Rubidium-Referenced Frequency-Doubled Pockels Laser with High-Speed Electro-Optic Tuning

Abstract

Narrow-linewidth lasers with rapid frequency control are essential for atomic physics and quantum technologies, yet combining these capabilities in chip-integrated sources at visible wavelengths remains challenging. Here we demonstrate a hybrid integrated InP/thin-film lithium niobate Pockels laser that emits at 780 nm through intracavity second-harmonic generation and supports gigahertz-bandwidth frequency tuning. A periodically poled lithium niobate waveguide is embedded in a laser cavity terminated by an extended distributed Bragg reflector, which provides electro-optically tunable feedback only at the 1560 nm fundamental wavelength. This design yields a singly resonant cavity that enhances frequency conversion while allowing the second-harmonic output to follow rapid tuning without resonance alignment. The laser achieves intrinsic linewidths of 2.7 kHz at 1560 nm and 9.0 kHz at 780 nm, with electro-optic tuning bandwidths beyond 1 GHz at both wavelengths. A mode-hop-free tuning range of 6.48 GHz at 780 nm enables direct spectroscopy of the rubidium D2 transition. Locking the second-harmonic output to this transition reduces the standard deviation of its frequency fluctuations from 135 MHz to 8 MHz and transfers the atomic frequency reference to the fundamental. These results establish integrated frequency-doubled Pockels lasers as compact, rapidly tunable sources that could simplify the optical architectures for future atomic and quantum photonic systems.