Recently, a research team from the High Power Laser Unit Technology Laboratory of Shanghai Institute of Optics and Precision Machinery (SIPM) of the Chinese Academy of Sciences (CAS) has prepared a high-concentration ytterbium-doped quartz fiber by using improved chemical vapor deposition (MCVD) technology combined with a liquid-phase doping process, and built an ultrashort-cavity fiber laser with the fiber, which achieves a single-frequency and a highly-frequency-locked laser output in the 1-µm band, respectively. The results are presented as "High ytterbium concentration Yb/Al/P/Ce co-doped silica fiber for 1-μm ultra-short cavity fiber laser application". High ytterbium concentration Yb/Al/P/Ce co-doped silica fiber for 1-μm ultra-short cavity fiber laser application" was published in Optics Express.
High-performance single-frequency and high-frequency mode-locked fiber lasers require ytterbium-doped fibers with high gain coefficients, high conversion efficiencies and low photon darkening. Due to the low dissolution of rare earth ions in the quartz matrix, the rare earth ion clustering effect caused by high doping concentration will seriously affect the laser performance of the fiber. The research team prepared a Yb/Al/P/Ce co-doped quartz fiber by optimizing the core components, in which the Yb ion doping concentration is 2.5 wt%, and the core absorption coefficient reaches 1400 dB/m at 976 nm.
Figure 1. Characteristics of highly doped Yb/Al/P/Ce quartz fiber. a) refractive index distribution, b) doping element distribution, c) core loss spectrum, and d) core absorption spectrum.
In order to characterize the laser performance of the self-developed high-concentration fiber in practical application scenarios, the researchers used the fiber to build two ultrashort resonant cavities with all-fiber structures for laser experiments. First, a Distributed Bragg Reflection (DBR) laser cavity was constructed using a 1-cm ytterbium-doped fiber, and a single longitudinal-mode laser output with a power of 75 mW and a linewidth of 14 kHz was successfully achieved. Subsequently, a passive mode-locked fiber laser based on a semiconductor saturable absorber mirror (SESAM) was constructed with a gain fiber length of 8.4 cm, and a pulsed laser output with a repetition frequency of 1.23 GHz and a pulse width of 6.4 ps was achieved. The results of this study show that the preparation of high concentration ytterbium-doped quartz fiber with excellent laser performance, is expected to be applied to high-precision fiber sensing, optical frequency comb and other areas of high-performance fiber laser research and development.
