Programmable Spatial Light Modulator Research Articles

Nanophotonic phased array XY Hamiltonian solver

Solving large-scale computationally hard optimization problems using existing computers has hit a bottleneck. A promising alternative approach uses physics-based phenomena to naturally solve optimization problems, wherein the physical phenomena evolve to their minimum energy. In this regard, photonics devices have shown promise as alternative optimization architectures, benefiting from high-speed, high-bandwidth, and parallelism in the optical domain. Among photonic devices, programmable spatial light modulators (SLMs) have shown promise in solving large scale Ising model problems, to which many computationally hard problems can be mapped. Despite much progress, existing SLMs for solving the Ising model and similar problems suffer from slow update rates and physical bulkiness. Here, we show that using a compact silicon photonic integrated circuit optical phased array (PIC-OPA), we can simulate an XY Hamiltonian, a generalized form of the Ising Hamiltonian, where spins can vary continuously. In this nanophotonic XY Hamiltonian solver, the spins are implemented using analog phase shifters in the optical phased array. The far field intensity pattern of the PIC-OPA represents an all-to-all coupled XY Hamiltonian energy and can be optimized with the tunable phase-shifters, allowing us to solve an all-to-all coupled XY model. Our results show the utility of PIC-OPAs as compact, low power, and high-speed solvers for nondeterministic polynomial-hard problems. The scalability of the silicon PIC-OPA and its compatibility with monolithic integration with CMOS electronics further promise the realization of a powerful hybrid photonic/electronic non-Von Neumann compute engine.

Scalable and ultralow power silicon photonic two-dimensional phased array

Photonic integrated circuit based optical phased arrays (PIC-OPAs) are emerging as promising programmable processors and spatial light modulators, combining the best of planar and free-space optics. Their implementation on silicon photonic platforms has been especially fruitful. Despite much progress in this field, demonstrating steerable two-dimensional (2D) OPAs that are scalable to a large number of array elements and operate with a single wavelength has proven a challenge. In addition, the phase shifters used in the array for programming the far-field beam are either power hungry or have a large footprint, preventing the implementation of large scale 2D arrays. Here, we demonstrate a two-dimensional silicon photonic phased array with high-speed (∼330 kHz) and ultralow power microresonator phase-shifters with a compact radius (∼3 µm) and 2π phase shift ability. Each phase-shifter consumes an average of ∼250 µW of static power for resonance alignment and ∼50 µW of power for far-field beamforming, a more than one order of magnitude improvement compared to prior OPA works based on waveguide-based thermo-optic phase shifters. Such PIC-OPA devices can enable a new generation of compact and scalable low power processors and sensors.

Optimizing nonconfigurable, transversely displaced masks for illumination patterns in classical ghost imaging

Classical ghost imaging is a new paradigm in imaging where the image of an object is not measured directly with a pixelated detector. Rather, the object is subject to a set of illumination patterns and the total interaction of the object, e.g., reflected or transmitted photons or particles, is measured for each pattern with a single-pixel or bucket detector. An image of the object is then computed through the correlation of each pattern and the corresponding bucket value. Assuming no prior knowledge of the object, the set of patterns used to compute the ghost image dictates the image quality. In the visible-light regime, programmable spatial light modulators (SLMs) can generate the illumination patterns. In many other regimes, such as x rays, electrons, and neutrons, no such dynamically configurable modulators exist, and patterns are commonly produced by employing a transversely translated mask. Moreover, in visible-light regimes, mask switching rates exceeding the fastest SLMs may often be achieved through transverse translation (e.g., rotation) of a nonconfigurable mask. In this simulations-based paper we explore some of the properties of masks or speckle that should be considered to maximize ghost-image quality, given a certain experimental classical ghost-imaging setup employing a transversely displaced but otherwise nonconfigurable mask.

High-speed optical pulse shaping based on programmable lithium niobate spatial light modulators.

Pulse shaping plays a key role in various applications of ultrafast lasers, such as optical communications, laser micromachining, microscopy, and quantum coherent control. Conventional pulse shaping devices based on liquid crystal spatial light modulators (LCSLMs) or digital micromirror devices (DMDs) only have the shaping speed of several hertz to kilohertz, which is not suitable for applications requiring a high-speed response. Here, we demonstrate a high-speed programmable lithium niobate spatial light modulator (LNSLM) with 128 individual modulation channels and a modulation speed that can reach 1 MHz. Then we establish a high-speed LNSLM-based Fourier-transform (FT) pulse shaper to realize high-speed pulse shaping, and the update rate can reach 350 kHz, only limited by the electric circuit. The proposed high-speed pulse shaper scheme opens new avenues for future applications of ultrafast science, such as microscopic imaging, interaction between light and matter, and spectroscopy.

