Jun Wang

Laser power converters (LPCs) are the core photovoltaic devices that act as receivers in optical wireless power transmission systems. In these devices, tunnel junctions (TJs) are employed to vertically interconnect multiple absorption sub-cells in series to construct high-voltage multi-junction LPCs. This work systematically investigates the effects of the Al composition, growth temperature, and doping levels on the performance of AlxGa(1−x)As TJs. Furthermore, the performance of TJs employing different doping schemes (conventional doping, Si + Te co-doping, and delta-doping) and structural designs [quantum well (QW) insertion] was evaluated. For samples with Al compositions of 0%, 7%, 22%, and 28%, the maximum peak tunneling current densities reached 31.0k, 20.3k, 4.8k, and 0.5k A/cm2, respectively, while the lowest tunneling resistivities achieved 1.17 × 10−5, 1.08 × 10−5, 1.89 × 10−5, and 1.39 × 10−4 Ω cm2, respectively. The optimized Al0.28Ga0.72As TJ, featuring a hybrid structure of Si + Te delta-doping and QW insertion, exhibited a peak tunneling current density of 14.6k A/cm2 in the as-grown state and maintained 1.1k A/cm2 after annealing. By applying this TJ structure to a 10-junction GaAs LPC, a photovoltaic conversion efficiency exceeding 60% was achieved.

Laser power converters (LPCs) are key components in laser wireless power transmission systems. In this work, accelerated lifetime tests were conducted on GaAs single-junction and InGaAs single-junction LPCs by elevating the device temperature to 160, 175, and 190 °C to induce accelerated aging. Dark current injections of 8.06 and 8.62 A were applied to GaAs and InGaAs LPCs, respectively, corresponding to simulated photocurrent under laser power densities of 14.65 and 12.78 W/cm2. The failure distributions were fitted using the Arrhenius model, yielding activation energies of 1.11 eV for GaAs single-junction LPCs and 1.15 eV for InGaAs single-junction LPCs. The estimated lifetimes of both devices under an operating temperature of 85 °C are approximately 64 years. Post-aging characterization reveals that device degradation is mainly caused by an increase in series resistance, which leads to a reduction in fill factor and maximum power point. The increase in series resistance is attributed to the degradation of grid electrodes. In addition, the formation of surface cracks is likely associated with the curvature of the LPC exceeding its strain limit.

High-brightness yellow lasers are in high demand for applications such as atomic cooling and trapping, optogenetics, and sodium laser guide stars. Herein, we demonstrate the potential of Metal-Organic Chemical Vapor Deposition (MOCVD) for the rapid mass production of high-strain 1.2 μm InGaAs quantum well vertical external cavity surface emitting lasers (VECSELs). Two distinct growth strategies were explored, with a primary focus on enhancing crystal thermal stability and mitigating indium segregation. The as-grown gain chips achieved over 45 W of output power and a slope efficiency exceeding 50%. Furthermore, we verified the feasibility of generating yellow second harmonic generation (SHG), attaining a 590 nm CW power of ~6.2 W with a slope efficiency of 17%. The beam quality factor ( M ²) was −2 sr ⁻¹ . Overall, these investigations not only expand the performance envelope of MOCVD-grown semiconductor lasers but also deepen the understanding of indium segregation behaviors.

Photonic-crystal surface-emitting lasers (PCSELs) are a new type of semiconductor laser with the potential for high-power output and high-beam-quality operation. Integrating a distributed Bragg reflector (DBR) into PCSELs can significantly enhance device performance. However, the growth of high-aluminum-content DBRs on photonic crystal layers with buried air holes presents two major challenges. First, the low mobility of aluminum atoms increases the propagation of surface roughness from the substrate into the DBR, increasing defect density. Second, the high growth temperatures required for DBR growth can deform the thermally unstable air holes. In this work, we investigated a metal–organic chemical vapor deposition (MOCVD) regrowth process for fabricating DBRs on PCSELs. By adjusting the epitaxial growth temperature and V/III ratio, we effectively controlled the diffusion of adatoms on both the sample surface and inside the holes. As a result, the root mean square (RMS) surface roughness decreased by ~96%, and uniform buried air holes were obtained, with a filling factor of ~ 18.8% and a depth of ~ 270 nm, without significant deformation. Finally, we fabricated a PCSEL device with a DBR structure, exhibiting a beam divergence angle of ~ 0.5° and a peak power of about 0.86 W. This study provides a key process solution for the development of PCSELs with high-quality DBR structures, enabling further improvement in optical output performance.

