单模硫系玻璃光纤的制备及其超连续谱的产生特性

摘要

Chalcogenide (ChG) glasses are well known for their unique characteristics in infrared (IR) and strong nonlinearities, endowing them as promising candidates for Mid-IR supercontinuum generation (SCG). Here, step-index As-S fiber with a small core was fabricated via twice-extrusion method. The fiber is single-mode when the propagating light wavelength is longer than 6.3 μm. Loss baseline of the step-index fiber is about 1 dB/m. Ze-ro-dispersion-wavelength (ZDW) of the fiber is located at near 5.2 μm. By pumping the fiber with a femtosecond laser of optical parametric amplifier (OPA), Mid-IR SCG was investigated in multi-length scale fibers with different pumping wavelengths. Launching intense ultra-short pulses (～150 fs, 1 kHz) into a 23-cm-long fiber, Mid-IR SC spanning from 1.5 μm to 8.7 μm can be observed when pumping at a central wavelength of either 4.5 μm or 5.2 μm, corresponding to absorption peak at normal dispersion regime and ZDW, respectively. Besides, the spectra spanning would be extended in shorter fiber length under optimized pumping laser power. For ChG glass fiber, shorter fiber length is much more suitable for SC spanning than longer fiber length.%硫系玻璃具有独特的红外光学性能和极高的光学非线性等特点, 使得硫系光纤成为中红外超连续谱产生的优选材料.基于二次挤压法制备了单模As-S光纤, 并利用飞秒脉冲和光参量放大器作为泵浦源研究了该光纤的中红外超连续谱的产生特性, 包括光纤长度、泵浦波长、泵浦功率对超连续谱产生的影响.结果表明该单模光纤具有较低的传输损耗和较小的材料色散分布; 相比于传统零色散点波长附近泵浦, 在正常色散区且杂质吸收峰附近泵浦也可获得脉冲的极大展宽(泵浦参数: 4.5 μm, 1 kHz, 150 fs, 光纤长度23 cm, 输出谱宽为1.5～8.7 μm@60 dB带宽); 较短长度的硫系光纤便可产生超宽频谱输出, 相反, 光纤长度越长输出频谱越窄且平坦性变差.