ABSTRACT
We demonstrate high-extraction-rate Ta2O5-core/SiO2-clad photonic waveguides on silicon fabricated by the photolithography-assisted chemo-mechanical etching technique. Low-confinement waveguides of larger than 70% coupling efficiency with optical fibers and medium propagation loss around 1 dB/cm are investigated in the experiment. Monolithic microring resonators based on Ta2O5 waveguides have shown the quality factors to be above 105 near 1550 nm. The demonstrated Ta2O5 waveguides and their fabrication method hold great promise in various cost-effective applications, such as optical interconnecting and switching.
ABSTRACT
The passive sensing and active control of electromagnetic (EM) waves have always been attractive in electronic and information areas, especially during the intelligent era. Here a new method is presented to achieve the angle sensing of incident wave and adaptive control of backward scattering using the intelligent metasurface. The proposed unit cells have the ability to dynamically manipulate the receiving and reflection of the EM energy respectively. The angle sensing of incident waves can be actualized using the method of compressive sensing based on multiple receiving patterns, which are generated by randomly switching the receiving and reflection states of the unit cells. Afterward, the customized performances of backward scattering waves according to the cognitive incident angle can be realized by controlling the programmable reflective phases of unit cells correspondingly. One prototype composed of the metasurface and the module for sensing and adaptive feedback control is fabricated. The whole intelligent metasurface with customizing the function of retro-reflection or low scattering is measured without human intervention and the good results acquired can verify the validity of the proposed concept and design.
ABSTRACT
In synthetic aperture radar (SAR) ocean remote sensing, it is very difficult to estimate an accurate azimuth antenna pattern (AAP) from low-scattering SAR images without strong scattering targets. Therefore, an azimuth antenna pattern estimation method based on Doppler spectrum in SAR ocean images is proposed in this paper. In order to preserve the complete AAP information, an azimuth unweighted matched filter is used to re-image the SAR raw data in the proposed method. Then, the shape factor of AAP can be obtained by linear statistics of the relationship between Doppler center and edge frequency spectrum in Doppler spectrum of each distance gate. In addition, the impact of the uniformity and signal-to-noise ratio of SAR ocean images on the estimation results are also analyzed by simulation. Finally, the feasibility of proposed method is verified by data from ERS-2 (European remote sensing satellite (ERS) was the European Space Agency's first Earth-observing satellite). Experimental results show that the AAP estimated by proposed method has a good estimation result.