Optical Pulse-Drive for the Pulse-Driven AC Josephson Voltage Standard

We developed an optical pulse-drive for the operation of the Josephson Arbitrary Waveform Synthesizer (JAWS) using a fast photodiode (PD) operated at 4 K, close to the JAWS chip. The optical pulses are transmitted to the PD by an easily removable optical fiber attached to it. A bare-lensed PD is mounted by flip-chip technique to a custom-made silicon-carrier chip. This carrier chip is equipped with coplanar waveguides to transmit the electrical pulses from the PD to the JAWS chip mounted on a separate printed circtuit board (PCB). The main components of this optical setup are a laser source, a high-speed Mach-Zehnder modulator, and the modulator driver. The waveform pattern is supplied by a commercial pulse pattern generator providing up to 15 GHz electrical return-to-zero (RTZ)-pulses. Unipolar sinusoidal waveforms were synthesized. Using a JAWS array with 3000 junctions, an effective output voltage of 6.6 mV root mean square (RMS) at the maximum available clock-frequency of 15 GHz was achieved. Higher harmonics were suppressed by more than 90 dBc at laser-bias operation margins of more than 1 mA.