A fully photonics-based coherent radar system

Abstract

The next generation of radar (radio detection and ranging) systems needs to be based on software-defined radio to adapt to variable environments, with higher carrier frequencies for smaller antennas and broadened bandwidth for increased resolution. Today's digital microwave components (synthesizers and analogue-to-digital converters) suffer from limited bandwidth with high noise at increasing frequencies, so that fully digital radar systems can work up to only a few gigahertz, and noisy analogue up- and downconversions are necessary for higher frequencies. In contrast, photonics provide high precision and ultrawide bandwidth, allowing both the flexible generation of extremely stable radio-frequency signals with arbitrary waveforms up to millimetre waves, and the detection of such signals and their precise direct digitization without downconversion. Until now, the photonics-based generation and detection of radio-frequency signals have been studied separately and have not been tested in a radar system. Here we present the development and the field trial results of a fully photonics-based coherent radar demonstrator carried out within the project PHODIR. The proposed architecture exploits a single pulsed laser for generating tunable radar signals and receiving their echoes, avoiding radio-frequency up- and downconversion and guaranteeing both the software-defined approach and high resolution. Its performance exceeds state-of-the-art electronics at carrier frequencies above two gigahertz, and the detection of non-cooperating aeroplanes confirms the effectiveness and expected precision of the system.

Low-power, chip-based stimulated Brillouin scattering microwave photonic filter with ultrahigh selectivity

“…We further show that for a given SBS gain, this approach allows the flexibility to redistribute the pump optical power into modulated optical power, thereby reducing the filter insertion loss. The results presented here point to new possibilities for creating high performance SBS-based reconfigurable MWP filters that will play a key role in modern RF systems for next generation radar [46] and high data rate wireless communication [47], with a potential for monolithic integration in silicon chips (Figure 1a). …”

1.5 μm Lasers with Sub-10 mHz Linewidth

“…Oscillators with coherence times of tens to hundreds of seconds will allow for investigations of extremely small energy shifts in the clock transition, caused by sources such as interactions amongst atoms [6,7]. Ultrastable oscillators beyond the state of the art will find useful applications in sub-mm very long baseline interferometry (VLBI) [8], atom interferometry and future atombased gravitational wave detection [9][10][11], novel radar applications [12], the search for dark matter [13], and deep space navigation [14]. Consequently, large effort has been put into the development of extremely coherent sources based on highly stable optical Fabry-Pérot resonators [15][16][17][18].…”

Programmable optical processor chips: toward photonic RF filters with DSP-level flexibility and MHz-band selectivity

“…>20 GHz) in a compact device. RF filters with these features are highly desired in many wideband, frequency-agile systems such as radar and cognitive radio communications [57,58], where a breakthrough of filter performance would lead to a significant improvement of the existing systems or the possibility of enabling new system functions. Integrated microwave photonic filters open an alternative path for this purpose, enjoying intrinsic advantages in terms of bandwidth, tunability, and size.…”