One of the aspects of the merging of microwave and optical technologies is the use of optical signals to switch electronic circuits in general and microwave circuits in particular. It is shown in this paper how a thin-film M(etamorpic) HEMT can be used as a photosensitive component. The advantage of this novel approach is the possibility of illuminating the backside of the thin (2-3 Pm) device. The contact metal (of gate, source and drain) is not hindering the light, penetrating into the semiconductor. The thin-film device has a much larger responsivity than a regular, frontside illuminated device. A test set-up, consisting of a 1550 nm laser and a large signal network analyser, enables us not only to do DC and S-parameter measurements, but also time-domain measurements with a modulated telecom laser source
