High-speed Spatial Light Modulator Research Articles

Hybrid silicon-organic Huygens' metasurface for phase modulation.

Spatial light modulators have desirable applications in sensing and free space communication because they create an interface between the optical and electronic realms. Electro-optic modulators allow for high-speed intensity manipulation of an electromagnetic wavefront. However, most surfaces of this sort pose limitations due to their ability to modulate intensity rather than phase. Here we investigate an electro-optic modulator formed from a silicon-organic Huygens' metasurface. In a simulation-based study, we discover a metasurface design immersed in high-performance electro-optic molecules that can achieve near-full resonant transmission with phase coverage over the full 2π range. Through the electro-optic effect, we show 140 ∘ (0.79π) modulation over a range of -100 to 100 V at 1330 nm while maintaining near-constant transmitted field intensity (between 0.66 and 0.8). These results potentiate the fabrication of a high-speed spatial light modulator with the resolved parameters.

Using an acousto-optic modulator as a fast spatial light modulator.

High-speed spatial light modulators (SLM) are crucial components for free-space communication and structured illumination imaging. Current approaches for dynamical spatial mode generation, such as liquid crystal SLMs or digital micromirror devices, are limited to a maximum pattern refresh rate of 10 kHz and have a low damage threshold. We demonstrate that arbitrary spatial profiles in a laser pulse can be generated by mapping the temporal radio-frequency (RF) waveform sent to an acousto-optic modulator (AOM) onto the optical field. We find that the fidelity of the SLM performance can be improved through numerical optimization of the RF waveform to overcome the nonlinear effect of AOM. An AOM can thus be used as a 1-dimensional SLM, a technique we call acousto-optic spatial light modulator (AO-SLM), which has 50 µm pixel pitch, over 1 MHz update rate, and high damage threshold. We simulate the application of AO-SLM to single-pixel imaging, which can reconstruct a 32×32 pixel complex object at a rate of 11.6 kHz with 98% fidelity.

Polarization independent high-speed spatial modulators based on an electro-optic polymer and silicon hybrid metasurface

Dynamical control of the constitutive properties of a light beam is important for many applications in photonics and is achieved with spatial light modulators (SLMs). Performances of the current demonstrations, such as liquid-crystal or micro-electrical mechanical SLMs, are typically limited by low (∼kHz) switching speeds. Here, we report a high-speed SLM based on the electro-optic (EO) polymer and silicon hybrid metasurface. The specially configured metasurface can not only support a high-Q resonance and large “optical–electrical” overlap factor, but also overcome the challenge of polarization dependence in traditional EO modulators. Combined with the high EO coefficient of the polymer, a 400 MHz modulation with an RF driving source of 15 dBm has been observed in the proof-of-concept device near the wavelength of 1310 nm. The device with the desired merits of high speed, high efficiency, and micrometer size may provide new opportunities for high-speed smart-pixel imaging, free-space communication, and more.

High Spatio-Temporal Resolution Condenser-Free Quantitative Phase Contrast Microscopy

Quantitative phase-contrast microscopy (QPCM) provides an effective approach for label-free detection of transparent samples. In this study, we propose a condenser-free quantitative phase-contrast microscopy (CF-QPCM), in which several light-emitting diodes (LEDs) distributed on a ring are used for direct ultra-oblique illumination. Such condenser-free design greatly simplifies the system’s structure and releases the space for installing samples. Quantitative phase maps are reconstructed by retarding the unscattered components of the object waves for a series of phases 0, π/2, π, and 3π/2 through a high-speed spatial light modulator (SLM). With this system, quantitative phase imaging of live cells has been achieved at a spatial resolution of 231 nm (lateral) and a frame rate of 250 Hz. We believe that the proposed CF-QPCM can contribute to biomedical, industrial, chemistry fields, etc.

Measuring the orbital angular momentum mode of vortex beam based on phase matching sequence

Measuring the orbital angular momentum(OAM) mode of vortex beams is of great significance in applications based on vortex beams.we propose a method of phase matching characteristics of vortex beams to measure the OAM mode. The method first use a high-speed spatial light modulator(SLM) to sequentially load a set of helical phase sequence images, so that the vortex beam is modulated by this SLM. Then obtain the modulated optical field through pinhole filtering, and then the synchronized tilt phase modulation is performed by the 4f system and high-speed SLM. When the OAM mode of vortex beam is opposite to the topological charge of helical phase image, that is, the incident vortex beam degenerates to the fundamental Gaussian mode beam,and through our optical system, the output plane obtained a indicating spot with the position related to the OAM mode. The Simulation and experimental results show that the method obtains a clear OAM mode indicating spot on the final output plane, which verifies the theoretical derivation.

Aerial holographic 3D display with an enlarged field of view by the time-division method.

