Independent Color Filtering of Differently Polarized Light Using Metal-Insulator-Metal Type Guided Mode Resonance Structure

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  • ABSTRACT

    The independent operation of a color filter for incident polarization is demonstrated using a guided-mode resonance (GMR) filter employing a metal-insulator-metal (MIM) waveguide. To achieve independent operation, a rectangular MIM grating is proposed as a wave-guide resonator. The design considerations are discussed and include how to determine the grating period and slit width. Power flow distribution is observed with slit width variation. Blue-green, green-red, and blue-red filters for corresponding x- and y-polarizations are demonstrated as application examples with numerical simulation with rectangle-shaped MIM grating. As a practical application, feasibility as a chromatic polarizer is discussed.


  • KEYWORD

    Guided-mode resonance , GMR filter , Plasmon , Color filter , MIM waveguide

  • I. INTRODUCTION

    Many studies have been conducted on dielectric guided-mode resonance (GMR) filters [1], and various practical applications have been suggested such as narrow-line feedback elements [2], biosensors [3], tunable optical filters [4], dispersion engineering [5], polarization beam splitters [6, 7], high power microwave frequency selective elements [8], and color filters [9-12].

    Meanwhile, a lot of attention has been given to various types of plasmon-assisted filters after the subwavelength transmission effect through metal holes, which is known as extraordinary transmission, was reported [13-17]. Various types of plasmonic color filters have been proposed, investigated, and demonstrated, with suggestions put forward regarding their application areas [18-27].

    A GMR filter can be utilized by plasmons to manipulate light and provide additional functionalities. Recently, metal-insulator- metal (MIM) structures have been employed as a wave-guiding element for GMR filters, and visible wavelength color filters have been realized [28]. Compared to the general dielectric-based GMR filter, the GMR filter employing MIM structures in [28] is more compact and has the embedded functionality of a polarizer, which is advantageous for applications in liquid crystal displays (LCDs) by eliminating the need for a separate polarizer layer. Though it is suitable for the aforementioned application (i.e., in LCDs), it is restricted to applications involving single polarization due the other polarizations being blocked.

    To make the best use of the light-manipulation ability of the MIM-type GMR structure, attention must be paid to the fact that the MIM waveguide can support a polarization-selective mode in accordance with the excited plasmon mode at the edge of the metal. This study aims to achieve GMR in both x- and y-polarizations instead of blocking one of the polarizations. Independent color filtering of differently polarized light is possible with a rectangular MIM grating by exciting GMR in both polarizations with the appropriate selection and variation of the material and geometric parameters.

    A numerical simulation was performed for the independent color filtering of differently polarized light with the proposed rectangular MIM grating. Independent color filters such as red/green/blue filters for both x-polarization and y-polarization have been demonstrated as examples and their practical application was discussed.

    II. DESIGN CONSIDERATIONS

    Figure 1 shows a functional description of the proposed independent color filtering of differently polarized light. The proposed structure can work as a red color filter for x-polarized light and a blue color filter for y-polarized light. If unpolarized white light is incident on the proposed structure, red and blue light can be transmitted for x- and y-polarization, respectively.

    A detailed geometric structure is shown in Fig. 2. Where sx, sy are the slit widths along the x and y axes; gx, gy are the grating widths along the x and y axes; TI, Tm are the thicknesses of the insulator and metal, respectively. Metal/insulator/metal layers are stacked on the substrate as a MIM waveguide and patterned in a rectangle shape, as shown in the figure.

    The operation principle of the proposed structure is the same as that in [28] except for the diffraction dimension. The proposed structure uses a rectangular-shaped two-dimensional grating while the reference study uses a line-shaped one-dimensional grating. Hence, the proposed structure can support both directions of polarization. However, it is noteworthy that so