Experimental and theoretical investigation of the tunability of polarization-multiplexed pulse characteristics in a birefringent fiber laser

Tunable polarization-multiplexed fiber laser is widely regarded as a cost-effective and multifunctional source for single-cavity dual-comb metrology. Nevertheless, the issues regarding its tunability such as the tunable law and quantitative control of repetition rate difference, and tunability of other pulse parameters are not yet deeply investigated to promote the application. In this paper, we experimentally and theoretically investigated the tunability of multiple polarization-multiplexed pulse characteristics, including repetition rate difference, relative intensity difference, and the state of polarization, in a birefringent fiber laser. The relationship between the pulse tunability and polarization controller induced phase delay and angle rotation are revealed. When continuously tuning the rotation angle of incident light by rotating the polarization controller, the tunable law of repetition rate difference, relative intensity difference and state of polarization is experimentally revealed. In addition, except for the widely reported intracavity polarization mode dispersion and nonlinearity, it is revealed polarization controller-induced phase delay could also limit the available tunable range of repetition rate difference of the polarization-multiplexed pulses. These results provide further physical understanding of multiple tunable pulse characteristics of polarization-multiplexed birefringent fiber laser. Meanwhile, investigation of the tunability could be beneficial for fine and intelligent control of laser source and practical applications such as versatile updating speed, precision optimization and relative intensity adjustment in polarization-multiplexed dual-comb spectroscopy and ranging.