All-optical Parallel Random Bit Generation Using Chaotic Semiconductor Lasers

Semiconductor lasers in chaotic dynamics are unique light sources with random-like intensity oscillations. Emissions from these chaotic lasers with their intrinsic noise are excellent for generating broadband electrical signals, which can be sampled, digitized, and sent through proper electronic signal processing to yield sequences of random bits. Such approach of random bit generation using laser chaos excels in its extraordinarily high bit rate compared to the conventional methods. The output bit sequences are of perfect or high randomness as indicated by some practical statistical tests. Our research group and many other groups around the globe have spent continual efforts on improving the techniques of random bit generation using chaotic lasers. However, most of the investigations have relied heavily on high-speed electronics. The chaotic emission from a laser needs to go through an optical-to-electronic (O/E) conversion using a photodetector and enter an analogue-to-digital converter (ADC). High-speed post-processing electronics are also needed to eliminate any residual orders of the digitized waveforms for maintaining sufficiently high randomness at the output. An operation of discarding the most significant bits (MSBs) is commonly used by adopting high-resolution ADCs. The disadvantages of relying on these electronics include the relatively high cost for the high-speed components and the restrictions on only partially using the chaotic emission bandwidths. In this proposal, all-optical parallel chaos-based random bit generation without using high-speed electronics is considered. A parallel detection scheme is proposed by optical heterodyning the chaotic emission into different channels, where different slices of the chaotic optical spectrum is down-converted into the baseband for detection using photodetectors of moderate bandwidths. Then, an all-optical post-processing scheme is considered by injecting the chaotic emission into a laser in period-one (P1) oscillation. Because the P1 frequency is dependent on the injection, the resultant emission can exhibit strong chaotic frequency modulation. A delayed interferometer can then introduce a wrapping of the chaotic waveforms, which is equivalent to an operation of discarding MSBs. Such all-optical post-processing replaces the electrical one, thereby alleviating the ADC resolution requirements. Additionally, with the above schemes, the output optical signal is slow enough for feeding into commercial field-programmable gate arrays, which offer great computation power in allowing transformation of the bit statistics. Random bits of not only uniform distribution but also other important statistical distributions can be generated. Success of the proposed all-optical parallel schemes will improve the practicality of applying chaotic lasers for random bit generation.