2D asymmetric propagation based on CPA in helical photonic lattices

We propose a method for realizing two-dimensional (2D) non-reciprocal (one-way) transmission of discretized light based on the unidirectional coherent perfect absorption (CPA) in a helical optical waveguide array. By introducing a lossy element as a defect, the linear, purely passive optical lattice achieved the one-way propagation between the first and third waveguide layers. In recent years renewed attention has been directed toward the optical transmission in dynamical systems [1, 2]. The asymmetric transmission of light would be used for optical diode and all-optical isolation. In previous studies, one-way transmission on-chip isolators was realized by the introduction of asymmetric defects and some nonlinear in lattices [3], or using magnetic media [4]. In this paper, we introduce a lossy element between two lattice chains (see Fig. 1, the red spot). By dynamically adjusting the phases between the adjacent waveguide sites and the defect, Fig. 4(a) shows if a light beam is incident from region i, it will transmit to region ii. However, if the light beam is incident from region ii, it will transmit to region iii. Note that there is a little energy leaky in Fig. 2(b) due to the coupling effect between adjacent waveguides in the same layer. Although the geometry of layers I and III are symmetric, the output sites of the light beam incident from layer III slightly differ from the upper cases due to the asymmetric phase distribution. Our study provided a simple way to excellently realize the 2D asymmetric propagation in the helical waveguide arrays.