Search

Due to the slowdown of Moore’s law that led to a search for alternative computing technologies, optical information processing is again in the spotlight. The application of optical techniques allows for the possibility of accelerated computation technologies. By incorporating light into the computation, this research investigates methods and strategies for achieving high bit-precision integer multiplication. A novel encoding scheme is presented for integer multiplication in free-space opto-electronic systems. The scheme circumvents hardware constraints imposed by modern material and technology stacks. Without sacrificing numerical accuracy, the method reduces the modulation requirements for each spatial light modulator (SLM) from a standard greyscale level scheme to a system with significantly fewer levels. Bipolar data preservation is performed through a novel threshold-based method. An experimental system employing intensity encoding is developed as a proof-of-concept for the encoding scheme. The system consists of a binary-phase SLM utilising a custom HoloBlade driver stack and a commercial multi-phase SLM. After establishing the system, the noise characteristics of such an optical setup are investigated further. Numerous performance parameters are demonstrated and analysed in a systematic approach. In addition, a number of mitigation strategies and performance enhancement methodologies are proposed and validated for practical implementations. Experimentally, it is demonstrated that a system with inputs greater than 9 bits and multiplication outputs of 18 bits delivers deterministic multiplication results by incorporating a time-multiplexing technique for the first time. This level of accuracy and bit-precision improvement has already made the encoding method itself promising, given that only 5 and 25 resolvable levels are required for the multi-level SLM and the detector, respectively. To practically implement the scheme within the system, novel techniques to minimise error within a performance-limited system are also introduced, such as the demonstration of *in situ* calibration and numerical encoding optimisation based on experimental data. Additional simulation analysis investigates the system’s potential for higher-precision computations using 17-bit unsigned inputs and 34-bit outputs. Integrating low-precision optical processing with high-precision digital electronics relaxes the requirement for high-bit-depth devices by a significant factor. It could prove useful for spatially scalable computations while being less sensitive to the measurement noise and errors of analogue optics. The combination of a novel encoding scheme with an intensity-encoded dual-SLM optical system enables hybrid opto-electronic techniques for element-by-element multiplications that are highly precise and accurate.

In the fields of optics and photonics, phase-only spatial light modulators (SLMs) play an increasingly important role in wave-front engineering. However, the SLMs are subject to wavefront distortion arising from the imperfection in the birefringence effect and physical structure of modulators. This paper presents a simple self-interference phase calibration method applicable to liquid-crystal SLM. We build a interferometric imaging system basing on the Pancharatnam-phase-shifting to measure the phase distribution of a light beam coming from SLMs. Two types of phase modulation errors of SLMs can be characterized in the measurement process: the erroneous gamma curve and shape aberration. The former belongs to dynamic phase distortion and is measured through a four-step Pancharatnam phase shifting interference, which allows a one-shot recording of interference pattern via a polarization camera; the latter represents static phase distortion and is extracted from the interference between light waves coming from different regions of the SLM panel by using Zernike polynomial fitting. Our method has the advantages of high-precision pixel-wise phase correction and robustness against environmental disturbance, and thus can facilitate the applications of SLM in the optical field manipulation.

Multi-focal laser direct writing (LDW) based on phase-only spatial light modulation (SLM) can realize flexible and parallel nanofabrication with high-throughput potential. In this investigation, a novel approach of combining two-photon absorption, SLM, and vector path-guided by scalable vector graphics (SVGs), termed SVG-guided SLM LDW, was developed and preliminarily tested for fast, flexible, and parallel nanofabrication. Three laser focuses were independently controlled with different paths, which were optimized according to the SVG to improve fabrication and promote time efficiency. The minimum structure width could be as low as 81 nm. Accompanied by a translation stage, a carp structure of 18.10 μm × 24.56 μm was fabricated. This method shows the possibility of developing LDW techniques toward fully electrical systems, and provides a potential way to efficiently engrave complex structures on nanoscales.

Moiré patterns are generated by the superposition of two periodic patterns of close frequencies. This present paper proposes a simple method to bridge the conventional gap between interferometry and moiré patterns by generating moiré patterns using straight-line interference fringes from a Michelson interferometer like setup and a circular grating pattern generated on a Spatial Light Modulator (SLM). The visible variation in the geometrical shapes of the moiré patterns by varying the ratio of the periods of the two periodic patterns has also been presented. The experimental results match with the simulation results. Keywords: Moiré, Interferometry, Spatial Light Modulator, Optics, Engineering physics

Optical vortex is of great value in optical trapping, manipulating, and arranging. Here, we propose a dual-helical dielectric cone to generate a dual-vortex beam which can be used to manipulate and arrange dielectric microparticles in three-dimensional space. With the finite-difference time-domain simulation, we calculate the electromagnetic field intensity distribution, phase, and Poynting vector during the propagation of the dual-vortex beam, the optical force and optical torque on the microparticles in the range of dual-vortex beam is also considered. In the experiment, we use the phase mask projected on spatial light modulator to generate a dual-vortex beam, which can trap, manipulate, and arrange the fluorescent microparticles to a specific and stable shape, which is consistent with the results of our simulation calculations. The dual-vortex beam generated by the dual-helical dielectric cone provides a feasible method three-dimensional optical manipulation, which is significant in biophotonical researches.

