Polarization-multiplexed, synchronous ultrashort pulse generation from a linear-cavity fiber laser with a polarization-rotation loop mirror

Multiple pulse generation in a single cavity attracts increasing attention from scientists and engineers. It could greatly simplify the laser system for applications requiring multiple pulses. Here, with a polarization-rotation loop mirror and a Faraday mirror at the ends of the isolator-free linear fiber cavity, the polarization states of the beams could be switched in each trip across the cavity, and pulses with different state of polarization may circulate in the loop mirror in different directions. Thus, two pulses with orthogonal polarization states could exist and propagate in the cavity separately. Pumped at 13 mW, polarization-multiplexed picosecond pulse outputs centered at 1564.40 nm and 1564.42 nm could be experimentally observed from the 2*2 output coupler, respectively. By examining the RF spectrum at both the fundamental and 100 times repetition rate and the temporal pulse trains, it is determined that the polarization multiplexed pulses have the exact same repetition rate, which is attributed to the completely common propagation path and compensated polarization mode dispersion due to the end mirrors. Such polarization-multiplexed, synchronous ultrashort pulse generation from a linear-cavity fiber laser provides a simple laser configuration and method to generate stable synchronous pulses.