Analysis of Tapered Nanopillars for Reflective Metalens: The Role of Higher-Order Modes

Abstract

Despite the widespread interest in the metalens technology, few works show the errors during fabrication and analyze how they influence the focusing performance. In this work, we proposed a reflective metalens design and carry out a fundamental study on how a mild tapering angle (<6°) of the nanopillars would influence the performance of a reflective metalens. By analyzing the interaction of Mie resonance in the lateral direction and Fabry-Pérot resonance in the longitudinal direction using numerical simulations, we reveal the detrimental role the tapering angle plays due to the low transmission near the resonance. We observe the weakening of the electric quadrupole and magnetic dipole response, and the increase of the electric dipole response for tapered nanopillars. Moreover, the Fabry-Pérot resonance is disturbed due to the broken symmetry. These factors contribute to lower Q factor resonance and hence the low transmission. The results presented in this work can guide the analysis of fabrication errors and provide insights on how to compensate them.

Multipolar Analysis in Symmetrical Meta-Atoms Sustaining Fano Resonances

“…At P = 350 nm, the resonance almost vanishes and the absorption falls below 10%. It is worth noticing that such strong variation of the resonance depth is inherently related to the intrinsic losses included in the model, for such behavior was not observed in previous studies where intrinsic losses were neglected [46,47]. By further increasing the pitch, the absorption and the transmittance dip increase again, reaching almost zero transmittance at P = 380 nm.…”

The Effect of Height Error on Performance of Propagation Phase-Based Metalens

“…This conclusion can be confirmed by comparing Figure 4c,d. Figure 4b shows that when a = 155 nm and the height of the nanobricks has a negative deviation, there is no expected phase shift theoretically, mainly because the appearance of Fabry-Pérot resonance alleviates the phase shift caused by the waveguide mode [28,50]. Specifically, the side length a affects the shape and size of the nanobricks, which in turn affects the effective refractive index of the structural unit.…”

“…Despite significant advancements in design theory enabling the creation of highly efficient metalenses, the introduction of fabrication errors during manufacturing has often led to final device performances falling short of expectations [23][24][25][26][27]. In recent years, some researchers have delved into the effects of sidewall tilting, lateral dimension variation, and process defects of structural units on the performance of metalenses [28,29]. They have discovered that sidewall tilting leads to the proximity of neighboring structures, resulting in stronger structural resonance, which affects the efficiency of the metalens.…”