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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]

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]

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]

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]

Single-pixel imaging techniques as an alternative to focal-plane detector arrays are being widely investigated. The interest in these single-pixel techniques is partly their compatibility with compressed sensing but also their applicability to spectral regions where focal planes arrays are simply not obtainable. Here, we show how a phased-array modulator source can be used to create Hadamard intensity patterns in the far-field, thereby enabling single-pixel imaging. Further, we successfully illustrate an implementation of compressed sensing for image reconstruction in conditions of high noise. In combination, this robust technique could be applied to any spectral region where spatial light phase modulators or phased-array sources are available. [ABSTRACT FROM AUTHOR]

We consider the problem of achieving high stability and linearity of phase liquid-crystal space-time light modulators, which are widely used for optical reconstruction of diffractive optical elements, including holograms. Modern high-resolution space-time light modulators one uses a digital signal addressing circuit, which leads to phase shift fluctuations during the frame. For the modern high-resolution phase liquid crystal space-time light modulator Santec SLM-200, the dependences of the phase shift on the level of the addressed signal and time from the beginning of the frame have been measured. Using the Santec SLM-200 light modulator, optical reconstruction of images from diffractive elements of different types was performed, their diffraction efficiency and the quality of the reconstructed images were evaluated. The values of the diffraction efficiency were obtained in the range of 3–10%; a sharp drop in the brightness of the reconstructed images is observed with distance from the optical axis in the plane of reconstruction. [ABSTRACT FROM AUTHOR]

Vortex beams carrying orbital angular momentum (OAM), which featuring helical phase front, have been regarded as an alternative spatial degree of freedom for optical mode coding and multiplexing. For most reported OAM-based mode coding schemes, data information is only encoded by different OAM mode states. In this paper, we introduce a novel design technique to construct vortex array phase grating (VAPGs) for the flexible generation of vortex arrays, and employ the proposed VAPGs to realize multi-dimensional space/mode/amplitude coding/decoding. By designing VAPGs with different parameters and loading them on to a single spatial light modulator (SLM), we successfully generate vortex array with different mode states and relative power in the experiments. Moreover, a 10-bit multi-dimensional space/mode/amplitude data coding/decoding scheme for image transfer in free-space link with a zero bit-error-rate is experimentally demonstrated, which confirm the feasibility of our proposed VAPG-based coding/decoding scheme. [ABSTRACT FROM AUTHOR]

In this work we demonstrate customized depolarization spatial patterns by imaging a dynamical time-dependent pixelated retarder. A proof-of-concept of the proposed method is presented, where a liquid–crystal spatial light modulator is used as a spatial retarder that emulates a controlled spatially variant depolarizing sample by addressing a time-dependent phase pattern. We apply an imaging Mueller polarimetric system based on a polarization camera to verify the effective depolarization effect. Experimental validation is provided by temporal integration on the detection system. The effective depolarizance results are fully described within a simple graphical approach which agrees with standard Mueller matrix decomposition methods. The potential of the method is discussed by means of three practical cases, which include non-reported depolarization spatial patterns, including exotic structures as a spirally shaped depolarization pattern. [ABSTRACT FROM AUTHOR]

We demonstrate an alternative approach for generating zeroth- and first-order long range non-diffracting Gauss–Bessel beams (GBBs). Starting from a Gaussian beam, the key point is the creation of a bright ring-shaped beam with a large radius-to-width ratio, which is subsequently Fourier-transformed by a thin lens. The phase profile required for creating zeroth-order GBBs is flat and helical for first-order GBBs with unit topological charge (TC). Both the ring-shaped beam and the required phase profile can be realized by creating highly charged optical vortices by a spatial light modulator and annihilating them by using a second modulator of the same type. The generated long-range GBBs are proven to have negligible transverse evolution up to 2 m and can be regarded as non-diffracting. The influences of the charge state of the TCs, the propagation distance behind the focusing lens, and the GBB profiles on the relative intensities of the peak/rings are discussed. The method is much more efficient as compared to this using annular slits in the back focal plane of lenses. Moreover, at large propagation distances the quality of the generated GBBs significantly surpasses this of GBBs created by low angle axicons. The developed analytical model reproduces the experimental data. The presented method is flexible, easily realizable by using a spatial light modulator, does not require any special optical elements and, thus, is accessible in many laboratories. [ABSTRACT FROM AUTHOR]

We present a new scheme to produce a tunable converge elliptical optical vortex (EOV) with a phase-only element: elliptical helical lens (EHL), which is studied theoretically and experimentally. As a result, the properties of converge EOVs can be controlled by adjusting the parameters of EHL. The topological charges of the EOVs can be directly read from the received intensity pattern. Because EHL is a hologram programmed in space light modulator (SLM), converge EOVs can be controlled just by reprogramming the SLM instead of replacing actual instruments. This work has potential applications in particle manipulation, as well as generation of OAM-entangled photons. [ABSTRACT FROM AUTHOR]

