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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Spontaneous Parametric Down Conversion in Orientation-Patterned Gallium Phosphide Waveguides at Telecom Wavelength

Alice Marceau, Sylvain Combrié, Inès Ghorbel, Isabelle Sagnes, Alfredo De Rossi, Konstantinos Panzas, Arnaud Grisard

Published Jun 26, 2023• 0 citations
Publisher

Abstract

Generation of entangled photon pairs at telecom wavelength has been garnering a growing interest in the context of quantum communications and quantum computing. Several generation techniques have been proposed, including spontaneous Four-Wave Mixing in resonators or Spontaneous Parametric Down Conversion (SPDC) in Periodically Polled Lithium Niobate (PPLN) waveguides. Large photon pair efficiencies have been demonstrated in particular in PPLN on insulator [3]. However, polarization entangled photon pair generation (Type II phase matching configuration) suffers from a less favourable non-linear coefficient and optical mode birefringence in PPLN.

DOI
10.1109/cleo/europe-eqec57999.2023.10231458

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Generation of entangled photon pairs at telecom wavelength has been garnering a growing interest in the context of quantum communications and quantum computing. Several generation techniques have been proposed, including spontaneous Four-Wave Mixing in resonators or Spontaneous Parametric Down Conversion (SPDC) in Periodically Polled Lithium Niobate (PPLN) waveguides. Large photon pair efficiencies have been demonstrated in particular in PPLN on insulator [3]. However, polarization entangled photon pair generation (Type II phase matching configuration) suffers from a less favourable non-linear coefficient and optical mode birefringence in PPLN.
Spontaneous parametric down-conversion (SPDC) presents a convenient method of producing highly correlated heralded entangled photon pairs for quantum applications and networking. Of particular interest is Type-II SPDC, where signal and idler photons possess orthogonal polarisations, permitting straightforward entanglement in the useful polarisation basis. To the best of our knowledge, this has hitherto not been demonstrated in Zn-indiffused MgO:PPLN ridge waveguides, which offer excellent mode matching to standard telecoms fibers [1]. A particular difficulty in achieving SPDC in waveguides is to establish optimal phase-matching conditions. A common approach [2] is to perform standard SHG from the target SPDC wavelength first, leveraging the greater conversion efficiencies available in this regime. For example, in this work we target generation of Type-II SPDC photon pairs at 1310nm telecoms wavelengths suited to long-distance quantum networking protocols such as quantum key distribution [3], prompting initial testing of phase matching conditions via Type-II SHG.
Spontaneous parametric down-conversion (SPDC) in nonlinear crystals is the most commonly used means to generate single photon pairs for quantum key distribution systems [1]. By using waveguides instead of bulk crystals, highly efficient devices can be obtained. Both, type-I and type-II phase-matched integrated devices have been demonstrated in periodically poled lithium niobate (PPLN) [2–4]. Although the type-II process is less efficient, it has two favourable properties: the spectrum of down-converted photons is narrower compared to type-I and orthogonally polarised photons are emitted.
Abstract Polarisation-entangled photon pairs generated through nonlinear optical processes are crucial ingredients for a range of quantum information processing applications, such as quantum sensing and communication. In this work, we report an optimised design of a lithium niobate on insulator waveguide that is capable of directly generating polarisation-entangled photon pairs enabled through two different spontaneous parametric down-conversion processes simultaneously in the telecommunication wavelength band with a single poling period, based on Type II phase matching. The generated photon pairs cover wavelengths in telecom O (1310 nm) and telecom C (1550 nm) bands with the computed spectral brightness of ≈ 2 × 10 9 pairs sec − 1 mW − 1 . We also study the effect of temporal delay on the quality of entanglement, which is minimised by selecting an appropriate length of the waveguide and pump bandwidth. The optimised integrated quantum light source, presented here, eliminates the need for complex domain engineering or intermodal dispersion and will serve as a valuable resource for various quantum-optical experiments.
an entangled photon source is an essential tool for quantum information experiments, such as tests of Bell inequalities, quantum teleportation and entanglement swapping. We report the generation of polarization-entangled photon pairs using grating structures of nonlinear materials such as Tidiffused lithium niobate. This approach is useful for quantum integrated optics because the size of this element is less than 325 micron. Polarizationentangled photon pairs are created using the nonlinear optical process of type-II spontaneous parametric down-conversion. The pump laser at 800 nm was doubled to a wavelength of 400 nm, which was used to produce SPDC in the grating structure of Lithium Niobate. The photon pairs were generated at wavelengths 692nm and 950nm.
We develop and demonstrate a source of polarization-entangled photon pairs using spontaneous parametric down-conversion (SPDC) in domain-engineered, periodically poled lithium niobate (PPLN) at telecom wavelengths. Pumped at 775 nm, this domain-engineered type-II SPDC source produces non-degenerate signal and idler pairs at 1530 nm and 1569 nm. Because of birefringence, the photon pair with horizontally polarized signal and vertically polarized idler has a different phasematching condition than the pair with vertically polarized signal and horizontally polarized idler. Using phase-modulation of the domain structure, we produced a crystal that can simultaneously generate both states in a distributed fashion throughout a single crystal. Performing SPDC using this aperiodically poled crystal, we observed polarization entanglement visibility above 93%. We compare the phase-modulated crystal to other aperiodic structures, including dual-periodically-poled and interlaced biperiodic structures.
Entangled photon pair sources are of key importance in the emerging field of quantum information technology. A common method to generate entangled pairs is based on type II phase-matched spontaneous parametric down conversion (SPDC) followed by a spatial separation of the pair using a conventional beam splitter (see e.g.). This scheme can be used to generate entangled pairs at degeneracy with the drawback that half of the generated pairs are “lost” if both photons leave the beam splitter at the same output port. Recently, we have demonstrated a new scheme providing non-degenerated pairs by employing a sophisticated poling pattern. In this contribution we report a source of non-degenerated polarization entangled photon pairs using such a PPLN waveguide together with a polarization maintaining fiber as quantum eraser and a commercially available fiber-based coarse WDM coupler.