Passive parity-time symmetry in organic thin film waveguides

Periodic media are fundamentally important for controlling the flow of light in photonics. Recently, the emerging field of non-Hermitian optics has generalized the notion of periodic media to include a new class of materials that obey parity-time (PT) symmetry, with real and imaginary refractive index variations that transform into one another upon spatial inversion, leading to a variety of unusual optical phenomena. Here, we introduce a simple approach based on interference lithography and oblique angle deposition to achieve PT-symmetric modulation in the effective index of large area organic thin film waveguides with the functional form Δñ_eff(z) ∼ e^iqz. Passive PT symmetry breaking is observed through asymmetry in the forward and backward diffraction of waveguided light that maximizes at the exceptional point, resulting in unidirectional reflectionless behavior that is visualized directly via leakage radiation microscopy. These results establish the basis for organic PT waveguide media that can be tuned for operation throughout the visible to near-infrared spectrum and provide a direct pathway to incorporate gain sufficient to achieve active PT symmetric lattices and gratings.