ABSTRACT Nanophotonic color routers promise higher photon utilization than absorptive color filters for complementary metal‐oxide‐semiconductor (CMOS) image sensors, yet most reported designs remain optimized for normal incidence, with efficiency dropping to about half of its peak by . Here, we present an angle‐specific inverse‐design framework in which the sensor plane is partitioned into local angular zones, and each zone is assigned a dedicated color‐router unit cell. To enable practical assembly of these heterogeneous unit cells, we introduce an optical structural similarity (OSS) constraint that enforces permittivity‐level continuity between neighboring cells during topology optimization without additional full‐wave simulations. In a three‐dimensional freeform library, the optimized unit cells achieve average optical efficiencies of 91.1%, 80.9%, and 83.9% for the red, green, and blue channels, respectively, with optical cross talk below 2.0%. OSS reduces the average stitching error from 24.6% to 5.99%, suggesting that it may provide an effective means of suppressing stitching errors in metasurface designs based on the locally periodic approximation. The framework further extends to a five‐layer architecture with a comparable stitching error of 5.65%, establishing a practical route to oblique‐incidence‐robust, library‐based color routing and, more broadly, to large‐area metasurfaces requiring spatially varying functionality with robust inter‐cell compatibility.
Kim et al. (Mon,) studied this question.