半导体激光器输出混沌光的延时特性和带宽

提出一个新的方案用于抑制半导体激光器输出混沌光的延时特性并研究其带宽.在该方案中,将由伪随机信号驱动的相位调制器加到具有双路光反馈的半导体激光器的两个反馈腔中,从而构成具有双路相位调制光反馈的分布反馈半导体激光器系统.数值研究了延迟时间和反馈系数等参数对该系统输出混沌光的延时特性的影响,用自相关函数曲线中的延时特征峰的最大值表示延时特性.然后将该系统对延时特性的抑制效果和具有双路光反馈的分布反馈半导体激光器系统以及具有单路相位调制光反馈的分布反馈半导体激光器系统进行比较,结果表明本文所提出方案的抑制效果最好.进而基于能有效抑制延时特性的参数条件研究了具有双路相位调制光反馈的分布反馈半导体激光器输出混沌光的带宽,结果表明,抽运因子的增大和反馈系数的增加都能使系统输出混沌光的带宽变大.

Time delay characteristics and bandwidth of chaotic laser from semiconductor laser

The center wavelength of the distribution feedback semiconductor laser is about 1550 nm, and it is in the lowest loss window of the optical fiber communication. A distribution feedback semiconductor laser (DFB-SL) can generate wideband chaotic signals under external disturbances such as optical feedback, optical injection, etc. Thus, due to the simple structure, DFB-SLs with the optical feedback are widely applied to many fields, including information security, lasers radar, and physical entropy sources for generating physical random numbers. However, optical feedback can cause weak periodicity in chaotic signals from the semiconductor laser, and increase the time delay characteristics of chaotic laser, moreover reduce the quality of random numbers generated by using chaotic signals. Meanwhile, to meet the needs of the current high speed and large capacity communication, the DFB-SL, which can generate wideband chaotic laser with low time delay characteristics, has received wide attention and become a hot research subject.
In this paper, we present a new scheme for suppressing the time delay characteristics and investigating the bandwidth (BW) of chaotic signals from the semiconductor laser. In this scheme, we build a system that is a distribution feedback semiconductor laser with double phase modulated optical feedback (DFB-SL-DPMOF). In this system, two phase modulators driven by the pseudorandom signals are respectively added to the two optical feedback cavities to eliminate the weak periodicity of the generated chaotic signals. For this system, we numerically investigate the influence of the system parameter, such as the delay time, feedback coefficient, etc., on the time delay characteristic of the chaotic laser. In this paper, the time delay characteristic of chaotic signal is expressed by the maximum value of the time delay signature (TDS) peak of the autocorrelation function curve. Then, to illuminate the effectiveness of this system, other two systems, i.e., DFB-SL with double optical feedback (DFB-SL-DOF) and DFB-SL with single phase modulated optical feedback (DFB-SL-SPMOF) are considered. We study the suppression effect of the system on the TDS among DFB-SL-DPMOF, DFB-SL-DOF and DFB-SL-SPMOF. For these three systems, we give and analyze the simulation curves of the time delay characteristic values with the feedback coefficient and the pumping factor respectively. The results indicate that our proposed scheme has the best suppression effect. Moreover, we numerically investigate the BW of chaotic signals from DFB-SL-DPMOF based on the parameter conditions suppressing TDS effectively. The results show that BW becomes large with the pumping factor and feedback coefficient increasing, and the maximum BW value of the obtained chaotic laser is about 7.2 GHz. Therefore the effectiveness of the presented scheme is numerically clarified. And the conclusions of this paper are useful for applying the chaotic laser to the secure communication field.