Monolithic Microlens VCSELs With High Beam Quality

• Main Authors: Youwen Huang, Xing Zhang, Jianwei Zhang, Yiyang Xie, Werner Hofmann, Yongqiang Ning, Lijun Wang
• Format: Article
• Language: English
• Published: IEEE 2017-01-01
• Series: IEEE Photonics Journal
• Subjects: Semiconductor laser; VCSEL; micro-lens; high beam quality; wet-etching.
• Online Access: https://ieeexplore.ieee.org/document/7959035/
• ISSN: 1943-0655

In this paper, we report on high beam quality vertical-cavity surface-emitting lasers (VCSELs) featuring a monolithically integrated aspherical microlens. This lens is fabricated by a one-step diffusion-limited wet etch process. VCSELs with microlenses with different curvature radius are designed, fabricated, and characterized, as well as reference VCSEL devices without the microlens. Significant improvement of beam divergence and single-mode performance are demonstrated in microlens VCSELs. The divergence angles of a conventional VCSEL are 14.5°, 16.0°, and 17.0° (full width at D4σ) at 2 mA, 3 mA, and 4 mA, respectively, with a M² value measured to be 6.9 at 3 mA. Under the same current injection, the divergence angles of a comparable VCSEL with a micro-lens (curvature radius of 31.8 μm) are reduced to 4.8°, 5.5°, and 5.7°, respectively. The M² value of the lensed VCSEL is as low as 1.9 at 3 mA.