偶极子位置及偏振对激发光子晶体H1微腔的影响

光子晶体微腔和量子点的集成是实现量子信息处理非常具有潜力的平台之一,利用微腔和量子点的耦合可以制备纠缠光子对,实现对量子态的操控.因为光子晶体微腔具有品质因子高、模场体积小等优点,可以极大地增强光与物质之间的相互作用,从而易于实现量子态在不同物理体系之间的转换.通过单量子点和光子晶体H1微腔的耦合可以产生纠缠光子对,因为H1微腔具有简并的、模式偏振正交的基态模式.通常微腔模式的激发随着量子点在微腔中的位置变化而改变,本文用时域有限差分方法研究了偶极子光源的位置及偏振对激发光子晶体H1微腔模式的影响.结果表明:通过改变偶极子光源位置可以选择性地激发H1微腔简并模式中的一个;具有某一偏振的偶极子光源只能激发相应偏振的微腔模式;模式激发强度的大小也是由偶极子光源在微腔中的位置决定的.鉴于目前量子点在微腔中的位置尚不能精确控制,所以微腔模式受激发光源位置的影响的研究具有重要意义.

Effects of location and polarization of a dipole source on the excitation of a photonic crystal H1 cavity

The integration of photonic crystal cavity with quantum dot paves the way for photonic-based quantum information processing. Photonic crystal cavity has a high-quality factor and small mode volume, which can be utilized to enhance the interaction between light and matter. Two degenerate fundamental modes with orthogonal polarizations exist in photonic crystal H1 cavity. Entangled photon pairs can be generated with a single quantum dot coupled to degenerate H1 cavity modes. Therefore a coupling system comprised of quantum dot and photonic crystal H1 cavity is a promising platform to implement quantum information processing. The excitations of cavity modes are mostly affected by the location of the single quantum dot, namely a dipole source. For the two degenerate photonic crystal H1 cavity modes, the location of the dipole source determines which mode is excited. In this paper, the effects of location and polarization of a dipole source on the excitation of photonic crystal H1 cavity are investigated with the finite-difference time-domain method, a numerical analysis technique for computing the electrodynamics. We first design a photonic crystal slab structure patterned with hexagonal lattice of air holes. Combining the light modulation by the period lattice in the slab plane and the total internal reflection in the perpendicular direction, photonic bandgap is generated, which inhibits the propagation of photon with certain frequencies. By removing one of the air holes from the photonic crystal slab, an H1 cavity is formed with two degenerate fundamental modes. One mode is x-polarized, and the other one is y-polarized. Next, a dipole source is used to excite the H1 cavity modes. When the dipole source is located at the left to the H1 cavity center, only y-polarized mode is excited. While locating the dipole source above the H1 cavity center, only x-polarized mode is excited. Therefore each degenerate mode of H1 cavity can be selectively excited with the diploe source located at different positions in the cavity. Following that, the H1 cavity modes excited with the dipole sources with different polarizations are also studied. The x-polarized dipole source can only excite the cavity mode with x-polarization, while the y-polarized dipole source can only excite the y-polarized cavity mode accordingly. It can be seen that the dipole source with specific polarization can only excite the modes with corresponding polarization. The effects of location and polarization of a dipole source on the excitation of a photonic crystal H1 cavity are important for understanding the fundamental physics of entangled photon generation with a coupled quantum dot and photonic crystal system.