulator; by multiplexing the reference wavefront, an accurate phase shift is generated between two independent recording channels, and a common-path self-reference vortex interference structure is built for precise spatial registration. Meanwhile, according to the speckle statistical principle, a novel two-frame phase-shifting algorithm as well as a two-step spatial registration strategy is presented to strengthen the robustness of intensity and position differences caused by spatial-multiplexing; thereby, accurate transient deformation can be directly obtained from phase-shifting speckle interferograms recorded before and after deformation. The effectiveness and accuracy of the proposal are validated from the out-of-plane deformation measurement experiment by comparing with the traditional two-step and four-step phase-shifting methods. The dynamic ability is exhibited through reconstructing mechanical and thermal deformations across various application scenarios.

Direct amplitude-only hologram realized by broken symmetry.

Holographic displays have been a long-standing ambition for decades to realize true-to-life reconstruction. However, their practical adoption is hindered by their subpar image quality compared to two-dimensional displays, which is fundamentally limited by restricted spatial frequency bandwidth and artifacts. We address the limitation by using a symmetry-broken amplitude-only spatial light modulator, demonstrating image quality comparable to that of two-dimensional displays. The broken conjugate symmetry induced by phase noise of modulators eliminates conjugate image that causes issues in amplitude-only holograms and allows direct reconstruction without additional optical elements. The proposed method provides enhanced robustness against artifacts caused by sub-pixel structures of modulators, enabling experimental reconstruction of high-quality holograms. The full bandwidth and the robustness result in a 5-decibel improvement in peak signal-to-noise ratio compared to state-of-the-art holograms. Furthermore, the hologram has 24 times higher optical efficiency and a smaller volume than the traditional amplitude-only holograms while real-time synthesis is enabled by using a neural network.

Experimental Verification of the Gouy Phase for Higher-Order Hermite-Gaussian Beams

The Gouy phase is related to the axial phase shift experienced by any focused light beam with respect to a reference plane wave when passing through its focus. Generally, the Gouy phase ΦG for a higher-order Hermite-Gaussian (HG) beam is this for the fundamental Gaussian beam multiplied by a factor, which is the sum of the mode indices of the HG beam plus unity. Although this result is a paradigm in optics, we are not aware of its experimental verification. In this paper, we present experimental results obtained with a single-lens interferometer for higher-order HG modes generated using spatial light modulator. The retrieved Gouy phase ΦG is found in a very good quantitative agreement with the mentioned theoretical result.

Single-pulse three-dimensional parallel recording in glass using a feedback system.

High-quality three-dimensional computer-generated holograms (3D-CGHs) are crucial for programmable 3D femtosecond laser parallel recording (3D-FLPR). In this study, we introduced an innovative feedback approach for the rapid optimization of 3D-CGHs by incorporating the superposition of the calculated lens phases (CLPs) onto the 3D-CGHs within a feedback system. This feedback system, governed by coordinated control of a spatial light modulator (SLM) and a camera, served to avoid the poor quality of the ordinary CGH system. As a result, we successfully demonstrated coaxial 3D-FLPR in Ag-doped phosphate glass solely using a single fs laser pulse. Additionally, we regulated the energy distribution of the generated 3D multi-focus (3D-MF) to compensate the laser energy losses inside the glass. The presented single-pulse 3D parallel recording indicated the significant advancement facilitated by our method, particularly in enhancing the writing efficiency of optical storage.

Three-directional digital shearography based on SLM using a honeycomb-like pattern.

The possibility of utilizing a honeycomb-like modulation pattern in a spatial light modulator (SLM) for multi-directional synchronous digital shearography measurements has been investigated. Each modulation pixel in the honeycomb-like pattern modulates the shearing amount in different directions, thus avoiding the resolution loss associated with previous methods where a single pixel could only modulate a specific shearing direction. It was demonstrated that high-quality phase maps for different shearing directions can be simultaneously obtained with a single exposure.

Computational ghost imaging enhanced by degradation models for under-sampling.

Computational ghost imaging (CGI) allows two-dimensional (2D) imaging by using spatial light modulators and bucket detectors. However, most CGI methods attempt to obtain 2D images through measurements with a single sampling ratio. Here, we propose a CGI method enhanced by degradation models for under-sampling, which can be reflected by results from measurements with different sampling ratios. We utilize results from low-sampling-ratio measurements and normal-sampling-ratio measurements to train the neural network for the degradation model, which is fitted through self-supervised learning. We obtain final results by importing normal-sampling-ratio results into the neural network with optimal parameters. We experimentally demonstrate improved results from the CGI method using degradation models for under-sampling. Our proposed method would promote the development of CGI in many applications.

