Linear and Nonlinear Light Manipulation on-a-Chip by Parity-Time Symmetry
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Metamaterials are the artificial materials that can be managed to have certain properties never found in nature. While the past metamaterial designs are focused on the real permittivity-permeability plane, recent explorations on non-Hermitian optical systems discover intriguing optical properties by considering the interplay with gain and loss. Parity-time symmetric material is an example in which the non-Hermitian Hamiltonians even possess real eigenvalues. A two-coupled waveguide system with gain and loss can show the properties of PT symmetry previously studied in the quantum field theory, as well as the related spontaneous PT breaking. Moreover, by adding the Kerr nonlinearity into this system, the PT breaking phase transition point can be systematically controlled by the intensity of nonlinearity. With the manipulation of permittivity and permeability in such non-Hermitian metamaterials, a coherent perfect absorber (CPA) modulator is proposed, where a small signal can be applied to modulate a relatively large signal.