Fully passive quantum bits encoding scheme based on dual-laser interference.

This Letter presents a transmitter-side fully passive QKD encoding scheme based on dual-laser interference, eliminating delay-line structures and active modulation components. Two independent laser diodes are precisely controlled in time and frequency domains to achieve consistent pulse timing, intensity, and spectra. Experimental interference results agree well with theoretical intensity distributions. Numerical simulations using the FP-QKD protocol based on a dual-laser passive encoding source show secure key extraction over distances exceeding 100 km with a 1012 block size, and an SKR above 105 bits/s for short distances. The scheme offers improved stability and significantly higher encoding rates compared to prior implementations.