HPE X130 10G SFP+ LC LH80, Руководство пользователя, Страница: 6 / 63

2
Transmission distances supported by optical transceiver modules are mainly limited by signal
attenuation and dispersion suffered during the transmission of fiber signals over fibers.
•
Signal attenuation occurs because of absorption, dispersion, and leakage over the media as
light travels through optical fibers. This attenuation increases in direct ratio to transmission
distance.
•
Dispersion occurs because a fiber transmits light with different wavelengths at different
speeds. Light with different wavelengths reaches the receiving end at different time. This
results in spread and blurred pulses.
Central wavelength
Central wavelength represents the wave band used for optical signal transmission. The following
central wavelengths (wave bands) are available for common optical transceiver modules: 850 nm,
1310 nm, and 1550 nm.
• The 850 nm wave band is used for short-reach transmission.
• The 1310 nm and 1550 nm wave bands are used for middle-reach and long-haul
transmissions.
Fiber
Fiber types
Fibers are classified into multimode fibers and single-mode fibers.
• Multimode fibers
Multimode fibers (MMFs) have thicker fiber cores than single-mode fibers and can transport
light in multiple modes. However, the intermodal dispersion is greater and worsens as the
transmission distance increases.
Multimode fibers can be classified into multiple grades according to their diameters and modal
bandwidth, as shown in Table 1 . The modal bandwidth is a comprehensive index that reflects
the optical characteristics of a multimode fiber. The modal bandwidth of a multimode fiber is
equal to
the modulation frequency of the maximum modulation frequency pulse that can pass
a fiber
×
the fiber length
.
International Telecommunication Union (ITU) defines multimode fiber types in its G series
standards. The most commonly used multimode fiber is defined in the ITU G.651 standard.
The G.651-compliant fiber transmits light in the wavelength range of 800 nm to 900 nm or
1200 nm to 1350 nm.
Table 1 Multimode fiber grades
Fiber grade Fiber diameter (μm) Modal bandwidth at 850 nm (MHz*km)
OM1 62.5/125 200
OM2 50/125 500
OM3 50/125 2000
OM4 50/125 4700
Other factors that determine the transmission distance of multimode fibers include interface
type, central wavelength, and fiber grade, as shown in Table 2 .
Table 2 Multimode fiber specifications
Interface type Central wavelength (n m) Fiber grade Transmission distance
1000BASE-SX 850 OM1 < 275 m (902.23 ft)