Abstract: An electronic system includes a three terminal device having a light emitting portion and a magnetically sensitive portion. The magnetically sensitive portion is for modulating light emission from the light emitting portion. The device is a spin valve transistor having a light-emitting quantum well in its collector. The device can convert a magnetic digital signal to both an electrical digital signal and an optical digital signal, wherein either or both of these signals can be provided as a device output. The magnetically sensitive portion of the device is formed of a pair of magnetically permeable layers. When the layers are aligned electron current can pass through with sufficient energy to reach a quantum well where they recombine, generating light. The device may be used to read a magnetic storage medium, such as a disk drive. Or it can be used to provide a display or a memory array composed of single device magnetic write, optical read memory cells.