Electrically tunable optical spatial differentiation with graphene.

In recent years, optical analog computing has experienced rapid development, among which optical differential operation has attracted great attention. Here, based on the unique optical properties of graphene, we propose an electrically tunable optical spatial differentiation by introducing a graphene layer at a quartz substrate. It is found that the output light field is sensitive to the graphene layer near the Brewster angle for small polarization output at the graphene-quartz substrate interface and can be modulated by changing the Fermi energy of graphene. In this case, the result of the optical differential operation can be dynamically regulated. Almost strict one-dimensional differential operations in different directions and almost perfect two-dimensional differential operations can be achieved. In addition, two-dimensional edge detection with different degrees of distortion in different directions can also be realized when applied to image processing. This new modulation method may provide more possibilities for tunable image edge detection and provide a potential way for developing more versatile optical simulators in the future.

Designable optical differential operation based on surface plasmon resonance.

Various optical differential computing devices have been designed, which have advantages of high speed and low power consumption compared with traditional digital computing. In this paper, considering the reflection of a light beam through a three-layer structure composed of glass, metal and air, we propose a designable optical differential operation based on surface plasmon resonance (SPR). When the SPR is excited under certain conditions, the spin-dependent splitting in the photonic spin Hall effect (SHE) changes dramatically. We first prove theoretically that this three-layer structure can realize one-dimensional optical differential operation. By discussing the transverse beam displacement under different conditions, it is found that the designable differential operation with high sensitivity can be realized by slightly adjusting the incident angle and the thickness of metal film. We design the differentiator which can obtain the image of measured target edge in real time and get different edge effects at different times. This will provide more possible applications for autonomous driving and target recognition.

Tunable optical differential operation based on the cross-polarization effect at the optical interface.

To achieve optical differential operation based on the cross-polarization effect at the optical interface, one just needs an optical interface composed of two uniform media with different refractive indices. When certain conditions are satisfied, the reflection co-efficient of the light field at the interface conforms to the form of the spatial spectrum transfer function required by the spatial differentiation, the spatial analog operation can be achieved with a single interface. In this paper, based on the optical differentiation of Brewster effect, we propose a tunable optical differentiation based on the cross-polarization effect at the optical interface. We theoretically derive the tunable optical differentiation and then conduct an experiment to demonstrate theoretical results. It is found that the differentiator can achieve the tunable optical differentiation by adjusting the polarization of output beam. While getting the clear edge of the object, we can also observe the imaging of the middle part to different degrees, which realizes the multi-degree of freedom imaging for the measured target. This provides a potential way to develop devices more suitable for microscopic imaging and target detection.