Synchronous nanosecond and femtosecond pulses delivered from a low-repetition-rate Er-doped fiber laser mode-locked by nonlinear polarization evolution is experimentally proposed. Here, the repetition rate is set as ~4.5 MHz by introducing sufficiently long fiber in a ring cavity. By fully exploiting long fiber and anti-saturation absorption characteristics, it is experimentally observed that dissipative-soliton-resonance pulse with the nanosecond-level pulsewidth and femtosecond soliton pulse synchronously propagate in the same cavity. Besides, the pulsewidth of dissipative-soliton-resonance pulse and laser output power could be tailored by finely configuring the bidirectional pump powers. These results provide deep understanding of low-repetition-rate pulse laser and an intriguing way to obtain tunable dual-scale synchronous pulses, indicating the high potential for multiple-pulse laser processing and so on.
We proposed an absolute distance measurement method with a large non-ambiguity range based on a polarization-multiplexed dual-comb fiber laser. By fully exploiting the intracavity linear loss based gain profile tilting and residual birefringence, polarization-multiplexed dual-comb pulses with tunable repetition rate difference and overlapping spectra in the 1530-nm gain region are obtained. The repetition frequency difference could be continuously tuned from ~89 to ~194 Hz. The alternative sampling under different repetition rate difference is experimentally verified to be effective approach to extend the non-ambiguity range in the single-cavity dual-comb ranging. The non-ambiguity range could reach thousands of kilometer while the precision could reach at least on the order of hundreds of micrometers. These results indicate a simple and intriguing route with a free-running laser source to obtain ranging with large non-ambiguity range, showing high potential in the applications such as satellite formation flying, large-scale 3D surface morphology measurement and so on.
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.
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