High speed, high frequency optical interconnections are needed for computers and for controlling microwave and millimeter wave phased arrays in radar and communications systems. Direct modulation of semiconductor lasers to 3db frequency limits of 28-30 GHz(1,2) has been achieved, and this limit may be doubled in the next five years. External modulation of continuous optical signals has been used to achieve, for example, a 3db bandwidth of -40 GHz with ~2V-mm modulation sensitivity using multiquantum- well, waveguide modulators. This frequency response may also be doubled in the next five years. In addition, narrow band operation can be achieved, by mode locking, at center frequencies up to 350 GHz(3), and this also can be doubled in the next five years.