In various fields of photonics, there is a tendency to pass from elements of physical optics to elements of flat optics, primarily, due to a decrease in the dimensions of instruments and devices. Most frequently, spatial light modulators are used to efficiently and immediately simulate flat phase elements. In this work, we investigate the possibility of replacing a lens optical system with a computer-generated lens. The novelty of the work is a comparative analysis of the point spread functions of the lens optical system and the computer-generated lens. Numerous experiments confirm the obtained result. [ABSTRACT FROM AUTHOR]

In this paper, a graphene–dielectric–graphene modulator with a dual-ring resonator structure is designed. To achieve the dynamic modulation of the light intensity, the modulator is combined with the selective frequency filtering characteristic of the dual-ring resonator and the electrically tunable characteristic of the graphene. The finite element method is used to study the radius of the ring, the dielectric material, the wavelength and the chemical potential of graphene. The simulation results show that when the incident wavelength is 1580 nm, the chemical potential drops from 0.854 to 0.834 eV, for a 5 μm-long graphene light modulator, the extinction ratio of the modulator reaches 7.56 dB. Compare the previously proposed graphene light modulator, the device can not only be combined with the high extinction ratio and small size, but also has the high speed modulation rate, which is of great significance for large-scale production and integration of optoelectronic devices. [ABSTRACT FROM AUTHOR]

Characteristic features of anisotropic light diffraction in a spatially periodic acoustic field created by a sectioned piezoelectric transducer with antiphase excitation of adjacent sections are studied theoretically. The numerical calculation is carried out for a cell of a paratellurite crystal with a shear acoustic mode propagating at an angle of 3° to the (001) plane of the crystal. It is shown that this type of acoustooptic interaction has some interesting features that can be used when developing acoustooptic devices, in particular, modulators of nonpolarized light. [ABSTRACT FROM AUTHOR]

Differential quadrature phase shift keying (DQPSK) encodes the phase change from one symbol period to the next. The precoder is designed for this purpose. The main objective of this paper is to design a simple precoder of the DQPSK transmitter. The precoder is designed using various blocks such as multiplexers, logic gates and flip-flops. The blocks are designed using Mach-Zehnder Interferometer-Semiconductor Optical Amplifier. The designed optical precoder is simulated and tested. It is capable of mapping input bit streams to quadrature components at a data rate up to 10 Gbps. Performance parameters such as Q factor and BER are analyzed for various data rates from 2 to 10 Gbps. The values of Q factor and BER at a data rate of 10 Gbps are found to be 5.4 and 1.5e−8 respectively. Hence, it is suitable for the high-speed transmission system. [ABSTRACT FROM AUTHOR]

A comparison was established between two iterative Fourier transform algorithms (IFTAs), such as the original Gerchberg-Saxton (GS) and the mixed-region amplitude freedom (MRAF) algorithms, for the hologram reconstruction of different target images through the full reference image quality estimation (IQE) and pixel homogeneity in the Fourier plane presented theoretically and experimentally. The comparison was applied depending upon both algorithms based on a computer-generated hologram (CGH) implemented utilizing a reflective phase-modulated liquid-crystal spatial light modulator (LC-SLM) to obtain the digital kinoform holograms of the desired intensity distributions. These digital holograms were applied to reconstruct the intensity patterns for 852 nm, which represents a laser beam source. The theoretical and experimental results of the reconstructed patterns obtained using the MRAF algorithm were found to be smoother and better than the patterns obtained using the GS algorithm. Unmodulated light beam (dc term) is removed from the reconstructed patterns attributed to digital kinoform holograms of MRAF algorithm as an alternative to the theoretical and experimental results without using any additional optic equipment at the light path. Moreover, this paper discussed the full reference objective quality estimations, such as mean square error (MSE), peak signal-to-noise ratio (PSNR), structural content (SC), normalized absolute error (NAE), normalized cross correlation (NK), and homogeneity of pixels, through the contrast (Cont) and inverse difference moment (IDM) for numerical and experimental results. According to the two desired intensity distributions processed theoretically and experimentally, the results of MRAF algorithm were found to be in the highly accurate recovered phase, the quality of image was enhanced, and the dc term was decreased. Image quality estimation of full reference objective relay on the feedback algorithms experimental attestation has not been implemented yet. [ABSTRACT FROM AUTHOR]

