One of the first optocouplersusedforhighreliability applications was the simple phototransistor optocoupler. The basic devices were the 4N22, 23, 24 and the4N47, 48, 49 series of hermetic phototransistor optocouplers in TOfive type transistor cans made for military applications developed in the early 1970s. However, these devices were never designed specifically for space radiation environments. By Steve Ching and Manor Narayanan, Isolink, a subsidiary of Skyworks Solutions, Inc.