We propose a method to enlarge the field of view (FOV) of holographic 3D displays in both the horizontal and vertical directions. The FOV was enlarged by using two galvano mirrors and a high-speed spatial light modulator. These optical elements were placed so that the imaging relation was satisfied among them and they were synchronously driven at a high speed to implement the time-division method. Using this method, a floating 3D object could be successfully reconstructed in mid-air near the focal point of the final lens at the rate of 10 Hz. The FOV was enlarged five times and two times in the horizontal and vertical directions, respectively.

Two-photon multifocal structured light microscopy based on high-speed phase-type spatial light modulator

Multifocal structured illumination microscopy (MSIM) can achieve a doubled improvement in the resolution of the diffraction limit within an imaging depth of 50 μm. But when imaging thick samples, scattered light and defocused light limit its optical sectioning capability and image contrast. Two-photon MSIM (2P-MSIM) overcomes the influence of sample tissue scattering and further improves the imaging depth and imaging characteristics. However, the existing 2P-MSIM usually adopts galvanometer based scanning mirrors for precisely scanning imaging, which is a complicated and poor flexibility system. Here we propose a simpler 2P-MSIM. Two-photon multifocal scanning imaging can be realized by a spatial light modulator (SLM) with a high frame rate (< 845 Hz). The phase map of generating multi-focus array and linear phase grating loaded on the SLM simultaneously, high-precision parallel digital random address scanning and excitation imaging on the sample surface can be realized. The mechanical inertia problem of the galvanometer scanner in multifocal imaging can be solved by the proposed method while reducing the complexity of the system and improving flexibility. We finally realize two-photon multifocal imaging of mouse kidney tissue slices and lily of the valley rhizome by this system, which verifies the three-dimensional super-resolution imaging capability of this method. It is of great significance in developing the 2P-MSIM.

Image-free real-time 3-D tracking of a fast-moving object using dual-pixel detection

Real-time 3-D tracking of a fast-moving object has found important applications in industry, traffic control, sports, biomedicine, defense, etc. However, it is difficult to adopt typical image-based object tracking systems in a fast-moving object tracking in real time and for a long duration, because reliable and robust image processing and analysis algorithms are often computationally exhausted, and limited storage and bandwidth can hardly fulfill the great demand of high-speed photography. Here we report an image-free 3-D tracking approach. The approach uses only two single-pixel detectors and a high-speed spatial light modulator for data acquisition. By illuminating the target moving object with six single-period Fourier basis patterns, the approach is able to analytically calculate the position of the object with the corresponding single-pixel measurements. The approach is low-cost, and data- and computation-efficient. We experimentally demonstrate that the proposed approach can detect and track a fast-moving object at a frame rate of 1666 frames per second by using a 10,000 Hz digital micromirror device. Benefiting from the wide working spectrum of single-pixel detectors, the reported approach might be applicable for hidden fast-moving object tracking.

In situ optical backpropagation training of diffractive optical neural networks

Training an artificial neural network with backpropagation algorithms to perform advanced machine learning tasks requires an extensive computational process. This paper proposes to implement the backpropagation algorithm optically for in situ training of both linear and nonlinear diffractive optical neural networks, which enables the acceleration of training speed and improvement in energy efficiency on core computing modules. We demonstrate that the gradient of a loss function with respect to the weights of diffractive layers can be accurately calculated by measuring the forward and backward propagated optical fields based on light reciprocity and phase conjunction principles. The diffractive modulation weights are updated by programming a high-speed spatial light modulator to minimize the error between prediction and target output and perform inference tasks at the speed of light. We numerically validate the effectiveness of our approach on simulated networks for various applications. The proposed in situ optical learning architecture achieves accuracy comparable to in silico training with an electronic computer on the tasks of object classification and matrix-vector multiplication, which further allows the diffractive optical neural network to adapt to system imperfections. Also, the self-adaptive property of our approach facilitates the novel application of the network for all-optical imaging through scattering media. The proposed approach paves the way for robust implementation of large-scale diffractive neural networks to perform distinctive tasks all-optically.

