Today, Inline Closure manufacturers share a variety of reasons for fiber attenuation:

The main factors causing fiber attenuation are: intrinsic, bending, extrusion, impurities, unevenness and docking.

Intrinsic: is the inherent loss of fiber, including: Rayleigh scattering, inherent absorption.
Bending: When the fiber is bent, the light in some of the fibers will be lost due to scattering, resulting in loss.
Extrusion: Loss caused by tiny bends in the fiber when it is squeezed.
Impurities: Impurities in the fiber that absorb and scatter light propagating in the fiber.
Uneven: loss due to uneven refractive index of the fiber material.
Docking: Loss caused when the fiber is docked, such as: different axes (single mode fiber coaxiality requirement is less than 0.8μm), the end face is not perpendicular to the axis, the end face is not flat, the butt diameter is not matched, and the welding quality is poor.

When light is incident from one end of the fiber and emitted from the other end, the intensity of the light is weakened. This means that after the optical signal propagates through the fiber, the light energy is attenuated. This means that some substances in the fiber or for some reason block the passage of the light signal. This is the transmission loss of the fiber. Only by reducing the fiber loss can the optical signal be unobstructed.

information about Inline Closure : https://www.greentelftth.com/product/fiber-optical-splice-closure/inline-fiber-optical-splice-closure/