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Optics Continuum

Comparative study on quasi-phase-matching of Type-0, Type-I, and Type-II configurations for SPDC in PPLN crystals

Di Song, Liancong Gao, Dongdong Wang, Rui‐Bo Jin, Yaqing Jin, Chenzhi Yuan, Cai He, Song Wang, Qing Wei Luo, Jiaqi Wang, You Wang

Published Jun 10, 2025• 2 citations

Abstract

The characteristics of quantum entangled light sources directly influence the application scenarios and overall performance of quantum systems. By modeling the process of generating time-energy entangled photons via spontaneous parametric down-conversion (SPDC) in a periodically poled lithium niobate (PPLN) crystal, with energy entanglement constituting an essential dimension of this source, the properties of energy entanglement have been systematically investigated in Type-I (e→o + o), Type-II (o→o + e), and Type-0 (e→e + e) quasi-phase matching (QPM) configurations. Through establishing a multivariate correlation model, we quantitatively analyzed the effects of pump parameters (pump linewidth and central wavelength deviation) and crystal parameters (crystal length and temperature) on entanglement metrics including single-photon spectral characteristics, Schmidt number K, measurable parameter R, and frequency overlap O for entangled sources generated by three QPM configurations. The results reveal the strong robustness of Type-I crystals to the pump central wavelength variation and Type-0 systems to the temperature variation. The conclusions might provide theoretical foundations and regulation paradigms for designing time-energy entangled sources tailored to different applications.

DOI: 10.1364/optcon.566084

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The characteristics of quantum entangled light sources directly influence the application scenarios and overall performance of quantum systems. By modeling the process of generating time-energy entangled photons via spontaneous parametric down-conversion (SPDC) in a periodically poled lithium niobate (PPLN) crystal, with energy entanglement constituting an essential dimension of this source, the properties of energy entanglement have been systematically investigated in Type-I (e→o + o), Type-II (o→o + e), and Type-0 (e→e + e) quasi-phase matching (QPM) configurations. Through establishing a multivariate correlation model, we quantitatively analyzed the effects of pump parameters (pump linewidth and central wavelength deviation) and crystal parameters (crystal length and temperature) on entanglement metrics including single-photon spectral characteristics, Schmidt number K, measurable parameter R, and frequency overlap O for entangled sources generated by three QPM configurations. The results reveal the strong robustness of Type-I crystals to the pump central wavelength variation and Type-0 systems to the temperature variation. The conclusions might provide theoretical foundations and regulation paradigms for designing time-energy entangled sources tailored to different applications.

We propose the generation of two-channel time-energy entangled twin photons based on two simultaneous first-order quasi-phase-matched (QPM) spontaneous parametric down-conversion processes in a periodically poled lithium niobate (PPLN) with a monochromatic pump. The theoretical model for the generation of the entangled photons is established, and the analytical solution is obtained in a lossless crystal with an undepleted pump assumption. The generated condition of entangled photons is achieved in terms of the QPM grating period and the pump wavelength. It is shown that two channels of entangled twin photons with different wavelengths can be created by suitably choosing the PPLN grating period once the pump wavelength is fixed, which provides the potential to introduce the wavelength division multiplexed technique into quantum information systems.

We theoretically present the bandwidth enhancement methods of the telecom-region entangled twin photons generated by quasi-phase-matched (QPM) spontaneous parametric down-conversion (SPDC) in periodically poled lithium niobate (PPLN) crystals. By using type I (e → e + e) SPDC, the degenerate entangled twin photons will have a broad bandwidth and it can be further enhanced by shortening the crystal length, detuning the pump wavelength or adjusting the working temperature of the PPLN crystal. This principle provides the possibility to introduce wavelength-division-multiplexed technique into quantum information systems.

The wavelength management method was theoretically investigated for the polarization-entangled twin photons in telecommunication band generated by type-II quasi-phase-matched (QPM) spontaneous parametric down-conversion (SPDC) in periodically poled lithium niobate (PPLN) crystals. The wavelength of single-color twin photons from degenerate SPDC can be controlled freely through adjusting the QPM grating period or the working temperature. Especially, adjusting the temperature is more convenient since the QPM grating period is hardly changed once the PPLN structure is fabricated. For the two-color twin photons created by nondegenerate SPDC, strict wavelength exchange of the o-polarization and the e-polarization photons can be realized easily only by tuning the working temperature without pump or structure change.

The “quantum” system of optical radiation metrology based on spontaneous parametric down-conversion (SPDC) correlated photon sources and coincidence measurement technology has important applications in the field of extremely weak optical radiation detection. To acquire widely tunable entangled photon sources, 532 nm continuous laser was used to pump periodically poled LiNbO3 (PPLN) crystal. And 676 nm~2500 nm correlated photons were got by switching the crystal period and tuning the temperature. Firstly, the parameters such as polarization period, length and temperature control precision of PPLN crystal were made a theoretical study. Thus, the polarization period of PPLN crystals, the bandwidth distribution curve of the signal light in different wavelength, and temperature control precision curve of the different wavelength of signal light are further calculated. The results show that, the 676 nm~2500 nm correlated photon can be got by using 9 PPLN crystals in the temperature range of 50°C~200°C. The bandwidth of the signal light has negative correlation with the crystal length; The temperature control precision of PPLN crystals was from 3.96°C to 7.64°C, and the temperature control precision requires more higher with the increase of signal light wavelength. The research results will lay a foundation for the design of high-throughput wide-spectrum tunable entangled photon sources.

A periodically poled lithium niobate (PPLN) crystal has been used as an efficient source of non-collinearly generated polarization-entangled photon pairs at 810 and 1550 nm. The PPLN crystal was endowed with a specially designed poling pattern and the entangled photons were generated via the nonlinear optical process of spontaneous parametric down conversion (SPDC). A novel design based on overlapping two concurrent type-I quasi-phase-matching structures in a single PPLN crystals produced correlated pairs of alternatively polarized photons in largely separated spectral regions. The phase of the resulting two-photon state is directly linked to parameters of the nonlinear grating. Continuous tunability of the generated Bell state, from Phi(+) to Phi(-), has been demonstrated by translating a slightly wedged crystal perpendicular to the pump beam.

We study the temperature-dependent type II spontaneous parametric down-conversion (SPDC) in the linearly chirped quasi-phase-matching (QPM) periodically poled lithium niobate (PPLN) crystal. The SPDC process can generate the biphotons with the single-cycle level. It shows that the chirp rate of the poled grating periods is the main influence factor for the phase matching function, frequency response range, Fedorov parameter and the count rate of the biphotons. Meanwhile, the temperature plays an important role for the type of

e\rightarrow o+e

, the higher temperature makes the frequency response range be wider, Fedorov parameter and count rate be higher. However, the appropriate chirp rate and temperature can help the type II SPDC generate the single cycle biphotons in chirp QPM PPLN.