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To protect image information security, we propose an encryption algorithm based on chaotic sequences and bits' cross-diffusion. First, two chaotic sequences are generated by two-dimensional logic-sine coupling mapping, and the original image is scrambled with the two sequences. Secondly, the scrambled image is transformed into a one-dimensional sequence, and the low-order bits between every two pixels are fused to change the detailed information of the image, improved the ability to resist differential attacks. Finally, chaotic sequences are generated by iterative logical mapping to perform pixel replacement and ciphertext diffusion. The known plaintext attack can be effectively resisted because of the stochastic combination of diffusion scheme and chaotic sequence. It also has a significant effect on resisting differential attack. Take Lena image as an example, NPCR and UACI can reach 99.6063% and 33.4477%, respectively, which are very close to the ideal value. The encryption scheme has good key sensitivity and strong ability to resist statistical attacks, which shows that the algorithm has adequate security.

An ultra-broadband polarization beam splitter (PBS) consisting of cascaded Mach-Zehnder interferometers (MZIs) is proposed on 220 nm-thick silicon-on-insulator (SOI) platform. The configuration of the cascaded MZIs has a point symmetry in order to broaden the bandwidth of the cross-coupling for the TM polarization. The sub-wavelength grating (SWG) structures act as effectively anisotropic cladding to enhance the separation of the two fundamental polarizations. Two filters with cascaded bends and a Bragg reflection structure at the two outputs, respectively, are used to further improve the extinction ratio (ER). The proposed PBS has a remarkable performance with ER > 20 dB over a record broad bandwidth of 310 nm (IL

A novel photonic vector THz-wave signal generation at terahertz-wave (THz-wave) band by Mach Zendell modulator (MZM) -based optical frequency comb and in-phase and quadrature (IQ) modulator for signal modulation scheme is proposed. And we demonstrate 16 quadrature-amplitude-modulation (QAM) vector THz-wave signal generation and transmission by simulation. The IQ modulator is driven by a 2-Gbaud/3-Gbaud 16-QAM-modulated baseband signal.The MZM is driven by a radio frequency signal at the frequency of 30 GHz to generate optical frequency comb. The generated 390 GHz THz-wave radio frequency signal after heterodyne beating in uni-travelling photodiode (UTC-PD) is transmitted over 0 km/10 km single-mode-fiber transmission. The 390-GHz electrical vector THz-wave signal carring 16-QAM modulation can be generated with a bit error ratio (BER) of less than the hard-decision forward-error-correction (HD-FEC) threshold of 3.8e-3. To the best of our knowledge, it's the first time to generate 390 GHz photonic vector THz-wave signal on the basis of simple MZM-based optical frequency comb.

In this paper, an implementation method of high sensitivity thin film fiber optic pressure sensor based on air blowing method is proposed. The utility model is characterized in that a film ultra-thin microbubble structure is firstly formed on the surface of the AB epoxy glue solution by using high-pressure air, and then the film portion of the end portion of the microbubble is transferred to a single-mode fiber head with a hollow glass tube at the top. Finally, a thin film structure fiber Fabry-Perot fiber pressure sensor is formed. The experimental results show that the thickness of the thin film layer at the end of the FP sensor is only 16 μm. Correspondingly, the maximum pressure sensitivity can reach 263.15 pm/kPa. Meanwhile, due to the decrease of film thickness, the sensor's resistance to temperature interference is improved. The prepared fiber Fabry-Perot pressure sensor has the advantages of ultra-thin film thickness, high-pressure sensitivity, low cost and good repeatability. Therefore, it has good application value in high sensitivity pressure and sound wave detection.

We demonstrate experimentally an optoelectronic oscillator (OEO) in which high side-mode suppression is achieved by cascading a phase modulator-based single passband tunable microwave photonic (MWP) filter with an optoelectronic feedback loop-based infinite impulse response (IIR) MWP filter. The OEO provides an RF oscillation that can be tuned from 6.5 GHz to 17.8 GHz with a phase noise lower than -103 dBc/Hz. Experimental results show that inclusion of the IIR section leads to a 20 dB reduction of phase noise close to the carrier and an increase of 10 dB in side mode suppression, compared to the equivalent OEO without an IIR section. The OEO was used to drive an optical frequency comb generator to generate a THz signal at 242.6 GHz by optical heterodyning; inclusion of the IIR section increases suppression of the side modes neighboring the THz carrier. A radio over fiber link was then implemented at a 242.6 GHz carrier frequency, with transmission of a 24 Gbps signal over 40 km of fiber and a 30 cm wireless path at a bit error rate below the forward error correction limit. The proposed system may be applied to frequency reconfigurable THz links and radars.

The imaging quality of sparse aperture telescope systems is degraded by several factors including design, manufacturing, and arrangement errors. To achieve a high-resolution, the optical system requires an accurate control of not only the wave-front errors such as the piston and tip-tilt but also the decenter errors. Decenter diminishes the field of view of synthetic systems heavily and causes frequency shifting as well. In this paper, we firstly present an approach to sense the decenter of the sparse aperture telescope using the multi-beam interference method based on phase shift and centroid extraction algorithm. The most attractive point of our method is that it can sense not only the decenter but also the other wave-front errors simultaneously, but does not need to install any additional sensors. The numerical simulations are described and preliminary experiments are performed for validation, demonstrating that this technique is efficient and accurate and could be used to guide future sparse aperture telescope error correction.