Ultra-broadband long-wavelength infrared (LWIR) lasers covering 8–15 μm wavelength range are uniquely valuable for spectroscopic applications in chemical sensing, environmental monitoring, and biomedical diagnostics, owing to their alignment with fundamental molecular vibrational fingerprints. To resolve multiple complex molecular signatures and probe transient chemical dynamics, broad spectral coverage and stable temporal characteristics are two essential requirements, which remain as significant technical challenges. Optical-optical modulation of continuous-wave (CW) quantum cascade lasers (QCLs) has recently been demonstrated for generating broadband stable mid-infrared radiation below 5 μm, however, its extension into the more critical LWIR region has not yet been realized. Here, we demonstrate a CW QCL seeded optical parametric amplifier (OPA) generating coherent ultra-broadband LWIR radiation spanning from 6.5 to 12 μm. A high temporal stability with a standard deviation of 1.2% is measured. At a pump energy of 4.5 μJ, the CW-seeded OPA achieves a LWIR peak-power gain of 7 orders. As a proof of concept, a multi-wavelength absorption spectroscopic measurement of polystyrene is demonstrated, employing the ultra-broadband LWIR laser. Our results showcase a simple and effective method in generating LWIR radiation with a broad spectral coverage, high peak-power gain and stable temporal characteristics for advanced spectroscopic applications.

Ultra-broadband long-wavelength infrared (LWIR) lasers covering 8–15 μm wavelength range are uniquely valuable for spectroscopic applications in chemical sensing, environmental monitoring, and biomedical diagnostics, owing to their alignment with fundamental molecular vibrational fingerprints. To resolve multiple complex molecular signatures and probe transient chemical dynamics, broad spectral coverage and stable temporal characteristics are two essential requirements, which remain as significant technical challenges. Optical-optical modulation of continuous-wave (CW) quantum cascade lasers (QCLs) has recently been demonstrated for generating broadband stable mid-infrared radiation below 5 μm, however, its extension into the more critical LWIR region has not yet been realized. Here, we demonstrate a CW QCL seeded optical parametric amplifier (OPA) generating coherent ultra-broadband LWIR radiation spanning from 6.5 to 12 μm. A high temporal stability with a standard deviation of 1.2% is measured. At a pump energy of 4.5 μJ, the CW-seeded OPA achieves a LWIR peak-power gain of 7 orders. As a proof of concept, a multi-wavelength absorption spectroscopic measurement of polystyrene is demonstrated, employing the ultra-broadband LWIR laser. Our results showcase a simple and effective method in generating LWIR radiation with a broad spectral coverage, high peak-power gain and stable temporal characteristics for advanced spectroscopic applications.

The 7xx nm laser diode is the core pump source for Diode Pumped Alkali Vapor Laser (DPAL). For these applications, high power and narrow spectral width are essential. Traditional Fabry-Pérot (FP) diode lasers can provide high continuous output power, but their spectral width is too broad for many applications. By burying a Bragg grating within the semiconductor, a narrow and temperature-stable spectrum can be achieved. In this paper, we investigate the factors limiting the power enhancement of distributed feedback (DFB) lasers and characterize the grown gratings using transmission electron microscopy. We discuss the effects of grating coupling strength, wavelength detuning, and oxygen contamination in the grating region on performance. Under optimized growth conditions, a high-performance 780 nm DFB laser based on InGaAsP/InGaP gratings has been developed, achieving a continuous output power exceeding 10 W, which is the highest power for a 780 nm DFB laser to date. The spectral linewidth (FWHM) is less than 0.5 nm, and the device maintains locking across the entire operating current and a wide temperature range.

808 nm ten-junction laser power converters (LPCs) with different areas were designed and grown by metal-organic chemical vapor deposition. The I–V characteristics of the chips under three different testing conditions were compared to reveal the effect of heat accumulation on the performance of the LPCs. At the same time, the chip size effect was studied. In addition, the temperature of the LPCs was estimated based on its linear relationship with open-circuit voltage ( V _oc ). Finally, the experiment of simultaneous wireless information and power transfer (SWIPT) was conducted to study the limitations on the performance of SWIPT based on the laser. A power transmission of 1.59 W and a data transmission rate of 200 kbit/s was achieved simultaneously.

Improving the output power and efficiency of broad-area diode lasers is a prerequisite for the further development of fiber lasers, solid-state laser industries, and direct semiconductor laser applications. At present, the large amount of Joule heat generated by large drive currents and limited wall-plug efficiency presents the largest challenge for improving these lasers. In this paper, a multi-junction cascade laser with low Joule heat generation is demonstrated, showing large power and conversion efficiency. We fabricated devices with different junction numbers and compared their output power. We present double-junction lasers emitting at ~915 nm with an emitter width of 500 μm, delivering 132.5 W continuous wave output power at 70 A, which is the highest power reported so far for any single-emitter laser. The power conversion efficiencies are 66.7% and 60%, at 100 W and 132 W, respectively.

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.