Ultra-broadband optical absorbers are essential components in modern photonic and sensing systems, where efficient light absorption over a wide spectral range is required to enhance device performance and environmental adaptability. In this study, a simple yet highly efficient ultra-broadband optical absorber is proposed using only two materials: silicon nitride (Si3N4) and chromium (Cr). The absorber features a nine-layer architecture, in which a Cr reflective layer forms the bottom substrate, followed by alternating planar Cr and Si3N4 layers from the second to the eighth layer. The topmost layer consists of Cr cylindrical structures that further enhance broadband absorption through additional optical coupling and intrinsic material loss. By systematically optimizing key structural parameters, including layer thicknesses and cylinder diameters, the proposed design achieves absorptivity exceeding 0.900 over an ultra-broadband wavelength range from 300 to 3850 nm. Compared with previously reported ultra-broadband absorbers that rely on complex nanostructures and multiple-material systems, the present design significantly simplifies fabrication and reduces the risk of vacuum process contamination while maintaining excellent optical performance. These results demonstrate a practical and scalable approach for realizing high-performance ultra-broadband optical absorbers, offering strong potential for applications in optical sensing, photodetection, and energy-related devices.