Abstract
We present a hybrid gyromagnetic photonic crystal (GPC) waveguide composed of different GPC waveguide segments possessing various cylinder radii and waveguide widths but biased by a uniform external magnetic field. We demonstrate in frequency and time domains that based on the strong coupling of two counter-propagating topologically protected one-way edge states, the intriguing slow light rainbow trapping (SLRT) of electromagnetic (EM) waves can be achieved, that is, EM waves of different frequencies can be slowed down and trapped at different positions without cross talk and overlap. More importantly, due to the existence of one-way edge states, external EM waves can be non-reciprocally coupled to the SLRT waveguide channel, although the incident position of the EM wave is far away from the waveguide channel. Besides, the frequency range of the slow light states can also be easily regulated by tuning the intensity of an external magnetic field, which is very beneficial to solve the contradiction between slow light and broad bandwidth. Our results can be applied to the design of high-performance photonic devices, such as an optical buffer, optical switch, and optical filter.
Highlights
The frequency of slow light states can be regulated when the intensity of external magnetic field is tuned, which is very beneficial to solve the contradiction between slow light and broad bandwidth
These results show the great potential of slow light rainbow trapping (SLRT) waveguide for the design of photonic applications with high performance, for example, an optical buffer, optical switch, and optical filter
We present a novel means to create an SLRT waveguide being made of a hybrid gyromagnetic photonic crystal (GPC) biased by a uniform external magnetic field so that the EM wave of different frequencies can be slowed down and trapped at different positions without cross talk and overlap
Summary
The recent realization of topological photonic insulators has been an emerging research area, which has brought the discovery of topological photonic states (TPSs) (Khanikaev et al, 2013; Lu et al, 2014; Lu et al, 2016; Khanikaev and Shvets, 2017; Xie et al, 2018; Ozawa et al, 2019; Tang et al, 2019; Kim et al, 2020; Wang et al, 2020; Chen et al, 2021a). It can be seen clearly that the slow light states originating from the strongly coupling of two counter-propagating topological one-way edge states can be achieved and conveniently modulated by changing the geometrical parameters of the structure and intensity of the external magnetic field These features are very beneficial to create extremely broadband-tunable slow light states and the SLRT phenomenon and can provide a powerful path to solve the contradiction between slow light and broad bandwidths. The distribution length of each footprint in the slow light rainbow is about 2.7λ; it will be very valuable for the realization of a more compact rainbow waveguide if we can explore a novel physical mechanism that enables the EM wave to be captured in a small space, even a point
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