2D patch antenna array on a double metal quantum cascade laser with >90% coupling to a Gaussian beam and selectable facet transparency at 1.9 THz.

Abstract

2×2 parallel fed and 3×3 serial fed patch antenna arrays on a benzocyclobutene (BCB) polymer layer are integrated with a 70 μm wide, dry etched, double metal waveguide quantum cascade laser, operating at about 1.9 THz. The BCB surrounds the quantum cascade laser ridge and is planarized to fit precisely its height. The patch antenna arrays emit a linearly polarized, highly symmetric beam perpendicular to the antenna plane. The beams have a FWHM angle of 49° (2×2) and 35° (3×3). Both measurements and simulations indicate coupling factors to a Gaussian beam of over 90%. The antenna design is strongly governed by the high thickness (h=13.6 μm) and the low dielectric constant (ϵr=2.45) of the BCB substrate. Because the patch array has a very low input reflectivity of -13 to -20 dB over the 1.7-2.1 THz operation band, the laser needs a partially transmitting reflector to maintain the Q-factor of the active medium resonator to assure lasing in the antennas operation band. By changing the dimensions of the reflector, the facet transparency can be designed in a wide range from fully transmissive to highly reflective.