光子晶体光纤产生超连续谱的相干性研究

研究光子晶体光纤中超连续谱的时间相干性和空间相干性.采用时间分辨率为飞秒级的迈克尔逊干涉仪,通过在零点附近改变两光路的延迟,对超连续谱的复时间相干度曲线进行测量,得到超连续谱的相干长度为3.71μm.采用同样系统对飞秒泵浦源的复时间相干度曲线进行测量,计算得到其相干长度为62.24μm.通过计算光程差为零点处的互相干度得到超连续谱的空间相干度为0.77,表明光纤小的发光面积使其空间相干性较好.利用准直透镜和分光棱镜将光纤输出的光束进行分光,得到超连续谱中几种不同颜色的输出光谱及对应的脉冲序列,其脉冲序列与泵浦激光有相同的重复频率.

Analysis on the coherence properties of supercontinuum spectra generated in a photonic crystal fiber

Coherence properties of supercontinuum (SC) spectra with a bandwidth of about 500 nm were experimentally studied by using Michelson interferometer whose temporal resolution was up to femtosecond level.Degree of coherence of supercontinuum was measured to be 0.77 which indicated that good spatial coherence property was achieved due to the small emitting area of the polarization maintaining photonic crystal fiber (PM-PCF).Under the same experimental condition,coherence length of supercontinuum and pump light were measured to be 3.71 μm and 62.24 μm,respectively.It was shown that the coherence length of supercontinuum was much shortened which was of advantage to improve the longitudinal resolution of optical coherence tomography (OCT).Pulse sequences of supercontinuum with different wavelength range were observed which had the same repetition rate with the pump laser.