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Optics Express

Intracavity-SHG telecom modelocked oscillator for compact quantum homodyne detection

Cody W. Mart, Nicholas V. Nardelli, Michael B. Grayson, Lynden K. Shalm, Tara M. Fortier

Published May 25, 2026• 0 citations
Publisher

Abstract

We demonstrate a compact telecom-wavelength modelocked laser source designed for pumping spontaneous parametric downconversion (SPDC), based on an erbium-ytterbium co-doped phosphate glass laser with intracavity second harmonic generation (SHG) to 773.5 nm. Using a 0.4 mm thick β-barium borate crystal, the system produces nearly 35 mW of average power with 191 fs pulses at 773.5 nm. This represents a 1000-fold increase in average power compared to previously reported intracavity SHG modelocked fs-level telecom oscillators (C. Hu, Y. Zhang, Q. Gao, et al., Jap. J. of App. Phys.59080902 (2020)10.35848/1347-4065/aba37c). This architecture provides a path toward homodyne detection of SPDC-generated single photons using a phase-coherent local oscillator derived from the same cavity.

DOI
10.1364/oe.587564

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We demonstrate a compact telecom-wavelength modelocked laser source designed for pumping spontaneous parametric downconversion (SPDC), based on an erbium-ytterbium co-doped phosphate glass laser with intracavity second harmonic generation (SHG) to 773.5 nm. Using a 0.4 mm thick β-barium borate crystal, the system produces nearly 35 mW of average power with 191 fs pulses at 773.5 nm. This represents a 1000-fold increase in average power compared to previously reported intracavity SHG modelocked fs-level telecom oscillators (C. Hu, Y. Zhang, Q. Gao, et al., Jap. J. of App. Phys.59080902 (2020)10.35848/1347-4065/aba37c). This architecture provides a path toward homodyne detection of SPDC-generated single photons using a phase-coherent local oscillator derived from the same cavity.
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.
The frequency correlation (or decorrelation) of photon pairs is of great importance in long-range quantum communications and photonic quantum computing. We experimentally characterize a spontaneous parametric down conversion (SPDC) source, based on a β-Barium Borate (BBO) crystal cut for type-II phase matching at 1550 nm which has the capability to emit photons with positive or no spectral correlations. Our system, depicted in Fig. 1a), employs a carefully designed detection method exploiting two InGaAs detectors.
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.
Widespread commercial adoption of telecom-band quantum-key-distribution (QKD) will require fully integrated, room-temperature transmitters. Implementing highly efficient spontaneous parametric down-conversion (SPDC) on a platform that offers co-integration of the pump laser has been an outstanding challenge. Here, using such a platform based on AlGaAs-on-insulator waveguides, we report telecom-band SPDC (and second harmonic generation) with exceedingly large efficiencies of 26 GHz generated pairs/mW over a 7 THz bandwidth, which would saturate the usable photon-flux for a 70-channel wavelength-multiplexed QKD-system at merely 1.6 mW of pump laser power.
Abstract Widespread commercial adoption of telecom‐band quantum key distribution (QKD) will require fully integrated, room‐temperature transmitters. Implementing highly efficient spontaneous parametric down‐conversion (SPDC) on a platform that offers co‐integration of the pump laser has been an outstanding challenge. Here, using such a platform based on AlGaAs‐on‐insulator waveguides, telecom‐band SPDC (and SHG, second harmonic generation) is reported with exceedingly large efficiencies of 26 GHz generated pairs per mW over a 7 THz bandwidth, which would saturate the usable photon‐flux for a 70‐channel wavelength‐multiplexed QKD system at merely 1.7 mW of pump laser power.