Search

Stepwise photopolymerization is a miraculous strategy modulating the polymer skeleton and electro-optical properties of light modulators based on liquid crystal/polymer composites. However, owing to the indistinct polymerization mechanism and curing condition discrepancy, the required polymer structures and electro-optical properties are hard to be controlled precisely. Herein, a novel polymer-stabilized liquid crystal film based on acrylate/epoxy resin is proposed, fabricated and the relationships between preparation process, polymer content, polymer morphology and electro-optical properties are studied. The in-situ photopolymerization of acrylate/epoxy resin liquid crystalline polymer is fulfilled using cation photo-initiator UV 6976. The distinct photopolymerization speed between acrylate and epoxy resin benefits the polymer morphology control, and with accurate containment of the polymerization process and polymer composition, the superior electro-optical properties at a higher polymer content are acquired. The polymer morphology and electro-optical properties are influenced by the polymer content and mass ratio between acrylate and epoxy resin. The best electro-optical properties among samples are attained by controlling the mass ratio between acrylate and epoxy resin to 1:1, integrating higher densities of scattering centers and lower anchoring effect. With higher polymer content, the strategy of increasing the mass ratio of E6M benefits the improvement of E-O properties for alleviating polymer density. This work provides insights to stepwise polymerization of liquid crystalline monomers and offers a fancy strategy for the preparation of novel liquid crystal dimming films. [ABSTRACT FROM AUTHOR]

For a diverse range of semiconductor devices, the charge carrier lifetime is an essential characteristic. However, the carrier lifetime is difficult to control, as it is usually determined by a variety of recombination processes. For indirect bandgap materials, it is well known that effective carrier lifetimes can be improved by passivating the surface, effectively extinguishing surface-related recombination processes. However, for some applications, such as photomodulators for sub-infrared radiation, it is beneficial to tailor lifetimes to specific values, in this particular case trading off between photo-efficiency and switching speed. In this paper, we design a new type of silicon-based metamaterial with a tunable electron–hole lifetime. By periodically patterning a dielectric surface passivation layer, we create a metamaterial whereby the filling fraction of passivated relative to unpassivated areas dictates the effective charge carrier lifetime. We demonstrate tunable lifetimes between 200 μs and 8 ms in a 670 μm thick Si wafer, though in principle our approach allows one to generate any lifetime between the fully passivated and unpassivated limits of a bulk semiconductor. Finally, we investigate the application of these metamaterials as photomodulators, finding switching times that depend upon both the photoexcitation intensity, wafer thickness, and the carrier lifetime. [ABSTRACT FROM AUTHOR]

In this work, we introduce a novel coherent perfect absorber, accentuating its novelty by emphasizing the broad bandwidth, reduced thickness, tunable property, and straightforward design achieved through the use of an asymmetric graphene metasurface. This design incorporates both square and circular graphene patches arranged on either side of a silicon substrate. With an optimized structural design, this absorber consistently captures over 90% of incoming waves across the frequency range of 1.65 to 4.49 THz, with a graphene Fermi level of 0.8 eV, and the whole device measures just 1.5 um thick. This makes our absorber significantly more effective and compact than previous designs. The absorber's effectiveness can be significantly enhanced by combining the metasurface's geometric design with the graphene Fermi level. It is anticipated that this ultrathin, wideband coherent perfect absorption device will play a crucial role in emerging on-chip THz communication technologies, including light modulators, photodetectors, and so on. [ABSTRACT FROM AUTHOR]

In this study, a traveling wave Mach-Zehnder intensity modulator (TW-MZM) was designed and optimized for six different electro-optical (EO) crystals: lithium niobate (LNB), potassium niobate (KNB), lithium titanate (LTO), beta barium borate (BBO), cadmium telluride (CdTe), and indium phosphide (InP). The performance of each EO crystal, including optical and radio frequency (RF) loss, applied voltage, and modulation bandwidth, was estimated and compared. The results suggest that, in theory, KNB, LTO, BBO, and CdTe have the potential to outperform LNB. However, it should be noted that the loss associated with KNB and LTO is comparable to that of LNB. The findings demonstrated that BBO and CdTe exhibit a modulation bandwidth exceeding 100 GHz and demonstrate the lowest loss among the considered crystals based on the assumed geometry. [ABSTRACT FROM AUTHOR]

In this paper, we present a fast and efficiently scalable 3D holographic video processor using a layer‐based method using a modified inverse Fresnel transform. In our previous paper, we designed a single‐layer holographic core using a fixed‐point model and tested its operation on an FPGA. This paper implements an 8‐layer, 15FPS real‐time hologram processor by receiving RGB and depth input. For fast CGH processing, we utilized HBM memory, which is faster than DDR4, to store FFT results. After applying 2× linear interpolation, the implemented real‐time holography processor converts into real‐time holograms using a 4K color space light modulator [ABSTRACT FROM AUTHOR]

