Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Crystals

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

Donghwa Lee, Il Hwan Kim, Kwang Jo Lee

Published May 26, 2021• 4 citations
Publisher

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.

DOI
10.3390/cryst11060599

Related papers

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

Ilhwan Kim, Donghwa Lee, Kwang Jo Lee

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.

Crystals•Apr 10, 2021•8 citations

Numerical Investigation of High-Purity Polarization-Entangled Photon-Pair Generation in Non-Poled KTP Isomorphs

Ilhwan Kim, Donghwa Lee, Kwang Jo Lee

We investigated the high-purity entangled photon-pair generation in five kinds of “non-poled” potassium titanyl phosphate (KTP) isomorphs (i.e., KTiOPO4, RbTiOPO4, KTiOAsO4, RbTiOAsO4, and CsTiOAsO4). The technique is based on the spontaneous parametric down-conversion (SPDC) under Type II extended phase matching (EPM), where the phase matching and the group velocity matching are simultaneously achieved between the interacting photons in non-poled crystals rather than periodically poled (PP) KTPs that are widely used for quantum experiments. We discussed both theoretically and numerically all aspects required to generate photon pairs in non-poled KTP isomorphs, in terms of the range of the beam propagation direction (or the spectral range of photons) and the corresponding effective nonlinearities and beam walk-offs. We showed that the SPDC efficiency can be increased in non-poled KTP isomorphs by 29% to 77% compared to PPKTP cases. The joint spectral analyses showed that photon pairs can be generated with high purities of 0.995–0.997 with proper pump filtering. In contrast to the PPKTP case, where the EPM is achieved only at one specific wavelength, the spectral position of photon pairs in the non-poled KTP isomorphs can be chosen over the wide range of 1883.8–2068.1 nm.

Applied Sciences•Jan 8, 2021•8 citations

Extended phase-matching properties of periodically poled potassium niobate crystals for mid-infrared polarization-entangled photon-pair generation

Kwang Jo Lee, Sunmi Lee, Heedeuk Shin

or KN) crystals (i.e., periodic 180°- and 90°-domain structures) that are highly useful for the generation of polarization-entangled photon pairs in the mid-infrared (IR) spectral region. Under the degenerate Type II spontaneous parametric downconversion process satisfying the EPM condition, an input single photon with a frequency of 2ω generates a pair of synchronized photons with identical frequencies of ω that are orthogonally polarized with respect to each other (i.e., the frequency-coincident, polarization-entangled biphoton states). Our simulation results illustrate that the EPM is achievable in the mid-IR spectral region: at the wavelengths of 3.80 μm and 4.03 μm for periodic 90°- and 180°-domain structures, respectively. We will describe in detail the EPM properties of both cases in terms of interaction types and the corresponding nonlinear optic coefficients, phase-matching bandwidths, and domain poling periods. The calculated EPM bandwidths are much broader than 200 nm in the mid-IR for both cases, exhibiting a great potential for nonlinear-optic signal processing in quantum communication systems operating in the mid-IR bands.

Applied Optics•Nov 23, 2016•8 citations

Bright photon pair source with high spectral and spatial purity

J. Schaake, Ryan S. Bennink, Philip G. Evans +2 more

Spontaneous parametric down-conversion (SPDC) is a reliable and robust source of photons for quantum information applications. For applications that involve operations such as entanglement swapping or single-photon heralding, two-photon states are required to be factorable (uncorrelated) in their spectral and spatial degrees of freedom. We report the design and experimental characterization of an SPDC source that has been optimized for high spectral and spatial purity. The source is pumped by the 776 nm output of a mode-locked Ti:Sapphire laser and consists of a periodically-poled Potassium Titanyl Phosphate (PPKTP) crystal phase-matched for collinear type-II SPDC. The dispersive properties of PPKTP at these wavelengths is such that it is possible to minimize the spectral entanglement by matching the widths of the pump to the spectral phase-matching function. The spatial entanglement is minimized through careful control of the pump focus, yielding nearly single-mode emission. An advantage of this approach is that the emission rate into the collection modes is very high, resulting in a very bright SPDC source. We also report a scheme that employs the output of collinear sources such as these to produce polarization-entangled photon pairs. The scheme, which requires only simple polarization elements, can be scaled to N-photon GHZ states.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•May 13, 2011•1 citation

