1. Concept of Optical Fiber

An optical fiber communication system achieves communication by transmitting light waves that carry information through optical fibers.

2. Working Principle of Optical Fiber

Optical Fiber Dispersion

Optical Fiber Loss

• Intrinsic Absorption: The inherent absorption property of the fiber material itself.
• Impurity Absorption: The absorption of light by impurities present in the optical fiber.

Other LossesSuch as microbending loss. Optical fibers are flexible and can be bent, but beyond a certain bending radius, although the fiber can still guide light, the light transmission path will change. This causes a conversion from guided modes to radiation modes, where part of the optical energy penetrates into the cladding or escapes through the cladding as radiation modes, resulting in power loss. When the bending radius is larger than 5–10 cm, the loss caused by bending is negligible.

3. Advantages of Optical Fiber Communication

1. Huge Communication CapacityTheoretically, a single optical fiber can transmit 10 billion voice channels simultaneously. At present, tests for simultaneous transmission of 500,000 voice channels have been successfully completed, which is thousands to hundreds of thousands of times higher than that of traditional coaxial cables and microwave systems.
2. Long Relay DistanceOptical fibers feature an extremely low attenuation coefficient. When equipped with appropriate optical transmitting/receiving equipment, optical amplifiers, forward error correction (FEC) and RZ coding modulation technologies, the relay distance can reach thousands of kilometers. By contrast, traditional cables can only transmit signals over 1.5 km and microwave systems over 50 km, which are simply incomparable.
3. Excellent Confidentiality and Strong AdaptabilityOptical fiber communication is immune to external strong electromagnetic interference and resistant to corrosion.
   Since the core component of optical fibers is silica, they only transmit light signals without conducting electricity and are not affected by electromagnetic fields. Therefore, the optical signals transmitted through them are free from electromagnetic interference, giving optical fiber transmission strong resistance to electromagnetic and industrial interference. For the same reason, signals transmitted via optical fibers are not easily tapped, which facilitates secure communication.
4. Small Size and Light WeightOptical fibers have the advantages of compact dimensions and low weight.
5. Abundant Raw Material Sources and Low CostThe primary raw material for optical fibers is silica, which is widely available in nature and low in extraction cost.

Part 2: Types of Optical Fiber

4. Classification by Transmission Mode

Multimode Fiber (MMF)

Single-mode Fiber (SMF)

Comparison Between Multimode and Single-mode Fiber

Applications of Multimode and Single-mode Fiber

5. Optical Fiber Patch Cord/Cable

Single-mode Fiber Patch Cord

• Generally yellow in color, with blue connectors and protective sleeves.
• Suitable for long-distance transmission; a single-mode fiber cable can support a connection distance of up to 10 km.

Multi-mode Fiber Patch Cord

• Generally orange (or sometimes gray) in color, with beige or black connectors and protective sleeves.
• Designed for short-distance transmission; the connection distance of a multi-mode fiber cable is much shorter, typically 300 m or 500 m. This variation mainly depends on the laser type: there are two common light sources emitting short-wavelength lasers, corresponding to the 62.5 μm and 50 μm core diameter specifications respectively.

Common Types of Optical Fiber Interfaces

• FC Interface: Short for Ferrule Connector, it was first applied in storage area networks (SANs). It features a metal housing and a threaded interface, which ensures a secure and stable connection with optical modules.
  
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• ST Interface：Short for Stab & Twist, it features a metal housing and a bayonet-style locking mechanism. It is commonly used in fiber optic distribution frames.

SC Interface：Short for Square Connector, it has a plastic housing and adopts a push-pull connection mechanism. The interface can be securely locked onto optical modules, and it is commonly used in switches.

LC Interface：Short for Lucent Connector, it has a plastic housing and is designed for connecting to SFP optical modules, with the interface being securely lockable onto the modules.

6. Optical Fiber Pigtail

Classification of Optical Fiber Pigtails

• Multimode pigtails: Typically orange in color, with an operating wavelength of 850 nm and a transmission distance of around 500 m.
• Single-mode pigtails: Typically yellow in color, with operating wavelengths of 1310 nm or 1550 nm, and a longer transmission distance ranging from 10 km to 40 km.

