Multi-chirp LFM Waveforms Generation with Reconfigurable Chirp Rates Using Optical Injection in a Semiconductor Laser

We propose and experimentally demonstrate a photonics-based technique for generating simultaneous up-down multiple chirp-rate linear frequency modulated (SUDMC-LFM) waveforms using a dual beam injection technique in a distributed feedback (DFB) laser. To generate waveforms with multiple chirps, drive waveforms of different amplitude-time slopes for each sub-interval time are designed in an arbitrary waveform generator (AWG) and fed into the intensity modulator, which in turn, controls the intensity of the injected beam. Consequently, the rate of redshift of the emission wavelength is controlled. In the experiment, the intensity of only one beam is controlled with the designed AWG signal. For the proof-of-concept demonstration, we generate continuous multiple chirps (CMC), simultaneous up-down multiple chirps (SUDMC), and simultaneous up-down frequency hopped multiple chirps (SUDFHMC) LFM waveforms. Furthermore, re-configurability of the generated waveforms in terms of center frequency, bandwidth, number of chirps and chirp-rates are obtained by either changing the wavelength of the injected beams or by changing the parameters of the AWG signal. In the experiment, the SUDFHMC waveform with four frequency-hopping with sub-interval chirps of 4 GHz/μs, 1.2 GHz/μs, 2.4 GHz/μs, and 2.8 GHz/μs for both the up-chirps and down-chirps, respectively is generated. The auto-ambiguity analysis at -3 dB full-width half maximum (FWHM) shows the time-bandwidth product (TBWP) of >4545, and unambiguous Doppler of <0.75 MHz for CMC, SUDMC, and SUDFHMC signals with three chirps. These results indicate that the proposed waveforms have the potential to provide high performance in multi-radar and multi-target applications.