Fiber
Light in glass. Huge bandwidth, long reach, immunity to electrical noise.
Level: beginner
What is it?
Optical fiber carries data as light through a glass or plastic waveguide. Common network systems use single-mode or multimode fiber with transceivers selected for wavelength, reach, and supported line rate.
Why does it matter?
Fiber supports high capacity over long distances and avoids electromagnetic interference. It is widely used for backbone and data-center links, although connectors, optics, and handling require care.
Mental model
The transmitter maps data to light pulses or modulation; the fiber guides the optical signal; the receiver converts the received signal back into electrical data.
How it works
- Single-mode fiber supports long-distance propagation with a small core; multimode fiber is common over shorter data-center distances.
- Optical budget includes transmitter power, receiver sensitivity, connector loss, splices, and fiber attenuation.
- Wavelength and transceiver types must match the fiber and supported distance specification.
- Fiber is immune to electromagnetic interference but can still suffer bends, dirty connectors, breaks, or optic faults.
- Optical links require careful connector cleaning and safe handling; never look into an active fiber.
Steps
- Choose a compatible optic and fiber type for the required distance and rate.
- Clean and connect the optical interfaces, respecting polarity where applicable.
- Verify link state, receive power, and error counters using supported diagnostics.
- Test throughput and errors; inspect bends and connectors if the link is unstable.
Real-world usage
- Campus, metropolitan, and data-center backbone links.
- Interconnecting switches across long or electrically noisy paths.
Common mistakes
- Assuming every fiber connector or optic is interoperable.
- Ignoring optical power budget and maximum reach specifications.
- Handling or inspecting active fiber without appropriate safety precautions.
Interview questions
What is a common single-mode vs multimode distinction?
Single-mode fiber is designed for one propagation mode and is used for long reach; multimode supports multiple modes and is commonly used for shorter links.
Why must optical power be checked?
Too little received power can cause errors or link failure; excessive power can also exceed the receiver's supported range.