Motoneuron properties and their firing patterns undergo significant changes throughout development and in response to neuromodulators such as serotonin. Here, we examined the age‐related development of self‐sustained firing and general excitability of tibialis anterior motoneurons in a young development (7–17 years), young adult (18–28 years) and adult (32–53 years) group, as well as in a separate group of participants taking selective serotonin reuptake inhibitors (SSRIs, aged 11–28 years). Self‐sustained firing, as measured by ΔF, was larger in the young development (∼5.8 Hz, n = 20) compared to the young adult (∼4.9 Hz, n = 13) and adult (∼4.8 Hz, n = 8) groups, consistent with a developmental decrease in self‐sustained firing mediated by persistent inward currents (PIC). ΔF was also larger in participants taking SSRIs (∼6.5 Hz, n = 9) compared to their age‐matched controls (∼5.3 Hz, n = 26), consistent with increased levels of spinal serotonin facilitating the motoneuron PIC. Participants in the young development and SSRI groups also had higher firing rates and a steeper acceleration in initial firing rates (secondary ranges), consistent with the PIC producing a steeper acceleration in membrane depolarization at the onset of motoneuron firing. In summary, both the young development and SSRI groups exhibited increased intrinsic motoneuron excitability compared to the adults, which, in the young development group, was also associated with a larger unsteadiness in the dorsiflexion torque profiles. We propose several intrinsic and extrinsic factors that affect both motoneuron PICs and cell discharge which vary during development, with a time course similar to the changes in motoneuron firing behaviour observed in the present study. Key points: Neurons in the spinal cord that activate muscles in the limbs (motoneurons) undergo increases in excitability shortly after birth to help animals stand and walk.We examined whether the excitability of human ankle flexor motoneurons also continues to change from child to adulthood by recording the activity of the muscle fibres they innervate.Motoneurons in children and adolescents aged 7–17 years (young development group) had higher signatures of excitability that included faster firing rates and more self‐sustained activity compared to adults aged ≥18 years.Participants aged 11–28 years of age taking serotonin reuptake inhibitors had the highest measures of motoneuron excitability compared to their age‐matched controls.The young development group also had more unstable contractions, which might partly be related to the high excitability of the motoneurons. [ABSTRACT FROM AUTHOR]

Smart windows are crucial to dynamic control over light transmission to fulfill various demands in energy saving, privacy, and information display; however, most present technologies still perform a single function (often tint or haze adjustment) and require continuous electricity for operation. In this study, novel self‐assembled ionic liquid crystals (ILCs) doped with negative cholesteric liquid crystals (CLCs) to offer electrically switchable and stable scattering‐mode light modulators are presented. The novel smectic A phase based on the ILCs exhibits high solubility in the adopted nematics, enhancing the LC device's performance in several ways, including improved homogeneity, stable alignment quality, prolonged stability, and simplified fabrication. The LC device can potentially offer a dynamically rapid switching function between stable transparent (imperfect fingerprint textures) states and stable scattering (focal conic textures with small domains) states by using external stimuli and highly maintained multistable states for prolonged periods, even when the external stimuli are removed. The LC device also offers polarization‐independent scattering and transparent‐mode LC light modulators, low operating voltage, excellent contrast, and broad viewing angles. Its versatility and outstanding field‐off stability make it ideal for various applications such as smart lighting, building climate control, energy‐saving displays, and augmented reality (AR) glasses. [ABSTRACT FROM AUTHOR]

This paper demonstrated the efficient employment of vertical cavity surface emitting laser (VCSEL) light sources in high speed dispersion compensation systems. VCSEL are compared with CW laser and distributed feedback laser in the modulated light output power, signal quality factor and minimum data error rates through the fiber system. Light signal base band modulated power is clarified with spectral frequencies after LiNb MZ modulators. Light signal base band modulated amplitude is simulated against base band time frequencies after LiNb MZ modulators. The total light signal index base band modulated power/amplitude value is estimated after LiNb MZ modulators for various light sources. The light signal base band modulated power is demonstrated with both spectral frequencies and time interval after fiber loop control length with compensation system. Total light signal index base band modulated power/amplitude value is estimated numerically after fiber loop control length with compensation system. The modulated electronic signal base band modulated power is indicated with spectral frequencies after PIN receiver. The light signal base band modulated amplitude is studied clearly against base band time frequencies after PIN receiver. The signal quality factor, BER, and modulated lighted output power are clarified and sketched against fiber system lengths for various light sources. [ABSTRACT FROM AUTHOR]

