Broadband Achromatic Metasurface Devices

Metasurfaces have shown extraordinary ability to manipulate the wavefront of electromagnetic wave and varieties of functional devices have been proposed. However, due to the dispersion of the phase accumulated in the light path, the metasurfaces suffer from large chromatic aberration and thus limit their usages in many domains. Here, a metasurface-based circularly polarized broadband reflective device is proposed, focusing on the directional reflectors and focusers constructed by metasurface elements, to eliminate the chromatic aberration. Utilizing the principle of the generalized Snell's laws and focusingcompensation, a one-dimensional deflector with 16 sub-arrays consisted of 19 geometricresonance combined phase shift elements is proposed. The reflector covers a continuous phase range from 90 to 360 and its efficiency remains over 50 percent in an expanded spectrum Compared with previously proposed structures, a much broader bandwidth and higher efficient achromatic aberration has been achieved, spanning from 0.37 THz to 0.5 THz, a relative bandwidth of 35 percent, which remains the fixed reflective angle of 20° stably, highly in consistent with the theory angle of 19.84°. Based on the one-dimensional achromatic sub-array, we further construct a two-dimensional wide-band parabolic-like focusing metasurface. The focal length is 40 mm fixed and its NA (numerical aperture) is 0.291. The simulation results are in good accordance with theoretical prediction. The proposed method to suppress the chromatic aberration paves an innovative way to control the phase dispersion at will and allow some advancement in optical systems, corrected imaging systems, and in full-color detection.