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Differential evolution and transfer matrix simulations for designing high performance broadband near-IR to longwave-IR optical coatings

Broadband and omnidirectional anti-reflection coatings, Distributed Bragg Reflectors (DBR), and optical bandpass filter coatings in the 3-5 μm and 1-12 μm IR ranges are of crucial importance in the design of high-efficiency MWIR / LWIR detectors, Thermophotovoltaic devices, and IR imaging systems. We discuss a novel inverse design approach to multilayer optical coatings by a Transfer Matrix Method simulation and optimization algorithm. This algorithm iteratively simulates a multilayer structure's reflection and transmission characteristics by the Transfer Matrix Method and updates layer thicknesses to optimize a performance metric – whether reflection, transmission, or filter performance – over a given band and range of angles of incidence. The optimization procedure provides a systematic, computational approach to designing optical coatings with desired reflection, transmission, and absorption characteristics over wavelength bands and angles of incidence of interest in an application. We show that Distributed Bragg Reflectors and Anti-reflection coatings generated by the algorithm outperform conventional quarter-wavelength layer coatings over broadband MWIR and LWIR ranges and angles of incidence as high as 70 degrees, while reducing total component thickness significantly – a major benefit when fabricating optical coatings on semiconducting substrates directly. We also discuss how the approach can be extended to sharp-cutoff broadband bandpass filter design.