Chip-encoded high-security classical optical key distribution.

The information security plays a significant role in both our daily life and national security. As the traditional algorithm-based secure key distribution (SKD) is challenged by the quantum computers, the optical physical-layer SKD has attracted great attentions such as quantum SKD, chaos SKD, and reciprocity-based SKD. However, the cost of quantum SKD is still unaffordable and the latter two classical SKDs are only reliable with some preshared information or under simple eavesdrop. So far, there still lacks a high-security and low-cost optical SKD scheme. In this paper, we propose and demonstrate a high-security chip-encoded classical optical SKD paradigm based on the reciprocity of incoherent matrix. The security of SKD is facilitated by the incoherence of input light, and it is the first time that the classical optical SKD is achieved with silicon photonic chips and commercial optical fiber link. Experimentally, we set up a chip-to-chip communication link and achieve key generation rate of 100 bit/s over a 40 km single mode fiber, with key error rate of only 1.89 %. Moreover, we demonstrate the key capacity expansion of the proposed scheme with four-channel wavelength division multiplexing. Our proposal paves the way for the low-cost, high-security, and miniaturized optical SKD.