In this study, we investigated the interaction of base sequence-assigned single-stranded DNA (ssDNA) molecules with the surfaces of single-walled carbon nanotube (SWNT)-thymine (T30)/cytosine (C30) hybrids (T30/C30-SWNT), by measuring the modulation of near-infrared (NIR) photoluminescence (PL). Significant PL shifts were observed when T30/C30-SWNTs were reacted with 30-mers of adenine (A30)/guanine (G30). In contrast, when non-complementary ssDNA was used, no significant energy shift was observed in the PL modulation except when T30-SWNTs were reacted with G30. Furthermore, atomic force microscopy (AFM) measurements revealed that the average heights of the T30-SWNTs and C30-SWNTs, after reaction with A30 were 2 ± 0.6 and 1.1 ± 0.3 nm, respectively. This result was in good agreement with the results of PL measurements. Our data reveal that DNA hybridization could be detected by measuring PL from SWNTs, without the use of fluorescent molecules. This leads to the possibility of developing nanotube-based photoelectric conversion or optical switch devices driven by organic molecules. [ABSTRACT FROM AUTHOR]

Advanced photonic probing techniques are of great importance for the development of noncontact wafer-scale testing of photonic chips. Ultrafast photomodulation has been identified as a powerful new tool capable of remotely mapping photonic devices through a scanning perturbation. Here, we develop photomodulation maps into a quantitative technique through a general and rigorous method based on Lorentz reciprocity that allows the prediction of transmittance perturbation maps for arbitrary linear photonic systems with great accuracy and minimal computational cost. Excellent agreement is obtained between predicted and experimental maps of various optical multimode-interference devices, thereby allowing direct comparison of a device under test with a physical model of an ideal design structure. In addition to constituting a promising route for optical testing in photonics manufacturing, ultrafast perturbation mapping may be used for design optimization of photonic structures with reconfigurable functionalities. [ABSTRACT FROM AUTHOR]

A novel scheme for the generation of ultraflat and broadband optical frequency comb (OFC) is proposed based on cascaded two dual-electrode Mach-Zehnder modulators (DE-MZM). The first DE-MZM can generate a four-comb-line OFC, then the OFC is injected into the second DE-MZM as a carrier, which can increase the number of comb lines. Our modified scheme finally can generate a broadband OFC with high flatness by simply modifying the electrical power and the bias voltage of the DE-MZM. Theoretical analysis and simulation results reveal that a 16-comb-line OFC with a frequency spacing that two times the frequency of the RF signal can be obtained. The power fluctuation of the OFC lines is 0.48 dB and the unwanted-mode suppression ratio (UMSR) can reach 16.5 dB. Additionally, whether the bias drift of the DE-MZMs has little influence on the power fluctuation is also analyzed. These results demonstrate the robustness of our scheme and verify its good accuracy and high stability with perfect flatness. [ABSTRACT FROM AUTHOR]

In this paper, an autostereoscopic three-dimensional (3D) display system based on synthetic hologram reconstruction is proposed and implemented. The system uses a single phase-only spatial light modulator to load the synthetic hologram of the left and right stereo images, and the parallax angle between two reconstructed stereo images is enlarged by a grating to meet the split angle requirement of normal stereoscopic vision. To realize the crosstalk-free autostereoscopic 3D display with high light utilization efficiency, the groove parameters of the grating are specifically designed by the rigorous coupled-wave theory for suppressing the zero-order diffraction, and then the zero-order nulled grating is fabricated by the holographic lithography and the ion beam etching. Furthermore, the diffraction efficiency of the fabricated grating is measured under the illumination of a laser beam with a wavelength of 532 nm. Finally, the experimental verification system for the proposed autostereoscopic 3D display is presented. The experimental results prove that the proposed system is able to generate stereoscopic 3D images with good performances. [ABSTRACT FROM AUTHOR]

Organic nonlinear optical materials have been widely explored because of their advantages in the design of materials with large electro-optic coefficients used in the fabrication of novel optoelectronic and telecommunication devices. However, the huge dipole-dipole interactions between organic nonlinear optical chromophores have limited further improvements in the electro-optic coefficients and long-term material stability. Here, a novel polymer based on poly(aryl ether ketone) was designed and prepared to enhance the electro-optic coefficients and achieve higher long-term stability. This novel poly(aryl ether ketone) has a relatively high glass transition temperature and offers active functional groups for the attachment of organic nonlinear optical chromophores. After attachment of nonlinear optical chromophores the materials showed higher chromophore loading density, less inter-molecular interaction, and suitable solubility. This resulted in better film-forming ability, higher electro-optics coefficients and better long-term stability. Quantum chemical simulations of the second order hyperpolarizabilities and ground sate dipole moments were done to understand the origin of the effects. [ABSTRACT FROM AUTHOR]