Featured Application: Light modulators, sensors, and non-contact evaluation of thermoelectric performance as potential applications. When an electric field is applied between two electrodes facing each other immersed in a liquid, the interfacial Pockels effect, a refractive index change proportional to the electric field, occurs in the electric double layer at the liquid–electrode interface. Here, we report that the Pockels effect of interfacial water can be observed even when an electric field is applied parallel to the surface of a "single" electrode in an electrolyte solution. This is a non-trivial result since the electric field parallel to the interface should not cause a broken spatial inversion symmetry, which is required for the Pockels effect. The Pockels signal was detected as a change in the transmitted light intensity due to the field-induced spectral shift of the interference fringes of the transparent conductive oxide electrode layer on a glass substrate. The magnitude of the signal increased as it approached the ends of the electrode, and the sign reversed across the center of the electrode. The electric field distribution calculated from the interfacial potential difference due to the in-plane parallel current showed that an electric field perpendicular to the interface was induced, whose distribution was consistent with the position dependence of the Pockels signal. A similar phenomenon was also observed for a single copper electrode, confirming that this is a universal effect. [ABSTRACT FROM AUTHOR]

The applications of liquid crystals continue to expand. They include conventional and advanced liquid crystal displays, electrically controlled lenses, tunable optical elements such as filters, light shutters, waveplates, and spatial light modulators, smart windows and sensors, and reconfigurable antennas and microwave devices, to name a few. As a rule, liquid crystal devices are controlled by applying an external electric field. This field reorients liquid crystals in a desirable way, thus leading to the tunability of their physical properties. The electric-field-induced reorientation of liquid crystals can be affected by ions typically present in molecular liquid crystals. In the case of liquid crystal displays, ions in liquid crystals can lead to image sticking, a reduced voltage holding ratio, and altered electro-optical performance. Therefore, the development of efficient ways to better control ions in liquid crystal devices is of utmost importance to existing and future liquid crystal technologies. In this paper, we discuss how nanomaterials can affect the electrical properties of molecular liquid crystals. In general, nanomaterials in molecular liquid crystals can behave as ion-capturing objects or act as a source of ions. Ion-capturing nanomaterials in molecular liquid crystals can enhance their electrical resistivity. On the other hand, ion-releasing nanoparticles can lead to the opposite effect. By considering the competition between two nanoparticle-induced ionic processes, namely the ion capturing and ion releasing effects, the electrical resistivity of liquid crystals can be controlled in a desirable way. [ABSTRACT FROM AUTHOR]

The last decade has witnessed an increasing interest in metamaterial absorbers (MMAs) because of their huge potential in a wide range of applications including energy harvesting, photodetectors, sensors, light modulators, infrared camouflage and wireless communication. Recently, machine learning (ML) has become one of the modern and powerful tools that can examine the design data in order to forecast the absorption behavior with much less effort and cost-effectiveness than conventional experimental and computation approaches. In this work, we utilize two ML algorithms, Polynomial Regression (PR) and Random Forest Regression (RFR), to predict the absorption strength and frequency of a symmetric disk-shape metamaterial structure operating within 10 and 16 GHz. The proposed models are trained on hundreds of simulation-generated samples. We show that fine-tuning some hyperparameters results in higher forecasting performance. The dependence of predicted results on input parameters demonstrates that PR has better performance in predicting absorption strength, while both algorithms share similar accuracy in predicting the absorption frequency. [ABSTRACT FROM AUTHOR]

This study examines the use of optical encoding to prevent unauthorized access to various categories of information (including video) during operational transmission. Experimentally implemented holographic coding in spatially incoherent radiation of a 4K color video stream with digital input of information and dynamically changing coding elements-holograms was used to improve the quality of video stream coding and ensure high throughput of the coding system. High-resolution liquid-crystal spatial-temporal light modulators were used to input encoded video information and display holograms. The encoding method is based on registering an optical convolution of the input scene image with the encoding response of the hologram. In this case, individual color channels of each frame of the video stream are encoded in turn. Numerical methods of inverse filtering and regularization were used for decoding. The results of the present studies will be useful in creating a new generation of secure high-resolution video communication systems. [ABSTRACT FROM AUTHOR]

The results of the research in the field of the electro-optics of nematic and smectic (ferroelectric) liquid crystals, performed at the Lebedev Physical Institute of the Russian Academy of Sciences (FIAN), as well as their applications in modulation of the amplitude, phase, or scattering of laser radiation in electrically and optically controlled transparencies (spatial light modulators); holographic memory devices; wave-field formers and image converters (including three-dimensional ones); and recognition, sensor, and other laser technique devices, are presented. [ABSTRACT FROM AUTHOR]

Dynamic optical metasurfaces with ultrafast temporal response, i.e., spatiotemporal optical metasurfaces, provide attractive solutions and open fascinating perspectives for modern highly integrated optics and photonics. In this work, electro-optically controlled optical metasurfaces operating in reflection and utilizing resonant waveguide mode excitation are demonstrated from the viewpoint of free-space propagating light modulation. The modulation of reflected light power with superior characteristics in comparison with prior research is achieved by identifying a suitable low-loss waveguide mode and exploiting its resonant excitation. The electro-optic Pockels effect in a 300 nm-thick lithium niobate (LN) film sandwiched between a continuous thick gold film and an array of gold nanostripes, serving also as control electrodes, is exploited to realize fast and efficient light modulation. The fabricated compact (active area <1000 µm2) modulators operate in the wavelength range of 850–950 nm, featuring a maximum intensity modulation depth of 42 % at the driving voltage of ±10 V within the bandwidth of 13.5 MHz (with the potential bandwidth of 6.5 GHz). The introduced nonlocal electro-optic metasurface configuration opens new avenues towards the realization of ultrafast, efficient, and robust free-space light modulators based on an LN flat optics approach. [ABSTRACT FROM AUTHOR]

