Laser Range Research Articles

Aerial geodetic total station platform for precise active positioning in GNSS-degraded environments

One of the main applications of UAVs (Uncrewed Aerial Vehicles) is precise mapping; however, most of the studies are specialized either on rapid-mapping without focusing on characteristic point localization, or point positioning without concentrating upon the real-time or high accuracy. In this study, an active localization method for GNSS (Global Navigation Satellite System)-degraded environments is proposed using a custom-built UAV as an aerial geodetic total station platform. The UAV equipped with an RTK (Real-time-Kinematics)-GNSS receiver and an optimized gimbal that carries an optical sensor and a laser range-finder, is able to autonomously detect, track and localize fiducial targets, using the UAV's orientation and position, exporting their coordinates in WGS 84 geodetic reference system during the flight. The system has been validated with a significant number of experiments in various environments with increasing difficulty, providing a three-dimensional error in a range of 4–15 cm.

A Low-Cost and Robust Multi-Sensor Data Fusion Scheme for Heterogeneous Multi-Robot Cooperative Positioning in Indoor Environments

The latest development of multi-robot collaborative systems has put forward higher requirements for multi-sensor fusion localization. Current position methods mainly focus on the fusion of the carrier’s own sensor information, and how to fully utilize the information of multiple robots to achieve high-precision positioning is a major challenge. However, due to the comprehensive impact of factors such as poor performance, variety, complex calculations, and accumulation of environmental errors used by commercial robots, the difficulty of high-precision collaborative positioning is further exacerbated. To address this challenge, we propose a low-cost and robust multi-sensor data fusion scheme for heterogeneous multi-robot collaborative navigation in indoor environments, which integrates data from inertial measurement units (IMUs), laser rangefinders, cameras, and so on, into heterogeneous multi-robot navigation. Based on Discrete Kalman Filter (DKF) and Extended Kalman Filter (EKF) principles, a three-step joint filtering model is used to improve the state estimation and the visual data are processed using the YOLO deep learning target detection algorithm before updating the integrated filter. The proposed integration is tested at multiple levels in an open indoor environment following various formation paths. The results show that the three-dimensional root mean square error (RMSE) of indoor cooperative localization is 11.3 mm, the maximum error is less than 21.4 mm, and the motion error in occluded environments is suppressed. The proposed fusion scheme is able to satisfy the localization accuracy requirements for efficient and coordinated motion of autonomous mobile robots.

Recent Advances in Light Detection and Ranging: Optical Modulation Solutions and Novel Nanotechnologies

AbstractLight detection and ranging (LiDAR) sensor is widely recognized as a critical component for accurate perception. However, there are a host of challenges that impede their performance, including low spatial resolution, high costs, large size, low reliability, and susceptibility to interference. It is challenging to overcome these issues using a single LiDAR module, necessitating the need for a review of current LiDAR technologies. The paper commences by introducing the fundamental principles of various laser rangefinders and discussing the optical modulation technologies used to prevent interference and ghost images. Next, the paper delves into the latest developments in laser technology, with a focus on enhancing the switching rate, compliance with eye safety regulations, miniaturization, and improving stability. One highly promising innovation is the photonic crystal surface emitting laser (PCSEL), a novel light source that boasts high‐speed, small divergence angles, and high‐power output. Finally, the paper discusses the advancements made in non‐solid‐state scanning and solid‐state scanning, such as improving stability, increasing scanning angles, and optimizing the manufacturing of mechanical and micro‐electromechanical systems (MEMS). Additionally, the paper highlights the recent advancements in nanotechnology, specifically metasurface technology, which offers superior capabilities such as beam deflection, enhanced field‐of‐view (FOV), and dynamic modulation.

A human-centric system combining smartwatch and LiDAR data to assess the risk of musculoskeletal disorders and improve ergonomics of Industry 5.0 manufacturing workers

