Department of Physics, Bilkent University, Ankara, Turkey.
Opt Lett. 2012 Aug 1;37(15):3042-4. doi: 10.1364/OL.37.003042.
Thermal effects, which limit the average power, can be minimized by using low-doped, longer gain fibers, whereas the presence of nonlinear effects requires use of high-doped, shorter fibers to maximize the peak power. We propose the use of varying doping levels along the gain fiber to circumvent these opposing requirements. By analogy to dispersion management and nonlinearity management, we refer to this scheme as doping management. As a practical first implementation, we report on the development of a fiber laser-amplifier system, the last stage of which has a hybrid gain fiber composed of high-doped and low-doped Yb fibers. The amplifier generates 100 W at 100 MHz with pulse energy of 1 μJ. The seed source is a passively mode-locked fiber oscillator operating in the all-normal-dispersion regime. The amplifier comprises three stages, which are all-fiber-integrated, delivering 13 ps pulses at full power. By optionally placing a grating compressor after the first stage amplifier, chirp of the seed pulses can be controlled, which allows an extra degree of freedom in the interplay between dispersion and self-phase modulation. This way, the laser delivers 4.5 ps pulses with ~200 kW peak power directly from fiber, without using external pulse compression.
热效应会限制平均功率，使用低掺杂、长增益光纤可以最小化热效应，而非线性效应的存在则要求使用高掺杂、短光纤来最大化峰值功率。我们提出沿增益光纤使用不同的掺杂水平来规避这些相互矛盾的要求。通过类比色散管理和非线性管理，我们将这种方案称为掺杂管理。作为实际的初步实现，我们报告了一种光纤激光放大器系统的开发情况，其最后一级由高掺杂和低掺杂 Yb 光纤组成的混合增益光纤。该放大器在 100MHz 时产生 100W 的功率，脉冲能量为 1μJ。种子源是在全正色散区工作的被动锁模光纤振荡器。放大器包括三个全光纤集成级，可在全功率下提供 13ps 的脉冲。通过在第一级放大器之后选择性地放置一个光栅压缩器，可以控制种子脉冲的啁啾，这在色散和自相位调制之间的相互作用中提供了额外的自由度。这样，激光可以直接从光纤输出 4.5ps 脉冲，峰值功率约为 200kW，无需使用外部脉冲压缩。
