Spatial Light Modulator Research Articles

Phase-modulated multi-foci microscopy for rapid 3D imaging

3D imaging technology is pivotal in monitoring the functional dynamics and morphological alterations in living cells and tissues. However, conventional volumetric imaging associated with mechanical z-scanning encounters challenges in limited 3D imaging speed with inertial artifact. Here, we present a unique phase-modulated multi-foci microscopy (PM3) technique to achieve snapshot 3D imaging with the advantages of extended imaging depths and adjustable imaging intervals between each focus in a rapid fashion. To accomplish the tasks, we utilize a spatial light modulator (SLM) to encode the phases of the scattered or fluorescence light emanating from a volumetric sample and then project the multiple-depth images of the sample onto a single charge-coupled device camera for rapid 3D imaging. We demonstrate that the PM3 technique provides ∼55-fold improvement in imaging depth in polystyrene beads phantom compared to the depth of field of the objective lens used. PM3 also enables the real-time monitoring of Brownian motion of fluorescent beads in water at a 15 Hz volume rate. By precisely manipulating the phase of scattered light on the SLM, PM3 can pinpoint the specific depth information in living zebrafish and rapidly observe the 3D dynamic processes of blood flow in the zebrafish trunk. This work shows that the PM3 technique developed is robust and versatile for fast 3D dynamic imaging in biological and biomedical systems.

Generation of wavelength- and orbital angular momentum-tunable extreme-ultraviolet vortex beams using a spiral phase mirror

To generate or manipulate the orbital angular momentum (OAM) of light, various optical elements, such as spiral phase plates, spatial light modulators, diffractive optical elements, and spiral phase mirrors (SPMs) have been used. In contrast to other optical components, the SPM depends only on the angle of incidence, which allows for the manipulation of the OAM values by simply rotating a single SPM or changing the angle of incidence of light. This study theoretically demonstrated the generation of high-quality vortex beams in the X-ray region (within a range of several tens of nanometers) beyond the existing visible and infrared regions using a SPM. Based on the geometry of grazing incidence, by rotating a single SPM, we obtained wavelength-tunable vortex beams with an identical OAM value of l = 1 in the 20–40 nm wavelength range and OAM-tunable vortex beams with various OAM values ranging from l = 3 to l = 5 at a 10 nm wavelength. Based on these characteristics, the tuning range of an SPM was discussed and the variation in the major radius of the elliptical beam formed on the SPM by grazing incidence was analyzed to realize SPM manufacturing. This novel optical technique holds great promise for enabling light-matter interactions at the nanometer scale, such as in the molecular or atomic regions, by implementing easily controllable wavelength- and OAM-tunable vortex beams based on a single SPM.

Time-of-flight resolved stimulated Raman scattering microscopy using counter-propagating ultraslow Bessel light bullets generation

We present a novel time-of-flight resolved Bessel light bullet-enabled stimulated Raman scattering (B2-SRS) microscopy for deeper tissue 3D chemical imaging with high resolution without a need for mechanical z-scanning. To accomplish the tasks, we conceive a unique method to enable optical sectioning by generating the counter-propagating pump and Stokes Bessel light bullets in the sample, in which the group velocities of the Bessel light bullets are made ultraslow (e.g., vg ≈ 0.1c) and tunable by introducing programmable angular dispersions with a spatial light modulator. We theoretically analyze the working principle of the collinear multicolor Bessel light bullet generations and velocity controls with the relative time-of-flight resolved detection for SRS 3D deep tissue imaging. We have also built the B2-SRS imaging system and present the first demonstration of B2-SRS microscopy with Bessel light bullets for 3D chemical imaging in a variety of samples (e.g., polymer bead phantoms, biological samples such as spring onion tissue and porcine brain) with high resolution. The B2-SRS technique provides a > 2-fold improvement in imaging depth in porcine brain tissue compared to conventional SRS microscopy. The method of optical sectioning in tissue using counter-propagating ultraslow Bessel light bullets developed in B2-SRS is generic and easy to perform and can be readily extended to other nonlinear optical imaging modalities to advance 3D microscopic imaging in biological and biomedical systems and beyond.

Full-Dimensional Geometric-Phase Spatial Light Metamodulation.

Full-dimensional spatial light modulation requires simultaneous, arbitrary, and independent manipulation of the spatial phase, amplitude, and polarization. This is crucial for leveraging the complete physical dimension resources of light. However, full-dimensional metamodulation can be challenging due to the need for multiple independent control factors. To address this challenge, here we propose parallel-tasking metasurfaces to enable full-dimensional spatial light metamodulation based fully on the geometric-phase concept. Indeed, the meta-atoms are divided into several subphases, each of which serves as an independent control factor to manipulate light phase, amplitude, and polarization through geometric phase, interference, and orthogonal polarization superposition, respectively. Therefore, the macroscopic group of meta-atoms leads to metasurfaces that can achieve broadband full-dimensional spatial light metamodulation, as demonstrated by various types of structured light generation. This approach paves the way to future wide applications of light manipulation enabled by full-dimensional spatial light metamodulation.

