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 YBa2Cu3O7-x, (YBCO) transmission lines containing microbridges and grain-boundary Josephson junctions. The structures were patterned in Y BCO films grown by laser ablation on MgO bicrystals and consisted of 20-mu m-wide coplanar lines, separated by a 20-mu m-wide gap. Each transmission l ine contained a 5-mu m-wide and 10-mu m-long microbridge and a 5-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 microb ridge with 100-fs-wide 400-nm-wavelength optical pulses and studied respons e of our test structures, utilizing a cryogenic electro-optic sampling syst em, 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 respe ct to the excitation electrical pulse, and exhibited single-flux-quantum-li ke characteristics. Our test structures can be regarded as examples of all- YBCO ultrafast optoelectronic circuits.