Mid-infrared spectrally-uncorrelated biphotons generation from doped PPLN: a theoretical investigation

Abstract

We theoretically investigate the preparation of mid-infrared (MIR) spectrally-uncorrelated biphotons from a spontaneous parametric down-conversion process using doped LN crystals, including MgO doped LN, ZnO doped LN, and In2O3 doped ZnLN with doping ratio from 0 to 7 mol%. The tilt angle of the phase-matching function and the corresponding poling period are calculated under type-II, type-I, and type-0 phase-matching conditions. We also calculate the thermal properties of the doped LN crystals and their performance in Hong-Ou-Mandel interference. It is found that the doping ratio has a substantial impact on the group-velocity-matching (GVM) wavelengths. Especially, the GVM2 wavelength of co-doped InZnLN crystal has a tunable range of 678.7 nm, which is much broader than the tunable range of less than 100 nm achieved by the conventional method of adjusting the temperature. It can be concluded that the doping ratio can be utilized as a degree of freedom to manipulate the biphoton state. The spectrally uncorrelated biphotons can be used to prepare pure single-photon source and entangled photon source, which may have promising applications for quantum-enhanced sensing, imaging, and communications at the MIR range.

Optimized design of the lithium niobate for spectrally-pure-state generation at MIR wavelengths using metaheuristic algorithm

“…[26][27][28][29][30][31]. In particular, the current reported best purity under the 3 rd GVM condition is around 0.82, where the degradation is mainly caused by the phase-matching condition in PPLN [15]. As shown in Fig.…”

“…Firstly, PPLN has a large nonlinear coefficient and wide transparency range [14]. Secondly, the group-velocity-matched (GVM) wavelengths of LN crystal are intrinsically at the MIR wavelengths [15]. Thirdly, PPLN plays an important role in integrated quantum optics [16], as it possesses the characteristic of scalability and microminiaturization, which is beneficial in waveguide substrate [17][18][19] and thin-film material [20,21].…”

“…Thirdly, PPLN plays an important role in integrated quantum optics [16], as it possesses the characteristic of scalability and microminiaturization, which is beneficial in waveguide substrate [17][18][19] and thin-film material [20,21]. Up to now, many theoretical and experimental works have utilized PPLN as the medium to prepare the single-photon source [15,[22][23][24] or entangled photon source [25] at MIR wavelengths. Recently we theoretically proposed that mid-infrared spectrallyuncorrelated biphotons generation from doped LN crystals, and we find the doping ratio can be utilized as a degree of freedom to manipulate the biphoton state [15].…”

“…Up to now, many theoretical and experimental works have utilized PPLN as the medium to prepare the single-photon source [15,[22][23][24] or entangled photon source [25] at MIR wavelengths. Recently we theoretically proposed that mid-infrared spectrallyuncorrelated biphotons generation from doped LN crystals, and we find the doping ratio can be utilized as a degree of freedom to manipulate the biphoton state [15]. However, PPLN crystals investigated in the previous research are still not optimum due to the low purity of the generated biphotons.…”

Spectrally pure photon pair generation in asymmetric heterogeneously coupled waveguides

“…A common strategy is to use narrow-band spectral filters to remove these correlations, which, however, is obtained at the expense of heralding efficiency and increased source complexity. While microresonators which provide enhanced nonlinear interactions can be used to remove spectral correlations [11], for typical nonresonant waveguides, group velocity matching (GVM) [12,13] needs to be employed in order to directly generate uncorrelated photon pairs on-chip. For example, material dispersion in potassium titanyl phosphate (KTP) naturally satisfies GVM in a certain wavelength range, thus allowing the generation of pure heralded single photons in periodically poled KTP (PP-KTP) waveguides in a given wavelength range [14,15].…”