Large Brillouin amplification in silicon

Journal name:
Nature Photonics
Year published:
Published online

Both Kerr and Raman nonlinearities are radically enhanced by tight optical-mode confinement in nanoscale silicon waveguides1, 2, 3, 4. Counterintuitively, Brillouin nonlinearities—originating from coupling between photons and acoustic phonons—are exceedingly weak in these same nonlinear waveguides5. Strong Brillouin interactions have only recently been realized in a new class of optomechanical structures that control the interaction between guided photons and phonons5, 6, 7. Despite these major advances, appreciable Brillouin-based optical amplification has yet to be observed in silicon. Using a membrane-suspended waveguide, we report large Brillouin amplification in silicon for the first time, reaching levels greater than 5 dB for modest pump powers, and demonstrate a record low (5 mW) threshold for net amplification. This work represents an important step towards the realization of high-performance Brillouin lasers and amplifiers in silicon.

At a glance


  1. Hybrid photonic–phononic silicon waveguide.
    Figure 1: Hybrid photonic–phononic silicon waveguide.

    a, Schematic of the continuously suspended silicon Brillouin-active waveguide. b, Cross-section of the active region. c, Diagram showing the critical device dimensions. d, The x component of the electric field for the guided optical mode. e, The x component of the electrostrictive body force. f, The elastic displacement field of the Brillouin-active phonon mode. g, Cross-sectional SEM image of the waveguide core. h,i, Top-down SEM images of the fabricated device (h) and a magnified section (i). Scale bars, 500 nm (g); 10 μm (h); and 5 μm (i). j, Phase-matching diagram. k, Optical dispersion relation.

  2. Experimental results showing the Brillouin gain and net on-chip amplification.
    Figure 2: Experimental results showing the Brillouin gain and net on-chip amplification.

    a, Diagram of the experimental apparatus. BC, d.c. bias controller; DUT, device under test; EDFA, erbium-doped fibre amplifier; IM, Mach–Zehnder intensity modulator; ISO, optical isolator; NF, notch filter; PD, photodetector; RFSA, radiofrequency spectrum analyser. b, Brillouin gain spectra obtained for pump powers of 21 mW, 36 mW and 62 mW. c, Plots of peak gain (red), linear loss (dash) and total loss (green) versus on-chip pump power at 1,550 nm. d, Net amplification as a function of pump power. The threshold for amplification is 5 mW.

  3. Set-up and results of an energy-transfer (two-tone) experiment.
    Figure 3: Set-up and results of an energy-transfer (two-tone) experiment.

    a, Experimental diagram to measure power transfer driven by two pump fields of equal magnitude. AOM, acousto-optic modulator. b, Theory (black) and data (blue circles) that represent the frequency spectrum of the output light for total input powers of 0.1 mW, 26 mW and 65 mW are shown. c, Power transfer as a function of on-chip power showing the theoretical calculations (lines) and measured amplitudes for pump fields ω0 and ω1 (solid black and solid red) and the first cascaded fields ω−1 and ω2 (dashed black and dashed red) fields. The vertical blue lines correspond to the plots in b.


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Author information

  1. These authors contributed equally to this work

    • Eric A. Kittlaus &
    • Heedeuk Shin


  1. Department of Applied Physics, Yale University, New Haven, Connecticut 06520, USA

    • Eric A. Kittlaus,
    • Heedeuk Shin &
    • Peter T. Rakich
  2. Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea.

    • Heedeuk Shin


E.A.K. and H.S. fabricated the waveguide devices. P.T.R., H.S. and E.A.K. developed multiphysics simulations for and designed the devices. E.A.K. and H.S. conducted experiments with the assistance of P.T.R. P.T.R., H.S. and E.A.K. developed analytical models to interpret measured data. All authors contributed to the writing of this paper.

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