Laser Channel Research Articles

Unsupervised Clustering-based 3D Static Scene Construction Using LiDAR Channel and Azimuth Angle

Abstract. Cameras are typically used at road intersections to collect data to perform object detection but struggle in low-light and harsh weather. On the other hand, Light Detection and Ranging (LiDAR) is used as a key technology in 3D vision systems. It gives the 3D point cloud, which includes accurate depth information, but its resolution is cost-dependent, with higher resolutions being more expensive. Deep learning-based method requires large, labelled dataset which increases the cost, time and accuracy depending on the model trained on labelled dataset. To perform object detection in point cloud data is a challenging task due to the incomplete representations, data sparsity and unavailability of training data. To overcome this by using an unsupervised approach, it is important to identify the static scene and then detect the moving object. This work incorporated a novel approach to construct static scene using azimuth angle and laser channel information using an unsupervised clustering approach. This work incorporates two modules I) data collection using VLP-16 LiDAR, and II) static scene construction using DBSCAN (density-based spatial clustering and noise) clustering-based approach. Data is collected at a 4-legged intersection and pre-processed to extract aggregated distances corresponding to the unique pair of azimuth angle and laser channel. DBSCAN is used to perform clustering on the aggregated distances, based on the highest silhouette score and lowest intra distance between points in cluster, static points are identified, and static scene constructed. The qualitative evaluation of method demonstrates that the algorithm effectively and accurately filters out background points.

Time evolution of coherent state’s photon number statistics in laser channel gained via cumulant calculation

In this paper, by using the method of integration within the ordered product of operators and entangled state representation, the degree of second-order coherence of coherent state evolving in a laser channel is derived for the first time, which exhibits its anti-bunching property. The master equation of the laser channel is solved by entangled state representation, and the cumulant for deriving mean and mean-square photon numbers is evaluated.

Characterization of bright betatron radiation generated by direct laser acceleration of electrons in plasma of near critical density

Directed x-rays produced in the interaction of sub-picosecond laser pulses of moderate relativistic intensity with plasma of near-critical density are investigated. Synchrotron-like (betatron) radiation occurs in the process of direct laser acceleration (DLA) of electrons in a relativistic laser channel when the electrons undergo transverse betatron oscillations in self-generated quasi-static electric and magnetic fields. In an experiment at the PHELIX laser system, high-current directed beams of DLA electrons with a mean energy ten times higher than the ponderomotive potential and maximum energy up to 100 MeV were measured at 1019 W/cm2 laser intensity. The spectrum of directed x-rays in the range of 5–60 keV was evaluated using two sets of Ross filters placed at 0° and 10° to the laser pulse propagation axis. The differential x-ray absorption method allowed for absolute measurements of the angular-dependent photon fluence. We report 1013 photons/sr with energies >5 keV measured at 0° to the laser axis and a brilliance of 1021 photons s−1 mm−2 mrad−2 (0.1%BW)−1. The angular distribution of the emission has an FWHM of 14°–16°. Thanks to the ultra-high photon fluence, point-like radiation source, and ultra-short emission time, DLA-based keV backlighters are promising for various applications in high-energy-density research with kilojoule petawatt-class laser facilities.

Photo-Receiving Device for Conversion of Energy and Data Transmitted Via Atmospheric Laser Channel

Photo-Receiving Device for Conversion of Energy and Data Transmitted Via Atmospheric Laser Channel

C + L band ultra-widely tunable SOA hybrid fiber laser based on acousto-optic add-drop filter induced by polarization conversion

Scientific and industrial applications have put forward new requirements for the wavelength tuning range of continuous-wave lasers. Herein, the constructed filter based on the acoustically-induced polarization conversion in single-mode fiber (SMF) covers the wavelength from 1464.2–1640.8 nm, and the tuning range is about ∼176.6 nm. The lasing wavelength is managed by the acousto-optical interaction in the SMF. Moreover, the gain spectrum of semiconductor optical amplifier (SOA) is flat and wide, which can achieve a wide range of laser tuning. Hence, we propose and demonstrate an ultra-widely tuning range ring cavity C + L tunable SOA hybrid fiber laser. Eventually, the tuning channel of the fiber laser is from 1527.3–1613 nm with the tuning range of about ∼85.7 nm, and its tuning range is determined by the gain bandwidth of SOA. The measured output power and center wavelength variations of the proposed fiber laser over a long-term observation are less than 0.11 mW and 0.44 nm, respectively. This work opens up a new way to expand the tuning range of other types of lasers.