Ion beam finishing techniques of aluminium mirrors have a high potential to meet the increasing demands on applications of high-performance mirror devices for visible and ultraviolet spectral range. Reactively driven ion beam machining using oxygen and nitrogen gases enables the direct figure error correction up to 1 μm machining depth while preserving the initial roughness. However, the periodic turning mark structures, which result from preliminary device shaping by single-point diamond turning, often limit the applicability of mirror surfaces in the short-periodic spectral range. Ion beam planarization with the aid of a sacrificial layer is a promising process route for surface smoothing, resulting in successfully reduction of the turning mark structures. A combination with direct surface smoothing to perform a subsequent improvement of the microroughness is presented with a special focus on roughness evolution, chemical composition, and optical surface properties. As a result, an ion beam based process route is suggested, which allows almost to recover the reflective properties and an increased long-term stability of smoothed aluminium surfaces.

Telecommunication networks are becoming the central linking institution of the Fourth Industrial Revolution. To cope with the associated capacity and connectivity challenges, transportation networks may explore the -neglected so far- remaining transmission bands in the second and third low attenuation windows of the optical fibre overcoming the C-band barrier. To assess the potential of optical multi-band transmission systems to upgrade a European Operator's network, we have developed a planning tool based on a routing engine that exploits a novel Physical Layer Aware, Routing, Modulation and Spectral Assignment algorithm. We considered unrepeatered transmission exploiting fibre amplifiers tailored to each transmission band. Taking into account the performance of close to commercialization fibre amplifier devices, we estimated the impact for the most detrimental effects in multi-band transmission like ASE accumulation, FWM and SRS. With the aid of this planning tool, we demonstrate the potential of multi-band systems to upgrade network capacity without compromising the connectivity between Core nodes, albeit new physical layer challenges. Nevertheless, it is shown that multi-band systems allow higher operational flexibility that may slow-down the need to deploy additional C-band fibres. Moreover, we have shown that the roll out of these multi-band systems could be planned in phases in order to limit first-day capital expenditure.

A novel photonic scheme of binary modulated microwave signals generation based on a dual-polarization quadrature phase-shift keying (DP-QPSK) modulator is proposed and experimentally demonstrated. The scheme is highly reconfigurable, amplitude keying signal (ASK), phase-shift keying signal (PSK) or frequency-shift keying (FSK) signal can be generated by appropriately setting the amplitude of the binary coding signal. The coding signal and local oscillator (LO) signals are independent with each other, binary modulated microwave signals can be generated with arbitrary coding rate and carrier frequency. The frequency deviation of the FSK signal can also be adjusted flexibly. No filter is used in the scheme and the tuning range is large. A proof-of-concept experiment is carried out to verify the feasibility of the proposed system. A 1-Gbps 8-GHz microwave ASK signal, a 0.5-Gbps 6-GHz microwave PSK signal, and a 0.5-Gbps 8/12-GHz microwave FSK signal are g[enerated in the experiment.

Highly nonlinear multimode optical integrated devices hold great promise for the emerging large-capacity mode division multiplexing (MDM) technology, and they correspondingly enable multimode optical signal processing at nodes of the MDM network. Here, we propose a highly nonlinear multimode organic-silicon slot waveguide (HN-OSSW) whose nonlinearity is greatly improved by the intensive optical field confinement in the nano-gaps filled with highly nonlinear organic material. Specifically, the achieved nonlinear coefficients of the HN-OSSW under TE0 and TE1 modes are estimated higher than 7000 W-1m-1 and 5800 W-1m-1, respectively. Also, by phase mismatch optimization, this nanostructure exhibits superior intramode four-wave mixing conversion efficiency but ignorable intermode crosstalk. Coupling efficiency of the mode multiplexer and the optimal nonlinear interaction length are discussed in detail. Based on the HN-OSSW, we then numerically demonstrate a multimode all-optical hexadecimal addition and subtraction for sixteen phase-shift keying (16PSK) signals with the operation rate of 1.28Tb/s. Six different logic operations including A+B-C, A+C-B, B+C-A, A+B, A-B and B-A are simultaneously obtained with good performance evaluations, indicating the promising prospect of the HN-OSSW applied in ultrafast multimode signal processing.

A tunable photonic microwave frequency up-conversion scheme using opto-electronic oscillator (OEO) based on a monolithic integrated three-section laser without any electro-optic modulator (EOM) or filter is proposed. By adjusting the monolithic integrated three-section laser to operate in the period-one (P1) dynamical state, the signal carrier frequency up-converted from the intermediate frequency (IF) to the frequency at the difference and the summation between the oscillation frequency of OEO and IF can be realized. The tunability of the up-converted frequency can also be greatly guaranteed just by altering the control currents of the monolithic integrated three-section laser induced P1 frequency. In this paper, an IF of 2 GHz with 10 Msymbol/s 16-QAM signals is successfully up-converted to 16 GHz and 20 GHz simultaneously. The up-converted frequencies can be tuned from 16 GHz/20 GHz to 19 GHz/23 GHz, and the error vector magnitudes (EVMs) of all those up-converted signals satisfy the limitation in satellite communication.

Visible light communication(VLC), which combines communication and illumination, is regarded as a potential wireless communication. For illumination requirements of VLC systems, dimming control is a significant function. Many schemes have been proposed for multi-input multi-output (MIMO) VLC systems or dimmable VLC systems, but few schemes combine the two. The dimming control scheme that has been proposed for MIMO-VLC systems in the reference still has a probability for improvement in spectral efficiency and error performance. This paper proposes a dimming control scheme that utilizes the constant weight space-time codes (CWSTC) to improve spectral efficiency and error performance for MIMO-VLC systems. Simultaneously, we also present the codeword structure and a low implementation complexity detection algorithm for the scheme. Finally, performance analysis and simulation results provide comparisons between the proposed scheme and other existing dimming control schemes.

