3D printed designer color routers with low refractive index for low-light imaging.

Color imaging systems that underpin modern technologies still suffer in low-light conditions because of the inherently lossy filtering mechanism of conventional Bayer color filters. Although Bayer-type filters integrated with complementary metal-oxide-semiconductor sensors remain the dominant architecture, they typically transmit only about 30% of incident white light, leading to noisy images under weak illumination. Color routers offer an alternative by redirecting different spectral components of light to corresponding photodiodes in the near field. While recent color routers based on high-refractive-index metasurfaces have shown promise, low-refractive-index materials remain largely unexplored despite their potential for higher transmittance and cost-effective mass production. Here, we demonstrate inverse-designed, two-photon-polymerization 3D-printed pixel-level color routers using low-index IP-L resin (n ≈ 1.5). The color routers achieve transmittance of ~87% in simulation and ~70% experimentally across the visible spectrum. Monochrome-sensor imaging further confirms improved color fidelity and shorter exposure times, highlighting their potential for next-generation high-efficiency imaging platforms.