A novel design of optical wavelength switch, based on an asymmetric switching architecture for edge node implementation, is presented in this paper. Compared to previous research for optical core transport network applications, the proposed work has a unique aspect to build dynamic multicasting and spectral equalization, vital functionalities for optical wavelength switch in the edge of optical access networks. An optical wavelength switch was experimentally implemented and evaluated in a 4 × 16 switching architecture to demonstrate the concept. This dynamic multicasting and spectral equalization were achieved by utilizing liquid crystal on a silicon spatial light modulator (LCoS-SLM) device. An optimal design of computer-generated holograms (CGHs) through an improved GS algorithm was used to perform the beam steering and wavelength switching. A variety of wavelength switching scenarios has been experimentally evaluated. The measurement results showed an average insertion loss of around −12.5 dB, and the calculated crosstalks were all less than −28 dB. Its applications in digital data transmissions were evaluated to achieve a transmission speed larger than 2.5 Gbps. The eye diagram measurement results showed that most wavelength switching scenarios have nearly bit-error-free transmission. The scenario includes the multicasting with spectral equalization within the proposed asymmetrical switching architecture.

Light sheet fluorescence microscopy has become a basic tool in biology and medical research with its fast imaging speed, low phototoxicity and high spatiotemporal resolution. Here, we report a novel method to generate multiplane parallel light sheets with a micro structure named isosceles triangular array. The thickness of light sheet in each plane can approach 3.12 μm along with the working distance of 152.20 μm directly generated with the isosceles triangular array. We experimentally recorded the multiplane parallel light sheets illumination, which is consistent with the corresponding simulation by using ray-tracing method. To evaluate the imaging quality, we compared the light field generated with and without projected phase mask onto the spatial light modulator by using polystyrene fluorescent microspheres nanoparticles and transgenic zebrafish. This study provides a potential method for the building of volumetric imaging light sheet fluorescence microscopy with high resolution and low phototoxicity.

Dynamic control over the conduction band electrons of a semiconductor is a central technological pursuit. Beyond electronic circuitry, flexible control over the spatial and temporal character of semiconductor currents enables precise spatiotemporal structuring of magnetic fields. Despite their importance in science and technology, the control of magnetic fields at the micrometre spatial scale and femtosecond temporal scale using conventional electromagnets remains challenging. Here, we apply structured light beams to interfering photoexcitation pathways in gallium arsenide to sculpt the spatial and momentum configuration of its conduction band population. Programmable control over several hundred micrometre-scale current elements is achieved by manipulating the wavefronts of an optical beam using a spatial light modulator, enabling vast flexibility in the excited current patterns. Using this platform, we demonstrate dynamic optoelectronic interconnects, circuits for spatially tailored magnetic fields and magnetic field lattices. Structured beams of light are used to engineer conduction band populations and pattern currents. Using the approach, dynamic optoelectronic interconnects and other applications are demonstrated.

Liquid crystal (LC)-based spatial light modulators (SLMs) have the ability to shape the wavefront of a light beam and are widely used in applications where phase or amplitude modulation is required. In this work we study the LC director configuration in vertically aligned nematic (VAN) SLMs, with a focus on 1D binary gratings with different driving voltages. By comparing experimental microscopy measurements with simulations, we demonstrate that the director can rotate out of the plane determined by the pretilt of the SLM. By twisting out of the pretilt plane, the formation of a reverse tilt zone in the LC director configuration is avoided. The twist effect is asymmetric and only occurs at the edges where the fringe-field of the high voltage pixel is inclined in the same direction as the pretilt. Due to the out-of-plane reorientation of the director at one side of the pixel, binary gratings show strongly asymmetric diffraction in the pretilt plane. The out-of-plane reorientation also induces changes in the polarisation state of the light beam and the competition between two different out-of-plane reorientation directions may lead to slow switching. It is therefore of utmost importance to consider this effect when using VAN SLMs in applications.

Due to the unique nature of offering minimal invasiveness and high spatial resolution simultaneously, multimode fibers (MMFs) are receiving significant attention in bio-imaging applications. While a spatial light modulator is typically used for controlling the wavefront of the light emitted from the MMF, it makes the system slow, bulky, and expensive. To solve this problem, in this work, we demonstrate the use of a chip-scale integrated optical phased array (OPA) for imaging through an MMF. A silicon OPA with 128 independent phase shifters is fabricated and combined with a 3D waveguide interface to generate speckle patterns at the MMF output. Using the generated speckles and the optical power detected by a bucket detector, we experimentally obtain fine 2D images of the target. From the point spread function analysis of the system, the number of resolvable points is derived to be 1007 points, which is much larger than the number of phase shifters.

We have designed an optical separation device called dual-area mirror for the data link of orbital angular momentum (OAM) multiplexing. Experiments show that the OAM multiplexed beams can be switched by using dual-area mirrors, using OOK to modulate four channels separately to form two inputs, channel A and channel B. There are two OAM beams that are multiplexed in each of channel A and channel B, using a spatial light modulator (SLM) to convert the OAM multiplexed beams in each channel. One of the beams is converted into a Gaussian beam, and then separated by a dual-area mirror, so as to realize the switch of a beam carrying different data in the two channels. Then these channels are detected. The waveform indicates that the switch is successful, and the measured optical power indicates that the dual-area mirror can reduce the bit error rate in the communication links. In addition, the device reduces the experimental cost, is easy to implement, is easy to integrate, and increases the angle between the separated beams.