Metal halide perovskite semiconductors fabricated with simple low-temperature solution processes are a unique class of materials anticipated for use in photonic devices such as solar cells, light-emitting diodes, and light modulators. The metal halide perovskites in the form of nanocrystals are particularly attracting attention as novel functional materials because of their exceptionally high luminescence efficiencies and wide range of possible luminescence wavelengths. By combining different optical characterization techniques, that is, single-dot spectroscopy, photon correlation spectroscopy, femtosecond transient absorption spectroscopy, and time-resolved photoluminescence spectroscopy, we study the dynamics of excitons, trions, and biexcitons in perovskite nanocrystals. Here, we provide a concise review of recent developments in this research field with a focus on trions in lead halide perovskite nanocrystals. A deep understanding of trion dynamics is especially important because they determine the luminescence properties of nanocrystals and are related to the ionization processes of nanocrystals. [ABSTRACT FROM AUTHOR]

The recently proposed concept of metamaterials has opened exciting venues to control wave-matter interactions in unprecedented ways. Here, we demonstrate the relevance of metamaterials for inducing acoustic birefringence, a phenomenon which has already found its versatile applications in optics in designing light modulators or filters, and nonlinear optic components. This is achieved in a suitably designed acoustic metamaterial which is non-Eulerian, in the sense that at low frequencies, it cannot be homogenized to a uniform acoustic medium whose behavior is characterized by the Euler equation. Thanks to the feasibility of engineering its subwavelength structure, such a non-Eulerian metamaterial allows one to desirably manipulate the birefringence process. Our findings may give rise to the generation of novel devices such as tunable acoustic splitters and filters. [ABSTRACT FROM AUTHOR]

Graphene is emerging as an ideal material for new-generation optoelectronic devices. In this paper, a novel graphene metasurface-based electrically switchable and tunable infrared light modulator has been proposed and theoretically studied. The functional modulator comprises a monolayer graphene sheet sandwiched in a Fabry–Perot (FP) like nanostructure consisting of a metal reflector, a dielectric spacer, and an ellipse patterned anisotropy antenna layer. As a result of the photon localization effect of the guided-mode resonance (GMR) in the FP structure, the graphene electroabsorption can be significantly enhanced to enable a high-performance light modulator. By fine-tuning the Fermi energy (Ef) of graphene via controlling its bias-gate voltage, the proposed modulator can switch between a perfect absorber and a reflective polarization converter of high conversion efficiency (i.e., >90%) at 1550 nm. The conversion mechanism and the geometric dependences of the infrared light modulator have been investigated. We further demonstrated the tunability of the highly-efficient polarization converter over a broad spectrum by adjusting the real dispersion of Ef. Our design concept provides an effective strategy for customizing novel optoelectronic devices by combining an electrically-tunable 2D material with a functional metasurface. [ABSTRACT FROM AUTHOR]

In this paper, we theoretically investigate intersubband absorption in La-doped BaSnO3/BaO perovskite-oxide double and triple symmetrical quantum wells. The goal is to assess the emerging possibilities offered by perovskite heterostructures for realization of oxide-based quantum well optoelectronic devices. Properties such as small electron effective mass, very high room-temperature mobility of BaSnO3, large conduction band offset between the two materials, are all promising for technological applications. Some of the possible applications include active n-channel materials in p-n junctions, field-effect transistors, ferroelectric field-effect transistors, sensitive UV photoconductors, and electron transport layers in perovskite solar cells. We are interested in tuning of the absorption spectra via quantum well width modulation, changing of doping density and variation of external electric field along the growth direction which is important for application in electro-optical light modulators. The electronic structure is calculated self-consistently by solving the Schrödinger–Poisson system of equations where the exchange correlation effects are also taken into the account. [ABSTRACT FROM AUTHOR]

Light use is rising steeply, mainly because of the advent of light-emitting diode (LED) devices. LEDs are frequently blue-enriched light sources and may have different impacts on the non-image forming (NIF) system, which is maximally sensitive to blue-wavelength light. Most importantly, the timing of LED device use is widespread, leading to novel light exposure patterns on the NIF system. The goal of this narrative review is to discuss the multiple aspects that we think should be accounted for when attempting to predict how this situation will affect the NIF impact of light on brain functions. We first cover both the image-forming and NIF pathways of the brain. We then detail our current understanding of the impact of light on human cognition, sleep, alertness, and mood. Finally, we discuss questions concerning the adoption of LED lighting and screens, which offer new opportunities to improve well-being, but also raise concerns about increasing light exposure, which may be detrimental to health, particularly in the evening. [ABSTRACT FROM AUTHOR]

