Topologically protected multiple resonant modes in a one-dimensional photonic crystal heterostructure

This paper proposed and theoretically examined a double-interfaced one-dimensional photonic crystal heterostructure for strong localization of topologically protected resonant modes. It is challenging to achieve these modes for a range of wavelengths using a single photonic crystal. The design proposed in this study is a heterostructure of photonic crystals 1 (PC1) and 2 (PC2), and it provides distributed localized modes from the infrared to ultraviolet wavelength ranges. In addition, multiple resonant modes occur at certain photonic bandgaps due to the addition of the third photonic crystal (PC3), which is analytically modeled with the heterostructure of PC1 and PC2. The enhancement in the number of resonant modes depends on the PC2 number of unit-cells and the reflection phase of the proposed heterostructure. The reflection phase is abruptly changing from 0 to π for several wavelengths inside the bandgap. These resonance modes are also dependent on the topological behavior of each connected photonic crystal and are immune to small disorder and back-scattering within the crystal. The high-quality factor (Q-factor ∼10⁷) shows strong light-matter interaction of these multiple resonant modes. The characterization was done in terms of the Zak phase, sign of the reflection phase, and bandgap overlapping. Consequently, this heterostructure may pave the way for new topological photonics and new applications in optoelectronics, frequency up-conversion, photonic devices, rainbow trapping, multiwavelength optical filters, and so on.