Fast Physical Random Bit Generation Based On An Optoelectronic Delay Loop Pumped By A SL Under A Modulated Optical Feedback

Compared with pseudo-random bits,physical random bits(PRBs)have unique advantages in non-determinism,unpredictability and non-repeatability,hence PRBs possess greatly potential applications in the fields of cryptography,communication and statistical simulation.Traditional PRB generators are based on electronic technologies.Most of them generate PRBs at a rate of Mbit/s,which cannot meet the requirements of the development of high-speed communications.With the development of optoelectronic technology,fast PRBs of the order of Gbit/s can be extracted from optical chaotic signals.At present,there are two main methods for obtaining PRBs using optical chaotic signals as entropy sources.One is based on the chaotic signals output from semiconductor lasers(SL)under external disturbance,and the other is based on the chaotic signals output from optoelectronic delay loop(OEDL)systems.Compared with these two schemes,studies have shown that the performances of the chaotic signals,which are output from the OEDL systems pumped by a SL under an externally disturbance,have some improvement.But as far as we know,there is no scheme to generate random bits using OEDL system pumped by an externally disturbed SL as an entropy source.In this paper,we propose and experimentally demonstrate a scheme for obtaining fast PRBs.In this scheme,the chaotic signal output from the OEDL system,which is pumped by a SL under modulated optical feedback,is used as the entropy source,where the optical signal fed back to the SL is modulated by the OEDL.The post-processing methods include the m least significant bits(mLSBs)extraction and the logical exclusive OR(XOR).First of all,in order to obtain the parameter range that the system can generate high-quality chaotic signals with wide effective bandwidth(EBW)and weak time-delay signatures(TDS),the dependences of EBW and TDS on the optical feedback strength and the optoelectronic feedback intensity are investigated in two bias voltages.In the meanwhile,the differences of the EBW and TDS of the output signals from the OEDL pumped by a SL under a modulated optical feedback and the OEDL pumped by continuous wave laser are compared.Next,a high-quality chaotic signal is selected as the entropy source within the optimized parameter range,and an 8-bit analog-to-digital converter(ADC)is used to sample and transferred the chaotic signal at a rate of 80 GS/s to obtain the original binary sequence.Then,the original binary sequence is processed by m-LSBs and logical XOR operation to obtain the final PRBs.Finally,in order to prove the randomness of the random bit sequence,the probability density distribution(PDD)of the sequence,the NIST SP 800-22 test results,the statistical bias and serial autocorrelation coefficients of the long binary sequence are analyzed.The experimental results show that the OEDL system pumped by a modulated optical feedback could expand the parameter range for obtaining high-quality chaotic signals.Based on this system,the PRBs at a rate of 400 Gbit/s,which can pass all the NIST test and have a good randomness under the long sequence scale,could be obtained.