Direct modulation of injection lasers

A laser diode system for modulating microwave signals wherein microwave signals of at least about 5 GHz frequency are caused to impinge on a laser diode, whereby said singals are translated to optical output consistent with the microwave signal, said system comprising a microwave channel for bringing microwave signals to said diode, a bias post for imposing a direct current bias signal on said diode, and an optical channel for carrying said optical signal out of the device, wherein said microwave channel comprises an annular space between said optical channel and a housing enclosing said system, and wherein said microwave channel, said bias post and said optical channel are colinear and said optical channel comprises means for essentially suppressing the propagation of microwave signals adventitiously present in said optical channel.