Fundamentals of Optical Communication: Principles, Advantages, and Technologies

Using optical networks, information sent by each individual can be transmitted worldwide; the following introduces technology that can rapidly transmit massive amounts of data in a single operation.

What is Optical Communication?

In short, optical communication is the technology that uses light to transmit information to a receiver.

Basic Structure of Optical Communication

Our computers and phones send information via electrical signals (0s and 1s). Optical communication consists of a transmitter that converts electrical signals to optical signals, a receiver that converts optical signals back to electrical signals, and the optical fiber that carries the light.

Advantages of Optical Communication

Long transmission distance and energy efficiency

Massive data can be transmitted in a single burst

High communication speed

1) Long transmission distance and energy efficiency – Transmitting 10 Gb of data per second with electrical communication requires signal adjustment every 100 m, whereas optical communication can adjust at intervals of over 100 km, reducing equipment count and saving energy.

Compared with satellite‑based electrical links, undersea optical fiber cables provide faster, higher‑capacity connections because the signal path is much shorter.

2) Massive data in a single transmission – While electrical communication can transmit up to 10 Gb/s, optical communication can reach 1 Tb/s, allowing many users to receive large files such as movies simultaneously.

3) High communication speed – Electrical signals suffer from noise‑induced errors that slow transmission, whereas optical signals are immune to such noise, enabling faster data rates.

Where Optical Communication Is Used

Internet, mobile phones, IP‑telephony and other networked devices rely on optical communication to connect users locally, nationally, and globally via undersea fiber‑optic cables.

Various Network‑Connected Devices

All everyday devices can be networked, making life more convenient.

Why Optical Communication Technology Is Needed

Communication Volume

The amount of data exchanged each year keeps growing as devices become more capable, demanding higher‑capacity transmission technologies such as optical communication.

Transmission Capacity

Increasing societal data traffic drives the need for technologies that can carry more information over a single fiber.

Unit of Transmission

Transmission speed is measured in bits per second (bps); for example, 1 bps means one bit per second.

Optical Transmission Devices (光传输装置)

Key functions of optical transmission devices include:

Signal conversion (transmit): electrical to optical

Multiplexing: combining multiple narrow signals into a wide one

Relay: long‑distance transmission with intermediate regeneration

Switching: directing signal flow

Demultiplexing: separating combined signals

Signal conversion (receive): optical to electrical

Components of an Optical Transmission Device

The device contains several parts that perform conversion, multiplexing, relay, switching, demultiplexing, and reconversion.

1. Conversion (transmit): electrical signal → optical signal.

2. Multiplexing: multiple signals sent simultaneously.

3. Relay: signal degradation is compensated by regenerating the waveform, sometimes converting back to electrical form temporarily.

4. Switching: optical switches change the direction of the light based on destination.

5. Demultiplexing: separating combined signals back into individual streams.

6. Conversion (receive): optical signal → electrical signal.

Communication Methods (Now and Future)

An analogy using cars and lanes illustrates that each wavelength is a lane, each car represents a time slot, and the cargo represents the amount of data.

Current Communication Speed : 10 Gbps–40 Gbps per wavelength.

• Time Division Multiplexing (TDM): data is sent in separate time slots, which can cause congestion when many users share a single lane.

• Wavelength Division Multiplexing (WDM): multiple wavelengths carry separate data streams simultaneously, reducing congestion.

• Multi‑Level Modulation (MM): multiple bits are encoded per symbol on a single wavelength, e.g., Differential Quadrature Phase‑Shift Keying (DQPSK) doubles the bits per symbol.

Future Communication Speed : 100 Gbps per wavelength, roughly the amount needed to transfer a DVD in 0.4 seconds.

• Polarization Multiplexing: using orthogonal polarizations (vertical and horizontal) to carry independent data streams without interference.

Powerful Optical Networks – Example Cases

Fiber‑optic cables span the globe, providing high‑quality services in many scenarios.

Little Story – Why Is the Sky Blue and the Sunset Red?

Short‑wavelength blue light scatters more easily by atmospheric particles, filling the sky with blue, while longer‑wavelength red light passes through the atmosphere with less scattering, giving sunsets their red hue.

Wavelength of Sunlight

Sunlight appears white because it contains a mixture of wavelengths from red to blue.

Why the Sky Appears Blue

Blue light’s short wavelength causes it to scatter in all directions, making the whole sky appear blue.

Why Sunsets Appear Red

When the sun is low, its light travels through a longer atmospheric path; short‑wavelength blue light is scattered out, leaving longer‑wavelength red light to dominate the sky.

Optical communication exploits the same principle by using slightly longer wavelengths to reduce scattering in fibers, enabling long‑distance transmission.

Prerequisite Knowledge – What Is Wavelength?

Wavelength is the physical length of one cycle of a wave, applicable to sound, radio, and light waves.

Different wavelengths produce different colors and pitch; in optical communication, typical wavelengths are 1.3 µm or 1.55 µm, which lie in the infrared range.

Source: Fujitsu R&D Center

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