Terahertz Reflective Metalens For Arbitrary Off-Axis Focusing With Large Depth of Focus

This paper reports a reflective metalens composed of fifteen rotationally symmetrical metal resonator-dielectric- metal structure with 24° step phase response by changing the geometry of the resonators and arranged by the derived phase distribution formula. An off-axis focusing with an angle of 1.20° is realized by the metalens at 2.52THz. The depth of focus (DOF) is at least 16mm. The off-axis metalens can reduce the interference between the incident and reflected wave, and arbitrarily control the spatial location of the focus, which remains stable while the position of the incident wave changes within a certain range.