Optimized optical nonreciprocal transmission in defective one-dimensional photonic bandgap structures with weak asymmetry

Abstract

A novel and compact one-dimensional (1D) geometry for optical nonreciprocal transmission was proposed in this paper. Different from previous designs with high spatial asymmetry, by simply introducing a few dielectric periods of (BA) and (AB) into a typical nonlinear Fabry–Perot resonator with symmetric Bragg mirrors (AB)ND(BA)N, excellent optical nonreciprocal transmission properties can be achieved in the optical communication wavelength range. The optimized structure can be generally expressed as: (AB)ND(BA)M(AB)L, where M=N+1, L=1; M=N+2, L=2; M=N+3, L=3;…… and N≥6. The relationship between the bistability and the local field distribution of the Kerr defect layer D and the optical nonreciprocal transmission of the whole 1D system was analyzed theoretically. The direction- and incident wavelength-dependent shift of defect mode are confirmed to be responsible for the optimized optical nonreciprocity. The proposed optimized structures (AB)6D(BA)8(AB)2 and (AB)7D(BA)8(AB)1 are shown to have advantages over previously reported 1D designs with wide unidirectional transmission range (UTR) width (>3.1nm), high transmission for the forward incidence (>88%) and low transmission for the backward incidence (<1.22%) at lower input intensity (10 MW/cm2) with fewer layers (33 layers). Interestingly, the asymmetry degree of the proposed structures can be as low as 11.12%, which is only 1/4 or less of that of previous designs. The effects of the incident angle and polarization on the nonreciprocal transmission properties were also discussed for practical applications. These results are of great importance to the design of high-performance optical nonreciprocal devices, such as all-optical diodes, isolators and limiters.