Single Spatial Light Modulator Research Articles

Experimental optical encryption with full complex modulation

We present, to our knowledge, a novel method to achieve experimental encryption using double random phase encoding with full complex modulation and a single phase-only spatial light modulator. Our approach uses double phase encoding to generate phase-only holograms containing complex-valued input planes for a joint transform correlator (JTC) cryptosystem. This approach enables users to independently manipulate both the phase and amplitude of the cryptographic keys and objects, thereby significantly enhancing the versatility of the optical cryptosystem. We validate the capabilities of our proposed scheme by generating optimized random phase masks and using them to experimentally encrypt various grayscale and binary objects. The experimental complex modulation obtained with the system detailed in this work, in conjunction with optimized random phase masks, results in an enhancement in the quality of the decrypted objects during reconstruction. Both numerical simulations and experimental findings corroborate the effectiveness of our proposal.

Direct imprint of optical skyrmions in azopolymers as photoinduced relief structures

Skyrmions, topologically stable configurations of a three-component vector field with sophisticated textures, have been considered in many contexts, including atomic physics, Bose–Einstein condensates, liquid crystals, and magnetic materials. Although optical counterparts of skyrmions have extensively been studied theoretically and recently demonstrated in the laboratory experiments, their experimental mapping is challenging due to the fine, three-dimensional, and complicated structure of their polarization distributions. Here, we propose and demonstrate a straightforward mapping of the polarization textures of optical Néel-, Bloch-, and anti-skyrmions based on the radiation pressure and direct imprinting of the skyrmion textures on azopolymers. These results not only elucidate the exotic interaction that occurs between topologically protected quasiparticles of light and matter but also provide a simple approach for generation and characterization of optical skyrmions, based on a dual-path polarization shaping configuration with a single spatial light modulator, and their measurements based on the radiation pressure.

Color liquid crystal grating based color holographic 3D display system with large viewing angle

Holographic 3D display is highly desirable for numerous applications ranging from medical treatments to military affairs. However, it is challenging to simultaneously achieve large viewing angle and high-fidelity color reconstruction due to the intractable constraints of existing technology. Here, we conceptually propose and experimentally demonstrate a simple and feasible pathway of using a well-designed color liquid crystal grating to overcome the inevitable chromatic aberration and enlarge the holographic viewing angle, thus enabling large-viewing-angle and color holographic 3D display. The use of color liquid crystal grating allows performing secondary diffraction modulation on red, green and blue reproduced images simultaneously and extending the viewing angle in the holographic 3D display system. In principle, a chromatic aberration-free hologram generation mechanism in combination with the color liquid crystal grating is proposed to pave the way for on such a superior holographic 3D display. The proposed system shows a color viewing angle of ~50.12°, which is about 7 times that of the traditional system with a single spatial light modulator. This work presents a paradigm for achieving desirable holographic 3D display, and is expected to provide a new way for the wide application of holographic display.

StainedSweeper: Compact, Variable-Intensity Light-Attenuation Display with Sweeping Tunable Retarders.

Light Attenuation Displays (LADs) are a type of Optical See-Through Head-Mounted Display (OST-HMD) that present images by attenuating incoming light with a pixel-wise polarizing color filter. Although LADs can display images in bright environments, there is a trade-off between the number of Spatial Light Modulators (SLMs) and the color gamut and contrast that can be expressed, making it difficult to achieve both high-fidelity image display and a small form factor. To address this problem, we propose StainedSweeper, a LAD that achieves both the wide color gamut and the variable intensity with a single SLM. Our system synchronously controls a pixel-wise Digital Micromirror Device (DMD) and a nonpixel polarizing color filter to pass light when each pixel is the desired color. By sweeping this control at high speed, the human eye perceives images in a time-multiplexed, integrated manner. To achieve this, we develop the OST-HMD design using a reflective Solc filter as a polarized color filter and a color reproduction algorithm based on the optimization of the time-multiplexing matrix for the selected primary color filters. Our proof-of-concept prototype showed that our single SLM design can produce subtractive images with variable contrast and a wider color gamut than conventional LADs.

