Ring Laser Research Articles

A Low-Cost Modulated Laser-Based Imaging System Using Square Ring Laser Illumination for Depressing Underwater Backscatter

Underwater vision data facilitate a variety of underwater operations, including underwater ecosystem monitoring, topographical mapping, mariculture, and marine resource exploration. Conventional laser-based underwater imaging systems with complex system architecture rely on high-cost laser systems with high power, and software-based methods can not enrich the physical information captured by cameras. In this manuscript, a low-cost modulated laser-based imaging system is proposed with a spot in the shape of a square ring to eliminate the overlap between the illumination light path and the imaging path, which could reduce the negative effect of backscatter on the imaging process and enhance imaging quality. The imaging system is able to achieve underwater imaging at long distance (e.g., 10 m) with turbidity in the range of 2.49 to 7.82 NTUs, and the adjustable divergence angle of the laser tubes enables the flexibility of the proposed system to image on the basis of application requirements, such as the overall view or partial detail information of targets. Compared with a conventional underwater imaging camera (DS-2XC6244F, Hikvision, Hangzhou, China), the developed system could provide better imaging performance regarding visual effects and quantitative evaluation (e.g., UCIQUE and IE). Through integration with the CycleGAN-based method, the imaging results can be further improved, with the UCIQUE increased by 0.4. The proposed low-cost imaging system with a compact system structure and low consumption of energy could be equipped with platforms, such as underwater robots and AUVs, to facilitate real-world underwater applications.

Generation of dark pulses in mode-locked erbium-doped fiber ring laser using Ti2SnC absorber

Abstract We report the experimental observation of domain-wall type dark solitons in an all-fiber ring cavity erbium-doped fiber laser (EDFL) mode-locked with a Titanium Tin Carbide (Ti2SnC) saturable absorber (SA). The SA, featuring a modulation depth of 8.2%, was created by incorporating Ti2SnC particles into a polyvinyl film. Dark pulse formation is attributed to cross-phase coupling resulting from cavity birefringence. The mode-locked laser operates at 1559 nm with pump power ranging from 30.9 mW to 90.0 mW, achieving a maximum pulse energy of 1.73 nJ, a repetition rate of 1.78 MHz, and a pulse width of 261.2 ns.

A Tunable and Switchable Multi-Wavelength Erbium-Doped Fiber Ring Laser Enabled by Adjusting the Spectral Fringe Visibility of a Mach-Zehnder Fiber Interferometer

This paper presents a tunable, switchable multi-wavelength emission from an erbium-doped fiber ring laser, enabled by adjusting the spectral fringe visibility of a fiber interferometer filter. The filter is formed with specially designed concatenated tapered fibers to configure a Mach-Zehnder fiber interferometer (MZFI). The laser emission is highly flexible and reconfigurable, allowing for tuning between single- and dual-wavelength operation. The laser can switch sequentially from one up to six wavelengths by fixing the curvature and adjusting the polarization state. The lasing emission is generated over a stable wavelength range between 1559.59 nm and 1563.54 nm, exhibiting an optical signal-to-noise ratio (OSNR) exceeding ~35 dB. The performance of amplitude and wavelength fluctuations were evaluated, indicating an appropriate stability of ~3 dB and a shift less than 0.1 nm within a 45 min period at room temperature. A detailed comparison with the literature is given.

Technique and early results of endovenous laser ablation in morphologically complex varicose vein recurrence after small saphenous vein surgery.

