Optimization Of Random Number Generator Based On Chaotic Semiconductor Lasers

The random number has been widely used in multiple areas, such as secure communications, Monte Carlo simulation, numerical simulations. The random number is playing important role in the field of code division multiple access systems, digital communications, radar testing, remote telemetry, and cryptography. It is used as a ranging signal in radar systems, used as monitoring and control signals in remote telemetry, used as encryption and decryption signals in digital synchronization communications, used as spreading codes and address code in Code Division Multiple Access systems and as the keys used in cryptography systems. In addition, the digital signature or cryptographic protocols also require random numbers in the networks. With development in the recent years, Random number generator is applied to an increasingly wide range of areas. Requirements are getting more rigorous such as increasingly high bit rate and randomness of the random number. But currently the bit rate of random number generators is very low. That is a serious impediment to the application of random numbers. It is obvious that high-speed, high-quality random number generators are great of importance for the national scientific and technological development and information security strategy.Semiconductor laser with feedback of the external cavity or with optical injection could generate chaotic laser signal with a bandwidth of several gigahertz to tens of gigahertz. And the amplitude of random chaotic laser signals is random. With the characteristics of big amplitude and a flat spectrum as noise characteristics the chaotic laser signal can be used as a entropy source for fast random number generation. Therefore, high-speed physical random number generation based on chaotic lasers has become a hot research topic in recent years. As is known to all, the output of the chaotic lasers with optical feedback of the external cavity is extremely sensitive to initial conditions. Any slightly changes in the initial conditions such as the initial value of the injection current, feedback strength or the external cavity length will cause great changes in amplitude fluctuations of the chaotic laser signal. This is a great disadvantage for the randomness of the sequence generates by the random number generators and will degrade the randomness of the sequence, is a slight change in the chaotic output occurs generated by the random number generator is very negative, will affect the randomness of the random sequence. In addition, there is a certain periodicity in the chaotic signal generate by the semiconductor lasers with optical feedback, optoelectronic feedback or optical injection. And the random sequence generated has a corresponding periodicity. Therefore, the stability of random number generators based on chaotic laser has become an obstacle in the process of commercialization of the random number generators. How to eliminate periodicity in the chaos laser has become a scientific proposition.In this article semiconductor chaotic lasers with feedback of external cavity are used as the physical entropy source. The characteristics of the random number generator are studied in the way of combination of simulation and experiment. Solutions are proposed to problems that the output of chaotic laser is sensitive to initial condition. A robust random number generator scheme is proposed based on the the analog signal differential processing. Another processing method of random number generator is proposed based on digital signal processing to eliminate the periodicity in the random sequence that introduced by the external cavity of the chaotic semiconductor lasers, That is the Circulation Exclusive OR method. We call it CXOR method. Details are as follows:1. According to our teams previous research, I analysis of the dynamic characteristics of semiconductor lasers in different external conditions. For example, the spectrum of the chaotic laser changes with the injection current increased and the spectrum of the chaotic laser changes with the strength of the feedback laser from the external cavity. We confirm that the optimal conditions for chaotic laser to generate random numbers. The results show that:Under the conditions that the laser is not damaged, the spectrum of the chaos signal is getting more flat as the injection current increase and feedback strength getting stronger. Correspondingly random numbers generated is easier to pass the standard statistical tests of randomness.2. Temporal correlation of the chaotic laser is analyzed.Beyond the relevant time, analog signal difference is used to eliminate the influence in random sequence that cause by the fluctuations of the chaotic laser. That means this method can resist the interference of a variety of external conditions on the random sequence. thus improving the robustness of the random number generator. The robustness of the random number generator is improved.3. The output signal of the chaotic semiconductor laser has a certain amount periodicity in it. In this article digital signal processing methods is use to improve the characteristics of random numbers. Digital circulation exclusive OR is used to make the random sequence to implement several exclusive OR operations. After processing the periodicity in the random sequence that introduced by the external cavity of the chaotic semiconductor lasers is eliminated. In addition, the deviations of0/1ratio of the random bit sequence input in the processing method is larger than any of the previous methods. It is discussed in detail that how the periodicity disappeared gradually with the increase number of Circulation Exclusive OR operations.