The effect of the electronic tuning of the acoustic resonances in an acousto-optic mode-locking device of a laser is investigated theoretically and experimentally. The problem of the excitation of a Fabry-Perot acoustic resonator by a plate-like piezoelectric transducer (PET) is solved in the approximation of plane acoustic waves taking into consideration the actual parameters of an RF generator and the elements for matching the PET to the generator. Resonances are tuned by changing the matching inductance that was connected in parallel to the transducer of the acousto-optic cell. The cell used in the experiment was manufactured from fused silica and included a lithium niobate PET. Changes in the matching inductance in the range of 0.025 to 0.2 μH provided the acoustic-resonance frequency tuning by 0.19 MHz, which exceeds the acoustic- resonance half-width. [ABSTRACT FROM AUTHOR]

In this study, we explored the effects of a longer term application, up to 12 weeks, of photobiomodulation in normal, naïve macaque monkeys. Monkeys ( n = 5) were implanted intracranially with an optical fibre device delivering photobiomodulation (red light, 670 nm) to a midline midbrain region. Animals were then aldehyde-fixed and their brains were processed for immunohistochemistry. In general, our results showed that longer term intracranial application of photobiomodulation had no adverse effects on the surrounding brain parenchyma or on the nearby dopaminergic cell system. We found no evidence for photobiomodulation generating an inflammatory glial response or neuronal degeneration near the implant site; further, photobiomodulation did not induce an abnormal activation or mitochondrial stress in nearby cells, nor did it cause an abnormal arrangement of the surrounding vasculature (endothelial basement membrane). Finally, because of our interest in Parkinson's disease, we noted that photobiomodulation had no impact on the number of midbrain dopaminergic cells and the density of their terminations in the striatum. In summary, we found no histological basis for any major biosafety concerns associated with photobiomodulation delivered by our intracranial approach and our findings set a key template for progress onto clinical trial on patients with Parkinson's disease. [ABSTRACT FROM AUTHOR]

The auto-focusing and auto-healing profiles of linearly polarized ring Airy Gaussian vortex (RAiGV) beams in linear media are investigated experimentally based on spatial light modulators and computer-generated holograms. It is found that the parameters of incident beams greatly affect the auto-focusing profiles of RAiGV. The focal length increases as the radius of the primary ring, scaling factor and waist radius increases, and the focal length decreases slightly as topological charges increase. The peak intensity at focal point increases with the increasing topological charges and waist radius, or with the decreasing scaling factor and the radius of the primary ring. The phase singularity of the RAiGV beams remains unchanged during propagation. The RAiGV beams also exhibit remarkable resilience against perturbations and tend to reconstruct its intensity sharp. Meanwhile, the abruptly auto-focusing property can be controlled by blocking few inner or outer rings of the RAiGV beams. These studies provide useful insight in the study of Airy vortex beam and its further applications. [ABSTRACT FROM AUTHOR]

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

An optically tunable frequency-decuple optoelectronic oscillator based on optical frequency comb (OFC) and stimulated Brillouin scattering has been proposed and theoretically analyzed. In the proposed structure, the OFC is generated using a cascaded Mach-Zehnder modulator and a dual-parallel Mach-Zehnder modulator (DPMZM), and multi-pump lights could be obtained instead of one pump. A quintuple Brillouin frequency shift oscillation signal generated by using Brillouin gain-loss compensation principle and carrier phase-shifted double sideband modulation is realized by using the DPMZM to double the oscillation frequency. As a consequence, a decuple frequency shift microwave signal is achieved. Profit from the wavelength-dependent nature of Brillouin frequency shift, a frequency-decuple signal at 10 $$f_{b}$$ which could be tunable from 87.9750 to 94.4750 GHz by simply tuning the wavelength of the tunable laser source is obtained in theory. [ABSTRACT FROM AUTHOR]

In this paper, an optical generation of millimeter waves (MM-Wave) through frequency decupling using dual parallel Mach-Zehnder Modulator (DP-MZM) with Radio over Fiber transmission is demonstrated. The phases of the RF local oscillator (LO) and the modulation indices of the MZMs are carefully adjusted in order to generate 60 GHz optical MM-Wave signal from a 6 GHz RF LO. The impact of the non-ideal parameters such as modulation index, extinction ratio and the RF LO phases over the optical MM-Wave is analyzed and presented. Further, data transmission performance of the generated millimeter wave over fiber using dual tone and single tone data modulation schemes are also analyzed. The power penalty of 2.5 dB for 20 km with the dual tone modulation and 0.4 dB for 75 km with single tone modulation is achieved. [ABSTRACT FROM AUTHOR]

