Signal Loss In Multimode And Single-Mode Fiber-Optic Cables - Juniper QFX10008 Hardware Manual

QFX10008 Switch Hardware Guide
Table 57: QSFP+ MPO Fiber-Optic Crossover Cable Pinouts (continued)
Pin
7
8
9
10
11
12
Understanding QFX Series Fiber-Optic Cable Signal Loss, Attenuation, and Dispersion
132
To determine the power budget and power margin needed for fiber-optic connections,
you need to understand how signal loss, attenuation, and dispersion affect transmission.
The QFX Series uses various types of network cables, including multimode and
single-mode fiber-optic cables.
Signal Loss in Multimode and Single-Mode Fiber-Optic Cables on page 132
Attenuation and Dispersion in Fiber-Optic Cable on page 133

Signal Loss in Multimode and Single-Mode Fiber-Optic Cables

Multimode fiber is large enough in diameter to allow rays of light to reflect internally
(bounce off the walls of the fiber). Interfaces with multimode optics typically use LEDs
as light sources. However, LEDs are not coherent light sources. They spray varying
wavelengths of light into the multimode fiber, which reflect the light at different angles.
Light rays travel in jagged lines through a multimode fiber, causing signal dispersion.
When light traveling in the fiber core radiates into the fiber cladding (layers of lower
refractive index material in close contact with a core material of higher refractive index),
higher-order mode loss occurs. Together, these factors reduce the transmission distance
of multimode fiber compared to that of single-mode fiber.
Single-mode fiber is so small in diameter that rays of light reflect internally through one
layer only. Interfaces with single-mode optics use lasers as light sources. Lasers generate
a single wavelength of light, which travels in a straight line through the single-mode fiber.
Compared to multimode fiber, single-mode fiber has a higher bandwidth and can carry
signals for longer distances. It is consequently more expensive.
For information about the maximum transmission distance and supported wavelength
range for the types of single-mode and multimode fiber-optic cables that are connected
to the QFX Series, see
the Hardware Compatibility Tool
transmission distances can result in significant signal loss, which causes unreliable
transmission.
Pin
6
5
4
3
2
1
. Exceeding the maximum
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