Electro-optical Conversion Efficiency Research Articles

Multi-junction cascaded vertical-cavity surface-emitting laser with a high power conversion efficiency of 74%

High electro-optical conversion efficiency is one of the most distinctive features of semiconductor lasers as compared to other types of lasers. Its further increase remains a significant objective. Further enhancing the efficiency of edge-emitting lasers (EEL), which represent the highest efficiency among semiconductor lasers at present, is challenging. The efficiency of vertical cavity surface emitting lasers (VCSELs) has always been relatively low compared to EEL. This paper, combining modeling with experiments, demonstrates the potential of multi-junction cascaded VCSELs to achieve high efficiency beyond that of EELs, our simulations show, that a 20-junction VCSEL can achieve an efficiency of more than 88% at room temperature. We fabricated VCSEL devices with different numbers of junctions and compared their energy efficiency. 15-junction VCSELs achieved a maximum efficiency of 74% at room temperature under nanosecond driving current, the corresponding differential quantum efficiency exceeds 1100%, being the largest electro-optical conversion efficiency and differential quantum efficiency reported until now for VCSELs.

Robust high-efficiency LuAG: Ce phosphor-in-silica glass (PiSG) for high-brightness laser lighting

Blue laser diodes (LDs), owing to their high electro-optical conversion efficiency, strong directivity, and small size under high power, have paved new paths in the semiconductor lighting and display industry. Blue LDs are expected to replace LED lighting in laser displays, automotive headlights, and other advanced lighting fields. In this study, the Lu3Al5O12: Ce3+ phosphor-in-silica glass (LuAG: Ce-PiSG) is fabricated using spark plasma sintering at 1060 °C. This method enables rapid sintering while maintaining the stability of the silica glass matrix, resulting in high transparency and minimal destruction of the crystal structure of the LuAG: Ce phosphor. The phosphor-converted LDs made from LuAG: Ce-PiSG exhibit high luminous efficacy (298 lm·W−1) and luminous flux (1069 lm). The results show that LuAG: Ce-PiSG has significant potential for application as a robust, high-efficiency phosphor conversion material for high-brightness laser lighting applications.

Research and Optimization Design of Thermal Management for LED

LED, a lighting source that has gained popularity in the 21st century, possesses characteristics such as energy efficiency, eco-friendliness, compactness, and durability. However, its electro-optical conversion efficiency remains relatively low, as approximately 80% to 90% of the input power is dissipated as thermal energy. Consequently, the temperature of the LED rises, leading to a decrease in its luminous efficiency. Hence, it is crucial to conduct research on efficient heat dissipation methods for LEDs. We have compiled research plans from various scientific institutions and observed that through optimized design, the heat dissipation capability of LEDs has significantly improved. This improvement has resulted in reduced thermal stress within the chips and packaging, ultimately enhancing their reliability.

Identification of intrinsic defects and hydrogen passivation in InP using hybrid functional

Indium phosphide is widely used in electronics and photovoltaic devices due to its high electro-optical conversion efficiency, high electron mobility, and good radiation resistance. Defects are the main limitation for the performance of InP devices. In this work, based on hybrid functional with finite size correction, electronic properties of intrinsic and H-related defects have been investigated in InP. We found that PIn defect is the most stable intrinsic defect with the lowest formation energy. Defect signals detected experimentally are defined by our calculated results. Experimentally observed electron traps with the energy level of EC − 0.66 eV and EC − 0.68 eV are ascribed to the transition level ɛ(−1/−2) and ɛ(−2/−3) of In vacancies. The hydrogenated vacancies in InP have been systematically reported in the present work. Formation energies of H-related defects indicate that hydrogen atoms prefer to bind to In vacancy than P vacancy. The formation energy of In vacancy decreases with the addition of H, while that of P vacancy increases. For hydrogenated In vacancies, it captures fewer electrons than bare In vacancies when the Fermi level is close to CBM. Especially for the VIn − 3H structure, it is 0 charge state in all Fermi levels so that it will not tend to capture electron or hole. Our work is helpful to explain experimental phenomena and radiation-induced damages and improve the performance of InP devices.

