Extending the operating wavelength range of high-isolation-ratio narrowband asymmetric transmission based on a grating–film–grating nanostructure

A series of asymmetric transmission (AT) nanodevices based on the grating–film–grating (G-F-G) structure are studied, stimulated by a previous work [ Opt. Express 27 , 25107 ( 2019 ) OPEXFF 1094-4087 10.1364/OE.27.025107 ]. By showing the results of three different nanodevices as examples, it is demonstrated that this kind of G-F-G nanostructure can achieve high-isolation-ratio AT at wavelength bands within a certain range by designing the parameters of the structure. These three nanodevices can achieve high forward transmittivities of 0.69, 0.71, and 0.87 at the wavelengths of 714, 810, and 905 nm, respectively, and the isolation ratio between forward and backward transmittivities are all more than 10 dB. In addition, the effects of the lateral displacement of upper gratings on device performance are also investigated, revealing that optimal AT is achieved under normal incidence and zero displacement. The proposed G-F-G structure provides a feasible solution for passive and easily manufacturable optical isolators with potential applications in sensing systems.