Functions of Optical Fiber Pigtails

Common Types of Optical Fiber Pigtails

1. FC-SC Pigtail: Commonly known as a round-to-square pigtail. The FC end connects to an ODF (Optical Distribution Frame), while the SC end connects to the optical port of a device. This type of fiber connector was widely used in early SBS and Optix equipment.
2. FC-FC Pigtail: Commonly known as a round-to-round pigtail. It is generally used as a jumper between ODF racks.
3. SC-SC Pigtail: Commonly known as a square-to-square pigtail. It is typically used for connecting the optical line cards between devices.
4. SC-LC Pigtail: The LC interface is commonly referred to as a small square connector pigtail, which is a snap-on type connector. Currently, this fiber connector is adopted in Huawei OSN series equipment, ZTE S series equipment, as well as early Lucent wavelength division multiplexing (WDM) equipment.
5. LC-LC Pigtail: It is generally used for internal fiber connections between wavelength division multiplexing (WDM) devices, and has a relatively narrow range of applications.
   
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7. MPO (Multi-fiber Push On) Optical Cable

• OM1: Supports Ethernet transmission up to 1 Gb/s.
• OM3 & OM4: Commonly deployed in data center cabling environments, supporting high-speed Ethernet transmission at 10G/40G/100G rates.
• OM5: Expands the bandwidth channel based on OM4, providing a solution for 100 Gb/s and 400 Gb/s wavelength transmission. OM5 fibers offer three key advantages:
  1. Exceptional Scalability: OM5 patch cords integrate short-wave wavelength division multiplexing (SWDM) and parallel transmission technologies, and can support 200/400G Ethernet applications with only 8 fibers of wideband multimode fiber.
  2. Effective Reduction of Construction and Operational Costs: Drawing on the wavelength division multiplexing (WDM) technology of single-mode fibers, OM5 patch cords extend the usable wavelength range for network transmission, enabling support for 4 wavelengths over a single multimode fiber, which greatly reduces network cabling costs.
  3. Outstanding Compatibility and Interoperability: OM5 fibers support legacy applications just like OM3 and OM4 patch cords, achieving full compatibility and high interoperability with traditional OM3 and OM4 patch cords. In the 400G era, OM5 multimode fibers boast broad application prospects and deliver excellent performance even during the upgrade of low-rate equipment to high-rate devices.

OM Fiber Specifications and Features

Key Features of OM5

1. Fewer Fibers for Higher Bandwidth ApplicationsOM5 patch cords operate at wavelengths of 850/1300 nm and support at least four wavelengths, while OM3 and OM4 typically operate at 850 nm and 1300 nm. In other words, traditional OM1, OM2, OM3, and OM4 multimode fibers only offer a single channel, whereas OM5 provides four channels, quadrupling the transmission capacity. By combining Short-Wave Wavelength Division Multiplexing (SWDM) and parallel transmission technologies, OM5 only requires 8 fibers of WBMMF to support 200/400 GbE applications. This significantly reduces the fiber count and cuts down network cabling costs substantially.
2. Longer Transmission DistanceOM5 offers longer transmission distances than OM3 and OM4. OM4 is designed to support 100G-SWDM4 transceivers over distances of at least 100 meters, while OM5 can support the same transceivers over distances up to 150 meters.
3. Lower Fiber AttenuationThe attenuation of OM5 WBMMF is reduced from 3.5 dB/km (typical of OM3 and OM4) to 3.0 dB/km. Additionally, it has enhanced bandwidth requirements at the 953 nm wavelength.OM5 has the same fiber dimensions as OM3 and OM4, meaning it is fully compatible with them. There is no need to modify existing cabling infrastructure to deploy OM5. With superior scalability and flexibility, OM5 can support higher-speed network transmission with fewer multimode fibers, while its cost and power consumption are far lower than those of single-mode fibers. Therefore, it is expected to be widely adopted in 100G/400G/1T hyperscale data centers in the future.

Summary of OM Fiber Applications

• OM1 and OM2 have been widely deployed for in-building applications for many years, supporting Ethernet transmission up to 1 Gb/s.
• OM3 and OM4 cables are typically used in data center cabling environments, supporting high-speed Ethernet transmission at 10 Gb/s and even 40/100 Gb/s.
• OM5 is designed for 40 Gb/s and 100 Gb/s transmission, and can reduce the number of fibers required for high-speed transmission.

