Apparatus and method for making and using devices that generate optical signals, and optionally also electrical signals in combination with one or more such optical signals, to stimulate (i.e., trigger) and/or simulate a sensory-nerve signal in nerve and/or brain tissue of a living animal (e.g., a human), for example to treat nerve damage in the peripheral nervous system (PNS) or the central nervous system (CNS) and provide sensations to stimulate and/or simulate “sensory” signals in nerves and/or brain tissue of a living animal (e.g., a human) to treat other sensory deficiencies (e.g., touch, feel, balance, visual, taste, or olfactory) and provide sensations related to those sensory deficiencies, and/or to stimulate (i.e., trigger) and/or simulate a motor-nerve signal in nerve and/or brain tissue of a living animal (e.g., a human), for example to control a muscle or a robotic prosthesis.