Treatment of muscle injuries usually results in the interruption of sports practice; thus, studies aimed at accelerating the return to activity, with proper tissue repair, are important. Therefore, this study aimed to evaluate the effects of photobiomodulation (PBM), associated or not with platelet-rich plasma (PRP), on the treatment of muscle injury. Thirty-five animals were used and divided into five groups (n = 7): control (C), control lesion (CL), lesion treated with low-level laser therapy (LLLT) (LLt), lesion treated with PRP (LP), and lesion treated with both techniques, LLLT and PRP (LLtP). Muscle injury was induced by stretching the gastrocnemius muscle, and the animals in the LLtP and LP groups received the application of PRP immediately following the injury. The LLLT was applied daily for 7 days. The animals were euthanized 7 days after the injury. Analysis of the NADH/NAD ratio and collagen was performed by Raman spectroscopy; in addition to which, histological analysis of the gastrocnemius muscle was performed. The LLtP group demonstrated a reduction in the area of injury, regenerating cells and a healthy appearance of muscle fibers. The Raman analyses showed a reduction in the NADH/NAD ratio in the CL group, demonstrating oxidative stress, and the collagen presented a reduction in the CL and LLt groups, when compared with the C group. It is concluded that either PBM or PRP, and the association of both, was able to reduce the oxidative stress promoted by injury and modulate collagen production at the site of the injury. Furthermore, although both treatments individually were effective for repairing the damage caused by muscle injury, the association of both demonstrated a better histological aspect. [ABSTRACT FROM AUTHOR]

A 360-degree realistic 3D image display system based on direct light scanning method, so-called Holo-Table has been introduced in this paper. High-density directional continuous 3D motion images can be displayed easily with only one spatial light modulator. Using the holographic screen as the beam deflector, 360-degree full horizontal viewing angle was achieved. As an accompany part of the system, CMOS camera based image acquisition platform was built to feed the display engine, which can take a full 360-degree continuous imaging of the sample at the center. Customized image processing techniques such as scaling, rotation, format transformation were also developed and embedded into the system control software platform. In the end several samples were imaged to demonstrate the capability of our system. [ABSTRACT FROM AUTHOR]

We present an experimental setup for creating arbitrary two-dimensional arrays of optical microtraps to trap single atoms for experiments with Rydberg atoms. We use a spatial light modulator to manipulate the spatial phase of a far red-detuned optical dipole trap beam, which allows us to create arbitrary arrays of optical microtraps, by focusing the beam with an in-vacuum high numerical-aperture aspheric lens. We load atoms in the microtraps from a dilute cloud of cold atoms, having at most one atom in each trap due to fast light-assisted collisions. Real-time analysis of the atomic fluorescence with a sensitive CCD camera allows us to determine the filling of each trap individually with a >10 Hz rate. We can create strong interactions between the atoms by exciting them to Rydberg states, with an efficiency of single atom resolved Rydberg detection of >95%. [ABSTRACT FROM AUTHOR]

Gaining accuracy with indoor positioning of individuals is important as many location-based services rely on the user's current position to provide them with useful services. Many researchers have studied indoor positioning techniques based on WiFi and Bluetooth. However, they have disadvantages such as low accuracy or high cost. In this paper, we propose an indoor positioning system in which visible light radiated from light-emitting diodes is used to locate the position of receivers. Compared with existing methods using light-emitting diode light, we present a high-precision and simple implementation collaborative indoor visible light positioning system based on an improved spring model. We first estimate coordinate position information using the visible light positioning system, and then use the spring model to correct positioning errors. The system can be employed easily because it does not require additional sensors and the occlusion problem of visible light would be alleviated. We also describe simulation experiments, which confirm the feasibility of our proposed method. [ABSTRACT FROM AUTHOR]

The formation of light fields of various structure and real-time control of their parameters with the help of inexpensive and technologically simple adaptive devices is an urgent problem of modern optics. A 4-channel liquid-crystal (LC) modulator (LC focusing device) can serve as such a device. An analysis of longitudinal light lines and hollow light beams formed by this device is performed. Such fields are realized due to the possibility of creating a phase delay distribution over the aperture of an LC focusing device in the form of a truncated cone (quasi-axicon). Spatial and energetic characteristics of these light fields are considered from the standpoint of their potential applications in problems of three-dimensional manipulation. It is shown that by varying the voltages applied to the contacts of the focusing device it is possible to control the width of the light contour, the size of the zero-intensity region, the lengths of the light tube and light line segment, and the energy characteristics of the formed fields. The results obtained may be of use in the formation of three-dimensional optical traps in problems involving the manipulation of transparent and nontransparent micro-objects. [ABSTRACT FROM AUTHOR]