Terahertz (THz) technology is promising in several applications such as imaging, spectroscopy and communications. Among several methods in the generation and detection of THz waves, a THz time-domain system that is developed using photoconductive antennas (PCA) as emitter and detector presents several advantages such as simple alignment, low cost, high performance etc. In this work, we report the design, fabrication and characterization of a 2-D PCA array that is capable of detecting both the amplitude and phase of the THz pulse. The PCA array is fabricated using LT-GaAs and has 8 channels with 64 pixels ( $8 \times 8$ ). A novel approach using a spatial light modulator (SLM) to steer and focus the infrared probe beam towards pixels of the PCA array is presented. Each channel records the photocurrent generated by the THz signal (amplitude and phase) separately and frequencies up to 1.4 THz can be detected. Furthermore, the parameters such as directional time delay of the THz pulse, crosstalk between the channels etc., were characterized. Finally, we show that the proposed 2D PCA array design is flexible and can be used for accelerated THz spectral image acquisition.

The data matrix (DM) code has large information storage capacity, wide coding range and high reliability, which is an important carrier of people’s daily information exchange. In order to realize the parallel processing method of DM code, the influence of the distance value and gray value of DM code on the recognition time was analyzed experimentally. The DM codes under different conditions were scanned several times, and the reading time was recorded. The critical dot diameter value of DM code was determined to be 11 pixels, and the critical gray value was 220. On this basis, a parallel processing method of DM code based on spatial light modulator was designed, and experimental verification of laser parallel processing of DM code was carried out in quartz glass. Compared with the traditional single-beam laser marking two-dimensional code, the processing efficiency was improved.

Directed concentrating of micro- and nanoparticles via laser-generated plasmonic microbubbles in a liquid environment is an emerging technology. For effective heating, visible light has been primarily employed in existing demonstrations. In this paper, we demonstrate a new plasmonic platform based on nanoporous gold disk (NPGD) array. Thanks to the highly tunable localized surface plasmon resonance of the NPGD array, microbubbles of controlled size can be generated by near-infrared (NIR) light. Using NIR light provides several key advantages over visible light in less interference with standard microscopy and fluorescence imaging, preventing fluorescence photobleaching, less susceptible to absorption and scattering in turbid biological media, and much reduced photochemistry, phototoxicity, and so forth. The large surface-to-volume ratio of NPGD further facilitates the heat transfer from these gold nanoheaters to the surroundings. While the microbubble is formed, the surrounding liquid circulates and direct microparticles randomly dispersed in the liquid to the bottom NPGD surface, which can be made to yield a unique collection of 3D hollow dome microstructures with bubbles larger than 5 μm. Such capability can also be employed in concentrating suspended colloidal nanoparticles at desirable sites and with the preferred configuration enhancing the sensor performance. Specifically, the interaction among concentrated nanoparticles and their interactions with the underlying substrate have been investigated for the first time. These collections have been characterized using optical microscopy, scanning electron microscopy, hyperspectral localized surface plasmon resonance imaging, and hyperspectral Raman imaging. In addition to various micro- and nanoparticles, the plasmonic microbubbles are also shown to collect biological cells and extracellular nanovesicles such as exosomes. By using a spatial light modulator to project the laser in arbitrary patterns, parallel concentrating can be achieved to fabricate an array of clusters.

Spatial light modulators are essential optical elements in applications that require the ability to regulate the amplitude, phase and polarization of light, such as digital holography, optical communications and biomedical imaging. With the push towards miniaturization of optical components, static metasurfaces are used as competent alternatives. These evolved to active metasurfaces in which light-wavefront manipulation can be done in a time-dependent fashion. The active metasurfaces reported so far, however, still show incomplete phase modulation (below 360°). Here we present an all-solid-state, electrically tunable and reflective metasurface array that can generate a specific phase or a continuous sweep between 0 and 360° at an estimated rate of 5.4 MHz while independently adjusting the amplitude. The metasurface features 550 individually addressable nanoresonators in a 250 × 250 μm2 area with no micromechanical elements or liquid crystals. A key feature of our design is the presence of two independent control parameters (top and bottom gate voltages) in each nanoresonator, which are used to adjust the real and imaginary parts of the reflection coefficient independently. To demonstrate this array’s use in light detection and ranging, we performed a three-dimensional depth scan of an emulated street scene that consisted of a model car and a human figure up to a distance of 4.7 m. By controlling two voltage gates separately from one another, a spatial light modulator has been made that can continuously vary the phase of 360 degrees while independently adjusting the amplitude.

A new and simple strategy towards electric-field-driven multiple chirality switching device has been designed and fabricated by combining a newly synthesized base-responsive chiroptical polymer switch (R-FLMA) and p-benzoquinone (p-BQ) via proton-coupled electron transfer (PCET) mechanism. Clear and stable triple chirality states (silence, positive, negative) of this device in visible band can be regulated reversibly (>1000 cycles) by adjusting voltage programs. Furthermore, such chiral switching phenomena are also accompanied by apparent changes of color and fluorescence. More importantly, the potential application of this device for a spatial light modulator has also been demonstrated.

