Cisco Systems 7609 manual Appendix B Connector and Cable Specifications

Appendix B Connector and Cable Specifications

Cable Specifications

Lasers launch light in a more concentrated fashion. A laser transmitter couples light into only a fraction of the existing modes or optical pathways present in the fiber-optic cable. (See Figure B-9.)

The solution is to condition the laser light launched from the source (transmitter) so that it spreads the light evenly across the diameter of the fiber-optic cable, making the launch look more like an LED source to the cable. The objective is to scramble the modes of light to distribute the power more equally in all modes and prevent the light from being concentrated in just a few modes.

An unconditioned launch, in the worst case, might concentrate all of its light in the center of the fiber-optic cable, exciting only two or more modes equally.

A significant variation in the amount of DMD is produced from one MMF cable to the next. No reasonable test can be performed to survey an installed cable plant to assess the effect of DMD. Therefore, you must use the mode-conditioning patch cords for all uplink modules using MMF when the link span exceeds

984feet (300 meters). For link spans less than 300 meters, you can omit the patch cord (although there is no problem using it on short links).

For link spans less than 984 feet (300 meters), you can omit the patch cord. (We do not recommend using the LX/LH GBIC and MMF without a patch cord for very short link distances of 33 to 328 feet (10 to 100 meters.) The result could be an elevated bit error rate [BER]).

	Cisco 7609 Internet Router Installation Guide
B-16	OL-5079-04