Browsing by Author "Yang, G."

Now showing 1 - 8 of 8

Open Access
48 W continuous-wave output from a high- efficiency single emitter laser diode at 915 nm
(Institute of Electrical and Electronics Engineers, 2022-09-19) Liu, Y.; Yang, G.; Zhao, Y.; Tang, S.; Lan, Y.; Zhao, Y.; Demir, Abdullah
Improving the power and efficiency of 9xx-nm broad-area laser diodes has a great help in reducing the cost of laser systems and expanding applications. This letter presents an optimized epitaxial structure with high power and conversion efficiency. Laser diodes with 230 μm emitter width and 5 mm cavity length deliver continuous-wave output power up to 48.5 W at 48 A, 30 °C, the highest power reported for 9xx-nm single emitter lasers so far. The slope efficiency is as high as 1.23 W/A due to a low internal optical loss of 0.31 cm−1 and a high internal efficiency of 96%. The maximum power conversion efficiency reaches 72.6% at 15.3 W and 67.3% at the operating power of 30 W under a heatsink temperature of 25 °C. Life test results show no failure in 1000 hours for 55 laser diodes.
Open Access
48 W continuous-wave output power with high efficiency from a single emitter laser diode at 915 nm
(SPIE - International Society for Optical Engineering, 2023-03-14) Yang, G.; Liu, Y.; Zhao, Yongming; Tang, S.; Zhao, Yuliang; Lan, Y.; Bai, L.; Li, Y.; Wang, X.; Demir, Abdullah; Zediker, Mark S.; Zucker, Erik P.
Improving the power and efficiency of 9xx-nm broad-area laser diodes reduces the cost of laser systems and expands applications. LDs with more than 25 W output power combined with power conversion efficiency (PCE) above 65% can provide a cost-effective high-power laser module. We report a high output power and high conversion efficiency laser diode operating at 915 nm by investigating the influence of the laser internal parameters on its output. The asymmetric epitaxial structure is optimized to achieve low optical loss while considering high internal efficiency, low series resistance, and modest optical confinement factor. Experimental results show an internal optical loss of 0.31 cm-1 and internal efficiency of 96%, in agreement with our simulation results. Laser diodes with 230 μm emitter width and 5 mm cavity length have T0 and T1 characteristic temperatures of 152 and 567 K, respectively. The maximum power conversion efficiency reaches 74.2% at 5 °C and 72.6% at 25 °C, and the maximum output power is 48.5 W at 48 A (at 30 ℃), the highest reported for a 9xx-nm single emitter laser diode. At 25 oC, a high PCE of 67.5% is achieved for the operating power of 30 W at 27.5 A, and the lateral far-field angle with 95% power content is around 8°. Life test results show no failure in 1200 hours for 55 laser diodes. In addition, 55.5 W output was achieved at 55 A from a laser diode with 400 μm emitter width and 5.5 mm cavity length. A high PCE of 64.3% is obtained at 50 W with 47 A. © 2023 SPIE.
Open Access
808 nm broad-area laser diodes designed for high efficiency at high-temperature operation
(Institute of Physics Publishing Ltd., 2021-09-21) Lan, Y.; Yang, G.; Liu, Y.; Zhao, Y.; Wang, Z.; Li, T.; Demir, Abdullah
Semiconductor lasers with high power conversion efficiency (PCE) and output power are heavily investigated driven by more energy-efficient commercial applications. In this paper, an asymmetric broad area laser (A-BAL) design is studied and compared with a conventional symmetric broad area laser (S-BAL) design for 808 nm single emitter laser diodes. We present a comparative theoretical and experimental investigation by studying the thermal effects on the laser parameters. The output characteristics and efficiency loss paths for the designs were analyzed. The leakage of carriers was identified as the primary source of the PCE reduction with temperature. Suppressing this leakage by optimization of the A-BAL design, a record continuous-wave PCE of 68% at 25 °C and 60.4% at 75 °C were achieved for a single emitter laser with 10 W output power. These devices deliver high efficiency at high temperatures with reliable operation achieving 2000 h of an accelerated aging lifetime without failures.
Open Access
COMD-free continuous-wave high-power laser diodes by using the multi-section waveguide method
(SPIE - International Society for Optical Engineering, 2023-03-14) Demir, Abdullah; Ebadi, Kaveh; Liu, Y.; Sünnetçioğlu, Ali Kaan; Gündoğdu, Sinan; Şengül, Serdar; Zhao, Y.; Lan, Y.; Yang, G.; Zediker, Mark S.; Zucker, Erik P.
