Spatial Light Modulator Research Articles

Metasurface for programmable quantum algorithms with classical and quantum light

Abstract Metasurfaces have recently opened up applications in the quantum regime, including quantum tomography and the generation of quantum entangled states. With their capability to store a vast amount of information by utilizing the various geometric degrees of freedom of nanostructures, metasurfaces are expected to be useful for processing quantum information. Here, we propose and experimentally demonstrate a programmable metasurface capable of performing quantum algorithms using both classical and quantum light with single photons. Our approach encodes multiple programmable quantum algorithms and operations, such as Grover’s search algorithm and the quantum Fourier transform, onto the same metalens array on a metasurface. A spatial light modulator selectively excites different sets of metalenses to carry out the quantum algorithms, while the interference patterns captured by a single-photon camera are used to extract information about the output state at the selected output directions. Our programmable quantum metasurface approach holds promising potential as a cost-effective means of miniaturizing components for quantum computing and information processing.

Structurally Invariant Higher-Order Ince-Gaussian Beams and Their Expansions into Hermite-Gaussian or Laguerre-Gaussian Beams

Paraxial beam modes, which propagate in space and focus without changing their transverse intensity pattern, are of great value for multiplexing transmitted data in optical communications, both in waveguides and in free space. The best-known paraxial modes are the Hermite-Gaussian and Laguerre-Gaussian beams. Here, we derive explicit analytical expressions for Ince-Gaussian (IG) beams for several first values of the indices p = 3, 4, 5, and 6. In total, we obtain expressions for the amplitudes of 24 IG beams. These formulae are written as superpositions of the Laguerre-Gaussian (LG) or Hermite-Gaussian (HG) beams, with the superposition coefficients explicitly depending on the ellipticity parameter. Due to simultaneous representation of the IG modes via the LG and HG modes, it is easy to obtain the IG modes in the limiting cases wherein the ellipticity parameter is zero or approaches infinity. The explicit dependence of the obtained expressions for the IG modes on the ellipticity parameter makes it possible to change the intensity pattern at the beam cross-section by continuously varying the parameter values. For the first time, the intensity distributions of the IG beams are obtained for negative values of the ellipticity parameter. The obtained expressions could facilitate a theoretical analysis of properties of the IG modes and could find practical applications in the numerical simulation or generation of such beams with a liquid-crystal spatial light modulator.

High-Throughput Two-Photon 3D Printing Enabled by Holographic Multi-Foci High-Speed Scanning.

The emerging two-photon polymerization (TPP) technique enables high-resolution printing of complex 3D structures, revolutionizing micro/nano additive manufacturing. Various fast scanning and parallel processing strategies have been proposed to promote its efficiency. However, obtaining large numbers of uniform focal spots for parallel high-speed scanning remains challenging, which hampers the realization of higher throughput. We report a TPP printing platform that combines galvanometric mirrors and liquid crystal on silicon spatial light modulator (LCoS-SLM). By setting the target light field at LCoS-SLM's diffraction center, sufficient energy is acquired to support simultaneous polymerization of over 400 foci. With fast scanning, the maximum printing speed achieves 1.49 × 108 voxels s-1, surpassing the existing scanning-based TPP methods while maintaining high printing resolution and flexibility. To demonstrate the processing capability, functional 3D microstructure arrays are rapidly fabricated and applied in micro-optics and micro-object manipulation. Our method may expand the prospects of TPP in large-scale micro/nanomanufacturing.

