Abstract

High-speed optical sampling of electrical signals is usually carried out by either electrooptic¹ or photoconductive² sampling. These methods are capable of sub-picosecond temporal resolution and have found widespread use in the characterization of optoelectronic devices, but suffer certain drawbacks. To achieve responses in the one-picosecond regime³,⁴, photoconductive techniques rely on short-lifetime material such as low-temperature-grown or ion-damaged GaAs. Short-lifetime material may be well-suited for devices such as photodetectors, but more complicated integrated circuits generally use high-quality, long-lifetime material. Photoconductive measurements on such circuits can be accomplished by selectively ion-damaging the desired region, but this requires additional processing steps. The method of electro-optic sampling^5,6 is capable of sub-picosecond resolution but has more complicated optical requirements and several limitations. With substrate probing, the substrate must exhibit the Pockels effect and must be transparent to the probe beam. With external-crystal probing, a sufficiently small electro-optic crystal is required and must be positioned within the electric field of the signal to be sampled. This paper describes a new high-speed method of photoconductive sampling intended to overcome these drawbacks. The method relies on electromagnetic coupling to generate the time derivative of a signal; a slow sampling gate fabricated on long-lifetime material then integrates the coupled signal to produce the desired waveform.

© 1995 Optical Society of America