通过加热光子晶体光纤, 其包层中空气孔由于表面张力的作用而塌缩减小。理论和实验结果表明, 空气孔的塌缩在满足波导的渐变条件下, 引入的能量损耗非常小。空气孔的塌缩减小, 可以有效地增加光子晶体光纤的模场直径, 从而不仅可以提高光耦合的效率和光纤端面的损伤阈值, 而且可以降低与其它模场直径不匹配的普通光纤的熔接损耗。

A method for effectively increasing mode field diameter (MFD) of photonic crystal fibers (PCFs) is demonstrated in this paper. Air holes in the cladding of a PCF will be collapse when the PCF is heated due to surface tension. Theoretical and experimental results show that energy loss is very low if the transition connecting the original PCF and the collapsed section is adiabatic. The collapse of air holes can effectively increase the MFD of PCFs. The increase of MFD can not only evidently enhance optical coupling efficiency and surface damage limit, but also apparently reduce splicing loss caused by the mismatch of MFDs with other conventional step fibers．