Conventional surface plasmon (SP) interferometry allows a microscopic sensing of materials using the so-called $V\!(z)$ curve, which actually refers to the module of complex $V\!(z)$ effect while the phase information is lost. This article proposes a simple and compact configuration to measure the plasmonic phase of tested materials within the localized focal spot region of radially polarized light using $\varphi (z)$ curve. A home-developed experimental configuration is applied, involving the basic concepts of virtual confocal annulus and embedded phase-shifting configuration. A modified model of confocal SP interferometry is established to explain why an attenuated beam profile is strictly required in the phase measurement. Moreover, the procedures on how to achieve beam profile attenuation and phase-shifting simultaneously using a single phase-sensitive spatial light modulator (SLM) is elaborated. The experimental verification is demonstrated as well.

This report discusses the effect of speckle size on the quality of holographic images based on a liquid-crystal-on-silicon (LCoS) spatial light modulator (SLM). Further, it proposes methods of quantifying the average speckle size and holographic image resolution. These methods enable both characteristics to be compared using the same unit (the number of pixels in the holographic image), providing an intuitive and effective comparative analysis method. In particular, by varying the LCoS resolution ratio, the change in the resolvable minimum pixels of the holographic image is interpreted in conjunction with the average speckle size; moreover, an analysis of the correlation between the latter two is presented. This approach, based on LCoS resolution division, could provide useful insights into single-SLM-based, full-color holographic displays using space division. Furthermore, it could be extended to other components, including more advanced LCoS SLMs, and used to identify the relative effects on image quality with speckles.

We describe the principle, design, and prototyping of a free-space-optics-based core selective switch (CSS) for spatial channel (SCh) networks (SCNs) in the age of space division multiplexing (SDM). A CSS in an SCN corresponds to a conventional wavelength selective switch (WSS) in a current wavelength division multiplexing network. It incorporates functionalities for spatially demultiplexing SChs from an input SDM port and for switching and multiplexing any of them into any of output SDM ports. We discuss the design for free-space-optics-based CSSs that is applicable to CSSs supporting various numbers of cores per multicore fiber (MCF) and various numbers of MCF ports. We show an example of an implemented 5-core 1 × 6 CSS prototype that integrates an MCF collimator, spatial multiplexer/demultiplexer array, and liquid-crystal-on-silicon spatial light modulator. Although some output MCF ports exhibit relatively high insertion loss (IL), the CSS prototype shows that a CSS will potentially provide low net IL at the level of approximately 2 dB. To verify that there are no unknown deteriorating factors in the CSS prototype, we tested the prototype implemented in a hierarchical optical cross-connect configuration by measuring the pre-forward error correction bit error rate. Spatial bypassing and spectral grooming of a 900-Gb/s SCh employing a CSS-based spatial cross-connect and a conventional wavelength cross-connect are successfully demonstrated with no optical signal-to-noise ratio penalty.

A spatial light modulator (SLM) unit by using polycrystalline silicon (poly-Si) as resonant thin film is demonstrated here in order to improve the extinction ratios in C band (1530 to 1565 nm). The curves of the reflectivity of SLM unit versus wavelength with voltage OFF and ON are simulated and verified by experiments. The SLM unit presents high extinction ratios in C band with maximum of 42.2 dB at 1547.5 nm. The high extinction ratio is due not only to the excellent thermo-optic effect but also to the thermo-elastic deformation effect of the poly-Si thin film. The resonance wavelength has a red shift of 2 nm. The high-extinction-ratio C-band spatial light modulator unit has a giant application potential in the space optical communication field.

Electrically tuneable high mobility charges on graphene yield an efficient electro-optical platform to control and manipulate terahertz (THz) waves. Real-world applications require a multiplex THz device with efficient modulation over a large active area. The trade-off between the efficient gating and switching speed, however, hinders the realization of these applications. Here, we demonstrate a large-format 256-pixel THz modulator which provides high-frame-rate reconfigurable transmission patterns. The time-domain and frequency-domain THz characterizations of graphene devices reveal the relaxation pathways of gate-induced charges and ion packing at graphene-electrolyte interface. The fundamental understanding of these limiting factors enables us to break the trade-off permitting switching frequencies up to 1 kHz. To show the promises of these devices, we demonstrate a single-pixel THz camera which allows spatial and spectroscopic imaging of large-area objects without any moving components. These results provide a significant advancement towards the achievement of non-invasive THz imaging systems using graphene-based platforms., Comment: 16 pages, 5 figures

Traditionally, optical vortices (OVs) were generated with diffractive optical elements (DOEs) such as spiral phase plate (SPP), fork grating, spatial light modulator (SLM), and liquid crystal display (LCD). Here, a method was proposed for generating OVs by employing all-dielectric polarization-insensitive metasurfaces with cylinder arrays, which have high transmission efficiency. The polarization insensitivity of the metasurfaces was illustrated with the incidence of two pairs of orthogonal polarization, both the phase and transmission efficiency were consistent for the cylinder unit cell, and similar OVs were generated with the cylinder array. The topological charges of the generated OVs can be adjusted through the design of the metasurfaces. OVs with additional characteristics as vector beams, focused beams and Bessel beams were further generated. This work has potential applications in beam shaping, optical tweezers, and optical communication.

