In fiber Optic cable, data is transmitted and received in the form of light.
(Spelt “Fiber” in American English and “Fibre” in UK English.)
The speed of light as we generally refer to it, is the speed of light in a vacuum. The cores of optic fiber cables, where the signals travel, are not vacuums but mostly consist of transparent glass or transparent plastic.
There are several factors that will affect how fast data will travel in a fiber optic cable. Because of these factors, data does not travel at exactly the same speed in all fiber optic cables. I will go into some of these factors in more detail further down in this article.
The short answer is that, in optic fiber cable, the light will travel at around two thirds of what the speed of light would be in a vacuum.
Light in a vacuum travel at roughly 186 000 miles per second, or 300 000 Kilometers per second.
Data in the form of light in optic fiber cable travel at roughly 124 000 miles per second, or 200 000 Kilometers per second.
To put this in perspective:
Let’s imagine that the surface of the earth was a perfectly smooth sphere, and we could run fiber optic cable in a straight line around the equator. We would also have to ignore things like signal degradation (attenuation) over such a long distance.
The formula for the time that it will take to travel a given distance is Time = Distance ÷ Speed
The circumference of the earth at the equator is 24 901 miles or 40 075 Km.
24 901 miles ÷ 124 000 miles per second = 0.2 seconds
40 075 Km ÷ 200 000 Kilometers per second. = 0.2 seconds
This means that it will take the data in our optic fiber cable about 0.2 seconds to travel around the earth once. At this speed, data can go around the earth five times per second.
Time delay in optic fiber cable calculator.
You can use the Timbercon calculator to do your own calculations, but you may want to read the below first to get a better understanding of things that you have to enter to do the calculation.
Factors that will influence the speed of data in a fiber optic cable
As mentioned earlier, there are many factors that will affect the speed of the data in the cable.
Keep in mind however that when you send and receive data, the data does not simply go into one end of a single fiber optic cable and comes out at the destination at the other end. Instead, it must be routed through an infrastructure that is not in a straight and level line and passes through various types of equipment and cables.
Wavelength
As with radio signals, data in fiber optic cables are also sent in various wavelengths. Different wavelengths bring about different attenuation factors, which are the losses in the cable.
Higher wavelengths are more suitable for longer distances and higher speed.
Wavelengths in fiber optic transmission are measured in nanometers. (nm)
850nm, 1300nm, and 1550nm are commonly used wavelengths in fiber optic data transmission.
850nm wavelengths are used for shorter distances at lower speed. 1550nm are used for longer distances at higher speed.
Mode
Data can be sent through an Optic Fiber cable in single mode, or multi-mode.
Single mode cables have a smaller core diameter than multimode cables.
Multimode
Multimode is when light is sent down the core at a shallow angle and reflected off the inside of the core in a zig zag pattern along the length of the cable.
This allows for multiple signals, or modes to be sent through the core at the same time.
Multimode is more suitable for shorter distances at lower speed.
Single mode
Single mode is when data is transmitted in a single core in a single beam of light down the center of the core with minimal reflection of the light. The data will travel further, and the distance will be shorter as the light follows a more direct path inside the core. Single mode cable is therefore more suitable for use over long distances at higher speed.
Cable material
Light travels at different speeds through different types of material. The type of material that is used in the manufacture will have a significant impact on the speed at which the signal will travel through the material.
This is then given as the refraction index of the cable by dividing the speed of light through a vacuum, by the speed of light through the cable material.
Core diameter
The diameter of the cores of fiber optic cable are measured in microns. (um / µm)
1 µm = 0.00003937 inch, or 0.001 mm
Core dimeters vary, but common core diameters are 8.3µm, 50µm and 62.5 µm
8.3µm is used for Single mode over longer distances.
50µm and 62.5 µm are used for Multimode over shorter distances.
Internet speed.
Although not directly related to the speed at which data will travel in fiber optic cable, this is an important factor.
When you send and receive data, the data volume is a substantial factor that will affect your noticeable internet speed.
When you sign up for an internet plan, or do a speed test, the speed is not measured in how fast your data will travel along the cable, but rather how much data you can upload and download in a given time. This is measured in Megabits per second (Mbps). (Which is not to be confused with Megabytes per second. (MBps) )
The internet speed will also be affected by available bandwidth along the route that your data must travel. When many internet users send and receive data on the same network at the same time, it will slow the internet speed when bandwidth limits are reached.
If you have more Bandwidth available to you, you will be able to send larger volumes of data in a shorter time, which you will experience as faster internet.