Multi-Mode Vector Light Field Generation Using Modified Off-Axis Interferometric Holography and Liquid Crystal Spatial Light Modulators

The increasing enhancement in the modulation accuracy of spatial light modulators has garnered significant attention towards real-time control technology for light fields based on these modulators. It has been demonstrated that this technology possesses a remarkable capability to generate vector beams with arbitrary complex amplitude distributions. Nevertheless, past studies indicate that the generation of only one vector beam at a time has been observed. The simultaneous generation of numerous vector light fields can give rise to several challenges, including compromised picture quality, limited single-mode operation, and intricate optical path configurations. In pursuit of this objective, we present a novel methodology that integrates the coding methodology of modified off-axis interferometric holography with the idea of optical superposition. This technique facilitates the concurrent generation of several vector beams. In this study, we present a demonstration of the simultaneous creation of twelve vector beams using a single spatial light modulator (SLM) as a proof of concept. Significantly, this technology has the ability to generate an unlimited quantity of vector light fields concurrently under the assumption that the resolution of the SLM does not impose any limitations. The findings indicate that the imaging quality achieved by this technology is of a high standard. Furthermore, it is possible to separately control the beam waist radius, topological charge, polarization order, and extra phase of each beam.

Accommodation-capable holographic waveguide head-up display with extended field of view

Augmented reality (AR) displays are enhancing user experiences by offering immersive three- dimensional (3D) content, with head-up display (HUD) being a prime application for driving safety. To enable AR-HUDs to provide sufficient information to driver, it is essential to ensure a wide field of view (FOV). Traditional methods like the magnifier principle have limitations stemming from optical aberrations and bulky form factor. Recently, optical waveguide has been used as pupil expander, which has attracted increasing attention as an optical element for compact form factor and exit-pupil expansion. However, waveguide display as exit-pupil expander only offer 2D images with infinite depth, causing mismatch issue between virtual content and real scenes. In this paper, we propose a lensless holographic waveguide display consisting of a laser light source, a spatial light modulator (SLM), a waveguide to generate accommodation-capable images, effectively extending FOV. The key distinction of this research lies in the optical design of the waveguide, which defines multiple shifted copies of the modulated wavefield as replicated virtual SLMs. A formalized algorithm is devised based on a bold assumption that numerous virtual SLMs replicated by a waveguide are considered as a single ultra-high resolution SLM. The effectiveness of the algorithm has been demonstrated through extensive validation through numerical observation simulations and optical experiments. Notably, optical experiments convincingly demonstrate the system’s ability to produce accommodation-capable true 3D content, with a four-fold extension of FOV compared to a single SLM at an observation distance of 150 mm. Additional optical experiments highlight the successful integration of AR technology, an important component for automotive HUD.

Tailored photoacoustic apertures with superimposed optical holograms.

A new method of generating potentially arbitrary photoacoustic wavefronts with optical holograms is presented. This method uses nanosecond laser pulses at 1064 nm that are split into four time-delayed components by means of a configurable multipass optical delay apparatus, which serves to map the pulses onto phase-delayed regions of a given acoustic wavefront. A single spatial light modulator generates separate holograms for each component, which are imaged onto a photoacoustic transducer comprised of a thermoelastic polymer. As a proof of concept of the broader arbitrary wavefront construction technique, the spatially- and temporally-modulated holograms in this study produce a phased array effect that enables beam steering of the resulting acoustic pulse. For a first experimental demonstration of the method, as verified by simulation, the acoustic beam is steered in four directions by around 5 degrees.

Generation of structured light beams by dual phase modulation with a single spatial light modulator

Precise control of amplitude and wavefront of optical fields are prerequisites for many applications, especially in singular optics. This has led to the increasing efforts for developing efficient techniques to control the shape of the light in different dimensions. A spatial light modulator (SLM) can be efficiently used for phase-only or amplitude-only modulation; but offers limitation in complex light field modulation. Hence, shaping the complex amplitude of optical beams is challenging mainly because there are no complex modulators. While there is ongoing research to develop complex amplitude modulating SLMs, a solution is still non-existent. In this study, to achieve complex light modulations, a simple experimental set-up employing single phase-only SLM has been proposed. The SLM has been used as operating in a split-screen-mode. The non-iterative approach of dual-pass modulation has been applied where two cascaded phase value distributions (PVD) are encoded side-by-side onto the SLM. The first PVD is designed to enable amplitude modulation in the second PVD plane which finally helps achieve wavefront shaping. Hence, both amplitude and phase modulation of light beam are possible in this configuration. Commonly known singular beams such as Laguerre–Gaussian and Bessel-Gaussian modes have been generated theoretically as well as experimentally to verify the feasibility of the proposed technique. The method used helps to achieve arbitrary shaped beams as well.

Aberration-free holographic microscope for simultaneous imaging and stimulation of neuronal populations.

