CCNA RnS #10 - Fiber-optics Cable

CCNA RnS Article #10 – Fiber Optics Cable

Today in this article I am going to over the fiber Optic cable components and data transmission concepts over it. Fiber optic cable uses glass as the medium through which light passes this varying light over time encodes 0s and 1s.

This fiber optic glass is not the same that we use for commercial constructions but it’s a fiberglass. This allows long cables to hold thin strings of flexible glass. Figure 1 shows the components of the fiber optic cable – the outer 3 layers (Cable Jacket, Strengthening Fiber, and Coating) protect the inner 2 layers (Cladding & core). The inner layers the cladding and core build an environment that allows light to travel through the core.

Figure 1: Fiber-optic Cable components
Figure 1: Fiber-optic Cable components

The light source at each end is called the optical transmitter and it shines a light into the core. Cladding reflects the light back to the core as it travels.

Figure 2: Multi-Mode Fiber

Figure 2 shows the multimode fiber cable operation where the cable allows multiple angles of light to enter the core. Single-mode fiber uses a smaller core and a laser-based transmitter is used to send the light at a single angle – therefore it is called the single-mode fiber optic cable.

Figure 3: Single-Mode Fiber

Single-mode fiber has a smaller core size of 9 microns and has a single light path. A smaller light path allows single-mode cable to cover a much distance of up to 100 km.

Figure 4: Diameter SMF & MMF

 MMF and SMF difference – the table below highlights some of the differences between the two.

Multi-mode Fiber

Single-mode Fiber

Carry multiple light rays

Single light ray

Low cost compared to SMF


Distance - up to 2km

Distance up to 100km

Core – 50 microns

Core – 9 microns

 We need Ethernet switches with built-in compatible ports that support fiber connectivity. These ports are kinds of slots that can hold different types of SFP transceivers (RJ-45, Single-Mode or Multi-Mode transceivers). Distance is the first consideration when thinking about UTP or Fiber Cables to be used. If the distance is less than 2 km multi-mode fiber can be used and for more than 2km up to 100 km, the single-mode cable can be used.

Another reason customers prefer fiber over UTP is resistance to EMI interference and there is no faint single possibility outside the cable. So for secure environments such as manufacturing plants fiber optic cable is preferred. Hope you find this informative.

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