Fiber optic cables often are classified as either indoor or outdoor fiber optic cables. This post will focus on the outdoor fiber optic cables, including the difference between indoor and outdoor fiber optic cables, basic types of outdoor fiber optic cables in terms of construction and their distinct features, and standard types of outdoor fiber optic cables in terms of installation methods.
Figure 1: indoor/outdoor fiber optic cable
Difference between indoor and outdoor fiber optic cables
Generally, they differ in water-blocking grade, flammability, and ruggedness.
Indoor fiber optic cables are required to be equipped with higher flame retardancy, like OFNP (optical fiber, nonconductive, plenum) used in the plenum space. This fiber optic cable would produce little smoke and nontoxic gas when exposed to fire. As used in-wall, indoor fiber optic cables are unnecessary to be much rugged or water-proof.
In contrast, harsh environments, like rocky conditions, moisture, temperature fluctuation, and heavier abrasion require outdoor fiber optic cables to resist environmental elements. They’re usually much more rugged due to thicker jackets or armored jackets, waterproof, and more resistant to abrasions and handling.
Basic types of outdoor fiber optic cables in terms of construction and their distinct features
There’re three most common outdoor fiber constructions: loose tube, ribbon, standard indoor/outdoor, ruggedized indoor/outdoor, and direct burial armored. We’ll examine their details individually by the sequential order of ruggedness.
Loose tube fiber optic cable
This is the most widely used cable construction for outside plant trunks. It is made with loose tubes filled with water-blocking gel, absorbent powder, or tape. The loose tube cable contains several fibers inside a small plastic/stainless steel tube, jacketed, with a central strength member or many strength members.
Figure 2: loose-tube gel-filled cable inner structure
Ribbon fiber optic cable
This cable has the most high-density bandwidth capacity because the fibers, typically 12 fibers, are laid out in rows in ribbons, and the ribbons are laid on top of each other. 144 fibers in ribbons only have a cross-section of about 1/4 inch or 6 mm, and the jacket is only 13 mm or 1/2 inch in diameter.
Figure 3: mini ribbon fiber optic cable, 3.0mm 12 core optical fiber cable with round OFNP jacket
We’ve previously discussed the difference between indoor and outdoor fiber optic cables and underlined that outdoor fiber cables are much more durable and solid. However, there is one type of fiber optic cable which can both be applied indoors and outdoors. This is the standard indoor/outdoor fiber optic cable.
The standard indoor/outdoor fiber optic cable is among the most popular fiber cables as it doesn’t cost much and is easy to handle. It can survive direct exposure to water and UV. Of course, its environment rating is not high, but enough for applications that span indoors and outdoors. Caution that it can’t bear regular handling or heavier abrasion due to its not enough robust jacket. Also, it can’t be directly stapled in place. Thus, it is often installed in a duct or conduit when used outdoors.
Figure 4: breakout style indoor/outdoor plenum fiber optic cable
Compared to the standard indoor/outdoor, the ruggedized indoor/outdoor construction, as its name implies, has a thicker jacket and a slightly larger core diameter. Therefore, it is suitable for harsh environments, providing additional protection against abrasion, handling, and rodents.
It costs a little higher than the standard indoor/outdoor, but it does this for good reasons. Because it’s even comparable in weight and bend-rating with the latter, yet with much higher performance. When deployed underground, it’s better installed in an underground duct or conduit as it won’t bear a long corrasion. It can be stapled directly in place.
figure 5: ruggedized indoor/outdoor riser breakout cable
Direct Burial Armored
As outdoor applications require, this direct burial armored outdoor fiber optic cable has an internal mental armoring, which significantly enhances its ability to resist abrasion, handling, and rodents effectively. This feature allows it to be directly buried below grade without a duct or conduit. It is most tolerant of harsh environments. However, it shouldn’t be installed indoors as it lacks the necessary features required for in-wall installation. It’s often terminated into an outdoor wall-box with an indoor fiber optic cable via an adapter.
The figure below depicts the detailed comparison between these three outdoor fiber cable construction types.
Figure 6: the comparison between the standard indoor/outdoor, ruggedized indoor/outdoor, and outdoor direct burial
Standard types of outdoor fiber optic cable in terms of installation methods
Underground duct or conduit pulling or air blowing
Underground fiber cables are either pulling or air blowing within a duct or conduit several meters deep below grade. Lubricants are often necessitated to reduce friction.
Figure 7: Gyty53 Double Jacket Outdoor Loose Tube Underground Duct Fiber Optical Cable
As the term suggests, direct buried fiber optic cables are buried underground alone. Unlike underground duct or conduit cabling, it stands alone and doesn’t have to recourse to a duct or conduit. It is tough enough to withstand moisture, pressure, or rodents.
Direct buried cables are more robust than underground cabling cables.
Figure 8: China Steel Stranded Loose Tube Direct Buried Armored Outdoor Fiber Optic Cable (GYTS)
Aerial outdoor fiber optic cables
These cables are installed aerially via poles, pylons, or buildings. It has a central strength member and a rugged outside jacket. It is easy to install via existing poles, mainly used for secondary trunk level and below, and usually applied to flat terrain or low fluctuation area. Due to the exposure to natural disasters, it has a higher failure rate than the previously mentioned cables. This fiber optic cable can also be subdivided into catenary wire and self-supporting. The All-Dielectric Self-Supporting (ADSS) cables, made of heavier jackets and more robust metal or aramid strength members, are subject to the self-supporting category. Another typical self-supporting outdoor aerial fiber optic cable is GYTC8S.
Figure 9: GYTC8S self-supporting outdoor fiber optic cable inner structure.
Submarine/Underwater outdoor fiber optic cables
Figure 10: new submarine fiber cable connects Europe and Latin America via Morocco
These submarine/underwater fiber optic cables must be waterproof, usually made of either a water-blocking gel, absorbent powder, or tape, applied to loose tubes or ribbon cables. These cables are built extremely ruggedly. At the center are fibers inside stainless steel tubes. Outside the fibers are many steel strength members to reduce tensions. These submarine cables are laid from the ship while operational.