To address the challenge of increasing data rates, next-generation optical communication networks will require the co-integration of electronics and photonics. Heterogeneous integration of these technologies has shown promise, but will eventually become bandwidth-limited. Faster monolithic approaches will therefore be needed, but monolithic approaches using complementary metal–oxide–semiconductor (CMOS) electronics and silicon photonics are typically limited by their underlying electronic or photonic technologies. Here, we report a monolithically integrated electro-optical transmitter that can achieve symbol rates beyond 100 GBd. Our approach combines advanced bipolar CMOS with silicon plasmonics, and addresses key challenges in monolithic integration through co-design of the electronic and plasmonic layers, including thermal design, packaging and a nonlinear organic electro-optic material. To illustrate the potential of our technology, we develop two modulator concepts—an ultra-compact plasmonic modulator and a silicon-plasmonic modulator with photonic routing—both directly processed onto the bipolar CMOS electronics.
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The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.
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This work was funded in part by EU projects PLASMOfab (688166) and plaCMOS (980997) and the Air Force Office of Scientific Research (FA9550-19-1-0069). This work was carried out in part at the Binnig and Rohrer Nanotechnology Center.
C.H., W.H., B.B. are involved in activities toward commercializing high-speed plasmonic modulators at Polariton Technologies Ltd. The other authors declare no competing interests.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Extended Data Fig. 1 Simplified interface between electronic output stage and plasmonic Mach–Zehnder modulator (MZM).
Typically, both output stage and modulator are terminated by 50 Ω. In our case, the plasmonic MZM can be modelled as electrically lumped, which allows for single end termination. Hence, the driving voltage is doubled without increase in energy consumption. Additionally, such an approach allows tuning of the output impedance to specific needs.
The operation-critical functions (2:1 SEL and clock distribution) are separated from the optional parts for advanced functionalities and for measurement purposes.
Thermal simulations of the electronic circuit revealed the temperatures listed in the table inset, which have been compared to measurements with on-chip temperature diodes. Ideal and reduced thermal conduction to the substrate match well with measurements on a raw electronic chip and a post-processed transmitter chip, respectively.
Stable operation until about 140 °C was measured with a drastic degradation when reaching the glass temperature of 150 °C. The small dip at 120 °C is due to thermally induced set-up fluctuations. The trend line (dashed) serves to guide the eye.
Extended Data Fig. 5 Data modulation experiment for externally driven monolithic plasmonic modulator.
An amplified external source applies the electrical signal to the modulator. 100 GBd NRZ-OOK has been modulated and transmitted to the receiver for direct detection. The insets show the received optical eye after equalization.
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Koch, U., Uhl, C., Hettrich, H. et al. A monolithic bipolar CMOS electronic–plasmonic high-speed transmitter. Nat Electron 3, 338–345 (2020). https://doi.org/10.1038/s41928-020-0417-9
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