Though metalenses are a promising advance in scaling down the size of optical systems, there are challenges, both in designing them and manufacturing them to scale.
One challenge with metalenses is designing a metalens with millions of variable subwavelength unit-cells, called meta-atoms, to modulate light locally and coherently requires design experience and a deep understanding of fundamental physics. Metalens designs involve defined lens phase profiles, a meta-atom library, and layout of the meta-atoms on the metalens surface. Then, the optical designer must choose an approach to simulate the built metalens to evaluate its performance.
If manually designing a metalens, the approach relies on a pre-defined phase profile, which is valid for a fixed incident condition only because the transfer function of the meta-atoms varies at different wavelength, incident angle, and polarization. Therefore, a phase profile optimized at a particular incident condition is not valid at others. As a result, it is very difficult to design a metalens with multiple functions, such as an achromatic lens for a wide spectral range or a large field of view (FOV) lens for wide incident angles.
Could there be a user-friendly design tool to automate metalens design for engineers to design metalens systems quickly and easily? Though significant efforts have been made worldwide to develop automation flows with inverse design capabilities, Synopsys has developed the first fully automated commercial tool, MetaOptic Designer, that provides inverse design capabilities for metaoptics. The optimization algorithm employs the well-known adjoint method, which can easily handle millions of design variables.
To design a metalens in MetaOptic Designer, the user specifies the set of lenses in the optical system and the BSDF database for each, as well as the desired target patterns and focus lengths. Then, the tool determines the design parameters across each metasurface and exports GDS and optimization results, shown in figure 1.