Plasmonic quasicrystals with broadband transmission enhancement

Abstract

Plasmonic quasicrystals (PlQCs), by integrating the properties of quasicrystals (rotational symmetry and long range ordering but lack translational symmetry) and surface plasmon polariton mediated effects, offer several advantages over plasmonic crystals (PlCs). For example, in PlQCs one could have broadband, polarization independent response. However, large area patterning by electron beam lithography requires precise lattice coordinates as well as a practical way to design the structures for specific spectral response. We demonstrate design and fabrication of large area quasicrystal air hole patterns of π/5 symmetry in metal film in which broadband, polarization and launch angle independent transmission enhancement is observed. We demonstrate bi-grating quasicrystals to show that designable transmission response is possible over visible to near infrared wavelength regions with about 15 times enhancement. These would be useful in many applications like energy harvesting, nonlinear optics and quantum plasmonics.

Broadband linear and nonlinear optical response of plasmonic quasicrystals

“…More recently, designable spectral response as well as broadband transmission enhancement have been reported by us in large area (1 mm 2 ) PlQCs [18]. The broadband response due to dense k-space is found to be near polarization independent as well as near dispersionless [18]. Second harmonic generation in PlQCs has been reported by Xu et al on 80 Â 80 mm 2 area patterns [12].…”

“…Transmission enhancement, discrete energy levels in small area plasmonic quasicrystal structures, comparison of PlQC transmission with periodic and random hole patterns were made earlier [15][16][17]. More recently, designable spectral response as well as broadband transmission enhancement have been reported by us in large area (1 mm 2 ) PlQCs [18]. The broadband response due to dense k-space is found to be near polarization independent as well as near dispersionless [18].…”

“…The structure realized has very low inhomogeneity with hole diameter variation within 90 77 nm. Our earlier study showed that the inhomogeneity results in a smoothening of spectral response while retaining the same broad spectral features [18]. The surface plasmon mediated linear transmission enhancement spectrum shown in Fig.1c is obtained by finding the ratio of the transmission spectrum of the PlQC patterned gold film and the transmission spectrum of unpatterned gold film.…”

“…Plasmonic quasicrystal pattern was designed using a modified oblique tiling method based on our previous work [18]. In this method the lines are replaced by an array of dots with well-defined period, a. Quasicrystal lattice with n-fold symmetry is generated by n successive rotations (by π/n) and superposition of these arrays with a common center.…”

Shedding light on fractals : exploration of the Sierpinski carpet optical antenna

“…There are many different types of aperiodic arrays which have been proposed and investigated such as quasicrystalline arrays [90] [91] [92], Fibonacci arrays [70] [93], Thue-Morse arrays and Rudin-Shapiro arrays [94], etc. Among all of these aperiodic arrays, the quasicrystalline arrays has drawn most of attentions.…”