Juniper EX4100 User Manual

Overview of EX Series Switches: Fiber-Opc Cable Signal Loss,
Aenuaon, and Dispersion
IN THIS SECTION
Signal Loss in Mulmode and Single-Mode Fiber-Opc Cable | 105
Aenuaon and Dispersion in Fiber-Opc Cable | 105
To determine the power budget and power margin needed for
ber-opc connecons, you need to
understand how signal loss, aenuaon, and dispersion aect transmission. EX Series switches use
various types of network cables, including mulmode and single-mode ber-opc cable.
Signal Loss in Mulmode and Single-Mode Fiber-Opc Cable
Mulmode ber is large enough in diameter to allow rays of light to reect internally (bounce o the
walls of the ber). Interfaces with mulmode opcs typically use LEDs as light sources. However, LEDs
are not coherent light sources. They spray varying wavelengths of light into the mulmode ber, which
reects the light at dierent angles. Light rays travel in jagged lines through a mulmode ber, causing
signal dispersion. When light traveling in the ber core radiates into the ber), higher-order mode loss
(HOL) occurs. (Cladding consists of layers of lower-refracve index material in close contact with a core
material of higher refracve index.) Together, these factors reduce the transmission distance of
mulmode ber compared to that of single-mode ber.
Single-mode ber is so small in diameter that rays of light reect internally through one layer only.
Interfaces with single-mode opcs use lasers as light sources. Lasers generate a single wavelength of
light, which travels in a straight line through the single-mode ber. Compared to mulmode ber, single-
mode ber has a higher bandwidth and can carry signals for longer distances. Single-mode ber is
consequently more expensive than mulmode ber.
Exceeding the maximum transmission distances can result in signicant signal loss, which causes
unreliable transmission.
Aenuaon and Dispersion in Fiber-Opc Cable
An opcal data link funcons correctly provided that modulated light reaching the receiver has enough
power to be demodulated correctly. Aenuaon is the reducon in strength of the light signal during
transmission. Passive media components such as cables, cable splices, and connectors cause
aenuaon. Although aenuaon is signicantly lower for opcal ber than for other media, it sll
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Juniper EX4100 Specifications

General

Brand	Juniper
Model	EX4100
Category	Switch
Language	English