Optical modulators encode electrical signals to the optical domain and thus constitute a key element in high-capacity communication links 1,2 . Ideally, they should feature operation at the highest speed with the least power consumption on the smallest footprint, and at low cost 3 . Unfortunately, current technologies fall short of these criteria 4 . Recently, plasmonics has emerged as a solution offering compact and fast devices 5-7 . 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.Mach-Zehnder modulators (MZMs) are the most versatile electro-optical converters in high-end communication systems. MZMs are unique, as they can be used to encode multiple bits within one symbol with the highest quality. They are thus instrumental in increasing the capacity of modern communication links 1 . Until now, MZMs have mostly been based on the lithium niobate material system, which requires footprints on the order of cm 2 . Recently, more compact silicon-based modulators have emerged. These devices have already shown operation at bandwidths up to 55 GHz (ref. 8), they are cost-effective, and they feature lengths on the order of hundreds of micrometres to millimetres 2,3,8-12 . Yet, complementary metal-oxide semiconductor electronics (CMOS) house hundreds of transistors on a single μm 2 , making a co-integration of today's silicon MZMs with CMOS electronics impractical 4 . In pursuit of more compact silicon modulators, various approaches have been demonstrated, such as resonant silicon ring modulators 13,14 or germanium-based electro-absorption modulators 15,16 . However, encoding advanced modulation formats is challenging 17 , and high-capacity transmission has, so far, only been achieved with MZMs 2,12 . Instead, plasmonics has drawn significant interest as an alternative solution 6,7 . In plasmonics, optical signals are converted to surface plasmon polaritons (SPPs) propagating at metal-dielectric interfaces, where they can be confined below the diffraction limit of optics 18 . This means that plasmonic devices require only a few µm 2 of footprint 19,20 . With such reduced dimensions, the technology is much closer to bridging the size gap with respect to CMOS electronics. Furthermore, there are various theoretical studies indicating that plasmonic MZMs should offer hundreds of gigahertz of bandwidth 5,21 . To date, however, there is very little experimental evidence to support this claim. Recently, a plasmonic phase modulator demonstrated operation at 40 Gbit s −1 (ref. 22). One could now envision integrating such plasmonic phase modulators into a silicon waveguide MZM configuration. However, by combining plasmonics and silicon photoni...

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Graphene has shown great potentials for high-speed photodetection. Yet, the responsivities of graphene-based high-speed photodetectors are commonly limited by the weak effective absorption of atomically thin graphene. Here, we propose and experimentally demonstrate a plasmonically enhanced waveguide-integrated graphene photodetector. The device which combines a 6 m long layer of graphene with field-enhancing nano-sized metallic structures, demonstrates a high external responsivity of 0.5 A/W and a fast photoresponse way beyond 110 GHz. The high efficiency and fast response of the device enables for the first time 100 Gbit/s PAM-2 and 100 Gbit/s PAM-4 data reception with a graphene based device. The results show the potential of graphene as a new technology for highest-speed communication applications.

For nearly two decades, the field of plasmonics1 - which studies the coupling of electromagnetic waves to the motion of free electrons in a metal2 - has sought to realize subwavelength optical devices for information technology3–6, sensing7,8, nonlinear optics9,10, optical nanotweezers11 and biomedical applications12. Although the heat generated by ohmic losses is desired for some applications (e.g. photo-thermal therapy), plasmonic devices for sensing and information technology have largely suffered from these losses inherent to metals13. This has led to a widespread stereotype that plasmonics is simply too lossy to be practical. Here, we demonstrate that these losses can be bypassed by employing “resonant switching”. In the proposed approach, light is only coupled to the lossy surface plasmon polaritons in the device’s off-state (in resonance) where attenuation is desired to ensure large extinction ratios and facilitate sub-ps switching. In the on state (out of resonance), light is prevented from coupling to the lossy plasmonic section by destructive interference. To validate the approach, we fabricated a plasmonic electro-optic ring modulator. The experiments confirm that low on-chip optical losses (2.5 dB), high-speed operation (>>100 GHz), good energy efficiency (12 fJ/bit), low thermal drift (4‰ K-1), and a compact footprint (sub-λ radius of 1 μm) can be realized within a single device. Our result illustrates the potential of plasmonics to render fast and compact on-chip sensing and communications technologies.