外腔反馈半导体激光器在合适的反馈强度下将呈现混沌态,其输出的激光混沌信号可作为物理熵源获取物理随机数序列.着重研究了外腔反馈强度对最后获取的二元码序列的随机性的影响.数值仿真结果表明,随着反馈强度的增加,外腔反馈半导体激光器输出的混沌信号的延时时间特征峰值呈现先逐渐减小再逐渐增大的过程,而对应的排列熵特征值呈现先增大、后缓慢降低的过程,即存在一个优化的反馈强度可使输出的混沌信号的延时特征得到有效抑制且复杂度高.利用NIST Special Publication 800-22软件对基于不同反馈强度下外腔半导体激光器输出的混沌信号所产生的二元码序列的随机性进行了相关测试,并讨论了反馈强度的大小对测试结果的影响.
采用两个借助光纤连接的相互注入半导体激光器,实验获取了10GHz超宽带混沌种子信号.通过8-bit模数转换器将混沌信号转换为二进制数据流,并进行进一步的逻辑异或处理和舍弃最高有效位操作,最终获得了能顺利通过美国国家标准与技术研究院(National Institute of Standard and Technology,简记为NIST)800-22标准测试以及Diehard测试,速率达17.5Gbit/s的高速随机码.
The time-delay signature(TDS) of chaos output in a 1550 nm vertical-cavity surface-emitting laser(VCSEL) subject to fiber Bragg grating(FBG) feedback is investigated experimentally. Autocorrelation function(ACF) and mutual information(MI) are used for quantitatively identifying the TDS of chaos. For various bias currents, the TDS evolution with the feedback strength is different, as the FBG provides wavelength-selective feedback. Furthermore,based on the TDS map of the FBG feedback VCSEL(FBGF-VCSEL) in the parameter space of feedback strength and bias current, the optimal TDS suppression regions, where the dominant polarization mode of FBGF-VCSEL locates at the edge of the main lobe of FBG reflection spectrum, have been determined. Finally, for comparative purpose,the TDS of chaos in mirror feedback VCSEL(MF-VCSEL) also has been presented, and the results show that an FBGF-VCSEL possesses better TDS suppression performance than an MF-VCSEL.
Based on a semiconductor laser(SL) with incoherent optical feedback, a novel all-optical scheme for generating tunable and broadband microwave frequency combs(MFCs) is proposed and investigated numerically. The results show that, under suitable operation parameters, the SL with incoherent optical feedback can be driven to operate at a regular pulsing state, and the generated MFCs have bandwidths broader than 40 GHz within a 10 d B amplitude variation. For a fixed bias current, the line spacing(or repetition frequency) of the MFCs can be easily tuned by varying the feedback delay time and the feedback strength, and the tuning range of the line spacing increases with the increase in the bias current. The linewidth of the MFCs is sensitive to the variation of the feedback delay time and the feedback strength, and a linewidth of tens of KHz can be achieved through finely adjusting the feedback delay time and the feedback strength. In addition,mappings of amplitude variation, repetition frequency, and linewidth of MFCs in the parameter space of the feedback delay time and the feedback strength are presented.
