The Structure of a 250um Coated Fiber (Bare Fiber)
- Core (9um for standard single mode fibers, 50um or 62.5um for multimode fibers)
- Cladding (125um)
- Coating (soft plastic, 250um is the most popular, sometimes 400um is also used)
The Structure of 900um Tight-buffered Fiber
- Core (9um for standard single mode fibers, 50um or 62.5um for multimode fibers)
- Cladding (125um)
- Coating (soft plastic, 250um)
- Tight buffer (hard plastic, 900um)
Loose tuber fiber (250um) places up to 12 bare 250um fibers inside a flexible plastic tube, which are also color coded and situated around a central strength member with Kevlar or aramid yarn for protection.
The fiber counts of loose-tube 250um fiber cable range from 6 to 144, and besides the 6-fiber cable, the fibers are also grouped into sets of 12 for maximum density. Loose-tube 250um fiber cables are less than half the size of 900um fiber cables.
Tight-buffered 900um fiber includes an additional 900um layer of hard plastic over the 250um fibers for protection.
Within the cable, several of these color-coded 900um tight buffered fibers are situated around a central strength member
and then covered with Kevlar or aramid yarn for protection, a rip cord and then the jacket.
Tight-buffered 900um fiber cable comes in various fiber counts that typically range from 2 to 144 fibers,
with larger fiber counts featuring fiber subunits of 6 or 12 fibers within the cable.
For example, a 144-fiber cable usually has twelve 12-fiber subunits while a 36-fiber cable could
have six 6-fiber subunits or three 12-fiber subunits.
From Outdoor to Indoor Applications
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Generally speaking, tight-buffered 900um fiber cables are used for indoor applications, including intra-building riser and plenum applications and in the data center. Loose-tube 250um fiber cables are typically used in outside plant (OSP) applications, such as inter-building duct, aerial and direct buried installations.
While indoor/outdoor cables are popular for eliminating the need for service entrance splicing to in-building cable, OSP loose-tube 250um cabling must be terminated within 50 feet of entering a facility. To accomplish this, breakout kits are used to build the 250um cable up for protection and termination to 900um connector boots.
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The problem with breakout kits is that they add additional material costs and a significant amount of labor. One option is to terminate the 250um fiber directly to 250um connector boots. This can speed network deployment in the data center and fiber-to-the-home applications.
