Fiber optic cable transmits data as pulses of light along thin strands of glass or plastic. Light stays inside the core by total internal reflection, so signals can travel long distances with little loss and without electrical interference.
Why it matters
Fiber underpins the internet backbone, undersea cables, data centers and many home connections (FTTH, fiber to the home). It supports far more bandwidth than copper and is immune to electromagnetic noise. There are two main types: single-mode fiber, with a very narrow core, for distances of many kilometers, and multimode fiber, with a wider core, for shorter runs such as inside a building or data center. Light is generated by lasers or LEDs in transceiver modules such as SFP.
Example
A 10 Gbit/s link between two switches 300 m apart in one campus can use multimode fiber with short-reach transceivers, while a 10 km link between sites typically uses single-mode fiber with long-reach optics. A copper Ethernet cable is limited to 100 m for most speeds.
Common mistakes
- Mixing single-mode and multimode fiber or the wrong transceivers; they are not interchangeable.
- Bending the cable too tightly, which leaks light and raises loss.
- Leaving connector ends dirty; microscopic dust is a leading cause of errors.
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