| 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 successfully encode and decode four BB84 states at 156.25-MHz repetition rate. Fast phase-encoding of 0 or $\pi $ is achieved, with interference fringe visibilities 78.53% and 82.68% for states $|+\rangle$ and $|-\rangle$, respectively. With the aid of an extra off-chip LN intensity modulator, two time-bin states are prepared and the extinction ratios are 18.65 dB and 15.46 dB for states $|0\rangle$ and $|1\rangle$, respectively. |
