One example includes an apparatus that includes a plurality of input/output (I/O) ports and a body portion. The plurality of I/O ports can be arranged at a plurality of peripheral surfaces of the body portion. The body portion includes a solid dielectric material having a substantially constant index of refraction. The body portion also includes parallel planar surfaces spaced apart by and bounded by the plurality of peripheral surfaces. The solid dielectric material in the body portion can be writable via a laser-writing process to form an optical waveguide extending between a set of the plurality of I/O ports.