实验研究了滤波对光反馈混沌半导体激光器输出信号中时延特征的抑制。在100 MHz和500 MHz低通滤波条件下, 利用在反馈时延附近的自相关峰值和排列熵峰值量化提取混沌信号的时延特征。测量了不同偏置电流下时延特征随反馈强度的变化。结果表明,经过滤波, 在1.5Ith、-7.5 dB条件下, 时延附近的自相关从0.264降低到0.036, 排列熵从0.985上升到0.997, 同时随着反馈强度的增大, 反馈时延附近的自相关峰值与排列熵呈反比关系; 混沌激光的复杂度和混沌强弱随反馈强度的增大呈先增强后减弱的趋势。滤波作用使混沌复杂度在更低的反馈强度下趋于最大, 并随着反馈强度的增大保持混沌复杂度不变。此外, 在抑制时延特征的同时, 滤波作用有效改善了混沌信号强度分布的随机统计特性。

The effect of filtering on the suppression of time-delay signature in the output signal of the optical feedback chaotic semiconductor laser is studied experimentally. Under the condition of the chaotic signal 100 MHz and 500 MHz low pass filter, the peak values of the autocorrelation coefficient and the permutation entropy at the feedback round trip time are used to quantitative extract the time-delay signature. The time-delay signatures with various feedback strengths are measured at different bias currents. The results show that the filtering effect suppresses the time-delay signature of the chaotic signal effectively. Under the condition of 1.5Ith bias current and -7.5 dB feedback strength, the autocorrelation function near the external cavity delay decreases from 0.264 to 0.036, and the permutation entropy increases from 0.985 to 0.997. Meanwhile, the peak value of the autocorrelation coefficient at the feedback round trip time is inversely proportional to the permutation entropy with the feedback strength increasing. The results also show that the complexity and strength of chaotic laser first rise, and then fall with the increase of feedback strength. The filtering effect induces the complexity of chaos to approach the maximum under lower feedback strength, and the complexity remains unchanged with the feedback strength increasing. Moreover, the filtering can also improve the intensity distribution and enhance the symmetry of probability-density function, which leads to substantial increase in the rate of random number generators.