Background: The common regime of eccentric exercise in use for Achilles tendinopathy is somewhat arduous and compliance issues can arise. This is the first study to investigate the effectiveness of a regime of fewer exercise sessions combined with photobiomodulation for the treatment of Achilles tendinopathy.Methods: A double blind randomized controlled trial and intention-to-treat analysis were performed. Eighty participants, 18-65 years with Achilles tendinopathy and symptoms for longer than 3 months, were included in the trial. Participants randomized into one of four groups; 1 (Placebo + Ex Regime 1) or 2 (Laser + Ex Regime 1) or 3 (Placebo + Ex Regime 2) or 4 (Laser + Ex Regime 2). The primary outcome measure was the Victorian Institute of Sports Assessment-Achilles (VISA-A) questionnaire. Outcomes were collected at baseline, week 4 and week 12.Results: Sixteen participants were lost to follow-up at 12 weeks, 4 of which due to adverse reactions. As per intention to treat, missing data were imputed, 80 participants were included in the final analysis. For VISA-A at 12 weeks, group 4 achieved significant gains over the other 3 groups: group 1 (18.5 [9.1, 27.9]), group 2 (10.4 [1.5, 19.2]), group 3 (11.3 [3.0, 19.6]). There was a moderate effect size in favour of exercise twice per week (7.2 [-1.8, 16.2], ES .7).Conclusions: Twice-daily exercise sessions are not necessary as equivalent results can be obtained with two exercise sessions per week. The addition of photobiomodulation as adjunct to exercise can bring added benefit. [ABSTRACT FROM AUTHOR]

Debris deposited around laser-processed structures is a critical issue in high-precision laser processing and should be removed. We demonstrated a new debris removal method that is performed during laser processing. A line-focused beam that is radiated onto a target material simultaneously with a processing beam sweeps away the debris generated by laser ablation. Two physical processes are involved: One is direct photon excitation of the attached debris, similar to laser ablation, due to a smaller ablation threshold of the debris, and the other is blowing away the debris with a laser-induced pressure wave. The laser processing setup for debris sweeping has a simple and practical configuration composed of beam transmission optics from a laser source to the target and a spatial light modulator that displays a computer-generated hologram. This in-process debris removal method has the advantages of needing no additional equipment other than the optics, no additional operations, no special materials, and no specific operating environment. [ABSTRACT FROM AUTHOR]

A revised modulated free carrier absorption (MFCA) theory is proposed, in which photomodulated thermal reflectance (PMTR) is subtracted from the transmitted signals of semiconductors. With this theory, one simultaneously extracts the carrier transport properties, such as the carrier lifetime, carrier diffusion coefficient, and the front surface recombination velocity, of silicon wafers. Proof-of-concept experiments were performed on a single crystal p-type, 100 cut silicon having $$8\,\Omega {\cdot }\hbox {cm}$$ to $$12\,\Omega {\cdot }\hbox {cm}$$ resistivity. MFCA and transmitted data (composed of MFCA and PMTR) are fitted to an MFCA theoretical model. Fitted results showed that the accuracies of fitted transport properties can be greatly improved by the MFCA technique if the PMTR component is subtracted from the transmitted signal. [ABSTRACT FROM AUTHOR]

We describe application of the phase liquid-crystal spatial light modulator HoloEyePLUTOVIS as an encoding element in the image optical encryption scheme with spatially incoherent illumination. Optical encryption and numerical decryption of test images were conducted. The results of experiments demonstrate the efficiency of the constructed optical encryption scheme. [ABSTRACT FROM AUTHOR]

Specific features of the formation of frequency-modulated pulses with large peak powers in amplifier-modulator-compressor cascade schemes based on length-inhomogeneous optic fibers are considered. Optimum profiles of fiber parameters ensuring the most effective amplification and modulation of pico- and subpicosecond frequency-modulated pulses are proposed. It is established that the use of a cascade consisting of active (gain) and passive (modulating) fibers with optimized profiles of the normal group-velocity dispersion and mode area can ensure the formation of pico- and subpicosecond pulses with energies higher than 100 nJ and peak powers above 100 kW. [ABSTRACT FROM AUTHOR]

Manipulating optical signals below the diffraction limit is crucial for next-generation data-storage and telecommunication technologies. Although controlling the flow of light around nanoscale waveguides was achieved over a decade ago, modulating optical signals at terahertz frequencies within nanoscale volumes remains a challenge. Since the physics underlying any modulator relies on changes in dielectric properties, the incorporation of strongly electron-correlated materials (SECMs) has been proposed because they can exhibit orders of magnitude changes in electrical and optical properties with modest thermal, electrical or optical trigger signals. Here we demonstrate a hybrid nanomodulator of deep sub-wavelength dimensions with an active volume of only 0.002 μm3 by spatially confining light on the nanometre length scale using a plasmonic nanostructure while simultaneously controlling the reactive near-field environment at its optical focus with a single, precisely positioned SECM nanostructure. Since the nanomodulator functionality hinges on this near-field electromagnetic interaction, the modulation is also selectively responsive to polarization. This architecture suggests one path for designing reconfigurable optoelectronic building blocks with responses that can be tailored with exquisite precision by varying size, geometry, and the intrinsic materials properties of the hybrid elements. [ABSTRACT FROM AUTHOR]

