What are the primary causes of intrinsic loss in single-mode fiber?

The primary causes of intrinsic loss in single-mode fiber are material absorption and Rayleigh scattering.

Material absorption occurs when the light propagating through the fiber is absorbed by the materials that make up the fiber, such as glass. This loss is a fundamental characteristic of the fiber's material properties and is influenced by the wavelength of the light being transmitted. In a single-mode fiber, the refractive index profile and purity of the glass significantly affect how much light is absorbed.

Rayleigh scattering is another intrinsic loss mechanism that arises from the microscopic variations in the density of the glass material. As light travels through the fiber, it encounters these density fluctuations, causing some of the light to scatter in different directions. This scattering increases with shorter wavelengths and contributes to the overall attenuation of the signal.

Understanding these intrinsic losses is crucial for optimizing fiber optic systems, especially in long-distance communication, as they directly affect the performance and efficiency of the fiber. Other options in the question involve factors that either do not represent intrinsic losses (like connector and splice losses, which are extrinsic) or refer to physical conditions affecting fiber performance rather than losses inherent to the fiber's material properties.