Low divergence single-mode surface-emitting concentric-circular-grating terahertz quantum cascade lasers

• Main Authors: Liang, Guozhen, Liang, Houkun, Zhang, Ying, Li, Lianhe, Davies, A. Giles, Linfield, Edmund, Yu, Siu Fung, Liu, Hui Chun, Wang, Qi Jie
• Other Authors: School of Electrical and Electronic Engineering
• Format: Article
• Language: English
• Published: 2014
• Subjects: DRNTU::Science::Physics::Optics and light
• Online Access: https://hdl.handle.net/10356/101635; http://hdl.handle.net/10220/18734
• Institution: Nanyang Technological University

We report the design, fabrication and experimental characterization of surface-emitting terahertz (THz) frequency quantum cascade lasers (QCLs) with distributed feedback concentric-circular-gratings. Single-mode operation is achieved at 3.73 THz with a side-mode suppression ratio as high as ~30 dB. The device emits ~5 times the power of a ridge laser of similar dimensions, with little degradation in the maximum operation temperature. Two lobes are observed in the far-field emission pattern, each of which has a divergence angle as narrow as ~13.5° × 7°. We demonstrate that deformation of the device boundary, caused by anisotropic wet chemical etching is the cause of this double-lobed profile, rather than the expected ring-shaped pattern.