# Inverse Design of Optical Color Routers with Improved Fabrication Compatibility

## TL;DR

This paper introduces a new design framework for optical color routers that improves fabrication compatibility and efficiency using a genetic algorithm and nano-patterned surfaces.

## Contribution

The novel contribution is a fabrication-compatible, single-layer nano-patterned surface for efficient color routing in optical systems.

## Key findings

- The nano-patterned surface achieved peak optical efficiencies of 76%, 72%, and 78% for blue, green, and red channels.
- Parametric studies showed performance dependence on pillar geometry, refractive index, and unit cell scaling.
- The design enables tunable-mirror-based reflective displays with an expanded color gamut beyond sRGB.

## Abstract

We present a Genetic Algorithm (GA)-based inverse design framework for creating a single-layer, fabrication-compatible dielectric nano-patterned surface that enables efficient color routing in both transmissive and reflective optical systems. Unlike traditional multilayer or absorption-based color filters, the proposed structure employs a fabrication-compatible architecture that spatially routes red, green, and blue light into designated output channels, significantly enhancing light utilization and color fidelity. The design process integrates a GA with full-wave finite-difference time-domain (FDTD) simulations to optimize the structural pillar height distribution, using a figure of merit that simultaneously maximizes optical efficiency and minimizes spectral crosstalk. For CMOS image sensor-scale designs, the nano-patterned surface achieved peak optical efficiencies of 76%, 72%, and 78% for blue, green, and red channels, respectively, with an average efficiency of 75.5%. Parametric studies further revealed the dependence of performance on pillar geometry, refractive index, and unit cell scaling, providing practical design insights for scalable fabrication using nanoimprint or grayscale lithography. Extending the approach to reflective displays, we demonstrate tunable-mirror-based architectures that emulate electrophoretic microcapsules, achieving efficient color reflection and an expanded color gamut beyond the sRGB standard. This single-layer, inverse-designed nano-patterned surface offers a high-performance and fabrication-ready solution for compact, energy-efficient imaging and display technologies.