Doping profile architecture towards lower loss and higher efficiency for laser diodes.

A doping optimization model towards lower loss and higher efficiency at the target operating current is investigated. This model considers the effect of doping concentration on the series resistance and the internal loss. 780 nm lasers doped with a normal doping profile (Dop_normal) and an optimized doping profile (Dop_optimize) are both designed and fabricated. After doping optimization, the power loss decreased by 17%, the output power of the lasers increased by 26% and the electro-optical conversion efficiency increased by 22%. The model provides significant theoretical guidance for the optimization of the laser doping.

High–Power 792 nm Fiber–Coupled Semiconductor Laser

The pumping of Tm-doped crystal or fiber by a 792 nm semiconductor laser is an important way to generate a mid-infrared laser, which is widely used in various fields. In this paper, a high–power 792 nm fiber–coupled semiconductor laser module was successfully fabricated with the output power of 232 W at a 10 A continuous current and the electro-optic conversion efficiency of 48.6%. The laser module is coupled with 24 chips into a fiber by spatial multiplexing and polarization combination technology. For a single emitting laser chip, the continuous wave (CW) output power and threshold current are 10.45 W at 10 A and 1.55 A, respectively. A polarization as high as 94% can also be realized, which is more suitable for laser spatial beam combining. The laser module was aged for more than 4000 h at 12 A and 25 °C without obvious power degradation.

Mode-Modulation Structure Based on 650 nm Ridge Waveguide Edge-Emitting Laser

Traditional laser diodes operating at 650 nm are more prone to high-order mode excitation, resulting in poorer beam quality. In this paper, we designed GaInP–AlGaInP laser diodes (LD) with a 650 nm range and a trench mode-modulation structure based on the structure of edge-emitting laser (EEL) diodes. The effect of the three-trench structure was investigated theoretically and experimentally. The right trench structure laser chips demonstrated good beam quality while maintaining a high power output. An electro-optical conversion efficiency of 56% was demonstrated with a slope efficiency of 1.32 W/A at a 40 mA current. The maximum optical output power reached 40.8 mW.

High-efficiency spectral beam combining of an individual laser diode bar with polarization multiplexing.

In this Letter, a new strategy for the spectral beam combining (SBC) of an individual laser diode (LD) bar based on a polarization multiplexing external cavity is proposed and demonstrated. The maximum combining efficiency is up to 95.51%, which leads to an output power of 76.6 W and an electro-optic conversion efficiency of 48.33% under continuous wave operation at a current of 100 A. Compared to the conventional SBC, the combining efficiency, the output power, and the electro-optical conversion efficiency present improvements of 12%, 10W, and 6%, respectively. The results show that this novel SBC method is a prospective technique for increasing the combining efficiency of LD bars.

Study of Temperature Effects on the Design of Active Region for 808 nm High-Power Semiconductor Laser

High-power, broad-area, semiconductor lasers are attractive sources for material processing, aerospace, and laser pumping. The design of the active region is crucial to achieve the required high power and electro-optical conversion efficiency, since the temperature significantly affects the performance of the quantum well, including the internal quantum efficiency and mode gain. In this work, the temperature effects on the active region of a 808 nm high-power semiconductor laser were investigated theoretically and experimentally. The simulations were performed with a Quasi-3D model, which involved complete steady-state semiconductor and carrier confinement efficiency combined with a new mathematical method. The critical aluminum content of the quantum barrier was proposed and the relationship between temperature and various loss sources was disclosed in the temperature range of 213 to 333 K, which provides a reliable reference for the design of epitaxial structures of high-power semiconductor lasers in different operating conditions. Subsequently, the optimized epitaxial structure was determined and used to fabricate standard laser bar chips with a cavity length of 2 mm. The experimental electro-optical conversion efficiency of 71% was demonstrated with a slope efficiency of 1.34 W/A and an injection current of 600 A at the heatsink temperature of 223 K. A record high electro-optical conversion efficiency of 73.5% was reached at the injection current of 400 A, while the carrier confinement efficiency was as high as 98%.

