尽管最近将元面积纳入了广泛的介电应用中（其中一些包括腹部镜头，次序聚焦设备，梁偏转器和转换器，全息图和抗反射涂层），但通常仅限于指定的带宽操作。为了进一步扩展元信息的潜在使用，必须将其功能放大其活性和可重新配置。
为此，2019年纳米光子学论文研究了热可调性在元整日中的作用，以及这些特性的知识如何扩展MetadeVices的可调性和可重构功能。
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热光（TO）可调性和可重新配置的MetadeVices
One of the main challenges that researchers have faced in attempting to reconfigure metasurfaces is the ability to obtain large and continuous modulations to the optical properties of these planar optical structures; within both subwavelength and low-Q meta-atom resonators. Several different approaches have looked into the potential of several techniques, including ultrafast free-carrier injection, coupling active tuning to liquid crystals, and MEMS, to confront this challenge.
Despite these attempts, no viable solution to fully reconfigure metasurface devices has been achieved. The current study investigated the thermal-optic (TO) effects of high-index silicon (Si) and germanium (Ge) semiconductor resonators over a large temperature range, in an effort to elucidate any available reconfigurable properties.
Methodology
Both the Si and Ge resonators used in this study were spherical and fabricated by femtosecond laser ablation. To characterize the optical properties of both metasurface devices, single particle spectroscopy was conducted at various temperatures, using a Fourier-transform infrared spectroscopy (FTIR) device that was coupled to an infrared microscope.
The thermal tuning capabilities of both the Si and Ge single resonators and their metasurfaces were examined over a temperature range of 80 to 873 Kelvin (K).
结果
加利福尼亚大学的研究人员发现，通过修改传统作用，发生了依赖温度的共振频移。此外，在低温和中等温度下，研究人员发现所有共振均表现出红移，遵循正常的阳性热光系数。
When exposed to higher temperatures and longer wavelengths, the thermal excitation of the free carriers (FCs) were found to exhibit significant bandgap shrinkage, which ultimately caused the TOC value to become negative and yield a dn/dT value that was less than 0. This transition is believed to result from a continuous change in the resonance shift from red-shift at the low and moderate temperature to a blue-shift at the higher temperatures.
结论
通过发现SI共振器中短近红外（NIR）波长存在的重要TOC，这项研究的研究人员确定了SI Metasurfaces存在的振幅调节剂和可调式元滤器。该发现突出了Si Metasurfaces中存在的热重配置功能。
As a result, the research discussed here provides an opportunity for semiconductor engineers to continue to investigate the thermally tunable properties of semiconductor metasurfaces in order to one day develop high-Q reconfigurable metadevices.
参考
- Lewi, T., Butakov, N. A., & Schuller, J. A. (2019). Thermal tuning capabilities of semiconductor metasurface resonators. Nanophotonics 8(2); 331-338.DOI: 10.1515/nanoph-2018-0178。
The research discussed in this article was conducted by researchers from the Department of Electrical and Computer Engineering at the University of California Santa Barbara. This work was also supported by the Air Force Office of Scientific Research and the University of California Office of the President Multi-campus Research Programs and Initiatives.
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