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single mode vs multimode

Can somebody please explain to be what is the difference b/w single mode and multimode fiber? what is the selection criteria?

neil

  • WAN Routing and Switching
3 REPLIES
Cisco Employee

Re: single mode vs multimode

Hi Neil,

MMF allows multiple modes of light to propagate through the fiber. Multiple modes of light that propagate through the fiber travel different distances, based on the entry angles. The differences in travel speeds cause the modes to arrive at the destination at different times. MMF typically uses Light-Emitting Diodes (LEDs) to launch the optical signal.

SMF allows only one mode of light to propagate through the fiber. It uses lasers to 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. Therefore, it is capable of higher bandwidth and greater cable run distances than MMF.

Selection criteria is going to be based on transmission distance to be covered as well as the overall budget allowed, since SM fiber as well as the longer range transceivers will cost more.

HTH,

Bobby

Please rate helpful posts

Cisco Employee

Re: single mode vs multimode

Hi Neil,

MMF allows multiple modes of light to propagate through the fiber. Multiple modes of light that propagate through the fiber travel different distances, based on the entry angles. The differences in travel speeds cause the modes to arrive at the destination at different times. MMF typically uses Light-Emitting Diodes (LEDs) to launch the optical signal.

SMF allows only one mode of light to propagate through the fiber. It uses lasers to 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. Therefore, it is capable of higher bandwidth and greater cable run distances than MMF.

Selection criteria is going to be based on transmission distance to be covered as well as the overall budget allowed, since SM fiber as well as the longer range transceivers will cost more.

HTH,

Bobby

Please rate helpful posts

Silver

Re: single mode vs multimode

To add to the previous explanation and to give you an idea as to the physical size of the fibers. Multimode fibers come in sizes of 52um to 65um (millionth of a meter). Single mode fiber comes in a size of 9um.. You can see why multimode allows multiple wavelengths through. Also multimode is alot cheaper then single mode. Usually singlemode is used in carrier applications to support major pipes. Multimode is commonly used for Gig-E, FDDI, OC-3, Escon applications.....

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