物理方面差异：

物理差异主要在于直径，护套颜色，光源和带宽，如下表所述。

实际差异：

多模光纤能够以各种数据速率传输不同的距离范围。可以根据实际应用选择最合适的一种。下面指定了不同数据速率下的最大多模光纤距离比较。

Physical Differences

Practical Performance Differences

Differences Between MPO and MTP

Key Features of MTP® Connectors

1. Removable Housing ComponentsThe outer housing components of MTP® connectors can be easily removed, facilitating maintenance and reconfiguration.
2. Reusable MT Ferrule DesignThe MT ferrule design ensures no performance degradation during production rework or re-polishing. The gender (male/female) of the connector can be flexibly changed even after assembly or on-site deployment, and the ferrule can pass interference testing post-assembly.
3. Floating Ferrule for Enhanced AlignmentThe floating ferrule design of MTP® connectors improves transmission performance during mechanical mating. It allows the mating ferrules to maintain optimal physical contact even when subjected to external forces.
4. Stainless Steel Oval Guide PinsMTP® connectors adopt stainless steel oval guide pins, which enhance mating precision and reduce wear on guide holes, enabling MTP® connectors to maintain high-performance transmission over an extended service life.
5. Integrated Metal Pin ClampA built-in metal pin clamp secures the push ring, providing three key benefits:
   • Prevents loss of guide pins;
   • Concentrates the pressure exerted by the spring;
   • Avoids spring contact or friction with optical fibers during mechanical expansion/contraction, thus preventing fiber damage.
6. Optimized Spring Design for Ribbon FibersThe spring design of MTP® connectors maximizes the ribbon gap for 12-fiber and multi-fiber ribbon applications, preventing fiber damage.
7. Versatile Adapter CompatibilityMTP® connectors offer at least four standard adapter options to accommodate different cable types, enhancing practicality:
   • Loose-tube round cables;
   • Ribbon cables with elliptical jackets;
   • Bare ribbon fibers;
   • Ultra-short boot connector components, ideal for space-constrained installations, reducing volume by 45%.
     
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8. AOC (Active Optical Cable)

AOC is the abbreviation of Active Optical Cable. It refers to an integrated active optical cable that combines optical transceivers and optical fibers, featuring simple and convenient operation.

An AOC integrates two optical transceivers and an optical cable into a single package. Since the transmission medium in between is optical fiber, the transceivers in an AOC are equipped with laser devices, resulting in a higher cost compared to DACs. However, its optical ports are not exposed, which ensures extremely high reliability. Another advantage is that its operating distance can be customized for long-reach applications within 100 meters.

In essence, an AOC is an optical fiber patch cord with built-in optical transceivers. AOCs are generally available in short lengths, up to a few hundred meters at most. Their most distinctive feature is that the optical transceivers and fibers are integrated into an inseparable unit.

This integrated design helps reduce the overall cost, as fixing the fibers inside the transceivers eliminates the need for certain optical components during manufacturing. AOCs are suitable for short-distance application scenarios but not for long-haul transmission — this is obvious, as optical cables cannot be made infinitely long. AOCs are widely deployed in IDC (Internet Data Center) server rooms.

Advantages of AOCs:

Low environmental requirements, with no need for cleaning optical fiber connectors.

Cost-optimized design, and they do not come with DDM (Digital Diagnostic Monitoring) functionality.

Disadvantages of AOCs:

Inflexible distance configuration — the transmission distance must be confirmed in advance before factory shipment.

Comparison Between AOC and DAC

DAC, short for Direct Attach Cable, is simply a cable fitted with optical transceivers at both ends. It is widely used in storage area networks, data centers, and high-performance computing connections, and is gradually gaining traction in network communications. Specifically, DACs are constructed with silver-plated conductors and foamed insulated cores, adopting pair-wise shielding and overall shielding to achieve high-speed signal transmission.

Advantages of DACs:

High Interchangeability: With the advancement of copper cable technology, DACs are interchangeable and hot-swappable with fiber optic transceivers.

Low Cost: Copper cables are cheaper than optical fibers, so using DACs helps reduce cabling costs.

Excellent Heat Dissipation: DACs are made of copper cores, which offer good heat dissipation performance.

Disadvantages of DACs:

Short transmission distance, heavy weight, large volume, difficult management, and susceptibility to electromagnetic interference — which may cause issues such as signal malfunction and degradation.

The main disadvantage of AOCs, by contrast, is their relatively high cost.