Light field 3D display has attracted great attention as the hardware interface for a virtual 3D application. The design and fabrication of light-modulating structures directly affect the authenticity of the reconstructed 3D image. The critical challenges in 3D display, such as visual fatigue, limited motion parallax, and insufficient light efficiency, are closely related to the inaccurate phase or angular reconstruction of the virtual light field. While the designs of light field modulators are widely introduced in all kinds of studies, the importance of fabrication for 3D display is usually under-estimated. Large format, small feature size, and high precision in shape are the three critical requirements of fabrication for 3D display. In this paper, we focus on the fabrication technologies for light-modulating structures. Fabrication tools for both microstructures and nanostructures are introduced. The fabrication capability, critical challenges and its applications in light field 3D display are discussed. Finally, the future development of 3D display related fabrication technologies are highlighted. [ABSTRACT FROM AUTHOR]

• Dynamic tunable and switchable broadband light modulator based on graphene metasurface. • Graphene electromagnetic absorption enhancement: excitation of the magnetic toroidal dipole. • Tunability and switchability: adjusting the Fermi energy of graphene. The integration of graphene with metasurfaces enables devices with remarkable dynamic tunability, propelling electromagnetic (EM) manipulations to new heights by transitioning from static to dynamic control. In this study, we theoretically investigate a broadband absorption modulator with dynamic tunability based on a graphene hybrid metasurface. The metasurface consists of a monolayer graphene sheet sandwiched between a square silver block and a silica layer. The excitation of the magnetic toroidal dipole (MTD) leads to a significant enhancement of graphene's electromagnetic absorption. By arranging four blocks as a supercell to support multi-resonance, we achieve a broadband modulator spanning from 1000 to 1210 nm, with graphene absorption exceeding 57 %. Notably, there is no plasmonic hybridization among adjacent components within the super unit. By tuning the Fermi energy of graphene, narrow-band tunability can be achieved at any wavelength within the operation spectrum. Furthermore, the designed device exhibits a perfect modulation depth (∼100 %). We demonstrate the switchability of the proposed device by showcasing its ON/OFF status at representative wavelengths of 1205 nm, 1119 nm, and 1052 nm. Thus, the proposed graphene-based hybrid metasurface fulfills the requirements for broadband tunability and switchability, offering a high ON/OFF ratio, full modulation depth, and a small switch voltage gap. This design holds significant potential for future developments. [ABSTRACT FROM AUTHOR]

We report the first Pseudo-random Modulation Continuous Wave (PMCW) narrowband sodium temperature/wind lidar developed at the University of Science and Technology of China (USTC). The laser system uses an 1178 nm diode seed-laser and a fiber Raman amplifier with a fiber-coupled Acoustic Optical Modulator (AOM) to generate a narrowband 589.158 nm light with a power output of 1.5 W at v 0, v + and v_ frequencies. Based on an innovative technique and algorithm, the main beam and the residual beam modulated by Electro-Optic Modulator (EOM) with M-code are separately directed to the vertical and eastward directions. The 3-frequency light is designed in timing with the multiple-period 127-bit M-code groups. The uncertainties of the temperature and wind with the vertical and temporal resolutions of 1 km and 30 min/1 hr under the clear-sky condition are estimated to be 5.0 K and 10 m/s, respectively at the sodium peak. The temperature and wind results are in good agreement with those observed by satellite and nearby ground-based meteor radar, demonstrating the reliability of the PMCW narrowband sodium lidar system for measuring mesopause region temperature and wind. [ABSTRACT FROM AUTHOR]

Holographic optical tweezers (HOT) is a programmable technique used for manipulation of microsized samples. In combination with computer-generation holography (CGH), a spatial light modulator reshapes the light distribution within the focal area of the optical tweezers. HOT can be used to realize real-time multiple-point manipulation in fluid, and this is useful in biological research. In this article, we summarize the HOT technique, discuss its recent developments, and present an overview of its biological applications. [ABSTRACT FROM AUTHOR]

As a new emerging semiconductor with interlayer bandgap, lead selenide (PbSe) have broad prospects in the fields of electrocatalysis, photocatalysis, infrared optoelectronic devices, optoelectronics, and ultrafast photonics. Among them, ultrafast photonics is receiving a lot of attention due to its ultrashort pulse, strong peak power, narrow bandwidth, and high repetition frequency. Herein, the properties are systematically studied of PbSe through various characterization methods. The modulation depth of PbSe is up to 30%, and its saturation light intensity is 7.86 MW cm−2. Using the evanescent field effect, nonlinear fiber‐based photonics devices has been successfully prepared based on the PbSe nanosheet solution, which can increase the bearable pump power. The 36th picosecond harmonic mode‐locked soliton molecule is generated in the erbium‐doped fiber laser, which corresponds to a maximum repetition frequency of 222 MHz. The results show that the signal‐to‐noise ratio can reach up to 49.1 dB which is higher than most previous works by now. The results revealed the potential of PbSe as an excellent photonics material in applications such as nonlinear optics, ultrafast photonics equipment, photoconductive detectors, and light modulators. [ABSTRACT FROM AUTHOR]

