Broadband photonic control for dual-mode terahertz laser emission

Short, holographically designed, aperiodic distributed feedback (ADFB) gratings are able to provide multi-band spectral filtering over arbitrarily wide bandwidths, offering a complimentary photonic technology to ultra-broadband terahertz quantum cascade lasers (THz QCLs). Using an ADFB grating, ion milled directly into the laser waveguide, high resolution spectral filtering is achieved in THz QCLs with heterogeneous active regions producing two distinct spectral gain peaks centred around 2.65 and 2.9 THz. Simultaneous dual-mode emission is achieved from a single section laser, with up to 20-dB side-mode suppression. Discrete electronic mode tuning occurs between ADFB bands, giving a switchable mode separation ranging from 163 to 267 GHz, along with continuous electronic and thermal tuning of up to ∼2 GHz.