In this study, we present the design and numerical investigation of a six-layer planar optical absorber with ultra-broadband absorption characteristics. The proposed structure consists of alternating metallic and dielectric multilayer thin films, enabling efficient electromagnetic energy dissipation over a wide spectral range from 300 to 4000 nm. Finite element simulations using COMSOL Multiphysics (version 6.0) were performed to evaluate the optical response, including reflectance, transmittance, and absorptivity, based on the energy conservation relation A = 1 − R − T. The results show that the absorber achieves absorptivity exceeding 0.9 across a broad wavelength range, demonstrating strong robustness against structural variations. The broadband absorption behavior is associated with electromagnetic coupling and energy attenuation within the multilayer structure. Electric and magnetic field distributions at representative wavelengths of 320, 540, and 1920 nm reveal progressive field attenuation through the stacked layers, suggesting wavelength-dependent electromagnetic interactions and material losses. These characteristics contribute to the broadband optical response and provide useful design considerations for optical sensing and energy absorption applications. From a sensing perspective, such non–cavity-based absorption behavior provides improved spectral stability and consistent response across wavelengths, which is advantageous for broadband optical sensing applications. The fully planar configuration offers potential advantages in fabrication simplicity and structural scalability. Although experimental validation remains necessary, the simulated broadband absorption characteristics suggest possible applications in optical sensing, infrared detection, and solar energy harvesting systems.