Photonic microwave generation based on period-one dynamics of an optically injected VCSEL has been study experimentally. The results have shown that the frequency of the generated microwave signal can be broadly tunable through the adjustment of the injection power and the frequency detuning. Strong optical injection power and higher frequency detuning are favorable for obtaining a high frequency microwave signal. These results are similar to those found in systems based on distributed feedback lasers and quantum dot lasers. The variation of the microwave power at the fundamental frequency and the second-harmonic distortion have also been characterized.

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The time-delay signature and chaos bandwidth in three-cascaded vertical-cavity surface-emitting lasers (VCSELs) has been investigated experimentally. A peak value of autocorrelation coefficient at the feedback round trip time and the ratio between this peak value and its background are used to quantitatively identify the time-delay (TD) signature of chaos. A new conceptpeak to side-peak ratio is introduced for better quantification of the TD signature concealment. The peak to side-peak ratio is defined as the ratio between the peak value of autocorrelation coefficient at the TD and the peak value at a delay time other than the TD and zero delay time. Three injection cases, small bandwidth, intermediate bandwidth and wide bandwidth of the injecting chaos signals, have been used to study the effect of the bandwidth of the injecting chaos on the TD concealment. The experimental results show that the time-delay signature can be totally concealed in the slave laser subject to the intermediate bandwidth of chaotic optical injection over a wide frequency detuning range.

A narrow-linewidth single-frequency photonic-microwave-generation scheme using an optically injected semiconductor laser with a filtered optical feedback has been proposed. The filtered feedback comes from a single feedback loop, which includes a narrow bandpass filter. With the filtered feedback, the linewidth of the generated microwave can be significantly reduced from 22.4 MHz to 9.0 kHz, with the side peaks suppression of 28 dB. The proposed scheme shows superior performance compared to the conventional single-feedback configuration in terms of linewidth reduction and side peaks suppression. The proposed scheme also achieves better results compared to the complex dual-feedback setting. The mechanism for a better performance of filtered optical feedback is that the filtered feedback can effectively limit the external cavity modes and stabilize the period-one dynamics. In addition, the microwave linewidth decreases with the increase of the filter width until the optimized filter width is reached. Furthermore, the linewidth reduction and the side peaks suppression of a photonic microwave using filtered optical feedback is relatively insensitive to the frequency detuning between the filter center frequency and the free-running frequency of the semiconductor laser.

The effect of data acquisition on the complexity of chaos using permutation entropy has been studied experimentally and numerically. The complexity of chaos is quantified using the normalized permutation entropy at the feedback round-trip time. Two "abnormal" variations of the complexity of chaos with bias current have been observed experimentally. The different vertical scales of the oscilloscope in data acquisition are attributed to this abnormal change. The method to remove the effect of data acquisition has also been proposed.

Characteristics of microwave photonic signal generation based on P1 dynamic in an optically injected vertical-cavity surface-emitting laser are studied systematically. The evolutions of the linewidth, power and second harmonic ratio of the generated microwave are investigated as a function of injection strength and frequency detuning. The effect of optical feedback on the linewidth and the phase noise of the generated microwave photonic signal is also studied in detail. With the help of optical feedback, the linewidth can be effectively reduced by increasing the feedback strength and feedback delay time. However, there is an optimal feedback delay time to minimize the phase noise.

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