Coherent terabit communications with microresonator Kerr frequency combs

Journal name:
Nature Photonics
Year published:
Published online

Optical frequency combs have the potential to revolutionize terabit communications1. The generation of Kerr combs in nonlinear microresonators2 is particularly promising3, enabling line spacings of tens of gigahertz. However, such combs may exhibit strong phase noise4, 5, 6, which has made high-speed data transmission impossible up to now. Here, we demonstrate that systematic adjustment of the pump conditions for low phase noise4, 7, 8, 9 enables coherent data transmission with advanced modulation formats that pose stringent requirements on the spectral purity of the comb. In a first experiment, we encode a data stream of 392 Gbit s−1 on a Kerr comb using quadrature phase-shift keying and 16-state quadrature amplitude modulation. A second experiment demonstrates feedback stabilization of the comb and transmission of a 1.44 Tbit s–1 data stream over up to 300 km. The results show that Kerr combs meet the highly demanding requirements of coherent communications and thus offer an attractive route towards chip-scale terabit-per-second transceivers.

At a glance


  1. Principles of coherent terabit-per-second communications with Kerr frequency combs.
    Figure 1: Principles of coherent terabit-per-second communications with Kerr frequency combs.

    a, Artist's view of a future chip-scale terabit-per-second transmitter, leveraging a Kerr frequency comb source. The demonstration of coherent data transmission with Kerr combs is the subject of this work. DEMUX, de-multiplexer; VOA, variable optical attenuator; IQ-Mod, IQ-modulator; MUX, multiplexer. b, Illustration of Kerr comb formation by multi-stage FWM. Degenerate FWM (1) converts two photons at the pump frequency to a pair of photons that are up- and downshifted in frequency, whereas cascaded non-degenerate FWM (2) populates the remaining resonances. c, SEM image of an integrated high-Q SiN microresonator. High-index-contrast SiN waveguides enable dense integration. d, Constellation diagrams of QPSK and 16QAM signals, where information is encoded both in the amplitude and the phase of the optical carrier, which can be represented by the in-phase (I, horizontal axis) and quadrature (Q, vertical axis) components of the complex electrical field amplitude.

  2. Comb generation set-up.
    Figure 2: Comb generation set-up.

    a, The optical pump comprises a tunable laser source (TLS), a polarization controller (PC) and an erbium-doped fibre amplifier (EDFA). Lensed fibres (LF) couple light to and from the microresonator chip. A fibre Bragg grating (FBG 1) serves as a tunable narrowband notch filter to suppress residual pump light. For adjustment of the pump parameters, we monitor the power conversion from the pump to the adjacent lines (PM, power meter). An electronic spectrum analyser (ESA) is used to measure the RF linewidth in the photocurrent spectrum of the photodetector (PD). A 5-nm-wide spectral section is extracted from the comb spectrum and used for data transmission. b, Waveguide cross-section and mode profile. c, Optical micrograph of the resonator. d, RF spectrum of a high phase-noise comb state (RBW = 10 kHz). e, RF spectrum of a low phase-noise comb state (RBW = 30 kHz). f, Selected part of the comb spectrum (OSA, optical spectrum analyser). RBW, resolution bandwidth.

  3. Coherent data transmission using a Kerr microresonator frequency comb.
    Figure 3: Coherent data transmission using a Kerr microresonator frequency comb.

    a, Spectrum of modulated carriers for all six data channels, measured at the input of the OMA. b, Constellation diagrams for each channel and for both polarizations, as well as the corresponding error vector magnitude (EVM). The constellation diagrams show no sign of excessive phase noise, which would result in constellation points that are elongated along the azimuthal direction. For QPSK, the BER of all channels is below 4.5 × 10−3, which corresponds to an EVM of 38%; for channels 4 and 5 the BER is even smaller than 1 × 10−9 (EVM < 16.7%). The good quality of channel 5 enables transmission of a 16QAM signal with a measured BER of 7.5 × 10−4.

  4. Coherent terabit-per-second data transmission using a feedback-stabilized Kerr frequency comb.
    Figure 4: Coherent terabit-per-second data transmission using a feedback-stabilized Kerr frequency comb.

    a, Optical spectrum of the 1.44 Tbit s−1 data stream. The spectrum was flattened before modulation. b, EVM for all data channels and fibre spans. The carriers are modulated at a symbol rate of 18 GBd using QPSK and Nyquist pulse shaping. Using polarization multiplexing at each of the 20 WDM channels, an aggregate data rate of 1.44 Tbit s−1 is achieved. The polarizations are distinguished by diamonds and squares, while the different fibre spans (0 km, 75 km, 150 km, 225 km, 300 km) are colour-coded and slightly offset in the horizontal direction, as indicated by the arrow. The red dashed line indicates an EVM of 38%, which corresponds to the BER threshold for second-generation FEC.


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Author information


  1. Institute of Photonics and Quantum Electronics (IPQ) and Institute of Microstructure Technology (IMT), Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany

    • Joerg Pfeifle,
    • Matthias Lauermann,
    • Yimin Yu,
    • Daniel Wegner,
    • Philipp Schindler,
    • Jingshi Li,
    • David Hillerkuss,
    • Rene Schmogrow,
    • Claudius Weimann,
    • Wolfgang Freude,
    • Juerg Leuthold &
    • Christian Koos
  2. École Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland

    • Victor Brasch,
    • Tobias Herr &
    • Tobias J. Kippenberg
  3. Menlo Systems GmbH, 82152 Martinsried, Germany

    • Klaus Hartinger &
    • Ronald Holzwarth
  4. Present address: Electromagnetic Fields & Microwave Electronics Laboratory (IFH), ETH Zurich, 8092 Zurich, Switzerland

    • David Hillerkuss &
    • Juerg Leuthold


J.P. conceived and performed the data transmission experiments and analysed the data. V.B. and K.H. conceived, designed and fabricated the devices, which were characterized jointly by V.B. and T.H. M.L., Y.Y., D.W., P.S. and C.W. performed the data transmission experiments and analysed the data. The feedback stabilization of the comb source for the second experiment was implemented jointly by J.P. and Y.Y. J.Li, D.H. and R.S. contributed subsystems to the data transmission experiments. The project was supervised by R.H., W.F., J.L., T.J.K. and C.K. T.J.K. conceived and supervised the comb generation scheme and fabrication of the devices, C.K. conceived the data transmission and comb stabilization schemes and supervised the experiments. All authors discussed the data and wrote the manuscript jointly.

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