The Difference Between Loose Tube & Tight-Buffered Cables

The Difference Between Loose Tube & Tight-Buffered Cables

07/11/2022

The world of fiber optics is vast and contains a wide spectrum of variations, specs, configurations and applications. While the scope of possibilities may seem overwhelming at first, there are some distinctions that will assist in choosing the desired specifications for your ideal product. One of these distinctions is the construction style of the cable and deciding between a loose tube or a tight-buffered configuration.  

What is a loose tube fiber optic cable? 

A loose tube fiber optic cable is a classic construction style that is ideal for harsh environments, particularly the outdoors. The fiber core, cladding and coating are enclosed within semi-rigid protective sleeves or tubes which can be tailored to meet the requirements of the application. With this design, the enclosed fiber can move freely inside the protective sleeve or tube. If the cable will be holding more than one optical fiber, each individually sleeved core is bundled loosely within an all-encompassing outer jacket. Due to its construction, loose tube cables can be prepared more easily and expand and contract with temperature changes.

For some applications, loose tube cables can be made with a water-resistant gel that surrounds the fibers; this gel helps protect the fibers from moisture, which is particularly useful in environments with high humidity. However, a dry compound is more commonly used today instead of a gel. These cables require extra time for preparation as the operator has to clean the gel or the dry compound beforehand.

What is a tight-buffered fiber optic cable?

While the loose tube cable has many positive aspects, its relative, the tight-buffered fiber optic cable, provides several benefits for different applications. In a tight-buffered cable, the fiber core is coated with plastic and a waterproof acrylate which prevents moisture from entering the cable and ensures the fiber is never exposed. This two-layer coating also results in a sturdier structure than a loose tube structure and it has the added advantage of being easier to install. For underwater applications or those intended to be routed around multiple bends, a tight-buffered cable is preferable. Unlike a loose tube style where too much strain on the cable during routing will force fibers to emerge, the tight-buffered cable will remain stable.

A combination of these two cable structures is used for semi-loose tube construction. This configuration includes a tight-buffered fiber within a layer of strength members and an outside jacket. As defined in the ARINC 802 aerospace standards, this type of structure is built to allow for limited movement of the optical fiber and secondary buffer within the outer jacket. Semi-loose cables are commonly used in the aerospace industry to combine ease of preparation, installation and environmental performance.

Connector options: Pull-Proof and Non Pull-Proof

Depending on the fiber optic cable construction you choose, two types of optical contact designs are available: pull-proof and non pull-proof. 

A pull-proof connector is used with a loose tube cable or semi-loose construction; the connector is attached to the jacket or buffer independent of the fiber and ferrule inside, so when the jacket or buffer receives any pull force, the fiber and ferrule are unaffected. 

Tight-buffered cables will be terminated with non pull-proof connectors; the buffer or jacket is attached to the fiber and cannot move independently, so they will both be attached to the connector. Pulling on the buffer or jacket will result in pulling on both the fiber and the ferrule which is going to move backward, cutting the optical link. It is important to not use tight-buffered cables with pull-proof connectors, otherwise, the piston of the ferrule will damage the fiber.

To gain a deeper understanding of connector options for these types of cables, a great example is the LuxCis series from Radiall.

Timbercon specializes in offering unique custom builds to fit your needs, whether they be loose tube or tight-buffered. To learn more about what fiber optic solutions are ideal for your project, contact us to speak with one of our experts. 

 

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