More than one in four workers reportedly suffer from back pain worldwide, leading to 264 million work days lost yearly. In the U.S. alone, it causes $50 billion in healthcare costs every year, up to $100 billion if including decreased productivity and lost wages. The upcoming Industry 5.0 revolution will introduce human-centric manufacturing systems where workers’ well-being comes first while safeguarding their rights: privacy, autonomy, and human dignity. This paper presents a privacy-preserving system based on artificial intelligence that tracks the posture of assembly/disassembly line workers while performing typical standardized tasks on repeat: connecting and separating parts; screwing and unscrewing using an electric screwdriver; tin soldering and unsoldering. The proposed solution assesses the upper-body (dominant arm, dominant shoulder, and trunk) and lower-body (legs) postures according to the ISO 11226 European standard, based on inertial data recorded by a smartwatch and using Laser imaging Detection and Ranging (LiDAR), respectively. These techniques preserve privacy as they collect data that cannot reveal the worker’s identity or sensitive information. Experiments showed that the system recognized a worker’s posture with a mean accuracy close to 98%. The system could help detect bad posture habits and reduce the chances of musculoskeletal disorders while preserving the workers’ privacy, in compliance with the upcoming Industry 5.0 paradigm.

LiDAR point cloud quality optimization method based on BIM and affine transformation

Laser Detection and Ranging (LiDAR) systems possess the capability to generate high-resolution three-dimensional (3D) data of indoor environments. The inherent uncertainties pertaining to relative spatial positioning and the centimeter-level precision of LiDAR ranging, however, contribute to discernible constraints within contexts requiring elevated degrees of precision, particularly in the domain of high-precision sensing applications. In response to this concern, this paper introduces an approach designed to mitigate and appraise the uncertainty associated with plane positioning through the utilization of point cloud fitting methodologies, concurrently integrating principles of building information modeling (BIM) and anisotropic affine transformations (AAT). Primarily, the methodology involves the extraction of precise plane characteristics employing the tenets of robustly weighted total least squares theory within the context of point cloud fitting. Subsequently, the method synergistically incorporates geometric information emanating from the Building Information Model alongside the accurately determined plane positioning data derived from LiDAR point clouds via AAT. This integration markedly enhances the precision of the ranging system’s datasets. Ultimately, the assessment of ranging uncertainty is conducted by quantifying the deviations of individual points from the conforming plane and employing a probability approximative scheme grounded in higher-order moments. Experimental results demonstrate the method’s precision and efficacy, offering a solution to the challenge of achieving higher perception precision in LiDAR-based ranging systems.

Enhanced precise orbit determination for GPS and BDS-2/3 with real LEO onboard and ground observations

Due to the current geographical situation in China that it is difficult to achieve globally well distributed ground monitoring stations for Chinese BeiDou Navigation System (BDS), the BDS Medium Earth Orbit (MEO) satellite orbital accuracy can be seriously affected by the insufficient length of continuous observation arc based on regional ground network. What is more, the highly static characteristics of BDS Geosynchronous Orbiting (GEO) satellites resulting in meter-level orbit determination accuracy is far from satisfactory for precise positioning services. In order to overcome these problems, the low Earth orbit (LEO) satellites serving as fast-moving space monitoring stations can be used as a good supplement for the current BDS ground monitoring stations layout. In this study, real measured spaceborne data from two LEO satellites, namely Fengyun-3D (FY-3D) and Tianjin University No. 1 (TJU-01), are collected and studied for the augmentation of BDS precise orbit determination (POD). The multipath errors of spaceborne code observations are comprehensively analyzed. It is found that not only BDS-2 relevant satellite-induced code bias but also near-field multipath errors, especially distinct in GPS, exist in a spaceborne environment. The piece-wise linear model is therefore established and applied to correct the code observations to reduce the multipath errors in the integrated POD processing. The GPS and BDS-2/3 POD solutions are compared with orbital overlapping differences and Satellite Laser Ranging (SLR) residuals validation. It is demonstrated that including the two LEO satellites can improve the orbit determination accuracy of GPS and BDS-2/3 significantly under a regional ground network, especially in the along component. The average overlapping orbital Root Mean Square (RMS) is decreased by 18.4 %, 34.3 %, 24.9 %, 21.4 %, and 7.8 % for the GPS, GEO, Inclined Geosynchronous Orbit (IGSO), BDS-2 MEO, and BDS-3 MEO satellites, respectively, in the along component. The RMS of SLR residuals is decreased from 37.1 cm to 17.8 cm for the GEO satellites, and the overall improvement is about 8 %-12 % for the BDS MEO satellites. There has also been a slight improvement under a global network, with an average improvement of 2–3 cm in the SLR residuals RMS. However, significant systematic errors are also observed in the SLR residuals in BDS GEO, IGSO, and MEO satellites, and are expected to be improved with refined observation models based on more LEO satellites, i.e., the phase center variation (PCV).