Single-pixel camera (SPC) is an alternative architecture for imaging systems that emerged as an application of the compressive sensing theory. The SPC’s distinctive feature is the single detector that measures the linear combinations of pixels instead of pixels as in imaging array cameras. The measurements are obtained by projecting the scene on a spatial light modulator (SLM), the other distinctive component of the SPC architecture. This paper discusses the problem of resolution in SPC. We show that in terms of point spread function (PSF), the resolution model is similar to that of an imaging array camera except the fact that the role of the imaging array is taken over by the SLM. This reduces the contribution of the optics to the SPC resolution comparing with the CCD cameras. Relying on an existing method, we develop a procedure that uses a circular chart to measure the camera PSF. Our procedure has additional facilities: the correction of chart tilt and the capability to work with non-circular apertures. At low noise, tilts up to 15° are practically removed.

Perfect vortex beam has the characteristics of optical orbital angular momentum and is widely studied because of its advantages of a uniform ring profile and fixed radius. However, the current method of generating perfect vortex beam is mainly based on the phase modulation of spatial light modulator. We have proposed and demonstrated the fabrication of polymer-based phase plate to generate the first and higher-order perfect vortex beams by using maskless lithography exposure technique. According to the relationship of the lithographic depth of polymer and grayscale exposure, the phase plates with different topological charges and axicon parameters are fabricated. By using such polymer-based phase plate, the radius and ring width of perfect vortex beams are analyzed theoretically and experimentally. The fabricated phase plate shows high transmittance as well as perfect vortex beam generation with high quality in the bandwidth range from 1460 nm to 1640 nm. The obtained results prove the feasibility of the attempt of polymer to generate perfect vortex beams, showing great potential in the application of highly miniaturized and integrated optical vortex applications.

The photochemical coupling of fullerene molecules into covalently connected oligomeric or polymeric structures can result in drastically lowered solubility in common solvents with retained semiconductor properties. Here, we exploit this combination of properties for the utilization of fullerenes as a negative photoresist material with electronic functionality. Specifically, we develop an easily tunable exposure system, essentially comprising a laser and a computer-controlled spatial light modulator (SLM) featuring >8 million independently controlled pixels, for the spatially selective photochemical transformation of nanometer-thin C60 fullerene films. With a carefully designed laser-SLM-exposure/solvent-development cycle, we are able to realize well-resolved two-dimensional hexagonal or square patterns of circular C60 microdots with a center-to-center distance of 1–5 μm and a maximum thickness of 20–35 nm over several square-millimeter-sized areas on a substrate. The functionality of such a hexagonal C60 pattern was demonstrated by its inclusion in between the transparent electrode and the active material in a light-emitting electrochemical cell, which featured an enhanced light output by >50% in comparison to a reference device void of the patterned C60 layer. Previously included in thesis in manuscript form.

In this work, a contemporary optical system is designed using a technology of spatial light modulator (SLM). This system is depending on the ability of altering light beam into different optical patterns according to a signal feedback injected computationally to the SLM. The effects of control parameters on the SLM operation are studied such us brightness (B) which determines the constant DC voltage applied to SLM pixels, and contrast (C) determines the maximum AC voltage amount that can be applied to the SLM. The influences of the transmission linearity of image intensity are controlled by the gamma adjustment which can be used to align non linearity of image intensity. The grey scale is used to control and imagine which signals corresponding to grey levels and image location. The resolution and orientation of the obtained images are altered by the screen format to make optical experiments more satisfied, hence different ratios of amplitude and phase modulation can be understood.

Occlusion is a powerful visual cue that is crucial for depth perception and realism in optical see-through augmented reality (OST-AR). However, existing OST-AR systems additively overlay physical and digital content with beam combiners - an approach that does not easily support mutual occlusion, resulting in virtual objects that appear semi-transparent and unrealistic. In this work, we propose a new type of occlusion-capable OST-AR system. Rather than additively combining the real and virtual worlds, we employ a single digital micromirror device (DMD) to merge the respective light paths in a multiplicative manner. This unique approach allows us to simultaneously block light incident from the physical scene on a pixel-by-pixel basis while also modulating the light emitted by a light-emitting diode (LED) to display digital content. Our technique builds on mixed binary/continuous factorization algorithms to optimize time-multiplexed binary DMD patterns and their corresponding LED colors to approximate a target augmented reality (AR) scene. In simulations and with a prototype benchtop display, we demonstrate hard-edge occlusions, plausible shadows, and also gaze-contingent optimization of this novel display mode, which only requires a single spatial light modulator.

International audience; We develop an improved phase calibration method of a reflective SLM using interferometry by employing novel phase masks. In the process, we definitively determine the actual maximum phase throw of our SLM which provides a recipe for users to verify supplier specifications. We generate optimised phase masks by using Iterative Fourier Transform Algorithm (IFTA) and compare their performance with global linear corrections in the look-up table (LUT) and find that the former perform with around 20% better efficiency. Besides obtaining an array of 1D/2D spots having high uniformity (90%) using IFTA, our result exemplifies the use of iterative algorithms for improving efficiency of phase limited SLMs. Finally, our improved phase calibration method enables threefold faster phase measurements, and to the best of our knowledge, is the first endeavour directed towards enabling rapid phase characterisation of an SLM using interferometric measurements. We believe that it can have very useful applications in settings which may require fast phase calibrations as well as for real-time, multi-wavelength spectroscopic applications.

