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.

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.

In this paper, we propose and experimentally demonstrate a technique of mitigating multi-radar interference in a photonic radar using a sliding window long short-term memory (SW-LSTM)-based recurrent neural network. For the proof-of-concept experimental demonstration, a photonics-based victim radar (VR) with an 8 GHz linear frequency modulated (LFM) signal is generated using optical injection in a semiconductor laser. This VR is used to detect two objects separated by 10 cm in the presence of multiple interference sources. To perform the analysis of mitigating interference in the multi-radar environment, we generated random interference LFM signals (IR-LFM) with diverse bandwidths (4 GHz to 10 GHz) and chirp rates (±1 GHz/μs to ±20 GHz/μs), both experimentally and synthetically. The generated IR-LFM signals consist of both coherent and non-coherent interferences and are added to the echo signal and trained using SW-LSTM. During the training stage, learning rate, stacked layers, nodes, batch size, and window size are optimized. In the test stage, we use signals with both coherent and non-coherent interferences, which are distinct from the interferences in the training stage. The proposed model is evaluated for one, four, and eight interference test scenarios, in which it successively achieves a mean R ² value of > 93% for all test scenarios, taken over ten trials in each test scenario. Furthermore, a mean error vector magnitude( EVM )of < 0.07 and a mean signal-to-interference plus noise ratio ( SINR ) of > 11 dB are obtained. These results indicate a strong similarity between the range profile calculated in the interference-free and the multi-interference environments with our proposed scheme of mitigating interference using SW-LSTM.

This paper proposes and experimentally demonstrate sub-bands fusion of photonically generated linear frequency modulated (Ph-LFM) radar signals with unidentical bandwidth and chirp rates using an adaptive, delay-less feed-forward network equalizer (FFNE). We demonstrate this using optical injection in a semiconductor laser to generate Ph-LFM signals at different IEEE X-KA radar sub-bands: 19.25–23.94 GHz and 24.06–28.31 GHz (bandgap 0.12 GHz), 19.69–23.06 GHz and 23.625–27 GHz (bandgap 0.56 GHz), and 8–11.5 GHz and 12.75–17 GHz (bandgap 1.25 GHz). Time-frequency analysis (TFA) was used to obtain sub-bandgap signals of 0.12 GHz, 0.56 GHz, and 1.25 GHz which are coherently fused using the FFNE with a particle swarm optimization (PSO) algorithm to optimize complex-valued weights. The method is evaluated by measuring the range resolution and peak-to-sidelobe level (PSL) in detecting two objects separated by 2 cm and 3 cm. The FFNE achieves significant improvement over 10 dB in PSL and resolves previously unresolvable distances, with maximum range resolutions of 1.8 cm, 2.2 cm, and 2 cm, closely matching theoretical values for full-band LFM signals with bandwidth of 9.06 GHz, 7.31 GHz, and 9 GHz, respectively. Experimental results demonstrate the FFNE’s superior performance in enhancing range resolution and PSL in multi-sub-band radar systems compared to scenarios without FFNE.