Multi-frequency self-injection locking of a FSR-tunable multimode laser diode.

This study presents the controllable multi-frequency self-injection locking regimes realization with an original experimental setup composed of a reflective semiconductor optical amplifier, an external feedback mirror, and a high-Q chip-scale Si3N4 ring microresonator. Our findings demonstrate the conditions of multiple modes' simultaneous locking being analogous to Vernier effect. We varied the free spectral range of the external-cavity laser by its length tuning, enabling the robust generations from 1 to 4 self-injection locked narrow lines on demand, that is important for optical telecommunications, and photonic-based microwave and THz sources.

Features of application in critical structures of products made by fused deposition using 3D printing technology

The technology of hot-melt 3D printing has prospects for military equipment and other special applications, provided that necessary requirements for the quality, strength and durability of plastic components are met. However, there is a problem of insufficient accuracy and unexplored patterns of change in technological parameters during 3D printing, which makes it necessary to manufacture critical structures using plasma deposition technology. The main purpose of the article is to study and evaluate the features of using the fused deposition method in 3D printing technology for the manufacture of products that are critical special-purpose structures and require increased strength and durability. To achieve this purpose, the technology and means of 3D printing by fused deposition method (filament feed control system with a circular encoder) have been improved. It has been established that the use of the filament feed control system can reduce the number of visually detected defects on the surface of printed products by an average of 71.7%, but increase the amount of wire consumed by 13% and the average printing time by 15-17%, which is due to the lack of supporting structures for the resulting surfaces. The research conducted in this paper has shown an increase in delamination strength of elements of critical structures, such as brackets for mounting a laser rangefinder to the body of an unmanned aerial vehicle. With the help of the filament feed control system, the strength of these elements has increased from 27.4 (tensile) and 32.1 (compressive) to 38 (tensile) and 44.3 MPa (compressive). There is also a more than 2.7-fold increase in the number of dynamic load cycles during endurance tests. This study indicates greater dynamic stability and less fatigue of the elements manufactured by fused 3D printing using a filament feed control system. The results will have practical applications in various fields, including military applications

High-precision and high-efficiency measurement method of accelerator tunnel control network based on total station angle observation

Given the importance of accelerator devices, major developed and emerging countries around the world have invested substantial human and material resources into the development, construction, and operation of more advanced large-scale accelerator devices. High-precision and high-efficiency alignment of the control network is crucial for the stable operation of accelerators. This study proposes a method for measuring tunnel control networks using total station angle observation. By taking advantage of the high precision of angle observation with a total station, we use the measured results of the designed and deployed control points measured by the laser tracker to simulate the total station angle observations, combined with some length scale values in the control network measured by the laser range finder. With the angle observations and several known distances, the point coordinates can be calculated by angle intersection methods. Only angle observations are used from total stations, while different length scale reference conditions are added to constrain the control network. This is done by calculating the point accuracy of the China Spallation Neutron Source circular accelerator. The overall plane point accuracy can reach 66 μm. By using this method, personnel will spend less time on the site and are at lower risk of radiation exposure, for example by automating measurements at night. This method can be used at nighttime for measurements, avoiding the need for daytime work and shielding employees from severe radiation exposure. By employing this method, efficiency can be increased twice. For on-site measurement, it enables monitoring and automated measurement during operation, as well as providing reference for the installation and measurement of tunnel control networks for large scale accelerators such as the Circular Electron Positron Collider.

A Novel Scouring Method to Monitor Nocturnal Mammals Using Uncrewed Aerial Vehicles and Thermal Cameras—A Comparison to Line Transect Spotlight Counts

Wildlife abundance surveys are important tools for making decisions regarding nature conservation and management. Cryptic and nocturnal mammals can be difficult to monitor, and methods to obtain more accurate data on density and population trends of these species are needed. We propose a novel monitoring method using an aerial drone with a laser rangefinder and high zoom capabilities for thermal imagery. By manually operating the drone, the survey area can be initially scanned in a radius of several kilometers, and when a point of interest is observed, animals could be identified from up to one kilometer away by zooming in while the drone maintains an altitude of 120 m. With the laser rangefinder, a precise coordinate of the detected animal could be recorded instantly. Over ten surveys, the scouring drone method recorded significantly more hares than traditional transect spotlight count surveys, conducted by trained volunteers scanning the same farmland area within the same timeframe (p = 0.002, Wilcoxon paired rank test). The difference between the drone method and the transect spotlight method was hare density-dependent (R = 0.45, p = 0.19, Pearson’s product–moment correlation); the larger the density of hares, the larger the difference between the two methods to the benefit of the drone method. There was a linear relation between the records of deer by the drone and by spotlight (R = 0.69, p = 0.027), while no relation was found between the records of carnivores by drone and spotlight counts. This may be due to carnivores’ speed and vigilance or lack of data. Furthermore, the drone method could cover up to three times the area within the same timeframe as the transect spotlight counts.