Efficient heralding of polarization-entangled photons from type-0 and type-II spontaneous parametric downconversion in periodically poled KTiOPO_4

Fabian Steinlechner, Marta Gilaberte Basset, Marc Jofre +4 more

Ultrabright sources of entangled photon pairs with high heralding efficiency are an important step in the pursuit of high-bit-rate entanglement-base quantum key distribution, as well as an enabling tool for loss-sensitive quantum optics experiments. Here, we present a robust single-mode fiber-coupled source of polarization-entangled photons around 810 nm with both high brightness and heralding efficiency. Our approach is based on quasi-phase-matched spontaneous parametric downconversion (SPDC) from periodically poled KTiOPO4 in a Sagnac loop configuration. We demonstrate a high degree of two-photon polarization entanglement for single-frequency-pumped type-0 and type-II SPDC, and conduct a conclusive comparison in terms of efficiency and spectral characteristics. In light of applications outside a laboratory environment, we evaluate the feasibility of pumping nonlinear crystals with free-running laser diodes.

Journal of the Optical Society of America B•Aug 6, 2014•88 citations

Numerical Investigation of High-Purity Entangled Photon-Pair Generation in Ba3Mg3(BO3)3F3 Crystals

Donghwa Lee, Ilhwan Kim, Kwang Jo Lee

We investigate the high-purity entangled photon pair generation in a recently developed borate crystal, Ba3Mg3(BO3)3F3. The technique is based on the spontaneous parametric down-conversion under the extended phase matching (EPM), where the phase matching and the group velocity matching between the interacting photons are satisfied simultaneously in bulk crystals with point symmetry of orthorhombic mm2 (thus showing biaxial birefringence). We will discuss all the theoretical aspects required for the generation of photon pairs in mm2 biaxial crystals, which are much more complex than the cases of uniaxial crystals (e.g., β-BaB2O4 and LiNbO3) and periodically poled crystals that are widely used in the field. Our study includes theoretical and numerical investigations of two types of EPM and their corresponding effective nonlinearities and spatial walk-offs. The results show that two types of EPM are satisfied over the specific range in the direction of pump wave vector, corresponding to its spectral ranges of 876.15–1052.77 nm for Type I and 883.92–914.33 nm for Type II. The joint spectral analyses show that photon-pairs can be generated with high purities of 0.997 with a proper pump filtering (for Type II), and 0.833 even without pump filtering (for Type I).

