Picosecond response of optically driven Y-Ba-Cu-O microbridge and Josephson-junction integrated structures

We report our studies on single-picosecond electrical pulse excitation and detection in YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) transmission lines containing microbridges and grain-boundary Josephson junctions. The structures were patterned in YBCO films grown by laser ablation on MgO bicrystals and consisted of 20-/spl mu/m-wide coplanar lines, separated by a 20-/spl mu/m-wide gap. Each transmission line contained a 5-/spl mu/m-wide and 10-/spl mu/m-long microbridge and a 5-/spl mu/m-wide grain-boundary weak link, and was overlaid with 50 nm of Au to improve its high frequency properties. Using a Ti:sapphire laser, we excited the microbridge with 100-fs-wide 400-nm-wavelength optical pulses and studied response of our test structures, utilizing a cryogenic electro-optic sampling system. We directly observed 2.1-ps-wide pulses generated by YBCO microbridges, as well as the single-picosecond Josephson junction response. The junction response depended directly on the current bias and its polarity with respect to the excitation electrical pulse, and exhibited single-flux-quantum-like characteristics. Our test structures can be regarded as examples of all-YBCO ultrafast optoelectronic circuits.