High efficiency and a compact footprint are desired properties for electro-optic modulators. In this paper, we propose, theoretically investigate, and experimentally demonstrate a recirculating phase modulator, which increases the modulation efficiency by modulating the optical field several times in a non-resonant waveguide structure. The "recycling" of light is achieved by looping the optical path that exits the phase modulator back and coupling it to a higher order waveguide mode, which then repeats its passage through the phase modulator. By looping the light back twice, we were able to demonstrate a recirculating phase modulator that requires nine times lower power to generate the same modulation index of a single pass phase modulator. This approach to modulation efficiency enhancement is promising for the design of advanced tunable electro-optical frequency comb generators and other electro-optical devices with defined operational frequency bandwidths. [ABSTRACT FROM AUTHOR]

This article discusses optical methods and technologies that can register, transform, store, transmit, and reproduce large arrays of information. Digital holograms recorded using photographic equipment of various types is common carriers of experimentally recorded information. The size of digital hologram files is several tens of megabytes. Hence, for the storage and transmission of holographic data archives via communication channels, holograms should be compressed. Binarization represents one of the options for reducing the hologram size. For binarization, an iterative adaptive method for selecting the weight coefficients of the error diffusion procedure is proposed. The method has been tested on digital holograms that were optically recorded under various conditions. The quality of the measured objects was evaluated through numerical methods of image reconstruction and after displaying digital holograms on a micromirror light modulator. The proposed method can be used for compressing and storing holographic data, measuring the characteristics and shape of micro- and macroobjects, and fast optical image reconstruction using a micromirror light modulator. [ABSTRACT FROM AUTHOR]

Real-time, simultaneous, and adaptive beam steering into multiple regions of interest replaces conventional raster scanning with a less time-consuming and flexible beam steering framework, where only regions of interest are scanned by a laser beam. CUDA-OpenGL interoperability with a computationally time-efficient computer-generated hologram (CGH) calculation algorithm enables such beam steering by employing a MEMS-based phase light modulator (PLM) and a Texas Instruments Phase Light Modulator (TI-PLM). The real-time CGH generation and display algorithm is incorporated into the beam steering system with variable power and scan resolution, which are adaptively controlled by camera-based object recognition. With a mid-range laptop GPU and the current version of the MEMS-PLM, the demonstrated scanning speed can exceed 1000 points/s (number of beams > 5) and potentially exceeds 4000 points/s with state-of-the-art GPUs. [ABSTRACT FROM AUTHOR]

Phase light modulator (PLM) by MEMS mirror array operating in a piston-mode motion enables a high-speed diffractive beam steering in a random-access and flexible manner that makes a lidar system more intelligent and adaptive. Diffraction efficiency is determined by the range of the piston motion of the MEMS array; consequently, a larger range of the piston motion is required for beam steering in infrared, such as for lidar. We demonstrated how the range of the piston motion is optically enhanced by a factor of two with a light-recycling optics based on Talbot self-imaging. The proposed optical architecture extends the usable range of the wavelength so that a MEMS-PLM designed for visible wavelength is applicable for a high-efficiency beam steering at an infrared wavelength of 1550 nm with an improved diffraction efficiency of 30%. [ABSTRACT FROM AUTHOR]

Ultraviolet (UV) electro-optic modulation system based on graphene-plasmonic metamaterials nanomechanical system (NEMS) with superlubricity is investigated. Due to the strong optical absorption intensity of graphene in the UV region and the combination of metamaterial structure based on surface plasmons, the modulation depth of the UV NEMS electro-optic modulator approaches as high as 8.5 times compared to the counterpart modulator in visible light region. Meanwhile, the superlubricity significantly reduces the power consumption of the UV electro-optic modulation system due to its extremely low friction coefficient. It also significantly increases the response speed of the modulator, with response time down to nanoseconds. The modulation voltage can be equal to or less than 150 mV. The proposed electro-optic modulation system has a simple structure and high sensitivity, which is supposed to have important applications in UV optoelectronic devices and systems. [ABSTRACT FROM AUTHOR]

Designing and optimizing systems by end-to-end deep learning is a recently emerging field. We present a novel physics-constrained autoencoder (PyCAE) for the design and optimization of a physically realizable sensing model. As a case study, we design a compressive hyperspectral imaging system for remote sensing based on this approach, which allows capturing hundreds of spectral bands with as few as four compressed measurements. We demonstrate our deep learning approach to design spectral compression with a spectral light modulator (SpLM) encoder and a reconstruction neural network decoder. The SpLM consists of a set of modified Fabry–Pérot resonator (mFPR) etalons that are designed to have a staircase-shaped geometry. Each stair occupies a few pixel columns of a push-broom-like spectral imager. The mFPR's stairs can sample the earth terrain in along-track scanning from an airborne or spaceborne moving platform. The SpLM is jointly designed with an autoencoder by a data-driven approach, while spectra from remote sensing databases are used to train the system. The SpLM's parameters are optimized by integrating its physically realizable sensing model in the encoder part of the PyCAE. The decoder part of the PyCAE implements the spectral reconstruction. [ABSTRACT FROM AUTHOR]

