Studies Of Subwavelength Focusing Based On Surface Plasmon Polaritons And Photonic Crystal Phase Shifter

The steadily decreasing dimensions in semiconductor devices are for filling the rapid development of the scientific technology, especially for the high-end nano-optical imaging technology. Nano-optical devices are widely required in many fields, such as optical integrated circuit, optical imaging, optical lithography, high-density optical storage, bio-sensor, etc. However, traditional optical techniques have been blocked for the diffraction limit. Therefore, nanoscale optical manipulation and breaking the diffraction limit to become an important research direction.Firstly, based on the analysis of zero-refractive-index PCs, we present a novel phase-shifter. A refractive index of zero implies that light enters a state of quasi-infinite phase velocity and infinite wavelength. Thus, a plane wave incident from the left air region can pass through the zero-refractive-index metamaterials (ZRIM) as if it were not there and the shape of the wavefronts leaving the ZRIM depends solely on the shape of the exit surfaces of the ZRIM, which provides high flexibility in the design of phase patterns. By the way of reasonably adjusting the distance between the ZRIMs, the wave phase on the right side of the second ZRIM can be changed linearly compared to the incident wave phase. This structure can decrease the loss and avoid the effect of operation voltage fluctuation. It can be easily nanofabricated within current silicon foundries, suggesting significant potential for the development of future electronic-photonic integrated circuits.Following, Based on SPPs, beam optical focusing structures capable of double side beam focusing are proposed. The relationships between focal intensity, focal length, focal width and the distance from optical source to lens structure are investigated and numerically simulated. We found that the optimal focusing point of this lens model appears at a period of half wavelength. When the distance became501nm, the focused energy peak reached1215and focal length was2.67um. These excellent focusing characteristics are of great value for the focusing model design and application.Finally, a beam optical focusing structure with double subwavelength metal slits surrounded by tapered surface trapezoid dielectric gratings (DTDG) is proposed. By increasing the incident wavelength from560nm to591nm at a step of1nm, the focal length decreases monotonously from2.4um to2.34um, and the focal length maintains constant in the wavelength domain. The FWHM of focal width and peak intensity decrease monotonously from438.5nm to347.7nm and3to2.1respectively as well. Above all, it maintains constant for a large wavelength domain (560nm-591nm), which is a great potential for integrated optics, biomedicine sensing, nanophotonics, optical measurement and related applications.