A new type of multimode fiber called OM5

could be deployed more quickly than expected in datacenter environments.

Datacenters, key players in the digital chain and Web 3.0, have become an essential network node where a multitude of data and services intersect ranging from file storage to total virtualization of network functions and collecting big amount of data through the Internet of Things (IoT). The explosion in data traffic due to the proliferation of connected devices and new applications is resulting in record bandwidth consumption in data centers. 
 
To meet these new challenges and the ever growing need for more bandwidth and higher switching speeds, datacenters are constantly adapting their network and server infrastructures.

Recent years have seen massive deployments of fiber optic cabling infrastructures, and more particularly MPO type high-density multi-fiber connectors.
The installation of multi-fiber connectors is the result of Ethernet or Fiber Channel communication protocols using several pairs of fibers simultaneously thanks to a single optical interface (QSFP module with MPO connector), in order to increase data rates up to 100Gbit/s.

Ethernet protocols such as 40GBase-SR4 or 100Gbase-SR4 are thus based on a parallel simultaneous transmission over 4 pairs of optical fibers at 850nm wavelength (4x10Gbit/s or 4x25Gbit/s). Optical interface (Fig 1) of the Quad SFP (QSFP) module enabling this type of transmission features a multi-channel MPO connectivity massively deployed in recent years. These protocols have been (and still are) very successful partly due to a rapid time-to-market and compatibility with the types of multimode fibers already deployed up to then (OM3, or even OM4), thus representing a cost effective solution that is immediately operational and backward compatible with regular systems.
However, it has been necessary to multiply the count of fibers by four, to increase the space required for the optical modules in the switches. Maximum transmission distances were also reduced as a result (100m on OM4 in 100GBase-SR4). In terms of cabling costs, the bill can potentially run up quite quickly. 
                                                                                                                                                                                   Fig 1

To address these distance problems, several options were put to the test when finally one technology stood out from the rest: Short wavelength division multiplexing (Fig 2) (SWDM). Early work showed that it was possible to communicate at speeds of around 40Gbit/s over a simple pair of OM3 fibers, while extending the distance to over 200 m, by injecting optical signals at 4 simultaneous wavelengths between ≈ 840nm and 960nm. Up to now wavelength division multiplexing technology was operated on singlemode fibers but remains quite expensive. New tests on OM4 fibers then helped extend the transmission distance while maintaining optimal characteristics in terms of power consumption and the optical power of the QSFP modules. The major advantage of SWDM systems is the drop in the fiber count required as well as the ability to use an LC duplex connector without a major impact on CAPEX, nor OPEX.


 Fig 2

Why a new OM5 fiber?
 
Even though the link models established on OM4 fiber and LC connections seem satisfactory, not all OM3 or OM4 fibers on the market present the same bandwidth response in the optical spectrum 850nm to 940nm. Indeed TIA or IEC standards specifying OM3 and OM4 fibers parameters are based on optimal operation of these fibers at 850nm (EMB bandwidth : 4700MHz.km). With the coming of new SWDM4 (Table2) protocols that require a broader spectrum, the definition of a new medium is required to ensure the effective operation, interoperability and scalability. This is why a new type of OM5 fiber has been developed and standardized.


The American organisation ANSI/TIA already published in October 2016, its TIA-492AAAE standard on OM5 optical fiber requirements (Table1). In particular, it sets down minimum bandwidth specifications (Table1) at given wavelengths as well as the maximum attenuation of the non-cabled fiber. While the IEC has not yet ratified its publication on the OM5 fiber, the problem has been taken into consideration and the IEC document IEC 60793-2-10 Ed.6 should be published in the course of the 1st quarter 2017. OM5 fibers (core diameter of 50µm) are obviously compatible with the existing OM4 fibers. Note that the TIA 568-D.3 and ISO/IEC 11801 Ed.3 Cabling standards under review (planned publication H1 2017) both plan to list OM5 fiber as a potential media for multimode applications.
 


While OM5 fiber deployments are not yet “on air”, they could quickly become so and GIGAMEDIA is placing its expertise at your disposal to accompany you.