Study of AlGaN-based deep ultraviolet laser diodes using one-way step-shaped quantum barriers and symmetrical step-shaped electron and hole blocking layers

To improve the carrier injection efficiency and optimize the performance of the AlGaN-based deep ultraviolet laser diodes (DUV-LDs), one-way step-shaped quantum barriers (OWS-QBs), a symmetrical step-shaped electron blocking layer (SS-EBL), and a symmetrical step-shaped hole blocking layer (SS-HBL) are proposed. Crosslight software is used to simulate the DUV-LDs with a traditional structure, with OWS-QBs, and with OWS-QBs, a SS-EBL, and a SS-HBL. The simulation results and physical mechanism analysis indicate that the SS-EBL, SS-HBL, and OWS-QBs contribute to the increased carrier concentration in the quantum wells, the reduced carrier leakage in the nonactive regions, the increased stimulated emission rate, the reduced threshold current and threshold voltage, and the enhanced output power and electro-optical conversion efficiency of DUV-LDs.

High-brightness and high-efficiency diode laser module based on double wavelength division multiplexing external cavities.

In this Letter, a new, to the best of our knowledge, external cavity structure based on double wavelength division multiplexing external cavities is proposed and demonstrated. The electro-optical conversion efficiency is improved and the brightness of the spectral beam combining diode lasers is enhanced. One wavelength division multiplexing external cavity is placed on the rear-side of the laser emitters to provide the strong optical feedback for wavelength locking and the other wavelength division multiplexing external cavity is placed on the front-side of laser emitters to combine three emitter beams to one beam. A maximum output power of up to 7.5 W is obtained and the brightness of the laser diode is 100 MW cm-2 sr-1 with an electro-optical conversion efficiency of 46.5%. Compared with a standard cavity for spectral beam combining, the use of double wavelength division multiplexing external cavities results in an electro-optical conversion efficiency improvement of 6.5%. The whole structure provides a new technology to achieve high-brightness and high electro-optical conversion efficiency for a laser diode source.

Synthesis of a Novel Nanoparticle BaCoO2.6 through Sol-Gel Method and Elucidation of Its Structure and Electrical Properties

The physical properties of cobalt oxide with varied oxidation states, and coordination numbers, in the transition series, have numerous applications. The present study explores the physical properties of BaCoO2.6 nanoparticles synthesized through the sol-gel method. The X-ray diffraction figure exhibits a 25 nm crystallite size hexagonal phase. The observational data shows the reduction in the real part of impedance ( Z ’ ), dielectric constant ( ξ ’ ), dielectric loss ( ξ ” ), and a raise in ac conductivity of mixed type of conduction with an elevation in frequency analyzed through impedance spectroscopy. The conductivity due to grain and grain boundaries is shown foremost in the complex impedance analysis. The plot of ∆ V / ∆ T (Seebeck coefficient) in the low-temperature range indicates p-type behavior and the metal-insulator transition in the as-synthesized sample. The sample characteristics suggest applications in optical and switching devices. The Seebeck coefficient is the generation of potential difference when subjected to temperature difference. Thermoelectric materials are associated with the concept of high electrical conductivity like crystals and low thermal conductivity to that of glass. Nanothermoelectric materials can decrease further the thermal conductivity through phonon scattering. Electrical characterization suggests the presence of both NTCR and PTCR behavior in the sample, and hence, it explores the application in thermistor/resistance temperature detector’s (RTD) and low dielectric constant and loss to electro-optical and higher conversion efficiency to storage devices. Additionally, impedance spectroscopy helps in the study of electrochemical systems and solid-state devices wherein the transition of metal-insulator is an add-on to the research.

