300-GHz-bandwidth network analysis using time-domain electro-optic sampling

The authors have demonstrated S-parameter measurements on simple passive circuit elements with 300-GHz bandwidth using an external-electrooptic, time-domain sampling technique. Clean, wideband input pulses were generated and transmitted to the device under test in a test fixture which integrated the optoelectronic signal source, the coplanar transmission lines, and the element to be measured on a monolithic low-permittivity substrate. A marked increase in the fidelity of short-electrical-pulse transmission, as evidenced by a 75% improvement of 3-dB bandwidth after 2 mm of propagation, was observed on a coplanar stripline supported by a quartz substrate when compared with a circuit fabricated on a GaAs substrate having permittivity approximately three times greater. The availability of this enhanced bandwidth has led to the demonstrated network analysis in the submillimeter-wave range using guided signals.<>