Microstrip Antenna Coupled Distributed Feedback Terahertz Quantum-Cascade Lasers

By introducing coupled microstrip antennas on THz Distributed Feedback (DFB) Quantum Cascade Lasers (QCLs), the radiation efficiency of each feedback aperture is greatly enhanced. Single mode emission similar to 3 THz from a 31-period antenna-coupled third-order DFB laser yields similar to 4 times improvement in output power comparing with a corrugated third-order device fabricated on the same gain medium. This 31-period device has similar to 15x25 degrees beam divergence and 4 mW pulsed power (4%) at 10 K with maximum lasing temperature (T-max) at 134 K (pulsed). When phase matching condition is met, emissions from 81 apertures (4-mm long) are coherently combined to form a narrow beam with 12.5 degrees divergence. Further experiment demonstrated the new device at 4 THz (25-period, similar to 18 mu mx1-mm long. The 4 THz device reaches >8 mW pulsed power (10%) at 12 K with T-max 109 K (pulsed) and >77 K (cw). The slope efficiency is 450 mW/A with 0.57% wall-plug. It is worth pointing out although the antennas would be excited differently, similar enhancement in out-coupling efficiency can also be observed in second-order surface-emitting THz DFB lasers. Begin the abstract two lines below author names and addresses.