光子晶体光纤纤芯整形获得中空模式输出

实验研究了高非线性光子晶体光纤中模式控制的非线性过程，利用激发出高阶模式获得上转换到可见光波段的色散波.通过控制输入飞秒激光的偏振方向，获得了两组相互正交的高阶模式的非线性输出.进一步在光子晶体光纤空气孔包层中注入蜡修整纤芯结构，使得正交模式的有效模折射率差降低，从而形成简并的模式，并通过叠加简并模式获得了中空模场的输出. 关键词： 光子晶体光纤 飞秒激光 频率变换 中空模式

Hollow beam generation from a highly nonlinear photonic crystal fiber with a modified core

The mode-controlled nonlinear process in a highly nonlinear photonic crystal fiber is studied experimentally. The central wavelength of frequency-upconverted dispersive wave and its transverse intensity profile are controlled through a selective coupling of the pump field to the higher order modes of the fiber and a polarization-sensitive phase matching process. However, due to their large effective index difference, the two orthogonal modes cant be excited simultaneously. The index difference is lowered by injecting wax into the air holes which effectively modifies the core structure. This modification degenerates the two orthogonal high-order modes. As a result, they are excited simultaneously and form a hollow beam output.