Optical frequency comb-based multichannel parallel continuous-variable quantum key distribution.

Continuous-variable quantum key distribution (CVQKD) provides an approach for secure communication in optical fiber communication systems. However, its practical implementation has been hindered by low secret key bit rates that are usually limited to several bits/s to hundreds of kbits/s at distances of more than 25 kilometers. In this paper, we use a pair of optical frequency combs (OFCs) for both multiple parallel transmission and coherent reception, which assign multiple sub-channels involving multiple independent secret keys in a single fiber to increase the key bit rate. The first and last sub-channels are selected for propagating phase references to compensate the phase offset between two free-running combs. We analyze possible excess noise caused by dispersive walk-off in the transmission, imperfect phase compensation in the reception and photon leakage from the phase references. Compared to the previous single-channel CVQKD method, simulation results show more than a factor of 20 increase in the secret key rate at a transmission distance of 35 km and the number of comb lines of 35.

Investigation on the intense fringe formation phenomenon downstream hot-image plane.

The propagation of a high-power flat-topped Gaussian beam, which is modulated by three parallel wirelike scatterers, passing through a downstream Kerr medium slab and free spaces is investigated. A new phenomenon is found that a kind of intense fringe with intensity several times that of the incident beam can be formed in a plane downstream the Kerr medium. This kind of intense fringe is another result in the propagation process of nonlinear imaging and it locates scores of centimeters downstream the predicted hot image plane. Moreover, the intensity of this fringe can achieve the magnitude of that of hot image in corresponding single-scatterer case, and this phenomenon can arise only under certain conditions. As for the corresponding hot images, they are also formed but largely suppressed. The cause of the formation of such an intense fringe is analyzed and found related to interference in the free space downstream the Kerr medium. Moreover, the ways it is influenced by some important factors such as the wavelength of incident beam and the properties of scatterers and Kerr medium are discussed, and some important properties and relations are revealed.