Here, we theoretically present an on-chip nanophotonic asymmetric transmission device (ATD) based on the photonic crystal (PhC) waveguide structure with complete photonic bandgaps (CPBGs). The ATD comprises two-dimensional silica and germanium PhCs with CPBGs, within which line defects are introduced to create highly efficient waveguides to achieve high forward transmittance. In the meantime, the total internal reflection principle is applied to block the backward incidence, achieving asymmetric transmission. We optimize the design of the PhCs and the waveguide structure by scanning different structure parameters. The optimized ATD shows a high forward transmittance of 0.581 and contrast ratio of 0.989 at the wavelength of 1582 nm for TE mode. The results deepen the understanding and open up the new possibility in designing novel ATDs. The on-chip ATD will find broad applications in optical communications and quantum computing.

Here we theoretically design valley photonic crystals (VPCs) based on two-dimensional (2D) hexagonal boron nitride (hBN) materials, which are able to support topological edge states in the visible region. The edge states can achieve spin-dependent unidirectional transmission with a high forward transmittance up to 0.96 and a transmission contrast of 0.99. We further study the effect of refractive index on transmittance and bandwidth, and it is found that with the increase of refractive index, both transmittance and bandwidth increased accordingly. This study opens new possibilities in designing unidirectional transmission devices in the visible region and will find broad applications.

High performance on-chip asymmetric transmission devices are indispensable for all-optical computing and information processing, but has been difficult to achieve. Currently, on-chip asymmetric transmission devices still have some limitations, such as low forward transmittance, narrow working bandwidth and polarization selectivity, which fail to meet the requirements of practical applications. In order to solve above-mentioned problems, we propose to design an on-chip reciprocal asymmetric transmission device based on the generalized total reflection (TR) principle. The on-chip reciprocal asymmetric transmission device consists of two photonic crystals (PCs) with different effective refractive indices. TR of the backward incident light is achieved at the interface by controlling the effective refractive index of the PC structures. This principle eliminates polarization selectivity and increases forward transmittance, contrast and operating bandwidth. The results show that in a broad wavelength region, the PC heterostructure demonstrates asymmetric transmissions for both TE and TM polarization modes with forward transmittance up to 0.58 and 0.78, respectively. And the contrast ratio is higher than 0.9. Our solution provides a new strategy and platform for an on-chip reciprocal asymmetric transmission device that meets the requirements of practical applications.

No abstract

No abstract