High power surface emitting terahertz laser with hybrid second- and fourth-order Bragg gratings.

ABSTRACT: A surface-emitting distributed feedback (DFB) laser with second-order gratings typically excites an antisymmetric mode that has low radiative efficiency and a double-lobed far-field beam. The radiative efficiency could be increased by using curved and chirped gratings for infrared diode lasers, plasmon-assisted mode selection for mid-infrared quantum cascade lasers (QCLs), and graded photonic structures for terahertz QCLs. Here, we demonstrate a new hybrid grating scheme that uses a superposition of second and fourth-order Bragg gratings that excite a symmetric mode with much greater radiative efficiency. The scheme is implemented for terahertz QCLs with metallic waveguides. Peak power output of 170?mW with a slope-efficiency of 993?mW A-1 is detected with robust single-mode single-lobed emission for a 3.4?THz QCL operating at 62?K. The hybrid grating scheme is arguably simpler to implement than aforementioned DFB schemes and could be used to increase power output for surface-emitting DFB lasers at any wavelength.

SUBMITTER: Jin Y 

PROVIDER: S-EPMC5895695 | biostudies-other | 2018 Apr

REPOSITORIES: biostudies-other