Confocal structured illumination microscopy for improving the signal-to-noise ratio and depth of fluorescent optical section imaging

Light scattering from the sample is an unavoidable problem in fluorescence imaging. Compared with laser scanning confocal scanning microscopy, although optical-sectioning structured illumination microscopy (OS-SIM) has the advantages of fast imaging speed and low phototoxicity, it faces the challenge of removing the scattering fluorescent noise particularly when imaging thick and densely labeled sampling. To improve the imaging performance of OS-SIM, we introduce the concept of confocal imaging to OS-SIM and propose confocal structured illumination microscopy (CSIM). CSIM exploits the principle of dual imaging to reconstruct a dual image from each camera pixel. The scattered fluorescent noise and the unscattered fluorescent signal recorded by the camera pixel are separated in the reconstructed dual image. By extracting the unscattered fluorescent signal from each dual image based on the conjugate relationship between the camera and the spatial light modulator, we can eliminate the scattered fluorescent noise and reconstruct a confocal image. We have built the theoretical framework of CSIM. Experimental results of fluorescent optical-sectioning demonstrate that CSIM achieves a superior performance in eliminating scattered fluorescent noise and in extending imaging depth compared with existing OS-SIM. CSIM is expected to broaden the application range of OS-SIM.

The rise of electrically tunable metasurfaces.

Metasurfaces, which offer a diverse range of functionalities in a remarkably compact size, have captured the interest of both scientific and industrial sectors. However, their inherent static nature limits their adaptability for their further applications. Reconfigurable metasurfaces have emerged as a solution to this challenge, expanding the potential for diverse applications. Among the series of tunable devices, electrically controllable devices have garnered particular attention owing to their seamless integration with existing electronic equipment. This review presents recent progress reported with respect to electrically tunable devices, providing an overview of their technological development trajectory and current state of the art. In particular, we analyze the major tuning strategies and discuss the applications in spatial light modulators, tunable optical waveguides, and adaptable emissivity regulators. Furthermore, the challenges and opportunities associated with their implementation are explored, thereby highlighting their potential to bridge the gap between electronics and photonics to enable the development of groundbreaking optical systems.

Extending the operational limit of a cooled spatial light modulator exposed to 200 W average power for holographic picosecond laser materials processing

The phase range of a Spatial Light Modulator (SLM) requires full 2π response for accurate phase modulation of the incident laser wavefront to create the desired structured intensity distribution. While cooled SLM’s allow increased power exposures, degradation in performance occurs with average powers P>100 W in a Gaussian beam due to residual absorption and consequent heating of the liquid crystal (LC) layer which seriously limits the phase stroke and diffraction efficiency. By introducing a refractive flat top intensity generator ahead of a cooled SLM, we have extended the phase range to Δφ = 2π at incident power P=210 W with only a small light field depolarisation. The operational limit has therefore been extended significantly, allowing efficient, parallel laser materials processing with a high-power picosecond laser. The calculation and implementation of binary Damman gratings for multi-beam laser processing is also shown to be useful at high power exposure.

Generation of UV Ellipsoidal Pulses by 3D Amplitude Shaping for Application in High-Brightness Photoinjectors

Photocathode laser pulse shaping is a crucial technology for enhancing the performance of X-ray free-electron lasers by optimizing the quality of electron beams generated from photocathodes within high-gradient radio frequency guns. By precisely shaping these laser pulses, it is possible to significantly reduce the transverse emittance of produced electron bunches. The optimal pulse shape is an ellipsoidal distribution, commonly referred to as the Kapchinskij–Vladimirskij profile. A pulse-shaping scheme utilizing a commercial Yb:KGW laser operating at 514 nm with a repetition rate of 1 MHz and duration of 260 fs has been developed for generating electron bunches with high peak and average power. This study presents the experimental realization of ellipsoidal pulses via three-dimensional amplitude shaping using spatial light modulators at 514 nm, followed by conversion to UV (257 nm) suitable for Cs 2Te photocathodes. The preservation of pulse shape and a high conversion efficiency during this process are investigated and our experiments pave the way for future emittance minimization for X-ray free-electron lasers.