Multimode Laser Research Articles

Manipulating winding numbers and multiple topological bound states via long-range coupling in chiral photonic lattices

The topological bound states are limited to one pair in traditional one-dimensional (1D) topological chiral models as the winding number can only take the value of 0 or 1. It was increased to 2 or 3 via long-range couplings (LRCs) that were restricted to second- or third-order in recent experimental or theoretical researches. How to generate larger winding number to manipulate more topological bound states remains a challenge. Here, we propose an effective method by introducing arbitrary Nth order LRC stronger than the sum of other order couplings. The resulting winding number has been computed by getting the winding loop's envelope in parameter space. The coupling-inverted 1D photonic topological insulators supporting up to three pairs of highly localized multiple topological bound states are realized by fabricating photonic lattices with multi-layer waveguide arrays. Furthermore, these topological bound states are closely spaced, offering a promising implementation approach of multimode topological lasers in gain media. Our work highlights the advantages of LRCs in manipulating the topological phases of matter. Published by the American Physical Society 2024

Random Raman Lasing in Diode-Pumped Multi-Mode Graded-Index Fiber with Femtosecond Laser-Inscribed Random Refractive Index Structures of Various Shapes

Diode-pumped multi-mode graded-index (GRIN) fiber Raman lasers provide prominent brightness enhancement both in linear and half-open cavities with random distributed feedback via natural Rayleigh backscattering. Femtosecond laser-inscribed random refractive index structures allow for the sufficient reduction in the Raman threshold by means of Rayleigh backscattering signal enhancement by +50 + 66 dB relative to the intrinsic fiber level. At the same time, they offer an opportunity to generate Stokes beams with a shape close to fundamental transverse mode (LP01), as well as to select higher-order modes such as LP11 with a near-1D longitudinal random structure shifted off the fiber axis. Further development of the inscription technology includes the fabrication of 3D ring-shaped random structures using a spatial light modulator (SLM) in a 100/140 μm GRIN multi-mode fiber. This allows for the generation of a multi-mode diode-pumped GRIN fiber random Raman laser at 976 nm with a ring-shaped output beam at a relatively low pumping threshold (~160 W), demonstrated for the first time to our knowledge.

A high-resolution spectroscopic technique for the analysis of the external quantum efficiency of a multimode semiconductor laser

The high-resolution emission spectra of a GaN-based semiconductor laser were utilized to investigate the external differential quantum efficiency variation with temperature and stability over an extended period of continuous operation time. Moreover, the dynamics and evolution of the optical gain and longitudinal modes emitted both below and above threshold current were also reported. Upon studying the L-I curves over the full range of operating current and temperature, three distinct temperature regimes of the quantum efficiency were identified, with the regime of the temperature range 285–301 K yielding the highest stability. The thermal stability of the laser was also assessed by monitoring the variation of threshold current with temperature.

Dual‐channel, high‐frequency optoelectronic oscillators utilizing optically‐injected lasers

AbstractWe propose a novel approach to dual‐channel optoelectronic oscillators (OEOs) with enhanced frequency band by leveraging directly modulated (DM) semiconductor lasers under optical injection. In this configuration, the frequency‐tuned optical signal from a master laser is introduced into a single‐mode slave laser, facilitating multioptical‐mode operation. The resulting multiple optical frequencies emitted by the slave laser facilitates a DM‐OEO signal at a frequency exceeding the laser's intrinsic modulation bandwidth. Through the deployment of a dual‐channel OEO based on the DM multimode laser signal, stable oscillation signals have been successfully achieved simultaneously at 15 and 18 GHz with phase noise levels of 96.43 and 95.62 dBc/Hz, respectively, at a 10‐kHz offset frequency.

