高非线性光子晶体光纤中飞秒脉冲的传输特性和超连续谱产生机制的实验研究及模拟分析

Experimental study and numerical analysis of femtosecond pulse propagation and supercontinuum generation in highly nonlinear photonic crystal fiber

用实验和数值模拟两种方法研究了高非线性光子晶体光纤中飞秒激光脉冲的传输特性和超连续谱的产生机理,给出了抽运脉冲在三种不同中心波长情况下输出光谱展宽并形成超连续谱的实际测量及理论模拟结果.研究表明:在零色散波长抽运时,光谱展宽以自相位调制为主,同时三阶色散的影响明显,传输脉冲在时域内出现振荡次峰.而在反常色散区抽运时,光谱展宽的初期以自相位调制为主,随后根据抽运功率的不同孤子自频移、高阶光孤子的裂变和四波混频效应会逐渐增强,进而成为光谱展宽的主要原因.与此相应,在时域中能明显看到孤子的形成和红移,飞秒传输脉冲内不再有振荡次峰产生.研究还发现,在零色散波长附近的反常色散区较零色散波长点更易产生四波混频效应.

Femtoseeond laser pulse propagation and supercontinuum generation in a highly nonlinear photonic crystal fiber is investigated experimentally and numerically. Consistent results of continuum generation measured and calculated for 790, 800, and 820 nm pump wavelengths are presented. It is shown that when the pump wavelength overlaps with the zero-dispersion wavelength self-phase modulation and third-order dispersion play an important role, and the oscillation structure appears in the temporal waveform of the propagating pulses, whereas in anomalous dispersion region, the formation and the red-shift of solitons are evident, and the self phase modulation plays a dominant role only in the initial stage. Further spectral broadening is due to solitons self-frequency shift, fission of higher-order solitons and four-wave mixing. It is also found that four-wave mixing occurs more easily in anomalous dispersion region than at the zero-dispersion wavelength.