Abstract
We present a continuously tunable thulium(Tm)-doped fiber laser operating in the important 2.1 μm region, which is tandem-pumped by another Tm-doped fiber laser at 1908 nm. The advantages of pumping a Tm-doped fiber laser at the long-wavelength absorption tail (>1900 nm) of the fiber include a reduced quantum-defect, and efficient suppression of the amplified spontaneous noise (and potential parasitic lasing) at the short-wavelength region. This facilitates attainment of stable lasing operation in the long-wave emission tail of the Tm fiber at ~2.1 μm. By rotating a diffraction grating inside the Tm fiber laser cavity, we experimentally achieved a wavelength-tuning range of 2000-2172 nm. At central wavelengths of 2050 nm, 2150 nm, and 2172 nm, the slope efficiencies were 23%, 16%, and 9.9%, respectively. To the best of our knowledge, this is the first demonstration of long-wavelength operation of a Tm fiber laser system tandem-pumped at >1900 nm.
Highlights
Laser sources operating in the 2.1 μm region will benefit many applications, including environment monitoring, remote sensing and medical surgery [1,2,3], since the 2.1 μm waveband contains broad windows of high atmospheric transparency, and strong, narrowband molecular vibration absorption resonances of atmospheric constituents, such as water vapor and CO2 [4]
In most demonstrations of widely-tunable Tm fiber laser systems, in which fiber Bragg gratings (FBGs) were not used, the wavelength-tuning at the long-wave region were rather limited [8,14,15]
The wavelengthtunable Tm-doped fiber laser cavity, comprised an un-coated aspheric lens of 6 mm focal length and a diffraction grating with 450 grooves/mm in a Littrow configuration providing wavelength-selective feedback and a means for tuning the lasing wavelength
Summary
Laser sources operating in the 2.1 μm region will benefit many applications, including environment monitoring, remote sensing and medical surgery [1,2,3], since the 2.1 μm waveband contains broad windows of high atmospheric transparency, and strong, narrowband molecular vibration absorption resonances of atmospheric constituents, such as water vapor and CO2 [4]. At a pump-wavelength of 1910 nm, the gain difference between the peak wavelength and 2100 nm was only 8 dB, clearly illustrating the reduced parasitic gain in a Tm fiber by using of a longer pump wavelength Another advantage of using 1910 nm pump source is the potential of achieving improved SNR of the laser output. In the calculation of SNRs, the noise power was obtained by summarizing all the power over the wave region away from the central oscillating wavelength of the laser This clearly illustrates the benefit of using a 1910 nm pump source in improving the SNR of the laser output. A wavelength tuning range over 2.0-2.17 μm was obtained by rotating an intra-cavity diffraction grating inside the laser cavity
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