Spread-spectrum (SS) methods have long been used in
communications systems to achieve certain levels of transmission
efficiency and security. Unfortunately, traditional spread-
spectrum approaches have typically employed pseudorandom
sequences of codes characterized by an inherent periodicity
which can be detected over time. As a solution, true random
sequences generated by chaotic lasers can help achieve increased
SS gain at a lower bit error rate (BER) than traditional SS
systems based on pseudorandom bit sequences, while also
improving the communications security.  In traditional SS
systems, high-speed random codes are substituted for a 1-b
source stream, making these transmissions more robust in the
presence of interference. Typical techniques for spread spectrum
communications are direct-sequence spread spectrum (DSSS),
frequency-hopping spread spectrum (FHSS), time-hopping spread
spectrum (THSS), and chirp modulation. Among them, pseudorandom
sequences generated by an n-level m-sequence shift register wi