OPTOELECTRONIC GENERATION AND DETECTION OF SINGLE-FLUX-QUANTUM PULSES

We report on the direct observation of a single-flux-quantum (SFQ) pulse. The response of a metal-semiconductor-metal photodiode to a femtosecond laser pulse was used to switch Josephson junctions and to generate an SFQ voltage pulse on a superconducting microstrip line. The detailed shape of the pulse was measured optoelectronically, using a cryogenic electro-optic sampling system. The measured SFQ pulse had a width of 3.2 ps, an amplitude of 0.67 mV, and a total pulse content of 2.1±0.2 mV×ps, corresponding to the quantum of magnetic flux h/2e. With larger excitation, multiple SFQ pulses were observed. Numerical simulations are shown to be qualitatively similar to our experimental results.© 1995 American Institute of Physics.