Tunable image-mapping optical coherence tomography.

We present tunable image-mapping optical coherence tomography (TIM-OCT), which can provide optimized imaging performance for a given application by using a programmable phase-only spatial light modulator in a low-coherence full-field spectral-domain interferometer. The resultant system can provide either a high lateral resolution or a high axial resolution in a snapshot without moving parts. Alternatively, the system can achieve a high resolution along all dimensions through a multiple-shot acquisition. We evaluated TIM-OCT in imaging both standard targets and biological samples. Additionally, we demonstrated the integration of TIM-OCT with computational adaptive optics in correcting sample-induced optical aberrations.

Compact pulse shaper based on a tilted volume Bragg grating.

A compact optical layout of a pulse shaper for strongly chirped laser pulses of nanosecond time scale exploiting a tilted chirped volume Bragg grating and a programmable spatial light modulator is proposed. The setup has a non-zero frequency dispersion; thus it may be used for stretching or compressing the pulse and controlling its shape simultaneously. The feasibility of spectral shaping with a resolution of 0.16 nm, corresponding to a time resolution of 150 ps, and a contrast ratio of 102 is demonstrated experimentally.

Ion-based high-order harmonic generation from water window to keV region with a transverse disruptive pulse for quasi-phase-matching.

A scheme for ion-based high-harmonic generation from water window to keV x-ray is investigated. He1+ ions with 54.42-eV ionization potential extend the harmonic cutoff energy to 1 keV. The transverse selective-zoning method of quasi-phase-matching is utilized to overcome the severe plasma dispersion in a highly ionized medium. The calculated conversion efficiency reaches about 15% of the perfect phase-matching condition. Wavelength tunability is achieved by incorporating a programmable spatial-light modulator to control the quasi-phase-matching pattern.

Design of a digitally switchable multifocal microlens array for integral imaging systems.

This paper presents the optical design of a digitally switchable multi-focal microlens array which can be used to extend the depth of field in integral imaging systems. The proposed switchable multi-focal microlens array consists of a customized freeform multi-focal microlens array (MLA) and a programmable spatial light modulator. By switching among the different optical powers of the switchable multi-focal MLA, an integral imaging system can render or capture a 3D scene at a large depth range around several central depth planes. We demonstrate the design considerations for a dual-focal microlens array with a primary and secondary focal lengths of 4mm and 4.06mm, respectively. We further validated the design by providing both interferometric measurements of the surface profiles and image contrast and resolution tests of a manufactured MLA prototype.

Maskless fabrication of plasmonic metasurfaces in polymer film using a spatial light modulator.

We demonstrate a high-speed optical technique to fabricate plasmonic metasurfaces in a polymer film. The technique is based on a programmable spatial light modulator, which is used to spatially control the photoreduction sites of gold ions in a polyvinyl alcohol film doped with a gold precursor. After irradiation, annealing was used to induce the growth of nanoparticles, producing plasmonic microstructures. Using a 473 nm excitation wavelength, microscopic plasmonic gratings, and meta-atom arrays with arbitrary orientations, an effective nanostructure size of ∼700nm and constituent nanoparticles with average size of ∼37nm were created. The technique enables a cost-effective and straightforward light-based approach to fabricate plasmonic metasurfaces with tunable properties.

Snapshot compressive spectral depth imaging from coded aberrations.

Compressive spectral depth imaging (CSDI) is an emerging technology aiming to reconstruct spectral and depth information of a scene from a limited set of two-dimensional projections. CSDI architectures have conventionally relied on stereo setups that require the acquisition of multiple shots attained via dynamically programmable spatial light modulators (SLM). This work proposes a snapshot CSDI architecture that exploits both phase and amplitude modulation and uses a single image sensor. Specifically, we modulate the spectral-depth information in two steps. Firstly, a deformable mirror (DM) is used as a phase modulator to induce a focal length sweeping while simultaneously introducing a controlled aberration. The phase-modulated wavefront is then spatially modulated and spectrally dispersed by a digital micromirror device (DMD) and a prism, respectively. Therefore, each depth plane is modulated by a variable phase and binary code. Complimentary, we also propose a computational methodology to recover the underlying spectral depth hypercube efficiently. Through simulations and our experimental proof-of-concept implementation, we demonstrate that the proposed computational imaging system is a viable approach to capture spectral-depth hypercubes from a single image.