Multi-field coupling analysis of photovoltaic cells under long distance and multi-mode laser transmission

Most electronic devices are powered by electricity, and the transfer of energy to related electronic devices is a critical issue. Laser wireless power transmission (LWPT) has a broad prospect in the field of wireless energy transmission, such as distributed charging system (DLC), spacecraft sensor network, satellite-to-satellite communication and medium and long distance power transmission, ground to unmanned aerial vehicle (UAV), and so on. In this paper, a multi-field coupled model of LWPT system for laser transmission at medium and long distances is established. Through the existing LWPT experimental platform and test, the test obtained the correlation coefficient of the I-V relationship formula with the change of light intensity and temperature. On the basis of the modified parameters, the attenuation efficiency of laser power with transmission distance is calculated, and the heat transfer and electrical characteristics of photovoltaic cells are solved by finite element method. It is found that different atmospheric environment and laser transmission distance have obvious effects on the voltage, current and temperature variation of photovoltaic cells. The temperature of a photovoltaic cell has a huge impact on its output efficiency. The temperature can be controlled effectively by setting the laser interval of pulse mode reasonably. The cooling capacity of photovoltaic cells is the key to improve the electrical conversion efficiency of LWPT systems.

High-power diode laser spectrally narrowed with prism-etalon feedback.

A simple method for reducing the linewidth of a diode laser while maintaining high output power is described. It is based on a dispersive prism and a thin etalon for retroreflective feedback. The etalon creates two weak external cavities that provide spectral selectivity that is periodic with a period equal to the etalon's free spectral range. The method was applied to a multimode blue laser diode, which in the absence of feedback features a linewidth of several nanometers. The spectral properties of the laser were investigated for different etalon thicknesses and operating currents and tested in the presence of temperature fluctuations. With a SF11 equilateral uncoated prism near Brewster's angle and a 0.3 mm-thick uncoated fused silica etalon, the linewidth was reduced 20-fold to 70pm (3.6 cm-1) with an output power of 3W at a current of 2.15A. The largest diode current probed was 2.75A, which resulted in a linewidth of 100pm (5.1 cm-1) and an output power of 4W. In contrast to the use of, for example, a volume Bragg grating, a high degree of flexibility is afforded as the same prism-etalon pair can be used across the visible and near infrared.

The Role of Bone Edema in Plantar Fasciitis Treated with Temperature-Controlled High-Energy Adjustable Multi-Mode Emission Laser (THEAL) and Exercise: A Prospective Randomized Clinical Trial.

Plantar fasciitis is one of the most common causes of foot pain; in 35% of cases, it is also associated with bone edema of the heel. The aim of this study was to investigate the relationship between bone edema and the outcomes of temperature-controlled high-energy adjustable multi-mode emission laser (THEAL) and/or exercises in patients with plantar fasciitis. A prospective randomized clinical trial was designed, in which 48 patients suffering from plantar fasciitis, with or without bone edema, were treated with temperature-controlled high-energy adjustable multi-mode emission laser and exercises (the laser group) or with exercises only (the control group). The patients were evaluated at recruitment (T0) and at 2 (T1) and 6 months (T2), monitoring pain (with the Visual Analogue Scale), functionality (with the Foot Function Index), perception of improvement (with the Roles and Maudsley Score), and fascia thickness (with ultrasound examination). In both groups, there was a significant improvement in pain, functional recovery, perception of remission, and a reduction in plantar fascia thickness at T1 and T2. The laser group presented statistically better values at T2 for the Roles and Maudsley Score (z: 2.21; 0.027). The regression analysis showed that a greater reduction in fascia thickness occurred in the laser group (p-value: 0.047). In conclusion, the two conservative treatments were effective in patients suffering from plantar fasciitis, even in the presence of bone edema, but with lesser results.

