Photonic Generation Of Frequency-modulated Continuous-wave Based On A Semiconductor Laser With Optical Feedback Stabilization And Modulated Optical Injection

Frequency-modulated continuous-wave(FMCW)microwave signals in the form of a sinusoid with time-varying microwave frequencies can be widely utilized in ranging,imaging,and communication applications.Thus a FMCW signal with wide tunability,large sweep range,and fast sweep rate is highly desired to achieve long distance detection with high resolution.The generation methods of FMCW are mainly divided into electrical and optical.The frequency sweep range and the sweep rate of the generated FMCW signals are limited due to small electrical bandwidths.In order to obtain FMCW with large scanning range and fast scanning rate,many photon generation FMCW technologies have been proposed,which a method of generating a FMCW signal based on the nonlinear dynamics of semiconductor lasers(SLs)becomes the research focus in recent years due to large sweep range,and fast sweep rate of FMCW.In this work,we propose a distributed feedback semiconductor laser(DFB-SL)with modulated light injection and optical feedback to obtain a high-quality frequency-modulated continuous wave signal.And the influence of modulation parameters and injection parameters on the bandwidth of FMCW signal and the reciprocal of feedback delay time and the small deviation of modulation frequency on the quality of FMCW are studied experimentally.The feature of this scheme is that the light is injected into the DFB-SL to exhibit a period-one(P1)oscillation can be widely tuned,and then the injected light is amplitude-modulated to obtain a FMCW whose center frequency can be widely tuned,and the power spectrum of the generated FMCW signal is obtained.The power spectrum distribution of the generated FMCW signal is a frequency comb whose comb space is equal to the modulation frequency.The technique has many advantages such as wide tunability of central frequency,optical controllability and structural simplicity,but the generated FMCW signal inherently contains the phase noise due to the intrinsic spontaneous emission noise of the laser,resulting in low frequency comb contrast,so optical feedback is introduced to improve the frequency comb contrast.There is no high-frequency electronic devices included in the optical feedback loop,and therefore the optical feedback scheme is simple,low-cost and has no electronic bandwidth limitations.The experimental results show that,by carefully adjusting the modulation and injection parameters,an FMCW with a sweep range of 11.39 GHz(10.08 GHz-21.47 GHz)and a sweep speed of 0.72 GHz / ns can be obtained based on the P1 oscillation of an SL subject to modulated optical injection.However,the comb contrast of the FMCW signal is relatively small and is about 12.87 dB.After introducing an optical feedback,the comb contrast of the FMCW signal can be increased by 20 dB.