All-plasmonic Mach–Zehnder modulator enabling optical high-speed communication at the microscale

Journal name:
Nature Photonics
Volume:
9,
Pages:
525–528
Year published:
DOI:
doi:10.1038/nphoton.2015.127
Received
Accepted
Published online

Optical modulators encode electrical signals to the optical domain and thus constitute a key element in high-capacity communication links1, 2. Ideally, they should feature operation at the highest speed with the least power consumption on the smallest footprint, and at low cost3. Unfortunately, current technologies fall short of these criteria4. Recently, plasmonics has emerged as a solution offering compact and fast devices5, 6, 7. Yet, practical implementations have turned out to be rather elusive. Here, we introduce a 70 GHz all-plasmonic Mach–Zehnder modulator that fits into a silicon waveguide of 10 μm length. This dramatic reduction in size by more than two orders of magnitude compared with photonic Mach–Zehnder modulators results in a low energy consumption of 25 fJ per bit up to the highest speeds. The technology suggests a cheap co-integration with electronics.

At a glance

Figures

  1. Plasmonic circuit realizing the Mach–Zehnder modulator (MZM).
    Figure 1: Plasmonic circuit realizing the Mach–Zehnder modulator (MZM).

    a, Colourized SEM image of the MZM components. The suspended bridge enables electrical control of the device. b, Measured (symbols) and simulated (dashed lines) optical power transfer function versus applied voltage. The simulations indicate a best fit for a material with a nonlinear coefficient of 180 pm V–1.

  2. Enhanced nonlinear interaction.
    Figure 2: Enhanced nonlinear interaction.

    Comparison of the effective refractive group index change Δneff as a function of slot width in a plasmonic slot waveguide (PSW, solid line) and in an equivalent photonic silicon slot waveguide (dashed line). The electrical field in both slots is 1 MV cm–1. The green line in a represents propagation losses over the slot width for the PSW. a, A remarkable increase in Δneff can be observed for decreasing slot widths in the case of the PSW. b,c, The origin of this large nonlinearity can be traced back in part to a much higher field energy interaction factor (b) and in part to a slow-down of the energy velocity (c).

  3. Electro-optical frequency response.
    Figure 3: Electro-optical frequency response.

    Main plot: normalized frequency response as a function of applied sinusoidal RF signal for an optical carrier at 1,550 nm. The dashed line is a linear fit. Its slope does not indicate any bandwidth limitation up to 70 GHz. Insets: normalized electro-optical modulation efficiency for light at 1,520 nm and 1,620 nm, confirming a large optical bandwidth across more than 100 nm.

  4. Experimental high-speed set-up.
    Figure 4: Experimental high-speed set-up.

    The all-plasmonic MZM encodes electrical signals at 54 and 72 Gbit s−1 onto a laser signal at 1,534 nm. The respective eye diagrams at 72 Gbit s–1 before and after the electrical amplifier as well as the received eye diagrams are shown at the bottom. The BERs at the receiver are 7.3 × 10−5 and 3 × 10−3 for bit rates at 54 Gbit s−1 and 72 Gbit s−1, respectively. The performance at 72 Gbit s−1 is diminished by the limited electrical bandwidth of the transmitter, as can be seen from the degraded eye diagram at the input. Still, the nonlinear transfer function of the MZM converts the 72 Gbit s−1 signal into a received eye diagram with BER above the FEC limit.

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Author information

Affiliations

  1. Institute of Electromagnetic Fields (IEF), ETH Zurich, Zurich 8092, Switzerland

    • C. Haffner,
    • W. Heni,
    • Y. Fedoryshyn,
    • J. Niegemann,
    • B. Baeuerle,
    • Y. Salamin,
    • A. Josten,
    • U. Koch,
    • C. Hoessbacher,
    • F. Ducry,
    • L. Juchli,
    • A. Emboras,
    • D. Hillerkuss,
    • C. Hafner &
    • J. Leuthold
  2. Institute IMT, Karlsruhe Institute of Technology (KIT), Karlsruhe 76131, Germany

    • A. Melikyan &
    • M. Kohl
  3. Department of Chemistry, University of Washington, Seattle, Washington 98195-1700, USA

    • D. L. Elder &
    • L. R. Dalton

Contributions

C.H. conceived the concept, designed and fabricated the modulator, designed and performed the experiments, analysed the data and wrote the paper. W.H. installed and optimized the poling process, fabricated the devices, designed and performed the experiments and evaluated the data. Y.F. conceived the concept, designed the fabrication process, fabricated the modulator and wrote the manuscript. J.N. conceived the concept, designed the modulator and wrote the manuscript. A.M. conceived the concept. D.L.E. and L.R.D. developed and synthesized the DLD-164 nonlinear chromophore. B.B., A.J. and D.H. performed the data transmission experiment. Y.S. performed the bandwidth characterization, retrieved the electrical properties and wrote the manuscript. U.K. and C.H. performed and evaluated the ellipsometry experiment. A.E., F.D. and L.J. provided support for the design of the modulator. M.K. developed the concept. C.H. and J.L. conceived the concept, designed the experiment and wrote the manuscript.

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The authors declare no competing financial interests.

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