Optical chaotic communication using laser diode transmitter/receiver array

We propose a new scheme of digital chaotic communication using the array of transmitter/receiver that consists of two self-pulsating laser diodes (IDs), i.e., a receiver LD and a transmitter LD. Part of the output of a transmitter LD is injected into the corresponding receiver LD that receives a chaotically encoded signal. A neutral density (ND) filter is placed, after each transmitter LD to control the amount of light transmitted to and then injected into the corresponding receiver LD. According to the amount of the transmitter output which is injected into the receiver LD, two kinds of chaotic states with different Lyapunov exponents are induced in the receiver LD, and they are utilized to represent a binary digit. In addition, the distribution of the coupling factor between transmitter and receiver is used as a "key" Only the proper receiver who has been previously given the "key" is able to choose an appropriate threshold of the Lyapunov exponent calculated from the detected chaotic signal that is necessary to decipher each binary bit and to decode finally the entire message. By numerically analyzing the bit error rate, particularly its dependence on the error of the optical confinement coefficient as well as on that of the injection current, we confirmed that the present scheme can provide superior security compared to the conventional chaotic masking scheme.