Recurrences after varicose vein treatment occur frequently and represent a significant health and economic problem. In contrast to primary treatments of superficial truncal venous insufficiency, their management is often more difficult. Here we assessed the technical feasibility and early results of endovenous laser ablation (EVLA) for recurrences with stumps or subfascial meandering varices after small saphenous vein (SSV) surgery. This single-center retrospective study included 45 consecutive EVLA procedures from July 2019 to December 2021 in 40 patients (19 male, 21 female, mean age 62.8 ± 12.7 years). Patients had clinically relevant recurrent varicose veins after SSV surgery, with clinical, etiologic, anatomic and pathophysiologic (CEAP) classification stage of C2S or higher. We categorized the recurrences morphologically according to duplex sonographic criteria. Ablations were done with a 1470 nanometers laser and dual ring radial fibers and aimed at thermal closure as proximal as possible to the upper inflow. Analyses were performed by descriptive statistics and the Kaplan-Meier method. The primary outcome analyzed was the technical success, defined by thermal occlusion not requiring re-intervention during the observation period. The secondary outcome was the occurrence of postoperative complications. A complex morphology with residual stumps or tortuous venous connections to the popliteal vein was present in 35 cases (77.8%). Immediate technical success at the first postoperative visit after a median of 11 days (interquartile range 8-13 days) was 97.8%. During the follow-up period (median 77 days, interquartile range 13-256 days), 6 limbs (13.3%) required redo EVLA due to symptomatic persistent or newly presenting reflux. The median freedom from re-recurrence was 791 days. Otherwise, no medical or surgical complications requiring specific treatment were observed, particularly no endothermal heat-induced thrombosis (EHIT) or other thrombotic complications, and no nerve damage. According to our pilot data, EVLA is technically feasible for complex popliteal variceal recurrence, although the success rate appears substantially lower than for primary treatment of truncal venous insufficiency.

Stable and Tunable Erbium Ring Laser by Rayleigh Backscattering Feedback and Saturable Absorber for Single-Mode Operation

This work demonstrates a high-quality erbium-doped fiber (EDF) ring laser in the L-band gain range by combining the Rayleigh backscattering (RB) feedback signal and unpumped EDF induced saturable absorber (SA) filter. The optical filter effect induced by the RB feedback injection and EDF SA could generate single-longitudinal-mode (SLM) behavior and shrink the linewidth to sub-kHz. The output linewidth, power, and optical-signal-to-noise ratio (OSNR) of the fiber ring laser were also shown within the 42 nm wavelength bandwidth of 1565.0 to 1607.0 nm. Also, the instabilities of output power and central wavelength of each lasing lightwave were analyzed with a measurement time of 45 min.

Tunable Narrow Linewidth Erbium-Doped Fiber Ring Laser Based on Saturable Absorber and Self-Injection Feedback

Tunable Narrow Linewidth Erbium-Doped Fiber Ring Laser Based on Saturable Absorber and Self-Injection Feedback

Ultrasensitive detection of SCCA employing a graphene oxide integrated microfiber ring laser biosensor

Squamous cell carcinoma antigen (SCCA) is one of the most commonly detected cancer biomarkers for a variety of cancers. In this paper, a microfiber ring laser biosensor with a graphene oxide linking layer for SCCA detection was proposed and experimentally demonstrated. SCCA antibody immobilized on graphene oxide surface binds specifically to SCCA, and induces refractive index variation over the surface of the microfiber biosensor, which leads to a wavelength shift of the microfiber ring laser biosensor. The experimental results show that the proposed laser biosensor can detect SCCA with concentrations from 0.01 to 50 ng/mL, and the calculated detection limit can be as low as 1.3 pg/mL. Additionally, the label-free quantitative detection of SCCA using the proposed microfiber biosensor was verified experimentally according to the corresponding regression equation, and the results agree well with clinical examination detection. This constructed microfiber biosensor may have promising practical applications in analytical detection, medical diagnostics, etc.

Research on Point Cloud Acquisition and Calibration of Deep Hole Inner Surfaces Based on Collimated Ring Laser Beams.

In this study, a ring light point cloud calibration technique based on collimated laser beams is developed, aiming to reduce errors caused by the position and attitude changes of traditional ring light measurement devices. This article details the generation mechanism of the ring beam and the principle of deep hole measurement. It introduces the collimated beam as a reference, building on traditional ring light measurement devices, to achieve the synchronous acquisition of the ring beam and collimated spot images by an industrial camera. The Steger algorithm is employed to accurately extract the coordinates of the point cloud contours of both the ring beam and the collimated spot. By analyzing the shape and position changes of the collimated spot contour, the spatial position and attitude of the measuring device are precisely determined. This technique is applied to the 3D reconstruction of the inner surface of deep holes, ensuring the accurate restoration of the spatial positional attitude of the ring beam by incorporating the spatial positional attitude parameters of the measuring device to precisely calibrate the cross-sectional point cloud coordinates. Experimental results with ring gauges and deep hole workpieces demonstrate that this technique effectively reduces the percentage of point cloud data outside the tolerance range, and improves the accuracy of the 3D reconstruction model by 6.287%, thereby verifying the accuracy and practicality of this technique.

