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Opt Express. 2013 ;21(13):15998-6006.
Li Y, Wang J, Yang N, Liu J, Wang T, Liu F, Wang Z, Chu W, Duan S.
Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, 100083, Beijing, China.
Abstract
We report on Terahertz quantum cascade lasers with tapered waveguide structure operating at ≈ 103 um. The tapered waveguide effect on the output power and the laser beam divergence are experimentally studied with the tapered angle ranging from 0° to 8°. It is found that the peak output power of the devices with same length reaches the maximum at about 5° ≈ 6° tapered angle. Meanwhile, the horizontal divergence angle of the laser beam can be greatly reduced. The existence of such optimal tapered angle is explained by the finite-element simulation with the consideration of the self-focusing effect for the devices with larger tapered angle.
