A picosecond external electro-optic prober using laser diodes

Abstract
A compact and easy-to-handle optical prober developed for testing integrated circuits fabricated on any substrate is introduced. This prober is based on external electro-optic (EO) sampling using a semiconductor laser diode as an optical probing pulse source. The minimum detectable voltage is as small as 11 mV/ square root Hz, which is close to the shot noise limited value. Temporal resolution is 24 ps, which is limited by the optical probing pulsewidth. Comparison of the measured waveform of the EO sampling with that of a conventional electrical sampling oscilloscope shows excellent agreement between the two. The prober is successfully applied to waveform diagnosis at internal nodes in gigahertz-band analog integrated circuits.