A high-speed physical random number generator based on a chaotic laser was proposed and experimentally demonstrated.
The broadband chaotic laser generated by an external cavity laser diode was employed as the physical entropy source.
The chaotic signal was sampled and converted by an 1-bit analog-to-digital converter to a binary sequence with the rate
of up to 1 Gb/s. To overcome the periodicity in random sequence due to the photo round trip time in the external cavity,
the exclusive-or (XOR) operation on corresponding random bits in samples of the chaotic signal and its time-delay signal
from a same single chaotic laser was executed. The scheme was simpler than the present random number generator in
which random number sequences were obtained real-timely by doing XOR operation on the binary sequences from two
chaotic semiconductor lasers. In addition, the proper selection of delay length was analyzed. A large number experiments
show that when the corresponding delay time of autocorrelation trace with correlation coefficient of less than 0.007 is
considered as the delay time between the chaotic signal and its time-delay signal, streams of random numbers can be
generated with verified randomness.
The effects of dispersion on optical fiber chaotic secure communication are numerically investigated. A theoretical model
for fiber chaotic secure communication system which is consisted of a pair of synchronized chaotic lasers and an optical
fiber channel is presented. Chaotic secure communication for a 1-GHz sinusoidal message after propagating several
hundred kilometers is numerically analyzed. By numerically studying the effects of dispersion on the system's
performance, we show that the synchronization progressively degrades and the signal-to-noise ratio of the recovered
message decreases as the fiber length increases. We also find that the signal-to-noise ratio descends when the modulation
frequency of the encoding message increases. We propose a dispersion management scheme to compensate the
dispersion in fiber chaotic secure communication system. The proposed dispersion management map is consisted of a
segment of 5-km dispersion-compensating fiber with value of dispersion β<sub>2</sub>=-49ps<sup>2</sup>/km, a segment of 245-km nonzero dispersion-shifted fiber with value of dispersion β<sub>2</sub>=1ps<sup>2</sup>/km and optical amplifiers. The results show that the
signal-to-noise ratio of the extracted 1-GHz sinusoidal message increases from 2.75dB to 14.02dB when the length of
fiber is set to 500km.