Multistate Switching of Photonic Angular Momentum Coupling in Phase‐Change Metadevices

Abstract

The coupling between photonic spin and orbital angular momenta is significantly enhanced at the subwavelength scale and has found a plethora of applications in nanophotonics. However, it is still a great challenge to make such kind of coupling tunable with multiple sates. Here, a versatile metasurface platform based on polyatomic phase‐change resonators is provided to realize multiple‐state switching of photonic angular momentum coupling. As a proof of concept, three coupling modes, namely, symmetric coupling, asymmetric coupling, and no coupling, are experimentally demonstrated at three different crystallization levels of structured Ge2Sb2Te5 alloy. In practical applications, coded information can be encrypted in asymmetric mode using the spin degree of freedom, while revealing misleading one without proper phase change or after excessive crystallinity. With these findings, this study may open an exciting direction for subwavelength electromagnetics with unprecedented compactness, allowing to envision applications in active nanophotonics and information security engineering.

Extreme‐Angle Silicon Infrared Optics Enabled by Streamlined Surfaces

“…[ 20–22 ] Especially, multistate switching of photonic angular momentum coupling, namely, symmetric, asymmetric, and none coupling, have been experimentally demonstrated at different crystallization levels of phase‐change metasurfaces. [ 23 ] The subwavelength thickness of metasurfaces makes the absorption loss therein much smaller than bulky optical elements. For example, as the material basis of microelectronic technology, silicon is not considered for the long‐wave infrared region because of its high absorption in the region of 8–14 µm.…”

Programmable Controls to Scattering Properties of a Radiation Array

“…As a two‐dimensional version of metamaterial, metasurface has been introduced to control scattering properties of EM waves, and has been used to develop hyper lenses, perfect absorbers, gradient index lenses, energy harvesting systems, optofluidic barriers, polarization converters, vortex micro‐lasers, and multifunctional compact devices. [ 11–28 ] These intensive interests can be attributed to their simple fabrication, low cost, and powerful functionality to manipulate the EM waves in their phases, amplitudes, polarizations, propagations, and trajectories by arranging the artificial microstructures on a flat interface. For example, absorptive metasurface has been designed for radar cross‐section (RCS) reduction.…”

“…[ 22–24 ] By arranging different types of meta‐atoms on the metasurface, the scattering manipulation and RCS reduction can be achieved based on the principle of phase interference. [ 25–27 ] In general, the anisotropy metasurface with polarization conversion controls the scattering beams according to the polarization interference. [ 28–30 ] It is necessary to note that the metasurface has been used to improve the emission of radiation array with Fabry–Pérot cavity and the strong coupling effects.…”

Reconfigurable Continuous Meta-Grating for Broadband Polarization Conversion and Perfect Absorption

“…When tuning the crystallization level to a crystalline state (C-state) by outer stimuli, the device will behave as a perfect absorber, regardless of the incident polarizations, as shown in Figure 1 b. It should be mentioned that although previously reported works based on PCM have achieved reconfigurable devices with various functionalities, they could only modulate one aspect of the EM wave, such as changing the absorption peak or altering the implemented phase [ 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 ]. Whereas, the presented device can manipulate the polarization and amplitude in two crystallization levels, which may enable more fascinating applications in optics and photonics.…”