Net Optics GigaBit Media Converters - Manual (Page 9)

GigaBit Media Converter
5
Connecting to the Network
When installing the GigaBit Media Converter, care must be taken in choosing
the appropriate cabling to avoid Differential Mode Delay (DMD) effects.
DMD is caused by singlemode, (1310 nanometer) laser point sources
launching into multimode cable. Optical power is concentrated in the center of
the fiber core, propagating in less than 5% of possible modal paths. This can
result in reduced bandwidth and/or the appearance of individual data pulses,
refracting into multiple, overlapping, light pulses at the receiver end, causing
CRC errors.
The connection requires a Mode Conditioning patch cable to provide
the Conditioned Launch necessary to prevent (DMD) effects. Mode
Conditioning patch cables are not used with short wave length (850 nano-
meter) lasers. Note that fiber cable is typically certified for a particular
bandwidth using light emitting diodes (LEDs) that provide the “Overfilled
Launch” condition i.e. illuminate all possible modes and fibers.
For additional details see the Restricted Launch Specification defined by the
Telecommunications Industry Association. The TIA FO-2.2.1 Committee
has released two standards: (1) FOTP-203: Launched Power Distribution
Measurement Procedure for Graded-Index Multimode Fiber Transmitters, and
(2) FOTP-204: Measurement of Bandwidth on Multimode Fiber.