We show that a 70-nm dielectric nanoparticle placed on the optical axis near the surface (at a distance less than 100 nm) of a high-NA gradient microlens made of silicon, which is illuminated by a laser beam of 1.55 μm wavelength, is attracted to the lens surface with a piconewton force. The profile of the lens refractive index is described by a hyperbolic secant function. If a cut-out is made in the lens output surface, then the nanoparticle will be pulled into this cut-out, producing a kind of 'optical magnet'. If a reverse energy flow is to be generated on the optical axis near the output surface of such a gradient lens, this will lead to an absorbing dielectric nanoparticle being pulled toward the surface with a greater force than a similar non-absorbing particle. In the absence of a reverse flow, both absorbing and non-absorbing particles will be attracted to the surface with an equal force. The electromagnetic fields involved are calculated using a finite difference time domain (FDTD) method and the acting forces are calculated using a Maxwell stress tensor.

For several centuries, far-field optical microscopy has remained a key instrument in many scientific disciplines, including physical, chemical, and biomedical research. Nonetheless, far-field imaging has many limitations: the spatial resolution is controlled by the diffraction of light, and the imaging speed follows the Nyquist–Shannon sampling theorem. The recent development of super-resolution techniques has pushed the limits of spatial resolution. However, these methods typically require complicated setups and long acquisition times and are still not applicable to deep-tissue bioimaging. Here, we report imaging through an ultra-thin fibre probe with a spatial resolution beyond the Abbe limit and a temporal resolution beyond the Nyquist limit simultaneously in a simple and compact setup. We use the random nature of mode coupling in a multimode fibre, the sparsity constraint and compressive sensing reconstruction. The new approach of super-resolution endo-microscopy does not use any specific properties of the fluorescent label, such as depletion or stochastic activation of the molecular fluorescent state, and therefore can be used for label-free imaging. We demonstrate a spatial resolution more than 2 times better than the diffraction limit and an imaging speed 20 times faster than the Nyquist limit. The proposed approach can significantly expand the realm of the application of nanoscopy for bioimaging., Microscopy: Bio-imaging beyond limits A new procedure for imaging living cells and tissues using an ultra-fine optical fibre to detect light from fluorescent dyes overcomes fundamental limits restricting existing methods. Lyubov Amitonova and Johannes de Boer developed and demonstrated the technology at the Free University of Amsterdam in the Netherlands. Optical imaging has previously been subject to constraints known as the Abbe and Nyquist limits. The Abbe limit sets the smallest distance that can be resolved at about half the wavelength of the light. The Nyquist limit determines the fastest rate at which a light signal can be sampled. The researchers have achieved fluorescence microscopy more than three times better than the Abbe limit and 20 times faster than the Nyquist limit. Their breakthrough is based on innovative light manipulation and sampling procedures in a simple and compact set-up.

A filterless radio-over-fiber system to generate 40 and 80 GHz millimeter-wave was proposed by using two Mach-Zehnder modulators (MZMs). The two MZMs are biased at the maximum transmission point to suppress odd-order sidebands. By adjusting the modulation index of the two MZMs and the radio frequency drive signals, only the two 2nd and 4th order sidebands are retained. Subsequently, by adjusting the polarization direction to generate 40 and 80GHz frequency millimeter-wave signal. Detailed theoretical analyses and simulations are provided. The simulation results show that the 40 GHz millimeter-wave signal was obtained with 30 dB optical sideband suppression ratio (OSSR) and the 80 GHz millimeter-wave signal was obtained with 25 dB OSSR. Thanks to the higher OSSR, the generated MMW signal is not greatly affected by power fluctuations during transmission or frequency tuning. Furthermore, the effects of the modulation index, bias voltage and extinction ratios deviate from the ideal value on millimeter-wave performance are also analyzed and verified, showing the proposed scheme is relatively flexible from the limitation of filter fixed bandwidth and economical.

The establishment of laser communication relies on high probability acquisition and then stably track with a high precision. However, the limitation of laser divergence and the interference may lead to unstable acquisition and tracking. In this paper, we proposed a novel beaconless acquisition approach to achieve the coverage of a large uncertainty cone with a narrow communication beam, using a composite spiral scanning method based on fast steering mirror and servomechanism system. The modeling and an analytical expression of sub-regions searching in conjunction with spiral skip overlap are described to realize the effective coverage. A detailed analysis of optimal matching for acquisition parameter is presented to quantify the design result. For the tracking procedure, an experiment is presented to investigate the performance of servo system with the combination of coarse-fine tracking consideration, and iteration learning control scheme in additional to the traditional controller based on periodic external disturbance is introduced for dynamic target tracking system. The iterative control law is taken into account to adjust deviation value and further improve the tracking performance. The obtained tracking accuracy is within ±2μrad which demonstrates the effectiveness the control characteristic in the presence of laser fluctuation.

A novel approach to simultaneous radiofrequency self-interference cancellation (SIC) and frequency down-conversion in a unified system is proposed and demonstrated experimentally based on cascade Mach-Zehnder modulators (MZM). The local oscillator signal is injected into the MZM1, whereas the received RF signal and the reference signal are fed into MZM2 and MZM3. After photoelectrical conversion by a balanced photodetector, the desired intermediate frequency signal with SIC is obtained. The cancellation depth for the single frequency SIC with frequency down-conversion is around 38 dB, and that for a wideband signal is around 19 dB. No electrical delay and attenuation are used in the proposed system, so it can potentially reach a wider frequency band and a higher cancellation depth.