Composition-graded quantum barriers improve performance in AlGaN-based deep ultraviolet laser diodes

We propose two composition-graded quantum barriers (QBs) to improve the performance of AlGaN-based deep ultraviolet laser diodes (DUV-LDs). The optical and electrical properties of three LDs containing conventional QBs, graded increased QBs, and graded decreased QBs were numerically investigated. It was found that the LDs with graded decreased QBs significantly improved the carrier injection efficiency, raised the carrier concentration in the active region, reduced the carrier leakage, and enhanced the stimulated recombination rate of the LDs. Simulation results showed that, at an 80-mA injection current, the threshold current and threshold voltage were reduced to 29.5 mA and 4.78 V, respectively. The slope efficiency was improved to 2.52 W/A, and the electro-optical conversion efficiency was increased to 52.2%. Compared with the conventional structure of LDs, grading the QBs with decreasing Al-content improved the performance of the LD remarkably, which is essential for the development of DUV-LD.

Optimization of AlGaN-Based Deep Ultraviolet Laser Diodes with Graded Rectangular Superlattice Electron Blocking Layer and Graded Trapezoidal Superlattice Hole Blocking Layer

To improve the carrier confinement capability and optimize the performance of deep ultraviolet laser diodes (DUV-LDs), we propose the graded rectangular superlattice (GRSL) electron blocking layer (EBL) and the graded trapezoidal superlattice (GTSL) hole blocking layer (HBL) in this paper. Crosslight software is used to simulate and compare the DUV-LDs with rectangular superlattice (RSL) EBL and RSL HBL, GRSL EBL and GRSL HBL, and GRSL EBL and GTSL HBL. The simulation results indicate that GRSL EBL and GTSL HBL increase the carrier concentration in the quantum wells, reduce the electron leakage in the p-type region and the hole leakage in the n-type region, increase the radiation recombination rate, reduce the threshold voltage and threshold current, and increase the electro-optical conversion efficiency and output power of DUV-LDs more effectively.

电注入下的人工微结构模式调控激光研究进展

Electrically injected semiconductor lasers have several advantages over other lasers, such as high electro-optical conversion efficiency, small size, and long lifetime. Recently, the demand for semiconductor lasers has grown in several areas, including displays, material processing, medicine, communication, and other fields. Mode characteristics in lasers can directly modulate their performance, including the output power, beam quality, and spectrum linewidth. The performance of semiconductor lasers can be optimized by introducing artificial microstructures combined with mode control methods, including parity-time symmetry, bound states in the continuum, and compound cavity, which can expand relevant physical research and their commercial applications. In this paper, first, the objective of mode control is introduced. Then, the developments in electrically injected semiconductor lasers, including domestic and international research studies, physical principles, and corresponding applications, are reviewed. Finally, conclusions and future outlooks are discussed.

A High Precision and Multifunctional Electro-Optical Conversion Efficiency Measurement System for Metamaterial-Based Thermal Emitters.

In this study, a multifunctional high-vacuum system was established to measure the electro-optical conversion efficiency of metamaterial-based thermal emitters with built-in heaters. The system is composed of an environmental control module, an electro-optical conversion measurement module, and a system control module. The system can provide air, argon, high vacuum, and other conventional testing environments, combined with humidity control. The test chamber and sample holder are carefully designed to minimize heat transfer through thermal conduction and convection. The optical power measurements are realized using the combination of a water-cooled KBr flange, an integrating sphere, and thermopile detectors. This structure is very stable and can detect light emission at the μW level. The system can synchronously detect the heating voltage, heating current, optical power, sample temperatures (both top and bottom), ambient pressure, humidity, and other environmental parameters. The comprehensive parameter detection capability enables the system to monitor subtle sample changes and perform failure mechanism analysis with the aid of offline material analysis using scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. Furthermore, the system can be used for fatigue and high-low temperature impact tests.

Improved electro-optical and photoelectric performance of GaN-based micro-LEDs with an atomic layer deposited AlN passivation layer.

