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Nature volume  612, pages 56–61 (2022 )Cite this article STM32F405VGT6

The ability to amplify optical signals is of pivotal importance across science and technology typically using rare-earth-doped fibres or gain media based on III–V semiconductors. A different physical process to amplify optical signals is to use the Kerr nonlinearity of optical fibres through parametric interactions1,2. Pioneering work demonstrated continuous-wave net-gain travelling-wave parametric amplification in fibres3, enabling, for example, phase-sensitive (that is, noiseless) amplification4, link span increase5, signal regeneration and nonlinear phase noise mitigation6. Despite great progress7,8,9,10,11,12,13,14,15, all photonic integrated circuit-based demonstrations of net parametric gain have necessitated pulsed lasers, limiting their practical use. Until now, only bulk micromachined periodically poled lithium niobate (PPLN) waveguide chips have achieved continuous-wave gain16,17, yet their integration with silicon-wafer-based photonic circuits has not been shown. Here we demonstrate a photonic-integrated-circuit-based travelling-wave optical parametric amplifier with net signal gain in the continuous-wave regime. Using ultralow-loss, dispersion-engineered, metre-long, Si3N4 photonic integrated circuits18 on a silicon chip of dimensions 5 × 5 mm2, we achieve a continuous parametric gain of 12 dB that exceeds both the on-chip optical propagation loss and fibre–chip–fibre coupling losses in the telecommunication C band. Our work demonstrates the potential of photonic-integrated-circuit-based parametric amplifiers that have lithographically controlled gain spectrum, compact footprint, resilience to optical feedback and quantum-limited performance, and can operate in the wavelength ranges from visible to mid-infrared and outside conventional rare-earth amplification bands.

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The code and data used to produce the plots are found on the Zenodo repository https://doi.org/10.5281/zenodo.6989024.

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We thank T. Liu for assisting in the waveguide spiral design and M. H. Anderson for the discussion. The Si3N4 chips were fabricated in the EPFL Center of MicroNanoTechnology (CMi). This work was supported by the Air Force Office of Scientific Research (AFOSR) under award no. FA9550-19-1-0250, by contract HR0011-20-2-0046 (NOVEL) from the Defense Advanced Research Projects Agency (DARPA), Microsystems Technology Office (MTO) and by the Swiss National Science Foundation (SNSF) under grant agreement no. 192293. J.R. acknowledges support from the SNSF under an Ambizione Fellowship (201923).

Institute of Physics, Swiss Federal Institute of Technology Lausanne (EPFL), Lausanne, Switzerland

Johann Riemensberger, Nikolai Kuznetsov, Junqiu Liu, Jijun He, Rui Ning Wang & Tobias J. Kippenberg

Center for Quantum Science and Engineering, Swiss Federal Institute of Technology Lausanne (EPFL), Lausanne, Switzerland

Johann Riemensberger, Nikolai Kuznetsov, Rui Ning Wang & Tobias J. Kippenberg

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J.L. and R.N.W. designed and fabricated the samples. J.R., N.K. and J.H. performed the experiments and data analysis. J.R. performed the numerical simulations. J.R., J.L. and T.J.K. wrote the manuscript. T.J.K. supervised the project.

Correspondence to Johann Riemensberger or Tobias J. Kippenberg.

T.J.K. is a cofounder and shareholder of LiGenTec SA, a company that is engaged in making Si3N4 nonlinear photonic chips available through foundry service.

Nature thanks Dawn T. H. Tan and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

a, For a waveguide of cross section dimensions 2,450 nm × 910 nm and pump power of 4 W, as used in this study. The dotted grey lines represent the threshold for on-chip parametric gain. b, For optimized waveguide cross section of 2,100 nm × 670 nm using 0.75 W of pump power. The lowest waveguide loss value of 0.15 dB m−1 represents the waveguide absorption loss of Si3N4 structures fabricated using the photonic Damascene process at EPFL.

a, Optical setup. See text for description. b, Calibrated transmission spectrum through a spiral. The trace colours indicate the three individual external-cavity diode laser scans. c, Calibrated reflection spectrum inside and from a spiral. d, OFDR traces are analysed using segmented Fourier transformation and vertically offset by 15 dB. The shading indicates the centre frequency according to panel e. The propagation loss fitting region is marked with vertical orange lines. The propagation loss is determined from the dotted line fit. e, Propagation loss extracted from OFDR. Extracted propagation losses are relative to optical distance and must be multiplied by the group index of 2.08 for conversion to the physical waveguide length. The values represent upper bounds owing to a background of laser phase noise that induces an increased gradient. f,g, Zooming into OFDR traces around the front (f) and back (g) facets. Dots depict successful identification of backside facet reflection for valid dispersion measurement. h, Inverse group velocity β1 as a function of wavelength. Markers correspond to f,g. The black line indicates the fitted waveguide dispersion curve up to the third order.

a, Schematic indication of a typical 90° waveguide bend in a rectangular spiral. All bends are identical and have a radius of 230 μm. Insets show the normalized mode profile for the TE00, TE10 and TE20 modes. b, Simulated group refractive indices for the TE00, TE10 and TE20 modes of a 2.45 μm × 0.91 μm strip waveguide with vertical sidewalls. c, Calculated spectral frequencies for destructive interference between higher-order mode excitation at the beginning and at the end of the waveguide bend.

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Riemensberger, J., Kuznetsov, N., Liu, J. et al. A photonic integrated continuous-travelling-wave parametric amplifier. Nature 612, 56–61 (2022). https://doi.org/10.1038/s41586-022-05329-1

DOI: https://doi.org/10.1038/s41586-022-05329-1

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