Optimizing microlens arrays for incoherent HiLo microscopy

HiLo microscopy is a powerful, low-cost, and easily configurable technique for acquiring high-contrast optically-sectioned images. However, traditional HiLo microscopes are based on coherent light sources with diffusive glass plates or incoherent light sources with digital mirror devices (DMD) and spatial light modulators (SLM), which are more expensive. Here, we propose a new low-cost HiLo microscopy technique using MLAs and incoherent LED light sources. We simulated structured illumination (SI) patterns and HiLo image generation. To observe how MLAs affect HiLo images, we used three common MLAs with specific microlens pitch and numerical aperture (NA) to generate periodic illumination patterns. Our simulations concluded that the MLA's NA does not significantly affect HiLo images, and a larger lens pitch can bring a higher image contrast. However, there is an optimized lens pitch. If the lens pitch is equal to or higher than 140 μm, artifacts are observed in HiLo images. Based on our simulations, employing the cross-type MLA with a 0.01NA and a period of 120 μm yields the optimal HiLo image (94.6 % contrast). In our quantitative analysis with the traditional HiLo, where SI patterns were set with the same period, we calculated the SSIM index between each HiLo-Ground Truth image pair. The cross-type MLA HiLo performed slightly better (SSIM = 0.9554) than the traditional HiLo (SSIM = 0.9396). However, when using the hexagon-type MLA, artifacts were evident in the final HiLo image (SSIM = 0.9054). The cylinder-type MLA HiLo result (SSIM = 0.9366) is similar to the traditional HiLo. To our knowledge, this is the first numerical study about MLA-based HiLo microscopy. This study can benefit researchers using MLAs and incoherent light sources to configure their low-cost HiLo microscopes.

Fiber Bragg grating inscription assisted by a spatial light modulator.

In this Letter, we proposed a new technique for point-by-point fiber Bragg grating (FBG) writing in a static fiber by using a spatial light modulator to control the position of the focal point inside the fiber core. Various types of short-length FBGs (uniform, phase-shifted, and apodized) were demonstrated by this inscription technique. Moreover, the capability to tailor the transverse dimension of a grating pitch from a single point to more complex shapes, such as a wide plane covering a whole fiber core or a transverse ring, was shown.

Lithium niobate thin film electro-optic modulator

Abstract The linear electro-optic effect offers a valuable means to control light properties via an external electric field. Lithium niobate (LN), with its high electro-optic coefficients and broad optical transparency ranges, stands out as a prominent material for efficient electro-optic modulators. The recent advent of lithium niobate-on-insulator (LNOI) wafers has sparked renewed interest in LN for compact photonic devices. In this study, we present an electro-optic modulator utilizing a thin LN film sandwiched between top and bottom gold (Au) film electrodes, forming a Fabry–Pérot (F–P) resonator. This resonator exhibits spectral resonance shifts under an applied electric field, enabling efficient modulation of reflected light strength. The modulator achieved a 2.3 % modulation amplitude under ±10 V alternating voltage. Our approach not only presents a simpler fabrication process but also offers larger modulation amplitudes compared to previously reported metasurface based LN electro-optic modulators. Our results open up new opportunities for compact electro-optic modulators with applications in beam steering devices, dynamic holograms, and spatial light modulators, and more.

Evaluation of atmospheric coherent length of free-space optical links by using phase fluctuation.

Atmospheric coherence length is one of the most crucial parameters for free-space optical (FSO) links, which can reflect the level of phase and amplitude fluctuations caused by the atmospheric turbulence. In this paper, we study the evaluation of the atmospheric coherence length of the FSO links. The analytical expression of atmospheric coherence length is rendered based on the phase fluctuation resulting from atmospheric turbulence by using the most realistic Bump model. The proposed method is validated theoretically with the Monte Carlo phase screen. Also, the experimental setup with respect to FSO links is established with the spatial light modulator to validate the method experimentally, wherein the fluctuated phase is collected by Shack-Hartmann sensor. The results show that the evaluation of atmospheric coherence length by the analytical expression is consistent with the theoretical prediction as well as the experimental measurement. Thus, the proposed method enables the accurate evaluation of atmospheric coherence length under various turbulence conditions, which can assist the performance analysis as well as design of free-space optical communication systems.

High fidelity laser beam shaping using liquid crystal on silicon spatial light modulators as diffractive neural networks

Spatial light modulators (SLMs) based on liquid crystal on silicon (LCoS) are powerful tools for laser beam shaping as they can be used to dynamically create almost arbitrary intensity distributions. However, laser beam shaping with LCoS-SLMs often suffers from beam shaping artifacts in part caused by unconsidered properties of the LCoS devices: astigmatism that stems from the non-normal incidence of the laser beam on the SLM and the effect commonly referred to as the ’0-th diffraction order’ that is caused by both the crosstalk between neighboring pixels and the direct reflection at the cover glass of the SLM. We here present a method to consider and compensate for these inherent properties of LCoS devices by treating the SLM as a diffractive neural network.

