Tunable bilateral unidirectional transmissions in a grating and photonic crystal hybrid structure

In this work, bilateral unidirectional transmissions (UDTs) with opposite transmission directions in one hybrid structure are realized using two different resonant mechanisms. The hybrid structure consists of a dielectric grating and a one-dimensional photonic crystal (PC) with a defect sandwiched at its center. One resonant mode is the defect mode of the PC enabling one UDT for one transmission direction. The other resonant mode is the grating guided mode resonance which introduces UDT for the opposite direction. Numerical calculations demonstrate that for each UDT, its transmittance difference, transmittance contrast ratio, and isolation degree can reach 90%, 100%, and 20%, respectively. In addition, the operation wavelength of each UDT as well as the wavelength interval between the two UDTs with opposite transmission directions can be tuned easily by adjusting structural parameters. This novel bilateral UDT creates potential for applications in both free space optics and optical circuits.