Semiconductor THz frequency combs exploiting solution processed graphene

We nano-engineer a miniaturized optical frequency comb synthesizer (FCS) comprising a heterogeneous THz quantum cascade laser integrated with a tightly coupled on-chip solution-processed graphene saturable-absorber reflector. This enable a high power (8 mW) FCS with over 90 optical modes to be demonstrated over more than 55% of the laser dynamic range, with over three-decade reduction of phase-noise over an additional 15% of this range. Furthermore, stable injection locking is demonstrated, paving the way to impact a number of key technologies and applications, including high-precision tunable broadband spectroscopy, quantum metrology and broadband THz nanoscopy.