Catastrophic optical mirror damage (COMD) limits the output power and reliability of laser diodes (LDs). The self-heating of the laser contributes to the facet temperature, but it has not been addressed so far. This study investigates a two-section waveguide method targeting significantly reduced facet temperatures. The LD waveguide is divided into two electrically isolated sections along the cavity: laser and passive waveguide. The laser section is pumped at high current levels to achieve laser output. The passive waveguide is biased at low injection currents to obtain a transparent waveguide with negligible heat generation. This design limits the thermal impact of the laser section on the facet, and a transparent waveguide allows lossless transport of the laser to the output facet. Fabricated GaAs-based LDs have waveguide dimensions of (5-mm) x (100-µm) with passive waveguide section lengths varied from 250 to 1500 µm. The lasers were operated continuous-wave up to the maximum achievable power of around 15 W. We demonstrated that the two-section waveguide method effectively separates the heat load of the laser from the facet and results in much lower facet temperatures (Tf). For instance, at 8 A of laser current, the standard laser has Tf = 90 oC, and a two-section laser with a 1500 µm long passive waveguide section has Tf = 60 oC. While traditional LDs show COMD failures, the multi-section waveguide LDs are COMD-free. Our technique and results provide a pathway for high-reliability LDs, which would find diverse applications in semiconductor lasers. © 2023 SPIE.
Open Access
Editorial: generative adversarial networks in cardiovascular research
(Frontiers Research Foundation , 2023-10-23) Zhang, Q.; Çukur, Tolga; Greenspan, H.; Yang, G.
Open Access
Facet passivation process of high-power laser diodes by plasma cleaning and ZnO film
(Elsevier, 2022-09-15) Lan, Y.; Yang, G.; Zhao, Y.; Liu, Y.; Demir, Abdullah
Passivation of dangling bonds at the cleaved mirror facet and its durability are fundamental features of semiconductor lasers to obtain reliable operation with a long device lifetime. The high non-radiative recombination activity of the surface states needs to be controlled to prevent the Fermi level pinning before the deposition of mirror coating materials. Here, we report the incorporation of plasma cleaning of the facet and ZnO film as a passivation layer for the fabrication of high-power semiconductor lasers. The Argon plasma cleaning process was investigated to eliminate surface contamination without damaging the cavity surface. The ZnO passivation films were systematically studied by varying the chamber pressure and sputtering power of the radio frequency (RF) sputter coating process. We obtained homogeneous and dense ZnO films with high surface quality and optical absorption coefficient of zero. By incorporating the optimum plasma cleaning and passivation layer parameters, GaAs-based laser devices with significantly improved catastrophic optical mirror damage (COMD) power were achieved. COMD threshold was increased from 11.9 W to 20.7 W. The life test results demonstrate no failure for facet cleaned and passivated devices for more than 500 h, confirming the long-term effectiveness of the process for actual device integration.
Open Access
High efficiency 1.9 Kw single diode laser bar epitaxially stacked with a tunnel junction
(IEEE, 2021-04-21) Zhao, Y.; Wang, Z.; Demir, Abdullah; Yang, G.; Ma, S.; Xu, B.; Sun, C.; Li, B.; Qiu, B.
We report on the development of a 940-nm diode laser bar based on epitaxially stacked active regions by employing a tunnel junction structure. The tunnel junction and the device parameters were systematically optimized to achieve high output and power conversion efficiency. A record quasi-continuous wave (QCW) peak power of 1.91 kW at 25 °C was demonstrated from a 1-cm wide bar with a 2-mm cavity length at 1 kA drive current (200 μs pulse width and 10 Hz repetition rate). Below the onset of the thermal rollover, the slope efficiency was as high as 2.23 W/A. The maximum power conversion efficiency of 61.1% at 25 °C was measured at 300 A. Reducing the heatsink temperature to 15 °C led to a marginal increase in the peak power to 1.95 kW.
Open Access
High-power operation and lateral divergence angle reduction of broad-area laser diodes at 976 nm
(Elsevier, 2021-04-28) Liu, Y.; Yang, G.; Wang, Z.; Li, T.; Tang, S.; Zhao, Y.; Lan, Y.; Demir, Abdullah
Broad-area diode lasers with high output power and low lateral divergence angle are highly desired for extensive scientific and industrial applications. Here, we report on the epitaxial design for higher output power and a flared waveguide design for reduced divergence, which leads to high power operation with a low lateral divergence angle. A vertically asymmetric epitaxial structure was employed and optimized for low internal optical loss and high efficiency to realize high output power operation. Using a flared waveguide design, the lateral divergence angle was efficiently reduced by decreasing the number of high-order lateral optical modes significantly. The flared waveguide design introduces a smooth modification of the ridge width along the cavity without deteriorating laser performance. Based on the optimized epitaxial and waveguide design, we scaled the waveguide width to realize high continuous-wave power of 34.5 W at 25 °C. A low lateral divergence angle of 8° and high power conversion efficiency of 60% were achieved at the operating power level of 25 W. The life test data (30 A at 45 °C for 39 units, 0 failures in 1000 h) demonstrated reliable operation illustrating the efficient design for reduced lateral divergence angle and high operating power.