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Abstract An optical diode structure with two dislocated parallel metallic gratings is proposed and investigated numerically. Dichroic optical diode transmission is realized in this structure, i.e., optical diode effect is observed in two wavebands corresponding to inverse transmission directions. In the structure, two parallel metallic gratings with different grating constants are separated by a dielectric slab in between. The first illuminated grating acts as a selector for exciting surface plasmons at a proper wavelength. The other grating acts as an emitter to realize optical transmission. When the incident direction is reversed, the roles of two gratings exchange and surface plasmons are excited at another wavelength. In dichroic transmission wavebands, the optical diode structure exhibits extraordinary transmission and possesses high optical isolation up to 1. Furthermore, the operating wavebands can be modulated by changing structure parameters.