Fiber Types and Associated Optical Transceivers

An optical fiber is a flexible filament of very clear glass capable of carrying information in the form of light. Optical fibers are hair-thin structures created by forming pre-forms, which are glass rods drawn into fine threads of glass protected by a plastic coating. Fiber manufacturers use various vapor deposition processes to make the pre-forms. The fibers drawn from these pre-forms are then typically packaged into cable configurations, which are then placed into an operating environment for decades of reliable performance.

Core and cladding are the two main elements of an optical fiber. The core, made of silica glass, is the light transmission area of the fiber. Sometimes it may be treated with a “doping” element to change its refractive index and therefore the velocity of light down the fiber. The cladding is the layer completely surrounding the core. The difference in refractive index between the core and cladding is less than 0.5 percent. The refractive index of the core is higher than that of the cladding, so that light in the core strikes the interface with the cladding at a bouncing angle, gets trapped in the core by total internal reflection, and keeps traveling in the proper direction down the length of the fiber to its destination.

Surrounding the cladding is usually another layer, called coating, which typically consists of protective polymer layers applied during the fiber drawing process, before the fiber contacts any surface.

Fiber designs that are used today include single-mode and multimode fiber. Multimode fiber simply refers to the fact that numerous modes of light rays are carried simultaneously through the waveguide. Multimode fibers used in telecom or datacom applications have a core size of 50 or 62.5 microns. Single-mode fiber shrinks the core down so small that the light can only travel in one ray. The typical core size of a single-mode fiber is 9 microns.

The table below summarizes various optical interfaces and their performance over the different fiber types. The table is directly derived from the IEEE 802.3-2005 standard and specifies the maximum reach achievable over each fiber type and the requirement for a mode conditioning patch cord (MCP).

These performance levels are guaranteed. If we go beyond the standard, longer reaches may be achievable depending on the quality of each link. Fiber quality can vary for a specific type due to the aging factor or to the random imperfections it was built with. In order to really know if a link can work, the rule is to try and see if the performance is satisfactory. The link should be either error-free for critical applications, or the bit error should remain below 10-12 as per minimum standard requirement.

For example, it may be possible to reach much longer distances than 550 m with an OM3 laser-optimized fiber and 1000BASE-SX interfaces. Also, it may be possible to reach 2 km between two 1000BASE-LX devices over any fiber type with mode conditioning path cords properly installed at both ends.

The reaches in the table below illustrate typical performance observed in the field. They may vary with the rate and fiber type and should not be considered as guaranteed. NDSF refers to non-dispersion shifted fiber. DSF means dispersion shifted fiber with a zero dispersion centered at 1550 nm, while NZDSF means non-zero dispersion shifted fiber with a zero dispersion usually centered at 1510 nm.

Fiber optic cables are the medium of choice in telecommunications infrastructure, enabling the transmission of high-speed voice, video and data traffic in enterprise and service provider networks. This article has briefly explained optical fiber basis and its structure as well as the associated transceivers by the fiber types. As a professional supplier in optical industry, FS.COM has all kinds of transceivers, such as SFP-10G-ER, GLC-LH-SMD, etc. And Fiberstore also provides customized service according to your special requirements.