Microstructure and mechanical properties of 1 mm thin plate TC4 titanium alloy joint by ring laser welding

Abstract Ring laser welding was used to weld 1 mm thin plates TC4 titanium alloy, and the effects of different ring laser powers on the microstructure and mechanical properties of the weld were studied. The results indicate that the microstructure in the weld zone under different powers all contain basket structures, although the morphology of the martensite within the baskets differs. The microstructure in the weld zone is mainly composed of acicular α′ martensite, secondary α phase, and residual β phase. The microstructure in the heat-affected zone of the weld is mainly composed of acicular α′ martensite, initial α phase, secondary α phase, and residual β phase. The hardness of the weld is higher than that of the base metal, showing an overall trend of first increasing, then decreasing, and then increasing again before decreasing. The tensile specimens under different powers all fractured in the heat-affected zone of the weld, and the type of fracture is quasi-cleavage. At a laser power of 900 W, the weld has good formation, with minimal spatter on the surface, and good weld penetration. The microstructure of the weld is mainly composed of acicular α′ martensite, initial α phase, secondary α phase, and residual β phase. The hardness of the weld is 387.76 HV. The tensile strength and elongation are 1098.3 MPa and 12%, respectively.

Focal point technology: Controlling treatment depth and pattern of skin injury by a novel highly focused laser

Selective photothermolysis has limitations in efficacy and safety for dermal targets. We describe a novel concept using scanned focused laser microbeams for precise control of dermal depth and pattern of injury, using a 1550nm laser that generates an array of conical thermal zones while minimizing injury to the epidermis. To characterize the conical thermal zones invivo and determine safe starting parameters to transition to a second phase to explore potential clinical indications. A focused toroidal (ring) laser beam was delivered through a cold sapphire window, sparing epidermal injury in a central zone. Pulse energy, lesion depth, density, and energy delivery were titrated in exvivo human skin and subsequently on the backs of 21 human subjects. Histology showed microscale patterns of thermal injury, which varied predictably with laser parameters. Time-course healing through histology and skin surface imaging demonstrated the ability of the device to deliver high energies without sequelae. Clinical data are currently being collected to further explore the safety and efficacy of the device. The 1550nm laser with focal point technology enables precise control of lesion depth while simultaneously sparing a large portion of the epidermis, lowering the risk of adverse effects.

Enhancing Ring Laser Gyroscope data analysis through Neural Networks for Earthquake detection and Phenomenon identification

This work focuses on developing neural networks to optimize the ring laser gyroscope data analysis, for the GINGER experiment. The first neural network aims to provide data with minimal delays suitable to detect earthquakes. Comparing this neural network with a tool implemented in Labview based on the Fast Fourier Transform, the neural network is twice as precise with the same delay. The second network learns to recognize various phenomena in the data, such as transients from laser dynamics like split modes or mode jumps. These capabilities are realized through the automated labeling of data using neural networks and the implementation of a mask that facilitates the selection of high-quality data. The curated dataset can then undergo traditional offline analysis. The third network is a map to transform earthquake signals seen by the GIGS seismometer into the signals seen by the co-located GINGERINO ring laser prototype, useful to study rotational models of earthquakes.

Spacing mode multi-wavelength erbium doped fiber laser based on a symmetrical long-period fiber grating

We present a multiwavelength erbium-doped fiber laser based on a symmetrical long-period fiber grating (LPFG) with tunable spacing mode between single lasing mode and multiwavelength spectra. The LPFG was manufactured using a thermal expansion technique using an LZM-100 glass processing system equipped with a CO2 laser, and it was used as a wavelength-selective filter (WSF) in the laser ring cavity. The laser can emit single, double, triple, quadruple, quintuple, or sextuple lines in the range from 1546 to 1563 nm, which can be tunable by controlling the radius of curvature of the LPFG in the range 0–0.2662 m −1. A minimal spacing mode of 1.92 nm was observed in the multiwavelength region; meanwhile, the fiber laser offers an average spacing mode of 6.945 nm between the multiwavelength region and the single emission. This laser has a 3 dB linewidth of 0.11 nm and a side mode suppression ratio (SMSR) of 55.56 dB. Finally, according to experimental results, the laser has high wavelength stability at room temperature for 88 min.

