Study of Large Purcell Effect in Three-dimensional microcavities

随着互联网及其相关通信技术的不断发展，安全问题变得越来越重要。最安全的通信将是量子密码术，它分别用单个光子携带信息。光子是基本量子，在不干扰光子条件的情况下不可能获得信息。为此目的，在每个脉冲中应产生单个光子且不超过两个光子。这对于传统的半导体激光器是不可能的，因为光子数是泊松分布的。解决这个问题的方法是构建三维微腔并插入量子态与腔模强耦合的单个量子点。在这个方向上，人们提出了金字塔形三维微腔来实现单光子源。采用时域有限差分法对谐振模式进行了数值分析，并对谐振Q值进行了理论研究，以提高谐振Q值。实验观察到的Q值为5000，并通过在金字塔内插入CdS量子点，在共振模式的波长处观察到增强的自发辐射。峰值波长对温度变化非常稳定，发射峰正好在反射光谱测量中观察到的吸收峰处。这些结果显示了珀塞尔效应，虽然观察是间接的方法。通过提高条纹照相机的灵敏度，正在准备进行更多的直接时间分辨测量，目前正在研究直接测量。

With the extension of the internet and related communication technologies, the security issue is getting more and more important these days. The most secure communication will be the quantum cryptography which carries informations with individual photons separately. Photons are fundamental quantums and it is not possible to get the information without disturbing the photon conditions. For this purpose, single photon and not more than two photons should be generated in every pulse. This is not possible with conventional semiconductor lasers since the photon number is Poisson-distributed. The solution for this problem is the construction of 3-dimensional microcavities and insertion of single quantum dot of which quantum state is strongly coupled with the cavity mode. This will emit photons one by one.Toward this direction, pyramidal three-dimensional microcavities were proposed to realize the single photon source. The resonance modes were analyzed numerically with finite-difference time-domain method and the resonance Q values were theoretically investigated to increase the values. The Q value of 〜5000 was experimentally observed and the enhanced spontaneous emission was observed at the wavelength of the resonance mode by inserting CdS quantum dots inside the pyramid. The peak wavelength was very stable against the temperature change and the emission peak was Just at the absorption peak observed in reflection spectrum measurements. These results show the Purcell effect although the observations were done with indirect method. More direct time-resolved measurements are being prepared by increasing the sensitivity of a streak camera and the direct measurements are now under study.