a method for producing an optical output in substantially linear relationship with an electrical ac signal , includes the following steps : providing a light - emitting transistor having emitter , base , and collector regions , and associated respective emitter , base , and collector terminals , the transistor having a light - emitting output port ; applying the ac signal to a first input port defined across a given one of the terminals and a common one of the terminals ; applying an amplified version of the ac signal to a second input port defined across a further one of the terminals and the common one of the input terminals ; and selecting an amplification of the amplified version of the ac signal to substantially cancel a nonlinearity characteristic of the light emitting transistor .