Crystals•Dec 21, 2020•0 citations
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.
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.
We investigated the high-purity entangled photon-pair generation in five kinds of “non-poled” potassium titanyl phosphate (KTP) isomorphs (i.e., KTiOPO4, RbTiOPO4, KTiOAsO4, RbTiOAsO4, and CsTiOAsO4). The technique is based on the spontaneous parametric down-conversion (SPDC) under Type II extended phase matching (EPM), where the phase matching and the group velocity matching are simultaneously achieved between the interacting photons in non-poled crystals rather than periodically poled (PP) KTPs that are widely used for quantum experiments. We discussed both theoretically and numerically all aspects required to generate photon pairs in non-poled KTP isomorphs, in terms of the range of the beam propagation direction (or the spectral range of photons) and the corresponding effective nonlinearities and beam walk-offs. We showed that the SPDC efficiency can be increased in non-poled KTP isomorphs by 29% to 77% compared to PPKTP cases. The joint spectral analyses showed that photon pairs can be generated with high purities of 0.995–0.997 with proper pump filtering. In contrast to the PPKTP case, where the EPM is achieved only at one specific wavelength, the spectral position of photon pairs in the non-poled KTP isomorphs can be chosen over the wide range of 1883.8–2068.1 nm.
or KN) crystals (i.e., periodic 180°- and 90°-domain structures) that are highly useful for the generation of polarization-entangled photon pairs in the mid-infrared (IR) spectral region. Under the degenerate Type II spontaneous parametric downconversion process satisfying the EPM condition, an input single photon with a frequency of 2ω generates a pair of synchronized photons with identical frequencies of ω that are orthogonally polarized with respect to each other (i.e., the frequency-coincident, polarization-entangled biphoton states). Our simulation results illustrate that the EPM is achievable in the mid-IR spectral region: at the wavelengths of 3.80 μm and 4.03 μm for periodic 90°- and 180°-domain structures, respectively. We will describe in detail the EPM properties of both cases in terms of interaction types and the corresponding nonlinear optic coefficients, phase-matching bandwidths, and domain poling periods. The calculated EPM bandwidths are much broader than 200 nm in the mid-IR for both cases, exhibiting a great potential for nonlinear-optic signal processing in quantum communication systems operating in the mid-IR bands.
Spontaneous parametric down-conversion (SPDC) is a reliable and robust source of photons for quantum information applications. For applications that involve operations such as entanglement swapping or single-photon heralding, two-photon states are required to be factorable (uncorrelated) in their spectral and spatial degrees of freedom. We report the design and experimental characterization of an SPDC source that has been optimized for high spectral and spatial purity. The source is pumped by the 776 nm output of a mode-locked Ti:Sapphire laser and consists of a periodically-poled Potassium Titanyl Phosphate (PPKTP) crystal phase-matched for collinear type-II SPDC. The dispersive properties of PPKTP at these wavelengths is such that it is possible to minimize the spectral entanglement by matching the widths of the pump to the spectral phase-matching function. The spatial entanglement is minimized through careful control of the pump focus, yielding nearly single-mode emission. An advantage of this approach is that the emission rate into the collection modes is very high, resulting in a very bright SPDC source. We also report a scheme that employs the output of collinear sources such as these to produce polarization-entangled photon pairs. The scheme, which requires only simple polarization elements, can be scaled to N-photon GHZ states.
Ultrabright sources of entangled photon pairs with high heralding efficiency are an important step in the pursuit of high-bit-rate entanglement-base quantum key distribution, as well as an enabling tool for loss-sensitive quantum optics experiments. Here, we present a robust single-mode fiber-coupled source of polarization-entangled photons around 810 nm with both high brightness and heralding efficiency. Our approach is based on quasi-phase-matched spontaneous parametric downconversion (SPDC) from periodically poled KTiOPO4 in a Sagnac loop configuration. We demonstrate a high degree of two-photon polarization entanglement for single-frequency-pumped type-0 and type-II SPDC, and conduct a conclusive comparison in terms of efficiency and spectral characteristics. In light of applications outside a laboratory environment, we evaluate the feasibility of pumping nonlinear crystals with free-running laser diodes.
We investigate the high-purity entangled photon pair generation in a recently developed borate crystal, Ba3Mg3(BO3)3F3. The technique is based on the spontaneous parametric down-conversion under the extended phase matching (EPM), where the phase matching and the group velocity matching between the interacting photons are satisfied simultaneously in bulk crystals with point symmetry of orthorhombic mm2 (thus showing biaxial birefringence). We will discuss all the theoretical aspects required for the generation of photon pairs in mm2 biaxial crystals, which are much more complex than the cases of uniaxial crystals (e.g., β-BaB2O4 and LiNbO3) and periodically poled crystals that are widely used in the field. Our study includes theoretical and numerical investigations of two types of EPM and their corresponding effective nonlinearities and spatial walk-offs. The results show that two types of EPM are satisfied over the specific range in the direction of pump wave vector, corresponding to its spectral ranges of 876.15–1052.77 nm for Type I and 883.92–914.33 nm for Type II. The joint spectral analyses show that photon-pairs can be generated with high purities of 0.997 with a proper pump filtering (for Type II), and 0.833 even without pump filtering (for Type I).