Tunable triangular frequency modulated microwave waveform generation with improved linearity using an optically injected semiconductor laser

A photonic approach to generating a triangular frequency modulated microwave waveform with improved linearity using an optically injected semiconductor laser is proposed and demonstrated. By controlling the optical injection strength to the semiconductor laser at the period-one oscillation state to have a triangular shape, a triangular frequency modulated microwave waveform is generated after the optical-electrical conversion. A method based on a generalized regression neural network is proposed to improve the linearity of the generated waveform. By adjusting the parameters of the low-frequency electrical triangular control signal, the tunability of the center frequency, bandwidth, and time duration of the generated waveform can be realized. In the proof-of-concept experiment, a triangular frequency modulated microwave waveform with a frequency range from 14-24 GHz and a time duration of 2 μs has been successfully generated. The improvement of the linearity of the waveform is experimentally verified. The performance of the generated triangular frequency modulated microwave waveforms for reducing the range-Doppler coupling is verified through the analyses of the ambiguity function. The tunability of the center frequency, bandwidth, and time duration is also experimentally demonstrated.