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

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/Al₂O₃/Fe₃O₄/Ti heterostructure that functions as an ultra-broadband infrared extinction layer. By introducing a lossy Fe₃O₄ 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.