  An electro-optomechanical device capable of microwave-to-optics conversion
has recently been demonstrated, with the vision of enabling optical networks of
superconducting qubits. Here we present an improved converter design that uses
a three-dimensional (3D) microwave cavity for coupling between the microwave
transmission line and an integrated LC resonator on the converter chip. The new
design simplifies the optical assembly and decouples it from the microwave part
of the setup. Experimental demonstrations show that the modular device assembly
allows us to flexibly tune the microwave coupling to the converter chip while
maintaining small loss. We also find that electromechanical experiments are not
impacted by the additional microwave cavity. Our design is compatible with a
high-finesse optical cavity and will improve optical performance.