GINGER data analysis for seismology

Since several years, the ring laser gyroscope GINGERINO is operative inside the underground Gran Sasso laboratory. It monitors on a continuous basis the local Earth angular velocity in the horizontal plane. It provides unique information for geophysics in general, being one of the few top sensitivity angular velocity sensors. The present paper describes the analysis procedure developed for the data uploaded on the EIDA data base, suitable for seismological investigation in the frequency window 100 s up to 100 Hz. Typical errors and data quality will be discussed. This work is part of the data analysis tools under development for the GINGER project, a ring laser array, part of the UGSS (Underground Gran Sasso Seismology) multi components array at present in construction inside the Gran Sasso laboratory.

A Multi-Format, Multi-Wavelength Erbium-Doped Fiber Ring Laser Using a Tunable Delay Line Interferometer

This work demonstrates the use of an erbium-doped fiber amplifier (EDFA), a tunable bandpass filter (TBF), and a tunable delay line interferometer (TDLI) to form a ring laser that produces multi-format, multi-wavelength laser beams. The TDLI serves as the core of the proposed laser generation system. TDLI harnesses the weak Fabry–Pérot (FP) interferences generated by its built-in 50/50 beamsplitter (BS) with unalterable filtering characteristics and the interferences with free spectral range (FSR) adjustable from each of its two outputs with nearly complementary phases to superpose and generate a variable interference standing wave. The interferometric standing wave and weak FP interferences are used to form a spatial-hole burning to promote the excitation of multi-format and multi-wavelength lasers. The proposed system enables dual-wavelength spacing ranging from 0.3 nm to 3.35 nm, with a switchable wavelength position at approximately 1527 nm to 1535 nm, providing flexible tunability.

The influence of adjustable ring-mode laser on the formation of intermetallic compounds and mechanical properties of ultra-thin Al-Cu lap welded joints

Aluminum-copper dissimilar welding is a highly demanded connection process; however, welding defects and the excessive growth of intermetallic compounds (IMCs) cause pose challenges for its application. This study uses an adjustable ring-mode (ARM) laser technology to achieve lap welding of ultra-thin Al-Cu plates. Lap-welding experiments were conducted using three laser modes—fixed core power, fixed ring power, and varying welding speed—to investigate the evolution of material mixing, intermetallic compound distribution, and joint strength under different modes. Our results indicate that the high energy density of the core laser is beneficial for increasing the penetration depths of joints, whereas the large action area of the ring laser is beneficial for improving the stabilities of melt pools. The joint action of the adjustable ring-mode (ARM) laser increased the melting width and depth of the joint, and the mixing of Al and Cu was controlled in the Al-Cu mixed zone at the upper part of the weld, to limit element mixing in the Cu-rich zone of the weld interface and suppress the distribution of intermetallic compounds. In addition, the ring laser induced the aluminum in the upper part of the molten pool to invade from both sides of the interface to the bottom, forming a certain Al invasion depth. This limited the accumulation of intermetallic compounds at the interface, optimized the path of shear fracture propagation, and improved the shear strength of the joint. This study provides a research basis for further exploring the material flow mechanism and optimizing the intermetallic compound distribution during the Al-Cu adjustable ring-mode (ARM) laser dissimilar welding process.

Vibration-Induced Sweeping Operation in Fiber Lasers

A new vibration-based mechanism of optical frequency/wavelength sweeping in fiber lasers induced by optical path length modulation of a laser cavity section is proposed. The mechanism is implemented for an erbium-doped fiber ring laser with a saturable absorber. Without the vibrations, the laser generates a single longitudinal mode (SLM) radiation. We show experimentally for the first time that mechanical vibrations of the laser cavity section can lead to mode dynamics in both frequency and time domains. The possibility of obtaining various mode dynamics, such as vibration-induced sweeping in a wavelength range of up to 2.2 nm or SLM generation with periodic mode hopping between two fixed longitudinal modes depending on the pump wavelength, is experimentally shown. In this vibration-based approach, the interval between changes in the laser cavity modes has good stability, because it directly relates to the vibration period.

