Modification of optical response in quantum dots embedded in a photonic crystal waveguide via photonic band engineering
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Modification of optical response in quantum dots embedded in a photonic crystal waveguide via photonic band engineering Nobuhiko Ozaki1, Hayato Yoneda1, Koichi Takeuchi1, Hisaya Oda2, Naoki Ikeda3, Yoshimasa Sugimoto3, Yoshinori Watanabe3, and Kiyoshi Asakawa4 1 Faculty of Systems Engineering, Wakayama University, 930 Sakaedani, Wakayama 640-8510, Japan 2 Faculty of Photonics Science, Chitose Institute of Science and Technology, 758-65 Bibi, Chitose, Hokkaido 066-8655, Japan 3 National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan 4 Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8571, Japan ABSTRACT We propose to use Purcell effect emerged at slow light regions in photonic crystal waveguide (PC-WG) modes for controlling the relaxation time of excited carriers in QDs. Straight GaAs PC-WGs including InAs-QDs with various lattice constants of PC were prepared in order to control the wavelength of the slow light in the PC-WG modes. PL measurements of the PC-WGs indicated enhancements of emission from QDs at the localized wavelength of slow light regions due to the Purcell effect. The enhanced emission peak wavelength was continuously shifted with the PC lattice constant. These results suggest that the PC-WG can be utilized to modify the spontaneous emission rate and carrier relaxation time of the embedded QD. This modification can be applied and useful for various QD-based optical devices as well as our proposed all-optical switching device based on PC-WG/QD. INTRODUCTION All-optical switch, which operates optical signal switching without electronic/optical conversions, is promising for energy efficient optical telecommunication system due to its operation of ultra-fast and low energy consumption compared with a conventional electric router. We have proposed and developed a symmetcric Mach-Zehnder-type all-optical switch based on photonic crystal waveguides (PC-WGs) and quantum dots (QDs), PC-SMZ, as shown in Fig. 1 [1]. Single [2] and repetitive switching operations [3] by the PC-SMZ up to 40GHz have been demonstrated, however, the carrier-relaxation time of QDs becomes a siginificant factor for faster switching operations. The QD has generally long carrier-ralaxation time for spontaneous emission (SE), that is ~ns, thus carrier accumulations would affect in the case of fast repetitive switching operations [3]. On the other hand, controlling the SE rate through the photonic band engineering has been studied [4]. For instance, the SE rate from light emitters embedded in a photonic crystal (PC) cavity can be increased or decreased with the control of photon density of states at the frequency of the light emission, that is, the Purcell effect [5]. Where the PC cavity modes make high photon density of states, the SE rate is enhanced. In this paper, we propose to apply the modification by the Purcell effect to the PC-WG structure. There are extra modes in a PC band gap emerged from the PC-WG and frequency regions of high pho
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