Single-mode narrow beam divergence surface-emitting concentric-circular-grating terahertz quantum cascade lasers

• Main Authors: Khanna, Suraj P., Liang, Guozhen, Liang, Houkun, Zhang, Ying, Li, Lianhe, Davies, A. Giles, Linfield, Edmund, Lim, Dau Fatt, Tan, Chuan Seng, Yu, Siu Fung, Liu, Hui Chun, Wang, Qi Jie
• Other Authors: School of Electrical and Electronic Engineering
• Format: Conference or Workshop Item
• Language: English
• Published: 2013
• Online Access: https://hdl.handle.net/10356/97872; http://hdl.handle.net/10220/12199
• Institution: Nanyang Technological University

Single-mode surface-emitting terahertz quantum cascade lasers with second-order concentric-circular-gratings are firstly demonstrated. The gratings are designed for single-mode operation and surface emission for efficient and directional optical power out-coupling. The first structure exhibits single-mode operation over the entire dynamic range with a side-mode-suppression-ratio of around 30 dB, and a six-fold rotationally symmetric far-field pattern, while a modified structure demonstrates single-mode operation with an improved beam divergence, whose far-field patteren consists of two lobes, each of which has a beam divergence within 13.5°×7° (full-width at half-maximum, FWHM). In addition, the devices show a peak output power approximately three times higher than in conventional ridge-waveguide lasers of similar size, whilst maintaining similar threshold current densities and maximum operating temperatures.