Gallium Nitride (GaN) based light-emitting diodes (LEDs) are being utilized in an ever expanding number of applications. The persistent issues, however, have been the use of alternating current (AC) to direct current (DC) converters and the inefficient p-type doping compared to n-type doping. Here, a novel hybrid AC InGaN quantum well (QW) LED without a p-GaN layer is demonstrated at 450 nm. A tunneling LED is fabricated through use of InGaN QWs, combined with a thin Al2O3 dielectric with NiO as the source of the holes. This hybrid InGaN LED utilizes Fowler-Nordheim tunneling and band bending in order to inject holes into the active region. Due to the symmetric nature of the tunneling, hole or electron injection through the top oxide layer leads to AC performance. Room temperature and cryogenic I-V measurements are performed to evaluate the tunneling mechanism. Tunneling of holes is found to lead to earlier device turn-on of ~0.5 V compared with conventional blue LEDs at ~2 V. The presented work can lead to a number of novel applications such as on-chip communication, monolithic integration with transistors, and LiFi.

A novel method is proposed to select vortex beams carrying a specific orbital angular momentum (OAM) mode in turbulence heterodyne coherent mitigation (THCM) link. It is worth mentioning that intelligent phase matching (IPM) of the OAM beams based on the convolutional neural network (CNN) is the remarkable feature. Namely, CNN is particularly trained as the OAM modes classifier by the light intensity distribution patterns of different modes. The classifier actually acts as a mode detector to distinguish OAM modes by the map between the light intensity distribution and OAM mode, and then output mode information (MI). Specially, the phase matching technology is demonstrated to realize selection of specific OAM mode, where exploiting MI to select a specific phase mask is a characteristic of IPM. Subsequently, the phase mask is attached to the Gaussian beam to obtain the OAM beam carrying a special mode. Numerical results show a high IPM accuracy of 99% under medium strength atmospheric turbulence (AT).

A novel frequency quasi-linear swept light source based on multi-frequency time-matched spectrum stitching and recirculating frequency shifter loop (RFSL) is proposed and successfully demonstrated. The seed light with different frequencies enters RFSL in turn through optical delay line to complete the frequency sweep and spectrum stitching of each band. Spectrum stitching can effectively reset the noise, suppress the accumulation of amplified spontaneous emission (ASE) noise and the spectral sideband noise in RFSL, and expand the sweep range several times without affecting the sweep linearity. A swept range of 5.227 nm is experimentally achieved with the noise range of 7.78 dB. Compared with the single-frequency sweep scheme that the noise variation is 9.03 dB, the sweep range is extended by more than three times. The Pearson's correlation coefficients (r) of the output swept signal is higher than -0.99996.

The Facility for Rare Isotope Beams (FRIB) will be a new scientific user facility that produces rare-isotope beams for experiments from the fragmentation of heavy ions at energies of 100–200 MeV/u. During the projectile fragmentation, the rare isotope of interest is produced along with many contaminants that need to be removed before the beam reaches detectors. At FRIB, this is accomplished with a magnetic projectile fragment separator. However, to achieve higher beam purity, in particular for proton-rich rare isotopes, additional purification is necessary. RadiaBeam in collaboration with Michigan State University (MSU) has designed a 20.125 MHz radiofrequency (RF) fragment separator capable of producing a 4 MV kick with 18 cm aperture in order to remove contaminant isotopes based on their time of flight. In this paper, we will discuss the RF and engineering design considerations of this separator cavity.

Integrating multiple functionalities into one single device is of great importance for ever-growing demand of photonic device. Optical vortex beam contains orbital angular momentum (OAM) and spin angular momentum (SAM) associated with phase and polarization singularities respectively, which has contributed to various application including optical manipulation, optical trapping and high-speed optical communication. Traditional methods to detect its phase and polarization mostly focus on the functionality of single dimensional optical field. However, quite different from the previous reports, we here propose a novel approach to measure the phase and polarization state based on the full use of near and far-field light functionalities in one single metadevice, which supports spin-controlled surface plasmon polaritons (SPPs) and topological charge-dependent focus spot position. On the one hand, this design makes the most of multidimensional field optical scattering characteristics to rich the functions of metadevice. On the other hand, it provides a novel concept to recognize various angular momentum information of vortex beam. We believe that such design will have great potential for the integration of different sub-wavelength optical components.

Subject of Research. The paper analyzes the current concept of digital twins in relation to production systems. The review is given for characteristics and parameters of the digital twin that create advantages of using this concept for production systems at their life cycle stages. Technical implementation variants for the concept of digital twins are proposed aimed at improvement of the technological processes of production systems at the following stages of the life cycle: an idea, project, realization, operation, and disposal. Method. We performed a retrospective analysis of scientific papers on the methodology and practical application of software-based approaches to the design, implementation and operation of industrial systems in Industry 4.0. An expert assessment and applicability analysis of the digital twins at the stages of the life cycle of production systems are given. Main Results. The main characteristics of the digital twin affecting the effectiveness of the concept application in production systems are determined and arranged into groups according to their importance based on the analysis of the foreign studies over the past 10 years. The advantages and disadvantages of a software-oriented approach application to the design, implementation and operation of production systems are formulated. Practical Relevance. The digital twin characteristics are determined that affect the efficiency of its usage at the life cycle stages of production systems. Variants of the modern concept technical implementation of digital twins for production systems are proposed by applying of advanced digital technologies and intelligent electronic devices. Requirements are systematized concerning functionality, performance, correspondence accuracy of the virtual and physical environment state, as well as the qualitative characteristics of the digital twin. They provide for the assessment about the applicability of digital twins for solving existing problems of control and management in production systems.

We propose a new approach to non-contact recording of respiratory function based on the analysis of a sequence of Infrared-terahertz images of the human face, allowing the processes that occur during breathing to be visualized. To obtain quantitative estimates of the respiratory function, two methods are proposed. The first one utilizes a probe which implements the function of spatial differentiation and provides high sensitivity, but requires an increased accuracy of positioning the probe at the nasal opening and scaling in accordance with the camera angle. The other one is a histogram method for obtaining quantitative estimates of the external respiratory function, which is scale invariant and does not require precise positioning, but has a lower sensitivity compared to the first one. The methods proposed have made it possible to remotely evaluate the respiratory rate, which correlates well with the data obtained by a contact method of respiratory function registration.

