Visible Brillouin-quadratic microlaser in a high-Q thin-film lithium niobate microdisk

TL;DR

This paper demonstrates an integrated visible Brillouin-quadratic microlaser on a chip using a high-Q lithium niobate microdisk, achieving narrow linewidth, low threshold, and efficient second harmonic generation, advancing quantum and metrology applications.

Contribution

The work introduces the first on-chip visible Brillouin-quadratic microlaser with ultra-high Q and simultaneous SHG, enabling compact quantum and sensing technologies.

Findings

Achieved narrow-linewidth Brillouin lasing at 10.17 GHz with 254 Hz linewidth.

Demonstrated low threshold of 1.81 mW for lasing.

Observed efficient second harmonic generation at 780 nm with 3.61%/mW efficiency.

Abstract

Narrow-linewidth lasers at short/visible wavelengths are crucial for quantum and atomic applications, such as atomic clocks, quantum computing, atomic and molecular spectroscopy, and quantum sensing. However, such lasers are often only accessible in bulky tabletop systems and remain scarce in integrated photonic platform. Here, we report an on-chip visible Brillouin-quadratic microlaser in a 117-um-diameter thin-film lithium niobate (TFLN) microdisk via dispersion engineering. Enabled by the ultra-high Q factor of 4.0X10(6) and small mode volume, strong photon-phonon interaction and high second-order nonlinearity of the TFLN microdisk, narrow-linewidth Stokes Brillouin lasing (SBL) is demonstrated with 10.17 GHz Brillouin shift under a 1560-nm pump, exhibiting a short-term narrow linewidth of 254 Hz and a low threshold of only 1.81 mW. Meanwhile, efficient second harmonic generation (SHG) of the SBL signal is also observed at 780 nm, with a normalized conversion efficiency of 3.61%/mW, made possible by simultaneous phase matching fulfillments for both narrow-linewidth SBL and its SHG. This demonstration of an integrated ultra-narrow linewidth visible wavelength Brillouin-quadratic lasers opens new avenues toward chip-scale quantum information processing and precise metrology.