Tuning the focusing spot of plasmonic nanolens by aspect ratio under linear pola

A new plasmonic nanolens that can be tuned by varying the circular structure into an elliptical annulus and the aspect ratio from 1 to 0.1 and 1 to 2, respectively, is proposed. Using the rigorous finite-difference and time-domain algorithm, we find that when the aspect ratio ranges from 1 to 0.1, a