White Paper
MPO/MTP® – Introduction to Parallel Optics
Technology
White Paper | MPO and MTP® - Parallel Optical Interface Technology | EN | Pirmin Koller, Dr. Thomas Wellinger 2
MTO and MTP® – Introduction to Parallel Optics Technology
Contents
1. Data centers present and future 4
1.1. Bandwidth as the driving force ..............................................................................................4
1.2. 10 GbE as the status quo......................................................................................................5
1.3. 40/100 GbE in the not too distant future................................................................................6
2. Components and solutions for 40/100 GbE 7
2.1. OM3/OM4 – Laser-optimized multimode optical fibers .........................................................7
2.2. Parallel optical channels........................................................................................................8
2.3. MPO/MTP® – Multi-fiber connectors for high port density.....................................................9
2.3.1. MPO connectors: structure and function ...............................................................................9
2.3.2. MTP® connectors with Elite® ferrules from R&M .................................................................10
2.3.3. Trunk cables ........................................................................................................................14
3. The components in the system 16
4. Summary 16
© Copyright 2011 Reichle & De-Massari AG (R&M). All rights reserved.
It is not permitted to pass on and replicate this publication or parts of it for whatever reason and in whatever form without express
written permission from Reichle & De Massari AG. Information contained in this publication may be altered without prior notice. This
document was produced with the greatest possible care; it presents the state of the art at the time of preparation.
White Paper | MPO and MTP® - Parallel Optical Interface Technology | EN | Pirmin Koller, Dr. Thomas Wellinger 3
Multi-fiber connectors now becoming the stan-
dard
The number of network connections in data centers is on
the rise. Data centers have to achieve ultra-high density
in cabling to accommodate all this cabling in the first
place. Multimode fiber optics is the medium of the future
for satisfying the growing need for transmission speed
and data volume over short distances. Parallel optics
technology is what you get if you combine both trends –
cabling density and the use of fiber optics. It is a suitable
solution for high-performance data networks in data cen-
ters. New multi-fiber connectors bring together 12 or 24
fibers in a single interface just as compact as an RJ45
connector. Ultra-parallel connections involve tougher
requirements in terms of quality, the components and
the handling of the connectors. The multi-fiber push-on
(MPO) technology and especially the MTP® connectors
from the manufacturer US Conec in connection with
Elite® ferrules have proven to be a practical solution.
R&M has pushed for further advances in this technology,
setting new quality standards in the finish of the fiber
endfaces in particular. These endfaces far outperform
the standard and ensure lasting reliability and total
transmission quality. The groundwork is laid for a broad
introduction of the MPO technology in data centers,
where pre-terminated solutions are generally employed
anyway.
This white paper provides introductory information on parallel optics and MPO technology. It pre-
sents performance and quality criteria and is meant as an initial orientation for decision makers in
helping them plan their fiber optics strategy and select their connection technology.
Application: Data center networks,
10 and 40/100 Gigabit Ethernet
Technology: Multimode fiber optic cabling
Format: White Paper
Subjects: Multi-fiber connectors, MPO/MTP®
connectors, Elite® ferrules, per-
formance, precision of fiber end-
faces, core dip, fiber protrusion,
plug and play with pre-terminated
trunk cables, 10GBASE-SR,
40GBASE-SR4, 100GBASE-
SR10, EIA/TIA 604-5, IEC 61754-
7,
EN 50377-15-1:2011
Objective: To orient readers on MPO tech-
nology and inform them about
quality and performance criteria,
about the use of advanced high-
density fiber optic technologies in
data centers and about planning,
purchasing and operations. R&M's
stance on MPO/MTP®.
Target group: Data centers, data center plan-
ners, installers, network managers
Authors: Pirmin Koller,
Dr. Thomas Wellinger
Published: August 2011
White Paper | MPO and MTP® - Parallel Optical Interface Technology | EN | Pirmin Koller, Dr. Thomas Wellinger 4
1. Data centers present and future
The need for ever-greater bandwidths continues unabated. Data centers must respond early to provide suffi-
cient capacities and plan for upcoming requirements. This chapter explains the reasons for the relentless
growth in bandwidth and describes possible solutions to it.
1.1. Bandwidth as the driving force
The data quantity transmitted worldwide is growing exponentially. It will quadruple in the next four years
alone. The network outfitter Cisco issued that forecast in June 2011. It said just under one zettabyte
(1,000,000,000,000,000,000,000 bytes) of data will be transmitted over IP networks in 2015. The worldwide
IP data traffic from businesses will triple in this same period and reach 10.1 exabytes a month in 2015. IP
data traffic is currently increasing at a rate of 32 percent a year.
