Electro-optic modulators (EOMs) are critical elements in the optical communication networks that control the amplitude, phase, and polarization of a light via external electric signals. Aiming to realize ultracompact and high-performance EOMs, most investigations today target on-chip devices that combine semiconductor technologies with state-of-art tunable materials. Nevertheless, integrated EOMs, as an independent on-chip element, are commonly separated from light sources. Accordingly, extra interfaces that couple the light from light sources to the waveguides of on-chip devices are indispensable. Although state-of-art coupling schemes including edge coupling and grating coupling have been employed, they still suffer from limited integration densities and narrow-band operations, respectively. Further, both coupling schemes require extremely accurate alignments and complex encapsulations, making on-chip devices expensive. Therefore, an EOM device that circumvents coupling complexity and further reduces coupling losses is needed. (a) Experimental setups for direct current (DC) and alternating current (AC) modulation characterizations. (b) DC modulation performance of the plasmonic metafiber EOM. (c) AC modulation performances of plasmonic metafiber EOM at different driving frequencies. Courtesy of Westlake University and Hangzhou Dianzi University. Researchers from Chinese Academy of Sciences developed methods that directly integrated EOM devices on the facet of single-mode optical fiber jumpers, connecting EOM devices with light sources using standard interfaces of optical fibers. Using the standard nanofabrication methods developed in the team’s previous efforts, the EOM block can be directly integrated on the tips of single-mode optical fibers, so the metafiber EOMs intrinsically avoid the coupling treatment, said Min Qiu, a professor at Westlake University. Such plasmonic metafiber EOMs feature a well-defined plasmonic-organic hybrid configuration. Benefiting from ultrathin and high-quality-factor plasmonic metasurfaces, nanofabrication-friendly and highly efficient EO polymers, the spectral amplitude and quality factor of passed light are well controlled to promote resonance sensitivity for EO modulation. According to co-first authors Lei Zhang and Xinyu Sun, by rationally designing the plasmonic modes, resonant waveguided modes, and Fabry-Pérot modes, tunable dual-band operations can be achieved in the telecom O and S bands. The metafiber EOMs were further driven by DC/AC electrical signals. The modulation speed of metafiber EOM can reach as high as 1000 MHz with a bias voltage of ±9 V, which is the best performance for lumped fiber-integrated EOMs. “Such metafiber EOMs provide new perspectives on designing [an] ultracompact and high-performance EO device for applications where compact configuration, highly integrated capability, and low coupling loss are required, such as in active mode-locking fiber lasers and tunable broadband fiber polarizers. This work also offers an avenue to ‘plug-and-play’ implementations of EO devices and ultracompact ‘all-in-fibers’ optical systems for communications, imaging, sensing, and many others,” said Jiyong Wang, a professor at Hangzhou Dianzi University. The research was published in Light: Science & Applications (www.doi.org/10.1038/s41377-023-01255-7).