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

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). We introduce plasmon-enabled DBRs (PE DBRs) based on modulation-doped monolithic InP, where plasmonic dispersion in highly doped layers provides a strong refractive-index contrast. Using inverse-design optimization targeting reduced free-carrier absorption and maximized reflectivity, we demonstrate that PE DBRs can achieve reflectivities approaching 100%. Experimentally grown 14 μm thick InP PE DBRs exhibit up to 99% reflectance with bandwidths reaching 18% of the design wavelength. The monolithic, junction-free configuration ensures low resistivity and enhanced thermal performance, offering a scalable platform for efficient plasmonic mirrors in MIR photonics, with potential applications in photodetectors, light-emitting diodes and lasers.