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1. Introduction
2. Basic Structure of Fiber Optic Cables
2.1 Core
2.2 Cladding
2.3 Buffer Coating
2.4 Jacket
2.5 Strengthening Members and Additional Protection
3. Common indoor and outdoor fiber cable models
4. Conclusion
1. Introduction
Optical cable is a communication cable assembly consisting of optical fiber, plastic protective casing and plastic sheath. The basic structure of optical cable usually includes cable core, reinforcing steel wire, filler and sheath. It may also include waterproof layer, buffer layer, insulated metal wire and other components as needed.
Fiber optic cables are created through a process called drawing, where fibers are pulled from preforms that are themselves made by a process known as Modified Chemical Vapor Deposition (MCVD). During the drawing process, the diameter of the fiber is monitored precisely, and its protective plastic coating is applied immediately after the fiber is drawn.
Fiber optic technology represents a leap forward in telecommunications, offering significant advantages over traditional metal wire transmissions. By transmitting data as light rather than electrical signals, fiber optics overcome many limitations of earlier technologies.
This article will introduce you to what the optical cable looks like and what each part is.
2. Basic Structure of Fiber Optic Cables
Fiber optic cables are composed of multiple layers. At the core, there's a very thin strand of glass or plastic that carries light signals. This core is surrounded by a cladding which reflects light back into the core to prevent signal loss. Around the cladding, there's a buffer coating that protects the fiber from moisture and physical damage. The outer layer is the jacket, which shields the entire assembly from environmental and mechanical damage. These cables are often colored for easy identification.
2.1. Core:
The core is the central part of the fiber optic cable and is pivotal in light transmission. The core of a fiber optic cable is the thin glass or plastic fiber through which light signals are transmitted. The diameter of the core ranges typically between 8 to 62.5 microns. The core's size and material determine the cable's capacity and the distance it can cover without significant signal loss. And the core's primary function is to guide light along the cable’s length. Its diameter varies depending on the type of fiber:
·Single-mode fibers,have a small core size, approximately 8 to 10 microns in diameter(wavelengths of 1310 or 1550 nanometers), allowing light to travel straight down the fiber without much reflection, which significantly reduces attenuation and allows data to travel longer distances. Best suited for long-distance communications because it allows the signal to travel further without signal degradation.
The models of single-mode optical fibers mainly include G.652, G.653, G.654, G.655, G.656 and G.657.
G.652 is a conventional single-mode optical fiber, which is divided into four subcategories: G.652.A, G.652.B, G.652.C and G.652.D. G.652 optical fiber has a smaller dispersion at a wavelength of 1310nm, and a smaller loss at a wavelength of 1550nm, but a larger dispersion. The maximum transmission rate of G.652.A optical fiber is 2.5Gbps, while G.652.B, G.652.C and G.652.D optical fibers support a higher transmission rate of up to 10Gbps12.
·Multi-mode fibers , on the other hand, have larger cores, about 50 to 62.5 microns across(wavelengths of 850 or 1300nm meters) , which support multiple paths of light. While this design enables higher data transmission rates over shorter distances, it also leads to modal dispersion, a form of signal degradation. Multi-mode fibers are used for shorter distances as the modes of light tend to disperse over longer lengths, causing signal loss.
Commonly used models include OM1, OM2, OM3 and OM4. Among them, OM1 and OM2 are commonly used in 100M and 1000M networks; OM3 and OM4 are suitable for Ethernet transmission above 10Gbps.
The specific models are introduced as follows:
1. OM1 type: OM1 is a multi-mode fiber with a full injection bandwidth of more than 200/500MHz.km at 850/1300nm and a core diameter of 50um or 62.5um. This fiber has a core size of 62.5um, a data rate of up to 1GB @ 850nm, and a transmission distance of 300 meters. Its main application scenarios are short-distance networks, local area networks (LAN), and private networks. Compared with OM2, OM1 has a larger core diameter and numerical aperture, so it has stronger light collection ability and anti-bending characteristics. For many years, OM1 has been widely deployed in applications inside buildings, supporting Ethernet transmission with a maximum value of 1Gb.