9. Differences Between Optical Fiber and Optical Fiber Cable

Submarine Optical Fiber Cable

1. First, the optical fibers are embedded in a jelly-like compound to protect the cable from damage even when in contact with seawater.
2. Then, the fiber bundle is enclosed in a steel tube to withstand underwater pressure.
3. Next, the steel tube is wrapped in high-strength steel wires and enclosed in a copper tube for further protection.
4. Finally, an outer sheath made of polyethylene is applied to complete the cable structure.

Part 3: Major Manufacturers in the Optical Fiber Industry

In the global optical fiber and cable rankings, the top 10 enterprises are divided among 4 countries: the United States (Corning), Italy (Prysmian), Japan (Furukawa Electric/OFS, Sumitomo Electric, Fujikura), and China (Yangtze Optical Fibre and Cable, Hengtong Optic-Electric, FiberHome Telecommunication, Futong Group, Zhongtian Technology). Chinese enterprises hold half of the market share. Three Chinese companies — Yangtze Optical Fibre and Cable, Hengtong Optic-Electric, and FiberHome Telecommunication — account for a considerable market share.

Yangtze Optical Fibre and Cable ranks 2nd globally with a 12% market share, while Hengtong Optic-Electric takes the 3rd place with 11%. FiberHome Telecommunication, Futong Group, and Zhongtian Technology rank 5th, 6th, and 9th with 7%, 8%, and 8% market shares respectively. The respective market shares of other international players are: Corning 15%, Furukawa/OFS 10%, Sumitomo Electric 5%, Prysmian 6%, and Fujikura 4%.

10. Major International Manufacturers

• Corning: Its optical fiber manufacturing plant in Wilmington, North Carolina, USA, is the world’s first optical fiber production facility and remains one of the largest optical fiber manufacturers globally.
• Furukawa Electric: Headquartered in Tokyo, Japan, it is a large multinational corporation.
• Prysmian: Headquartered in Milan, Italy, it is a world leader in the energy and communication cable systems industry.
• Sumitomo Electric: It is Japan’s leading cable producer, and together with Furukawa Electric and Fujikura, it is known as the 'Big Three of Electric Wires' in Japan.
• Fujikura: Its business scope covers comprehensive cable products.

11. Major Domestic Manufacturers (China)

• Yangtze Optical Fibre and Cable: Based in Wuhan, Hubei, it ranks first in domestic optical fiber preform production capacity with strong R&D capabilities, accounting for over 30% of China’s total preform output. It is also the only domestic enterprise with the capability to export optical fiber preforms.
• Hengtong Optic-Electric: Headquartered in Suzhou, Jiangsu, it has a dual layout in optical fiber and optical modules, and seizes opportunities in marine communication.
• Zhongtian Technology: Located in Jiangsu, it has a multi-dimensional layout of 'cloud, pipe, terminal' and independently developed G.654 optical fiber technology.
• FiberHome Telecommunication: Based in Wuhan, Hubei, it advances hand in hand in optical communication and ICT (Information and Communications Technology) businesses.
• Tongding Interconnect: Headquartered in Suzhou, Jiangsu, it has basically formed an integrated advantage in the optical fiber and cable, and optical preform sectors. It has the production capacity of the entire industrial chain of communication cables, including optical fiber preforms, optical fibers, optical cables, communication cables, and power cables.
• Futong Cable: Based in Shenzhen, it mainly produces and sells optical fibers, optical cables, and semi-finished products, and provides manufacturing and processing services for related supporting products, components, and raw materials.

Part 4: Main Causes of Optical Fiber Failures

12. Causes of Optical Fiber Failures

1. Excessively Long Optical Cable
2. Excessive Bending
3. Cable Compression or Fracture: Optical fibers are subject to uneven stress, e.g., external pressure or micro-irregular bending and even fracture of the fiber axis caused by temperature changes in the coated fiber. This results in the conversion of guided modes into radiation modes, leading to optical power loss.
4. Poor Fusion Splicing of Cables
5. Core Diameter Mismatch
6. Filler Diameter Mismatch
7. Connector Contamination: Contamination of optical fiber connectors and moisture absorption of pigtails are among the primary causes of optical cable communication failures.
8. Poor Polishing at Connectors
9. Poor Contact at Connectors: This issue mainly occurs at optical path terminals, such as optical distribution frames and optical switches. It may be caused by operator negligence, equipment quality defects, or connector aging, leading to loose fiber connections, which results in reflective loss and leakage attenuation of optical signals.