High-speed programmable lithium niobate thin film spatial light modulator.

High-speed spatial modulation of light is the key technology in various applications, such as optical communications, imaging through scattering media, video projection, pulse shaping, and beam steering, in which spatial light modulators (SLMs) are the underpinning devices. Conventional SLMs, such as liquid crystal (LC), digital micromirror device (DMD), and micro-electro-mechanical system (MEMS) ones, operate at a typical speed on the order of several kilohertz as limited by the slow response of the pixels. Achieving high-speed spatial modulation is still challenging and highly desired. Here, we demonstrate a one-dimensional (1D) high-speed programmable spatial light modulator based on the electro-optic effect in lithium niobate thin film, which achieves a low driving voltage of 10 V and an overall high-speed modulation speed of 5 MHz. Furthermore, we transfer an image by using parallel data transmission based on the proposed lithium niobate SLM as a proof-of-principle demonstration. Our device exhibits improved performance over traditional SLMs and opens new avenues for future high-speed and real-time applications, such as light detection and ranging (LiDAR), pulse shaping, and beam steering.

Controllable singular skeleton formation by means of the Kummer optical-vortex diffraction at a rectilinear phase step

We study positions and morphology of optical vortices (OVs) within the field obtained after transmitting a circular single-charged OV-beam through the transparent screen with a rectilinear π-phase step. Experimental results are obtained with the help of a programmable spatial light modulator which is used for the Kummer beam formation and for introduction of the π-step phase difference at a desirable position within the incident beam cross section. The theory based on the Kirchhoff–Fresnel approximation shows a good agreement with the experimental data; peculiar features of the Kummer beam diffraction are elucidated in the course of confrontation against the results involving the Laguerre–Gaussian beam model with the same transverse size and spherical wavefront component. The diffracted field contains a system of interacting OVs (singular skeleton) which demonstrate a regular evolution (migration) within the diffracted beam cross section while the π-phase step translates across the incident beam; depending on the step position, new OV pairs may emerge and/or annihilate in the topological reactions. The morphology parameters of the separate diffracted-field OVs (orientations and form-factors of the near-core equal-intensity ellipses) also depend on the stage of the OV evolution and indicate conditions favorable for the efficient trapping and guiding of microparticles. The results may be useful for the diagnostics of OVs, experimental measurements of phase objects and in micromanipulation techniques.

Compressive Spectral Imaging Via Virtual Side Information

In recent years there has been an increasing interest in compressive imaging devices that capture spectral images with high spatial and spectral resolution with as few as a single snapshot. Nonetheless, there exists an intrinsic trade-off between spatial and spectral resolution which degrades one at the expense of the other. To alleviate this, state-of-art systems have relied on multiple snapshots attained via dynamically programmable spatial light modulators (SLM), or on side information from a second sensor attained via beam-splitters or stereo setups, which suffer from occlusion and demand registration tasks. This work proposes a compressive snapshot spectral imaging architecture that builds on the ideas of side information, but relies on a single image sensor. Specifically, we propose to split the incoming light into two paths, such as in a conventional interferometer, with one path dispersing the coded light, while the other just relaying it, so as to multiplex a traditional coded-and-dispersed measurement with a modulated grayscale version of the 3D cube in the image sensor. We have coined the latter, virtual side information. The proposed optical system is versatile in the sense that it can move from a fully-encoding system, to a spatially modulated grayscale camera, by switching/blocking the splitting response of the beam-splitters. Furthermore, we propose a computational algorithm to recover the underlying spectral cube exploiting the high spatial resolution provided by the virtual side information. We demonstrate through simulations from over fifty spectral images, and via an experimental proof-of-concept implementation, that the proposed imaging system together with the computational algorithm represents an efficient alternative to acquire spectral images without relying on additional sensors.

