Random Bit Generator Using Difference Of Amplified Spontaneous Emission

The random bit has been widely used in many areas, such as numerical simulations and secure communications. The random bit has also an important role in the field of cable fault detection, spread spectrum communication and radar testing. It can be used as a random signal in the cable fault detection and can also be used as keys in secure communications. With the development of communication, especially the popularity of optical communication, the application of random bit generator is more and more widely, but at the same time, the requirement of its rate and randomness are higher. But the rate of the product applied in the practical are very slow, so they can’t meet the requirements of modern communication. So the research of high random bit generator has become a hotspot.There are two kinds of random bit:pseudo random bit and true random bit. Pseudo random bit is generated by algorithm when given an initial value, if a network attacker steals the algorithm and its initial value, he can repeat the pseudo random bit. But true random bit is generated by physics entropy source, because the physics entropy source is random in nature, so the random sequence generated by it is absolutely security.With the development of modern high-speed optical communication, the requirement of rate of random bit is higher and higher. In recent years, chaotic laser as physics entropy source which is used to generate random bit has become a hot research topic. Chaotic laser signal has large amplitude and wide spectrum, so it is very suitable for generating random bit. As is known to all, the output of the chaotic laser is very sensitive to initial conditions under the condition of optical feedback, and these chaotic signals generated by optical feedback, photoelectric feedback or optical injection have a certain periodicity. The random bit generated by amplified spontaneous emission has large advantage for its nature randomness and lager amplitude than background noise.In this paper, we propose a scheme for random bit generation with filtered amplified spontaneous emission (ASE). Using the filtered ASE, we can get larger signal fluctuations than when using directly detected ASE with a photodetector. Utilizing the delayed self-difference and two ways mutual difference techniques to improve the symmetry of filtered ASE. Specific work is as follows: 1. On the basis of existing work, we filter the amplified spontaneous emission with a fiber Bragg grating, and improve the symmetry of filtered ASE by using delayed self-difference and two ways mutual difference techniques. Eventually we experimentally achieve random bit at different rates.2. For the method of delayed self-difference, experimental results show that the generated random sequence can pass NIST tests as long as the delayed time is beyond a threshold value, which is called the minimum delay time (MDT). Further simulation results indicate that there is a certain relationship between the MDT and bandwidth of the ASE signal.3. We eventually achieve real-time random bit with different rates that pass NIST tests. Further improve the rates by means of8-bit using ADC in the offline. In the last of this chapter, we introduce the application of random bit.