A Design of Terahertz Broadband Filters and its Effect in Eliminating Asymmetric Characteristics in Device Structures

Abstract

Abstract-We report a straightforward way to design and fabricate polarization-insensitive broadband bandstop filters in terahertz range by fabricating identical metal patterns on both sides of a dielectric substrate with one layer rotated 90 o to the other. The unit cells used in such designs are the well-studied split-ring-resonators, hence the frequency range of the stop band can be easily tuned by varying the dimensions of the unit cell structures. Through simulation analysis, we show that such fabrication method requires no alignment in lithography step and works with common dielectric substrates. Two types of substrates, 1 mm-thick quartz and 100 μm-thick polyethylene terephthalate, were used as a demonstration. The transmission level stayed below 12% for a stopband of 0.42 THz frequency range. Lastly, we reasoned with simulation results that the proposed broadband filters give consistent performance regardless of the gap location in the unit cell, which will further extend their use in practical applications.

A split-ring-resonator-based polarization-insensitive ultra broadband filter in terahertz range

“…As the substrate thickness of the double-layered device is greater than the attenuation length of the resonant electromagnetic modes [28,29], there is no near-field coupling between the two layers of SRRs. As was pointed out in our previous work [23], when a y-polarized THz wave is incident from the front of the device, it effectively passes two filters connected in series. The front layer SRRs will firstly filter out the frequency at 0.80 THz due to 0 o -polarization incidence, and the back layer will then filter out the frequency at 1.10 THz as it sees a 90 o -polarization incidence.…”

“…The design principle is to fabricate SRR patterns on both sides of a thick (comparable or larger than operating wavelength) substrate, but rotates the pattern on one side 90 o with respect to the other [23]. It is worth pointing out that similar designs are common in chiral metamaterials [24][25][26][27], but the design logics are completely different.…”

“…Since the two layers of SRRs are identical, an x-polarized light is filtered just the same, but in a reverse order. Therefore, such a device becomes polarization-insensitive [23]. The broadband filtering works for any randomly polarized light, as the polarization azimuth can all be decomposed into x-and y-direction.…”

“…In our previous work [23], we reported a method to design and fabricate broadband filter in terahertz (THz) frequency range using specially designed SRRs as the unit cell. The obtained stop band width was 0.42 THz.…”

The fascinating split-ring-resonators: progress in design, fabrication and applications of terahertz metamaterials

“…By looking into the coupling between SRRs and the effect of incident polarization, we proposed a way to continuously modulate their resonances, changing the transmission intensity at resonant frequency from 20% to 80% [1]. We also designed a SRR-based polarization-insensitive broadband filter in THz range and discovered its effect in eliminating asymmetric characteristics in device structure [2]. A stop band with bandwidth of as large as 1.40 THz was achieved.…”