Phosphate Fibers Can Serve as Ultrashort Pulsed Fiber Amplifiers

Update time: 2024-01-05
High energy, high peak power ultrashort pulsed laser has important applications in long-range Lidar, materials processing and so on. The main oscillation pulse amplification (MOPA) is usually used in ultrashort pulsed laser, in which the gain fiber is the key component. Active silica fibers face challenges in rare-earth solubility, the uniformity and very low numerical aperture, resulting in their lower nonlinear threshold and lower output pulse energy. As an alternative, multi-component oxide glass has advantages in high doping concentration, good optical uniformity and can obtain large mode field area and high nonlinear threshold of high-power pulse amplification. 
Most recently, a research team led by Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, has succeeded in preparing the high Yb doping phosphate fiber with large mode field area. The study was published in Chinese Journal of Lasers.
In their experiment, more than 27 W of average power has been achieved in self-developed Yb doped phosphate double-cladding fiber. The amplifier adopts the all-fiber configuration of Yb doped phosphate fiber and matched passive silica fiber (20/130 μm) through hetero fusion (loss of each fusion point is lower than 0.3 dB). The core and inner/outer cladding had diameter of 30 μm and 135/280 μm, respectively. The numerical apertures of core and inner cladding are 0.03 and 0.41 respectively, the concentration of Yb2O3 in the fiber core is 6 wt%, and the background loss is 0.6 dB/m@1300 nm, using a length of 30 cm. Using 976 nm cladding pumping, the average power of amplified pulse laser is obtained as shown in Figure 2. The maximum average output power is 27.3W, and the Slope efficiency is 71.4%. At the same time, nonlinear effects such as stimulated Brillouin scattering are not observed.
Moreover, compared with silica fiber, the studied Yb-phosphate fiber has a much higher concentration of Yb, a shorter length of fiber and high nonlinear threshold, indicating an excellent fiber host for high energy ultrashort pulse amplifier.    
This research leads to a host material for fiber amplifiers operated at L-band wavelength.
This work was supported by National Key R&D Program of China.

Fig. 1. Structural diagram of pulsed laser amplifier using Yb-doped large-mode-area phosphate fiber (Image by SIOM)

Fig. 2. Average power of amplified pulsed laser versus pump power with spot and spectrum of output laser shown in inset 
(Image by SIOM)

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Shanghai Institute of Optics and Fine Mechanics, CAS