Chip-based laser with 1-hertz integrated linewidth

J. Guo, C. A. McLemore, C. Xiang, D. Lee, L. Wu, W. Jin, M. Kelleher, N. Jin, D. Mason, L. Chang, A. Feshali, M. Paniccia, P. T. Rakich, K. J. Vahala, S. A. Diddams, F. Quinlan, J. E. Bowers
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A 500-mHz resolution bandwidth RF spectrum of the laser heterodyne beat
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Science Advances
8, 43

Lasers with hertz linewidths at time scales of seconds are critical for metrology, timekeeping, and manipulation of
quantum systems. Such frequency stability relies on bulk-optic lasers and reference cavities, where increased size
is leveraged to reduce noise but with the trade-off of cost, hand assembly, and limited applications. Alternatively,
planar waveguide–based lasers enjoy complementary metal-oxide semiconductor scalability yet are fundamentally
limited from achieving hertz linewidths by stochastic noise and thermal sensitivity. In this work, we demonstrate
a laser system with a 1-s linewidth of 1.1 Hz and fractional frequency instability below 10^−14 to 1 s. This low-noise
performance leverages integrated lasers together with an 8-ml vacuum-gap cavity using microfabricated mirrors.
All critical components are lithographically defined on planar substrates, holding potential for high-volume
manufacturing. Consequently, this work provides an important advance toward compact lasers with hertz
linewidths for portable optical clocks, radio frequency photonic oscillators, and related communication and
navigation systems.

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