Loose Tube

What Is the Loose Tube?

Loose tube refers to a type of protective structure used in fiber optic cables. It is designed to provide mechanical protection and environmental resistance to the delicate optical fibers inside the cable.

The loose tube construction consists of multiple individual optical fibers bundled together and enclosed within a protective tube. The tube is typically made of plastic or similar material and has a larger diameter than the individual fibers it contains. The term "loose" indicates that the fibers are not tightly bound or bonded to the tube.

Types of Loose Tube Fiber Optic Cable

There are several different types of loose-tube fiber used in fiber optic cables. These types vary in terms of their design, materials, and performance characteristics. Here are some common types:

1. 1. Single Mode Loose Tube Fiber: This type of loose-tube fiber is designed for single-mode applications, where light propagates through a single optical mode. It is optimized for long-distance transmission and offers low attenuation and high bandwidth.

2. 2. Multimode Loose Tube Fiber: Multimode loose-tube fiber is designed for multimode applications, where multiple optical modes are used to transmit light. It is commonly used for shorter-distance transmissions, such as within buildings or campuses, and offers higher bandwidth compared to single-mode fiber.

3. 3. Gel-Filled Loose Tube Fiber: Gel-filled loose-tube fiber cables have a gel compound inside the loose tubes surrounding the optical fibers. The gel acts as a moisture barrier, protecting the fibers from water ingress. This type of loose-tube fiber is commonly used in outdoor and underground installations where moisture protection is crucial.

4. 4. Dry Loose Tube Fiber: Dry loose-tube fiber cables do not contain gel inside the loose tubes. Instead, they may use water-blocking tapes or yarns to provide water resistance. Dry loose-tube fiber is suitable for applications where gel-filled cables are not preferred, such as where re-entry into the cable is required.

5. 5. All-Dielectric Loose Tube Fiber: All-dielectric loose-tube fiber cables are designed with non-metallic materials throughout, including the loose tubes and the cable jacket. They are used in environments where electrical conductivity is a concern, such as in high-voltage areas or where electromagnetic interference (EMI) must be minimized.

6. 6. Armored Loose Tube Fiber: Armored loose-tube fiber cables have an additional layer of armor, typically made of steel or aluminum, surrounding the loose tubes. This armor provides enhanced protection against physical damage, rodent attacks, and other external threats. It is commonly used in rugged or harsh environments.

These are some of the common types of loose-tube fiber used in fiber optic cables. The selection of the appropriate type depends on the specific application requirements, environmental conditions, and desired performance characteristics.

What Are the Advantages of Loose Tube Fiber？

Loose tube fiber optic cables offer several advantages over other types of fiber optic cable constructions. Here are some key advantages of loose tube fiber:

1. 1. Superior Protection: The loose tube design provides excellent protection to the optical fibers. The fibers are housed in individual tubes, which isolate them from external factors such as moisture, chemicals, temperature variations, and physical stresses. This protection ensures the long-term reliability and performance of the fibers, even in harsh environments.

2. 2. Flexibility: Loose tube fiber cables are highly flexible, allowing the fibers to move within the tubes. This flexibility helps absorb mechanical stresses, such as bending or twisting and prevents damage to the delicate fibers. It also allows for the expansion and contraction of the fibers due to temperature changes without affecting their performance.

3. 3. High Fiber Count: Loose tube cables can accommodate a high fiber count, housing a large number of individual fibers within the tubes. This makes them suitable for applications that require multiple fibers for high-capacity data transmission, such as long-distance telecommunications, data centers, or network backbones.

4. 4. Easy Maintenance and Repair: Loose tube fiber cables are designed for ease of maintenance and repair. The individual tube construction allows for easy identification and access to specific fibers, simplifying troubleshooting and repairs. It also enables selective replacement of damaged fibers without affecting the rest of the cable.

5. 5. Moisture Protection: In gel-filled loose tube cables, the gel compound inside the tubes acts as a moisture barrier, protecting the fibers from water ingress. This is particularly beneficial in outdoor and underground installations where moisture is a concern. Dry loose tube cables also use water-blocking materials to provide moisture resistance.

Rodent and Pest Resistance: The protective tubes in loose tube fiber cables provide a barrier against rodents, pests, and other external threats. This helps prevent damage to the fibers caused by animals or environmental factors, ensuring reliable and uninterrupted fiber optic communication.

Applications of Loose Tube Optical Cable

Loose Tube cable protects the fiber from stresses caused by the environment, namely moisture and temperature. The gel within the loose-tube construction stops the penetration of water and keeps it away from the fiber. Since fibers can move within the tube, the expansion and contraction that temperature variations produce in other materials do not transmit stress to the fibers. In this sense, loose-tube gel-filled cables offer the best protection in an outdoor environment. They are suitable for outdoor applications, including aerial, duct, CATV, long-distance, computer network systems, and LAN communication.

Although loose-tube fiber optical cables are used for high-fiber-count, long-distance telco applications, they are an inferior design for LAN applications where reliability, attenuation stability over a wide temperature range, and low installation cost are priorities. Since this cable is generally incompatible with indoor flammability codes, when it needs to be installed indoors, it must be normally terminated or spliced close to the cable entryway of a building. Due to the fragile bare fibers and gel filling, which must be cleaned prior to termination, loose-tube gel-filled cable is the most difficult to splice and terminate and also has the highest termination material costs. In the final termination process, all fibers must be either spliced or fed through the tubes of a breakout kit. These processes all add the complexity in termination and the splices inevitably decrease the reliability of the link. All the above reasons make loose-tube gel-filled cable an inappropriate choice for indoor/outdoor deployment. But it’s still good as an outdoor cable for its features.