Surface-emitting planarized THz quanum cascade laser frequency combs with inverse-designed waveguide facets

Abstract

We present a high-performance planarized waveguide THz quantum cascade laser frequency comb, where an inverse-designed active waveguide front facet with a reduced reflectivity is coupled to a patch array antenna, and all the components are optimized for an octave-spanning emission spectrum (2-4 THz). Broadband frequency comb states spanning over 800 GHz with a single narrow RF beatnote up to -50 dBm are measured at 20 K. The slope efficiency is improved by around five times, with a peak output power of 13 mW in pulsed mode (10% duty cycle at 20 K). Far-field measurements of the surface emission display a narrow symmetric pattern with a beam width of (21° x 20°).