Digital line scanning fluorescence microscopy based on digital micromirror device

Laser scanning confocal microscope (LSCM) is one of the most important tools for biological imaging due to its strong optical sectioning capability, high signal-to-noise ratio, and high resolution. On the basis of LSCM, line-scanning fluorescence microscopy (LSFM) uses linear scanning instead of point scanning to improve the speed of image acquisition. It has the advantages of simple system structure, fast imaging speed, and weak phototoxicity, and in addition, it is more suitable for high-resolution and fast imaging of living thick samples. It is of great significance for studying the life science, biomedicine, and others. However, the current LSFM technology still faces many urgent problems in terms of system flexibility, imaging speed, resolution and optical sectioning capabilities. Therefore, based on the existing multifocal structured illumination microscopy (MSIM) in our laboratory, a digital line-scanning fluorescence microscopy (DLSFM) based on digital micromirror device(DMD) is presented in this paper. In the illumination path, a high-speed spatial light modulator DMD is adopted to realize multi-line parallel scanning excitation, which simplies the optical system and improves the flexibility and scanning speed of the system. A DLSFM image reconstruction algorithm based on the standard deviation of fluorescence signal is proposed, which is combined withthree-dimensional (3D) Landweber deconvolution algorithm to achieve 3D high-resolution optical slice image reconstruction. On this basis, the imaging experiments on fluorescent beads and standard samples of mouse kidney section are carried out by using DLSFM. The experimental results show that the resolution of DLSFM in the <i>x</i>, <i>y</i> and <i>z</i> directions is 1.33 times, 1.42 times and 1.19 times that of wide field microscope, respectively, and the fast 3D high-resolution optical sectioning imaging of biological samples is realized, which lays a technical foundation for further developing the rapid high-resolution imaging of the whole cells and tissues in vivo.

High-speed multiplane structured illumination microscopy of living cells using an image-splitting prism

Abstract Super-resolution structured illumination microscopy (SR-SIM) can be conducted at video-rate acquisition speeds when combined with high-speed spatial light modulators and sCMOS cameras, rendering it particularly suitable for live-cell imaging. If, however, three-dimensional (3D) information is desired, the sequential acquisition of vertical image stacks employed by current setups significantly slows down the acquisition process. In this work, we present a multiplane approach to SR-SIM that overcomes this slowdown via the simultaneous acquisition of multiple object planes, employing a recently introduced multiplane image splitting prism combined with high-speed SIM illumination. This strategy requires only the introduction of a single optical element and the addition of a second camera to acquire a laterally highly resolved 3D image stack. We demonstrate the performance of multiplane SIM by applying this instrument to imaging the dynamics of mitochondria in living COS-7 cells.

Design of high-speed phase-only spatial light modulators with two-dimensional tunable microcavity arrays.

Spatial light modulators (SLMs) are central to numerous applications ranging from high-speed displays to adaptive optics, structured illumination microscopy, and holography. After decades of advances, SLM arrays based on liquid crystals can now reach large pixel counts exceeding 106 with phase-only modulation with a pixel pitch of less than 10 µm and reflectance around 75%. However, the rather slow modulation speed in such SLMs (below hundreds of Hz) presents limitations for many applications. Here we propose an SLM architecture that can achieve two-dimensional phase-only modulation at high speed in excess of GHz. The architecture consists of a tunable two-dimensional array of vertically oriented, one-sided microcavities that are tuned through an electro-optic material such as barium titanate (BTO). We calculate that the optimized microcavity design achieves a π phase shift under an applied bias voltage below 10 V, while maintaining nearly constant reflection amplitude. As two model applications, we consider high-speed 2D beam steering as well as beam forming. The outlined design methodology could also benefit future design of spatial light modulators with other specifications (for example amplitude modulators). This high-speed SLM architecture promises a wide range of new applications ranging from fully tunable metasurfaces to optical computing accelerators, high-speed interconnects, true 2D phased array beam steering, and quantum computing with cold atom arrays.

Super multi-view near-eye display to solve vergence–accommodation conflict

A super multi-view (SMV) technique is applied to near-eye displays to solve the vergence-accommodation conflict that causes visual fatigue. The proposed SMV near-eye display employs a high-speed spatial light modulator (SLM), a two-dimensional (2D) light source array, and an imaging optics for each eye. The imaging optics produces a virtual image of the SLM and real images of the light sources to generate a 2D array of viewpoints. The SMV images are generated using a time-multiplexing technique: the multiple light sources sequentially emit light while the SLM synchronously displays corresponding parallax images. A monocular experimental system was constructed using a ferroelectric liquid crystal display and an LED array. A full-parallax SMV image generation with 21 viewpoints was demonstrated and a comparison of full-parallax and horizontal parallax SMV images provided.

Full-color holographic 3D display with horizontal full viewing zone by spatiotemporal-division multiplexing.

A technical full-color reconstruction method is presented to develop our previous monochromatic holographic three-dimensional display with a horizontal full viewing zone. A digital micromirror device (DMD) is used as a high-speed spatial light modulator, and its modulation area is divided into three parts, which independently handle three sub-holograms corresponding to red, green, and blue components. The reconstructed images from a single frame of the DMD never form full-color images. However, given that this spatial division is combined with the time-division method for the full viewing zone, each monochromatic image is temporally mixed, and practically full-color images are reconstructed. After monochromatic reconstruction from a single frame was confirmed, full-color reconstruction with a horizontal full viewing zone was demonstrated.