Analysis of the Impact of Atmospheric Models on the Orbit Prediction of Space Debris

Atmospheric drag is an important influencing factor in precise orbit determination and the prediction of low-orbit space debris. It has received widespread attention. Currently, calculating atmospheric drag mainly relies on different atmospheric density models. This experiment was designed to explore the impact of different atmospheric density models on the orbit prediction of space debris. In the experiment, satellite laser ranging data published by the ILRS (International Laser Ranging Service) were used as the basis for the precise orbit determination for space debris. The prediction error of space debris orbits at different orbital heights using different atmospheric density models was used as a criterion to evaluate the impact of atmospheric density models on the determination of space-target orbits. Eight atmospheric density models, DTM78, DTM94, DTM2000, J71, RJ71, JB2006, MSIS86, and NRLMSISE00, were compared in the experiment. The experimental results indicated that the DTM2000 atmospheric density model is best for determining and predicting the orbits of LEO (low-Earth-orbit) targets.

Research and Experiment on Soybean Plant Identification Based on Laser Ranging Sensor

When endeavoring to study the complex growth conditions of soybean plants under natural conditions, a problem arises due to the similar appearances of both soybean plants and weeds. To address this issue, a soybean plant recognition model based on a laser ranging sensor is proposed. To demonstrate the applicability of the soybean plant recognition model, experiments are conducted using ultrasonic sensors and laser ranging sensors to analyze the diameter, height, and spacing conditions in the model. A test environment is built, and during the pre-test, the laser range sensor detects objects with diameters of 3 mm and 5 mm with two and three measurement points, respectively, at a speed of 0.2 m/s. At a speed of 0.3 m/s, there is one measurement point for objects with 3 mm diameter and two measurement points for objects with 5 mm diameter. At 0.4 m/s, there are also one and two measurement points for objects with diameters of 3 mm and 5 mm, respectively. These results demonstrate that the laser range sensor can more accurately recognize the diameter conditions of soybean plants and weeds and can distinguish between the diameters of soybean plants and weeds. Subsequently, the recognition rate of the model is evaluated by observing whether the weeding mechanism can synchronize seedling avoidance after the soybean plant passes through the sensor. The recognition rates of the optimized model at speeds of 0.2 m/s, 0.3 m/s, and 0.4 m/s are 100%, 98.75%, and 93.75%, respectively. Upon comprehensive analysis, the soybean plant recognition model is determined to achieve a recognition rate of 98.75% at a speed of 0.3 m/s, which is considered a moderate speed, and demonstrates more stable recognition of plant diameters. The test further verifies the reliability and effectiveness of the method for distinguishing between soybean plants and weeds. The research results can serve as a reference for recognizing soybean plants based on the use of laser ranging sensors.

A Tutorial on Retroreflectors and Arrays Used in Satellite and Lunar Laser Ranging

The present paper discusses the basics of retroreflector theory and the manner in which they are combined in arrays to service the laser tracking of artificial satellites and the Moon. We begin with a discussion of the relative advantages and disadvantages of solid versus hollow cube corners and the functional dependence of their optical cross-sections and far-field patterns on cube diameter. Because of velocity aberration effects, the design of an array for a particular space mission depends on many factors, including the desired range accuracy and the satellite’s orbital altitude, velocity, and pass geometry relative to the tracking station. This generally requires the individual retroreflectors in the array to be “spoiled” by perturbing one or more of the 90-degree angles that define a perfect cube corner, or alternatively, by adding a curved surface to a hollow cube. In order to obtain adequate return signal strengths from all points along the satellite path, the rotational orientation of the retroreflectors within the array may need to be varied or “clocked”. Possible approaches to developing millimeter-accuracy arrays with both large cross-sections and ultrashort satellite signatures are discussed, as are new designs proposed to replace aging reflectors on the Moon. Finally, we briefly discuss methods for laser ranging beyond the Moon.

