Gain-controlled broadband tuneability in self-mode-locked Thulium-doped fibre laser

Abstract

Ensuring self-driven mode-locking and broadband wavelength tuneability in all-fibre-integrated femtosecond laser sources enables a new level of their versatility and extends areas of their applications. Principle limitations for this are traditionally available ultrafast modulators and tuneability techniques. Here, we exploit Thulium-doped fibre to perform three roles in the cavity: laser gain, saturable absorber, and tuneability element via controlling its excitation level. We confirmed that Tm-doped fibre saturable absorption is defined by a reinforced quenching of Tm3+ pairs. As a result, we present both numerically and experimentally a highly stable sub-picosecond pulse generation with a ~90 nm tuneability range spanning from 1873 to 1962 nm via adjusting the cavity feedback. The maximum laser efficiency corresponds to 25% cavity feedback, enabling the highest output energy of 1 nJ in 600-fs solitons at 1877 nm. Overall, the presented laser system establishes a compact and straightforward approach for ultrafast generation, which can be translated to other fibre laser operation wavelengths.

High-peak-power random Yb-fiber laser with intracavity Raman-frequency comb generation

“…The radio frequency (RF) spectrum of the mode-locked pulses was measured with an RF analyzer and the results are shown in Figure S2 (Supplementary Material). The repetition rate of 855 kHz corresponds to the pulsing period of approximately 1.17 μs and the total cavity length of approximately 117 m. The self-ML here can be attributed to signal self-absorption and ion-pair induced energy-transfer upconversion in the highly doped gain fiber [ 38 , 39 ] .

Figure 2 (a) Output characteristics of the RFL as a function of pump power. Inset (from left to right): temporal pulse profiles in the mode-locking, hybrid and random Q -switching states, respectively.

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“…The radio frequency (RF) spectrum of the mode-locked pulses was measured with an RF analyzer and the results are shown in Figure S2 (Supplementary Material). The repetition rate of 855 kHz corresponds to the pulsing period of approximately 1.17 µs and the total cavity length of approximately 117 m. The self-ML here can be attributed to signal self-absorption and ion-pair induced energy-transfer upconversion in the highly doped gain fiber [38,39] .…”

Methods of Radiation Wavelength Tuning in Short-Pulsed Fibre Lasers

“…The spectral range of ~2.3-2.7 µm is still not spanned by tuning ranges of short-pulsed radiation from fibre lasers delivering significant average powers. [12,15,19,24,27,49,52,58,67,69,71,76,77,80,81,91,96,101,117,118,127,131]. Wavelength tuning ranges of short-pulsed fibre lasers with an average output power of over 10 mW [12,15,19,24,27,49,52,58,67,69,71,76,77,80,81,91,96,101,117,118,127,131].…”

Polarization domains and self-mode-locked pulses in an erbium-doped fiber laser

“…For example, the self-phase modulation and the longitudinal modes beating in the fiber cavity can lead to the occurrence of mode locking in the laser [24,25] . The gain fiber, such as erbium-doped fiber [26][27][28][29] and thulium-doped fiber [30][31][32][33] , can also be used as both gain medium and saturable absorber to realize self-Q-switching or self-mode locking, which results from the energy transfer processes such as ion pairs excited state absorption [32] and upconversion interaction [33] . These studies show that the operation mechanisms of self-pulses in fiber lasers are complex, which is worth further exploration.…”