Study of Type II SPDC in Lithium Niobate for High Spectral Purity Photon Pair Generation

Ilhwan Kim,Donghwa Lee,Kwang Jo Lee

doi:10.3390/cryst11040406

Abstract

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.

Highlights

Lithium niobate (LiNbO3, lithium niobate (LN)) has been the most preferred nonlinear optic platform for decades due to its high material quality, mature manufacturing technology, large second-order nonlinearity and electro-optic (EO) modulation efficiency [1]
The ion-cut technology for manufacturing wafer-size, low propagation loss, sub-micronthick crystalline LN thin films has made significant advances over the past decade [2,3]. This technique allows the successful integration of undoped or MgO/Fe/Er/Tm doped LN on insulators such as SiO2/Si, Si, sapphire, and quartz [4]. This rapid development of LN-on-insulator (LNOI) technology has revitalized the progress of novel chip-integrated LN-based photonic devices and accelerated application research [5,6,7,8,9,10,11,12,13,14,15,16,17]
The monolithically integrated LN modulator with on-chip loss of less than 0.5 dB and the high modulation rate of 210 Gb/s has been successfully demonstrated, which was followed by many promising applications including on-chip photonic integration, Kerr frequency comb or supercontinuum generation, and nonlinear-optic quasi-phase-matching (QPM) frequency conversion on an integrated platform [5,6,7]

Summary

Introduction

Lithium niobate (LiNbO3, LN) has been the most preferred nonlinear optic platform for decades due to its high material quality, mature manufacturing technology, large second-order nonlinearity and electro-optic (EO) modulation efficiency [1]. Type II EPM approach has not yet been reported for non-poled LNs. in order to generate high-purity photon pairs that are indistinguishable except for the state of polarization, SPDC based on frequency-degenerate Type II EPM is required. We investigate, both theoretically and numerically, Type II SPDC in two kinds of LNs (i.e., undoped and 5-mol% MgO doped LNs), which are expected to be useful as material platforms for the generation of entangled photon pairs of high spectral purity. In each case, both non-poled and PP crystals will be considered. The joint spectral analyses showed that photon pairs can be generated with high purities of 0.995–0.999 with proper pump filtering

Materials and Theories

Simulations and Discussion

Conclusions