Generating multiple polarization outputs using random binary patterns with cascaded spatial light modulators

Generating multiple polarization outputs using random binary patterns with cascaded spatial light modulators

Enhancing multi-plane light conversion orbital angular momentum multiplexer performance via error analysis

We present what we believe to be a novel orbital angular momentum (OAM) multiplexing apparatus capable of handling topological charges ranging from l = 0 to ±3 through multi-plane light conversion (MPLC) across four phase planes. Nevertheless, the fabricating process of MPLC devices is prone to errors that cannot be avoided. Our investigation primarily delves into the repercussions of misalignment and etching inaccuracies on the device's phase, with the assistance of a spatial light modulator. The scrutiny of fabrication errors associated with the device offers valuable insights for refining the fabricating of MPLC devices. The OAM multiplexing device converts the phase of MPLC onto a glass substrate through four etching steps, corresponding to a depth of 0-775 nm. OAM multiplexing/demultiplexing crosstalk based on MPLC is less than -20 dB and -18 dB, respectively. The insertion loss of the OAM mode generated by the OAM multiplexing device coupled to the few-mode fiber is less than 7 dB. In a communication experiment, we demonstrated multiplexed three OAM channels carrying 10 Gbit/s OOK signals over a 5 km few-mode fiber using two MPLC devices. Both the bit error rate curve and constellation diagram demonstrate the excellent performance of MPLC-based OAM multiplexing devices in communication networks.

Analysis of Factors Influencing the Generation of a Higher-Order Hermite–Gaussian Mode Based on Cascaded Spatial Light Modulators

Analysis of Factors Influencing the Generation of a Higher-Order Hermite–Gaussian Mode Based on Cascaded Spatial Light Modulators

Non-mechanical steering of the optical beam in spectral-domain optical coherence tomography

We demonstrate in a proof-of-concept experiment spectral-domain optical coherence tomography where steering of the optical beam that probes the sample in a transverse scan does not make use of any mechanical element. Steering is done with the help of a phase-only spatial light modulator, that introduces a spatially-dependent phase between the two orthogonal polarization components of an optical beam, and some optical elements that control the polarization of light. We demonstrate that making use of the non-mechanical beam steering system considered here, we can reproduce the main traits of imaging with standard OCT that makes use of mechanical-assisted optical beam steering.

A dynamic beam switching metasurface based on angular mode-hopping effect

Fast and versatile beam forming and steering technologies are now crucial for various emerging applications, including wireless optical communications and optical switches. However, these technologies often rely on expensive components, such as spatial light modulators (SLMs) and optical phase arrays (OPAs), which come with complex and power-consuming control systems. In response to this challenge, we propose a dynamic beam-switching method inspired by the mode-hopping effect of lasers. As a proof of concept, we introduce the dynamic beam switching metasurface (DBSM) design, featuring an in-plane mechanical actuation system. Our numerical analyses, based on the finite element method (FEM), demonstrate that the proposed DBSM exhibits versatile beam forming and steering functionalities. These include beam splitting and omnidirectional beam steering. Moreover, we anticipate that the tuning speed of the DBSM will reach the kilohertz (kHz) range or even higher when utilizing a microelectromechanical systems (MEMS) actuator, building upon pioneering research in this field. We envision it holds promising applications in areas such as light detection and ranging (LiDAR), optical wireless communication devices, and optical switches.

Simplifying tailored generation of complex structured femtosecond pulses with easily fabricated phase plates

This article presents a novel approach to targeted 4f pulse shaping using phase plates fabricated by single-point diamond turning (SPDT) machining. The manufacturing of the phase plates using SPDT is versatile, cost-effective, fast, robust, and applicable across a wide range of optical materials, spanning from visible to far-infrared spectra (e.g., PMMA, ZnSe). Manufactured profiles can be used for phase manipulation and pulse structuring, analogously to programable spatial light modulators (SLM). We demonstrate that the pulse waveforms can be reproduced with high fidelity by simple simulations based on calculating optical path differences induced by the phase plate for each wavelength and taking into account the finite focal spot. The simulated and reconstructed frequency-resolved optical gating spectrograms featured G errors between 1–2% and intensity errors between 0.02–0.06. Even for complex structured pulses with the rms value of the time-bandwidth product reaching 12, our method maintains high precision, in some cases even reaching lower G error compared to simpler waveforms. Finally, we also show that the phase plate can be used to attain a set of uncorrelated pulse waveforms by moving the plate relatively to the dispersed laser spectrum. Overall, this approach bypasses common limitations associated with pulse shaping using SLMs, such as pixelation, pixel cross-talk, and spectral or laser fluences constraints.

