title: High efficiency, single-lobe surface-emitting DFB/DBR quantum cascade lasers.
abstract: We demonstrate a surface-emitting quantum cascade laser (QCL) based on second-order buried distributed feedback/distributed Bragg reflector (DFB/DBR) gratings for feedback and outcoupling. The grating fabricated beneath the waveguide was found to fundamentally favor lasing in symmetric mode either through analysis or experiment. Single-lobe far-field radiation pattern with full width at half maximum (FWHM) of 0.18° was obtained along the cavity-length direction. Besides, the buried DFB/DBR grating structure successfully provided an efficient vertical outcoupling mechanism with low optical losses, which manages to achieve a high surface outcouping efficiency of 46% in continuous-wave (CW) operation and 60% in pulsed operation at room temperature. Single-mode emission with a side-mode suppression ratio (SMSR) about 25 dB was continuously tunable by heat sink temperature or injection current. Our work contributes to the realization of high efficiency surface-emitting devices with high far-field beam quality that are significantly needed in many application fields.
authors.forename: Ying-Hui
authors.initials: YH
authors.lastname: Liu
authors.forename: Jin-Chuan
authors.initials: JC
authors.lastname: Zhang
authors.forename: Fang-Liang
authors.initials: FL
authors.lastname: Yan
authors.forename: Zhi-Wei
authors.initials: ZW
authors.lastname: Jia
authors.forename: Feng-Qi
authors.initials: FQ
authors.lastname: Liu
authors.forename: Ping
authors.initials: P
authors.lastname: Liang
authors.forename: Ning
authors.initials: N
authors.lastname: Zhuo
authors.forename: Shen-Qiang
authors.initials: SQ
authors.lastname: Zhai
authors.forename: Li-Jun
authors.initials: LJ
authors.lastname: Wang
authors.forename: Jun-Qi
authors.initials: JQ
authors.lastname: Liu
authors.forename: Shu-Man
authors.initials: SM
authors.lastname: Liu
authors.forename: Zhan-Guo
authors.initials: ZG
authors.lastname: Wang