There are many different reasons for this rapid growth in bandwidth demand. For one thing, private use of
the Internet is constantly increasing. From 2001 to 2010 alone, the number of Internet users increased from
37 percent to 72 percent, thus nearly doubling. At the same time, people want ever-faster access. The flood
of data is being pushed to ever-greater volumes with flat rates and Internet telephony, cloud computing and
online navigation, mobile Internet with smart phones or tablet computers and video on demand. In the busi-
ness realm, the upsurge in bandwidth is being driven by cloud computing services, group-wide networking,
remote access to company networks, remote sessions and in particular by data-hungry video conferences.
The data volumes currently demanded in backbone cabling can still be handled with 10 Gigabit Ethernet
(GbE), but the forecast trends will require the introduction of the next technologies, 40 GbE and 100 GbE
(Figure 1).
Figure 1: Trend over time of Ethernet technologies (Source: IEEE, 2011)
White Paper | MPO and MTP® - Parallel Optical Interface Technology | EN | Pirmin Koller, Dr. Thomas Wellinger 5
1.2. 10 GbE as the status quo
There is no way around the migration to 40 and 100 GbE. As Figure 1 shows, 40 GbE will be broadly intro-
duced within five years at the latest and 100 GbE will follow just two years later. Data center managers
therefore have to lay the groundwork today and adapt their infrastructure to meet these future requirements.
This raises the question of how they should pick the connection technology in terms of performance and total
cost of ownership (TCO). Here is an all too brief assessment of the current situation.
The crucial criteria for selecting the right interface are costs and the product of bandwidth to length. This value
is a product of bandwidth and the transmission distance and underscores the compromise between signal
bandwidth and the length of the link over which the signal can be transmitted. Data centers currently have a mix
of copper cables and fiber optics. Links anywhere from 15 to 550 meters in length can be achieved depending
on the cable type used (copper/FO). The table below briefly summarizes the existing transmission technolo-
gies, cable types and maximum achievable links. The definitions are based on the standards IEEE 802.3ak
(Twinax) and 802.3an (twisted pair) for copper and 802.3ae for fiber optics.
Transmission tech-
nology Cable type
Maximum dis-
tance
10GBASE-CX4 Copper, Twinax 15 m
Cat. 5e 50 m 10GBASE-T Copper, twisted pair
Cat. 6a/7 100 m
Multimode 300 m 10GBASE-LX4 FO, 1310 nm
Singlemode 10 km
Multimode OM1/OM2 33/82 m
Multimode OM3 300 m
10GBASE-SR FO, 850 nm
Multimode OM4 550 m*
10GBASE-LR FO, 1310 nm Singlemode 10 km
10GBASE-ER FO, 1550 nm Singlemode 40 km
Multimode OM1/OM2 33/82 m
Multimode OM3 300 m
10GBASE-SW FO, 850 nm
Multimode OM4 550 m
10GBASE-LW FO, 1310 nm Singlemode 10 km
10GBASE-EW FO, 1550 nm Singlemode 40 km
* The OM4 solution over 550 meters is not standardized within the IEEE.
Table 1: 10 GbE – Transmission technologies, cable types and maximum achievable distances. The transmission
technologies and cable types most significant for data centers are shown against a gray background.
Links ranging in length from a few meters to several hundred meters have to be implemented in data centers
and singlemode solutions are usually much more expensive than multimode ones. The table can therefore
be reduced to the two transmission technologies 10GBASE-CX4 and 10GBASE-T for copper and 10GBASE-
SR for fiber optics.
White Paper | MPO and MTP® - Parallel Optical Interface Technology | EN | Pirmin Koller, Dr. Thomas Wellinger 6
1.3. 40/100 GbE in the not too distant future
The new transmission technologies 40 GbE and 100 GbE were enacted in June 2010 with the standard
802.3ba. To achieve practical lengths for these large bandwidths, too, data centers have to operate several
of the existing copper cables or optical fibers parallel to each other. Once again there are varying transmis-
sion technologies and distances resulting from this situation, both dependent on cable type. The table below
provides an overview:
Transmission technology Cable type Signal routing Maximum dis-tance
40GBASE-KR4 PCB (bus) 4 x 10 Gb/s 1 m
40GBASE-CR4 Copper, Twinax 4 x 10 Gb/s 7 m
Multimode, OM3 100 m 40GBASE-SR4
Multimode, OM4
4 x 10 Gb/s
150 m
40GBASE-LR4 Singlemode 4 x 10 Gb/s (CWDM) 10 km
100GBASE-CR10 Copper, Twinax 10 x 10 Gb/s 7 m
Multimode, OM3 100 m 100GBASE-SR10
Multimode, OM4
10 x 10 Gb/s
150 m
100GBASE-LR4 Singlemode 4 x 25 Gb/s (DWDM) 10 km
100GBASE-ER4 Singlemode 4 x 25 Gb/s (DWDM) 40 km
Table 2: 40/100 GbE – Transmission technologies, cable types and maximum achievable distances. The transmission
technologies and cable types most significant for data centers are shown against a gray background.
