The polarization selective light transmissions through two-dimensional (2D) periodic arrays of ladder like nano-structures are fabricated by simple cost effective LIL process. The polarization dependent optical spectrums over the wavelength range 3 μm – 15 μm are experimentally measured. It is found that a dip position in the reflection spectrum at around 4.5 μm, when the input electric field excitation of incoming plane wave along the short axis of the ladder structures. In addition, it is also shown that a broadband in reflection spectra when the electric field excitation of the incoming light along the long axis of the ladder structures. In order to understand the physical mechanism behind the resonant behaviour in the reflection spectrum, the structures are simulated by taking the geometrical parameters obtained from FESEM image study. The reflected simulation spectrum obtained by using the comsol multi-physics software, which is good agreement with the experimental results. The electric and magnetic field distribution at the resonant point clearly indicates that the slit mode resonance takes a key role for extra-ordinary transmission through these structures. It is shown through the simulating results on changing in refractive index of the surrounding medium leads to shift in resonant point in the transmission spectrum. Furthermore, the reflectance spectrum experimentally demonstrated on the effect of the film thickness and the lattice constant [1,2].
Fig 1 Figure (a) shows the FESEM image of 2 D ladder like structures fabricated on glass substrate with dimensional parameter as length short and long axis as 1.8 μm and 2.88 μm, lattice constant along long and short axis as 4.4 μm and 0.605 μm. (b) shows the experimental and simulation reflection spectrum of these sample with orthogonal two polarization.
References
[1] T. W. Ebbesen, et al, Extraordinary optical transmission through subwavelength hole arrays, Nature 391(6668), 667669 (1998).
[2] M. N. Abbas, et al, An omni-directional mid-infrared tunable plasmonic polarization filter, Nanotechnology 23(44), 444007 (2012).
gbehera@iitk.ac.in