The transmission loss of fiber optic cables is influenced by multiple factors, which can be categorized into four main types: fiber material and structural characteristics, construction defects, environmental stress, and improper operation and maintenance. Each category leads to optical signal energy attenuation through different mechanisms.
The fiber material and structural characteristics are the intrinsic basis for transmission loss. Fiber optics consist of a core, cladding, and coating. Loss primarily originates from material absorption, scattering, and structural defects. In terms of material absorption loss, quartz glass inherently absorbs light of specific wavelengths (such as ultraviolet and infrared), and impurities (such as iron and copper ions) enhance this absorption effect. Scattering loss is mainly Rayleigh scattering, the intensity of which is inversely proportional to the fourth power of the wavelength; shorter wavelength signals are more susceptible. Regarding structural defects, issues such as uneven core diameter, inconsistent mode field diameters, and misalignment between the core and cladding can cause mode coupling or energy leakage during transmission, resulting in inherent loss.
Construction defects are the direct cause of transmission loss. Splice loss is a typical example, and its occurrence is closely related to factors such as axial misalignment, axis tilt, end-face separation, and incomplete end-face. For example, axial misalignment can cause energy leakage of the optical signal at the splice point, while end-face contamination (such as dust and oil) can lead to scattering loss. Connector loss is also significant; poor contact, poor quality, and axial misalignment can disrupt continuous optical signal transmission. Furthermore, improper construction practices, such as excessively small fiber bending radii (less than 10 times the outer sheath diameter), excessively tight loops in the cable, and excessive traction, can cause macro-bending loss or micro-bending loss, leading to the conversion of the conducted mode into a radiating mode, which is then absorbed by the cladding.
Environmental stress is a dynamic factor contributing to transmission loss. Fiber optic cables are exposed to the natural environment for extended periods, enduring the combined effects of temperature changes, mechanical stress, and chemical corrosion. Temperature changes cause thermal expansion and contraction of the fiber, leading to micro-bending loss; mechanical stress (such as wind vibration or vehicle crushing) can cause tensile deformation or structural damage to the fiber; and chemical corrosion (such as acid rain and salt spray) can damage the coating and accelerate fiber aging. For example, if directly buried optical cables are not buried deep enough, they are easily damaged by heavy vehicles, leading to hydrogen loss (hydrogen molecules penetrate into the fiber to form hydroxide ions, increasing absorption loss).
Improper operation and maintenance are potential risks that exacerbate transmission loss. Problems such as improper cable mounting, inadequate heat shrink protection, and improper splice box sealing directly increase loss. For example, twisting multiple loose tubes or using excessively tight cable ties during cable mounting can cause sharp bend losses; poor quality heat fusion protection tubes or improper heating parameter settings can produce bubbles or deformation, damaging splice points; improper splice box sealing leading to water ingress can cause hydrogen loss or corrosion loss. Furthermore, long-term lack of maintenance can cause gradual accumulation of loss due to aging of the outer sheath and improper fiber coiling.
The transmission loss of fiber optic cables is the result of the combined effects of materials, construction, environment, and operation. To reduce loss, it is necessary to control fiber quality from the source, strictly standardize construction processes, strengthen environmental adaptability design, and establish a regular maintenance mechanism. For example, selecting high-quality optical fibers with consistent characteristics, adopting scientific and reasonable traction methods, choosing weather-resistant outer sheath materials, and regularly testing fiber attenuation can all effectively improve the transmission performance and reliability of fiber optic cables.
