13.4 High-Speed Lightwave Transceivers
531
• OM1 grade fiber is the original (often called legacy) multimode fiber that was
designed for use with LEDs. Most of these legacy fibers have a 62.5-μm-diameter
core, although in some cases the early installed fibers had a 50-μm-diameter
core. The bandwidth of these fibers is 200 MHz-km at 850 nm and 500 MHz-km
at 1310 nm. The data rates with LEDs are limited to about 100 Mb/s.
• OM2 grade fiber has an improved bandwidth and can be used to expand networks
that contain existing legacy 50-μm core diameter fibers. If only this fiber is used,
then at 850 nm it is possible to send 1-Gb/s signals over about 750 m distances
and 10 Gb/s over 82 m.
• OM3 grade fiber has a higher bandwidth and can support 10-Gb/s data rates over
distances up to 300 m.
• OM4 grade fiber has a bandwidth of 4700 MHz-km and increases the transmission distance to 550 m when using commercial 850-nm VCSELs for existing 1
and 10-Gb/s applications as well as for 40- and 100-Gb/s Ethernet systems.
• OM5 grade fiber has performance values similar to OM4 for insertion loss and
transmission distances. However, OM5 fiber is designed for use at wavelengths
of 850, 880, 910, and 940 nm, so that that it can support four simultaneous WDM
wavelengths. An attenuation value of 2.3 dB/km is specified for 953-nm operation,
but testing of installed links only needs to be done at 850 and 1300 nm wavelengths.
For a short-reach 10-Gb/s network to be compliant with installation standards, all
segments of the network should use the same grade of multimode fiber. However, in
some situations it may be impractical or too expensive to replace existing low-grade
multimode fiber with a higher-grade fiber. In this case most likely a link will contain a
mixture of, for example, OM2 and OM3 fibers that are spliced together. If the link is to
transport 10-Gb/s data, then the bandwidths of the fibers will determine the resulting
effective maximum link length. If all geometric parameters of the interconnected OM2
and OM3 fibers are the same, then a general expression for determining the effective
maximum length Lmax is given by
L max = L O M2
BW O M3
BW O M2
+ L O M3
(13.5)
where L OMx and BW OMx are the length and bandwidth, respectively, of the OMx
grade fiber. To be compliant with the maximum allowed dispersion, the effective
maximum link length calculated by Eq. (13.5) must be less than the achievable link
length if only OM3 fiber is used. For standard OM3 fiber this length is 300 m. With
OM4 fibers, the maximum length is 550 m at an 850-nm wavelength for operation
at 10 Gb/s.
Example 13.2 An engineer wants to create a link consisting of 40 m of OM2 fiber that
has a 500-MHz bandwidth and 100 m of OM3 fiber that has a 2000-MHz bandwidth.
What is the effective maximum link length?
Solution: From Eq. (13.5), the effective maximum link length is
531
• OM1 grade fiber is the original (often called legacy) multimode fiber that was
designed for use with LEDs. Most of these legacy fibers have a 62.5-μm-diameter
core, although in some cases the early installed fibers had a 50-μm-diameter
core. The bandwidth of these fibers is 200 MHz-km at 850 nm and 500 MHz-km
at 1310 nm. The data rates with LEDs are limited to about 100 Mb/s.
• OM2 grade fiber has an improved bandwidth and can be used to expand networks
that contain existing legacy 50-μm core diameter fibers. If only this fiber is used,
then at 850 nm it is possible to send 1-Gb/s signals over about 750 m distances
and 10 Gb/s over 82 m.
• OM3 grade fiber has a higher bandwidth and can support 10-Gb/s data rates over
distances up to 300 m.
• OM4 grade fiber has a bandwidth of 4700 MHz-km and increases the transmission distance to 550 m when using commercial 850-nm VCSELs for existing 1
and 10-Gb/s applications as well as for 40- and 100-Gb/s Ethernet systems.
• OM5 grade fiber has performance values similar to OM4 for insertion loss and
transmission distances. However, OM5 fiber is designed for use at wavelengths
of 850, 880, 910, and 940 nm, so that that it can support four simultaneous WDM
wavelengths. An attenuation value of 2.3 dB/km is specified for 953-nm operation,
but testing of installed links only needs to be done at 850 and 1300 nm wavelengths.
For a short-reach 10-Gb/s network to be compliant with installation standards, all
segments of the network should use the same grade of multimode fiber. However, in
some situations it may be impractical or too expensive to replace existing low-grade
multimode fiber with a higher-grade fiber. In this case most likely a link will contain a
mixture of, for example, OM2 and OM3 fibers that are spliced together. If the link is to
transport 10-Gb/s data, then the bandwidths of the fibers will determine the resulting
effective maximum link length. If all geometric parameters of the interconnected OM2
and OM3 fibers are the same, then a general expression for determining the effective
maximum length Lmax is given by
L max = L O M2
BW O M3
BW O M2
+ L O M3
(13.5)
where L OMx and BW OMx are the length and bandwidth, respectively, of the OMx
grade fiber. To be compliant with the maximum allowed dispersion, the effective
maximum link length calculated by Eq. (13.5) must be less than the achievable link
length if only OM3 fiber is used. For standard OM3 fiber this length is 300 m. With
OM4 fibers, the maximum length is 550 m at an 850-nm wavelength for operation
at 10 Gb/s.
Example 13.2 An engineer wants to create a link consisting of 40 m of OM2 fiber that
has a 500-MHz bandwidth and 100 m of OM3 fiber that has a 2000-MHz bandwidth.
What is the effective maximum link length?
Solution: From Eq. (13.5), the effective maximum link length is