Fiber Optic Cable Distance: A Comprehensive Guide

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Do you often receive questions like, “Where is the home fiber modem connected to the fiber?” or “What is the max distance of fiber optic cable?”

In this blog, I will discuss the fiber optic cable distance, the effect factors, how to choose the right fiber optic cables, and how to compare the transmission distances of single-mode and multimode fiber optic cables.

Let’s dive deeper together!

What Factors affect the fiber optic cable distance?

Many factors decide the fiber cable distance, but the key factors include the below six aspects.

#1. Attenuation

First is the attenuation of the optical fiber. Attenuation is the weakening of light as it comes in from the transmitting end of the fiber and out of the transmitting end. For some reason, some substance in the fiber blocks the transmission of the light signal inside the fiber.

Many factors cause attenuation in fiber optic cables: inherent loss, bending, impurities, refractive index, butt joints, and so on.

Intrinsic loss: Rayleigh scattering, inherent absorption.
Bending: The fiber is squeezed, and other reasons cause bending, which causes part of the light to be lost due to scattering, resulting in attenuation.
Impurities: impurities within the fiber absorb and scatter the light propagating in the fiber.
Refractive index: uneven refractive index of the fiber material causing loss.
Docking: Losses occur when optical fibers are docked.

#2. Chromatic Dispersion

Dispersion of an optical fiber directly affects the bandwidth and distance capability of the fiber optic link and reduces its efficiency. The higher the dispersion, the lower the potential data rate and transmission distance.

Leading causes of optical fiber dispersion include the physical characteristics of the fiber (e.g., core diameter and refractive index), the wavelength of the propagating light, and the operating temperature. In multimode fibers, the different path lengths taken by the light can also contribute to dispersion.

#3. Optical Power

The more power coupled into the fiber, the longer the transmission distance. There are three main reasons for this:

Firstly, the higher the power, the lower the loss of the optical signal as it travels through the fiber, allowing for longer distances.
Secondly, the high input power increases the signal strength at the receiving end, and the signal-to-noise ratio increases under a relatively constant noise level, increasing the sensitivity at the receiving end and thus increasing the transmission distance.
Finally, from a connector perspective, high optical power can allow more connectors to be used for the same receiver sensitivity, extending the transmission distance.

#4. Receiver Sensitivity

Higher receiver sensitivity means that it can detect weaker optical signals. Even if the optical signal power is low, the receiver can still detect and decode the signal correctly, extending the transmission distance of fiber optic communication.

Another consideration is that due to the lower received power, the optical signal can be transmitted longer distances in the fiber before it decays to the receiver’s minimum detection threshold.

#5. Bandwidth

Transmission distance decreases as the bandwidth increases. For example, a fiber optic cable with a distance of 1km supports a bandwidth of 500MHz, while a fiber optic cable with a distance of 2km can only support a bandwidth of 250MHz.

There are three main reasons for this:

First, high-bandwidth signals are more susceptible to chromatic dispersion than low-bandwidth signals, so the transmission distance is shortened.
Second, high-bandwidth optical signals are usually more lossy to the fiber.
Finally, high-bandwidth signals contain a more comprehensive spectral range and are subject to more attenuation and absorption.

#6. Number of Splices and Connectors

Splices and connectors are inevitable in most fiber optic cable systems. When light passes through them, it inevitably causes loss.

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