Image optimization of a computer-generated hologram by reusing zero-order beams and reflectors vibration

In computer-generated holography, spatial light modulators are predominantly used for image reconstruction. However, the quality of the reconstructed images is often compromised by laser speckle and zero-order light diffraction. To address these problems, we propose the reuse of the zero-order beam, which not only eliminates the interference caused by zero-order diffraction in the reconstructed images but also considerably enhances image brightness. Moreover, we propose the use of vibrating reflectors in the proposed structure for reusing the zero-order beam to reduce speckle, thereby suppressing the speckle contrast in reconstructed images to less than 4%.

Reducing beam tracking complexity using a phase ramp and Fresnel lens when steering beams using spatial light modulators.

Steering multiple laser beams using spatial light modulators (SLMs) creates unwanted diffraction and reflections that are not modulated by the SLM, which can make beam tracking difficult. A novel, to the best of our knowledge, and simple beam steering methodology is proposed, which aims at reducing the influence of this clutter while maintaining tracking performance. The beam(s) are deliberately defocused before steering with a superposition of a phase ramp and Fresnel lens (PRFL) phase screen on the SLM. As a result, the non-modulated reflections and diffracted light are decreased in relative intensity to the steered beam, in turn allowing simple and standard peak intensity and center of gravity (CG) algorithms for tracking. Hardware demonstration shows tracking performance using the PRFL remained on-par with more complex filtering approaches while adding no additional hardware. This method has potential to improve the communication performance of multi-beam laser communication terminals.

Rotation of liquid crystal microdroplets in the intensity minima of an optical vortex beam

An optical vortex is characterized by its donut-shaped intensity distribution and helical phase structure. In this study, we demonstrate that an optical vortex beam, generated by a spatial light modulator, can trap, circulate, and rotate liquid crystal microdroplets of various sizes at different positions within the beam. Our findings indicate that larger microdroplets are trapped at intensity minima without altering their internal liquid crystal orientation, which is fluid by nature, and the rotation of microdroplets were observed. This rotation, a rare phenomenon, occurs without damaging or altering the inner liquid crystal molecules, offering an advantage over traditional circularly polarized optical trapping, which can generally alter inner molecular arrangements of liquid crystal. This report details the relationship between trapped particle size, trapping position, and rotation angle of liquid crystal microdroplets within an optical vortex beam.

Eyebox expansion of a lensless near-eye display using diverging spherical wave illumination and a multiplexed holographic optical element

We expand the eyebox size of a lensless holographic near-eye-display (NED) using passive eyebox replication technique that incorporates a spatial light modulator (SLM) and a holographic optical element (HOE). In holographic NEDs, the space-bandwidth product (SBP) of the SLM determines the exit pupil dimensions and corresponding eyebox size. The base eyebox size is replicated in the horizontal direction by using the horizontal high-order diffractions of an SLM under spherical wave illumination and a multiplexed HOE combiner. When a digital blazed grating and a digital lens phase are added to the computed phase hologram sent to the SLM, two spatially separated, horizontal high-order diffraction terms with identical intensity and information can be uniformly formed without the zero-order term. When the eyebox size is expanded, the field-of-view (FOV) is not sacrificed; spherical divergence wave illumination alleviates the need for a tradeoff between FOV and eyebox size. The astigmatism introduced during HOE fabrication is counterbalanced by pre-correcting the target image using a computer-generated, holographic computation algorithm. The prototype system shows simple and effective, distortion-free eyebox expansion of a wide-angle, lensless, holographic NED.

Image authentication with exclusive-OR operated optical vortices

Optical vortices carrying orbital angular momentum have drawn much attention because they provide high-dimensional encoding. Employing an array of optical vortices, we demonstrate an authentication verification system. For security authentication, an exclusive-OR logic operation has been implemented employing a light beam consisting of an array of vortices. A liquid crystal spatial light modulator has been used to generate orthogonal states of optical vortices. The proposed technique can provide a secure method of authentication with straightforward implementation. We have presented simulation and experimental results to verify the proposed scheme.