We demonstrate a tunable polarization-independent ultranarrow perfect absorption (PA) in a hybrid metasurface consisting of graphene-dielectric nanodisk-metal mirror in the ultraviolet (UV) range. Through near-field interactions between the optical dissipation of graphene and surface plasmon polaritons supported by Al 2 O 3 nanodisk array on UV mirror, the UV Fano-like absorption peak can reach 99.92 % with linewidth as low as 3.4 nm, which is predicted by the impedance matching theory and a Fano model. Furthermore, a dynamic tuning of the UV PA and the associated high-performance optical switch are achieved via temperature change of the encapsulated ethanol. Importantly, the modulation depth of almost 100 %, the ultralarge modulation intensity of about 2.5 × 106 and the on/off ratio of 63 dB are reached for the graphene-based switch by a thermal control. Our work holds potential applications on the UV graphene based light modulators such as high-precision optical switch and nanodevices. [ABSTRACT FROM AUTHOR]

Dynamically controlled 'smart glass' is estimated to be able to contribute more than 30% energy savings to buildings, whilst contributing significantly to the quality of use of all such facilities. Here we describe a technology that can be manufactured on existing, redundant LCD manufacturing facilities. [ABSTRACT FROM AUTHOR]

The emergence of smart headlights with reconfigurable light distributions that provide optimal illumination, highlight road objects, and project symbols to communicate with traffic participants further enhances road safety. Integrating all these functions in a single headlight usually suffers from issues of bulky multi-functional add-on modules with high cost or the use of conventional spatial light modulators with low optical efficiency and complex thermal design requirements. This paper presents a novel laser headlight prototype based on biaxially resonant microelectromechanical systems (MEMS) mirror light modulator for mapping blue laser patterns on phosphor plate to create structured white illumination and tunable road projection. The proposed headlight prototype system enables reconfigurable light distribution by leveraging laser beam scanning with fewer back-end lens and simple thermal design requirements. Built with thin-film lead zirconate titanate oxide (PbZrTiO3) actuators, the MEMS mirror achieved high-frequency biaxial resonance of 17.328 kHz, 4.81 kHz, and optical scan angle of 12.9°. The large mirror design of 2.0 mm facilitates more refined resolvable projection pixels, delivers more optical power, and provides moderate optical aperture to possibly serve as the common spatial light modulator of headlight and the light detection and ranging (LiDAR) towards all-in-one integration. The carefully designed bi-axial resonant frequency improves the device's robustness by offsetting the lowest eigenmode away from the vehicle vibration. By establishing the laser headlight prototype systems of both 1D and 2D scanning modes, a mathematical model of laser modulation and MEMS electrical control principles of Lissajous scanning are proposed to tune the projection pattern density and shapes. It laid the foundation for developing a laser scanning control system with more complex project functions and prompting the application of MEMS for compact headlight system that addresses night driving visibility, eliminates glare effect, and renders interactive projection capabilities. [ABSTRACT FROM AUTHOR]

Thin-film lithium niobate (LN) modulators have significant potential for ultra-high-speed optical communications. Although a significant cost reduction of the modulator is needed to satisfy the growing demands of huge data communications, all the existing studies of thin-film LN modulators were fabricated using the adhesion process of bulk LN to a substrate, and it severely constrains the use case of LN modulators. In order to overcome this critical issue, we have deposited thin-film LN (006) directly on a Al2O3 sapphire (001) substrate and fabricated LN modulators by using the wafer process. Furthermore, previous studies have been largely limited to the use of infrared light (typical wavelengths λ = 1550 nm), which also constrains half-wave voltage and interaction electrode length (Vπ · L) required for modulation. Small Vπ · L is essentially important not only for small die size with lower cost but also for small voltage operation by using a complementary metal oxide semiconductor. Here, we demonstrate the modulation of red (λ = 637 nm), green (λ = 520 nm), and blue (λ = 473 nm) visible light using sputter-deposited thin-film LN; the product of the half-wave voltage and interaction electrode length (Vπ · L) was 1.9, 1.4, and 1.2 V cm, respectively: it decreased with the decreasing wavelength. Thus, LN modulators can be adopted for emerging applications of visible light communications, and wafer-level fabrication using sputter-deposited thin-film LN provides opportunities for future mass production with a much lower fabrication cost. [ABSTRACT FROM AUTHOR]