All-normal dispersion widely tunable dual-wavelength mode-locked fiber laser based on NALM.

We experimentally and numerically demonstrate the all-normal dispersion (ANDi) ytterbium (Yb)-doped fiber laser based on nonlinear amplifying loop mirror (NALM) mode-locked, which allows tunable single-wavelength and dual-wavelength outputs. The pulses tuning ranges of the dual-wavelength are from 1032.24 nm to 1053.13 nm and from 1047.94 nm to 1069.05 nm, and the repetition frequency difference varies from 1766Hz to 1834Hz. To our knowledge, this is the widest dual-wavelength tuning range of Yb-doped fiber lasers based on NALM mode-locked. We test for 90 minutes and have high stability in both single-wavelength and dual-wavelength. In addition, the pulsed collision dynamics between two solitons at different wavelengths are numerically studied. Numerical results show that during the pulse collision, the two solitons pass through each other and maintain their properties, which also confirms the particle nature of the isolated wave. Our research contributes to the dynamics of dual-wavelength solitons collision in NALM mode-locked fiber laser and provides what we believe to be is a new idea for tunable Yb-doped dual-comb sources.

Analysis of thermally-induced displacements of the HartRAO Lunar Laser Ranger optical tube: impact on pointing

The Hartebeesthoek Radio Astronomy Observatory (HartRAO) of South Africa is developing a Lunar Laser Ranging (LLR) system to achieve sub-centimetre range precision to the Moon. Key to this high precision expectation, which includes improving the overall operational performance of its telescope, is the thermal analysis of the telescope structure. In this study, thermal sensors were mounted on the thermally- important areas of the tube structure to measure the tube displacements emanating from the varying ambient air temperatures. A laser distance-measurement system was used for this purpose. Results showed that while the optical tube undergoes structural changes with changes in temperature, the tube position closer to the place where the spider assembly is mounted is unevenly displaced in three directions. In particular, for the time period considered in this study, it was found that the relative displacements on average at prisms 1, 2 and 3 in the vertical direction were 2.5540 ± 0.0007 m, 1.3750 ± 0.0008 m and 1.9780 ± 0.0007 m, respectively. The corresponding standard deviation (SD) values of ±0.0007 m, ±0.0008 m and ±0.0007 m denotes the average deviations that occurred in the vertical direction at the centre of prisms 1, 2 and 3, respectively. The generally higher SD of relative displacements in the vertical direction rather than in the easting and northing directions, suggest that the tube experienced greater variations in the vertical direction. Furthermore, the lower arc of the tube front, was found to have increased variability, and therefore it was hypothesised to introduce more elevation pointing offsets than azimuth for the LLR. This information constitutes an important input for guiding the efforts to determine the extent of the correction needed to be fed into the LLR telescope pointing model to counteract expected thermally induced pointing offsets.

Single-longitudinal-mode narrow linewidth broadband tunable Brillouin random laser including dispersion compensation fibers

We propose and demonstrate a single-longitudinal mode (SLM) narrow linewidth broadband tunable Brillouin random laser, including two segment dispersion compensated fibers (DCFs), in which enough narrowband Brillouin gain provided by a 2-km-length DCF to overcome the cavity loss, and Rayleigh backscattering (RBS) provided by a 1-km-length DCF form a mirrorless open cavity to continuously compress the laser linewidth. Compared to ordinary single mode fibers, DCF has an enhanced stimulated Brillouin scattering gain coefficient and RBS coefficient, which is attributed to its small core diameter structure, making the laser more compact and stable. Stronger random feedback effectively lowers the laser threshold, and enough Brillouin gain for multiple amplifications in random mode makes SLM operations more accessible. The proposed laser is with a threshold of ∼11 mW and an optical signal-to-noise ratio (OSNR) of ∼55.75 dB, the 3-dB linewidth and linewidth compression ratio of the output laser reaches ∼550 Hz and ∼236, respectively. By changing the wavelength of the pump laser, the laser wavelength can be continuously tuned in a broad wavelength range, which is only limited by tunable range of Brillouin pump laser. The laser wavelength fluctuation of 0.02 nm and the OSNR fluctuation of about 3 dB in a 30-minute measure period, indicating that the laser is with a good stability.

