Investigation of 1064-nm Pumped Type II SPDC in Potassium Niobate for Generation of High Spectral Purity Photon Pairs

Donghwa Lee,Ilhwan Kim,Kwangjo Lee

doi:10.3390/cryst11060599

Abstract

The generation and detection of nonclassical light of about 2 μm has good potential in an emerging field of high-sensitivity metrology, especially gravitational wave detection, as well as free-space quantum communication. A pair of photons is generated through a spontaneous parametric down-conversion (SPDC) process in a nonlinear optic crystal, which can be properly entangled in a spatial region where two beams with each polarization overlap or in a Sagnac-loop interferometer configuration. We investigated theoretically and numerically Type II SPDC in a potassium niobate (KNbO3, KN) crystal, which is useful as a material platform for generating photon pairs of high spectral purity in the 2-μm range. The technique is based on the frequency degenerate SPDC under Type II extended phase matching (EPM). We described the EPM characteristics of KN and showed that it is practically feasible for a 1064-nm pumped SPDC under moderate temperature conditions. The effective nonlinear optic coefficient of KN is at least four-times larger than those of other crystals using the Type II EPM approach, which implies a significant improvement in SPDC efficiency. The joint spectral analysis showed that a pair of photons can be generated with a high purity of 0.995 through proper pump filtering.

Highlights

The generation and detection of nonclassical light of about 2 μm has good potential in an emerging field of high-sensitivity metrology, especially in gravitational wave detection [1,2,3]
The wavelength of the photon pairs generated via the spontaneous parametric down-conversion (SPDC) pumped by the Nd:YAG laser is 2128 nm, which is within the high transparency range in the atmospheric absorption spectrum [5]. (3) The larger the nonlinearity of the crystal used for SPDC, the higher the SPDC efficiency
We will show that Type II extended phase matching (EPM) is feasible for a 1064-nm pumped SPDC under a moderate temperature condition, which is followed by the comparison of the effective nonlinear optic coefficients calculated under the given condition with those of other crystals using the Type II EPM

Summary

Introduction

The generation and detection of nonclassical light of about 2 μm has good potential in an emerging field of high-sensitivity metrology, especially in gravitational wave detection [1,2,3] Such long wavelengths can reduce quantum noise and scattering losses in interferometric gravitational wave detectors such as the laser interferometer gravitational wave observatory (LIGO)-Voyager [4]. The wavelength of the photon pairs generated via the SPDC pumped by the Nd:YAG laser is 2128 nm, which is within the high transparency range in the atmospheric absorption spectrum [5]. We theoretically and numerically investigate the Type II SPDC in a potassium niobate (KNbO3, KN) crystal, which is useful as a material platform for generating photon pairs of high spectral purity in the 2-μm spectral range. The joint spectral analysis showed that a pair of photons with a wavelength of 2128 nm can be generated by a 1064-nm pumped Type II SPDC, with a high purity of 0.995 through proper pump filtering

Materials and Theories

Simulations and Discussion

Conclusions