National Institute of Laser Enhanced Sciences, Cairo University, 12613, Giza, Egypt.
CREOL, The College of Optics & Photonics, University of Central Florida, Orlando, FL, 32816, USA.
Sci Rep. 2017 Jun 23;7(1):4169. doi: 10.1038/s41598-017-03023-1.
A crystal superlattice structure featuring nonlinear layers with alternating orthogonal optic axes interleaved with orthogonal poling directions, is shown to generate high-quality hyperentangled photon pairs via orthogonal quasi-phase-matched spontaneous parametric downconversion. We demonstrate that orthogonal quasi-phase matching (QPM) processes in a single nonlinear domain structure correct phase and group-velocity mismatches concurrently. Compared with the conventional two-orthogonal-crystals source and the double-nonlinearity single-crystal source, the orthogonal QPM superlattice is shown to suppress the spatial and temporal distinguishability of the generated photon pairs by several orders of magnitude, depending on the number of layers. This enhanced all-over-the-cone indistinguishability enables the generation of higher fluxes of photon-pairs by means of the combined use of (a) long nonlinear crystal in noncollinear geometry, (b) low coherence-time pumping and ultra-wide-band spectral detection, and (c) focused pumping and over-the-cone detection. While each of these three features is challenging by itself, it is remarkable that the orthogonal QPM superlattice meets all of these challenges without the need for separate spatial or temporal compensation.
一种具有非线性层的晶体超晶格结构，其特征在于具有交替的正交光轴和正交极化方向的层，通过正交准相位匹配自发参量下转换产生高质量的超纠缠光子对。我们证明了单个非线性域结构中的正交准相位匹配（QPM）过程可以同时校正相位和群速度失配。与传统的两个正交晶体源和双非线性单晶源相比，正交 QPM 超晶格能够根据层数将生成的光子对的空间和时间可分辨性抑制几个数量级。这种增强的全锥内不可分辨性使得通过以下方式产生更高通量的光子对成为可能：（a）在非共线几何形状中使用长非线性晶体，（b）低相干时间泵浦和超宽带光谱检测，以及（c）聚焦泵浦和全锥检测。虽然这三个特征本身都具有挑战性，但正交 QPM 超晶格无需单独的空间或时间补偿即可满足所有这些挑战，这是值得注意的。
