Fiber optic internet sends information as rapid pulses of light through very thin strands of glass or plastic. This matters because light can carry huge amounts of data over long distances with very little signal loss. Compared with copper wires, fiber usually provides higher bandwidth, lower delay, and better resistance to electrical interference.
A single cable can connect a home router to local equipment, data centers, and the wider global internet.
Key Facts
- Speed of light in a fiber: v = c/n, where c = 3.00 x 10^8 m/s and n is the refractive index.
- Total internal reflection occurs when light in the core hits the boundary at an angle greater than the critical angle.
- Critical angle formula: sin(theta_c) = n2/n1, where n1 is the core index and n2 is the cladding index.
- Bandwidth is the data-carrying capacity of a connection, often measured in bits per second.
- Latency from distance can be estimated by t = d/v, where d is path length and v is light speed in the fiber.
- Fiber optic systems use transmitters to convert electrical data into light and receivers to convert light back into electrical signals.
Vocabulary
- Core
- The central transparent strand of a fiber optic cable where most of the light signal travels.
- Cladding
- The outer glass or plastic layer around the core that keeps light trapped by total internal reflection.
- Total internal reflection
- The process in which light reflects completely back into a material instead of passing through a boundary.
- Bandwidth
- The maximum rate at which data can be transmitted through a communication channel.
- Optical network terminal
- A device at a home or business that converts fiber optic light signals into electrical signals for a router.
Common Mistakes to Avoid
- Thinking the light travels through empty air inside the fiber is wrong because the light travels through solid glass or plastic in the core.
- Assuming fiber internet is instant is wrong because signals still take time to travel, and routing equipment adds additional delay.
- Confusing bandwidth with latency is wrong because bandwidth measures data rate while latency measures time delay.
- Forgetting the role of cladding is wrong because the cladding has a lower refractive index that helps trap light inside the core.
Practice Questions
- 1 Light travels through a fiber with refractive index n = 1.50. Using v = c/n and c = 3.00 x 10^8 m/s, find the speed of light in the fiber.
- 2 A data signal travels 1200 km through fiber at 2.00 x 10^8 m/s. Estimate the one-way travel time in milliseconds, ignoring equipment delays.
- 3 Explain why a fiber optic cable can carry data through bends, but only if the bends are not too sharp.