Study of Large Purcell Effect in Three-dimensional microcavities

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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.