The quantum efficiency of GaN-based micro-light-emitting diodes (micro-LEDs) is of great significance for their luminescence and detection applications. Optimized passivation process can alleviate the trapping of carriers by sidewall defects, such as dangling bonds, and is regarded as an effective way to improve the quantum efficiency of micro-LEDs. In this work, an AlN passivation layer was prepared by atomic layer deposition to improve the electro-optical and photoelectric conversion efficiency in GaN-based micro-LEDs. Compared to conventional Al2O3 passivation, the AlN passivation process has a stronger ability to eliminate the sidewall defects of micro-LEDs due to the homogeneous passivation interface. Our experiments show that the AlN-passivated device exhibits two orders of magnitude lower forward leakage and a smaller ideality factor, which leads to significantly enhanced external quantum efficiency (EQE). For 25*25 μm2 micro-LEDs, the EQE of the AlN-passivated device was 18.3% and 57.7% higher than that of the Al2O3-passivated device in luminescence application and detection application, respectively.

Investigation on reduction of dross height by analyzing beam intensity distribution in fiber laser cutting

Nowadays, fiber lasers have become a main energy source in laser cutting because of their highly electro-optical conversion efficiency and high beam quality. However, the amount of dross produced by fiber laser cutting is larger than that by CO2 laser cutting, and postprocessing is required to obtain a flat surface without dross, which leads to increasing the processing cost. If fiber laser achieves dross-free cutting of a steel plate, further expansion of cutting applications can be expected. Therefore, in order to achieve further reduction of dross, the influence of beam intensity distribution on dross height was investigated by fiber laser cutting experiments and ray tracing analysis. The laser cutting experiment of steel plate cold commercial with 3.2 mm thickness was carried out by a 3 kW fiber laser with nitrogen assist gas, and a round Gaussian mode of 114 μm spot diameter and a square top-hat mode of 132 μm were used. The square top-hat mode can achieve smaller dross height below 12 μm, which is approximately half of the round Gaussian mode. Ray tracing analysis revealed that the square top-hat mode increased the uniformity of absorbed energy on the cutting front surface, and the more uniform intensity distribution contributed to a small ellipticity of the cutting front shape of the kerf. It was clarified that the shape of the cutting front with a small ellipticity reduced the amount of molten metal ejected from the side of the kerf, which resulted in the reduction of dross height by the fiber laser cutting.

1.5-W 520 nm continuous-wave output from a 50 μm/0.22NA fiber-coupled laser diode module

In this paper, a high brightness fiber-coupled module with a central wavelength of 520 nm is simulated and designed by ray-tracing software ZEMAX and then is experimentally implemented. Three 1-W continuous-wave green LD single emitters based on TO-9-package are successively collimated, spatially combined, and focused into an optical fiber with a core diameter of 50 μm and a numerical aperture of 0.22. The final output power of 1.53 W is obtained, corresponding to an optical–optical conversion efficiency of 51% and an electro-optical conversion efficiency of 10%. The tolerances between the simulation and the experimental result are analyzed and explained.

Integrated and spectrally selective thermal emitters enabled by layered metamaterials

Abstract Nanophotonic engineering of light–matter interaction at subwavelength scale allows thermal radiation that is fundamentally different from that of traditional thermal emitters and provides exciting opportunities for various thermal-photonic applications. We propose a new kind of integrated and electrically controlled thermal emitter that exploits layered metamaterials with lithography-free and dielectric/metallic nanolayers. We demonstrate both theoretically and experimentally that the proposed concept can create a strong photonic bandgap in the visible regime and allow small impedance mismatch at the infrared wavelengths, which gives rise to optical features of significantly enhanced emissivity at the broad infrared wavelengths of 1.4–14 μm as well as effectively suppressed emissivity in the visible region. The electrically driven metamaterial devices are optically and thermally stable at temperatures up to ∼800 K with electro-optical conversion efficiency reaching ∼30%. We believe that the proposed high-efficiency thermal emitters will pave the way toward integrated infrared light source platforms for various thermal-photonic applications and particularly provide a novel alternative for cost-effective, compact, low glare, and energy-efficient infrared heating.