TABLE 2: Evolution of VCSEL-based links over MMF. Question marks=still not determined.
October/November/December 2020 I 63
Data Rate
Gb/s
Ethernet Standard
Proprietary/MSA Module
IEEE
Standard/MSA/
# Fiber
Pairs # ’S Optical
Modulation
Reach (m)
OM3 OM4 OM5
100 100GBASE-SR4 Standard 4 1 25G NRZ 70 100 Same
as OM4
100 100G – SWDM4 MSA 1 4 25G NRZ 75 100 150
100 100G – BiDi Proprietary 1 2 50G PAM4 70 100 150
400 400GBASE-SR16
Standard
16 1 25G NRZ 70 100
Same
as OM4
50 50GBASE-SR 1 1 50G PAM4 70 100
100 100GBASE-SR2 2 1 50G PAM4 70 100
200 200GBASE-SR4 4 1 50G PAM4 70 100
400 400GBASE-SR8
Standard
8 1
50G PAM4 70 100
Same
as OM4
400 400GBASE-SR4.2 4 2 150
100 100GBASE-SR
IEEE 802.3
Study Group
1
1 100G PAM4 30? 50? Same
200 200GBASE-SR2 2 as OM4
400 400GBASE-SR4 4
800 800GBASE-SR8 Future
Technology
8 1 100G PAM4 50?
4/4/800/1600 4/800/1600GBASE-SRm.n. 1/2/4/8 TBD 100G PAM4 100M OVER MMF
breakout
to server
will be first
use of
100G/lane
VCSELs
Potential Next Generation MMF Links
Current MMF technology allows speeds of up to 200 Gb/s
in a single fiber pair by combining WDM and advanced
signal modulation. As 100 Gb/s lanes become available,
four wavelength WDM can provide the capability to support
400 Gb/s links over a pair of fibers and up to 1.6 Tb/s
over 4 pairs of fiber. Of course, significant work remains
in order to support four wavelength, 100 Gb/lane/s WDM,
primarily on the transceiver side.
MSAs Play an Important Role
In March 2017, an SWDM MSA was developed
and released with specifications for 40 Gb SWDM4 and
100 Gb SWDM4. Commercial 40 Gb SWDM4 and 100 Gb
SWDM4 products are currently available. These SWDM4
modules utilize four wavelengths with 30 nm spacing
(850 nm, 880 nm, 910 nm and 940 nm).
Essentially, 100 Gb BiDi uses two wavelengths
(857 and 908 nm) to extend the value of duplex cabling
and connectivity infrastructure. Commercial 100 Gb
BiDi products became available at the beginning of 2018
and have since been widely adopted.
The key value proposition of SWDM4 and 100 Gb
BiDi is the utilization of much lower cost, often already
installed, duplex fiber cabling and connectivity instead
of parallel fiber cabling and connectivity.
An MSA on 400 Gb BiDi was announced in July 2018
to define optical data link specifications and promote the
adoption of interoperable 400 Gb/s optical transceivers
based on a dual-wavelength bidirectional transmission
technology over MMF. These parts are expected to be fully
compliant and backward compatible with IEEE 802.3cm
400GBASE-SR4.2 standards-based products.
The supported reaches for OM3, OM4 and OM5 fiber
for 100 Gb-SWDM4, 100 Gb-BiDi, 400 Gb-BiDi, along
with MMF PMDs from 802.3bs, 802.3cd and 802.3cm are
shown in Table 2. Highlighted is the extended reach
benefit and future-proofing value proposition of OM5.
It also points out the potential of 100Gb/s lanes for
an 800 Gb solution.
CONCLUSION
Ultimately, successful technology will leverage both improved MMF and VCSEL-based transceiver properties in order
to minimize total link costs in the cost-sensitive short-reach enterprise/data center environment, preserving the
VCSEL-MMF link advantages far into the future.
The strong projected growth trends for MMF, in conjunction with standards advancements, ensure that MMF
solutions are here to stay—giving ICT designers and installers continually more flexibility for their customers’
cost-effective data center and enterprise high-speed applications.