Generation of GHz line-spacing tunable optical frequency combs using Talbot effects

In this paper, the generation of GHz line-spacing tunable optical frequency combs (OFCs) was demonstrated using an electro-optical (EO) Talbot laser and a phase modulator. In the EO Talbot laser, the frequency shifting was realized with a dual-parallel Mach-Zehnder modulator (DPMZM) working for carrier-suppressed single-sideband modulation. The PM was employed to achieve the spectral Talbot effect and compensate the phase introduced by the temporal Talbot effect in the laser loop. Arbitrary control of OFC line-spacing was realized using temporal and spectral Talbot effects. The principle of this OFC generator was theoretically modeled. In the experiments, the 2 GHz line spacing of an OFC was multiplied to be 4 GHz, 6 GHz, 8 GHz, and 10 GHz. The frequency spacing of the OFC can also be multiplied with a fractional factor of 3/4, 7/2, 8/5, and 10/7, which was confirmed by simulations.