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arXiv:2412.11371

Wavelength-Tunable and High-Heralding-Efficiency Quantum Photon Source in Birefringent Phase-Matched Lithium Niobate Waveguide

Tao, Zhu-Qi, Xiao‐Xu Fang, Lu He

Published Dec 16, 2024• 0 citations
arXivHTMLPDF

Abstract

Lithium niobate~(LN) is a birefringent material, where the strong birefringence thermo-optic effect is promising for the generation of quantum photon source with widely tunable wavelength. Here, we demonstrate birefringent phase-matching in a 20-mm-long waveguide fabricated on 5~$μ$m-thick x-cut lithium niobate on insulator. The waveguide is deviated from the optical axis of LN by an angle of 53.5$^\circ$, enabling the phase matching between telecom and visible wavelengths. The phase-matching wavelength of this device can be thermally tuned with rate of 0.617~nm/K. We demonstrate the type-1 spontaneous parametric down-conversion to generate photon pairs with brightness of 2.2~MHz/mW and coincidence-to-accidental ratio up to $2.8\times10^5$. Furthermore, the heralded single photon is obtained from the photon pair with efficiency of 13.8\% and count rate up to 37.8~kHz.

DOI
10.48550/arxiv.2412.11371

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Lithium niobate~(LN) is a birefringent material, where the strong birefringence thermo-optic effect is promising for the generation of quantum photon source with widely tunable wavelength. Here, we demonstrate birefringent phase-matching in a 20-mm-long waveguide fabricated on 5~μμμm-thick x-cut lithium niobate on insulator. The waveguide is deviated from the optical axis of LN by an angle of 53.5∘^\circ∘, enabling the phase matching between telecom and visible wavelengths. The phase-matching wavelength of this device can be thermally tuned with rate of 0.617nm/K. We demonstrate the type-1 spontaneous parametric down-conversion to generate photon pairs with brightness of 2.2MHz/mW and coincidence-to-accidental ratio up to 2.8×1052.8\times10^52.8×105. Furthermore, the heralded single photon is obtained from the photon pair with efficiency of 13.8% and count rate up to 37.8~kHz.
Lithium niobate (LN) is a birefringent material, where the strong birefringence thermo-optic effect is promising for the generation of a quantum photon source with a widely tunable wavelength. Here, we demonstrate birefringent phase matching in a 20-mm-long waveguide fabricated on a 5- μ m-thick x -cut lithium niobate on insulator (LNOI). The waveguide is deviated from the optical axis of LN by an angle of 53.5 ∘ , enabling the phase matching between telecom and visible wavelengths. The phase-matching wavelength of this device can be thermally tuned with rate of 0.6 nm/K. We demonstrate the type-1 spontaneous parametric downconversion to generate photon pairs with a brightness of 4.7 MHz/mW and a coincidence-to-accidental ratio of up to 2.8 × 10 5 . Furthermore, the heralded single photon is obtained from the photon pair with an efficiency of 13.8% and a count rate of up to 37.8 kHz.
Broadband nonlinear optical devices play a critical role in both classical and quantum optics. Here, we design and fabricate a 6.82-mm-long step-chirped periodically poled lithium niobate (CPPLN) waveguide on lithium niobate on insulator, which enables quasi-phase matching over a broad bandwidth for second-harmonic generation (SHG) and spontaneous parametric down-conversion (SPDC). The SHG achieves an average efficiency of 91%/W/cm 2 over the first-harmonic wavelength range of 1510 nm–1620 nm, paving the way for realizing SPDC across a wide range of pump wavelengths. For SPDC, by tuning the pump wavelength to 775 nm, 780 nm, and 785 nm, we achieve broadband photon-pair generation with a maximum full bandwidth and brightness up to 99 THz (846 nm) and 21 MHz/mW/nm, respectively. Our findings provide an efficient and experiment-friendly approach for generating broadband photon pairs, which holds significant promise for advancing applications in quantum metrology.
Broadband nonlinear optical devices play a critical role in both classical and quantum optics. Here, we design and fabricate a 6.82-mm-long step-chirped periodically poled lithium niobate~(CPPLN) waveguide on lithium niobate on insulator, which enables quasi-phase matching over a broad bandwidth for second-harmonic generation~(SHG) and spontaneous parametric down-conversion~(SPDC). The SHG achieves an average efficiency of 54.4\%/W/cm2^22 over the first-harmonic wavelength range of 1510~nm-1620~nm, paving the way for realizing SPDC across a wide range of pump wavelengths. For SPDC, by tuning the pump wavelength to 775~nm, 780~nm, and 785~nm, we achieve broadband photon-pair generation with a maximum full bandwidth and brightness up to 99~THz~(846~nm) and 20~GHz/mW/nm, respectively. Our findings provide an efficient and experiment-friendly approach for generating broadband photon pairs, which holds significant promise for advancing applications in quantum metrology.
Reliable generation of single photons is of key importance for fundamental physical experiments and quantum protocols.The periodically poled lithium niobate (LN) waveguide has shown promise for an integrated quantum source due to its large spectral tunability and high efficiency, benefiting from the quasi-phase-matching.Here we demonstrate photon-pair sources based on an LN waveguide periodically poled by a tightly focused femtosecond laser beam.The pair coincidence rate reaches ∼8000 counts per second for average pump power of 3.2 mW (peak power is 2.9 kW).Our results prove the possibility of application of the nonlinear photonics structure fabricated by femtosecond laser to the integrated quantum source.This method can be extended to three-dimensional domain structures, which provide a potential platform for steering the spatial degree of freedom of the entangled two-photon states.
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.
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.