Preparation of convex edges in fused silica by single pass perforation with a 2D Airy-Gaussian beam.

Following ultrafast laser machining of fused silica, post-processing such as polishing and honing are typically required for edges. In this study, we employed a spatial light modulator (SLM) to generate the 2D Airy-Gaussian beam to prepare the convex edges in fused silica by using a single pass of a picosecond laser. It is found that, if the speed exceeds 5mm/s, there would be plasma interference which is unfavorable for the separation process. A filament effect was observed when the internal laser peak power exceeds the damage threshold of fused silica. The shape of the convex edges was consistent with the propagation path of the 2D Airy-Gaussian beam inside the fused silica before separation. The inclination angle was 17° and 13°, respectively, on the upper and lower end of the edges. The results of this study provide a new, to our knowledge, method for the preparation of curved structures with different curvatures in transparent materials.

Digital inverse patterning solutions for fabrication of high-fidelity microstructures in spatial light modulator (SLM)-based projection lithography.

Digital mask projection lithography (DMPL) technology is gaining significant attention due to its characteristics of free-mask, flexibility, and low cost. However, when dealing with target layouts featuring sizes smaller than the wavelength scale, accurately producing resist patterns that closely match the target layout using conventional methods to design the modulation coefficients of digital masks produced by spatial light modulators (SLM) becomes challenging. Here, we present digital inversion lithography technology (DILT), which offers what we believe to be a novel approach to reverse engineer the modulation coefficients of digital masks. In the case of binary amplitude modulation, DILT achieves a remarkable reduction in pattern errors (PE), reaching the original 0.26. At the same time, in the case of the gray amplitude modulation, the PE can be reduced to the original 0.05, which greatly improves the high-fidelity transfer of the target layout. This significant improvement enhances the accuracy of target design transfer. By leveraging the capabilities of DILT, DMPL can now attain higher precision and reliability, paving the way for more advanced applications in the field of micro-nano device manufacturing.

Performance evaluation of the data transmission link with Bessel-Gaussian beams through a tunable smoke channel

We simulate and experimentally demonstrate a 1 Gbps free-space optical (FSO) communication system in a smoke chamber with the Bessel–Gaussian (BG) beam. Firstly, we simulate and analyze the attenuation and bit error rate (BER) of BG and Gaussian beams in the smoke channel based on the Monte Carlo method. The results show that BG beams have more advantages than Gaussian beams in smoke transmission. Then we generate a BG beam based on the spatial light modulator (SLM) method, the BG beam’s central spot shows a stable diameter of about 0.9 mm propagating 3.2 m in space. The 1 Gbps 1550 nm on/off keying (OOK) signal is loaded on the BG beam via a bit error rate test (BERT). Next, a tunable smoke channel is established based on an acrylic chamber, and the attenuation and visibility of the smoke channel are characterized in real-time. Finally, the intensity distributions, power stability, power attenuation and BER performance of the BG and Gaussian beams’ transmission links in the tunable smoke channel are investigated. The experimental results show the improvements in transmission performance under the smoke channel conditions using BG beams. Compared with Gaussian beams, BG beams exhibit lower power attenuation (reduced by up to 3.13 dB) and a more stable receiver (decreased by 23 % in standard deviation). Additionally, the BER of 1 Gbps of the transmission link with the BG beam improved by 7.18 dB–10.17 dB in the tunable smoke channel (0.5–2 m). As the length of the smoke channel increases, the improvement of the BG beam in the smoke channel increases as well. The BG beam has shown remarkable advantages in transmission links through the smoke channel. The research offers a robust and generalized proposal for FSO communications based on structured beams.

