In general, the disclosure is directed toward transmitting radiant energy across a boundary of a medical device via an optical feedthrough. A system for transmitting radiant energy across a boundary of a medical device includes a first functional module of a medical device, a second functional module of the medical device, an optical feedthrough assembly coupled to the first functional module, and a radiant energy source that emits a beam through the optical feedthrough assembly to perform a manufacturing process on the first functional module and the second functional module.