Know-how

05. May 2017

The new multimode fiber category OM5


The ever-growing demand for higher bandwidth doesn’t stop at multimode optical fibers. ISO/IEC are working on the specifications of OM5 fibers, capable of transmitting 100 Gigabit Ethernet over just two fibers. The standard isn’t finalized yet, but here is an overview on what’s going on.

Summary:

  • OM5 is a new multimode fiber category.
  • OM5 fibres are already standardized in the U.S.A., but international standards are still under development.
  • The current cabling standards do not recognize OM5 fibers yet, but the future issues of ISO/IEC 11801, EN 50173-1 and ANSI/TIA-568.3-D most likely will.
  • OM5 multimode fibers can transmit light of four different wavelengths simultaneously.
  • OM5 fibers are fully backwards compatible to OM3 and OM4 fibers.
  • New Ethernet types and link lengths based on OM5 multimode fibers are in discussion:
    • 100 Gigabit Ethernet over two fibers and LC Duplex connector over 150 meters
    • 400 Gigabit Ethernet over eight fibers and MPO connector over 150 meters

OM5 - general information

Faserquerschnitt.jpg

“OM” stands for “optical fiber multimode”.

The current European and global cabling standards specify the multimode fibre categories OM1 to OM4. These standards were published several years ago, e.g. EN 50173-1 was published in 2011. The new OM5 multimode fibres shall be capable of transmitting higher data rates than the current multimode types.

 


Cross section of a multimode fiber

Technical background

OM1 to OM4 multimode fibers are mostly used to transmit light of 850 nm wavelength; very rarely 1300 nm is used. This limits the transmission to just one channel in each direction. For a data connection, two fibers are used (one for transmitting and one for receiving data). This technology applies for data rates up to 10 gigabits per second.

40 and 100 Gigabit Ethernet over multimode fibers are based on another technology. Data rates of 40 or even 100 gigabits per second are too high for legacy multimode fibers. The transmitter splits the 40 or the 100 gigabits per second into several individual channels of 10 gigabits per second each and the receiver re-assembles them. This technology is called “parallel optics”. It can be compared to a motorway with several lanes leading to the same direction. For 100 Gigabit Ethernet ten fibers are used for transmitting and another ten for receiving data, totalling up to 20 fibers per link. This is technically feasible, however it means quite a big effort as far as fibers and electronics are concerned, as ten laser diodes have to be placed in very limited space.

With singlemode fibers, the cabling becomes much easier. Their enormous bandwidth enables multiple data streams (“channels”) simultaneously over the same fiber using light of different wavelengths. This technology has been common for decades with radio and TV, where many programs are aired in different parts of the frequency spectrum (”bands”) at the same time. With singlemode fibers it is called “WDM – wavelength division multiplexing”. A huge benefit of this technology is that only one fiber is needed to transmit several channels, and so much smaller and thus cheaper cables can be used. The drawback is the high costs of the electronics.

Apart from some rare cases, WDM technology has not been used for multimode fibers as the standard electronics used here is very cheap. However, having to use 20 fibers for 100 Gigabit Ethernet over multimode fiber, many users would greatly appreciate the easy handling of two fibers with LC duplex connectors they are used to with 10 Gigabit Ethernet. With “SWDM – short wavelength division multiplexing” this has become possible.

The solution: 100 Gigabit Ethernet with OM5 fibers

A new 100 Gigabit Ethernet version using four channels of 25 gigabits per second each is being discussed today. With SWDM technology, these four channels can be transmitted using light at four different wavelengths (850, 880, 910 and 940 nm). In order to do so, special multimode fibers that are capable of transmitting these four different wavelengths equally well are needed. The new OM5 fibers are optimized for transmitting light from 850 to 950 nm. With these new OM5 fibers, 100 gigabits per second over up to 150 meters would be possible using just two fibers and LC duplex connectors.

Even higher data rates

OM3 and OM4 multimode fibers can transmit up to 10 gigabits per second. For higher data rates, parallel optics is used. Today there is 40 Gigabit Ethernet using eight fibers (four for transmitting and four for receiving data) and 100 Gigabit Ethernet using twenty (ten for transmitting and ten for receiving data). With OM3 fibers, the maximum link length including patch cords is 100 meters, with OM4 it’s 150 meters.

SWDM technology and OM5 fibers are not necessarily meant for more than 150 meters of link length but as 25 gigabits per second can be transmitted per fiber, eight fibers now allow 400 gigabits per second over 150 meters.

Standards

The American fiber standard TIA-492AAAE is already published and applies to the US and Canada. The OM5 fiber is called TIA-492-AAAE fiber there.

The global fiber standard IEC 60793-2-10 is available as a draft, calling OM5 fibers “type A1a.4”.

Today, no cabling standard specifies OM5 fibers, but they will be included in the future global standard ISO/IEC 11081 Edition 3 and thus also in the future issue of EN 50173 for structured cabling as well as in the future American standard ANSI/TIA-568.3-D.

OM5 fibers are fully backwards-compatible to existing OM3 and OM4 fibers.

Applications

100 Gigabit Ethernet over just two OM5 multimode fibers could be a very interesting for connecting powerful switches and high-performance servers. With a maximum link length of 150 meters it can also be used in the riser of many buildings, for large server rooms and data centres.

400 Gigabit Ethernet using eight OM5 fibers will most likely be used in data centres and in future-proof riser cabling should the user decide to install pre-terminated cabling.

However, at the moment there are neither electronic devices (switches, etc.) which could make use of the benefits of the new fiber type nor are there valid cabling standards.

Telegärtner product portfolio

The standards are still under development. Global standards are available as drafts only, if they are available at all. Draft standards – especially at a very early stage – can change easily.

Telegärtner employees work actively in many standard committees and design future standards. As a reputable manufacturer and competent, reliable partner of our customers, Telegärtner offers product solutions when reliable and final versions of the relevant standards customers can rely on exist.