Quantum Key Distribution Transmitter Chip Based on Hybrid-integration of Silica and Lithium Niobates

Abstract

Abstract A quantum key distribution transmitter chip based on hybrid‐integration of silica planar light‐wave circuit (PLC) and lithium niobates (LN) modulator PLC is presented. The silica part consists of a tunable directional coupler and 400 ps delay line, and the LN part is made up of a Y‐branch, with electro‐optic modulators on both arms. The two parts are facet‐coupled to form an asymmetric Mach‐Zehnder interferometer. We have successfully encoded and decoded four BB84 states at 156.25 MHz repetition rate. Fast phase‐encoding of 0 or π has been achieved, with interference fringe visibilities 78.53% and 82.68% for state |+> and |‐>, respectively. With the aid of an extra off‐chip LN intensity modulator, two time‐bin states have been prepared and the extinction ratios are 18.65 dB and 15.46 dB for state |0> and |1>, respectively.