Subject of Research. The paper presents a study of prediction method for various properties of reactions, such as the type of reaction, suitable groups of solvents, catalysts for the reaction. Molecular fingerprint differences between products and reagents were calculated using the RdKit chemical library as a representation of the reactions. Molecular fingerprints are widely used to predict various properties of molecules. Knowledge of the reaction conditions is essential for successful planning of retrosynthesis. Chemical informatics methods can effectively find the relationship between reaction reagents and the necessary conditions for the reaction. At this, the costs of time and resources spent on the determination of the necessary set of conditions for the reaction are reduced. Prediction of solvent groups can significantly improve the quality of models and the applicability of approaches. Method. LightGBM and a neural network with Deep Feature Selection were taken as machine learning models. The results were evaluated with the F1-metric. For the models training and evaluation, the data was broken down into chemically dissimilar parts. Bayesian optimization was used to optimize the searching of parameters. Main Results. Experiments were carried out to predict the reaction type, catalysts and solvent groups for the reaction. The obtained results show that the MLP type of reaction can be predicted equal to 0.99, a MLP catalyst equal to 0.7, and MLP group of solvents equal to 0.68 with F1-metric based on the difference in molecular fingerprints between reagents and products of machine learning models. Significant quantity of catalysts and solvents are considered in the paper. Practical Relevance. Automated planning of retrosynthesis is one of the topical areas of research. During planning, a sequence of necessary reactions is drawn up. The considered method can be used for recommendation system development that can suggest a possible group of catalysts and solvents to a chemical specialist, and, thus, reduce the cost of resources and time to determine the necessary reaction conditions.

Subject of Research. The paper considers the inferring of gene regulatory networks in the form of Bayesian networks from gene expression data. We present this problem as the problem of the marginal probability estimation for each edge appearance in the true Bayesian network under the known gene expression levels. Monte Carlo approach based on the Markov chains is proposed. Method. The proposed method involved the sampling of Bayesian network pairs and a discretization policy, providing a way for the network to be applied to continuous gene expression data according to a posteriori distribution. The Markov chain Monte Carlo approach was used for sampling with implementation via the Metropolis-Hastings algorithm. Then, the desired probabilities were estimated based on the obtained sample. Main Results. The proposed method is tested on simulated data from the DREAM4 Challenges. Comparison with the leaders shows that the developed method quality surpasses the leader among the existing methods, the regularized gradient boosting machines method (RGBM), on some tests and is comparable on the others in view of the results. At the same time, the proposed method is flexible enough and can be adapted to the other types of experimental data. Practical Relevance. The method is applicable in computational biology for research of the gene regulation mechanisms in various processes, including the tumor growth or the immune system operation.

We investigate a multispiral phase plate (MSPP) with multiple centers of phase singularity arbitrarily located in the MSPP plane. Equations to describe the topological charge of an optical vortex in the initial plane immediately behind the MSPP and orbital angular momentum (OAM) normalized relative to the beam power are derived. The topological charge in the initial plane is found as a sum of the topological charges of all singularities if their centers are located inside a finite-radius circular aperture. If the phase singularity centers are partially located on the boundary of a circular diaphragm limiting the MSPP, the total topological charge is found as the sum of all singularities divided by 2. Total OAM that the vortex carries depends on the location of the singularity centers: the farther from the center of the plate the singularity center is located, the smaller is its contribution to the OAM. If all singularity centers are located on the boundary of the diaphragm limiting MSPP, then the OAM of the vortex beam equals zero, although in this case the topological charge of the beam is nonzero.

In this paper, we demonstrate a method to generate a low-chirp ultra-wideband pulse (UWB) signal based on a silicon single-drive push-pull segmented Mach-Zehnder modulator (SMZM). The concept is analyzed theoretically and demonstrated experimentally. We get positive monocycle pulses with different relative time delays between the two driving signals. The center frequency and fractional bandwidth of the generated positive monocycle pulse is 5.97 GHz and 161% with a relative time delay of 56 ps. By changing the operating point of the SMZM, we can get negative monocycle pulses. We modulate the UWB signals with on-off keying and pulse position formats by properly coding the driving signal. As far as we know, this is the first time to realize low-chirp UWB signals using only one silicon modulator. The successful generation of UWB signals poses a significant step in realizing a compact low-cost and low-chirp UWB generator on the silicon photonics platform.

TM-pass polarizers are pivotal components of photonic integrated circuits (PICs), especially those intended for biosensing applications. In the literature, several silicon TM-pass polarizers have been proposed, designed and experimentally demonstrated, but their insertion loss is not compatible with the current trend of silicon photonics aimed at exponentially increasing the component density within PICs. Herein, we propose and design a TM-pass polarizer whose insertion loss is carefully minimized to 0.05 dB at wavelength 1.55 μm by utilizing a combination of an asymmetric directional coupler and a mode evolution section. The adoption of appropriate technical solutions makes this record insertion loss value compatible with a high extinction ratio equal to 38 dB. With a device footprint of only 2.5 × 20 μm2, the design exhibits an insertion loss less than 1.7 dB and extinction ratio better than 30 dB over a large bandwidth of 200 nm. The design assumes the constraints of a typical silicon photonics open-access technological process and a standard 220 nm silicon-on-insulator (SOI) wafer. A very low sensitivity of the achieved performance to reasonable fabrication inaccuracies is demonstrated, with a worst-case insertion loss of only 0.32 dB at wavelength 1.55 μm.

