An implantable electronic device has a main housing with a leak-proof-sealed housing chamber containing electronic circuitry. An optical module is connected to the main housing, and has a module housing with a leak-proof-sealed transducer chamber isolated from the main housing chamber. The module housing has an optically-transmissive optical element, and the transducer chamber contains an optical transducer connected to the circuitry. The module housing includes a number of signal conductors extending from the transducer chamber to a location external to the transducer chamber, and connected to circuitry in the main housing chamber.