Investigation of Phase Modulation of an Analogue Temperature Signal in a Single-Mode Fibre

This article investigates the influence of temperature fluctuations on the performance of optical fibre communication systems. In the context of climate change, increasing environmental challenges, and the rising density of communication infrastructure, maintaining optimal system parameters---especially over long distances in harsh climates such as mountainous terrain or the Far North—poses significant difficulties. The research focuses on the characterisation of Rayleigh scattering losses ($\alpha_{RS}$) in single-mode optical fibres fabricated by different technological methods (VAD and MCVD), with varying germanium dioxide (GeO${}_2$) doping concentrations. A linear empirical relationship between $\alpha_{RS}$ and the relative refractive index difference ($\Delta$) was established based on experimental data. A dedicated experimental setup was developed to study the effect of temperature on scattering losses using a 10~km length of fibre exposed to controlled temperature conditions. Measurements demonstrated that $\alpha_{RS}$ increases significantly with higher GeO${}_2$ concentrations at sub-zero temperatures. However, in fibres with 3.5---5 mol~\% GeO${}_2$, the losses remain low enough to ensure long-distance data transmission without amplification. The findings suggest that thermal stabilisation may be unnecessary for systems operating in moderate cold climates. The article also discusses the influence of temperature variations on the phase modulation of analogue signals in fibre-optic communication lines.