High-Speed, Phase-Dominant Spatial Light Modulation with Silicon-Based Active Resonant Antennas

Spatiotemporal control of optical wavefronts is of great importance in numerous free-space optical applications including imaging in 3D and through scattering media, remote sensing, and generation of various beam profiles for microscopy. Progress in these applications is currently limited due to lack of compact and high-speed spatial light modulators. Here we report an active antenna comprising a free-space coupled asymmetric Fabry–Perot resonator that produces a phase-dominant thermo-optic modulation of reflected light at frequencies approaching tens of kilohertz. As a proof of concept for spatial light modulation, we demonstrate a 6 × 6 array of such active antennas with beam deflection capability. The robust design of our silicon-based active antenna will enable large-scale integration of high-speed, phase-dominant spatial light modulators.

Wide-field imaging through scattering media by scattered light fluorescence microscopy

To obtain images through scattering media, scattered light fluorescence (SLF) microscopy that utilizes the optical memory effect has been developed. However, the small field of view (FOV) of SLF microscopy limits its application. In this paper, we have introduced a re-modulation method to achieve wide-field imaging through scattering media by SLF microscopy. In the re-modulation method, to raster scan the focus across the object plane, the incident wavefront is re-modulated via a spatial light modulator (SLM) in the updated phase compensation calculated using the optimized iterative algorithm. Compared with the conventional optical memory effect method, the re-modulation method can greatly increase the FOV of a SLF microscope. With the phase compensation theoretically calculated, the process of updating the phase compensation of a high speed SLM is fast. The re-modulation method does not increase the imaging time. The re-modulation method is, therefore, expected to make SLF microscopy have much wider applications in biology, medicine and physiology.

Comparison of asymmetric double parabolic-inversed parabolic quantum wells for linear optical (1–2) transition

In present study, for asymmetric double parabolic quantum well (ADPQW) and asymmetric double inverse parabolic quantum well (ADIPQW) the linear optical absorption (OA) coefficient, the linear refractive index change (RIC), resonant peaks of the linear OA and the optical rectification (OR) coefficients are examined as dependent on the structural parameters (barrier width (b) and Al concentration at the well center (σ)). The results display that the variation of all OA and OR coefficients and RIC depend on b and σ-parameter. I have also shown that the σ-parameter has a significant effect on the electronic and optical properties of ADPQW and ADIPQW, and that the energy levels and the dipole moment matrix elements vary depending on the shape of the limiting potential. The intersubband absorption spectrum in the ADPQW shows the blue shift by increasing the b and σ values. Whereas the absorption spectrum for ADIPQW shows blue shift for σ=1 with increasing b-values, this spectrum shows red shifts for σ=5. The electro-optic properties of these structures promise many potential applications in high speed spatial light modulators and switches. So, it can be adjusted RIC and the resonant peak size of the linear OA and OR coefficient by changing Al density at the well center in addition to the barrier dimensions.

Gradation representation method using a binary-weighted computer-generated hologram based on pulse-width modulation

We propose a simple gradation representation method using a binary-weighted computer-generated hologram (CGH) to be displayed on a high-speed spatial light modulator that can be controlled by the pulse-width modulation technique. The proposed method uses multiple bit planes comprising binary-weighted CGHs with various pulse widths. The object points of a three-dimensional (3D) object are assigned to multiple bit planes according to their gray levels. The bit planes are sequentially displayed in a time-division-multiplexed manner. Consequently, the proposed method realizes a gradation representation of a reconstructed 3D object.

Dual-coded compressive hyperspectral imaging

This Letter presents a new snapshot approach to hyperspectral imaging via dual-optical coding and compressive computational reconstruction. We demonstrate that two high-speed spatial light modulators, located conjugate to the image and spectral plane, respectively, can code the hyperspectral datacube into a single sensor image such that the high-resolution signal can be recovered in postprocessing. We show various applications by designing different optical modulation functions, including programmable spatially varying color filtering, multiplexed hyperspectral imaging, and high-resolution compressive hyperspectral imaging.

Speckle-free, shaded 3D images produced by computer-generated holography

A hologram display technique that provides speckle-free, shaded reconstructed images is proposed. A three-dimensional object consists of object points; these object points are divided into plural object point groups that are generated in a time-sequential manner. Each object point group consists of a two-dimensional (2D) array of object points that are separated so as to prevent interference among them. Each object point group is generated by displaying a 2D array of zone plates on a high-speed spatial light modulator (SLM). The amplitude distribution of the zone plates is modulated two-dimensionally based on Phong shading to shade the reconstructed images. The 2D amplitude distribution of the zone plates is decomposed into multiple binary patterns that are displayed by the SLM in a time-sequential manner. The proposed method is experimentally verified.