40 GHz measurement on InP/air gap line by picosecond electro-optic sampling

An electro-optic sampling technique has been used to study an air gap microstrip line deposited on a semi-insulating InP substrate at frequencies up to 40 GHz. The 1 ps light pulses are obtained from a compressed mode locked Nd:YAG laser with a rubidium clock as a phase reference. The air gap line is compatible with III-V compound fabrication technology and can be used as an alternative to classical microstrip or coplanar plane wave interconnection techniques used in high speed devices. High frequency operation of this type of line does not require any thinning of the substrate and the effective dielectric constant is reduced by a factor of more than 3 compared with the dielectric constant of the substrate.