Abstract
An all-fiber Raman fiber oscillator operating at 2118 nm pumped by homemade thulium-doped fiber laser with continuous output power of 4.2 W has been demonstrated in this paper. By means of 26 m ultrahigh-numerical-aperture fibers, the average slope efficiency can be up to 23.6%. Because of the Raman spectrum broadening of the first Stokes light, the intensity of high order Raman Stokes has been suppressed. The mechanism of Raman spectrum broadening has been analyzed by group-velocity dispersion and Four-Wave Mixing frequency theories in detail. Two mode field adaptors have been used to reduce the intracavity loss and thermal deposition, which indicates that the proposed architecture is robust and has significant power scaling potential.
Highlights
Raman fiber laser has been listed as an interesting direction in mid-infrared laser region[5], due to the flexibility of laser emission at almost any desired >2.1 μm wavelength by means of nonlinear wavelength conversion
The proposed resonant cavity formed by a pair of fiber Bragg gratings (FBGs) can decrease the threshold of Raman fiber laser
The mechanism of spectral broadening and slightly red-shift of central wavelength are analyzed in detail through Figs 6 and 7 and considered to be related to Four- Wave Mixing (FWM)
Summary
Raman fiber laser has been listed as an interesting direction in mid-infrared laser region[5], due to the flexibility of laser emission at almost any desired >2.1 μm wavelength by means of nonlinear wavelength conversion. Because the absorption losses of guiding light in traditional silica fibers are naturally large, researchers usually construct Raman lasers by pulse mode[6,7]. The pump sources of pulse Raman lasers are complicated and the average powers are usually quite low. In 2004, single-mode Raman fiber lasers emitting a few hundreds of milliwatts at wavelength of 2.0 and 2.2 μm were demonstrated[8]. 11, and there is still some room for improvement It is noted for a long time that the intrinsic infrared absorption of GeO2 glass and the impurity of the Ge-OH absorption bands are shifted to longer wavelength than those in silica glass[12]. By using highly Ge-doped silica-based fiber, the longest wavelength of Raman laser is 2.43 μm with output power of 0.3 W has been obtained[7]. The average slope efficiency is achieved up to 23.6% with respect to incident pump light which is the highest record to the best of our knowledge
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