Upgrade to High Data Rate Transmission With Parallel Optics

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Parallel optics represent a type of optical communication technology as well as the devices on
either end of the link that transmit and receive information which are also known as parallel optical
transceivers. Compared with traditional optical communication, parallel optical communication
employs a different cabling structure for signal transmitting aiming at high-data transmission for
short reach multimode fibers that are less than 300 meters. Traditional fiber optic transceivers
cannot satisfy the increasing demand for high speed transmission, like 40GbE, while parallel optics
technology can be a cost effective solution for 40/100GbE transmission.
Comparison between parallel optics technology and the traditional serial optical communication
would better explain what parallel optics is and the reason why it is a cost effective solution to high
data rate transmission. The following of this article will offer the comparison between the two
optical communication technology from two aspects: connectivity method and key components.
Connectivity Method
Literally, parallel optics and serial optics transmit signals in different ways. In traditional serial
optical communication, on each end of the link, there are one transmitter and one receiver. For
example, the transmitter on End A communicates to the receiver on End B, sending a single stream
of data over a single optical fiber. And a separate fiber is connected between the transmitter on End
B and the receiver on End A. In this way, a duplex channel is achieved by two fibers.
While in parallel optical communication, duplex transmission is achieved in a different way. A signal
is transmitted and received through multiple paths, thus, the parallel optical communication can
support higher data rate than the traditional optical communication. This is because, the devices for
Upgrade to High Data
Rate Transmission With
Parallel Optics

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Fiberstore White Paper | Upgrade to High Data Rate Transmission With Parallel Optics
parallel optic communication on either end of the link contain multiple transmitters and receivers.
For instance, in 2010 IEEE 802.3ba approved the 40GBASE-SR4 physical-medium-dependent
multimode parallel optical solution, which uses eight fibers to transmit four duplex channels each at
10 Gigabit Ethernet. In this case, four 10Gbps transmitters on End A communicate with four 10Gbps
receivers on End B, spreading a single stream of data over four optical fibers at a total data rate of
40Gbps.
Key Components
The parallel optical communication transmitting signals over multiple fibers, which has great
advantages over traditional serial optical communication. It also means that it requires different
components to support its high data rate transmission.
Connector: As previously mentioned, duplex transmission in serial optical communication uses
2-fiber duplex connectors, like duplex LC connectors to link the optics with other devices, while in
parallel optical communication, multi-fibers are used to reach a higher data rate. Thus, multi-fiber
connectors, like 12-fiber MPO connectors are used to connect with other devices. MPO connector is
one key technology support parallel optical communication. This connectivity method is showed in
the following picture (Tx stands for transmit; Rx stands for receive).
Optical transceiver light source: Another complementary technology for parallel transmission is the
light source of parallel optics—VCSELs (Vertical Cavity Surface Emission Lasers). Comparing with the
edge-emitting semiconductor lasers in the traditional optics, VCSELs have better formed optical
output which enables them to couple that energy into optical fibers more efficiently. In addition,
VCSELs emit from the top surface, they may be tested while they are part of a large production
batch (wafer), before they are cut into individual devices, which dramatically lowers the cost of the
lasers. The following chart is about the comparison between VCSELs and edge-emitting
semiconductor lasers. Cheaper to manufacture, easier to test, less electrical current required,
supporting higher data rate, parallel optics using VCSELs could be a better choice to reach
40/100GbE transmission compared with traditional serial optics.

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VCSEL vs Edge-Emitting Laser
Feature VCSEL Edge-Emitting Laser
Power consumption 2-3 mW 20 mW
Beam quality/ease of coupling Better, round low divergence Fine, asymmetric
Speed 10 Gbps 1 Gbps
Temperature stability 0.06 nm/oC 0.25 nm/oC
Specral width 1 nm 1-2 nm
Speckle Low in an array High
Parallel Optics for 40/100GbE Transmission
IEEE has already included physical layer specifications and management parameters for 40Gbps and
100Gbps operation over fiber optic cable. Two popular parallel optics solutions for 40Gbps and
100Gbps over multimode fibers are introduced here. For 40G, 40GBASE-SR4 transceiver is usually
used, which requires a minimum of eight OM3/OM4 fibers for a transmit and receive link (4 fibers
for Tx and 4 fibers for Rx). 100GBASE-SR10 transceiver is for 100Gbps transmission, which requires a
minimum of 20 OM3/OM4 fibers for a Tx/Rx link, 10 fibers are used for Tx and the other 10 are for
Rx.
Conclusion
The capabilities and uses of parallel optics and MPO technology continue to evolve and take shape
as higher-speed fiber optic transmission, including 40/100GbE. It is uncertain that parallel optical
communication would be the trend in the future. However, many cabling and network experts have
pointed out that parallel optical communication supported with MPO technology is currently a way
to equip an environment well prepared for the 40/100GbE transmission.

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Notice: This document is for informational purposes only and does not set forth any warranty, expressed or
implied, concerning any equipment, equipment features, or service offered or to be offered by Fiberstore.
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