High-speed and high-power field effect transistors as drivers of optical modulation systems: physical limitations, state of the art, and trends

For developing the applications of integrated optics to microwave and millimeter wave systems, a key point is the very high speed modulation of the lightwave. As external modulations seem to constitute the best solution, they need the availability of specific driving devices. The main requirements of these devices are given, in terms of speed (current gain cut-off frequency), current density, and breakdown voltage. The principle and capabilities of various kinds of field effects transistors available are summarized, with a large insistance on those that present the greatest potential such as the High Electron Mobility Transistors (HEMT) on InP substrate. Finally, the recent improvement of performance (speed, current density, breakdown voltage) are presented and discussed. It appears that the requirement on breakdown voltage remains the most difficult to satisfy for very high speed devices such as HEMT on InP but recent results lets hope the availability of satisfying devices in near future.