Lossless Phase‐Change Material Enabled Wideband High‐Efficiency Spatial Light Phase Modulation at Near‐Infrared

AbstractHigh‐efficiency spatial light phase modulation with wide operating bandwidth is highly significant yet challenging. Dynamic metasurfaces leveraging active materials with tunable optical response provide a promising solution. Current work is generally confronted with restricted operation bandwidth and diminished modulation efficiency, constrained by the limited tunable range and inherent absorption of active materials particular at optical frequency. Recently, the emergence of lossless phase‐change material Sb2Se3 has garnered widespread attention. Its unique characteristics, including near‐zero absorption at near‐infrared and a substantial refractive index contrast ≈0.93 during phase transition, enable the possibility of high‐performance spatial light modulation. Pioneering studies have validated the capability of lossless phase‐change metasurfaces for wavefront control, but are typically restricted to limited efficiency. Here, a hybrid phase‐change metasurface utilizing over‐coupled resonances supported by Sb2Se3 nanoholes is proposed. For the first time in optical frequency, high‐efficiency 4‐level phase modulation covering over π range is experimentally demonstrated with a sizable operating bandwidth of 42 nm and a minimum reflectance of exceeding 0.5. Leveraging optically driven localized phase‐transition technique, dynamic beam deflection is further demonstrated. The work validates the tremendous potential of phase‐change metasurfaces in achieving advanced spatial light control, signifying significant progress for the development and application of phase‐change photonic devices.

Full-color time-sequential super multi-view near-eye display with front-lit waveguide illumination

Light field (LF) displays can offer a quasi-natural three-dimensional (3D) viewing experience by tailoring the four-dimensional light information. However, the primary drawback of conventional LF displays is their limited image quality due to restricted information. To address this limitation, time-multiplexing techniques are employed, but the resulting system configurations are often impractical for achieving compact systems. Here, we present a compact time-sequential super multi-view LF near-eye display integrated with a front-lit, multi-directional illumination module for virtual reality application. This illumination module consists of an RGB light-emitting diode array and a waveguide, allowing us to exploit a high-speed reflective-type spatial light modulator and provide high-bit depth, full-color 3D scenes with quasi-continuous parallax in a compact form factor display. The prototype is implemented for a live demo and evaluated with both simulation and experiment. Our work provides a viable path towards the wide adoption of 3D virtual reality head-mounted displays.

Rapid calculation of computer-generated holograms for line-drawn 3D objects with varying thicknesses

Accelerating the calculation of computer-generated holograms (CGHs) is an important requirement for three-dimensional (3D) electro-holography display systems. Among the several sophisticated algorithms for CGH acceleration, the CG-line method for projecting 3D wire-frame objects is highly promising due to its high acceleration capability. However, conventional algorithms cannot account for line thickness, and only lines with a constant thickness corresponding to the pixel pitch of the spatial light modulator can be drawn. This restricts the expressiveness and visibility of 3D images, particularly for high-resolution holograms. Therefore, we propose a method for widening the line thickness of the CG-line method. We successfully generated a 3D object comprising bold lines of different thicknesses without sacrificing speed.

Simple and robust 3D MINFLUX excitation with a variable phase plate

MINFLUX has achieved extraordinary resolution in superresolution imaging and single fluorophore tracking. It is based on localizing single fluorophores by rapid probing with a patterned beam that features a local intensity minimum. Current implementations, however, are complex and expensive and are limited in speed and robustness. Here, we show that a combination of an electro-optical modulator with a segmented birefringent element such as a spatial light modulator produces a variable phase plate for which the phase can be scanned on the MHz timescale. Bisected or top-hat phase patterns generate high-contrast compact excitation point-spread functions for MINFLUX localization in the x, y, and z-direction, respectively, which can be scanned across a fluorophore within a microsecond, switched within 60 microseconds and alternated among different excitation wavelengths. We discuss how to compensate for non-optimal performance of the components and present a robust 3D and multi-color MINFLUX excitation module, which we envision as an integral component of a high-performance and cost-effective open-source MINFLUX.

Electromechanically Reconfigurable Terahertz Stereo Metasurfaces.

Dynamic terahertz devices are vital for the next generation of wireless communication, sensing, and non-destructive imaging technologies. Metasurfaces have emerged as a paradigm-shifting platform, offering varied functionalities, miniaturization, and simplified fabrication compared to their 3D counterparts. However, the presence of in-plane mirror symmetry and reduced degree of freedom impose fundamental limitations on achieving advanced chiral response, beamforming, and reconfiguration capabilities. In this work, a platform composed of electrically actuated resonators that can be colossally reconfigured between planar and 3D geometries is demonstrated. To illustrate the platform, metadevices with 3D Split Ring Resonators are fabricated, wherein two counteracting driving forces are combined: i) folding induced by stress mismatch, which enables non-volatile state design and ii) unfolding triggered by the strain associated with insulator-to-metal transition in VO2, which facilitates volatile structural reconfiguration. This large structural reconfiguration space allows for resonance mode switching, widely tunable magnetic and electric polarizabilities, and increased frequency agility. Moreover, the unique properties of VO2, such as the hysteretic nature of its phase transition is harnessed to demonstrate a multi-state memory. Therefore, these VO2 integrated metadevices are highly attractive for the realization of 6G communication devices such as reconfigurable intelligent surfaces, holographic beam formers, and spatial light modulators.