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Laser Physics

Generation of high spectral purity photon-pairs with MgO-doped periodically poled lithium niobate

Mengying Zhan, Qi-Chao Sun, Tong Xiang, Xianfeng Chen

Published Nov 5, 2015• 2 citations
Publisher

Abstract

We study the spectral correlation of photon pairs generated via type-II spontaneous parametric down conversion in periodically poled lithium niobate crystals. By performing Schmidt decomposition on the two-photon wavefunction, we calculate the spectral purity of the two-photon state under various pump laser characteristics and doping concentrations of MgO in lithium niobate crystals. Our results show that periodically poled 5% MgO doped lithium niobate is a good candidate to generate photon-pairs with high spectral purity at telecom wavelength.

DOI
10.1088/1054-660x/25/12/125203

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We study the spectral correlation of photon pairs generated via type-II spontaneous parametric down conversion in periodically poled lithium niobate crystals. By performing Schmidt decomposition on the two-photon wavefunction, we calculate the spectral purity of the two-photon state under various pump laser characteristics and doping concentrations of MgO in lithium niobate crystals. Our results show that periodically poled 5% MgO doped lithium niobate is a good candidate to generate photon-pairs with high spectral purity at telecom wavelength.
By utilizing the extended phase-matching (EPM) method, we investigate the generation of single photons with high spectral-purity in a magnesium-doped periodically-poled lithium niobate (MgO:PPLN) crystal via the spontaneous parametric down-conversion (SPDC) process. By adjusting the temperature and pump wavelength, the wavelength of the single photons can be tuned from telecom to mid-infrared (MIR) wavelengths, for which the spectral-purity can be above 0.95 with high transmission filters. In experiments, we engineer a MgO:PPLN with poling period of 20.35 μm which emits the EPM photon pair centered at 1496.6 nm and 1644.0 nm and carry out the joint spectral intensity (JSI) and Glauber’s second-order self-correlation measurements to characterize the spectral purity. The results are in good agreement with the numerical simulations. Our work may provide a valuable approach for the generation of spectrally pure single photons at a wide range of wavelengths which is competent for various photonic quantum technologies.
Recent advances of high-quality lithium niobate (LN) on insulator technology have revitalized the progress of novel chip-integrated LN-based photonic devices and accelerated application research. One of the promising technologies of interest is the generation of entangled photon pairs based on spontaneous parametric down-conversion (SPDC) in LNs. In this paper, we investigated, theoretically and numerically, Type II SPDC in two kinds of LNs—undoped and 5-mol% MgO doped LNs. In each case, both non-poled and periodically poled crystals were considered. The technique is based on the SPDC under Type II extended phase matching, where the phase matching and the group velocity matching are simultaneously achieved between interacting photons. The proposed approach has not yet been reported for LNs. We discussed all factors required to generate photon pairs in LNs, in terms of the beam propagation direction, the spectral position of photons, and the corresponding effective nonlinearities and walk-offs. We showed that the spectral positions of the generated photon pairs fall into the mid-infrared region with high potential for free-space quantum communication, spectroscopy, and high-sensitivity metrology. The joint spectral analyses showed that photon pairs can be generated with high purities of 0.995–0.999 with proper pump filtering.
In this paper, we propose the generation of hyperentangled photon pairs using type-II spontaneous parametric down-conversion in a biperiod, 5% MgO-doped lithium-niobate ridge waveguide. The photon pairs are entangled in spatial mode and polarization degrees of freedom. A pulsed laser source at 687 nm, having an antisymmetric Hermite-Gaussian HG (1,0) spatial mode, is considered as the pump. Down-converted photon pairs, with the signal being at the telecommunication wavelength of 1550 nm, are characterized through a joint spectral amplitude analysis of their biphoton state.
In this work, the cascaded second-order spontaneous parametric down-conversion (SPDC) is considered to produce pure state photon triplets in periodically poled lithium niobite (PPLN) doped with 5% MgO. A set of parameters are optimized through calculating the Schmidt number of two-photon states generated by each down-conversion process with different pump durations and crystal lengths. We use a Gaussian filter in part and obtain three photons with 100% purity in spectrum. We provide a feasible and unprecedented scheme to manipulate the spectrum purity of photon triplets in the communication band (C-band).
We present a highly efficient source for discrete frequency-entangled photon pairs based on spontaneous parametric down-conversion using 3rd-order type-0 quasi-phase matching in a periodically poled MgO-doped stoichiometric LiTaO(3) crystal pumped by a 355.66-nm laser. Correlated two-photon states were generated with automatic conservation of energy and momentum in two given spatial modes. These states have a wide spectral range, even under small variations in crystal temperature, which consequently results in higher discreteness. Frequency entanglement was confirmed by measuring two-photon quantum interference fringes without any spectral filtering.
We demonstrate a spectrally correlated photon-pair source at telecom wavelengths (spanning across the S-, C-, and L-bands), based on type-0 spontaneous parametric downconversion (SPDC) in a fiber-coupled Zn-indiffused MgO doped periodically poled lithium niobate (PPLN) ridge waveguide. Modal analysis of the waveguide performed through numerical finite element method (FEM) simulation indicates that device temperature can be used to dramatically vary and control the emission spectrum. Efficient photon-pair generation is measured over a broad wavelength range from ∼1520 − 1580 nm [full width at half maximum (FWHM) > 45 nm] with a coincidence-to-accidental ratio (CAR) as high as ∼668 and spectral brightness ∼2.5 × 10 7 pairs/s/mW/nm. Such sources can be employed in wavelength division multiplexed (WDM) quantum key distribution (QKD) over existing fiber-optic networks.