Integrated flat-top reflection filters operating near bound states in the continuum

Abstract

We propose and theoretically and numerically investigate narrowband integrated filters consisting of identical resonant dielectric ridges on the surface of a single-mode dielectric slab waveguide. The proposed composite structures operate near a bound state in the continuum (BIC) and enable spectral filtering of transverse-electric-polarized guided modes propagating in the waveguide. We demonstrate that by proper choice of the distances between the ridges, flat-top reflectance profiles with steep slopes and virtually no sidelobes can be obtained using just a few ridges. In particular, the structure consisting of two ridges can optically implement the second-order Butterworth filter, whereas at a larger number of ridges, excellent approximations to higher-order Butterworth filters can be achieved. Owing to the BIC supported by the ridges constituting the composite structure, the flat-top reflection band can be made arbitrarily narrow without increasing the structure size. In addition to the filtering properties, the investigated structures support another type of BICs -Fabry-Pérot BICs arising when the distances between the adjacent ridges meet the Fabry-Pérot resonance condition. In the vicinity of the Fabry-Pérot BICs, an effect similar to the electromagnetically induced transparency is observed, namely, sharp transmittance peaks against the background of a wide transmittance dip.

Double Electromagnetically Induced Transparency and Its Slow Light Application Based on a Guided-Mode Resonance Grating Cascade Structure

“…Therefore, the Q factors of the two EITs were 9117 and 7753, respectively. Compared with the previous work that accidentally observed EIT-like characteristic spectra in several resonant grating structures [ 24 , 25 ], it is clear that we successfully used the GMR effect to achieve a double EIT-like effect with a narrow band and a high Q value in the resonance grating cascade structure.…”

“…In recent years, cascade resonant grating has attracted extensive attention and research due to its versatility. Not only can it be used to design filters [ 22 , 23 , 24 ], but optical phenomena very similar to EIT characteristic spectra were also observed in some work [ 24 , 25 , 26 ]. Therefore, it will be an interesting topic to study the EIT-like effect combining the characteristics of the GMR effect and cascade resonant grating.…”

Photonic Bound States in the Continuum: From Basics to Applications

“…Moreover, various on-chip photonic functionalities that rely on the rich physics of BICs have also been proposed. [96,97,[108][109][110][111] Examples include integrated Gires-Tournois interferometer, [96] shown in Figure 4m, spatial integration and differentiation of optical beams, [97] Figure 4n, integrated filters, [109] and many more.…”

Low‐Threshold Bound State in the Continuum Lasers in Hybrid Lattice Resonance Metasurfaces

“…The applications of BICs in many fields, especially topological photonics, have been widely discussed. [ 12,17,18 ] By using a topological design to create BICs, different types of metasurfaces or photonic crystals can be used in various applications, such as photonic integrated circuits, [ 19–22 ] sensors, [ 23–25 ] nonlinear effect enhancement, [ 26–30 ] low‐threshold lasers, [ 31,32 ] and vortex lasers. [ 33–36 ] Optical BICs have attracted attention not only as resonators for lasing but also as sources of thermal emission.…”