A new coding technique in serial data transmission and demodulation with Josephson junctions array

Abstract

We have developed a coding technique to drive an overdamped Josephson junction array (JJA) using modulated optical pulses for voltage standard applications. Our system is composed of a multi-channel pulse pattern generator (PPG), a LiNbO3 (LN) modulator with an electrical multiplexer (MUX), a photodiode (PD), and an over-damped JJA cooled with 4 K GM cryocooler. The modulated optical pulses are transmitted via an optical fiber to a PD that is installed close to the JJA on a cold stage, and they are then converted into an electrical current pulse train in order to drive the JJA. To avoid a problem in our LN modulator system, i.e., the duty-ratio dependence of the output pulse waveform, pseudo signals that maintain the duty ratio at approximately 50% are inserted in the original bit stream. We demonstraited that this technique is applicable for arbitrary return-to-zero (RZ) binary bit streams.