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Sub-hertz fundamental linewidth photonic integrated Brillouin laser


Spectrally pure lasers, the heart of precision high-end scientific and commercial applications, are poised to make the leap from the laboratory to integrated circuits. Translating this performance to integrated photonics will dramatically reduce cost and footprint for applications such as ultrahigh capacity fibre and data centre networks, atomic clocks and sensing. Despite the numerous applications, integrated lasers currently suffer from large linewidth. Brillouin lasers, with their unique properties, offer an intriguing solution, yet bringing their performance to integrated platforms has remained elusive. Here, we demonstrate a sub-hertz (~0.7 Hz) fundamental linewidth Brillouin laser in an integrated Si3N4 waveguide platform that translates advantages of non-integrated designs to the chip scale. This silicon-foundry-compatible design supports low loss from 405 to 2,350 nm and can be integrated with other components. Single- and multiple-frequency output operation provides a versatile low phase-noise solution. We highlight this by demonstrating an optical gyroscope and a low-phase-noise photonic oscillator.

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Fig. 1: Si3N4 waveguide Brillouin laser and application system-on-chip examples.
Fig. 2: Brillouin laser optical guiding, phonon generation and resonant gain.
Fig. 3: Laser resonator cold-cavity characteristics and Brillouin gain measurement and modelling.
Fig. 4: Experimental measurement setup and laser threshold, slope efficiency and cascaded-order power dynamics measurement.
Fig. 5: Laser linewidth measurement and linewidth narrowing.
Fig. 6: Integrated laser optical gyroscope and photonic microwave synthesizer demonstrations.

Data availability

The data that support the plots within this paper and other finding of this study are available from the corresponding author on reasonable request.


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This material is based on work supported by the Defense Advanced Research Projects Agency (DARPA) and Space and Naval Warfare Systems Center Pacific (SSC Pacific) under Contract No. N66001-16-C-4017. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing official policies of DARPA or the US Government. We thank R. Lutwak and J. Adeleman for useful discussions. We also thank B. Stamenic for help in processing samples in the UCSB nanofabrication facility, W. Renninger for help with the measurement techniques for Brillouin gain profiles and J. Sexton, J. Hunter and D. Larson at Honeywell for the cladding deposition, pre-cladding preparation and anneal process and Z. Su for help with the figures.

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S.G., G.M.B., R.B., P.T.R. and D.J.B. prepared the manuscript. S.G., G.M.B., M.P. and J.W. contributed equally to performing the system, lasing and noise measurements. T.H., D.B. and J.N. contributed to the Si3N4 integrated laser fabrication. M.P., S.G., D.B., P.T.R., R.B., J.N., K.D.N., M.S. and D.J.B. contributed to the laser design. R.B., P.T.R., M.P., T.Q., S.G. and K.D.N. contributed to the simulation and modelling. G.M.B., C.P., N.C. and S.G. built the radiofrequency calibrated Mach–Zehnder interferometer and ring-down systems and measured the laser resonator properties. S.G., G.M.B., C.P., M.P. and J.W. performed Brillouin gain measurements. All authors contributed to analysing simulated and experimental results. D.J.B., K.D.N., P.T.R. and M.S. supervised and led the scientific collaboration.

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Correspondence to Daniel J. Blumenthal.

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Gundavarapu, S., Brodnik, G.M., Puckett, M. et al. Sub-hertz fundamental linewidth photonic integrated Brillouin laser. Nature Photon 13, 60–67 (2019).

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