May 10 2021
Recently a research group from the Shanghai Institute of Optics and Fine Mechanics (SIOM) of the Chinese Academy of Sciences (CAS) performed numerical simulation and experimental demonstration of a pixelated metasurface based on the silicon-on-insulated (SOI) wafer.
Three-dimensional schematic of the pixel unit. The colors are used only for the distinguishment of the image and bear no wavelength information. (F0, F1, F2) and F3 represent linear polarizers and circular polarizer, respectively. Image Credit: Shanghai Institute of Optics and Fine Mechanics.
The team notes that the metasurface can achieve the detection of full-Stokes polarization vectors in the near-infrared. The study findings were reported in the Photonics Research journal on March 31st, 2021.
Focal plane imaging, a new polarization imaging technology developed recently, primarily depends on a pixelated metasurface and charge-coupled device (CCD) to detect the incident light’s polarization component.
Currently, the polarization imaging technology can just detect linear polarization components rather than circular polarization components. This is mainly because the pixel unit does not have a circular polarizer, particularly one that can be combined with a linear polarizer on a single chip. Existing circularly polarized films have a few drawbacks, like challenges of fabrication, low transmission of circularly polarized light, and low circular dichroism (CD). Thus, the search and making of high-performance pixelated metasurface that could help achieve full-Stokes vector detection is the focus of scientists.
The researchers suggested a high-performance pixelated metasurface to detect the full Stokes vector polarization of near-infrared incident light. Every pixel unit includes a circular polarizer with three linear polarizers and a two-dimensional structure with the same structure parameters and distinct gate line directions.
Thus, all the polarization components of the incident light could be detected by an individual exposure. A two-dimensional circular polarizer not only consists of high circular dichroism but is also simple to combine with a linear polarizer.
Besides, the metasurface element depends on SOI, which not only possesses a high transmission to circularly and linearly polarized light but also offers the possibility for combination with CCD in the next polarization imaging.
In the experiment performed, the pixelated metasurface was fabricated by the integration of an electron beam exposure system and inductively coupled plasma etching technology. The TM polarized light’s average transmittance in the 1.47 to 1.6 μm wavelength band was around 75%, and the extinction ratio was over 20dB.
The quantified average transmission of right-handed circularly polarized light in the 1.48 to 1.6 μm wavelength band was beyond 80%, and the highest value of CD was up to 70% at a wavelength of 1.6 μm, which can satisfy the needs of a majority of the applications.
The study was financially supported by the National Nature Science Foundation of China, the International Science and Technology Cooperation Program, the Shanghai Sailing Program, and the University Scientific Research Foundation of Jiangsu Province.
Journal Reference:
Zhang, C., et al. (2021) High efficiency all-dielectric pixelated metasurface for near-infrared full-Stokes polarization detection. Photonics Research. doi.org/10.1364/PRJ.415342.