INTEGRATION OF IPHONE LiDAR WITH QUADCOPTER AND FIXED WING UAV PHOTOGRAMMETRY FOR THE FORESTRY APPLICATIONS

Abstract. The recent innovations in remote sensing technologies have given rise to the efficient mapping and monitoring of forests. The developments in the sensor implementation have mainly focused on optimizing the payload of the UAV system and allowed the users to acquire the data simultaneously with a range of active and passive sensors like high-resolution RGB cameras and multispectral cameras LiDAR (Laser Imaging Detection and Ranging). The main objective of this research contribution is to combine the Digital Elevation Model (DEMs) from quadcopter Unmanned Aerial Vehicles (UAVs), Fixed Wing UAV-based cameras, and iPhone datasets for the forest plots. The datasets from two vegetation seasons, namely leaf-off and leaf-on, were used to combine the Digital Elevation Models from different data acquisition platforms. This internship research work aims to create and experiment with new methods, techniques, and technologies for the applications of UAV photogrammetry and iPhone LiDAR in forest napping and inventory management. CHMs are also generated in this work which helps assess the conditions of the forests in the recreational areas, and the possibility of solutions like iPhone LiDAR and UAV photogrammetry would be highly efficient and economical. The leaf-off and leaf-on datasets were processed in Agisoft Metashape Professional software to generate dense point clouds for the forest plots. The point cloud from the leaf-on dataset was rasterized to generate a DSM whereas the leaf-off point cloud generated a DSM of the forest plots after ground filtering with Cloth Simulation Filter (CSF) plugin. The iPhone LiDAR point was also rasterized to a DTM product after pre-processing steps and noise removal. The Canopy Height Models (CHMs) were generated by subtracting UAV and iPhone LiDAR based DTMs from the UAV leaf on DSM. Finally, the accuracy assessment of CHMs from UAB datasets and their integration with iPhone LiDAR has been assessed using the accurate tree heights measured during the forest field visits. The proposed methodology can be used for forest mapping purposes where a moderate accuracy is requested.

Reduction of Satellite Signature Effect in High-Accuracy Satellite Laser Ranging to Etalon

Etalon is considered to be one of the most promising satellites for studying crustal motions, Earth rotation, and other scientific applications. Unfortunately, its outsized shape and signature result in a measurement range bias of several millimeters. On the basis of simulations of the echo signals, we analyze the center of mass corrections (CoM) for Etalon due to variations in satellite signature effect at different incidence angles. To minimize range bias caused by satellite signature effects, a center of mass corrections filter has been proposed for the processing of standard SLR data. According to the relationship between RMS of CoM and the upper limits of the rejection criteria, the measurements with the lowest variability of CoM are selected for normal points. Statistics indicate that the center of mass corrections filter can improve the stability of the collected data by 79%, and reduce the mean RMS of normal points from 163.7 × 41.8 ps to 118.2 × 8.94 ps. Additionally, the new algorithm is applicable to Etalon-2. In particular, this paper enriches and provides a useful reference for minimizing the effects of satellite signatures on the production of SLR data by providing a theoretical model that incorporates systematic errors in SLR.

Integrating a UAV System Based on Pixhawk with a Laser Methane Mini Detector to Study Methane Emissions

This article describes the process of integrating one of the most commonly used laser methane detectors, the Laser Methane mini (LMm), and a multi-rotor unmanned aerial vehicle (UAV) based on the Pixhawk flight controller to create an unmanned aerial system designed to detect methane leakages from the air. The integration is performed via the LaserHub+, a newly developed device which receives data from the laser methane detector, decodes it and transmits it to the flight controller with the protocol used by the ArduPilot platform for laser rangefinders. The user receives a single data array from the UAV flight controller that contains both the values of the methane concentrations measured by the detector, and the co-ordinates of the corresponding measurement points in three-dimensional space. The transmission of data from the UAV is carried out in real time. It is shown in this project that the proposed technical solution (the LaserHub+) has clear advantages over not only similar serial commercial solutions (e.g., the SkyHub complex by SPH Engineering) but also experimental developments described in the scientific literature. The main reason is that LaserHub+ does not require a deep customization of the methane detector or the placement of additional complex devices on board the UAV. Tests using it were carried out in aerial gas surveys of a number of municipal solid waste disposal sites in Russia. The device has a low cost and is easy for the end user to assemble, connect to the UAV and set up. The authors believe that LaserHub+ can be recommended as a mass solution for aerial surveys of methane sources. Information is provided on the approval of LaserHub+ for aerial gas surveys of a number of Russian municipal waste disposal facilities.

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.