Lan Yu

A photonic approach to generate binary and quaternary phase-coded microwave pulses with tunable frequency multiplication factor (FMF) is proposed and demonstrated. By adjusting the input electrical signals, the scheme can generate pulsed radar waveforms with tunable FMF and reconfigurable phase coding pattern. In the scheme, two pairs of orthogonally polarized ±2nd-order or ±4th-order sidebands are separated into two single sideband signals through an optical sideband separation module. One of the sidebands is then modulated by the coding signal through a dual-drive Mach-Zehnder modulator. By detecting the recombined two sidebands, binary or quaternary phase-coded microwave pulses with FMF of 4 or 8 can be generated. In the simulation experiments, binary and quaternary phase-coded microwave pulses at 20 and 40 GHz are generated. The phase information of the pulses is consistent with the initial coding sequence. Furthermore, the generated phase-coded microwave pulses show great compression capability.

Extracting precise target characteristics from microwave image is needed and calls for high-resolution microwave imaging radar systems. In this paper, a Ka-band ultra-wideband microwave photonic (MWP) imaging radar is developed and experimentally demonstrated. In the transmitter, continuous ultra-wideband linear frequency modulation (LFM) wave is generated based on optical frequency sextupling technique. In the receiver, a combination of optical frequency mixer with fiber delay lines and electric analog-to-digital converter (ADC) is capable of receiving target echoes and imaging targets with different distances. The maximum instantaneous bandwidth of the transmitted waveform is measured to be 10.02 GHz and corresponding range resolution is calibrated to be 1.68 cm. Out-field tests with demonstrator working at synthetic aperture radar (SAR) or inverse synthetic aperture radar (ISAR) mode are carried out. Different targets such as an unmanned aerial vehicle (UAV), airliner and Leifeng pagoda are imaged. Based on corresponding high-resolution microwave images, quantitative information of the targets can be identified, which shows the great potential of the radar demonstrator for various remote sensing applications.

Photonic generation of radio-frequency (RF) arbitrary microwave waveform with ultra-wide frequency tunable range based on a dispersion compensated optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. Dispersion compensation scheme and specially designed fiber Bragg grating (FBG)-based Fabry–Perot (F-P) filters are employed in the OEO loop to realize a frequency tunable range of 3.5–45.4 GHz. An optimization process provided by the combination of an erbium-doped fiber amplifier (EDFA) and FBG is employed to improve the signal-to-noise ratio (SNR) of final RF signals. The generation of linear-frequency and phase-coded microwave waveforms, with a tunable carrier frequency ranging from 4 to 45 GHz and tuned chirping bandwidths or code rates, is experimentally demonstrated.