Title :
Single-mode narrow beam divergence surface-emitting concentric-circular-grating terahertz quantum cascade lasers
Author :
Guozhen Liang ; Houkun Liang ; Ying Zhang ; Khanna, Suraj P. ; Lianhe Li ; Davies, A. Giles ; Linfield, Edmund ; Dau Fatt Lim ; Chuan Seng Tan ; Siu Fung Yu ; Hui Chun Liu ; Qi Jie Wang
Author_Institution :
Sch. of Electr. & Electron. Eng., Nanyang Technol. Univ., Singapore, Singapore
Abstract :
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.
Keywords :
current density; diffraction gratings; laser beams; laser cavity resonators; microwave photonics; optical design techniques; quantum cascade lasers; surface emitting lasers; terahertz wave devices; directional optical power out-coupling; laser cavity resonators; maximum operating temperatures; optical design; second-order surface-emitting concentric-circular-grating; side-mode-suppression-ratio; single-mode narrow beam divergence; six-fold rotationally symmetric far-field pattern; surface emission; terahertz quantum cascade lasers; threshold current density; Gratings; Laser beams; Laser modes; Measurement by laser beam; Quantum cascade lasers; Surface emitting lasers;
Conference_Titel :
Photonics Global Conference (PGC), 2012
Conference_Location :
Singapore
Print_ISBN :
978-1-4673-2513-4
DOI :
10.1109/PGC.2012.6458023