Applied Engineering Sciences

Applied Engineering Sciences – Deng (Ed.)

© 2015 Taylor & Francis Group, London, 978-1-138-02649-0

Research on the transmission enhancement properties of a novel

subwavelength grating structure and mechanism

H.X. Chang, M.Q. Li, S. Zhang & Y. Ding

Key Laboratory of Intelligent Computing & Signal Processing, Ministry of Education,

Anhui University, Hefei, China

ABSTRACT: The subwavelength metal grating is designed and simulated by using the finite difference time

domain (FDTD) algorithm.The transmission characteristics of subwavelength metal grating structure are studied

based on the Lossy Drude dispersive medium model. The influence of grating geometry parameters on the

transmission characteristics are analyzed, especially for the zero transmission point location of the spectrum.

The difference between the designed and conventional gratings is that the former introduces the resonant cavity.

Results show that, compared with the single-layer grating, the triple-layer grating has a better filtering effect,

and the transmission spectrum peak is in excess of 82%. It concludes that the transmission peak drift is analyzed

by using the waveguide Fabry-Perot (F-P) cavity resonance effect, and the zero transmission point location of

the spectrum is independent of the metal layer thickness. The influence rules provide an available reference for

the design of the band-pass filters.

1 INTRODUCTION

When light passes through a metallic film with

subwavelength arrays of holes, it will produce an

extraordinary transmission phenomenon under cer-

tain wavelengths and its broad application prospects

have sparked extreme great interest since the work

of Ebbesen et al. [1]. In recent years, subwavelength

structures have mostly been studied around a hole

array periodic structure, square hole arrays and slit

grating [2]. However, this paper designed a triple-

layer subwavelength grating with the resonant cavity.

Based on Lossy Drude’s dispersive medium model

[3], a dispersion 2-d FDTD iteration equation was

deduced under the resonance of the metal surface

plasma membrane dispersion, to solve the instability

of the dispersion medium numerical calculation, and

study the cavity length, slit width, the refractive index

of the medium and other parameters for enhanced

transmission characteristics.

2 LOSSY DRUDE DISPERSIVE MEDIUM

FDTD ALGORITHM

When the dielectric constant of metal materials is

related to the frequency, the metal has dispersion char-

acteristic. The dispersion relationship of the Lossy

Drude model is given by [4]:

where ω is the bulk plasma frequency; ω

p

is the metal

plasma oscillation frequency; and γ is the damping

coefficient. The model formula (1) is substituted into

Maxwell’s equations by using the ADE method [5,6]

to transform the time-frequency domain operator. The

differential equations of the light transmission in the

metal are then given by [7]:

where E and H are respectively the electric field inten-

sity and magnetic field intensity; J is the current

density; ε

0

, µ

0

are respectively the vacuum permit-

tivity and permeability. The difference and discrete

Eq. (2b) is given by:

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