Generation of random-hopped LFM signal based on optical injection in a DFB laser

With an increase in applications of the photonics RADAR, managing the interference and spoofing becomes crucial for reducing false detection, increasing accuracy on range-resolution, and high-resolution imaging that directly impacts safety and security. One of the solutions to deal with intruders and interferers is to modify the transmitting signal, which is usually an FMCW on the present RADAR system. This paper proposes and experimentally demonstrates photonically generated random-hopped linear frequency modulated (RLFM) signal generation using an optical injection in a distributed-feedback (DFB) laser. The basic principle of the LFM signal is the redshift phenomena in the self-oscillating mode of the DFB laser with a change in the injected beam power. To generate an RLFM signal, a random waveform from an arbitrary waveform generator (AWG) is used rather than the linear waveform such as sawtooth, triangular waveforms. For the proof of the concept demonstration, the conventional LFM signal of 8 GHz bandwidth is divided into four equal sub-interval with the bandwidth of 2 GHz (LFM1: 8-10 GHz, LFM2: 14-16 GHz, LFM3: 12-14 GHz, LFM4: 10-12 GHz). Even though each generated LFM signal has a lower bandwidth of 2 GHz, the range resolution can be maintained at the receiver to that of the conventional LFM signal by concatenating the four beating signals in time domain.