In this article we propose to use electronically tunable metasurfaces as spatial microwave modulators. We demonstrate that like spatial light modulators, which have been recently proved to be ideal tools for controlling light propagation through multiple scattering media, spatial microwave modulators can efficiently shape in a passive way complex existing microwave fields in reverberating environments with a non-coherent energy feedback. Unlike in free space, we establish that a binary-only phase state tunable metasurface allows a very good control over the waves, owing to the random nature of the electromagnetic fields in these complex media. We prove in an everyday reverberating medium, that is, a typical office room, that a small spatial microwave modulator placed on the walls can passively increase the wireless transmission between two antennas by an order of magnitude, or on the contrary completely cancel it. Interestingly and contrary to free space, we show that this results in an isotropic shaped microwave field around the receiving antenna, which we attribute again to the reverberant nature of the propagation medium. We expect that spatial microwave modulators will be interesting tools for fundamental physics and will have applications in the field of wireless communications. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new method of using multiple spatial light modulators (SLMs) to increase the size of three-dimensional (3D) images that are displayed using electronic holography. The scalability of images produced by the previous method had an upper limit that was derived from the path length of the image-readout part. We were able to produce larger colour electronic holographic images with a newly devised space-saving image-readout optical system for multiple reflection-type SLMs. This optical system is designed so that the path length of the image-readout part is half that of the previous method. It consists of polarization beam splitters (PBSs), half-wave plates (HWPs), and polarizers. We used 16 (4 × 4) 4K×2K-pixel SLMs for displaying holograms. The experimental device we constructed was able to perform 20 fps video reproduction in colour of full-parallax holographic 3D images with a diagonal image size of 85 mm and a horizontal viewing-zone angle of 5.6 degrees. [ABSTRACT FROM AUTHOR]

An approach for laser marking surfaces using a liquid-crystal-based spatial light modulator (LC-SLM) for beam patterning and manipulation is presented, designed to avoid the speckle interference problem which is a typical drawback of current SLM-based laser marking processes. In our approach, the LC-SLM is used to generate complex two-dimensional micropatterns (e.g., 20 × 20 datamatrices) with overall dimensions of < 320 by 320 μm. The micropatterns are generated in a series of 16 steps, using a Fresnel zone lens (FZL) combined with a computer-generated hologram (CGH); for each step the whole kinoform (FZL + CGH) is spatially shifted off-axis by a different amount of pixels to build-up the required pattern. In comparison with other SLM-based laser marking approaches already reported in the literature, our method not only eliminates (or at least significantly reduces) unwanted speckle interference but also reduces the laser power required for marking. [ABSTRACT FROM AUTHOR]

We propose a new approach to spatiotemporally multiplex sub-holograms and stream hologram data in parallel by using multiple spatial light modulators (SLMs) to increase the spatiotemporal resolution of holographic display system. With the proposed approach, we have achieved a spatiotemporal resolution of 4.5 × 10 pixel/s, as compared with 1.89 × 10 pixel/s of a single SLM. Each frame of computer-generated hologram video has a pixel count of 378 Mpixels and is divided into 288 sub-holograms, each of 1.31 Mpixels. During the playback of holographic video, these sub-holograms are spatiotemporally multiplexed and streamed in parallel to form the integrated hologram within 16.67 ms, which enables full-color holographic video display with a 10-in. diagonal at a hologram data frame rate of 60 frames per second (fps). New SLM devices with higher spatiotemporal resolution need to be developed in order to meet the data bandwidth requirement of about 10-10 pixel/s for future 3D holographic displays. [ABSTRACT FROM AUTHOR]

This paper concentrates on the switching dynamics of a Nematic Liquid Crystal light modulator. This Liquid Crystal, called 1294-1b, has outstanding optical properties such as high birefringence which makes it a promising material for optical applications. Though this potential has been already implicated in optical data storage and integrated optics, it's high viscosity limits the application in light modulators and electro-optics. This paper uses methods such as alternation in sample thickness, temperature and applied voltage to overcome this shortage. Finally, with the mentioned techniques a variety of switching times ranging from seconds to micro second are obtained. [ABSTRACT FROM AUTHOR]

Electromagnetic resonances in conducting structures give rise to the enhancement of local fields and extinction efficiencies. Conducting structures are conventionally fabricated with a fixed geometry that determines their resonant response. Here, we challenge this conventional approach by demonstrating the photo-generation of THz linear antennas on a flat semiconductor layer by the structured optical illumination through a spatial light modulator. Free charge carriers are photo-excited only on selected areas, which enables the realization of different conducting antennas on the same sample by simply changing the illumination pattern, thus without the need of physically structuring the sample. These results open a wide range of possibilities for the all-optical spatial control of resonances on surfaces and the concomitant control of THz extinction and local fields. [ABSTRACT FROM AUTHOR]