A technical challenge in neuroscience is to record and specifically manipulate the activity of neurons in living animals. This can be achieved in some preparations with two-photon calcium imaging and photostimulation. These methods can be extended to three dimensions by holographic light sculpting with spatial light modulators (SLMs). At the same time, performing simultaneous holographic imaging and photostimulation is still cumbersome, requiring two light paths with separate SLMs. Here we present an integrated optical design using a single SLM for simultaneous imaging and photostimulation. Furthermore, we applied axially dependent adaptive optics to make the system aberration-free, and developed software for calibrations and closed-loop neuroscience experiments. Finally, we demonstrate the performance of the system with simultaneous calcium imaging and optogenetics in mouse primary auditory cortex in vivo. Our integrated holographic system could facilitate the systematic investigation of neural circuit function in awake behaving animals.

Simple Method of Light Field Calculation for Shaping of 3D Light Curves

We propose a method for generating three-dimensional light fields with given intensity and phase distributions using purely phase transmission functions. The method is based on a generalization of the well-known approach to the design of diffractive optical elements that focus an incident laser beam into an array of light spots in space. To calculate purely phase transmission functions, we use amplitude encoding, which made it possible to implement the designed elements using a single spatial light modulator. The generation of light beams in the form of rings, spirals, Lissajous figures, and multi-petal “rose” distributions uniformly elongated along the optical axis in the required segment is demonstrated. It is also possible to control the three-dimensional structure of the intensity and phase of the shaped light fields along the propagation axis. The experimentally generated intensity distributions are in good agreement with the numerically obtained results and show high potential for the application of the proposed method in laser manipulation with nano- and microparticles, as well as in laser material processing.

Generating scalar and vector modes of Bessel beams utilizing holographic axicon phase with spatial light modulator

This paper presents an efficient method for the generation of scalar as well as vector modes of Bessel–Gaussian (BG) beams by utilizing a computer generated phase-only mask encoded using the spatial light modulator (SLM). A phase-only hologram corresponding to the transmission function of axicon combined with a spatial phase plate (SPP) is used. The SPP converts a Gaussian field into a phase singular beam of order l associated with an azimuthally varying spiral wavefront structure and the axicon helps achieve non-diffracting BG beams. A compact experimental setup is proposed for the experimental realization of BG fields possessing both homogeneous as well as spatially varying polarization distributions across the transverse plane. Scalar BG beams are generated through the modulation of the combined phase patterns of axicon and SPP with the SLM. Vector BG beams are generated in two special cases: azimuthally and radially polarized inhomogeneous distributions through dual-passes from the SLM. A non-interferometric technique of dual-pass modulation, from the phase patterns displayed on a single SLM, which is divided into two halves, has been utilized. Here, scalar BG beams with orthogonal phase structure are encoded into orthogonal components of incoming light for vector BG beam generation.

Compact generation of light beams carrying robust higher-order Poincaré polarization states

We propose a protocol for compact and efficient synthesis of a random vectorial source with a higher-order Poincaré (HOP) polarization state encoded into the spatial coherence structure. The procedure is based on the complex-random-mode representation of the cross-spectral density matrix and employs a single phase-only spatial light modulator (SLM) and a common path interferometric system for the mode construction. The SLM displays a set of elaborated multiplexed holograms, which both encode the HOP polarization state and determine the statistical properties of the source. We demonstrate that the beam from the synthesized source can be highly robust against obstructions in the propagation path in the sense that the encoded HOP polarization state is well reconstructed in the far field (focal plane) even when an obstacle is introduced to largely block the source. The results are useful for the transmission of polarization-encoded information in complex media.

High-power laser beam in higher-order Hermite–Gaussian modes

The sensitivities of current gravitational-wave detectors are limited around signal frequencies of 100 Hz by mirror thermal noise. One proposed option to reduce this thermal noise is to operate the detectors in a higher-order spatial laser mode. This operation would require a high-power laser input beam in such a spatial mode. Here, we discuss the generation of the Hermite–Gaussian modes HG2,2, HG3,3, and HG4,4 using one water-cooled spatial light modulator (SLM) at a continuous-wave optical input power of up to 85 W. We report unprecedented conversion efficiencies for a single SLM of about 43%, 42%, and 41%, respectively, and demonstrate that the SLM operation is robust against the high laser power. This is an important step toward the implementation of higher-order laser modes in future gravitational-wave detectors.

Experimental Synthesis and Demonstration of the Twisted Laguerre–Gaussian Schell-Mode Beam

The twisted Laguerre–Gaussian Schell-model (TLGSM) beam is a novel type of partially coherent beam embedded with both the second-order twist phase and the classical vortex phase. The intriguing properties induced by the interaction of the two types of phases have been demonstrated theoretically quite recently. In this work, we introduce a flexible way to experimentally synthesize a TLGSM beam with controllable twist strength. The protocol relies on the discrete pseudo-mode representation for the cross-spectral density of a TLGSM beam, in which the beam is viewed as an incoherent superposition of a finite number of spatially coherent modes. We show that all these pseudo modes endowed with random phases are mutually uncorrelated and can be encoded into a single frame of a dynamic computer-generated hologram. By sequentially displaying dynamic holograms on a single spatial-light modulator, the controllable TLGSM beam can be synthesized experimentally. The joint effect of the two phases on the propagation and self-reconstruction characteristics of the synthesized beam has also been studied in the experiment.

