Specifications

RADring
Installation & Operation Manual Ethernet Design Considerations
3/11/98 12:25 Fiber Optic Design Considerations 7-5
7.3 Fiber Optic Design Considerations
Fiber Optic
Modules Network
Design
Considerations
• Use Fiber Optic Modules for long links, as a replacement for UTP
modules. You will achieve better performance and higher reliability.
• Use Fiber Optic Modules to carry sensitive information by fiber-optic
cable on exposed, outdoor segments.
• Use Fiber Optic Modules to convert copper segments to fiber-optic
segments where strong electrical interference (from industrial machines,
nearby radar or radio transmitters) may disrupt Ethernet operation, or
lightning strikes or high-voltage lines present a safety hazard.
Fiber Network
Design
Considerations
In general, Ethernet networks with several different transmission media -
UTP. COAX and fiber optic cable - can incorporate without any limitations.
Fiber Optic Budget
Calculations
A separate analysis must be performed on fiber optic Modules, to ensure that
their attenuation is not excessive. The maximum allowable attenuation of a
fiber optic link is determined as a function of the optical power budget
(described below).
Power Coupled in a Fiber
For short-distance links, the preferred light source is a LED. The
LED radiates a wide conical of light. The optical fiber has a much smaller
diameter, and the result is that a large part of LED light energy is lost. In fact,
the larger the fiber diameter, the more power is coupled into it.
The most common fiber diameters are: 50/125, 62.5/125 and 100/140
microns, where the first digits indicate core diameter (the active part), and
the second group of digits indicate clad diameter.
For example, let us compare the ratio of energy coupled into a 100/140
micron fiber, with respect to that coupled into a 50/125 micron fiber. Since
the LED is assumed to radiate uniformly within the angles of interest, the
power ratio is directly proportional to the area ratio, which is
(100/50)^2 = 4.
In dB, this means that 6dB more power (10 log4 = 6) is coupled into the
100/140 micron fiber. In practice, the ratio is even higher (close to 7dB,
considering the N.A. factor of the fiber). For the same reasons, the power
coupled into a 100/140 micron fiber is 4dB higher than the energy coupled
into a 62.5/125 micron fiber.
Note
The RADring modules can operate with all the common core diameters:
50/125, 62.5/125 and 100/140 microns.