The effects of the jet engine turbulence on a Gaussian Schell-Model (GSM) beam array propagating in a jet engine plume are studied theoretically. The analytical expressions of the cross-spectral density (CSD) function, the spectral degree of coherence (DOC) and the mean-squared beam width for a GSM beam array propagating through a jet engine plume region are derived based on the extended Huyens-Fresnel integral. It is found that the profile of spectral density and the DOC of a GSM beam array gradually transfer to an elliptical shape as the propagation distance increases, and the elliptical degree becomes greater with increasing source coherence length. Besides, as the source coherence length decreases, the effect of the jet engine turbulence on the beam broadening is smaller and the profile of the DOC appears sidelobes at short distance. It is also found that the values of effective coherence width nearly remain the same for different values of source coherence length after propagating a certain distance. Furthermore, the effects of the number of beamlets on the beam width and effective coherence width are investigated in detail.

High-precision positioning of two underwater mobile robots based on laser beams alignment has been investigated in this work. Usually, the control problem addressed in laser beams aims to maintain the position of the receiver robot aligned with the transmitter robot despite the effects of noise and active disturbances. In this paper, a new state space model is proposed. The latter is more precise than the usual used two state space model [1]. Furthermore, an estimation based control strategy using Extended Kalman Filter Estimator (EKF) and Linear Quadratic Regulator (LQR) is proposed to achieve the control objectives. LQR controller is well known as optimal control design with better tuning flexibility along with intrinsic robustness properties such as noise and output disturbance rejections. The achieved performance of the proposed controller is compared to the conventional proportional (P), Proportional-Integral-Derivative (PID) and Proportional-Integral (PI) controller to analyze the improvements and stability. In addition, an investigation of a sensitivity analysis is conducted to show robustness with different process noise variances of LQR controller.

Optical wireless communication (OWC) systems can exhibit high percentage availability, yet suffering from frequent intensity fades caused by turbulence effects and pointing errors. The intuitive method to character the link is using commercial bit error rate testers (BERT) by measuring the output sequence of the receiver, which provides limited information. Thus we propose the algorithms for measuring the outage and synchronization performance, bit error rate (BER), throughput, and fading statistics. The inputs consist of decoded data sequence and received optical power. Both the bit level and packet level measurements are presented. Then a fading characterization tester (FCT) having these functions is implemented based on a field programmable gate array (FPGA). Our indoor experiment reveals the measurement accuracy of the FCT by comparing the measured results with the derived theoretical ones. Another 1.9 km OWC experiment is also carried out. These measured results by FCT are presented, which can not only measure the OWC link, but also help the researchers to improve the system performance, such as the design of error correction approaches like forward error correction, the design of packet based network protocols.

Classification of the land cover types from multi- and hyperspectral (HS) imagery is traditionally carried out on the basis of analysis of scatter plots of pixel values in a multidimensional feature space, which are used as brightness in individual channels. To increase the reliability of HS image classification, approaches are used based on simultaneously accounting for the characteristics of each pixel and the nearest-neighbor pixels, i.e., on the joint analysis of spectral and spatial features. The pixel neighborhood analysis is performed at various stages of the classification process. In this work, using a test hyperspectral image, the efficiency of spectral-spatial data classification methods that take into account spatial information at various stages of processing is studied. Special attention is paid to selecting the size of the spatial processing core. It is shown that the best results are obtained by combining pre-processing of raw data before performing the procedures of pixel-by-pixel spectral classification and post-processing of the resulting maps. Prospects of multi-scale smoothing of initial images, with the increase of the number of spectral-spatial features being multiple of the number of the scales, are shown.

The buildings are very complex for detection on SAR images, where the basic features of those are shadows. There are many different representations for SAR shadow. As result it is no possible to use convolutional neural network for building detection directly. In this article we give property analysis of SAR shadows of different type buildings. After that, each region (ROI) prepared for training of building detection is corrected with its own SAR shadow properties. Reconstructions of ROI will be put in a modified YOLO network for building detection with better quality result.

A monolithic integrated dual-wavelength DFB laser with inverse-Gaussian apodized sampled Bragg grating (IGASBG) is proposed and investigated. The IGASBG in the DFB laser is achieved by varying the duty cycle of sampled Bragg grating. The frequency spacing between the two lasing modes can be designed from 38 GHz to 660 GHz which covers almost the entire millimeter-wave range and reaches terahertz. The results proposed in this paper have great reference value for fabricating dual-wavelength semiconductor lasers.

This paper presents a proposal of a new optical multi-context blind scrubbing that can not only increase the soft-error tolerance of the configuration memory of field programmable gate arrays (FPGAs) but also support high-speed dynamic reconfiguration suitable for accelerating FPGA operations. The optical multi-context blind scrubbing operation uses a holographic memory as a soft-error free radiation-hardened external memory. It exploits its two-dimensional large-bandwidth optical bus. Optical multi-context blind scrubbing operation was demonstrated with four configuration contexts. The soft-error tolerance of the scrubbing operation was evaluated using a radiation tolerance experiment using two 4-MBq Americium-241 alpha particle sources. Results show the worst case mean time to repair (MTTR) of the scrubbing operation as 560 ns, which can realize sufficient soft-error tolerance in radiation-rich space environments.

Subject of Research. The paper deals with Bayesian method for hyperparameter optimization of algorithms, used in machine learning for classification problems. A comprehensive survey is carried out about using a priori and a posteriori knowledge in classification task for hyperparameter optimization quality improvement. Method. The existing Bayesian optimization algorithm for hyperparameter setting in classification problems was expanded. We proposed a target function modification calculated on the basis of hyperparameters optimized for the similar problems and a metric for determination of similarity classification problems based on generated meta-features. Main Results. Experiments carried out on the real-world datasets from OpenML database have confirmed that the proposed algorithm achieves usually significantly better performance results than the existing Bayesian optimization algorithm within a fixed time limit. Practical Relevance. The proposed algorithm can be used for hyperparameter optimization in any classification problem, for example, in medicine, image processing or chemistry.

