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A Photonic Dechirp-on-Receive Pulse Synthetic Aperture Radar Using a Phase Correlated Optical Reference Signal in a DSP-based Optical Coherent Receiver

A pulse radar based on photonics-assisted signal generation and stretch processing is proposed and experimentally demonstrated. A radio frequency (RF) linear frequency modulated (LFM) pulse signal is generated by photonic frequency doubling from an intermediate frequency (IF) LFM pulse signal and fed into an antenna for transmitting. An optical reference signal is generated form another coherent IF-LFM pulse signal with an equaled bandwidth and a doubled pulse duration to IF-LFM used for generating the transmitted pulse, and the generated optical reference signal is split. The split optical reference signals are separately fed into a polarization and phase diversity coherent receiver (PPDCR) as an optical local oscillation signal (OLO) and a dual-polarization quadrature phase shift keying (DP-QPSK) modulator as an optical carrier. In the DP-QPSK modulator, the input light wave is split into two paths with light wave on one path being intensity-modulated by echoes and light wave on the other path not being modulated. The light waves are polarization orthogonally multiplexed at the output of the DP-QPSK modulator and coherently detected with the OLO in the PPDCR. The information of the echoes can be recovered by using a digital signal processing algorithm from the outputs of the PPDCR. Experiments verify the idea of a photonic dechirp pulse synthetic aperture radar (SAR), which can obtain microwave image with high resolution in a long-range.