Multifocal metalens with enhanced energy harvesting and wide acceptance angle characteristics.

Traditional metalenses prioritize diffraction-limited imaging, which frequently encounters nanofabrication bottlenecks due to steep phase gradients and high sensitivity to incident angles. This study shifts the design paradigm toward efficient energy harvesting by proposing a multifocal metalens. Instead of pursuing a singular diffraction-limited spot, we construct a focal-cluster architecture within a defined spatial region to enhance system robustness. To systematically verify this approach, twenty metalenses with varying numerical apertures (NA) and inter-focal distances were designed and fabricated on amorphous silicon (α-Si). Experimental results demonstrate that this multifocal strategy effectively smooths local phase gradients, significantly reducing manufacturing difficulty. For a high-NA design (NA = 0.92), the focusing efficiency was improved from 32% to 55%, representing a 72% relative improvement. Furthermore, the device maintains exceptional stability within an incident angle window of 0° to 10°, with efficiency fluctuations remaining below 10%. By delivering superior angular tolerance and throughput, this multifocal approach provides a highly reliable, hardware-level photon-collection solution for alignment-sensitive optoelectronic integration, a reliable micro-optical solution for alignment-sensitive non-imaging applications, such as photoelectric detection.