Supercontinuum covering the ultraviolet-blue region is highly useful for fluorescence microscopy. Four zero-dispersion wavelength decreasing photonic crystal fibers with different fiber cross structures and taper profiles are fabricated to extend the short wavelength edge of supercontinuum. Both nanosecond and picosecond pump pulses at 1 μm are used to generate supercontinuum. With a 3 ns pump pulse, the short wavelength edge of supercontinuum is extended to below 400 nm in a fiber with high air-hole ratio (named T3). The underlying mechanism of supercontinuum generation is explored. The short and long wavelength edges of supercontinuum are highly related with the phase-matching condition which decided by the group velocity curve of fiber small core end. With a 10 ps pump pulse, the spectral intensity around ~800 nm increases in all four fibers. However, the intensity in shorter wavelength band decreased in fibers with a high air-hole ratio (named T3, T4). The experimental results imply that a zero-dispersion wavelength decreasing photonic crystal fiber suitable for nanosecond pulse pumping is not necessarily suitable for picosecond pulse pumping, especially for fibers with high air-hole ratio.

We determined the optical and electrical characteristics of GaN-based, ultraviolet micro light emitting diodes (microLEDs). Such microLEDs are essential to next-generation high-resolution micro-displays. Square-shaped microLEDs of different sizes (side lengths: 5-50 μm) were designed. The peak emission wavelength of these devices shifted

Micro- and nanoscale photonic structures and devices play important roles in the development of advanced biophotonic systems, in particular, implantable light sources for optogenetic stimulations. In this paper, we numerically investigate silicon (Si) photonics based microprobes that can achieve multi-site, multi-spectral optical excitation in the deep animal brain. On Si substrates, silicon nitride (Si3N4) based planar waveguides can deliver visible light in the deep tissue with low losses, and couple to grating emitters diffracting light in targeted brain regions. In our model, we combine near-field wave optic and far-field ray tracing simulations, showing that the designed photonic structures spectrally split blue, green and red photons into different locations in the tissue. Furthermore, by introducing dual grating components, photons at different wavelengths can be spatially separated at different depths. Therefore, these photonic probes can be used to selectively activate or inhibit specific neurons and nuclei, when expressing various corresponding light sensitive opsins. We anticipate that such device strategies can find wide applications in the design of advanced implantable photonic systems for neuroscience and neuroengineering.

We numerically demonstrated six types of pulses in an Yb-doped fiber laser, including dissipative soliton (DS), dissipative soliton resonance (DSR), multipulse, noise-like pulse (NLP), breathing soliton and soliton explosion. The influence of cavity conditions on DSR pulse properties is discussed systematically. It is found that the change of the saturation power of saturable absorber (SA) could transform DSR into various types of pulses. Saturation power of SA and injected signal affect the number and shape of multipulse. Furthermore, the influence of the saturation power of SA and intra-cavity dispersion on pulse type is diagrammed intuitively. By properly adjusting the transmission curve of SA, breathing soliton and soliton explosion can be obtained as well.

We demonstrate a high-power on-chip 1550-nm laser implemented by passive flip-chip integration of a curved-channel, double-pass InGaAsP/InP slab-coupled optical waveguide amplifier (SCOWA) onto a photonic integrated circuit (PIC) containing a silicon nitride (SiN) waveguide and distributed Bragg reflector (DBR) grating. The combined chip-scale SCOW external cavity laser (SCOWECL) has single mode emission with 312 mW of optical power at a drive current of 2.5 A, and exhibits a side mode suppression ratio (SMSR) of 55 dB, peak photon conversion efficiency (PCE) of 10%, low relative-intensity noise (RIN) of ~160 dB/Hz, and an integrated linewidth of 192 kHz. Additionally, we demonstrate a multi-wavelength SCOWECL array comprised of four SCOWAs coupled to SiN-waveguide DBR gratings. The four-element array generates 80 mW per channel when the SCOWAs are driven in parallel (1.25 A/channel) with ~1-nm wavelength spacing centered at 1533 nm. We describe the fabrication and hybrid integration processes. The measured SCOWA-to-waveguide coupling loss is estimated to be 1.6 +/-1.0 dB which agrees well with the simulation.

We have experimentally demonstrated tunable multi-wavelength bright-dark and dark-bright pulse pairs in an all normal dispersion Yb-doped fiber laser (YDFL) with a long cavity configuration. By carefully adjusting the pump power and the polarization state, bright-dark pulse pairs could be converted into dark-bright pulse pairs at the same wavelength. The comb filter provided by the tapered fiber facilitated the formation of the multi-wavelength pulses. And the wavelength-tunable for both bright-dark pulse pairs and dark-bright pulse pairs could be achieved by using a tapered fiber and rotatable polarization controller in the cavity to control the cavity losses. The tunable ranges were 14 nm and 4 nm with wavelength spacings of ~3.5 nm and ~3.7 nm for dual-wavelength pulse pairs and triple-wavelength pulse pairs, respectively.

With the advantages of high positioning accuracy and low cost, visible light positioning (VLP) is becoming a promising solution for practical indoor positioning system. However, most of the VLP systems require at least two VLP LED lamps for accurate position calculation. Therefore, the application of VLP in practical scenarios may be restricted due to this limitation. In this paper, we propose a fast and high-accuracy single-LED based VLP system. Firstly, an unbalanced single-LED VLP algorithm is proposed to increase the positioning accuracy and reduce the computational complexity. Secondly, a fast beacon searching algorithm is proposed to further reduce the processing time for each captured image. Finally, since the proposed algorithms have the advantages of high accuracy and low complexity, the proposed system can also be implemented on a low-end hardware platform. Experimental results show that the average positioning error of the proposed system is decreased to 2.26 cm at the height of 3 m, and the average positioning time is reduced to 6.3 ms on a laptop and 60ms on a low-end embedded platform.

