Dual-comb source with a reconfigurable repetition frequency difference using intracavity Brillouin lasers

A Brillouin-assisted 80-GHz-spaced dual-comb source with a reconfigurable repetition frequency difference ranging from 48 MHz to 1.486 GHz is demonstrated. Two pairs of dual-pump seeds with an interval offset produce the corresponding dual Brillouin lasers in two fiber loops, and then the Brillouin lasers give rise to dual combs via the cavity-enhanced cascaded four-wave mixing effect. The repetition frequency difference is determined by the interval offset of the dual-pump seeds, which is induced by the Brillouin frequency shift difference between different fibers in a frequency shifter. Each comb provides 22 lasing lines, and the central 10 lines in a 20-dB power deviation feature high optical signal-to-noise ratios exceeding 50 dB. The linewidths of the dual-comb beating signals are less than 300 Hz, and the absolute linewidths of the comb lines are around 1.5 kHz. The dual-comb source enables substantial repetition frequency differences from 48 MHz to 1.486 GHz by changing the pluggable fibers in the frequency shifter.