The recent development of the Micro Electromechanical System (MEMS) Phase Light Modulator (PLM) enables fast laser beam steering for lidar applications by displaying a Computer-Generated Hologram (CGH) without employing an iterative CGH calculation algorithm. We discuss the application of MEMS PLM (Texas Instruments PLM) for quasi-continuous laser beam steering by deterministically calculated CGHs. The effect on the diffraction efficiency of PLM non-equally spaced phase levels was quantified. We also address the CGH calculation algorithm and an experimental demonstration that steered and scanned the beam into multiple regions of interest points, enabling beam steering for lidar without sequential raster scanning. [ABSTRACT FROM AUTHOR]

Featured Application: Interfacial sensors or light modulators made of transparent dielectric materials alone. A simple scheme for single-channel coherent perfect absorption (CPA) of transparent materials is proposed and experimentally realized using total internal reflection by grazing incidence, with a single dielectric layer sandwiched by semi-infinite dielectric layers. In a 1.48-µm thick polyvinylpyrrolidone (PVP) film, dip-coated on a MgF2 substrate both transparent in the visible, reflectance dips due to nearly 90% absorption by single-channel CPA were observed in the wavelength range of 370–800 nm, with white light from a Xe lamp incident on the side face of the substrate and extracted from the other side through multiple reflections in the PVP layer. This is a simple and inexpensive CPA scheme, and it is expected to have various applications by changing the substrate/polymer material or dispersing molecules in the polymer film. This paper also provides a design guideline for grazing-incidence waveguide-mode sensors using transparent dielectric materials. [ABSTRACT FROM AUTHOR]

We fabricated a domain–wall–motion-type light modulator array to measure the diffraction characteristics of a magneto-optical-type spatial light modulator (MO-SLM) driven by current-induced domain wall motion. The array imitated the structure of an SLM and displayed a predetermined 2-D magnetic grating by applying an external magnetic field. The pitch of the modulator was designed to be $1\,\,\mu \text{m}\,\,\times 2\,\,\mu \text{m}$. We investigated the relationship between the intensity of the diffracted beam and the figure of merit (FOM), which is the product of the reflectance and the square of the complex Kerr angle. We varied the multiple-reflection conditions by changing the incident beam angle and the cap layer thickness to compare the behavior of the diffracted beam and the FOM. The diffracted beam’s intensity was enhanced by adjusting the FOM. Furthermore, the diffracted beam exhibited polarization dependence even though the FOM was independent of the polarization direction. The diffracted beam’s intensity was enhanced by the incident beam polarized in the longitudinal direction of the modulator. This work demonstrates that not only FOM maximization but also polarization direction optimization is important for the enhancement of diffracted beams in narrow-pixel-pitch MO-SLMs with non-square pixel shapes. [ABSTRACT FROM AUTHOR]

In this work, a novel design of an electro-tunable narrow channel based on an anisotropic epsilon-near-zero metamaterial is presented. The ENZ condition can be flexibly tuned by an applied gate voltage. This permittivity-tunable channel is composed of periodic alternating layers of graphene and nanoglass with a thickness of 3 nm. Additionally, a dual output light modulator is utilized to expand its application. Numerical analysis results show that the maximum transmittance of the incident light can reach 96.7%, and the extinction ratio of the device is 14.8 dB when the gate voltage is added to 4.96 V at the near-infrared wavelength. This ultracompact optical device may open a new realm in highly integrated photonic circuits, especially on the nano-chips. [ABSTRACT FROM AUTHOR]

The results of targeted fundamental studies of the photochromism of organic compounds, systems and materials on their basis, performed at the Photochemistry Center of the Russian Academy of Sciences, have been analyzed. The scientific basis for the creation of photochromic materials for light-modulating devices and photosensitive recording media for three-dimensional (3D) optical memory with acceptable functional properties has been developed. Practically significant advances have been achieved in the development of photochromic nanoparticles, photochromic optical sensors, and light-adaptive coatings with negative photochromism. The prospects of using photochromic compounds in biomedical technologies are noted. [ABSTRACT FROM AUTHOR]

In the past, the waveguide electroabsorption effect has generally been used as an intensity modulator for quasi-monochromatic light, such as lasers. Here, we study how this effect affects polychromatic light spectra. We find that for light with a Gaussian distribution spectrum, the spectral peak shift (red shift or blue shift) can be controlled by the magnitude of the applied voltage, as long as the center wavelength and the spectral band are properly selected. This result can be used as a data transmission scheme at the integrated chip level or in free space. It may offer a good option for some other light sources, such as low-cost LED or ELED (edge emitting LED), with wider spectral bandwidths. [ABSTRACT FROM AUTHOR]

The effect of concentration, organic co-solvent, and salt modulators on the crystallisation of a hydrogen bonded framework was studied. The framework contains ∼1.4 nm wide channels and contains a diazobenzene based dicarboxylate anion. Light-induced cis/trans switching of this anion was also used to control crystallisation. [ABSTRACT FROM AUTHOR]