Abstract

A host of quantum key distribution (QKD) protocols have been proposed and built to obtain a high key refresh rate and long QKD link distance. Sophisticated key reconciliation and key distillation algorithms have also been implemented. As these systems mature, they call for the calibration and operation of more complex and expensive equipment to achieve high rates. For some applications, simplicity and low cost are paramount. For discrete variable QKD in the 1550 nm fiber transparency window, requisite photon counting technologies remain prohibitively expensive. Continuous variable QKD uses coherent detection so that efficient, inexpensive PiN photodiode detectors may be used. However, even a recent simplification requiring no modulator on the receiving side[1], will require fast modulation and driving optoelectronics and a fast stream of true random numbers for very high speed Gaussian modulation of coherent light. In this paper we propose and analyze a continuous variable QKD system that uses thermal light (or amplified spontaneous emission, or ASE) as a source of inherently Gaussian-modulated, truly random light (from an optical amplifier or an LED) and requires no modulators. This greatly simplifies experimental implementation and can lower system cost. Furthermore, it is easily scalable to higher bandwidths. On the other hand, the secrecy capacity of the system is degraded. The required optoelectronic parts are a moderately bright thermal source, a laser, and two balanced homodyne detection setups. Finally, such a system may have practical advantages for network QKD.

© 2007 IEEE