Photonic probing of radio waves for k-space tomography

A survey on photonics technologies for radar applications

Photonics is a fast and galloping technology related to both microwave and optics science. Photonics is a very vast and distinctive field in recent days. Due to the enlarged difficulty of the electronics component for large bandwidth, we had to rely on the delightful photonics system. Photonics-based system came to us as a blessing in science research in this era. Software-defined photonics-based radar must be the near forthcoming next-generation necessities. This paper has a detailed study of photonics radar and how its components work. A comparative study has been presented with the traditional electronics microwave radar systems and photonics radar systems. The slow evolution of optics system and how the application has been pushed to radar, microwave and antenna systems have been described here. In this survey repost starting from the historical storyline and basics of photonics radar, the concept of radar based on photonics system and its need, then the digitized PhoDIR system invention, radio frequency signal generation and modulation, beamforming over antenna array and signal transportation, we have discussed the important architecture of photonics radar, phase control process, sampling process, transceiver modules till the radar parameter measurements and various applications of photonics radar including quantum radar. Photonics radar seemed to be a very intense and bright research study area; many practical problems and its wonderful solution have been described here. In this paper, the advancement and progression of photonics-based radar communication system accomplishments of the last decades has been shown and also discussions about future study and development of photonics radar have been presented.

Instantaneous microwave-photonic spatial-spectral channelization via k-space imaging

The ability to both spatially and spectrally demultiplex wireless transmitters enables communication networks with higher spectral and energy efficiency. In practice, demultiplexing requires sub-millisecond latency to map the dynamics of the user space in real-time. Here, we present a system architecture, referred to as k-space imaging, which channelizes the radio frequency signals both spatially and spectrally through optical beamforming, where the latency is limited only by the speed of light traversing the optical components of the receiver. In this architecture, a phased antenna array samples radio signals, which are then coupled into electro-optic modulators (EOM) that coherently up-convert these signals to the optical domain, preserving their relative phases. The received signals, now optical sidebands, are transmitted in optical fibers of varying path lengths, which act as true time delays that yield frequency-dependent optical phases. The output facets of the optical fibers form a two-dimensional optical phased array in an arrangement preserving the phases generated by the angle of arrival (AoA) and the time-delay phases. Directing the beams emanating from the fibers through an optical lens produces a two-dimensional Fourier transform of the optical field at the fiber array. Accordingly, the optical beam formed at the back focal plane of the lens is steered based upon the phases, providing the angle of arrival and instantaneous frequency measurement (IFM), with latency determined by the speed of light over the optical path length. We present a numerical evaluation and experimental demonstration of this passive AoA- and frequency-detection capability.

Log-periodic temporal apertures for grating lobe suppression in k-space tomography

Millimeter-wave (mmW) imaging receivers have demonstrated the ability to sense radio-frequency (RF) waves using traditional phased antenna array techniques, and, through a coherent photonic up-conversion process, image these waves using free-space optical systems. Building upon the idea of coherent up-conversion, k-space tomography extends the functionality of the millimeter-wave imaging receiver as a two-dimensional spatial processing unit to three-dimensional sensing with the addition of frequency detection. In this configuration, an arrayed waveguide grating, or temporal aperture, is implemented following the photonic up-conversion of RF signals received by the phased array. These waveguides of varying length add a spectral beam-forming network to the existing spatial beam-forming of the mmW-imaging receiver. The introduction of three-dimensional phase information to the imaging system disrupts the ability to directly image the RF signal distribution on a photo-detector array, requiring the application of tomographic algorithms to reconstruct the power distribution of the received signals. In order to receive and properly recover the spatial-spectral distribution of RF sources, the antenna array and temporal array must be sampled adequately to avoid introduction of grating artifacts into the system response. Grating lobes, an artifact of regular spacing of elements within a grating, restrict the alias-free field of regard for antenna arrays, or the free spectral range for time-delay based arrays, thus limiting the spatial-spectral monitoring of RF sources via the k-space imaging modality. To alleviate this constraint, we present a non-uniform log-periodic array sampling for the k-space tomographic time-delay based aperture, greatly increasing the free spectral range of the system while maintaining the number of existing channels.