Electro-optic modulation at mm-wave frequencies in GaAs/AlGaAs guided wave devices

Travelling wave techniques permit electro-optic modulation at millimetre wave frequencies without prohibitive drive power requirements. In a long, low-voltage modulator the modulation accumulates monotonically only if the optical group keeps in step with the electrical phase: i.e. if the velocities are sufficiently well matched. This paper describes GaAs/AlGaAs technology which has been used to demonstrate modulation up to 60 GHz. The GaAs-AlGaAs travelling-wave modulator is distinguished by its segmented electrode arrangement; electrode elements sample the travelling voltage-wave on a coplanar transmission-line while providing capacitive loading to slow the RF phase-velocity to match that of the optical group