Electrolyte gated graphene terahertz amplitude modulators

Active manipulation of the amplitude of terahertz (THz) frequency waves, through electrical tuning, is key for next-generation THz imaging and essential for unlocking strategic applications, from wireless communication to quantum technologies. Here, we demonstrate high-performance THz amplitude modulators based on an electrolyte-gated single-layer graphene. Broadband modulation in the 1.5–6 THz range is achieved by optimizing the electric field coupling by carefully controlling the spacer thickness in a quarter-wavelength cavity structure, with a maximum modulation depth of 40% at around 2 THz. Raman characterization confirms a Fermi-level tuning of 0.39 eV via electrolyte gating of graphene. A test 2 × 2 modulator array with independent control of sub-millimeter regions is then developed and tested, with no crosstalk between pixels. The reported results highlight the potential of electrolyte-gated graphene for efficient THz modulation. The single-chip design offers compactness and ease of integration with other electronic components, making it a promising platform for THz spatial light modulators and adaptive optical components.

Speckle noise suppression method in a holographic display based on pixel processing.

In this paper, we propose a method to suppress the speckle noise in a holographic display based on pixel processing. Through the separation of object pixels in space, the recorded object is divided into multiple object point groups. The complex amplitude of the light field for each object point group is recorded as a sub-computer-generated hologram (sub-CGH). The phase of each pixel on a sub-CGH is optimized to generate the final sub-CGH. Therefore, the pixels of the recorded object and sub-CGH are processed. In the reconstruction process, the final sub-CGHs are loaded on the spatial light modulator sequentially. The speckle noise of the reconstructed image is suppressed by reducing the algorithm error and the overlapping area of adjacent image points. The experimental results prove the feasibility of the proposed method.

One-dimensional modulation single-pixel imaging: Exceeding spatial light modulator resolution

Although high-resolution single-pixel imaging (SPI) can be achieved by under-sampling, low sampling ratio (SR) strategies often result in a loss of image details and lower image quality. Due to the limited memory of the spatial light modulator (SLM) and the time necessary to load such vast numbers of patterns, high-resolution SPI at high sampling rates has not yet been realized. In this work, we propose a one-dimensional single-pixel imaging (1D-SPI) technique to reconstruct high-quality images that can even surpass the full resolution of the SLM at 100% sampling ratio with extremely low data throughput. Only nearly one-thousandth as many modulation patterns as traditional 2D modulation methods are required, which significantly reduces the demand for massive memory capacity and the time to load these patterns. A 1540×1024 resolution SPI image is successfully demonstrated experimentally, indicating its tremendous promise in applications such as industrial inspection and satellite remote sensing.

Contribution of optical resolution to the spatial precision of two-photon optogenetic photostimulation in vivo.

Two-photon optogenetics combines nonlinear excitation with noninvasive activation of neurons to enable the manipulation of neural circuits with a high degree of spatial precision. Combined with two-photon population calcium imaging, these approaches comprise a flexible platform for all-optical interrogation of neural circuits. However, a multitude of optical and biological factors dictate the exact precision of this approach in vivo, where it is most usefully applied. We aimed to assess how the optical point spread function (OPSF) contributes to the spatial precision of two-photon photostimulation in neurobiology. We altered the axial spread of the OPSF of the photostimulation beam using a spatial light modulator. Subsequently, calcium imaging was used to monitor the axial spatial precision of two-photon photostimulation of layer 2 neurons in the mouse neocortex. We found that optical resolution is not always the limiting factor of the spatial precision of two-photon optogenetic photostimulation and, by doing so, reveal the key factors that must be improved to achieve maximal precision. Our results enable future work to focus on the optimal factors by providing key insight from controlled experiments in a manner not previously reported. This research can be applied to advance the state-of-the-art of all-optical interrogation, extending the toolkit for neuroscience research to achieve spatiotemporal precision at the crucial levels in which neural circuits operate.

