Optically modulated superconducting delay lines

Optical modulation is investigated for superconducting microstrip delay lines on 2-in-diameter, 10-mil-thick LaAlO/sub 3/ substrates. The linewidth of 80 mu m yields a characteristic impedance of 50 Omega . The linepitch of 100 mil is chosen to minimize the coupling between adjacent lines. The total meander line length is 64 cm. The measured delay is 8 ns with operation from DC to 20 GHz. The design was implemented using niobium, niobium nitride, and YBCO. The measurements were performed in a dewar and in a closed-cycle refrigerator, with both RF and optical access. Optical illumination of the lines resulted in a phase shift of the transmitted signal. Using a 10-mW He-Ne laser, phase shifts of up to 360 degrees at 20 GHz were measured with NbN and YBCO. The phase shifts increased linearly with frequency and with optically intensity. The effect can be attributed to a small, bolometric modulation of the line inductance.<>