Terahertz (THz) technology is a developing and promising candidate for biological imaging, security inspection and communications, due to the low photon energy, the high transparency and the broad band properties of the THz radiation. However, a major encountered bottleneck is lack of efficient devices to manipulate the THz wave, especially to modulate the THz wave front. A wave front modulator should allow the optical or electrical control of the spatial transmission (or reflection) of an input THz wave and hence the ability to encode the information in a wave front. Here we propose a spatial THz modulator (STM) to dynamically control the THz wave front with photo-generated carriers. A computer generated THz hologram is projected onto a silicon wafer by a conventional spatial light modulator (SLM). The corresponding photo-generated carrier spatial distribution will be induced, which forms an amplitude hologram to modulate the wave front of the input THz beam. Some special intensity patterns and vortex beams are generated by using this method. This all-optical controllable STM is structure free, high resolution and broadband. It is expected to be widely used in future THz imaging and communication systems. [ABSTRACT FROM AUTHOR]

The secure transfer of information is an important problem in modern telecommunications. Quantum key distribution (QKD) provides a solution to this problem by using individual quantum systems to generate correlated bits between remote parties, that can be used to extract a secret key. QKD with D-dimensional quantum channels provides security advantages that grow with increasingD. However, the vast majority of QKD implementations has been restricted to two dimensions. Here we demonstrate the feasibility of using higher dimensions for real-world quantum cryptography by performing, for the first time, a fully automated QKD session based on the BB84 protocol with 16-dimensional quantum states. Information is encoded in the single-photon transverse momentum and the required states are dynamically generated with programmable spatial light modulators. Our setup paves the way for future developments in the field of experimental high-dimensional QKD. [ABSTRACT FROM AUTHOR]

We present and demonstrate an approach for femtosecond laser processing by using patterned vector optical fields (PVOFs) composed of multiple individual vector optical fields. The PVOFs can be flexibly engineered due to the diversity of individual vector optical fields in spatial arrangement and distribution of states of polarization, and it is easily created with the aid of a spatial light modulator. The focused PVOFs will certainly result in various interference patterns, which are then used to fabricate multi-microholes with various patterns on silicon. The present approach can be expanded to fabricate three-dimensional microstructures based on two-photon polymerization [ABSTRACT FROM AUTHOR]

The effect of ultraviolet irradiation of the surface of silicon-carbide (6 H-SiC) single crystals on their optical reflectivity in the visible and violet spectral regions is studied. It is shown that the photoreflection-signal intensity is maximal, if the light beam is incident at the Brewster angle and polarized parallel to the plane of incidence. The relative change induced in the refractive index of the surface layers of a crystal (10) upon exposure to nitrogen laser radiation, caused by the generation of nonequilibrium free charge carriers in the conduction band of the material, is established. [ABSTRACT FROM AUTHOR]

Photodynamic rejuvenation therapy (PDRT) is a growing field in cosmetic dermatology. In this study, different sources of light (a yellow laser, a red laser and ultraviolet A (UVA) lamps) were used to activate a second-generation photosensitiser, hypericin. Uptake of hypericin was monitored over 24 h and efficacy of PDRT was assessed using cell viability and reactive oxygen species (ROS) quantification assays. In addition, we show for the first time, a quantifiable assay for ROS production in human dermal fibroblasts incubated with hypericin and exposed to yellow laser light or UVA lamps. Furthermore, we optimised a protocol with regard to hypericin concentration and irradiation parameters using the XTT cell viability kit. This study showed that this photosensitiser, hypericin, was taken up by the cells in a concentration-dependent manner over 24 h with cell saturation occurring after approximately 16 h. The uptake seemed to be localised to the cell cytoplasm with no hypericin appearing in the nucleus. The levels of ROS increased in the cell when irradiated with the yellow laser (561 nm) however, it did not increase further with the addition of hypericin. Hypericin and UVA showed a significant increase in the amount of ROS produced. The results also show that cell viability is not affected by low power light (2 mW) from the yellow laser irrespective of the dose used. However, an increase to 10 mW power with 5 J/cm light dose, resulted in a significant drop ( p < 0.05) in cell viability at both 0.5 (77.53 ± 9.67 %) and 1 μM (48.51 ± 13.27 %) hypericin concentrations. In contrast, a 20 % increase in cell viability was seen with 1 J/cm and 20 mW and 0.25 μM hypericin. Overall, this study highlights an optimised protocol for hypericin-induced photorejuvenative therapy using laser light and proposes that parameters of 0.25 μM hypericin as a photosensitiser activated via a dosage of 1 J/cm yellow laser light produces an effective in vitro outcome to be considered as an important contribution towards optimising PDRT. [ABSTRACT FROM AUTHOR]