Polarimetry in the far ultraviolet (FUV) is a powerful tool in many applications such as UV/EUV ellipsometry, characterization and control of the beam polarization status in large scale facilities and solar physics. FUV polarizers are among the most difficult components to manufacture, mainly due to the lack of dichroic and transparent materials in this spectral range. Although many different solutions for their fabrication have been investigated in the last decades, surprisingly, the use of Wire Grid Polarizers (WGPs) is still poorly investigated in this spectral region. In this work, two different concepts of WGPs have been designed and optimized for the FUV range: one is based on absorptive nano-wires on top of an highly reflective substrate, and the second one is based on highly reflective nano-wires on top of an absorptive substrate. Different wires' shapes have been considered and relative structures optimized at a target wavelength of 121.6 nm. Two very promising solutions have been selected, which exhibit a polarization degree over 99.9% and a TE-reflectance over 0.2. Their sensitivity to the wires' dimension parameters have been investigated to assess their feasibility.

Measurements of the absolute sensitivity of three different optical cameras are presented. An absolutely calibrated tungsten strip-lamp was used for calibrating the devices. An experimental method for determining the solid angle which is accepted by the combination of the cameras with a broadband apochromatic lens is described. The results with five bandpass filters between 337nm and 740nm are shown. The signal to noise ratio and the spatial resolution of the camera systems is also discussed.

A photonic method of highly reconfigurable microwave waveform generation based on time-wavelength interleaving has been proposed and experimentally demonstrated. By modulating multi-wavelength laser sources with Mach-Zehnder modulators (MZMs), multiple Nyquist pulses corresponding to different wavelengths are generated and overlapped with each other in the time domain. A dispersion compensation fiber (DCF) is used to separate these pulses due to the wavelength dependent delay. These pulses add together after photodetection and form desired waveforms. By controlling the wavelengths and powers of multiple laser sources, we can obtain various desired waveforms with tunable repetition rates and duty cycles. Experimentally, 9 waveforms including square, triangle, sawtooth, reversed-sawtooth and trapezoid with tunable repetition rates from 3 GHz to 6 GHz and duty cycles from 20.9% to 58.4% are obtained. This work demonstrates the great potential of incoherent time-domain synthesis for highly versatile arbitrary waveform generation.

Subject of Research. The paper considers analysis of mechanical and optical properties of modern optical polymer materials. We present the result of design and quality characteristics of small magnification telescopic glasses, made of modern optical polymers and intended for application in medicine, production of microelectronic circuits, and jewelry. Method. Calculation of telescopic glasses is carried out according to Galileo scheme on the basis of the automated method of aberration correction. The requirements are fulfilled concerning the necessity exception of additional accommodation of eyes at transition from observation with and without glasses, due to the object and image location in one plane. Main Results. The obtained optical system has diffraction image quality, and the mass of fully polymer glasses is two times lower than that of analogues made of glass. Practical Relevance. Modern optical polymers have advanced mechanical and optical properties, and create the perspective of glass component replacement with polymer ones and fabrication of fully polymeric optical systems with high quality characteristics. At the same time, manufacturing technologies of components made of optical polymers provides to obtain surfaces of complex shape (kinoforms, aspherics, and “freeforms”). Technical problems can be solved associated with the scaling of production, reducing of the assembly labor intensity, updating of the design, reducing of the mass and dimensional properties, and the cost of products.

The numerical simulation and selection of optimal parameters of the diffraction grating for a newly developed technology for the manufacture of plane waveguide systems are performed. In contrast to the use of ready-made silicon wafers on an insulator, the new technology has been developed for the manufacture of a fully autonomous radiation input system, a coupling element and the waveguide itself. A general description of the technology of the ‘radiation input – propagation – radiation output’ system is given. Concrete fabrication parameters of the lattice height, the substrate and coating layers are found. The coupling efficiency of radiation input into the waveguide is found to be 30%.

Subject of Research. The paper presents a new method for distribution evaluation of the reflective characteristics over a given volume — control zone. This distribution makes it possible to identify inhomogeneities, detect and evaluate the reflective characteristics of small-size objects in a homogeneous environment. The problem is solved using a probing ultra-wideband continuous signal and a set of receiving sensors. Method. The method is based on the principles of the tomography approach in signal processing — multichannel tomography. The control zone is divided into resolution elements. The distribution of the reflective characteristics is searched in a discretized form as the reflective characteristics vector with each component equal to reflective characteristic of corresponding resolution element. Specific effective scattering surfaces are considered as reflective characteristics of resolution elements. According to the principles of the multichannel tomography, a vector-matrix mapping equation is obtained, in which the reflection vector is the original, and the mapping is the measurements of the receiving sensors combined into a vector. This equation is the starting point for the reflection vector evaluation. Three variants of estimation are considered: the pseudo-inversion method, the pseudo-inversion method with averaging, and a new method based on correlation processing. Main Results. The analysis is carried out on the capabilities of the proposed method by computer experiments for the distribution evaluation of reflective characteristics by resolution elements, into which the area of responsibility is divided. Experiments have shown the advantage of the correlation method: this method, in contrast to pseudo-inversion methods, makes it possible to identify reflective resolution elements both when their number increases in the control zone and in the presence of the probing signal distortions. Practical Relevance. The results of the work can find application, for example, in the field of subsurface probing to identify inhomogeneities in a homogeneous medium.