Watt-level cladding-pumped bismuth-doped fiber laser operating near 1.31 [formula omitted]m

We report, to the best of our knowledge, the first CW bismuth-doped fiber laser operating at around 1.31 μm with an output power of >1 W utilizing a cladding-pumping configuration with multimode semiconductor laser diodes emitting at a wavelength of 793 nm. The Bi-doped fiber (BDF) serving as an active medium of the laser was based on a pedestal-index design, where P2O5−SiO2 glass core surrounded by P-doped cladding. The BDF construction offers advanced gain characteristics and an increased mode size (∼13 μm). The fiber preform was fabricated by the conventional modified chemical vapor deposition (MCVD) method combined with all gas-phase doping technique. The BDF with low-index polymer coating provided sufficient cladding peak absorption at 750 nm belonging to bismuth active centers associated with phosphorus atoms (BACs-P) that allowed to develop a continuous-wave laser with a linear cavity configuration and enable a maximum slope efficiency of ∼ 4% with respect to the absorbed pump power. In addition, near-field spatial intensity distribution of optical beam has good quality (M2<1.13) and close to Gaussian mode profile in x and y directions. The perspectives for optimization of BDF design and laser system configurations based on such fibers for further power scaling are discussed.

Hyperfine Structure of the 609 nm transition of Lu I by RIMS with multi-mode lasers

Hyperfine Structure of the 609 nm transition of Lu I by RIMS with multi-mode lasers

High-average-power 216 MHz Kerr lens mode-locked Yb:KGW ring laser oscillator for application to laser spectroscopy

We report the development of a ring Yb:KGW laser oscillator with an average power of 4.22 W, a pulse duration of 312 fs at a repetition rate of 216 MHz. The ring laser oscillator is purely Kerr lens mode-locked (KLM) taking advantage of the high nonlinear refractive index of the laser crystal in spite of being pumped by a multimode laser diode. To the best of our knowledge, this is the highest average power obtained from a KLM ring Yb:KGW laser oscillator. Monitoring the repetition rate fluctuations after initial warm-up of the laser cavity, a peak to valley of only 354.28 Hz during 30 min of free-running operation has been achieved. This could make a free-running ring cavity a suitable light source for application to laser spectroscopy. Using the ring laser oscillator, we have measured the absorption of the second overtone of the ν1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ u _1$$\\end{document} mode of NH3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_3$$\\end{document}. We have also measured absorption spectra of the Yb:KGW crystal to evaluate the quality of the crystal affected by the doped impurities.

Flexible water-resistant bamboo-like perovskite-embedded polymer nano/microfibers exhibiting Fabry–Pérot lasing

Methylammonium lead bromide perovskite (MAPbBr3)-embedded nano- and micro-fibers are successfully fabricated by using the uniaxial electrospinning technique. Through the study of solidification and coordination between perovskite with hybrid polymers, polymethyl methacrylate, and polyacrylonitrile, the bamboo-like perovskite-embedded polymer nano/microfibers are unpredictably formed. Encapsulated in polymer, the passive perovskite-embedded polymer fibers exhibit a long-term fluorescence performance when simultaneously exposed to both water immersion and short-wavelength laser irradiation. Notably, due to the efficient gain media, the perovskite-rich region of the electrospun fiber can act as an optical microcavity. Multi-mode and single-mode lasing behaviors can be achieved via different cavity lengths. The mechanism of a microlaser within this perovskite fiber is confirmed through a Fabry–Pérot cavity, which provides an opportunity for optical components in lasers.

An experimental alternative of microwave signal generation through an optical heterodyning technique using a multimode laser diode and a tunable DFB laser

An experimental alternative of microwave signal generation through an optical heterodyning technique using a multimode laser diode and a tunable DFB laser