A wavelength-division-multiplexing (WDM) four-level pulse amplitude modulation (PAM4) free-space optical (FSO)–underwater wireless optical communication (UWOC) integrated system with a channel capacity of 100 Gb/s is proposed and attainably demonstrated. Analytic results reveal that 1.8-GHz 405-nm blue-violet-light and 1.7-GHz 450-nm blue-light laser diodes (LDs) with two-stage light injection and optoelectronic feedback techniques are competently adopted for 100 Gb/s PAM4 signal transmission through a 500-m free-space transmission with 5-m clear ocean underwater link. Combining dual-wavelength WDM scenario with PAM4 modulation, the channel capacity of FSO–UWOC integrated systems is significantly enhanced with an aggregate transmission rate of 100 Gb/s (25 Gbaud PAM4/wavelength × 2 wavelengths). With doublet lenses in FSO, laser beam reducer and transmissive spatial light modulator in UWOC, a sufficiently low bit error rate of 10−9 and acceptable PAM4 eye diagrams are acquired. This demonstrated 100 Gb/s PAM4 FSO–UWOC integrated system with a WDM scenario is advantageous for the enhancement of a high-speed optical wireless link with long-reach transmission.

One of the key trends in laser material processing is the usage of structured laser beams. One such example is the Bessel beam with an elongated focal area and self-healing properties. Higher-order Bessel beams can be formed by axicons, spiral phase plates, or equivalently by the phase masks (holograms). In this work, a demonstration of “optical drill” beams with dynamic intensity distributions resembling the spinning mechanical drill is shown. Bessel beam mixing of two different helicities is achieved by using a Spatial Light Modulator (SLM). Both Bessel beams are formed on the same optical component – the phase mask consisting of two parts. Each part consists of spirals with different winding numbers and different periods that correspond to different step plates and axicons. Such a mask forms the stationary optical drill beam. As the beam propagates the outer and inner parts start to overlap and form the resultant interfering beam. Now, to make it a true drill, it must rotate in time. In our experiment, that is achieved by rotating one part of the combined hologram. This induces an angular offset to the interference and as a result, the orientation of the helical intensity pattern starts to rotate in time. This continuous motion gives the impression of an optical drill. With the beams dynamic properties, it could become a new tool in laser material micromachining, as a mechanical drill was to construction.

All optical approaches to control and read out the electrical activity in a cardiac syncytium can improve our understanding of cardiac electrophysiology. Here, we demonstrate optogenetic stimulation of cardiomyocytes with high spatial precision using light foci generated with a ferroelectric spatial light modulator. Computer generated holograms binarized by bidirectional error diffusion create multiple foci with more even intensity distribution compared with thresholding approach. We evoke the electrical activity of cardiac HL1 cells expressing the channelrhodopsin-2 variant, ChR2(H134R) using single and multiple light foci and at the same time visualize the action potential using a calcium sensitive indicator called Cal-630. We show that localized regions in the cardiac monolayer can be stimulated enabling us to initiate signal propagation from a precise location. Furthermore, we demonstrate that probing the cardiac cells with multiple light foci enhances the excitability of the cardiac network. This approach opens new applications in manipulating and visualizing the electrical activity in a cardiac syncytium.

Reconstruction of 3D scenes from digital holograms is an important task in different areas of science, such as biology, medicine, ecology, etc. A lot of parameters, such as the object’s shape, number, position, rate and density, can be extracted. However, reconstruction of off-axis and especially inline holograms can be challenging due to the presence of optical noise, zero-order image and twin image. We have used a deep-multibranch neural network model, which we call HoloForkNet, to reconstruct different 2D sections of a 3D scene from a single inline hologram. This paper describes the proposed method and analyzes its performance for different types of objects. Both computer-generated and optically registered digital holograms with resolutions up to 2048 × 2048 pixels were reconstructed. High-quality image reconstruction for scenes consisting of up to eight planes was achieved. The average structural similarity index (SSIM) for 3D test scenes with eight object planes was 0.94. The HoloForkNet can be used to reconstruct 3D scenes consisting of micro- and macro-objects.

It is very important for holographic optical tweezers (OTs) to develop high-quality phase holograms through calculation by using some computer algorithms, and one of the most commonly used algorithms is the Gerchberg–Saxton (GS) algorithm. An improved GS algorithm is proposed in the paper to further enhance the capacities of holographic OTs, which can improve the calculation efficiencies compared with the traditional GS algorithm. The basic principle of the improved GS algorithm is first introduced, and then theoretical and experimental results are presented. A holographic OT is built by using a spatial light modulator (SLM), and the desired phase that is calculated by the improved GS algorithm is loaded onto the SLM to obtain expected optical traps. For the same sum of squares due to error SSE and fitting coefficient η, the iterative number from using the improved GS algorithm is smaller than that from using traditional GS algorithm, and the iteration speed is faster about 27%. Multi-particle trapping is first achieved, and dynamic multiple-particle rotation is further demonstrated, in which multiple changing hologram images are obtained continuously through the improved GS algorithm. The manipulation speed is faster than that from using the traditional GS algorithm. The iterative speed can be further improved if the computer capacities are further optimized.