Subwavelength Custom Wavefront Shaping by a Nonlinear Electro-optic Spatial Light Modulator

Subwavelength Custom Wavefront Shaping by a Nonlinear Electro-optic Spatial Light Modulator

All-optical triangular and honeycomb lattices of exciton–polaritons

We implement an all-optically reconfigurable triangular lattice of exciton–polariton condensates in a III–V semiconductor microcavity. For this, we utilize a spatial light modulator to structure an incident nonresonant excitation laser beam into a corresponding triangular lattice of Gaussian beams that are focused onto the cavity plane. The optical excitation pattern locally stimulates and blueshifts polaritons due to exciton interactions. At a critical pump power, polaritons condense into a macroscopically coherent Bloch state with sharp Bragg peaks. We reconstruct the full band structure of the system through energy tomography techniques as a function of lattice constant, allowing us to resolve polaritonic Bloch bands from the condensate emission. While for sufficiently large lattice constants, one observes the formation of triangular arrays of condensates, for small lattice constant and pump powers above condensation threshold, one observes the formation of honeycomb, instead of triangular, lattice of condensates, with clear evidence of condensation into the S-band. Our results underpin the quality of all-optically engineered polariton lattices to simulate condensed matter systems in the strong coupling regime.

64 picosecond time resolved time-correlated single photon counting imaging.

High-speed imaging of dynamic scenes is a challenging and important task in many applications. However, conventional imaging methods based on charge coupled devices or complementary metal oxide semiconductors have limitations in temporal resolution and photon sensitivity. To address this problem, we propose a novel high-speed imaging scheme that combines single-pixel imaging with single photon detection and time-correlated single photon counting. Our scheme can achieve high-speed imaging with 64ps resolution by repeating the motion scenes and using binary outputs from single photon detectors. We demonstrate our scheme by reconstructing the switching process of a digital micro-mirror device and a liquid crystal spatial light modulator. Our scheme can be further improved to 1ps resolution by using a more accurate time-correlated single photon counting system. Moreover, our scheme can adapt to different speed scenes by adjusting the temporal resolution and reducing the sampling time. Our high temporal resolution imaging scheme further expands the application areas of single-pixel imaging and provides solutions for scenes requiring single photon detection and higher temporal resolution, such as reproducible chemical reaction processes imaging, cellular or sub-cellular bio imaging, single-molecule imaging of rotary motors, high-speed equipment inspection, and other periodic high-speed scenes imaging.

High-performance digital shearography integrating spatial light modulator with micro-polarizer camera

Digital shearography (DS), a laser-based optical interferometric method, is widely employed for measuring the first-order derivative of an object's surface deformation. Unlike digital holography, DS integrates self-reference optics, enhancing resistance to environmental disturbance and improving detection sensitivity, making it ideal for non-destructive testing (NDT). DS finds applications in diverse fields such as material inspection, fluid property research, medical diagnostics, cultural heritage restoration, and military defense. The conventional temporal phase-shift (TPS) method encounters limitations in dynamic tests, leading to the introduction of the spatial phase-shift (SPS) method. However, SPS is restricted by aperture size, impacting the phase map quality. The spatial light modulator (SLM) introduces a novel approach to DS system development, enabling quantitative shearing adjustments through precise SLM control. Existing DS systems using traditional phase-shift technology rely on interferometers and struggle to achieve high-quality phase maps with a single exposure. The proposed high-performance DS, leveraging both SLM and a micro-polarizer camera, overcomes this limitation, facilitates single-exposure phase map evaluation with the polarization phase-shift technique, and eliminates the need for a tiny aperture, enhancing light beam utilization and phase map quality.

Oblique-Incidence Interferometric Measurement of Optical Surface Based on a Liquid-Crystal-on-Silicon Spatial Light Modulator

An oblique-incidence interferometric measurement method is proposed to measure and adjust optical surfaces with a liquid-crystal-on-silicon spatial light modulator (LCoS-SLM). The optical system only consists of an interferometer and an LCoS-SLM with precision mounts. It could reduce the measuring cost and time consumption due to the programmable function of the LCoS-SLM and offer the ability to align the optical system. The oblique-incidence measurement theory and optical system adjustment method are established based on an off-axis paraboloid model. The ray-tracing program to calculate the compensation phase map in the measurement is proposed with math models. In the optical alignment step, the off-axis paraboloid model is used to apply the LCoS-SLM as a phase compensator to generate a focusing spot or light spot array to adjust the measured optical surface. And in the interferometric measurement step, the calculated compensation phase map from the ray-tracing calculation is loaded on the LCoS-SLM using the same optical setup as the optical alignment step without any mechanical adjustment. Two interference measurement experiments of typical optical surfaces were carried out to verify the accuracy of the measuring system.