光子晶体光纤具有特殊的导光机制和结构可调性, 可以产生奇异的色散特性及高非线性, 为非线性光纤光学领域的研究提供了新的条件。 受多种非线性光学效应的共同作用, 在不同泵浦光脉冲参数条件下, 不同结构参数及传输特性的光子晶体光纤能产生丰富的非线性光谱。 利用分步傅里叶方法求解非线性薛定谔方程, 模拟飞秒激光脉冲在光子晶体光纤中的传输过程, 获得输出光谱与入射光脉冲参数(泵浦光峰值功率P、 泵浦光波长λ、 光脉冲形状、 光脉冲宽度TFWHM)、 光纤结构参数(孔间距Λ、 空气填充比d/Λ、 光纤长度z)、 传输特性(色散、 非线性系数)的关系, 分析拉曼孤子、 色散波、 自相位调制等非线性效应产生的光谱特性。 利用光子晶体光纤包层节区进行非线性光学实验研究, 获得了孤子波和色散波的宽带光谱输出。 理论分析与实验测量的光谱中都包括了波长0.5 μm附近可见光波段的蓝移色散波、 0.82 μm波段的剩余泵浦光、 1.1 μm波段的孤子波、 2 μm附近的红移宽带色散波。 理论分析与实验测量结果一致, 阐明光子晶体光纤中非线性光谱产生的物理原理, 实现了对宽带光谱的可控输出, 为高非线性光子晶体光纤的结构设计、 制备及非线性光谱的应用研究奠定基础。

Photonic crystal fiber can generate particular dispersion properties and highly nonlinear, because of the special guiding mechanism and the adjustable structure parameters, which provides new conditions for the study of nonlinear fiber optics. There are rich nonlinear spectral properties produced by a variety of nonlinear physical effect, under different pump light pulse parameters in photonic crystal fibers with different structure and transmission properties. At present many papers have reported the experimental results of nonlinear optical properties in photonic crystal fiber, but there is little theoretical analysis about the produced mechanism and the change rule of the nonlinear spectrum. In the paper, solving nonlinear Schrodinger equation with split-step Fourier method, transmission process of femtosecond laser pulse in photonic crystal fiber is simulated. The relationship between the output spectrum and incident light pulse parameters (the peak power of pump light P, the wavelength of pump light λ, the shape of light pulse, the width of light pulse TFWHM), the structure parameters of optical fiber (the pitch Λ, the hole-to-pitch ratio d/Λ, the length of fiber), the transmission characteristics (the dispersion properties, the nonlinear coefficient) is obtained. The spectral characteristics produced by nonlinear effects of the Raman soliton, dispersive wave, self-phase modulation are analyzed. The nonlinear optical spectrum of cladding note in photonic crystal fiber is studied in experiments, the broadband spectrum of soliton wave and dispersive wave is obtained. There are blue-shift dispersive wave near the wavelength of 0.5 μm, residual pump light near the wavelength of 0.82 μm, soliton wave near the wavelength of 1.1 μm, red-shift broadband dispersion wave near the wavelength of 2 μm in the spectrum obtained both in theory and experiment. The numerical simulation is confirmed through experimental observation. The physics principle of the nonlinear spectrum in photonic crystal fiber is revealed. These are useful and practical to realize the controllable output of broadband spectrum. These provide guidance for the structure design, fabrication, applied research of high nonlinear photonic crystal fiber.