We developed a novel universal eigenvalue analysis for 2D arbitrary nanostructures comprising dispersive and lossy materials. The complex dispersion relation (or complex Bloch band structure) of a metallic grating is rigorously calculated by the proposed algorithm with the finite-difference implementation. The abnormally large group velocity is observed at a plasmonic band edge with a large attenuation constant. Interestingly, we found the abnormal group velocity is caused by the leaky (radiation) loss, not by metallic absorption (ohmic) loss. The periodically modulated surface of the grating significantly modifies the original dispersion relation of the semi-infinite dielectric-metal structure and induces the extraordinarily large group velocity, which is different from the near-zero group velocity at photonic band edge. The work is fundamentally important to the design of plasmonic nanostructures.
© 2013 Optical Society of America
Original Manuscript: September 13, 2013
Revised Manuscript: November 22, 2013
Manuscript Accepted: November 23, 2013
Published: December 24, 2013
Wei E. I. Sha, Ling Ling Meng, Wallace C. H. Choy, and Weng Cho Chew, "Observing abnormally large group velocity at the plasmonic band edge via a universal eigenvalue analysis," Opt. Lett. 39, 158-161 (2014)