<p>This study presents the design and numerical analysis of an anti-resonant optical fiber structure based on a nested configuration for temperature sensing. The proposed sensor incorporates an elliptical cladding tube geometry. Gold (Au) and titanium dioxide (TiO₂) films are coated on the inner surface to form a dual-loss layer, enabling the excitation of coupled resonant modes. In addition, an internal elliptical nested structure is introduced to further tailor the modal characteristics and improve temperature sensitivity. Through structural and material optimization, numerical simulations indicate that the proposed sensor operates based on lossy mode resonance (LMR) and surface plasmon resonance (SPR) mechanisms. Within the temperature range of 20–40 ℃, a temperature sensitivity of up to 4.3&#xa0;nm/℃ is achieved, demonstrating enhanced spectral response to temperature variations. In addition to temperature sensing, the proposed configuration also exhibits potential for refractive index detection due to its resonance-based operating mechanism, suggesting broader applicability in sensing scenarios requiring high spectral sensitivity.</p>