KEYWORDS: Edge detection, Dielectrics, Phase imaging, Signal detection, Image processing, Signal to noise ratio, Microscopy, Data processing, Analog electronics, Signal processing
Metasurfaces consisting of engineered nano-structures have shown exceptional abilities in light manipulation and have led to various practical applications. Using designed dielectric metasurfaces, we demonstrate spatial differentiation, a key aspect of optical analog signal processing, for broadband edge detection. Combined with quantum optics, the metasurface enabled spatial differentiator allows for edge detections with significantly higher signal to noise ratio compared to using classical optics. Furthermore, Fourier optical spin splitting microscopy based on a dielectric phase metasurface realizes single-shot quantitative phase gradient imaging. The proposed ideas pave the way for next generation high-speed real-time and multi-functional imaging.
Optical analog signal processing technology has been widely studied and applied in a variety of science and engineering fields. It overcomes the low-speed and high-power consumption disadvantages compared with its digital counterparts. One kind of the optical analog signal processing, optical edge detection, is a useful method for characterizing boundaries. In another context, metasurface as a recently developed technology has been introduced to optical imaging and processing and attracted much attentions. Here, we propose a new mechanism to implement an optical spatial differentiator consisting of a designed Pancharatnam-Berry (PB) phase metasurface inserted between two orthogonally aligned linear polarizers. Unlike other spatial differentiator approaches, our method does not depend on complex layered structures or critical plasmonic coupling condition, but instead based on spin-to-orbit interactions. Experiment confirms that broadband optical analog computing enables the edge detection of an object and achieves tunable resolution at the resultant edges. Furthermore, metasurface orientation dependent edge detection is also demonstrated experimentally.
Our work combines the extreme nonlinear properties in MQWs with the implementation of metasurface. We introduce the quantum multilayer composed of TiN/Al2O3 as a tunable metamaterial, which couples with the localized plasmonic resonances (gap plasmon) of an array of gold nano-antennas forming a meta-device. When the metasurface sample is illuminated by a collimated low-intensity laser with a linear polarization, the reflected beam is being diffracted as the left- and right-handed circularly polarized (LCP and RCP) components into 1 order, respectively. While for the case of a high-intensity laser illumination, the metasurface will act as a mirror, i.e. the linear polarization remains unchanged with both RCP and LCP components reflected to its zero-order. Furthermore, a tunable hologram is demonstrated based on our proposed design. A clear image is observed when the metasurface is illuminated by a low-intensity laser, while for the high-intensity case, the image will disappears Our finding paves the way for nonlinear optical modulators25, high speed all-optical switchs26 and reflective tunable displays.
Here, we review our recent works about the realization of the spin-dependent manipulation of structured light by tailoring the polarization. We develop a theory for spin-dependent manipulation based on the polarization design. As the exemplary demonstration, our experimental results show that such a theory can attain the spin-dependent splitting, and spindependent diffraction. Furthermore, we demonstrate this theory can be also applied to the spindependent focusing. The scheme provides a possible route for the manipulation of spin states of photons, and enables spin-photonics applications.
Two-dimensional (2D) atomic crystals have extraordinary electronic and photonic properties and hold great promise in the applications of photonic and optoelectronics. Here, we review some of our works about the spin-orbit interaction of light on the surface of 2D atomic crystals. First, we propose a general model to describe the spin-orbit interaction of light of the 2D free standing atomic crystal, and find that it is not necessary to involve the effective refractive index to describe the spin-orbit interaction. By developing the quantum weak measurements, we detect the spin-orbit interaction of light in 2D atomic crystals, which can act as a simple method for defining the layer numbers of graphene. Moreover, we find the transverse spin-dependent splitting in the photonic spin Hall effect exhibits a quantized behavior. Furthermore, the spin-orbit interaction of light for the case of air-topological insulator interface can be routed by adjusting the strength of the axion coupling. These basic finding may enhance the comprehension of the spin-orbit interaction, and find the important application in optoelectronic.
Development of spin-photonic devices requires the integration of abundant functions and the miniaturization of the elements. Pancharatnam-Berry phase elements have fulfilled these requirements and can be attained by using dielectric metasurfaces with subwavelength nanostructures. Here, we review some of our works on Pancharatnam- Berry phase elements and make an introduction of some integrated spin-photonic devices. We propose to integrate Pancharatnam-Berry phase lens into dynamical phase lens, which can be conveniently used to modulate spin states of photons. By integrating a Pancharatnam-Berry phase lens into a conventional plano-concave lens, we can obtain spin-filtering of photons. Moreover, we demonstrate that the generation of complex wavefronts characterized with different spin states can be implemented by the Pancharatnam-Berry phase lens. Further, based on the spin-dependent property of Pancharatnam-Berry phase element, we realize the three-dimensional photonic spin Hall effect with lateral and longitudinal spin-dependent splitting simultaneously. We foresee that this optical integration concept of designing Pancharatnam-Berry phase elements, which circumvents the limitations of bulky optical components in conventional integrated optics, will significantly impact multipurpose optical elements, particularly spin-based photonics devices.
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