Binocular full-color holographic three-dimensional near eye display using a single SLM.

A binocular full-color holographic three-dimensional near eye display system using a single spatial light modulator (SLM) is proposed. In the display system, the frequency spectrum shifting operation and color spectrum shifting operation are adopted to realize the frequency division multiplexing (FDM) and frequency superposition multiplexing (FSM) by manipulating the frequency spectrums of each color- and view-channel sub-holograms. The FDM combined with polarization multiplexing will be used to implement binocular display using a single SLM, and the FSM working with a bandpass filter for each view-channel will be used to achieve full-color display from single frame hologram. The optical analysis and experiments with 3D color objects confirm the feasibility of the proposed system in the practical application.

Wavelength-Independent Correlation Detection of Aberrations Based on a Single Spatial Light Modulator

The cumulative achievements in the fields of science and technology have allowed us to substantially approach the solution of the phase problem in optics. Among all phasometric methods, single-beam methods are the most promising, since they are more variable and versatile. Single-beam methods are based either on the analysis of the intensity distribution, as is conducted by interferometers and wavefront sensors, or on the transformation of the phase into an intensity distribution due to spatial filtering, as is conducted by holographic methods. However, all these methods have the problem of working with polychromatic radiation and require spectral filters to process such radiation. This paper presents a new approach to the synthesis of Fourier holograms used in holographic wavefront sensors that make it possible to create achromatic elements and work with white light without the use of additional filters. The approach was numerically and experimentally verified.

Miniaturization and image optimization of a full-color holographic display system using a vibrating light guide.

In this study, a miniaturized full-color holographic reconstruction system that uses a single spatial light modulator to achieve full-color image reconstruction was developed. The reconstruction system uses a single light guide for light combination and is therefore less voluminous than conventional reconstruction systems. The experimental results demonstrated that the system had a full-color display, corrected light combination, and eliminated zero-order light. The vibrations of the light guide disrupted the temporal coherence of the laser beam, thus ensuring that the speckle in the reconstructed image was almost imperceptible to the human eye.

Tunable liquid crystal grating based holographic 3D display system with wide viewing angle and large size

As one of the most ideal display approaches, holographic 3-dimensional (3D) display has always been a research hotspot since the holographic images reproduced in such system are very similar to what humans see the actual environment. However, current holographic 3D displays suffer from critical bottlenecks of narrow viewing angle and small size. Here, we propose a tunable liquid crystal grating-based holographic 3D display system with wide viewing angle and large size. Our tunable liquid crystal grating, providing an adjustable period and the secondary diffraction of the reconstructed image, enables to simultaneously implement two different hologram generation methods in achieving wide viewing angle and enlarged size, respectively. By using the secondary diffraction mechanism of the tunable liquid crystal grating, the proposed system breaks through the limitations of narrow viewing angle and small size of holographic 3D display. The proposed system shows a viewing angle of 57.4°, which is nearly 7 times of the conventional case with a single spatial light modulator, and the size of the reconstructed image is enlarged by about 4.2. The proposed system will have wide applications in medical diagnosis, advertising, education and entertainment and other fields.

P‐145: Student Poster: AR HUD System Realized By Holographic Display Technology

The application of CGH display technology to AR multi‐depth head‐up displays is a very popular research topic nowadays. However, the system implementation requires multiple projection devices or spatial light modulators with Freeform Mirror or complex optical mechanisms to present multi‐depth projection of automotive head‐up display, which does not meet the development needs in terms of system size and cost. Thus, it is worthwhile to investigate how to realize a multi‐depth projection head‐up display system with a single spatial light modulator. In this study, we attempt to realize a miniaturized multi‐depth CGH head‐up display system with Space‐Division Method (SDM) and a single spatial light modulator.

Arbitrary spatially variant polarization by unitary transformations in a common path interferometer

We introduce a novel, common path interferometric technique, for generating hybrid spatially variant polarized fields and Poincaré beams. The technique is based on unitary polarization transformations employing a single spatial light modulator in a Sagnac-like common path interferometer. This technique allows generating arbitrary fields as a superposition of orthogonal elliptically polarized vortex basis with opposite handedness. We demonstrate the generation of such fields theoretically and verify it experimentally for azimuthal and spiral polarization. As an example of application, we generated a radially polarized ring-shaped field and characterize it by Stokes polarimetry.