Optical Fiber & Data Communications: Core Knowledge Points and Technology Panorama Overview

🔬 1. Basic Physics & Principles

Transmission Principle:Based on total internal reflection of light. An optical fiber consists of a high-refractive-index core and a low-refractive-index cladding. Optical signals undergo repeated reflections at the core-cladding interface, enabling low-loss long-distance transmission.

Physical Structure:The fiber core is extremely thin (approximately 125 µm in diameter), typically made of high-purity silica glass and coated with a protective layer. A fiber optic cable is composed of multiple fibers, strength members, and a jacket, providing mechanical and environmental protection.

🧭 2. Fiber Classification: Single-Mode vs. Multimode

Single-Mode Fiber (SMF):Core diameter of about 8–10 µm. Allows only one mode of light to propagate, no modal dispersion. Suitable for long-distance, high-capacity communication such as backbone networks and metro networks. Typical type: G.652.D.

Multimode Fiber (MMF):Core diameter of about 50–62.5 µm. Allows multiple modes to propagate, prone to modal dispersion. Suitable for short-distance, high-bandwidth scenarios such as data centers and enterprise campuses.

🛠️ 3. Optical Cable Structure & Engineering

Cable Structure:A fiber consists of core, cladding, and coating. Multiple fibers are combined with strength members (e.g., aramid yarn), a jacket, and water-blocking layers to form an optical cable that withstands mechanical stress and adapts to different installation environments.

Engineering Classification:According to application, cables are classified as duct, direct-buried, aerial, submarine, etc. As of June 2025, the total length of fiber optic cable lines in China reached 73.77 million kilometers, of which access network cables accounted for nearly 60%.

🏗️ 4. Data Communications & Networking

Protocol Layering Models:Data communications generally adopt the OSI seven-layer model (theoretical framework) and the TCP/IP four-layer model (de facto standard). Optical fiber serves as a physical layer medium, providing a basic bit-stream transmission channel for upper layers.

Core Technologies & Protocols:Key concepts include IP addressing and routing (network layer), TCP and UDP (transport layer), and Ethernet (typical data link layer protocol). In optical networks, wavelength division multiplexing (WDM) and optical transport network (OTN) technologies are often used to increase bandwidth and transmission efficiency.

📊 5. Key Technical Parameters

Attenuation:The energy loss of an optical signal during transmission, affecting transmission distance.

Dispersion:Pulse broadening caused by differences in propagation speed of different frequency components, limiting transmission bandwidth.

Nonlinear Effects:Signal distortion due to changes in the fiber's refractive index under high power, a critical limitation for long-distance transmission.

Bandwidth:The maximum data rate of a communication channel, measured in bps.

Optical Signal-to-Noise Ratio (OSNR):The ratio of optical signal power to noise power, indicating signal quality.

📜 6. Industry Standards System

International Standards:

- ITU-T (International Telecommunication Union):Develops recommendations for optical fibers and cables, such as the G.65x series (single-mode fiber) and G.657 (bend-insensitive fiber).
- IEEE (Institute of Electrical and Electronics Engineers):Develops Ethernet standards, such as the IEEE 802.3 series, defining 100G/400G/800G optical interface specifications.
- IEC (International Electrotechnical Commission):Develops optical cable product specifications, such as IEC 60793 and 60794 series.

Chinese Standards:A system of GB (national standards) and YD (communications industry standards) has been established, referencing international standards – for example, the GB/T 9771 series for single-mode fiber.

🗺️ 7. Industry Chain Overview

Upstream:Core is the manufacturing of optical fiber preforms, which has the highest technical barriers and accounts for 65–70% of fiber cost. Major suppliers include Corning (USA), Shin-Etsu and Sumitomo (Japan).

Midstream:Fiber drawing and cable manufacturing. Representative companies include YOFC, Hengtong Optoelectronics, FiberHome, and ZTT (all in China). In 2025, the total centralized procurement of fiber and cable by China's three major operators reached 183 million fiber-kilometers.

Downstream:Network operators (China Telecom, China Mobile, China Unicom, etc.) and various industry applications. The global optical fiber market size is expected to exceed US$30 billion in 2025.

🔮 8. Cutting-edge Technologies & Development Trends

AI-driven Demand:AI computing clusters are driving demand for high-speed optical modules (400G/800G) and high-density fiber connectivity, which is currently the core of market growth.

New Fiber Technologies:

- Hollow-core Fiber:Uses air as the transmission medium, offering ultra-low latency and ultra-low nonlinearity, with the potential to disrupt traditional optical communications.
- Space-division Multiplexing Fiber: Multiplies transmission capacity through multi-core fiber or few-mode fiber.
- Ultra-low-loss Fiber: G.654.E fiber has been commercially deployed at scale, supporting 400G/800G backbone transmission.

Network Evolution: Networks are evolving toward F5G‑A (10G intelligent era) and deep optoelectronic integration, promoting the deployment and trial of new technologies such as 50G‑PON.

💎 Summary

Optical fiber cables and data communications form an interconnected system. Optical cables serve as the physical foundation, while data communication protocols and architectures define the behavior logic of networks. Currently, this field is strongly driven by applications such as AI, 5G, and big data, accelerating toward next-generation networks featuring ultra-high speed, ultra-large capacity, and ultra-low latency.