Broadband Optical Frequency Comb Generation With Flexible Frequency Spacing and Center Wavelength

A broad-band optical frequency comb with flexible frequency spacing and center wavelength is proposed and experimentally demonstrated.The proposed scheme consists of a single continuous-wave laser, cascaded Mach-Zehnder modulator (MZM) and phase modulator (PM), two-stage dispersion-flattened highly nonlinear fibers (DF-HNLFs) and a single-mode fiber (SMF) in between.A narrow-band frequency comb is generated in the MZM and PM and a broad-band frequency comb is achieved by self-phase modulation (SPM) based spectral broadening in DF-HNLFs.Since the DF-HNLF has low dispersion over a wide wavelength range, the central wavelength of the generated frequency comb can be tuned from 1535 nm to 1564 nm.In addition, the central wavelength of frequency comb has a potential to be extended to L-band according to the dispersion profile of the DF-HNLF and the operation bandwidths of the MZM and PM.By tuning the driving radio-frequency (RF) signal, the frequency spacing of the generated frequency comb can be tuned.In the experiment, the frequency spacing of 25 GHz and 40 GHz has been achieved.