InP-based InGaAs (Sb) quantum well laser is a new type of short-wave mid-infrared semiconductor laser based on interband transition, and its emission wavelength can cover the range of 2 ∼ 3 μm. It has broad application prospects in the fields of trace gas detection and isotope measurement.
High-power, high-beam-quality single-mode lasers are an important focus in the field of photonics research. In recent years, both GaSb-based and InP-based short-wave mid-infrared quantum well lasers have achieved certain development, and GaSb-based quantum well lasers have achieved watt-level output power. Compared with GaSb-based quantum well lasers, InP-based quantum well lasers are limited by the band offset, and the output power is lower than GaSb-based quantum well lasers. However, they also have their distinctive features. First, the substrate material has the characteristics of high quality, low cost and large size. Secondly, the thermal conductivity of the substrate material is high, that is, the InP-based material system can be used for secondary epitaxy to make buried gratings, being conducive to device heat dissipation. Furthermore, it is compatible with the mature preparation process of traditional communication lasers, and is easy to achieve monolithic integration with other devices. Finally, it can be prepared by metal organic chemical vapor deposition (MOCVD), which has the application potential of large-scale production. Therefore, the InP-based material system has been receiving great attention in the development and application of lasers with a wavelength near 2 μm.
The team of Researcher Liu Fengqi from the Key Laboratory of Semiconductor Materials, Institute of Semiconductors, Chinese Academy of Sciences reported the research on InP-based InGaAs(Sb) quantum well lasers in the 2μm range of laser light sources. The research overcomes the difficulties of large-strain material lattice mismatch. And a 2 μm DFB laser combined with a second-order buried grating and a corrugated sidewall grating is designed and fabricated on this basis. This report realizes continuous wave edge emission and surface emission of InP-based InGaAs(Sb) 2μm F-P laser diode at room temperature. Its edge-emitting single-mode output power is as high as 81 mW, which is twice the highest output power record of 2 μm DFB lasers reported in the literature. The relevant research results were published in Photonics Research, Volume 11, No. 8, 2023 (Yongqiang Sun, Yunfei Xu, Jinchuan Zhang, Fengmin Chen, Junqi Liu, Shuman Liu, Quanyong Lu, Ning Zhuo, Lijun Wang, Fengqi Liu, Shenqiang Zhai. High-power distributed feedback lasers based on InP corrugated sidewalls at λ∼2 μm[J]. Photonics Research, 2023, 11(8): 1390).
Fig. 1(a) 3D cross-sectional model of a 2 μm DFB laser. (b) L-I-V characteristics at 300 K for devices with ridge widths of 5, 8, 12, and 15 μm (c) CW emission spectra of the second-order DFB laser at 288 to 318 K. (d) Far-field profile and simulation of edge emission.
Fig.1(a) shows a 3D cross-sectional model of a 2 μm DFB laser. The inset shows a magnified view of the device's buried and corrugated gratings. As shown in Fig. 2(b), the maximum continuous light output powers of edge-emitting and surface-emitting devices with a ridge width of 15 μm at 300 K can reach 81 and 42 mW, respectively. At output power, the side-mode rejection ratio of the device remains up to 30 dB, as shown in Fig. 2(c). Fig. 1(d) shows the far-field fundamental transverse mode under different ridge widths, revealing the good beam quality of the laser.
Zhang Jinchuan, a researcher from the Key Laboratory of Semiconductor Materials, said, "The high-performance epitaxial method of 2 μm lasers based on InP-based growth and large-strain lattice mismatching method has great potential and attractiveness. At the same time, the sidewall corrugated grating is introduced based on the secondary grating, which not only preferentially provides additional scattering loss for unwanted high-order lateral modes, but also acts as a high-order grating to promote the single longitudinal mode lasing of the device. This is a very clever idea. "
At present, there is still a lot of room for improvement in the 2 μm single-mode high-performance lasers based on InP-based growth. In the follow-up, on the one hand, the group optimized and improved the design and growth of energy-level materials, and on the other hand, it induced special design structures from the device structure to achieve high-power single-mode performance.
