Experimental Demonstration of Plasmon‐Enabled Monolithic Bragg Reflectors for Infrared Light via Inverse Design

ABSTRACT High‐reflectivity mirrors in the mid‐infrared (MIR) range are essential for next‐generation optoelectronic devices but are still constrained by strain accumulation, poor thermal conductivity, and growth instability of thick multi‐alloy stacks in conventional distributed Bragg reflectors (DBRs). Building on the previously proposed concept of plasmon‐enabled DBR (PE DBR), we demonstrate inverse‐designed PE DBR based on modulation‐doped monolithic InP, where plasmonic dispersion in highly doped layers provides a strong refractive‐index contrast required for Bragg reflection. Using inverse‐design optimization targeting reduced free‐carrier absorption and maximized reflectivity, we show that the reflectivity of PE DBRs gradually increases toward unity with an increasing number of layer pairs. Experimentally grown thick InP PE DBRs exhibit up to 99% reflectance with bandwidths reaching 18% of the design wavelength. The monolithic, junction‐free configuration provides low resistivity and is expected to reduce thermal limitations associated with alloy disorder and heterointerfaces, offering a scalable platform for efficient plasmonic mirrors in MIR photonics, with potential applications in photodetectors, light‐emitting diodes and lasers.