Designing high‐efficiency extended depth‐of‐focus metalens via topology‐shape optimization

Longitudinal optical field modulation is of critical importance in a wide range of applications, including optical imaging, spectroscopy, and optical manipulation. However, it remains a considerable challenge to realize a uniformly distributed light field with extended depth‐of‐focus. Here, a high‐efficiency extended depth‐of‐focus metalens is proposed by adjoint‐based topology‐shape optimization approach, wherein the theoretical electric field intensity corresponding to a variable focal‐length phase is utilized as the figure of merit. Using a dozen of metalens with random structure parameters as initial structures, the average focal depth of topology‐shape optimized metalens is greatly improved up to 18.80 μm (about 29.7 λ ), which is 1.54 times higher than the diffraction‐limited focal depth. Moreover, all the topology‐shape optimized metalens exhibit high diffraction efficiency exceeding 0.7 over the whole focal depth range, which is approximately three times greater than that of the forward design. Our results offer a new insight into the design of extended depth‐of‐focus metalens and may find potential applications in imaging, holography, and optical fabrication.