What are the differences between loose-sheathed optical cables and tight-sheathed optical cables?

Optical cable structures can be classified into two types based on whether the optical fibers are tightly wrapped: loose sleeve structure and tight sleeve structure. These two structures are designed for different usage environments. Loose-fitting structures are mostly used for outdoor optical cables, while tight-fitting structures are mostly used for indoor optical cables (this article takes indoor branch optical cables as an example). Now let's discuss the differences between loose-fitting and tight-fitting optical cables.

Both loose-sheathed and tight-sheathed optical cables are multi-core optical cables composed of multiple optical fibers, but they differ in the following aspects.

The difference in structure

The loose tube structure optical cable inserts 250um optical fibers into loose tubes made of high modulus materials, and fills the loose tubes with grease. The center of the cable core is a metal (non-metallic FRP is optional) reinforcing core. Loose tubes are twisted around the central reinforcing core to form a circular cable core, and water-blocking fillers are added to the gaps inside the cable core. The cable is formed by longitudinally wrapping coated aluminum tape (APL) or corrugated coated steel tape (PSP) and then extruding polyethylene (PE) sheaths.

Indoor branch optical cables use φ2.0mm single-core optical cables (φ 900um tight-sheathed optical fibers, aramid reinforcing elements) as sub-units. The sub-unit layers of the optical cable are twisted around the FRP central reinforcing core to form the cable core, and a layer of polyvinyl chloride (PVC) or low smoke zero halogen (LSZH) sheath is extruded on the outside to form the cable.

Protection

The optical fibers of loose-fitting optical cables are placed in loose sleeves filled with grease. The grease helps prevent the optical fibers from getting damp, making the optical cable an ideal choice for harsh, high-humidity environments where water or condensation problems may occur.

The optical fibers of tight-wrapped optical cables have two layers of protection (a 250um coating layer and a 900um tight-wrapped layer).

Application

Loose-fitting optical cables are used for outdoor overhead, pipeline and direct-buried applications, as well as for the installation of external equipment in local area networks (Lans), metropolitan area networks (mans), wide area networks (Wans), long-distance and broadband networks. Telecommunication, campus backbone network, short-range operation, data center, CATV, broadcasting, computer network system, user network system and 10, 40, 100 GBPS Ethernet.

Tightly wrapped optical cables are used for indoor, data centers, backbone networks, horizontal optical cables, patch cords, equipment optical cables, Lans, Wans, storage area networks (SAN), and long indoor horizontal or vertical cabling.

Comparison

Tight-sheathed optical cables are more expensive than loose-sheathed optical cables because they use more materials in the optical cable structure. Due to the difference between 900um optical fibers and 250um optical fibers, under the same diameter conditions, tightly wrapped optical cables can accommodate a smaller number of optical fibers.

In addition, tight-wrapped optical cables are easier to install than loose-tube optical cables because there is no need to clean the cable paste and no splitters for fusion or termination are required.

Summary

Loose tube optical cables offer stable and highly reliable optical transmission performance over a wide temperature range, provide the best protection for optical fibers under high tension, and can be easily moisture-proof with water-blocking grease. Tight-packed buffered optical cables offer high reliability, versatility and flexibility, are smaller in size and easy to install.