We investigate the high-purity polarization-entangled photon-pair generation in niobium-doped potassium titanyl phosphate (Nb:KTP). The technique is based on Type II spontaneous parametric down-conversion (SPDC). Two kinds of Nb:KTPs with Nb-doping concentrations of 3.4 mol% and 7.5 mol% will be considered in each periodically poled and non-poled case. The properties of Type II SPDC, including the range of the beam propagation direction (or the spectral range of photons) and the corresponding effective nonlinearities and beam walk-offs, will be discussed in detail both theoretically and numerically. This is followed by a joint spectral analysis is followed to quantify the heralded-state spectral purities of the photon pairs generated by Type II SPDC. The results show that photon-pairs can be generated with high purities of 0.995–0.997 with proper pump filtering. We will also show that the spectral positions of photon pairs can be chosen from a wide range, including 1520.0 nm, 1582.4 nm, 1811.6–1837.4 nm, and 1998.6–2026.8 nm.

我们调查了铌掺杂的钛氧基磷酸钾（Nb：KTP）中高纯度极化纠缠光子对的产生。该技术基于II型自发参数下变频（SPDC）。在每种周期性极化和非极化的情况下，将考虑两种Nb：KTP，其Nb掺杂浓度分别为3.4 mol％和7.5 mol％。II型SPDC的特性，包括光束传播方向的范围（或光子的光谱范围）以及相应的有效非线性和光束偏离，将在理论上和数值上进行详细讨论。接下来是联合光谱分析，以量化由II型SPDC生成的光子对的先驱态光谱纯度。结果表明，可以产生高纯度0.995-0的光子对。997，带有正确的泵过滤。我们还将表明，光子对的光谱位置可以在很宽的范围内选择，包括1520.0 nm，1582.4 nm，1811.6–1837.4 nm和1998.6-2026.8 nm。