Liquid crystal on silicon (LCOS) technology has initially been developed for imaging and display applications. This technology combines the unique light-modulating properties of liquid crystal materials and the advantages of high-performance silicon complementary metal oxide semiconductor (CMOS) technology through dedicated LCOS assembly processes. Phase-only LCOS SLM are becoming an important tool for laser processing in a range of systems. A recent breakthrough in laser-induced self-assembled nanostructure in glass has made it possible to store data in fused silica. The technology of 5D optical data storage in transparent materials paves a promising way to almost unlimited lifetime data storage for future cloud. The phase-only SLM has already shown its potential for this application in tailoring ultrafast lasers writing beam for optical data storage. In data writing process, a light filed of target data pattern (multi-beam arrays) with target linear polarization state is required to encode information onto the nanograting structure created by laser pulses. In data writing beam generation, phase-only LCOS SLM can generate arbitrary data pattern by using diffractive holographic imaging. However, the polarization control of output image is still achieved by using an external polarization modulator. This leads to the complication, bulkiness, and large delay in current methods. Therefore, this research aims to develop a phase and polarization modulation method based on phase-only LCOS SLMs to simultaneously control both the holographic image and its polarization state. Phase-only modulation of light can tailor the output image by using computer-generated holograms onto LCOS SLMs. This is very useful for generate arbitrary multi-beam data writing light field. To fully control the polarization state of the data writing light field, the amplitude and relative phase of two orthogonal polarization components needs to be independently modulated. However, the phase-only modulation cannot directly affect the polarization of light. Therefore, three methods are proposed to achieve the phase and polarization control using LCOS SLMs. Also, two customized LCOS SLMs were designed and fabricated by using in-house-developed die-level assembly technique. They are used in all experiments of this research. First method is parallel coding and two-beam combining. Two orthogonal input beams are parallelly and independently encoded with the same target image information but with the different amplitude information by using two phase holograms on two LCOS SLMs. Then, two modulated beams are now considered as two polarization components and be spatially superposed to form target polarization state. The first-order diffraction efficiency change controlled by using phase modulation depth on hologram is used to design a technique to encode amplitude information onto the hologram. This technique is used in all three methods for amplitude modulation of polarization components. This method requires high precision alignment process in beam combining. In the second method, to avoid beam combining in polarization control, instead of modulating two beams, the object of modulation is changed to two polarization components of a single input beam. By using the characteristic of polarization sensitivity of phase-only LCOS SLM, two polarization components of single beam are sequentially and independently coded with information target image and amplitude using two LCOS SLMs. Because the spatial status to components of single beam remain unchanged in the modulation, the phase and polarization control is achieved automatically. The third method is a compact system using only single LCOS SLM device. The principle of this method is two polarization components coding like in the second method, but the fundamental difference is in a polarization components rotation technique in compact system. Using this polarization rotation technique, two light components can be independently coded by separately using two holograms on the two halves of LCOS SLM. The prototype of the compact system is developed and fabricated, and the effectiveness of the system has been experimentally verified. To sum up, the phase and polarization modulation methods based on LCOS SLM has been explored and developed. They can provide dynamical control of both polarization sate and image of light field using only LCOS. The proposed methods can provide a more promising way to largely increase the data writing speed in the 5D optical data storage technology.

Spatial light modulators (SLMs) are versatile devices used for optical studies. These instruments have a wide area of application in photonics. Additionally, SLMs have potential utility in different applications, such as biomedical applications, laser based surgery for precise cutting and as optical tweezers to separate cells in a petri container. However, the high cost of SLM devices prevents their widespread use in many areas, including industrial areas and scientific research laboratories. This paper demonstrates how to design a digital light processor (DLP) based low-cost SLM and describes how to obtain structured electromagnetic waves with the designed SLM. Therefore, this research was undertaken to design and produce a low-cost SLM device for optical applications. For this purpose, two prerequisites had to be fulfilled, the first was to use suitable components of a projection device with DLP-based digital micro-mirror device (DMD), and the second was to eliminate unnecessary SLM components from the system. Finally, holographic images reflected on the SLM screen were created by using Mathematica software program to change the amplitude and phase of the electromagnetic waves in order to obtain the structured electromagnetic waves.

Compressive sensing (CS) has been proposed as a disruptive approach to developing a novel class of optical instrumentation used in diverse application domains. Thanks to sparsity as an inherent feature of many natural signals, CS allows for the acquisition of the signal in a very compact way, merging acquisition and compression in a single step and, furthermore, offering the capability of using a limited number of detector elements to obtain a reconstructed image with a larger number of pixels. Although the CS paradigm has already been applied in several application domains, from medical diagnostics to microscopy, studies related to space applications are very limited. In this paper, we present and discuss the instrumental concept, optical design, and performances of a CS imaging spectrometer for ultraviolet-visible (UV–Vis) stellar spectroscopy. The instrument—which is pixel-limited in the entire 300 nm–650 nm spectral range—features spectral sampling that ranges from 2.2 nm@300 nm to 22 nm@650 nm, with a total of 50 samples for each spectrum. For data reconstruction quality, the results showed good performance, measured by several quality metrics chosen from those recommended by CCSDS. The designed instrument can achieve compression ratios of 20 or higher without a significant loss of information. A pros and cons analysis of the CS approach is finally carried out, highlighting main differences with respect to a traditional system.

