Abstract
In this paper, we demonstrated an all-fiber bidirectional ultrafast thulium-doped fiber laser at 2 μm with a single-wall carbon nanotube presented as saturable absorber. We successfully obtained bidirectional mode-locking operations with pulse repetition frequency adjustable from 35 to 122 MHz by shortening the cavity length. Meanwhile, with the reduction of the intracavity dispersion, the number of Kelly sidebands was significantly decreased and the output energy was more concentrated on the soliton pulse. Besides, by manipulating the pump power and polarization controller, the two results of bidirectional mode-locked pulses with the same repetition frequency and differential repetition frequency were observed. We found that the repetition rate difference between the clockwise and counterclockwise pulse trains was adjustable by changing the pump power or controlling the intracavity polarization. When the pulse repetition frequency was 35 MHz and 122 MHz, the adjustment range of repetition rate difference was 764–922 Hz and 540–2000 Hz, respectively. It is believed that this novel laser source can support free-running dual optical comb spectroscopy to detect important air gases like H2O or CO2 in the future.
Highlights
The applications of femtosecond lasers have greatly expanded from time-resolved spectroscopy [1] to materials processing and manufacturing, microscopy [2], biomedical imaging, ranging and dimensional metrology, timing and synchronization, optical communication, and remote sensing
In this paper, we demonstrated an all-fiber bidirectional ultrafast thulium-doped fiber laser at 2 μm with a single-wall carbon nanotube presented as saturable absorber
Since the optical frequency comb was first proposed more than a decade ago, it profoundly impacted on various ultra-precise scientific fields, such as metrology and spectroscopy
Summary
The applications of femtosecond lasers have greatly expanded from time-resolved spectroscopy [1] to materials processing and manufacturing, microscopy [2], biomedical imaging, ranging and dimensional metrology, timing and synchronization, optical communication, and remote sensing. The development of dual-comb mode-locked laser allows rapid acquisition of molecular spectra with high resolution, which furnishes a powerful method in gas detection. Dual-comb spectroscopy (DCS) usually relies on the generation of two frequency combs, which have slightly different repetition rates between each other. With the rapid development of different laser multiplexing techniques, the free-running dual-comb lasers [3]–[8] have been proved to be effective tools for DCS, which make possible for the direct generation of two high-stability mode-locked laser outputs with different repetition frequencies from a single cavity [3], [9], [10]. As the two combs are generated from a single cavity, intrinsic phase coherence and no requirement for complicated servo locking systems enable compact and low-complexity DCS
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