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Optical Technologies for Telecommunications (OTT)

Calculation of the structure of the periodically poled lithium niobate nanowaveguide for generation of ultrabroadband biphotons in the near-infrared range

O. A. Ermishev, Арсланов Наркис Мусавирович, Maksim A. Smirnov

Published Oct 4, 2023• 0 citations
Publisher

Abstract

In this paper, we studied the properties of two-photon quantum states of light that emerge due to spontaneous parametric downconversion in a nonlinear waveguide with periodically poles structure. The spectral and entangled properties have been studied mainly for photon pairs whose spectra is located in the near-infrared range. We found that it is possible to select the geometric parameters of the structure of a lithium niobate nanowaveguide in such a way that the two-photon quantum state in the near-IR range will have a spectrum width of about 180THz.

DOI
10.1117/12.2681337

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arXiv:2406.17439•Optics Express•May 30, 2024•19 citations
In this paper, we studied the properties of two-photon quantum states of light that emerge due to spontaneous parametric downconversion in a nonlinear waveguide with periodically poles structure. The spectral and entangled properties have been studied mainly for photon pairs whose spectra is located in the near-infrared range. We found that it is possible to select the geometric parameters of the structure of a lithium niobate nanowaveguide in such a way that the two-photon quantum state in the near-IR range will have a spectrum width of about 180THz.
Abstract For quantum biomicroscopy, light sources need to provide a reliable signal at low intensity levels with a high rate generation in the near-infrared region. To develop this light source, we investigated the abilities of generating ultrabroadband two-photon states in the near-infrared in a periodically poled lithium niobate (LiNbO3) nanowaveguide with different geometrical cros-section and pump wavelength. Using modeling and numerical calculations the optimal nanowaveguide parameters providing the maximum width of the spectrum of two-photon states ~180 THz under the pump wavelength about 1.0 μm were determined.
Entangled photon pairs generated by a low-power continuous-wave laser could replicate pulsed laser-based tabletop spectroscopy by taking advantage of the inherent quantum correlations between the photons. Much of the current work in the thin-film lithium niobate platform has focused on infrared wavelengths, leaving shorter wavelengths still a largely unexplored space, particularly for spectroscopy. In this work, we have fabricated periodically poled lithium niobate nanophotonic waveguides for entangled photon generation through spontaneous parametric downconversion with a visible pump (406 nm). Characterization of the waveguided pair source confirms the spectral and temporal correlations of energy-time entangled photons with an on-chip pair generation efficiency of (2.3 ± 0.5) × 1011 pairs/s/mW, brightness of (1.6 ± 0.3) × 109 pairs/s/mW/nm, and two-photon interference visibility greater than 99%. With the same material platform, we have also demonstrated second harmonic generation with on-chip powers up to 30 μW and wavelengths as low as 355 nm, demonstrating lithium niobate's potential for ultraviolet nonlinear photonics and frequency doubling in the UV-A spectral region. Through design of larger cross-section waveguides, we have also explored how variations in the lithium niobate thin film thickness can affect quasi-phase matching. To date, this is the first reported demonstration of periodically poled lithium niobate nanophotonic waveguides for spontaneous parametric downconversion at a fully visible pump wavelength (406 nm) as well as second harmonic generation in the UV (355 nm). Future work towards fully on-chip spectroscopy will explore integrating an on-chip Mach-Zehnder interferometer with the entangled photon source.
Entangled photons, which may be generated through the process of spontaneous parametric down-conversion (SPDC) in a crystal with /spl chi//sup (2)/ nonlinearity, have long been in the spotlight for quantum-optics experiments. The generation of entangled photons by quasi-phase matching (QPM) in lithium niobate offers the promise of increased photon-pair production and, with the integration of a waveguide structure, control of the spatial characteristics of the down-converted photons. It turns out that the use of a waveguide structure, in conjunction with periodic poling to achieve quasi-phase matching, offers another critically important feature: the possibility of generating counterpropagating signal and idler photons. We consider the conditions required for generating counterpropagating photon beams and explore some of the unique properties of this source of light using a periodically poled LiNbO/sub 3/ waveguide.
In this paper, we propose the generation of hyperentangled photon pairs using type-II spontaneous parametric down-conversion in a biperiod, 5% MgO-doped lithium-niobate ridge waveguide. The photon pairs are entangled in spatial mode and polarization degrees of freedom. A pulsed laser source at 687 nm, having an antisymmetric Hermite-Gaussian HG (1,0) spatial mode, is considered as the pump. Down-converted photon pairs, with the signal being at the telecommunication wavelength of 1550 nm, are characterized through a joint spectral amplitude analysis of their biphoton state.
We report on the generation of narrowband photon pairs at telecommunication wavelengths using a periodically poled lithium niobate waveguide that utilizes the nonlinear tensor element d(24) for type-II quasi phase matching. The FWHM bandwidth of the spontaneous parametric downconversion was 1 nm. The brightness of the photon pair source was ~6x10(5)/s/GHz when the pump power was 1 mW. The indistinguishability of the signal and idler photons generated by the degenerate spontaneous parametric downconversion process was studied in a Hong-Ou-Mandel type interference experiment.
We design and fabricate shallow-etched periodically poled lithium niobate waveguides to realize highly efficient broadband spontaneous parametric down-conversion (SPDC) on nanophotonic chips. The shallow-etched waveguide can tolerate the non-uniformities of waveguide width induced by fabrication imperfections, enabling the generation of photon pairs with high count rate and bandwidth. We demonstrate photon-pair generation with a high brightness of 11.7 GHz/mW and bandwidth of 22 THz in a 5.7-mm-long PPLN waveguide. The generated photon pairs exhibit a strong temporal correlation with a coincidence-to-accidental ratio of up to 16262±850. Our results confirm the feasibility of shallow etching in the fabrication of an efficient SPDC device on the platform of lithium niobate on an insulator, and benefit quantum information processing with a broadband photon source.