54‐3: Digitally Switchable Micro Lens Array for Integral Imaging

This paper presents the design of a digitally switchable multi‐focal micro lens array to extend the depth of field without sacrificing the spatial resolution in integral imaging systems. The switchable multi‐focal micro lens array consists of a customized freeform micro lens array and a programmable spatial light modulator. A prototype with two foci was fabricated and focus tuning functionality was demonstrated using an LCoS together with a relay system.

High-dimensional states of light with full control of OAM and transverse linear momentum.

We present a compact scheme for the generation of high-dimensional states of light encoded in the transverse linear momentum of photons that carry orbital angular momentum (OAM). We use a programmable spatial light modulator in phase configuration to create correlations between these two spatial degrees of freedom. With our setup, we are able to control, independently, the relative phases and amplitudes of the spatial superposition in addition to the topological charge of the OAM. Moreover, we engineer correlations that emulate bipartite quantum states of dimensions d×m. Experimental results from the characterization of different generated states of dimensions up to 9×5 are in excellent agreement with the numerical simulations. Fidelity with the target state is, for all cases, above 95%.

Parallel-in-time optical simulation of history states

We present an experimental optical implementation of a parallel-in-time discrete model of quantum evolution, based on the entanglement between the quantum system and a finite dimensional quantum clock. The setup is based on a programmable spatial light modulator which entangles the polarization and transverse spatial degrees of freedom of a single photon. It enables the simulation of a qubit history state containing the whole evolution of the system, capturing its main features in a simple and configurable scheme. We experimentally determine the associated system-time entanglement, which is a measure of distinguishable quantum evolution, and also the time average of observables, which in the present realization can be obtained through one single measurement.

Compressive spectral imaging via deformable mirror and colored-mosaic detector

Compressive Spectral Imaging (CSI) is an emerging technology that aims at reconstructing a spectral image from a limited set of two-dimensional projections. To capture these projections, CSI architectures often combine light dispersive elements with coded apertures or programmable spatial light modulators. This work introduces a novel and compact CSI architecture based on a deformable mirror and a colored-filter detector to produce compressive spatio-spectral projections without the need of a grating or prism. Alongside, we propose a tensor-based reconstruction algorithm to recover the spatial-spectral information from the compressed measurements. Experimental results on both simulated and real datasets demonstrate efficacy of the proposed acquisition architecture and the especially crafted inversion algorithms.

Hexagonal vector field of polarization singularities with a gradient basis structure

The coherent superposition of vector fields can yield interesting field distributions. For example, the superposition of two right-handed polarization singularities can result in left-handed polarization singularities. Unlike the coherent superposition of scalar fields which modulate resultant intensity, the vector field superposition can modulate additional parameters such as ellipticity and azimuth in the field distribution. By making use of computational optics and programmable spatial light modulators, we demonstrate here the generation of a polarization singularity lattice structure with gradient basis, which is normally not possible by a conventional optical interference method.

Microdisplays as a versatile tool for the optical simulation of crystal diffraction in the classroom

Presented here is a flexible and low-cost setup for demonstrating X-ray, electron or neutron diffraction methods in the classroom. Using programmable spatial light modulators extracted from a commercial video projector, physical diffraction patterns are generated, in real time, of any two-dimensional structure which can be displayed on a computer screen. This concept enables hands-on experience beyond simplest-case scenarios of scattering phenomena, and for the students, the transfer to the regime of visible light greatly enhances intuitive understanding of diffraction in real and reciprocal space. The idea and working principle of the modified video projector are explained, technical advice is given for its choice and successful modification, and a Python-based open-source program code is provided. Program features include the design and interactive manipulation of two-dimensional crystal structures to allow a straightforward demonstration of concepts such as reciprocal space, structure factors, selection rules, symmetry and symmetry violation, as well as structural disorder. This approach has already proved helpful in teaching crystal diffraction to undergraduate students in materials science.

Multispectral Management of the Photon Orbital Angular Momentum.

We report on a programmable liquid crystal spatial light modulator enabling independent orbital angular momentum state control on multiple spectral channels. This is done by using electrically controllable "topological pixels" that independently behave as geometric phase micro-optical elements relying on self-engineered liquid crystal defects. These results open interesting opportunities in optical manipulation, sensing, imaging, and communications, as well as information processing. In particular, spectral vortex modulation allows considering singular spatiotemporal shaping of ultrashort pulses which may find applications in many areas such as material processing, spectroscopy, or elementary particles acceleration.