Abstract
A novel design of the Fabry–Pérot optical cavity is proposed, utilizing both the topological interface state structures and photonic bandgap materials with a controllable reflection phase. A one-to-one correspondence between the traditional Fabry–Pérot cavity and optical topological cavity is found, while the tunable reflection phase of the photonic crystal mirrors provides an extra degree of freedom on cavity mode selection. The relationship between the Zak phase and photonic bandgap provides theoretical guidance to the manipulation of the reflection phase of photonic crystals. The dispersions of interface states with different topology origins are explored. Linear interfacial dispersion emerging in photonic crystals with the valley–spin Hall effect leads to an extra n = 0 cavity mode compared to the Zak phase–induced deterministic interface states with quadratic dispersion. The frequency of the n = 0 cavity mode is not affected by the cavity length, whose quality factor can also be tuned by the thickness of the photonic crystal mirrors. With the recent help of topology photonics in the tuning reflection phase and dispersion relationship, we hope our results can provide more intriguing ideas to construct topological optical devices.
Highlights
In 2008, Haldane and Raghu [1, 2] introduced topology to photonics, opening a brand-new research direction in the realm of photonics: topological photonics [3, 4]
In optical topological cavities (OTCs) type I, the Zak phase–induced interface states are employed where PC2 is the counterpart of the cylinder-arrayed PC1 with a shifted lattice [15]
As various applications have been demonstrated utilizing the unidirectional interface states induced by the valley-spin Hall effect, we extend our work to construct OTC type II by using valley-spin Hall photonic crystals (PCs)
Summary
In 2008, Haldane and Raghu [1, 2] introduced topology to photonics, opening a brand-new research direction in the realm of photonics: topological photonics [3, 4]. The Fabry–Pérot (FP) cavity, in which photons bounce back and forth in the lasing medium between two parallel plane mirrors (as shown in Figure 1A), is an important component to provide light energy feedback. It plays an important role in frequency selection. Different from previous studies where only topologically induced interface modes were employed, we design the reflection mirrors of PCs based on topological photonics. By assembling different PCs with topologically induced interface states and different PC mirrors with different reflection properties, we can construct optical topological cavities (OTCs) with tunable properties. The PC-based reflection mirrors provide a degree of freedom for mode selection, and an efficient approach to tune the cavity fidelity is discussed
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