Humidity Sensing Using a Multimode Fiber Ring Laser with Thermal Compensation

We propose a multimode fiber laser sensor utilizing PI-SMF (polyimide-coated single mode fiber) for low-error relative humidity (RH) measurement, which is temperature compensated based on FBG. The PI-SMF in the laser cavity is used as a sensing element, and its length varies with humidity and temperature by volume-variation induced strain, which leads to frequency shift of the longitudinal mode beat frequency signal (BFS). When the 2000 MHz BFS is selected as the sensing signal, a RH sensitivity of −2.68 kHz/%RH and a temperature sensitivity of −14.05 kHz/°C are achieved. The peak shift of the FBG-based laser emission spectrum is only sensitive to temperature rather than RH with a temperature sensitivity of 9.95 pm/°C, which is used as the temperature compensation for RH measurements. By monitoring the response of the BFS and the laser wavelength, the cross-sensitivity effect of RH and temperature is overcome, and low-error RH measurement in the temperature range of 20 to 65 °C is realized with errors within ±0.67 %RH (25 to 85 %RH). The scheme does not require the design and production of complex structures and hygroscopic material coating processes, owning the advantages of simple structure, easy operation and high accuracy, and is expected to be practically applied in food safety and environmental monitoring.

Characterizing Extreme Events in a Fabry–Perot Laser with Optical Feedback

The study of extreme events (EEs) in photonics has expanded significantly due to straightforward implementation conditions. EEs have not been discussed systematically, to the best of our knowledge, in the chaotic dynamics of a Fabry–Perot laser with optical feedback, so we address this in the current contribution. Herein, we not only find EEs in all modes but also divide the EEs in total output into two categories for further discussion. The two types of EEs have similar statistical features to conventional rogue waves. The occurrence probability of EEs undergoes a saturation effect as the feedback strength increases. Additionally, we analyze the influence of feedback strength, feedback delay, and pump current on the probability of EEs defined by two criteria of EEs and find similar trends. We hope that this work contributes to a deep understanding and serves as inspiration for further research into various multimode semiconductor laser systems.

Theoretical analysis of the buried heterostructure laser for stable dual-wavelength generation

Stable dual-wavelength emission from a laser is desirable for microwave signal generation using the optical heterodyning method. As both optical wavelengths are generated from the same cavity, the phase noise of the generated microwave signal is minimized. In this work, we exploit the inherent birefringence in the buried heterostructure semiconductor laser to generate dual polarized modes. We carefully analyze the mode competition between various modes in the cavity and propose the desirable gain modification conditions for stable dual mode oscillations when the laser is operating near the threshold. We show that the required asymmetry in the gain for two stable modes can be obtained from the mode confinement factors and facet losses. We also show the applicability of our results to a homogeneously broadened multimode laser.

Emission behaviors from ZnO microwire pumped CsPbBr3 perovskite microwire.

Perovskite semiconductor materials have attracted significant attention in the fields of photovoltaics and luminescence due to their excellent photoelectric properties, such as high carrier mobility, high absorption coefficient, and high fluorescence quantum yield. In particular, low-dimensional metal-halide perovskite microcrystalline materials have been reported to exhibit low-dimensional lasing phenomena and laser devices due to their high gain and widely tunable bandgap. In this Letter, one-dimensional (1-D) ZnO microwires with their ultraviolet lasing emissions are utilized as an excitation source to pump CsPbBr3 microwire on hybrid ZnO-CsPbBr3 microscale structures. At higher excitation, the amplified spontaneous emission (ASE) behaviors from CsPbBr3 microwire are realized with ultralow threshold by indirect pumping from the ZnO lasing emission for the first time, to the best of our knowledge. In comparison, the ASE behaviors from the CsPbBr3 microwire directly pumped by Nd:YAG Q-switched laser and continuous wave laser are also performed at room temperature. There are also no multimode lasing behaviors observed. The paper provides a new method to achieve a low threshold on-chip microlaser by a high-quality perovskite micro-nano structure.

Deep learning-based monitoring system for predicting top and bottom bead widths during the laser welding of aluminum alloy

