We discuss the use of photonic crystal slab to accomplish a number of imaging processing tasks, including edge detection, image smoothing, white noise suppression and, suppression or extraction of periodic features. All these tasks involve filtering in the wavevector domain. Image filtering can be implemented electronically. However, in big-data applications requiring real-time and high-throughput image filtering, conventional digital computations become challenging. Nanophotonics-based optical analog computing may overcome this challenge by offering high-throughput low-energy-consumption filtering using compact devices. Here, we show that several types of isotropic two-dimensional image filters can be implemented with a single photonic crystal slab device. Such a device is carefully designed so that the guided resonance near the Γ point exhibits an isotropic band structure. Depending on the light frequency and the choice of transmission or reflection mode, this compact device realizes isotropic high-pass (Laplacian), low-pass, band-reject and band-pass filtering in the wavevector domain. We numerically demonstrate various important image processing tasks enabled by these filters as mentioned above. Our work points to new opportunities in optical analog computing as provided by nanophotonic structures.
We discuss novel electromagnetic effects in topological metamaterial and in complex birefringent meta material. In particular, we discuss the creation of novel topology using meta-material geometry., We also discuss three-dimensional meta-materials with balanced gain and loss for the purpose of achieving arbitrary control of a pair of polarization states.
Weyl fermions have not been found in nature as elementary particles, but they emerge as nodal points in the band structure of electronic and classical wave crystals. Novel phenomena such as Fermi arcs and chiral anomaly have fueled the interest in these topological points which are frequently perceived as monopoles in momentum space. We demonstrate that generalized Weyl points can exist in a parameter space and we report the first observation of such nodal points in one-dimensional photonic crystals in the optical range. The reflection phase inside the band gap of a truncated photonic crystal exhibits vortexes in the parameter space where the Weyl points are defined and they share the same topological charges as the Weyl points. These vortexes also guarantee the existence of interface states, the trajectory of which can be understood as “Fermi arcs” emerging from the Weyl nodes.
Topological invariant plays a more and more important role in modern physics with the discovery of new materials such as topological insulators. The concept of momentum space topology has also been extended to various photonic systems to realize interesting applications. In this work, a plasmonic interface state is introduced between a photonic crystal and a metasurface which is protected by the Z2 topological mirror symmetry of the photonic crystals. Here we propose a scheme to experimentally measure the topological phase in a photonic system. Using reflection spectrum measurement, we determined the existence of interface states in the gaps, and then obtained the Zak phases. The interface state is excited when the reflection phase matching condition is satisfied. The reflection phase of metasurface can be tuned by changing the structural parameter. The resonance properties of interface state can be manipulated in the process. By manipulating the anisotropic property of the metasurface, we can further tune the polarization of the interface state. Field enhancement induced by the interface state will have important applications in nonlinear and quantum optics.
We show that dynamic refractive index modulation provides a route towards non-reciprocal topological photonics. In particular, the phase of the modulation provides an effective gauge field for photons that breaks time-reversal symmetry, and can be used to create a wide range of topological effects, in both real space as well as in spaces that involve a synthetic frequency dimension. These topological effects are pointing to new capabilities for controlling the properties of light.
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