Multi-Chirp Piecewise Linearly Frequency Modulated Microwave Generation Using a Semiconductor Laser

A simple structured photonics-based multi-chirp piecewise linearly frequency modulated microwave (Ph-MPLFM) waveform is proposed and demonstrated experimentally for radar systems. The proposed technique consists of a main laser which is injected into a typical secondary laser, distributed feedback (DFB) laser, with a negative wavelength detuning for the radio frequency (RF) signal generation. The frequency of the generated RF signal is varied by implementing the redshift phenomenon in the emission wavelength of the secondary laser. We introduced a series of piecewise arbitrary waveform with different amplitude-time slopes to obtain the controlled redshift of an emission wavelength of a DFB laser. In this work, two- and three-chirp LFM waveforms are demonstrated. The generated Ph-MPLFMs have a total time period of
$1~\mu \text{s}$
with equal sub-interval periods. The generated two-chirp Ph-MPLFM has chirp rates of 6 GHz/
$\mu \text{s}$
and 10 GHz/
$\mu \text{s}$
. The chirp rate and the number of chirps can be reconfigured by modifying the applied piecewise arbitrary wave generator (AWG) signal to the intensity modulator. As part of reconfigurability, two and three-chirp PH-MPLFMs with different chirp rates, 3 GHz/us, 15 GHz/us, and 3 GHz/us; and 6 GHz/
$\mu \text{s}$
, 15 GHz/
$\mu \text{s}$
, and 3 GHz/
$\mu \text{s}$
are demonstrated. The generated Ph-MPLFM has the FWHM and Doppler resolution of 120 ps and 0.7 MHz for three-chirp waveforms. Hence, the proposed Ph-MPLFM radar waveform can be used as a promising and robust radar waveform in multi-radar environment applications.