Weld bead geometry visually represents the result of the welding process. However, ensuring a consistent weld bead is not always guaranteed due to the instability of the welding process. In this study, we present a deep learning-based monitoring system that predicts both the top and bottom bead widths simultaneously during the multi-mode fiber laser welding of aluminum alloy 1050P-H16. From the predicted top and bottom bead widths, rich information about the welding process can be obtained. Our deep learning model was constructed based on the VoVNet27-slim architecture, which was successfully trained using weld pool images obtained coaxially by a small optical camera. We were able to obtain very clean images of the aluminum weld pool, which provided plentiful information about the weld pool and the resulting top and bottom bead widths. We attempted to use one or two weld pool images as input to study how an additional weld pool image can enhance prediction accuracy. It was found that the top bead width was accurately predicted by both the one- and two-image models. However, the two-image model showed a clear improvement in the prediction of the bottom bead width because the bottom bead width fluctuates more widely and cannot be directly seen from the top-side weld pool image. The optimal separation distance between the two input images was found to be −0.1 mm, with which additional weld pool information about the past was supplied to the model and the denoising effect was achieved. Monitoring changes in both top and bottom bead widths provides rich information regarding the welding process, and we believe that the presented deep learning–based approach can serve as an effective monitoring tool.

Multimode Emission in GaN Microdisk Lasers

AbstractQuantum well nanolasers usually show single‐mode lasing, as gain saturation suppresses emissions in other modes. In contrast, for whispering gallery mode microdisk lasers with GaN quantum wells as active material, above threshold multimode laser emission is observed. This intriguing emission feature is manifested in the fact that several modes simultaneously show the characteristic kink in the input–output curve at the onset of lasing. A quantum theory for nanolasers is used to support the experimental finding and to analyze this behavior in the presence of gain saturation. Coupling effects between neighboring modes are identified as the origin of multimode lasing, which initiate photon exchange between modes via population pulsations similar to classical wave‐mixing effects. A reduction of this type of mode coupling with increasing mode spacing is demonstrated. The results can pave the way for multimode application of nanolasers in integrated photonic circuits.

Mode-Locked Operation of High-Order Transverse Modes in a Vertical-External-Cavity Surface-Emitting Laser.

Understanding the mechanism of mode-locking in a laser with high-order transverse mode is important for achieving an ultrashort pulses train under more complicated conditions. So far, mode-locking with high-order transverse mode has not been reported in other lasers except the multimode fiber laser. This paper demonstrates robust mode-locking with high-order transverse mode in a Kerr-lens mode-locked vertical-external-cavity surface-emitting laser for the first time, to the best of our knowledge. While the longitudinal modes are locked, continuous mode-locking accompanied by high-order transverse mode up to TEM40 is observed. The threshold of the mode-locking is only a little bigger than that of the lasing. After the laser oscillation is built up, the mode-locked pulse train can be obtained almost immediately and maintained until the thermal rollover of the laser. Output powers of 717 mW under fundamental mode and 666 mW under high-order transverse mode are achieved with a 4.3 ps pulse duration and 1.1 GHz pulses repetition rate, and some phenomenological explanations to the related characteristics of the mode-locked operation of high-order transverse mode in the vertical-external-cavity surface-emitting laser are proposed.

Single-Shot Intensity- and Phase-Sensitive Compressive Sensing-Based Coherent Modulation Ultrafast Imaging.

Ultrafast imaging can capture the dynamic scenes with a nanosecond and even femtosecond temporal resolution. Complementarily, phase imaging can provide the morphology, refractive index, or thickness information that intensity imaging cannot represent. Therefore, it is important to realize the simultaneous ultrafast intensity and phase imaging for achieving as much information as possible in the detection of ultrafast dynamic scenes. Here, we report a single-shot intensity- and phase-sensitive compressive sensing-based coherent modulation ultrafast imaging technique, shortened as CS-CMUI, which integrates coherent modulation imaging, compressive imaging, and streak imaging. We theoretically demonstrate through numerical simulations that CS-CMUI can obtain both the intensity and phase information of the dynamic scenes with ultrahigh fidelity. Furthermore, we experimentally build a CS-CMUI system and successfully measure the intensity and phase evolution of a multimode Q-switched laser pulse and the dynamical behavior of laser ablation on an indium tin oxide thin film. It is anticipated that CS-CMUI enables a profound comprehension of ultrafast phenomena and promotes the advancement of various practical applications, which will have substantial impact on fundamental and applied sciences.