Experimental Generation of Narrow-Band Paired Photons： from Damped Rabi Oscillation to Group Delay

We report the experimental generation of narrow-band paired photons through electromagnetically induced transparency and spontaneous four-wave mixing in a two-dimensional magneto-optical trap （2D MOT）. By controlling the optical depth of the 2D MOT from 0 to 40, the temporal length of the generated narrow-band paired photons can be varied from 50 to 900 ns. The ＇transition＇ between damped Rabi oscillation and group delay is observed undisputedly. In the damped Rabi oscillation regime, a violation factor of the Cauchy–Schwartz inequality as large as 6642 is observed. In the group delay regime, sub-MHz linewidth （～0.65 MHz） paired photons are obtained with a generation rate of about 0.8×105 s？1.     

弱双折射光纤布喇格光栅反射偏振对温度响应特性的研究

理论分析了切趾弱双折射光纤布喇格光栅反射偏振相关特性与温度之间的关系.数值模拟了切趾弱双折射光纤光栅的反射谱、偏振相关损耗和差分群时延随波长变化曲线.实验测出了不同温度下反射谱、偏振相关损耗和差分群时延随波长变化曲线.根据实验结果对偏振相关损耗和差分群时延的变化情况作出了分析.反射偏振相关损耗呈现两个峰值,随温度增加两峰漂移程度相同,表明偏振相关损耗无明显差异.差分群时延最大值随温度增加成线性向长波方向漂移,证明了光纤光栅正交模损耗变化的等同性.综合理论分析与实验结果表明:切趾弱双折射光纤布喇格光栅的偏振特性随温度产生明显的变化,其正交模变化呈现等比例特性.