Reconfigurable Radar Waveform Generation by P1 Dynamics of Optically Injected Semiconductor Laser （Invited）

To meet the demands of future high-performance radar systems with superior resolution， agility and adptability， a reconfigurable radar waveform generation method based on the period-one （P1） oscillation dynamics of optically injected semiconductor laser is comprehensively investigated. The underlying principle involves perturbing the oscillation state of semiconductor laser through the injection of external continuous wave light. This perturbation alters the intracavity photons and carrier densities of laser， thereby exciting various nonlinear dynamics. Among these， P1 oscillation state exhibits asymmetric sideband modulation， which provides a theoretical basis for microwave signal generation.Firstly， the characteristics of P1 oscillation， including the frequency tunability and fast frequency-switching capability， are numerically analysed by solving the nonlinear rate equations. Simulation results demonstrate that the transition between distinct oscillation frequencies can be achieved with a switching speed on the order of ns level， highlighting the inherent agility of the optical injection system. The evolution routing of the nonlinear dynamics is also explored through the dynamical map as a function of injection strength and detuning frequency， which provides a guide to achieve and maintain the desired P1 oscillation state. Based on this， the experimentally generation of broadband radar signals are demonstrated. To generate broadband radar signal， a dynamical control unit of injection parameters is proposed to manipulate the instantaneous frequency of generated wideband waveform. By programming the control signals， various broadband radar signals are generated successfully， including linear frequency modulated signal， triangular wave signal， stepped-frequency signal， frequency-codded signal， frequency-codded linear and frequency modulated signal. The key waveform parameters of broadband signal such as bandwidth， time period， operating band and duty cycle， can also be flexibly adjusted by tuning the injection parameters， which further validate the feasibility of the proposed system. However， the optical injection system in application falls short in performance due to a challenge induced by the intrinsic noise of semiconductor lasers. to address this， approaches for enhancing the system performance are proposed and demonstrated. For single-frequency signal generation， a dual-loop optoelectrical feedback structure incorporating balanced photodetection is employed to improve the Side-Mode Suppression Ratio （SMSR） and phase noise of generated signals.Compared with conventional optical injection system， the linewidth of generated signal based above method is significantly narrowed by three-orders of magnitude. The SMSR is enhanced by about 65.5 dB due to the Vernier effect. In addition， the system maintains excellent frequency tunability while achieving a phase noise of below -124.10 dBc/Hz at 10 kHz offset. For broadband radar waveform generation， pre-compensation of the injection intensity and Fourier Domain Mode Locking （FDML） mechanism are incorporated， through which the in-band Signal-to-Noise Ratio （SNR） and frequency accuracy of generated radar waveforms are significantly improved. In the experiment， a broadband signal with a bandwidth of 6.3 GHz is generated， of which in-band SNR is improved by about 47 dB. In addition， limited by the transient properties of semiconductor laser， when the P1 oscillation frequency is fast changed with a large frequency step， strong damping oscillation of the output frequency occurs， resulting in deterioration of the frequency stability and accuracy. The application of the FDML mechanism is shown to effectively suppress the damping oscillation， once again underscoring the advantages of the proposed signal generation method.To validate the practical utility of the proposed radar waveform generation method， both Single-Input Single-Output （SISO） radar and a Multiple-Input Single-Output （MISO） radar systems are established. Firstly， based on the proposed SISO radar system， high resolution radar ranging is successfully realized， clearly distinguishing two closely spaced targets. The measured result shows excellent agreement with the actual distance. For MISO radar system， in the transmitter， the generated signal is emitted by means of time-division multiplexing across multiple transmitter channels. In the receiver， broadband de-chirp processing is performed via IQ mixing. When detecting a drone in an experimental scenario， the target is precisely located， which verifies that the proposed radar waveform generation system is a promising solution to construct efficient and low-complexity microwave photonic radars.