Internal optical couplings and functions of vertically and directly integrated device of four phototransistors and a laser diode

An optoelectronic integrated device composed of four heterojunction phototransistors and a laser diode has been developed. Optical coupling between constituent devices is investigated, and it is shown that there are three coupling modes between any two phototransistors through the laser diode. Various functions such as optical tristability, light-controlled optical bistability, and light-controlled optical thresholding are demonstrated by utilizing these optical coupling phenomena.<>