Wavelength-switchable polarization-multiplexed dual-comb fiber laser based on intracavity loss and birefringence tuning

Due to the simple configuration, qualified passive coherence between pulses, and cost-effective characteristics, single-cavity dual-comb sources attract increasing research interest. Actually, such lasers have been experimentally verified in dual-comb metrology such as dual-comb frequency measurement and spectroscopy. Unlike the single-cavity dual-comb fiber laser multiplexed in other dimensions such as wavelength, direction and mode-locked mechanism, polarization-multiplexed pulses own the unique characteristics of overlapping spectra, intrinsic spectral coherence, and tunable repetition rate difference. They are beneficial for the simplification of additional optical amplification and the satisfaction of versatile requirements of dual-comb metrology. Here, we demonstrated a single-wall carbon nanotube saturable absorber mode-locked Er-doped fiber laser to emit wavelength-switchable polarization-multiplexed dual-comb pulses. The intracavity loss is carefully tuned by an additional optical variable attenuator to define the oscillation windows. In both the 1530- and 1550-nm gain regions, spectral-overlapping, polarization-multiplexed pulses are experimentally obtained with the fine configuration of the intracavity state of polarization. The polarization dynamics and tunable repetition rate difference are experimentally revealed. The repetition rate difference is at the tens-of-hertz level, which is somewhat lower than that of the reported polarization-multiplexed fiber laser with additionally introduced polarization-maintaining fiber. Since there are no additional birefringent media, the polarization mode dispersion for polarization-multiplexed pulses is attributed to the residual birefringence. Moreover, the passive mutual coherence is also highlighted. There results provide a simple yet effective way to design switchable and versatile single-cavity dual-comb pulses.