Switchable and tunable multi-wavelength random distributed feedback fiber laser based on parallel Lyot filter

A switchable and tunable multi-wavelength random distributed feedback fiber laser based on a parallel Lyot filter is designed, and the transmission characteristics of the filter are deduced in detail by using the transmission matrix theory. The randomly distributed backward Rayleigh scattering generated in single-mode fiber (SMF) serves as a feedback mechanism. The number of output wavelength increases linearly with the increase of pump power. By adjusting the polarization controller (PC) to control the polarization state of the beam into the polarization maintaining fiber (PMF), laser channels with wavelength interval of 0.88 nm or 0.46 nm can be output. Where the wavelength interval depends on the wavelength phase difference caused by the corresponding branch PMF. The intensity-dependent loss (IDL) caused by the nonlinear optical loop mirror (NOLM) in the experimental structure is not only used to suppress the intense mode competition caused by EDF, but also to control the spectral range of the output wavelength to achieve tunable laser output. When the wavelength interval is 0.88 nm, the wavelength tuning ranges of the three and four laser channels are 4.4 nm and 3.7 nm, respectively. When the wavelength interval is 0.46 nm, the wavelength tuning ranges of the three and four laser channels are 3.7 nm and 4 nm, respectively. Subsequently, the influence of using different lengths of SMF on the output wavelength is analyzed. It is found that longer SMF can increase the linewidth of the laser channel, and the side mode suppression ratio (SMSR) will be improved to 39 dB. In addition, the output power fluctuation of the laser is less than 0.32 dB within 30 min, and the power amplitude and SMSR are stable at −4.47dBm and 34.5 dB, respectively, indicating that the laser can achieve flat and stable multi-wavelength output at room temperature.

Elimination of signal amplitude disturbance in ghost imaging using an auxiliary laser channel.

Ghost imaging can be used to detect objects in a nonstationary environment or in the presence of variable ambient light, making it attractive when conventional imaging methods are ineffective. However, the conventional ghost imaging algorithm is susceptible to temporal fluctuations in the detected signal. In this work, we propose a polarization-multiplexed auxiliary laser channel propagating along the same optical path with the main one. The signal in the auxiliary channel is used as a reference and allows the elimination of signal disturbance. A quantitative analysis and comparison of the proposed method's performance to the high-pass filtering method are demonstrated. For an illumination pattern refresh rate of 10Hz, effective suppression of bucket signal fluctuations has been experimentally demonstrated. For a disturbance frequency from 1Hz to 10Hz, the auxiliary channel method demonstrated a ghost image Pearson correlation coefficient (PCC) of not less than 0.70, while the high-pass filtering method showed a PCC sharp drop from 0.65 to 0.02.

Tunable and switchable multi-wavelength actively Q-switched random fiber laser based on an electro-optic modulator and Sagnac loop filter.

In this article, an actively Q-switched multi-wavelength random fiber laser based on a Sagnac loop filter and electro-optic modulator is proposed and demonstrated experimentally. The random distributed feedback media is a section of a 25km long single-mode fiber. When the pump power is 350mW, the polarization angle of the Sagnac loop filter can be adjusted by polarization controller to achieve the switching of a single, double, triple, and quadruple channels laser output. In the case of a single laser channel, dual laser channels, and three laser channels output, multiple laser channels can be tuned simultaneously with a fixed wavelength interval. In addition, by changing the waveform of the external signal source, the light and dark pulses can be switched. Owing to the half-open cavity structure and the high gain of the erbium-doped fiber, the laser threshold was reduced to 25mW, and the light conversion efficiency was 0.67%. The laser is an ideal light source for medical imaging and long-distance sensing.

OCDMA Codeword Switching Technique to Avoid Interference of Time-of-Flight LiDAR System for Autonomous Vehicles

