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Optics Express

Concurrent optical parametric down-conversion in χ^(2) nonlinear photonic crystals

Lele Chen, Ping Xu, Y. F. Bai, Xu‐Feng Luo, M. L. Zhong, M. Dai, Ming‐Hui Lu, Shining N. Zhu

Published May 22, 2014• 13 citations
Publisher

Abstract

We experimentally investigated concurrent parametric downconversion processes in a two-dimensional hexagonally poled lithium tantalate crystal. The substantial enhancement of parametric gain was observed when concurrent processes shared a common parametric beam. Both degenerate and nondegenerate concurrent parametric downconversion processes were studied. Analyses of the spatial forms and output angles showed a strong dependence on the working temperature, during which a well-defined beamlike parametric output was observed. Our results will stimulate the design for coherent high-gain generation of multiple parametric beams and also shed light on the compact engineering of path-entanglement with specific spatial forms based on concurrent spontaneous parametric downconversion processes.

DOI
10.1364/oe.22.013164

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We experimentally investigated concurrent parametric downconversion processes in a two-dimensional hexagonally poled lithium tantalate crystal. The substantial enhancement of parametric gain was observed when concurrent processes shared a common parametric beam. Both degenerate and nondegenerate concurrent parametric downconversion processes were studied. Analyses of the spatial forms and output angles showed a strong dependence on the working temperature, during which a well-defined beamlike parametric output was observed. Our results will stimulate the design for coherent high-gain generation of multiple parametric beams and also shed light on the compact engineering of path-entanglement with specific spatial forms based on concurrent spontaneous parametric downconversion processes.
We propose a scheme for generating polarization-entangled photon pairs using a χ((2)) nonlinear photonic crystal, which is designed for enabling two concurrent quasi-phase-matched spontaneous parametric downconversion processes. Beamlike photon pairs produced from each process are collinear but noncollinear with the pump. Moreover, the source we design works in a postselection-free way and applies to both degenerate and nondegenerate cases. Combining possible waveguide technologies, our scheme may provide an integrated polarization entanglement source.
We review recent experimental and theoretical progress in the study of optical parametric generation and cascaded frequency up conversion in two-dimensional purely nonlinear lattices, relying on acoherent coupling of multiple resonances in the quadratic lattice. Since their original proposal (1), two dimensional (2D) nonlinear photonic crystals in periodically poled materials have been the subject of a number of experimental and theoretical investigations, exploring the enhanced possibilities to engineer the nonlinear dynamics of quadratic interactions afiorded in such structures (2,3). Most of the studies have concerned frequency up-conversion, until the recent demonstration of twin-beam optical parametric generation (TB-OPG) in 2D hexagonally poled crystals (4,5). TB-OPG experiments in hexagonally poled MgO:LiTaO3 lattices demonstrated enhanced para- metric gains as well as a rich spectral and angular response underpinned bythe coherent coupling of concurrent nonlinear processes throughshared signal or idlermodes. They provided evidence forrich interaction scenarios, generating multiple outputs in the infrared as well in the visible and encompassing also self-phase modulation and cascaded upconversion processes arising from the interplay of multiple lattice resonances.A good agreement was found with a simple model in- volving the cross-seeding of two non-collinear OPG processes via a common signal (idler), while the development of advanced ad-hoc simulation tools enabled to fully account for the complex nonlinear dynamics in the 2D lattices and faithfully reproduce the rich spectral-angular response seen in the experiments (6).
Abstract Concurrent spontaneous parametric down-conversion (SPDC) processes have proved to be an appealing approach for engineering the path-entangled photonic state with designable and tunable spatial modes. In this work, we propose a general scheme to construct high-dimensional path entanglement and demonstrate the basic properties of concurrent SPDC processes from domain-engineered quadratic nonlinear photonic crystals, including the spatial modes and the photon flux, as well as the anisotropy of spatial correlation under noncollinear quasi-phase-matching geometry. The overall understanding about the performance of concurrent SPDC processes will give valuable references to the construction of compact path entanglement and the development of new types of photonic quantum technologies.
We demonstrate a method to generate entangled photons with controlled spatial shape by parametric down conversion (PDC) in a 2D nonlinear crystal. A compact and novel crystal source was designed and fabricated, generating directly path entangled photons without the use of additional beam-splitters. This crystal supports two PDC processes, emitting biphotons into two beamlike modes simultaneously. Two coherent path entangled amplitudes of biphotons were created and their interference observed. Our method enables the generation of entangled photons with controlled spatial, spectral and polarization properties.
We present a parametric down-conversion (PDC) process in a nonlinear ß-barium borate (BBO) crystal, driven by two non-collinear pump beams, obtained from a Mach-Zehnder type interferometer. We show the possibility to reproduce in a bulk crystal a phenomenology analogue to that previously observed in a PDC process inside a χ 2 2D nonlinear photonic crystal (NPC) [1] , [2] . Each pump mode generates a family of cones of parametric radiation collinear with its direction. The intersection zones define an ensemble of modes shared by the two pumps, indistinguishably populated by the photons generated by pump 1 or by pump 2. As in [1] , in the high-gain regime these two possibilities sum up coherently, leading to a local increase of the parametric gain. Indeed we observe an unusual far-field distribution of the down-converted light, in the form of three bright branches of hot-spots against a more diffuse background [3] .
Multipartite quantum entanglement is a powerful resource for enriching the functionality of quantum computation and quantum communication. In this Letter, we propose a new method to generate a two-photon multipath Dicke state with concurrent spontaneous parametric downconversion processes from a single periodically poled nonlinear photonic crystal. We design the poling structure to produce a three-path Dicke state where three quasi-phase-matching conditions are fulfilled simultaneously by a hybrid one- and two-dimensionally poled nonlinear photonic crystal. We use genuine multipartite entanglement concurrence to quantify the entanglement of the Dicke state. Using a more complicated poling configuration like multiple-periodically poled two-dimensional nonlinear photonic crystal, we can also produce four-path, five-path, or multipath Dicke states by a single crystal. The multiple-periodically poled two-dimensional nonlinear photonic crystal provides a new method, to the best of our knowledge, for the integrated generation of multipartite quantum light sources.