Sub-THz passive harmonic mode-locking effects in monolithic and external-reflector compound cavity laser diodes

Passively harmonic mode-locked laser diodes are capable of generating pulses at repetition rates in excess of 1.5 THz. Harmonic mode-locking techniques fall into two main categories: colliding pulse mode-locking (CPM) and compound cavity mode-locking (CCM). The (asymmetric) CPM effect has previously been used to achieve mode-locking at frequencies up to 860 GHz. Various CCM constructions were previously used or proposed for mode-locking at even higher frequencies. Such lasers can be used as local oscillator sources for mm-wave imaging, radio astronomy and atmospheric sensing applications. Here, we report experimental results from multi-section monolithic QW laser diodes designed to mode-lock with the use of the CPM and CCM techniques, and demonstrate a hybrid approach which combines the two in an external reflector cavity.