The direct time-of-flight (d-ToF) technique is the most promising method for light detection and ranging (LiDAR) systems in long-range autonomous applications. However, the receiver cannot distinguish its own pulse signal from those of other LiDAR systems. This causes mutual interference between LiDAR systems, which degrades object recognition. The optical code division multiple access (OCDMA) modulation technique can be used to avoid mutual interference. However, it is difficult to secure sufficient orthogonal codes, because each laser channel uses a designated codeword. In addition, when interference occurs in a specific direction, it can occur continuously. Adversarial attacks on a LiDAR system can trick a vehicle to perform false object recognition without physical contact. This can endanger passengers, pedestrians, and other vehicles. Therefore, we propose an OCDMA codeword switching technique that can effectively solve these problems in driving environments. First, we analyzed the characteristics of optical orthogonal codes (OOC) and defined the interference generated in LiDAR systems. The proposed technique exhibits interference robustness by using a code index buffer based on differences in the received optical signal power. In addition, verification of the hardware implementation and its complexity was analyzed using LiDAR testbench and an FPGA. The interference and continuous interference of the proposed technique in various driving environments were verified using simulation model. Compared with using only a designated codeword, the proposed technique reduces interference by 82.59% and 85.51%, and continuous interference by 92.24% and 96.94% in straight-line and curved driving, respectively.

Условия проведения и баллистическая схема космического эксперимента по беспроводной передаче электрической энергии

The paper discusses conditions for conducting sessions of the Pelican space experiment on wireless transmission of electrical energy in the laser channel between the Russian Segment of the International Space Station and the Progress transport cargo spacecraft. Experiment objectives, composition and installation of the Pelican scientific equipment for its implementation are briefly considered. Ballistic schemes that meet requirements for conducting the space experiment, as well as the safety requirements, are proposed. Feasibility of the experiment sessions is shown from the point of view of compliance between parameters of the Progress spacecraft and the Station relative motion and capabilities of the emitter guidance system elements. Characteristic speed expenditures were evaluated with the Progress spacecraft maneuvering to perform repeated passages of the station. The estimates obtained confirm possibility of at least five sessions of the space experiment with one Progress spacecraft.

Superradiant parametric x-ray emission

We compute a spectrum of parametric x-ray radiation inside a crystal from a bunch of electrons, which is periodically modulated in density. We consider that the bunch of electrons is exiting from an x-ray free-electron laser (XFEL) channel. We demonstrate that in the case of a resonance between the frequency of parametric x-ray radiation and a frequency of modulation of an electron bunch, the sequence of strong quasimonochromatic x-ray pulses is formed---superradiant parametric x-ray emission (SPXE) with frequencies that are multiples of the modulation frequency. The number of photons in the pulse of SPXE in the case of extremely asymmetric diffraction is comparable with the photon number in the pulse of an XFEL. Moreover, the SPXE is directed under the large angle to the electron velocity and every harmonic in the spectrum is emitted under its own angle.

Compact Brillouin comb laser in Chalcogenide fiber assisted by four-wave mixing

We experimentally demonstrate a multiwavelength Brillouin comb generation employing a segment of As2S3 chalcogenide fiber as the Brillouin gain medium. The extremely high nonlinear and Brillouin gain coefficients allow the As2S3 fiber length to be as short as 4.2 m. A compact Brillouin comb laser composed of multiple Brillouin Stokes and anti-Stokes channels is generated from the As2S3 fiber either with or without ring cavity feedback through the interaction of stimulated Brillouin scattering and four-wave mixing effects. Different output couplings are used to extract the Brillouin comb laser when the cavity feedback is connected. A high laser power of 927 mW and multiple laser channels of 20 are achieved with an output coupling of 90 % and 10 %, respectively. A trade-off between the power threshold, laser channel number, output power and slope efficiency should be considered when optimizing the optical performance of the multiwavelength Brillouin laser.

GAN based simultaneous localization and mapping framework in dynamic environment

ObjectiveBecause of interference from dynamic objects, the traditional simultaneous localization and mapping (SLAM) framework execute poorly while operational in a dynamic environment. The Dynamic-SLAM model is introduced by considering the merits of deep learning in object discovery. At the semantic level, the dynamic objects in the new detection are detected to construct the prior knowledge with an SSD object detector. Among the radar and the LiDAR, the synchronization and conversion calibration makes the multi-sensor fusion. Localizing using a camera in a dynamic environment is more challenging because the localization process takes place in moving segments. This further results in unstable pose estimation. A large amount of information of the visual point cloud and high precision of the laser radar information enhances the accuracy of real-time positioning thereby attaining grid map and 3-D point cloud map. MethodsHere, we have proposed Generative Adversarial Network (GAN) with Aquila Optimizer for moving object detection. The LiDAR measurements check the Radar outcomes. The targeted moving objects are determined via Doppler velocity from the radar and their exact location and mass can be estimated with LiDAR and the proposed GAN-AO approach. Hence the GAN-based AO approach is used to segment the objects inside the point clouds. The arrangements of point clouds are made in a particular range to multiply the vertical points with the laser channel number. If the same objects are identified then the angles are analyzed among the image vectors and then labeled identically for the same points of the object. In addition to this, Velocity compensation is made to estimate the actual moving target from the world frame. This is due to the fact that the estimated velocity of the mmW-radar is in the radial direction with respect to the touching sensors. ResultsThe investigation is conducted between different state-of-art methods like Deep Learning (DL), Generative Adversarial Network (GAN), artificial neural network (ANN), Deep neural network (DNN) and propose methods. From this analysis, the proposed method provided 93.8% detection accuracy than other existing methods like DL, ANN, GAN and DNN respectively. ConclusionsWhile comparing to the state-of-art techniques, the proposed method demonstrated superior performance results in terms of tracking, detection, root mean square error (RMSE) and accuracy.

