Widely Tunable 1.7 μm Vector Dissipative Soliton All-Fiber Thulium Laser

Here, we report a tunable 1.7 μm dissipative soliton (DS) mode-locking (ML) laser. Without the use of any saturable absorbers (SAs), the ML operation is realized via intra-cavity cross phase modulation (XPM) induced by an externally injected ultrafast laser. The periodical phase modulation in XPM is the intrinsic mechanism of initiating this kind of ML. By optimizing the pump wavelength and the length of thulium (Tm)-doped fiber (TDF), the gain peak of the TDF can shift to the 1.7 μm waveband, allowing a direct generation of the 1.7 μm laser. This enables a truly all-fiberized 1.7 μm laser cavity without the use of any bulk bandpass filter. The typical central wavelength of the DS pulses we achieve is located at ∼ 1750 nm. The corresponding pulse duration is ∼ 4.358 ps, which can be further compressed to ∼264 fs. The soliton trapping in XPM causes a self-adaptive shift of the 1.7 μm laser wavelength, which can compensate for the cavity detuning between the 1.7 μm laser and the externally injected laser. Taking advantage of this self-adaptive shift of the laser wavelength, the wavelength of the 1.7 μm laser can be tuned continuously from 1733.71 nm to 1767.56 nm by changing the cavity length of the 1.56 μm pulsed laser. For each 0.1 ps cavity detuning, the 1.7 μm laser has a wavelength shift of ∼ 1.5 nm. Through a polarization controller (PC) and a polarization beam splitter (PBS), we further investigate the vector characteristics of the 1.7 μm DS pulses.