Surface-emitting distributed feedback terahertz quantum-cascade phase-locked laser arrays

Abstract

A new approach to achieve high-power, symmetric beam-pattern, single-mode THz emission from metal-metal waveguide quantum-cascade laser is proposed and implemented. Several surface-emitting distributed feedback terahertz lasers are coupled through the connection phase sectors between them. Through carefully choosing the length of phase sectors, each laser will be in-phase locked with each other and thus create a tighter beam-pattern along the phased-array direction. A clear proof of phase-locking phenomenon has been observed and the array can be operated in either in-phase or out-of-phase mode at different phase sector length. The phase sector can also be individually biased to provide another frequency tuning mechanism through gain-induced optical index change. A frequency tuning range of 1:5 GHz out of 3:9 THz was measured. Moreover, an electronically controlled "beam steering" device is also proposed based on the result of this work. This thesis focuses on the design, fabrication and measurement of the surface-emitting distributed feedback terahertz quantum-cascade phase-locked laser arrays.