Fiber-Optic Techniques - LAN Wiring - page 256

TABLE 11.3
Connector Color Code for Optical Fiber

Fiber type Core/cladding Connector color code Adapter color

Multimode 50/125 µm Black Black

Multimode 62.5/125 µm Beige Beige

Multimode 50/125 µm Aqua Aqua

laser-optimized

Single-mode N/A Blue Blue

Angled single-mode N/A Green Green

or to be unreliable. This relationship is so important that we have repeated it in
Table 11.3.
Installers and network managers should ensure that they use the proper color
code to indicate fiber mode on all connections and patch cords. However, there are
no special keying or connector differences to prevent mating single-mode to multi-
mode if that is really what you try to do. But you should easily be able to see the
color mismatch, if the color code is followed.

Optical Fiber Bandwidth

In multimode fiber, the most significant factor that limits link distance is called opti-
cal bandwidth . This term is a bit of a misnomer, as what is meant is the capacity for
information transmission. As with many of the optical parameters, there are signif-
icant differences between the commonly used coaxial cable transmission terms and
their corresponding optical-lingo meanings. The actual theoretical bandwidth of a
signal that can be carried on a fiber strand is extremely high, on the order of 50 to
300 GHz for short lengths. In practice, a system's bandwidth is determined by the
wavelength, the optics, the electronics, the connecting hardware, the fiber, and the
circuit length. Figure 11.6 shows some typical system bandwidth versus cable dis-
tance curves for single-mode and multimode fiber.
As you can clearly see, there is a vast performance difference in system band-
width between multimode and single-mode fiber types. Multimode fiber, as the
name implies, allows the propagation of many light modes, which gives rise to chro-
matic and modal distortion. This distortion of the light signal severely limits the
information capacity of multimode fiber. The minimum performance standards are
shown in Table 11.4. The useful bandwidth of a particular cable length can be
inferred by dividing the stated bandwidth-distance product by the actual length in
kilometers. Thus, from the table, a 100 m fiber run of 50/125 µm can be seen to
have a (500 MHz*km) / (0.1 km) = 5000 MHz effective bandwidth.