2. OM2 type: OM2 is a multi-mode fiber type with a core size of 50um, a data rate of up to 1GB @ 850nm, and a transmission distance of up to 600 meters. Compared with OM1, OM2 has a smaller core diameter and numerical aperture, which helps to reduce modal dispersion and thus significantly increase bandwidth. In addition, the production cost of OM2 is relatively low, about 1/3 of OM1. This fiber is mainly used for short-distance networks, local area networks (LANs) and private networks, and supports Ethernet transmission with a maximum value of 1Gb. In terms of design, OM2 is mainly based on LED as the light source.
3. OM3 type: OM3 is a 50um core multi-mode optical fiber optimized with 850nm laser. In 10Gb/s Ethernet using 850nm VCSEL, the transmission distance of this optical fiber can reach 300 meters. In addition, OM3 also has a 150m transmission distance version.
4. OM4 type: OM4 is a multi-mode fiber with a core size of 50um, a data rate of up to 10GB @ 850nm, and a transmission distance of up to 550 meters. This fiber is mainly used in high-speed networks such as data centers, financial centers, and corporate campuses. OM4 is an upgraded version of OM3 multi-mode fiber, and its transmission distance is longer than OM3. When using MPO connectors, OM4 can also support up to 100GB transmission rate to 150 meters.
5. OM5: Newest type, supports high bandwidths using wavelength division multiplexing (WDM) and can extend the reach and capacity of multi-mode fibers in data centers and local networks
2.2. Cladding:
Surrounding the core is the cladding, a layer that plays a critical role in maintaining the integrity of the transmitted light. Typically made from a lower-refractive-index glass or plastic, the cladding acts as a reflective boundary, preventing light from escaping the core. This reflection is not a surface mirror effect but a phenomenon known as total internal reflection, which is crucial for efficiently transmitting light over long distances.
2.3. Buffer Coating:
The cladding plays a core role in fiber optic technology, ensuring the efficiency and reliability of optical communication systems. With this structural design, fiber optics can operate stably in various environments, supporting the demands of modern communication infrastructure.
The cladding is typically made of glass or plastic, designed with a refractive index lower than that of the core to support total internal reflection of light within the core.
The thickness of the cladding can vary based on the design and application requirements of the fiber. Generally, it is sufficient to provide enough total internal reflection while protecting the core from physical damage.
What are the functions of the fiber optic cladding?
·Maintaining Light Propagation in the Core: Through total internal reflection, the cladding ensures that light beams can effectively transmit within the core, which is key for efficient data or signal transmission.
·Physical Protection: The cladding provides additional physical protection for the fiber core, preventing external factors such as moisture, chemicals, or mechanical damage from affecting the core.
·Minimizing Signal Loss: Proper cladding design can minimize signal loss during transmission, especially over longer distances.
·Fiber Identification and Classification: Different types of fibers may use claddings of different colors or materials to help identify and classify fiber types.
2.4 . Jacket:
The outermost layer of a fiber optic cable is the jacket, which further shields the cable from physical and chemical damages like moisture, fire, and mechanical stresses. The material used for the jacket depends on the installation environment, whether it's indoors, outdoors, or underground.
· PVC jackets are common for general indoor use, providing a balance of flexibility, durability, and affordability.
· Polyethylene jackets are used for outdoor cables, offering enhanced protection against UV rays and extreme temperatures.
· Specialized materials may also be used in environments that pose specific challenges, such as corrosive chemicals or the risk of rodent damage.