It quickly becomes apparent that the use of copper cables for transmission of 40/100 GbE is critical. Lines
seven meters in length pose problems but so too does the laying of ten lines parallel to each other. Given the
cramped space in cable runs and the difficulty of cooling them, the use of copper seems questionable. In the
connection area, too, Twinax cables need more space than multi-fiber connectors (MPO/MTP®, refer to
Chapter 2) for optical fibers. From today's perspective, the use of copper cables -- whether as Twinax or as
twisted pair Cat. 7 – does not appear to be a reasonable approach, technically or economically.
Category OM3 and OM4 optical fibers are the compelling solution for future-safe cabling in data centers giv-
en their much longer transmission distances and more compact design. OM3 has a link length of 100 meters
so it supports about 85 percent of all data center channels depending on architecture and size; OM4 fibers
have a link length of 150 meters so they cover nearly 100 percent of the required reach.
Note: According to IEEE 802.3ae, the link length for OM3 fibers with 10 GbE is 300 meters. Although the
OM4 fibers are not standardized, they can support solutions involving lengths of up to 550 meters. Although
with 40 GbE and 100 GbE, only 10 Gb/s are transmitted per fiber because of the parallel optical architecture,
802.3ba defines only 100 meters for OM3 and 150 meters for OM4. That is because the requirements for the
active components have become more lenient. They were reduced to cut the total costs of the link. Toler-
ances are greater especially for jitter. The link length has therefore had to be shortened so the admissible
total budget for jitter would not be exceeded. Jitter is the time variation of a periodic signal in the transmis-
sion of bits. It is caused, for example, by noise in electronics or by dispersion in optical fibers.
White Paper | MPO and MTP® - Parallel Optical Interface Technology | EN | Pirmin Koller, Dr. Thomas Wellinger 7
2. Components and solutions for 40/100 GbE
It is clear from Chapter 1 that data centers have to start now with preparing their passive infrastructure for
40/100 GbE. This chapter describes the components they need to do so.
2.1. OM3/OM4 – Laser-optimized multimode optical fibers
For OM3 and OM4, these components are laser-optimized 50/125 µm multimode optical fibers. Whereas
OM1 and OM2 fibers are operated with LEDs as signal sources, lasers are used for category OM3 and OM4
fibers. These lasers are generally vertical-cavity surface-emitting lasers (VCSELs). This type of laser is con-
siderably cheaper than, for example, Fabry-Perot lasers or distributed feedback lasers. Lasers have the ad-
vantage of being able to transmit data at higher rates, unlike LEDs which are limited to a maximum fre-
quency of 622 Mb/s. Lasers are more concentrated than LEDs in their coupling in the fiber core. That means
interference has a much bigger impact on transmission characteristics there than in LED-fed fibers.
Conventional multimode fibers often exhibit iimpairments of the refractive index profile in the fiber core. The-
se impairments include flat tops and peaks but especially centerline dips, which look like a notch in the re-
fractive index profile. The laser signal concentrates a large part of the total power on the fiber core so defor-
mations in the ideal transmission signal occur there, which increases the bit error ratio. This, in turn, leads to
a bad net data rate or can even go so far as to cause the transmission to fail. With laser-optimized fibers, the
refractive index profile is improved in comparison with conventional multimode fibers, so no centerline dips
occur. Figure 2 shows the interconnections:
Figure 2: Laser-optimized fibers with improved refractive index profile
Category OM3 and OM4 laser-optimized fibers are prerequisite for achieving sufficiently high ranges through
the use of lasers as the signal source. R&M offers a number of laser-optimized OM3 and OM4 cables, for
installation and pre-terminated. Maximum distances and maximum transmission reliability are therefore
guaranteed.