Effect of ultrasonic vibration on porosity suppression and columnar-to-equiaxed transition in laser-MIG hybrid welding of aluminum alloy

Severe porosity and coarse columnar grain are prone to be formed in the laser-MIG welded joint of aluminum alloy, deteriorating the strength and ductility seriously. In this study, the ultrasound was designed to assist the laser-MIG hybrid welding of aluminum alloy, and the influence of ultrasonic vibration on weld formation, porosity, and microstructure was investigated. The weld depth was increased from 3.6 to 4.2 mm when external ultrasound with the pressure of amplitude transformer (PAT) of 132 N was used, indicating that the penetration ability of hybrid heat sources to the welded plate could be improved. It was attributed to the dispersion effect of ultrasound on arc plasma in the laser channel. The porosity rate was reduced from 5.66 to 1.05% under PAT of 132 N, because of the increase in escape velocity of bubbles. Moreover, the columnar to equiaxed transformation (CET) of grain in the weld was promoted and the width of columnar grain zone was gradually reduced with the increasing ultrasonic energy, owing to the breaking effect of cavitation and the stirring effect of acoustic stream. As a result, lower porosity rate and finer grain size led to improvement of the microhardness and the strength of weld by ultrasound. The study provides more guidance on employing ultrasound to improve the quality of welded joints.

Optical Imaging Visualizes a Homogeneous and Horizontal Band-Like Biodistribution of Large- and Small-Size Hydrophilic Compounds Delivered by Ablative Fractional Laser.

The skin barrier generally limits the topical delivery of hydrophilic molecules. Ablative fractional laser (AFL) facilitates cutaneous drug uptake of smaller hydrophilic compounds in several studies. In this imaging-based study, we aim to investigate the cutaneous biodistribution of two different-sized hydrophilic compounds delivered by an ablative fractional CO2 laser at minimally invasive settings. Intact or CO2 AFL-pretreated (2.5 mJ/mb and 5% density) ex vivo porcine skin was topically applied with a large or small hydrophilic compound (fluorescence labeled antibody nivolumab (150,000 g/mol, n = 4) or ATTO 647N (746 g/mol, n = 3)). Samples were incubated for 20 h in a Franz cell setup, whereafter optical coherence tomography (OCT) was used to assess laser channel depth, and ex vivo confocal microscopy (EVCM) was used to assess epidermal thickness and cutaneous biodistribution of nivolumab and ATTO 647N. With an EVCM-assessed median epidermal thickness of 70.3 µm and OCT-assessed ablation depth of 31.9 µm, minimally invasive settings enabled shallow penetration into the mid-epidermis. The AFL-assisted uptake of the antibody nivolumab and the smaller compound ATTO 647N showed a similar homogenous and horizontal band-like biodistribution pattern that reached mid-dermis. No uptake of nivolumab or ATTO 647N was observed in intact skin. In conclusion, AFL-induced mid-epidermal laser channels facilitates the cutaneous delivery of two hydrophilic compounds that are distributed in a similar homogeneous and horizontal band-like pattern, irrespective of their molecular size.

Перспективы применения и отработка технологии беспроводной передачи электрической энергии между космическими аппаратами

The purpose of the study was to examine the state and possible fields of short-and-long term application of technology for spacecraft-to-spacecraft wireless transmission of electrical energy. The paper focuses on a space experiment on the transmission of electrical energy from the Russian Segment of the International Space Station to the Progress transport cargo ship in the laser channel and introduces an experiment scheme that provides the required duration of sessions, a given distance of energy transmission, as well as the fulfillment of the safety requirements for the station crew. The paper describes the scientific equipment “Pelican”, developed for the space experiment, specifies its features, gives its main characteristics and layout of blocks, and shows the ways to improve the equipment’s performance to ensure wireless transmission of energy in space.