2.5. Strengthening Members and Additional Protection
Fiber optic cable reinforcement is an essential component of the cable structure, primarily used to enhance the mechanical strength of the cable and protect the optical fibers from external pressures and environmental factors. Here are several main functions of fiber optic cable reinforcement:
Providing Mechanical Strength: Reinforcements offer additional mechanical support, helping the cable resist physical stresses such as tension, compression, and bending. This is a key factor in ensuring the stability of the cable during installation and operation.
·Preventing Fiber Breakage: When the cable is excessively stretched or bent, the reinforcements can reduce the pressure on the fibers, thereby lowering the risk of fiber breakage.
·Protecting Fibers from Environmental Effects: Reinforcements can protect the fibers from moisture, chemical erosion, and temperature changes, ensuring the performance and lifespan of the cable.
·Maintaining Cable Shape and Structural Integrity: Reinforcements help maintain the shape and structural integrity of the cable, ensuring its functionality even in cluttered or harsh installation environments.
The materials used for reinforcements often include steel wires, fiberglass, or synthetic fibers, chosen based on the application scenarios and specific requirements of the cable. Overall, fiber optic cable reinforcements provide necessary physical protection and structural support, key to ensuring the performance and safety of fiber optic communication systems.
3. Common indoor and outdoor cable models
Indoor and outdoor fiber optic cables are designed to meet different environmental and mechanical requirements. Here are some common models and their typical applications:
·Simplex Fiber Optic Cable:
Structure: Consists of a single fiber tightly buffered by a plastic layer for added durability.
Usage: Used for patch cords and connecting equipment in a data center or similar indoor environments.
·Duplex Fiber Optic Cable:
Structure: Contains two fibers, typically used for bidirectional communication.
Usage: Ideal for connections within buildings where two-way data transmission is needed, such as between switches and servers.
·Multi-Fiber Cable (Breakout Cable):
Structure: Houses several individually jacketed fibers within one larger cable, providing robust protection.
Usage: Suitable for direct equipment connection where multiple fibers are needed, offering easier handling and installation.
·Distribution Cable:
Structure: Contains multiple fibers bundled together under one outer jacket, without individual jackets on the fibers inside.
Usage: Used in indoor routing and can be connected to patch panels or equipment. Ideal for high-density applications within buildings.
·Loose Tube Cable:
Structure: Fibers are loosely encased in a waterproof tube filled with gel, which can house up to 12 fibers per tube.
Usage: Designed for harsh outdoor environments; the loose tubes provide excellent protection against moisture and temperature changes.
·Armored Fiber Optic Cable:
Structure: Includes a metal armor layer under the outer jacket to protect the cable from rodents, digging, and other physical damages.
Usage: Used in direct burial applications or in areas where the cable might be exposed to potential mechanical damages.
·Aerial Fiber Optic Cable:
Structure: Engineered to withstand environmental challenges specific to aerial installations, such as wind, ice, and UV exposure.
Usage: Hung on poles, often integrated with a supporting strand, or designed to self-support.
·ADSS (All-Dielectric Self-Supporting Cable):
Structure: A non-metallic cable that is strong enough to support itself between structures without the use of additional conductive metal elements.
Usage: Primarily used for installations along existing power lines or between utility poles without the need for grounding.
These cable models are tailored to specific environmental conditions and installation needs, ensuring the reliable transmission of data in both indoor and outdoor settings.
4.Conclusion
The basic structure of fiber optic cables is a testament to advanced engineering and material science, reflecting a design that balances performance, durability, and practical application challenges. Each layer, from the core to the jacket, is tailored to fulfill specific roles—transmitting light efficiently, protecting from environmental elements, and ensuring longevity and reliability of the communication link. As demand for higher bandwidth and faster internet speeds continues to grow, the role of fiber optics in global communication networks becomes increasingly vital, pushing the boundaries of what is possible in data transmission technology.
The incredible efficiency and capabilities of fiber optic cables make them a cornerstone of modern telecommunications infrastructure. As technology progresses, the role of fiber optics only grows, paving the way for more advanced applications in various fields.
