  Electrical control of light in integrated photonics is central to a wide
range of research and applications. It is conventionally achieved with
thermo-optic tuning, but this suffers from high energy consumption and
crosstalk. These challenges could be resolved with nanoelectromechanical
photonics but scalable platforms were so far not demonstrated because of
incompatibility with conventional multilayer metal architectures and because
conventional approaches do not allow crossings of electrical wires and photonic
waveguides. Here we use topology optimization to devise a single-layer
electronic-photonic circuit crossing with up to 99.8% optical transmission
across an isolation trench with excellent electrical isolation. We use the
crossing to demonstrate a monolithic silicon nano-electro-mechanical add-drop
switch in which the flow of photons, electrons, and mechanical motions are
fully integrated within the same layer. Our work enables hitherto impossible
opto-electro-mechanical topologies and may lead to new functionalities in
nano-opto-electro-mechanical systems, optomechanics, and integrated quantum
photonics.