Semi-natural simulation of the angular matching of the axes of the working and marker laser beams in a high-precision laser ranging system

This paper describes an automatic adjustment system designed to measure and automatically minimize the difference in angular mismatch between the optical axes of a working (probe) beam and a marker beam that simulates the optical axis of the detector channel in a laser ranging system. This paper is primarily focused on the specifications of the basic components of the measurement system (laser sources, controllable optomechanical components, and sensors used to measure the angular orientation of the laser beams) used to maintain precision angular matching of the working and marker laser beams in order to develop a process for semi-natural simulation of a precision laser ranging system to produce and study angular matching between the working and marker beam axes. This semi-natural simulation was used to model angular matching of the working and marker laser beams in a high-precision laser ranging system; the simulation was implemented using a laser system specifically developed for the purpose. The main results include a novel laser facility developed for semi-natural simulation of the angular matching of the probe (1064 nm) and marker (671 nm) beams in a laser ranging system where this difference in matching does not exceed 1″. The facility periodically relays images of the laser beams to a polarization-based unit for matching of the beams using spatial filters. The facility was used to obtain experimental data on the positional characteristics of a quadrant photodiode and CMOS-array digital camera used as a laser beam matching unit. We show that this type of digital camera is preferred since it does not require advance knowledge of the positional characteristic. Initially aligned laser beams were observed to randomly become misaligned due to angular instability in the laser beams. We have shown that the angular matching of the pulsed probe and CW marker beams can be automatically controlled using a motorized mirror installed outside the marker-beam optical system and also propose an algorithm for operation of the marker beam in this mode. The scientific value of this paper is based on the novel nature of the laser sensor facility, the experimentally measured characteristics of the hardware components used in the marker laser channel, and the fact that the matching of the pulsed and CW laser beams can be controlled by means of motorized mirrors. The paper has practical value in that a procedure has been developed for semi-natural simulation of the angular matching of probe and marker beams to support the design of high-precision laser ranging systems operating in the near-infrared spectrum.

Sub-nanosecond Intrinsic Response Time of PbS Nanocrystal IR-Photodetectors.

Colloidal nanocrystals (NCs), especially lead sulfide NCs, are promising candidates for solution-processed next-generation photodetectors with high-speed operation frequencies. However, the intrinsic response time of PbS-NC photodetectors, which is the material-specific physical limit, is still elusive, as the reported response times are typically limited by the device geometry. Here, we use the two-pulse coincidence photoresponse technique to identify the intrinsic response time of 1,2-ethanedithiol-functionalized PbS-NC photodetectors after femtosecond-pulsed 1560 nm excitation. We obtain an intrinsic response time of ∼1 ns, indicating an intrinsic bandwidth of ∼0.55 GHz as the material-specific limit. Examination of the dependence on laser power, gating, bias, temperature, channel length, and environmental conditions suggest that Auger recombination, assisted by NC-surface defects, is the dominant mechanism. Accordingly, the intrinsic response time might further be tuned by specifically controlling the ligand coverage and trap states. Thus, PbS-NC photodetectors are feasible for gigahertz optical communication in the third telecommunication window.

Modeling and analysis of channel impulse response for underwater wireless optical communication

Due to the uneven distribution of the underwater laser transmission channels, the transmission beam will be affected by water absorption and scattering effects, which induce inter-symbol interference and the degradation of link performance. Based on the binomial Henyey–Greenstein scattering phase function and considering the forward and backward effects, the pulse response expression of the non-line-of-sight underwater laser channel is derived. The effectiveness of the underwater photon transmission channel model established is simulated and verified by the Monte Carlo method. The fitting effects in the coastal waters between the theoretical calculation value of channel impulse response and simulation are better. Under the same simulation parameters, the pulse-broadening factor in coastal waters is higher than that in harbor waters, and the time-domain broadening effect of laser pulse transmission in harbor waters is large. When the asymmetry factor is large, the influence of front scattering on pulse broadening is greater.

Photo-receiving device for conversion of energy and data transmitted via atmospheric laser channel

A power-communicating photo-receiving device for an autonomous laser communication unit has been designed to receive energy from powerful laser radiation and convert it into electricity, as well as to simultaneously registration of information high-frequency optical signals. Keywords: wireless power transmission, laser beam, photo-receiving device, photovoltaic cell, high-speed photodiode.