Fiber Loss

What is Fiber Loss?

Fiber loss can be also called fiber optic attenuation or attenuation loss, which measures the amount of light loss between input and output. Factors causing fiber loss are various, such as intrinsic material absorption, bending, connector loss, etc.

What are the Types of Optical Fiber Losses？

Losses in the optical fiber can be categorized into intrinsic optical fiber losses and extrinsic optical fiber loss depending on whether the loss is caused by intrinsic fiber characteristics or operating conditions. Intrinsic optical fiber losses comprise absorption loss, dispersion loss, and scattering loss caused by structural defects. Extrinsic optical fiber losses contain splicing loss, connector loss, and bending loss.

Intrinsic Optical Fiber Losses

1. Absorption losses in optical fiber are the major cause of optical fiber losses during transmission. When the photon interacts with the components of the glass, an electron, or metal ions, the light power is absorbed and transferred into other forms of energy like heat, due to molecular resonance and wavelength impurities.

2. Dispersion losses are the result of the distortion of the optical signal when traveling along the fiber. Dispersion losses in optical fiber can be intermodal or intramodal. Intermodal dispersion is the pulse broadening due to the propagation delay differences between modes in multimode fiber. Intramoal dispersion is the pulse spreading in single mode fiber because the refractive index or the propagation constant varies with wavelength.

3. Scattering losses in optical fiber are due to microscopic variations in the material density, compositional fluctuations, structural inhomogeneities, and manufacturing defects.

Extrinsic Optical Fiber Losses

1. Fiber optic splicing is another type of loss in optical fiber. By joining two optical fibers end-to-end, splicing aims to ensure that the light passing through it is almost as strong as the virgin fiber itself. But no matter how good the splicing is, the splicing loss is inevitable. Fusion splicing losses of multimode fiber are 0.1-0.5 dB, 0.3 dB being a good average value. For single mode f fiber, the typical fusion splicing loss can be less than 0.05 dB.

2. Connector losses or insertion losses in optical fiber, are the losses of light power resulting from the insertion of a device in a transmission line or optical fiber. Multimode connectors will have losses of 0.2-0.5 dB (0.3 typical). Factory made single mode connectors will have losses of 0.1-0.2 dB and field terminated single mode connectors may have losses as high as 0.5-1.0 dB (0.75 dB, TIA-568 max acceptable).

3. Bending is a common problem that can cause optical fiber losses generated by improper fiber optic handling. There are two basic types. One is micro bending, and the other one is macro bending (shown in the picture below). Macro bending refers to a large bend in the fiber (with more than a 2mm radius).

How to Calculate Losses in Optical Fiber?

It is often the case to calculate the maximum signal loss across a given fiber link during optical cable installation. First, you should be aware of the fiber loss formula:

The Total Link Loss = Cable Attenuation + Connector Loss + Splice Loss

Cable Attenuation (dB) = Maximum Cable Attenuation Coefficient (dB/km) × Length (km)

Connector Loss (dB) = Number of Connector Pairs × Connector Loss Allowance (dB)

Splice Loss (dB) = Number of Splices × Splice Loss Allowance (dB)

As these formulas show, the total loss is the maximum sum of the worst variables within a fiber segment. It must be noted that the total loss calculated in this way is just an estimation that assumes the possible values of component losses so the actual loss could be higher or lower depending on various factors."