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Jing Bai1 Chao Wang1 Yu Yao1

1, Arizona State University, Tempe, Arizona, United States

Plasmonic metasurfaces provide great flexibility to control the amplitude, phase and polarization response of light in broad wavelength ranges from UV to THz, thus hold promise to realize ultra-compact chip-integrated photonic and optoelectronic devices for various applications. Chiral plasmonic metamaterial as artificial counterpart for the rare chiral material in nature enables generation, manipulation and detection of circularly polarized (CP) light. Plenty of works have demonstrated circular dichroism spectroscopy and circularly polarization detection based on chiral plasmonic metasurfaces2. Besides, full Stokes parameters detector have been proposed based on phase gradient arrays3, aperture antenna4 and in-line scatters5. Researchers are putting more efforts to develop new devices for high efficient and high performance polarization detection.
Here we present our experimental demonstration of highly efficient (>85% transmission efficiency) chiral metasurface structures as circular polarization (CP) filters with extinction ratio over 50 (defined as the ratio between transmission of CP light with the desired handedness and that of the other handedness). The proposed structures are composed of rationally designed plasmonic antennas and nanowires, which are vertically intergrated with a subwavelength-thick dielectric spacer layer. The total thickness of the device can be less than 1/10 of the operation wavelength. We investigated the design principle with anisotropic transfer matrix method and confirmed the design concepts with full wave simulation. According to our theoretical analysis, one can achieve CP filters with extinction ration over 1000 and transmission efficiency over 90%. In experiment, we have achieved over 85% efficiency and extinction ratio (r=TLCP/TRCP) over 50 at 4 µm. We have also integrated the CP polarization filters with nanowire grating linear polarization filters on the same chip for full stokes polarization detection. The measurement errors of our devices are 2%, 4% and 5% for S1, S2 and S3, respectively. And the errors for DOLP and DOCP are 5.4% and 6.6%, respectively, which to our knowledge are the best among the metasurfaces based polarization detection techniques presented in literature so far. The operation wavelength of the device can be engineered from NIR to FIR (1 µm to 30 µm) by simply changing the design parameters. Our designs can be directly integrated onto various semiconductor-based photodetectors and imaging arrays; thus enable on-chip polarization detection and imaging for various applications such as circular dichroism (CD) spectroscopy, polarimetric imaging and sensing, and molecular spectroscopy.

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