Numerical Investigation of Temperature-Induced Attenuation in Fibers for High-Temperature Well Applications

This study presents a systematic investigation of high-temperature effects on optical fiber telemetry and distributed sensing in oil and gas applications, integrating theoretical analysis with numerical simulations. Within the framework of the thermo-optic effect, this study investigated the signal attenuation mechanisms in multimode fibers (MMFs) and single-mode fibers (SMFs) under downhole temperatures ranging from 303.15 K to 473.15 K. First, numerical simulations indicate that at 473.15 K, MMFs exhibit significantly lower attenuation than SMFs. Second, quantitative analysis at the 1.55 μm communication wavelength shows that the thermo-optic effect substantially reduces signal bandwidth. MMFs demonstrate pronounced temperature-dependent dispersion, whereas SMFs display linear phase evolution at frequencies above 0.013 Hz. Finally, the attenuation characteristics of both fiber types were further evaluated across various operating wavelengths under high-temperature conditions. MMFs exhibit an attenuation peak at 1.55 μm, beyond which attenuation increases exponentially with wavelength. For SMFs, the mode field diameter (MFD) increases with wavelength but decreases linearly with rising temperature. These findings offer crucial insights for selecting optical fibers in high-temperature sensing applications. The SMFs exhibit significantly enhanced performance compared to MMFs in downhole optical telemetry applications under high-temperature conditions at the 1.55 μm communication wavelength. The characterized MFD variations in SMFs under different wavelengths and temperatures enable effective evaluation and compensation of thermal-induced MFD variations. This work establishes a theoretical foundation for developing temperature-compensated signal processing algorithms and advanced downhole optoelectronic telemetry systems.