Abstract
We report on investigation the potential of a 7 wt% (8.35 × 1020 Tm3+/cm3) doped silicate fibers for high-gain fiber amplifiers. Such a high ion concentration significantly reduces the required fiber length of high-power 2 μm fiber laser systems and allows the high-repetition rate operation in 2 μm mode-locked fiber lasers. To evaluate the feasibility of extracting high gain-per-unit-length from this gain medium, we measure several key material properties of the silicate fiber, including the absorption/emission cross-sections, upper-state lifetime, fiber background loss, and photodarkening resistance. We show through numerical simulations that a signal gain-per-unit-length of 3.78 dB/cm at 1950 nm can be achieved in a watt-level core-pumped Tm3+-doped silicate fiber amplifier. In addition, an 18-dB 2013-nm amplifier is demonstrated in a 50-cm 7 wt% Tm3+-doped double-clad silicate fiber. Finally, we experimentally confirm that the reported silicate host exhibits no observable photodarkening.
Highlights
Ultrafast laser sources in the 2-μm eye-safe region are of interest for many applications, such as frequency comb metrology, environmental sensing, eye-safe LIDAR, space communication, medical surgery, particle accelerators, and light sources for efficient mid-IR generation
We report in this paper our latest progress in silicate fiber fabrication as well as the simulation and testing of Tm3+-doped silicate fiber amplifier with one of the highest published concentrations (8.35 × 1020/cm3) for a Tm3+-doped fiber
To provide an experimental validation of the silicate fiber amplifier operation, we developed a 793-nm cladding-pumped Tm3+-doped silicate fiber master-oscillator power amplifiers (MOPAs)
Summary
Ultrafast laser sources in the 2-μm eye-safe region are of interest for many applications, such as frequency comb metrology, environmental sensing, eye-safe LIDAR, space communication, medical surgery, particle accelerators, and light sources for efficient mid-IR generation. To produce 2-μm laser emission in fibers, Tm3+ is a favorable ion because it offers high quantum efficiency, broad gain bandwidth, and strong absorption band around 800 nm, the wavelength available from commercial high-power diode lasers. The output power from Tm3+-doped fiber lasers and amplifiers have been scaled to well above the kilowatt level. The high Tm3+ concentration enables the efficient cross-relaxation processes leading to high quantum efficiencies. The minimum Tm3+ concentration to generate efficient cross-relaxation process is known to be around 3wt%. This doping level is hard to achieve in a silica fiber because excessive amounts of Tm3+ in silica fibers may cause concentration quenching and photodarkening
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