MPO means Multi-fiber, Push-on connector and it was originally developed by NTT in an attempt to reduce the amount of time required for fusion splicing individual connectors. MPO connectors were originally designed for ribbon fiber and they were available as 12, 24, 48 and 72 fiber variants. MPO connectors were used for FTTH (mass ribbon splicing) and Data Centers. MPO is the ‘type of connector’ (like LC, SC,ST etc) but there are other vendor specific variants like the MTP from USCONEC. Incidentally MTP means Mechanical Transfer Push-Pull. Vendor specific variants basically try to improve the basic standardised version of the MPO so that it has improved performance.
Why do customers like it?
The MPO has a lot of fibers in one connector and therefore it reduces the amount of time required to connect fibers. Instead of having 12 x ceramic ferrule connectors, you just have one MPO connector. Obviously this saves a lot of space as well….actually by a factor of 12/24/48 or 72!! The other significant benefit of the MPO connector is that it creates a demarcation point/flexibility point from which to add other equipment specific connectors. If you splice a cable at both ends, you effectively have no flexibility. You have to cut the fibers if you want to change the end connector. MPO gives you the ability to disconnect the end connections and change them when needed…..customers love this. This flexibility basically gives you a backbone cabling system that can be adapted to any technology change or connector change in the future. The MPO connector is a bit like having an electrical socket. You can plug many different types of cables into it for different purposes but the socket never changes.
Why the MPO 12?
The MPO 12 fiber connector was the first MPO connector which had enough repeatable performance to be accepted in Data Centers. The 24, 48 and 72 were OK for FTTX but they were not good enough for high data, loss-sensitive applications. So with the MPO 12 fiber connector we started to see a real trend towards Data Center Backbone cabling that could be adapted over time. This is called ‘future-proofing’ or ‘migrating’. If you build a backbone with a 12 fiber MPO connector, you can basically put any connection on the end to be future proofed (LC, MTRJ, SC etc). This was really advantageous in the early day of Data Centers because nobody really knew what type of connector interface they needed on the switch/server. So basically the MPO 12 became the connector of choice in most backbone cabling infrastructures. The majority of Data Centers today are built with MPO 12 fiber in the backbone and MPO-LC harnesses connecting to equipment such as switches and servers. Most of the equipment today still has an LC transceiver interface therefore the harness is required to convert from MPO in the backbone to LC at the port.
The 12 fiber MPO connector basically gives you 6 x serial LC duplex ports per connector. Each LC port has 1G or 10G of data rate capacity (Ethernet).
Later it was discovered that instead of just having serial transmission, you could actually have parallel optics. 10G of data could be transmitted over a single fiber and across multiple lanes. A 12 fiber MPO connector could effectively deliver 6 x 10G transmit fibers and 6 x 10G receive fibers. STOP!!!!!!! The transceivers and the equipment were only capable of supporting 40G data rates so here we have a dilemma. We have a 12 fiber MPO connector that can deliver 60G but is actually only delivering 40G. This means that 33% of the connectors fibers were not being used. Actually 8 fibers were being used at the transceiver and 4 were just spares.
“The MPO 12 fiber connector was not the best backbone choice in the long term because nobody could really foresee how the industry would evolve.”
Making the 12 fiber connector work
All of the companies that promoted the 12 fiber MPO connector suddenly realised that it no longer matched the requirements of the Data Center. Every piece of equipment that was coming into the Data Center was either 40G (8 fibers) or 100G (24 fibers). So what followed was a period where structured cabling vendors talked about upgrade path. “If you purchased our 12 fiber MPO system last year….you now need to purchase our upgrade products to make it work today…”
12 is not divisible by 8 but 24 is. Structured cabling vendors said to their customers…….”if you combine 2 x 12 fiber MPO connectors in the backbone….you can connect 3 x 8 fiber MPO connectors with zero fiber wasteage at the switch”. This continued for quite some time because everyone had a 12 fiber backbone that needed to connect to an 8 fiber switch. So here we started to see the introduction of “conversion modules” and “conversion harnesses” which would adapt the 12 fiber MPO backbone to an 8 fiber MPO equipment connection.
So why do we now have 24 fiber MPO connectors?
There are two main reasons why we have a 24 fiber MPO connector….these are the 100G development and the continuous development of the 12 fiber MPO.
Manufacturers have been improving the precision of the ferrules on MPO connectors for some time now. The 12 fiber MPO connector was definitely the best, but now the 24 fiber connector has similar performance to the 12 if not exactly the same. The problem with MPO connectors is that you need a consistent force across all of the fibers in the connector. The 24 fiber connector has two rows of 12 fibers and this additional row of fibers requires an increase in the spring force to push all of those fibers together……actually double what you need for 12.
So the 24 fiber connector started to be promoted by certain vendors who believe that this connector must be twice as good as a 12. Well this is true in many respects because it is the same size as a 12 fiber MPO and has double the amount of fibers. It also reduces the amount of cable required at the back end because a 24 fiber cable is only marginally bigger than a 12 fiber cable. Furthermore, why combine 2 x 12 fiber MPO connectors to make 3 x 8 when you can just have 1 x 24 fiber connector converting to 3 x 8?
The MPO 24 fiber connector also satisfied the demand for 100G data rates over a single connector. Actually 20 fibers are required for 100G (10 x transmit and 10 x receive) but some applications use the full 120G capability.
What’s happening now?
Well everyone knows that 12 fiber MPO backbones are not ideal. You can convert them to 8 fiber and 24 fiber equipment connections but this is not efficient. Every time you convert a backbone connection you basically add component cost and optical loss into the link. It is much better to build a backbone infrastructure that has the right quantity of fibers for the equipment that it is connecting to. All of the transceiver developments are currently based around 8 fibers, 16 fibers and 32 fibers. None of these developments match with 12 fiber backbones but they definitely match with 8.
“So 8 fiber MPO will be the preferred backbone MPO choice for anyone that wants to build a future-proofed infrastructure with minimal upgrade costs later.”