Tag Archives: Loose Tube

250um Bare Fiber vs. 900um Tight Buffer Fiber


Ever wonder the difference between loose-tube 250um bare fiber and tight-buffered 900um fiber? Loose-tube 250um and tight-buffered 900um fiber cables actually start with the same 250um bare fibers that feature the same size fiber core (i.e., 50um for multimode and 9um for singlemode), 125um cladding and soft 250um coating. The difference between these two cables all lies in the cable construction.

900um Fiber Adds an Additional Layer
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.

250um Bare Fiber vs. 900um Tight Buffer Fiber
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.

900um fiber cable

250um Fiber Is Enclosed in Tubes
Loose-tube 250um fiber 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. Buffered loose-tube cables feature an outer waterblocking tape around the tubes, beneath the outer jacket.

 250um fiber cableThe tubes themselves are gel-filled to prevent water migration, or they are available with a dry waterblocking technology—sometimes referred to as gel-free cable. Both of these materials are vital to prevent water from migrating into the tubes and potentially freezing, expanding and breaking the fiber. Dry waterblocking technology significantly reduces installation time by eliminating the need to clean off the gel prior to termination.

Loose-tube 250um fiber cable comes in various fiber counts that typically range from 6 to 144. With the exception of a 6-fiber cable, the fibers are grouped into sets of 12 for maximum density. Speaking of density, without the 900um plastic coating, loose-tube 250um fiber cables are less than half the size of 900um fiber cables—1.4 inch (35.6 mm) for a 144-fiber tight buffer cable and only 67 inch (17 mm) for an outdoor 144-fiber loose-tube cable.

From Outdoor to Indoor Applications
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.

cable terminationWhile 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. 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.

Loose Tube or Tight Buffered Fiber Optic Cable?


Fiber optic cable is available in many physical variations, such as single and multiple conductor constructions, aerial and direct burial styles, plenum and riser cables, etc. But there are two basic styles of fiber optic cable construction: loose tube fiber and tight buffered fiber. From the picture below, we can see that loose tube fiber holds more than one optical fiber, each individually sleeved core is bundled loosely within an all-encompassing outer jacket. However, in tight buffered cables, there are not so many cables as loose tube fibers.

loose tube fiber
Loose Tube Fiber

Loose tube fibers are designed for harsh environmental conditions in the outdoors. In loose tube cables, the coated fiber “floats” within a rugged, abrasion resistant, oversized tube which is filled with optical gel. Since the tube does not have direct contact with the fiber, any cable material expansion or contraction will not cause stress on the fiber. This gel also helps protect the fibers from moisture, making the cables ideal for high humidity environments. Cable containing loose buffer-tube fiber is generally very tolerant of axial forces of the type encountered when pulling through conduits or where constant mechanical stress is present such as cables employed for aerial use. Since the fiber is not under any significant strain, loose buffer-tube cables exhibit low optical attenuation losses. Although loose-tube gel-filled fiber optic cables are used for high-fiber-count, long-distance telco applications, they are an inferior design for the Local Area Network applications where reliability, attenuation stability over a wide temperature range and low installed cost are the priorities.

Tight Buffered Cable

Tight buffered cables, in contrast, are optimized for indoor applications. In the tight buffer construction, instead of using the gel layer loose tube cable has, it uses a two-layer coating. One is plastic and the other is waterproof acrylate. So tight buffered cables may be easier to install, because there is no gel to clean up and it does not require a fan out kit for splicing or termination. Because the fiber is not free to “float” however, tensile strength is not as great. Tight buffer cable is normally lighter in weight and more flexible than loose-tube cable and is usually employed for less severe applications. Such applications include moderate distance transmission for telco local loop, LAN, SAN, and point-to-point links in cities, buildings, factories, office parks and on campuses. Tight-buffered cables offer the flexibility, direct connectability and design versatility necessary to satisfy the diverse requirements existing in high performance fiber optic applications.

Each construction has inherent advantages. The loose buffer tube offers lower cable attenuation from microbending in any given fiber, plus a high level of isolation from external forces. Under continuous mechanical stress, the loose tube permits more stable transmission characteristics. The tight buffer construction permits smaller, lighter weight designs for similar fiber configuration, and generally yields a more flexible, crush resistant cable. So, you should choose the appropriate cable for your applications. Fiberstore offers both loose tube and tight buffer cables with high quality and low price. It may be your optimal choice to buy optic products.

Related article:

Tight-Buffered Distribution Cable Basis

Tight-Buffered Cable vs. Loose-Tube Gel-Filled Cable