In this study, we presented flat-topped coherent supercontinuum lasers with tunable repetition rates and programmable spectral bandwidths. Supercontinuum sources with ultra-broadband and high-repetition-rate coverage can be achieved by merging nonlinearly broadened electro-optic optical frequency combs with optical line-by-line spectrum shaping. Spectral bandwidth programming is implemented by iterative spectrum shaping and input power control of highly nonlinear stages, whereas repetition rate tuning is performed by modulation speed control in optical frequency combs. Herein, we implemented a programmable and tunable flat-topped supercontinuum with a maximum bandwidth and repetition rate of 55 nm at 10 dB and 50 GHz, respectively. To clarify the coherence of the supercontinuum during tuning and programming, we performed a phase-noise analysis. We proposed a remarkably modified self-heterodyne method to measure the phase noise of each mode precisely by filtering specific supercontinuum taps in a Mach-Zehnder interferometer. With this method, it has been proved that the single-sideband spectra in each mode are almost similar to that of the RF clock, indicating that our programmable and tunable supercontinuum generation process added minimal degradation to the phase noise properties. This study shows possibilities for generating hundreds of programmable and tunable flat-topped optical carriers with robustness and coherence.
© 2022. The Author(s).