Transmission symmetry is considered an inherent property of passive linear systems. It is believed that violating transmission symmetry would mean violating reciprocity which would require some active intervention, e.g., via an external magnetic field, or with time modulation or "non-linear self-biasing" of the system's optical components. Recent works though have shown that judiciously designed planar asymmetries at a linear passive structure's interfaces can cause polarization rotation and lead to transmission symmetry breaking without breaking reciprocity.
Here, we present a linear and passive class of metagratings which preserve the polarization of the input beam but break transmission symmetry while still obeying reciprocity [1]. We analyze the underpinning mechanism and explain why it does not violate reciprocity. Breaking transmission symmetry with these simple systems can open-up several capabilities in integrated photonics from infrared to optical frequencies.
[1] S. Foteinopoulou, Breaking Transmission Symmetry Without Breaking Reciprocity in Linear All-Dielectric Polarization-Preserving Metagratings, Phys. Rev. Applied 17, 024064 (2022); https://doi.org/10.1103/PhysRevApplied.17.024064
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