RF injection-locking of terahertz quantum cascade lasers

It is demonstrated that the cavity resonance frequency – the round-trip frequency – of terahertz quantum cascade lasers can be injection-locked by direct modulation of the bias current using an RF source. Metal-metal and single-plasmon waveguide devices with round-trip frequencies up to 35 GHz have been studied, and show locking ranges above 200 MHz. A square-root dependence of the locking range with RF-power was found to be in agreement with classical injection-locking theory. Inside this locking range the laser round-trip frequency is phase-locked, with a phase noise determined by the RF-synthesiser, leading to the generation of modelocked pulses with low timing jitter.