Holographic displays enable the formation of a three-dimensional particle field distribution and is promised to be one solution of the key problems in present virtual and augmented reality displays. The biggest challenge in the computer-generated holography (CGH) is the high consuming calculation time and the restricted field of view due to the micro display screen. In order to solve the above mentioned problems, we propose a method for machine learning accelerated lensless holographic projection, which is based on the reconstruction of complex amplitude image from phase-only CGH. The runtime of generating the phase-only CGH is half of traditional iterative method. The complex amplitude image can achieve the maximum diffraction bandwidth of the spatial light modulator (SLM). The feasibility of this method is verified by experiments.

To realize simplified cost-efficient optical networks with routing flexibility and scaling potential, a spatial-light-modulator-based optical-fiber joint switch for few-mode multicore fibers is proposed herein, which can route all spatial channels together as a unit. Numerical simulations and experiments were performed, and the results show that the signal paths for a 6-mode 19-core fiber can be simultaneously switched to the target output ports using the proposed method, and the mode-field patterns of the diffracted light can be maintained after joint switching. Further, the maximum port crosstalk can be reduced considerably from -11.6 to -25.1 dB by changing the position of the output port in the proposed method.

This research proposed a simple method to design the projected phase boundary of the SLM (spatial light modulator) of the digital laser for the generation of a structure light field of geometric shape. In the proposed method, the phase boundary of the digital laser was designed to match the convolution field of the specified geometric structure field and Gaussian field instead of matching the specified geometric structure field. The phase boundary design suppressed the light reflected from the SLM of a high-inclination angle that is difficult to achieve stable oscillation in the laser resonator. Using the proposed phase boundary design, the laser output with energy distribution closed to geometric structures such as a quadrangular pyramid, triangular pyramid, cone, and multi-ring was produced through experiments. The geometric structure light field generated in this research will be beneficial to the related applications of photolithography and photopolymerization for making micro-elements.

This paper proposes focal surface occlusion to provide focal cues of occlusion masks for multiple virtual objects at continuous depths in an occlusion-capable optical see-through head-mounted display. A phase-only spatial light modulator (PSLM) that acts as a dynamic free-form lens is used to conform the focal surface of an occlusion mask to the geometry of the virtual scene. To reproduce multiple and continuous focal blurs while reducing the distortion of the see-through view, an optical design based on afocal optics and edge-based optimization to exploit a property of the occlusion mask is established. The prototype with the PSLM and transmissive liquid crystal display can reproduce the focus blur of occluded objects at multiple and continuous depths with a field of view of 14.6°.

Specimen-induced aberration has been one of the major factors limiting the imaging depth in single-molecule localization microscopy (SMLM). In this study, we measured the wavefront of intrinsic reflectance signal at the fluorescence emission wavelength to construct a time-gated reflection matrix and find complex tissue aberration without resorting to fluorescence detection. Physically correcting the identified aberration via wavefront shaping with a liquid-crystal spatial light modulator (SLM) enables super-resolution imaging even when the aberration is too severe for initiating localization processes. We demonstrate the correction of complex tissue aberration, the root-mean-square (RMS) wavefront distortion of which is more than twice the 1 rad limit presented in previous studies; this leads to the recovery of single molecules by 77 times increased localization number. We visualised dendritic spines in mouse brain tissues and early myelination processes in a whole zebrafish at up to 102 μm depth with 28-39 nm localization precision. The proposed approach can expand the application range of SMLM to thick samples that cause the loss of localization points owing to severe aberration.

Recently, spatial photonic Ising machines (SPIM) have been demonstrated to compute the minima of Hamiltonians for large-scale spin systems. Here we propose to implement an antiferromagnetic model through optoelectronic correlation computing with SPIM. Also we exploit the gauge transformation which enables encoding the spins and the interaction strengths in a single phase-only spatial light modulator. With a simple setup, we experimentally show the ground state search of an antiferromagnetic model with $40000$ spins in number-partitioning problem. Thus such an optoelectronic computing exhibits great programmability and scalability for the practical applications of studying statistical systems and combinatorial optimization problems., 7 pages, 4 figures

A 400-Gb/s wavelength-division-multiplexing (WDM) four-level pulse amplitude modulation (PAM4) optical wireless communication (OWC) system through a 200-m free-space transmission with either an 8.8-m piped water–air–piped water link or a 6.5-m turbid water–air–turbid water link is successfully constructed. Incorporating PAM4 modulation with an 8-wavelength WDM scheme greatly increases the total transmission rate of the WDM-PAM4 OWC system to 400 Gb/s (50 Gb/s/λ × 8 λs). By adopting doublet lenses in free-space transmission, a laser beam reducer/expander and a reflective spatial light modulator (SLM) with an angle expander through the water–air–water link, good bit error rate performance and acceptable PAM4 eye diagrams are obtained. Using a reflective SLM with an angle expander not only adaptively adjusts the laser beam, but also effectively solves the oceanic engineering problems. This demonstrates WDM-PAM4 OWC system outperforms existing OWC systems through the free-space transmission with an air–water–air link because it can solve the practical engineering problems in actual oceanic environments.