Free-space Coupling Enhancement for Photonic Integrated Circuits Using Focusing Metalens

An inspiring free-space coupling strategy which may thrive the development of photonic integrated circuits (PIC) on weak signal applications is reported. By applying a metalens above grating coupler, the coupled power from free-space gets significantly enhanced. The theoretical estimation on coupling efficiency verified by coupling tests offers instructions on the optimization of metalens and coupler design. With a self-designed grating coupler and metalenses, a maximum enhanced power which is 1662.8 times as that of normal coupling strategy was obtained. Additionally, we tested the array-to-array coupling and achieved a remarkable enhancement which exhibits great potential for multi-channel PIC applications.