Optical comb for generation of a continuously tunable coherent THz signal from 122.5 GHz to >2.7 THz.

We present a continuously tunable optical frequency comb generator (OFCG), with comb lines spanning over 3.8 THz which, to the best of our knowledge, is the widest span yet reported for a single-phase modulator OFCG system. The line spacing, exactly determined by a microwave reference, can be continuously tuned and, by heterodyning two lines, enables the generation of a continuously tunable electrical signal from 122.5 GHz to >2.7  THz. The composite noise of the heterodyne between two lines has been measured up to a record frequency of 300 GHz and is -75  dBc/Hz at 10 kHz offset at 300 GHz, limited by the multiplied phase noise of the reference synthesizer.