外腔半导体激光器随机数熵源的腔长分析

Randomness analysis of external cavity semiconductor laser as entropy source

利用光反馈半导体激光器产生的混沌激光作为随机数熵源,详细研究了混沌源外腔长度对500Mbit/s随机数特性的影响.研究表明:在单路混沌源情况下,外腔反馈引起的谐振会使产生的随机序列具有弱周期性,且当外腔反馈时间与采样时间的比值为整数时,产生序列的随机性最差,仅能通过NIST统计测试2,3项;在两路混沌源情况下,当混沌源的外腔长不相等且不成比例时,通过两路异或处理可消除由外腔反馈引起的弱周期性,产生的随机序列能够通过NIST的全部统计测试项.

In this paper,we employ chaotic light as an entropy source,generated by semiconductor lasers with optical feedback induced by external cavity,to generate 500 Mbit/s random number sequence and then study specifically the influence of external cavity length on randomness.The results indicate that the generated random sequence has an weak periodicity caused by the external cavity feedback under a single-channel chaotic source,and can only pass two or three tests of the National Institure of Standards and Technology （NIST ） when the external-cavity round trip delay time is an integral multiple of the sampling time.On the other hand,the weak periodicity can be eliminated by using two different chaotic sources when their external cavity lengths are unproportional to each other,and the obtained random sequence can pass all tests of the NIST after XOR processing.