ABSTRACT
Substrate integrated waveguides (SIWs) components play a crucial role in microwave devices fabricated by printed circuit board (PCB) technology. Bound states in the continuum (BICs) have high-quality factors that approach infinity. So far, there is little research on BICs in SIWs. Therefore, we studied a symmetry-protected BIC generated by the coupling between SIW and SIW resonators to fill this gap. Using the revised coupled mode theory (CMT), we explored the mechanism of resonance generation in this system. In addition, the effect of the geometrical parameters on the resonance is also investigated and higher Q3dB factors are obtained. The findings offer new insights into the design of BIC devices by traditional PCB technology, thus contributing to future applications in the integrated circuits field.
ABSTRACT
Bound states in continua (BICs) have high-quality factors that may approach infinity. However, the wide-band continua in BICs are noise to the bound states, limiting their applications. Therefore, this study designed fully controlled superbound state (SBS) modes in the bandgap with ultra-high-quality factors approaching infinity. The operating mechanism of the SBS is based on the interference of the fields of two phase-opposite dipole sources. Quasi-SBSs can be obtained by breaking the cavity symmetry. The SBSs can also be used to produce high-Q Fano resonance and electromagnetically-induced-reflection-like modes. The line shapes and the quality factor values of these modes could be controlled separately. Our findings provide useful guidelines for the design and manufacture of compact and high-performance sensors, nonlinear effects, and optical switches.
ABSTRACT
Bound states in the continuum (BICs) garnered significant research interest in the field of sensors due to their exceptionally high-quality factors. However, the wide-band continuum in BICs are noise to the bound states, and it is difficult to control and filter. Therefore, we constructed a top-bottom symmetric cavity containing three high permittivity rectangular columns. The cavity supports a symmetry-protected (SP) superbound state (SBS) mode and an accidental (AC) SBS mode within the bandgap. With a period size of 5 × 15, the bandgap effectively filters out the continuum, allowing only the bound states to exist. This configuration enabled us to achieve a high signal-to-noise ratio and a wide free-spectral-range. The AC SBS and the SP SBS can be converted into quasi-SBS by adjusting different parameters. Consequently, the cavity can function as a single-band sensor or a dual-band sensor. The achieved bulk sensitivity was 38 µm/RIU in terahertz wave band, and a record-high FOM reached 2.8 × 108 RIU-1. The effect of fabrication error on the performance for sensor application was also discussed, showing that the application was feasible. Moreover, for experimental realization, a 3D schematic was presented. These achievements pave the way for compact, high-sensitivity biosensing, multi-wavelength sensing, and other promising applications.
ABSTRACT
Asymmetric transmission (AT) is useful for polarization manipulation. We report narrowband AT that utilizes a triple-layered symmetric trimeric metasurface with near-field coupling of the dark mode of the Fano resonance. The coupling strength of the dark mode was tuned by using a mid-layer to break the dim AT between two slit layers. The peak transmission of linearly polarized waves and percentage bandwidth reached 0.7719 and 1.26% (numerical simulations) and 0.49 and 1.9% (experiments), respectively. Coupled-mode theory and field patterns are utilized to explain the underlying physical mechanisms of the mid-layer assisted field coupling. These results are useful for Fano-resonance-based devices.