A Flexible Metamaterial Absorber via Loss Engineering for Large‐Area Ultra‐Broadband Infrared Extinction

ABSTRACT The advancement of compact and wearable optical systems is critically limited by the lack of high‐performance, integrable solutions for managing stray light, particularly in the mid‐infrared regime. Traditional approaches relying on bulky baffles or cryogenic cooling hinder miniaturization and flexibility. Herein, we report a large‐area, flexible metamaterial film based on a Ti/Al ₂ O ₃ /Fe ₃ O ₄ /Ti heterostructure that functions as an ultra‐broadband infrared extinction layer. By introducing a lossy Fe ₃ O ₄ interlayer, our design achieves an exceptional average absorptivity of 97.1% across the 3–5 µm atmospheric window, with a total thickness below 1 µm. This “loss engineering” strategy effectively broadens the absorption bandwidth and smoothens the spectral response compared to conventional metal‐insulator‐metal(MIM) absorbers. The film is fabricated on a flexible polyimide substrate via scalable lithography, demonstrating remarkable mechanical robustness. More importantly, we integrate it into a practical optical system as a cylindrical baffle, where it suppresses stray light intensity to a mere 0.6% after three reflections, significantly enhancing imaging contrast. This work presents not merely a high‐performance absorber, but a scalable, flexible material platform that paves the way for next generation miniaturized and flexible optical devices.