Conventional multimode fiber:
Refractive index profile with centerline dip
Laser-optimized fiber:
Refractive index profile with no centerline dip
Multimode fiber core: Diameter of 50 µm
Glass sheath: Total fiber diameter of 125 µm
White Paper | MPO and MTP® - Parallel Optical Interface Technology | EN | Pirmin Koller, Dr. Thomas Wellinger 8
2.2. Parallel optical channels
As noted in Chapter 1.3, the 802.3ba standard defines the parallel operation of four OM3/OM4 fibers for
40 GbE in 40GBASE-SR4 and the parallel operation of ten OM3/OM4 fibers for 100 GbE in 100GBASE-
SR10. Two fibers have to be used per link because this arrangement is full duplex operation, i.e. simultane-
ous transmission in both directions. Therefore the number of fibers increases to eight for 40GBASE-SR4 and
to 20 for 100GBASE-SR10.
Figure 3: Parallel optical channel for 40 GbE with eight fibers used
Figure 4: Parallel optical channel for 100 GbE with twenty fibers used
As Figures 3 and 4 show, four fibers remain unused in each case in connection with 12-fiber and 24-fiber
cables and MPO/MTP®connectors (refer to Chapter 2). In the parallel optical link, the signal is split, transmit-
ted over separate fibers and then joined again. That means the individual signals have to arrive at the re-
White Paper | MPO and MTP® - Parallel Optical Interface Technology | EN | Pirmin Koller, Dr. Thomas Wellinger 9
ceiver at the same time. Any skew in signal components has to be kept within tight tolerances. This fact
alone means a combination of single fibers is prohibited for parallel optical connections. Trunk cables pre-
terminated with MPO/MTP® connectors are therefore the best choice for reliable transmission. The following
chapters will thoroughly cover these two subjects – MPO/MTP® connectors and trunk cables.
2.3. MPO/MTP® – Multi-fiber connectors for high port density
As shown in the previous chapter, parallel optical channels with multi-fiber multimode optical fibers of the
categories OM3 and OM4 are used for implementing 40 GbE and 100 GbE. The small diameter of the optical
fibers poses no problems in laying the lines, but the ports suddenly have to accommodate four or even ten
times the number of connectors. This large number of connectors can no longer be covered with conven-
tional individual connectors. That is why the 802.3ba standard incorporated the MPO multi-fiber connector
for 40GBASE-SR4 and 100GBASE-SR10. It can contact 12 or 24 fibers in the tiniest of spaces. This chapter
describes this type of connector and explains how it differs from the much improved MTP® connectors of the
kind R&M offers.
2.3.1. MPO connectors: structure and function
The MPO connector (known as multi-fiber push-on and also as multi-path push-on) is a multi-fiber connector
defined according to IEC 61754-7 and TIA/EIA 604-5 that can accommodate up to 72 fibers in the tiniest of
spaces, comparable to an RJ45 connector. MPO connectors are most commonly used for 12 or 24 fibers
(Figure 5).
Figure 5: MPO connector for accommodating 12 fibers
As explained in Chapter 1.5 on parallel optical connections, eight fibers are needed for 40 GbE and 20 for
100 GbE. That means four contacts remain non-interconnected in each case. The diagrams below (Figure 6)
show the connection pattern:
Figure 6: Diagram of MPO connectors, 12-fold (left) and 24-fold (right). The fibers for sending and receiving are color-
coded, red and green, respectively.
White Paper | MPO and MTP® - Parallel Optical Interface Technology | EN | Pirmin Koller, Dr. Thomas Wellinger 10
The push-pull interlock with sliding sleeve and two alignment pins are meant to position the MPO connector
exactly for more than 1000 insertion cycles. As with every connector, the quality of the connection for the
MPO connector depends on the precision of the contacting. In this case, however, that precision must be
executed 12-fold or 24-fold. The tough requirements put on the MPO are what made it essential for R&M to
be able to understand and control the optimum endface geometry for low insertion loss (IL) and return loss
(RL).
The fibers are usually glued into holes within the ferrule body. Such holes have to be larger than the fiber
itself to allow the fiber to be fed through so there is always a certain amount of play in the hole. This play
causes two errors that are crucial for attenuation:
• Angle error (angle of deviation):
The fiber is not exactly parallel in the hole but at an angle of deviation. The fibers are therefore inclined
when they come into contact with each other in the connector and are also radially offset in relationship
to each other. The fibers are also subject to greater mechanical loading.
• Radial displacement (concentricity):
The two fiber cores in a connector do not touch each other fully but somewhat offset in relationship to
each other. This is referred to as concentricity. The true cylindrical cente
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