Startup drift compensation of RLG based on monotone constrained RBF neural network

Serious startup drift of the Ring Laser Gyroscope (RLG) is observed during cold startup process, which will dramatically degrade the performances of the corresponding Inertial Navigation System (INS). In this paper, correlation analysis method, which analyzes the relationship between the startup drift of the RLG and the temperature change, is used to determine the significant temperature-related terms during gyroscope startup. Based on the significant temperature-related terms and the startup time length, a startup drift compensation model for RLG based on monotonicity-constrained Radial Basis Function (RBF) neural network is proposed and validated. Compared with the raw RLG data without compensation, the standard deviation of the RLG output with the proposed constrained RBF network model is decreased by more than 46%, and the peak-to-peak value is decreased by more than 35%. Compared with the traditional multiple regression model, the standard deviation and peak-to-peak value of the RLG output are decreased by more than 10% and 6%, respectively. Compared with the common RBF network model, the standard deviation and peak-to-peak value of the RLG output are decreased by more than 8% and 3%, respectively. Navigation experiments also validate the effectiveness of the compensation model.

Mode management in Bottom‐Up, Parity‐Time‐Symmetric Micro‐Cavity Lasers

AbstractThe intrinsic non‐Hermiticity of photonic devices with tunable optical gain and loss makes them excellent platforms to explore and implement applications based on parity‐time symmetry, and a notable example is mode management in micro‐cavity lasers. Thus far, parity‐time‐symmetric lasers are fabricated via conventional top‐down etching processes, which are known to cause cavity sidewall roughness that is potentially detrimental to laser performance. Bottom‐up fabrication of parity‐time‐symmetric lasers, however, has seen limited success due to strict requirements on the uniformity of cavity morphology. Here, parity‐time‐symmetric lasing is demonstrated in coupled InP micro‐ring cavities grown directly by selective area epitaxy. With a facet engineering technique, ring laser cavities with a highly deterministic morphology are realized, enabling parity‐time‐symmetric laser designs. Furthermore, benefiting from the versatility and controllability of this bottom‐up process, lasing mode selectivity can be enhanced through coupling gap tuning and cavity shape engineering, leading to single‐mode lasing with a peak side mode suppression ratio exceeding 17 dB and a threefold single‐mode brightness enhancement compared to a single, uncoupled laser cavity. This work unlocks a lasing mode management strategy that is previously unavailable to bottom‐up laser cavities, which is a major step toward the realization of on‐chip, low‐loss, and single‐mode micro‐cavity lasers.

Research on the Inhibition and Transmission Properties of Photonic Spiking Dynamics in Semiconductor Ring Lasers

Significant progress has been made in the research of all-optical neural networks in recent years. In this paper, we theoretically explore the properties of a neural system composed of semiconductor ring lasers (SRLs). Our study demonstrates that external optical signals generated by a tunable laser (TL) are injected into the first semiconductor ring laser photonic neuron (SRL1). Subsequently, the responses of SRL1 in the clockwise (CW) and counterclockwise (CCW) directions are unidirectionally injected into the CW and CCW directions of the second semiconductor ring laser photonic neuron (SRL2), respectively, which then exhibits similar spiking inhibition behaviors. Numerical simulations reveal that the spiking inhibition behavior of the SRL response can be precisely controlled by adjusting the perturbation time and intensity of the external injection signal, and this behavior is highly repeatable. Most importantly, we successfully achieve the stable transmission of these responses between the two SRL photonic neurons. These inhibition behaviors are analogous to those of biological neurons, but with a response speed reaching the sub-nanosecond level. Additionally, we indicate that SRL photonic neurons undergo a refractory-period-like phenomenon when subjected to two consecutive perturbations. These findings highlight the immense potential for the design and implementation of future all-optical neural networks, providing critical theoretical foundations and support for them.

Integrated Reflective Lyot Filter and FBG Structure for Simultaneous Sensing of Temperature and Axial Strain in Fiber Ring Laser

Integrated Reflective Lyot Filter and FBG Structure for Simultaneous Sensing of Temperature and Axial Strain in Fiber Ring Laser