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Coherent optical communications provides the largest data transmission capacity with the highest spectral efficiency and therefore has a remarkable potential to satisfy today’s ever-growing bandwidth demands. It relies on so-called in-phase/quadrature (IQ) electro-optic modulators that encode information on both the amplitude and the phase of light. Ideally, such IQ modulators should offer energy-efficient operation and a most compact footprint, which would allow high-density integration and high spatial parallelism. Here, we present compact IQ modulators with an active section occupying a footprint of 4 × 25 µm × 3 µm, fabricated on the silicon platform and operated with sub-1-V driving electronics. The devices exhibit low electrical energy consumptions of only 0.07 fJ bit −1 at 50 Gbit s −1 , 0.3 fJ bit −1 at 200 Gbit s −1 , and 2 fJ bit −1 at 400 Gbit s −1 . Such IQ modulators may pave the way for application of IQ modulators in long-haul and short-haul communications alike.

Integrated ferroelectric plasmonic modulators featuring large bandwidths, broad optical operation range, resilience to high temperature and ultracompact footprint are introduced. Measurements show a modulation bandwidth of 70 GHz and a temperature stability up to 250°C. Mach-Zehnder interferometer modulators with 10-µm-long phase shifters were operated at 116 Gbit/s PAM-4 and 72 Gbit/s NRZ. Wide and open eye diagrams with extinction ratios beyond 15 dB were found. The fast and robust devices are apt to an employment in industrial environments.

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The perovskite compounds La 0.33 Sr 0.67 Cr 1−x−yFe x Ru y O 3−δ (LSCrFeRu, x = 0.62, 0.57, and 0.47; y = 0.05, 0.14, and 0.2, respectively) were synthesized and assessed as a new type of solid oxide fuel cell (SOFC) anode in composite with Gd 0.1 Ce 0.9 O 2-β (GDC) in La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3-ε / La 0.4 Ce 0.6 O 2 bilayer electrolyte-supported cells. By comparing anode polarization resistance R P,A values for the LSCrFeRu compounds to the either exclusively Fe-or Ru-substituted (La,Sr)CrO 3−δ perovskites, the present results demonstrate that the two substituent cations work synergistically to provide further reduction in R P,A from 0.290 Ω·cm 2 for La 0.33 Sr 0.67 Cr 0.33 -F e 0 . 6 7 O 3 − δ ( L S C r F e ) a n d 0 . 2 3 5 Ω · c m 2 f o r La 0.8 Sr 0.2 Cr 0.8 Ru 0.2 O 3−δ (LSCrRu) to 0.195 Ω·cm 2 for LSCrFeRu (all measured in humidified hydrogen at 800°C). These impedance results also strongly suggest that hydrogen dissociative adsorption was the rate-limiting step in the hydrogen oxidation reaction sequence for LSCrFe anodes at some of the pH 2 and temperatures measured. However, the formation of Ru nanoparticles on LSCrFeRu and LSCrRu surfaces, observed by scanning and transmission electron microscopy, appears to promote hydrogen dissociation. Substituting even small amounts of Ru into (La,Sr)(Cr,Fe)O 3−δ perovskites is thus sufficient to make hydrogen electrochemical oxidation the rate-limiting step, resulting in anodes with significantly reduced R P,A .

A new plasmonic transmitter solution offering 0.8 Tbit/s on an ultra-compact 90 µm × 5.5 µm footprint is introduced. It comprises a densely arranged four-channel plasmonic phase modulator array that directly interconnects an optical fiber array. Each plasmonic modulator features high-index grating couplers-for direct and efficient conversion from a fiber mode to a plasmonic slot mode and vice versa-and a plasmonic waveguide-for efficient high-speed modulation. The individual devices achieve data rates of 200 Gbit/s with a symbol rate of 100 GBd. Electrical and optical crosstalk between neighboring modulators were found to have no significant influence on the data modulation experiment. The modulator array has been tested in a 100 GBd experiment with signals at a single wavelength (mimicking a space division multiplexing scheme) and at different wavelengths (mimicking a wavelength division multiplexing experiment).

Resonant modulators encode electrical data onto wavelength-multiplexed optical carriers. Today, silicon microring modulators are perceived as promising to implement such links; however, they provide limited bandwidth and need thermal stabilization systems. Here we present plasmonic micro-racetrack modulators as a potential successor of silicon microrings: they are equally compact and compatible with complementary-metal–oxide–semiconductor-level driving voltages, but offer electro-optical bandwidths of 176 GHz, a 28 times improved stability against operating temperature changes and no self-heating effects. The temperature-resistant organic electro-optic material enables operation at 85 °C device temperature. We show intensity-modulated transmission of up to 408 Gbps at 12.3 femtojoules per bit with a single resonant modulator. Plasmonic micro-racetrack modulators offer a solution to encode high data rates (for example, the 1.6 Tbps envisioned by next-generation communications links) at a small footprint, with low power consumption and marginal, if no, temperature control.

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