Optical Communication
Overview
Optical communication (광 통신, 光通信) is a communication method that transmits information using light as a medium. Instead of electrical signals, it uses optical signals and is mainly used for long-distance transmission through optical fibers. As a foundational technology for ultra-high-speed internet, data centers, and communication networks, it is a core infrastructure of the modern information society.
Main Content
Principles and Basic Structure
The basic principle of optical communication is to convert electrical signals into optical signals for transmission, and then restore the optical signals back into electrical signals at the receiving end. Key components include a light source (laser diode or light-emitting diode), a modulator, an optical fiber, and a photodetector. An optical fiber consists of two layers with different refractive indices (core and cladding), and light is confined and propagated inside via total internal reflection.
Types of Optical Fibers
- Single-mode optical fiber: The core diameter is very thin, about 9 μm, and only a single mode propagates. It is suitable for long-distance high-speed transmission and has low loss.
- Multi-mode optical fiber: The core diameter is 50–62.5 μm, and multiple modes propagate simultaneously. It is used for short-distance and relatively low-speed applications.
System Components
- Transmitter: Converts electrical signals into optical signals using a laser or LED, and transmits data by encoding it onto the intensity or phase of the light.
- Receiver: A photodiode converts the optical signal back into an electrical signal.
- Optical amplifier: Amplifies attenuated signals during long-distance transmission; the EDFA (Erbium-Doped Fiber Amplifier) is a representative example.
- Optical switch: Used to switch paths and configure networks.
Advantages and Disadvantages
Compared to electrical communication, optical communication has a much wider bandwidth, enabling large-capacity data transmission. It is less affected by electromagnetic interference and is more resistant to wiretapping. In addition, its low loss makes long-distance transmission efficient. However, it has disadvantages such as high initial installation cost, sensitivity to bending, and fragility.
Application Fields
- Communication networks: Internet backbone, enterprise networks, subscriber networks (FTTH), etc.
- Data centers: High-speed data transmission between servers.
- Medical: Endoscopes, medical image transmission.
- Sensors: Temperature and strain measurement using distributed fiber optic sensors.
- Defense/Aerospace: Data buses in aircraft and ships.
Recent Trends
In 2024–2025, the field of optical communication is advancing toward faster and more efficient technologies. 400G and 800G transmission technologies have become common in commercial networks, and 1 Tbps-class transmission technologies are also being researched. In addition, efforts to dramatically increase transmission capacity by utilizing multiple spatial paths through space-division multiplexing (SDM) technology are active. Silicon photonics-based optical integrated circuits have been commercialized, leading to the development of compact, low-power modules. Free-space optical communication (FSO) is being applied to inter-satellite communication and unmanned aerial vehicle communication. Quantum communication is also attracting attention as an extension of optical communication, with practical implementation of quantum key distribution (QKD) underway.
Related Topics
- [[Optical fiber]]
- [[Laser]]
- [[Communication engineering]]
- [[Quantum communication]]