What is the Difference between OM3 & OM4 50/125 Multimode Fibre?


When you need to choose between OM3 vs OM4 for the right fibre for your application, the following questions are relevant.
 

  1. Price differential 
  2. Performance – Distance/Bandwidth/Speed
  3. Can we Mix OM3 & OM4 Fibres  
  4. Colour Identification

 

1. Price/Cost differential 

 

From a costing perspective, there is No significant cost advantage to choosing OM3 or OM4. The cost differential is minimal, so it is the question about performance differences that need to be asked.


2. Performance – Distance/Bandwidth/Speed 

 

Distance: OM4 would be the first choice where we have high bandwidth and distance.  This only becomes apparent as you approach the maximum limits of the spec. So, for 10/40/100gig you would use OM4 for the maximum permissible distance.

Bandwidth: Main difference between OM3 v OM4 is Bandwidth (Modal Bandwidth) Modal bandwidth indicates a fibre’s ability to transmit a specific amount of information over a certain amount of distance, which means OM4 fibre can send more information within the same distance than OM3 fibre. 

Speed: OM3 was designed to address 10Gb/s and has been adapted to enable it to be used on 40/100Gb/s. OM4 was designed to be used on 10/40/100Gb/s.
 

3. Can we mix OM3 & OM4 Fibres  

 

Yes, OM4 is 100% backward compatible with OM3. You can deploy OM4 fibre in any OM3 network with no issues. 


4. Colour identification 

 

Generally, the accepted colour identification is as follows: - 
OM3: Aqua/ OM4: Violet  

For a more detailed response to the above questions see below.


Price comparison of OM3 vs OM4, 50/125 Fibre 


Construction and other materials other than the fibre represents a significant proportion of the costs. This will vary dependant upon the cable type chosen, either Loose Tube/Tight Buffered or Ribbon Cable. The price difference between the 2 fibres types OM3 & OM4 is very small when comparing like for like cable construction, so using either OM3 or OM4 will result in a very small price differential. Additionally, there is little or no price difference on other associated items such as Patch Panels, Optical Distribution Frame (ODF), Splice trays, Patch Panels, Connectors, Pigtails & Patchcords.


Distance that Data can Travel on OM3 or OM4 Fibres
 

To explain the cable lengths that fibre can operate, whilst maintaining transmission protocols, the following table may be of more benefit:

 

  1000BASE-SX 10GBASE-SR 40GBASE-SR4 100GBASE-SR10
OM1 275m 33m Not Specified Not Specified
OM2 550m 82m Not Specified Not Specified
OM3 Not Specified 300m 100m 100m
OM4 Not Specified 400m* 400m* 150m
OM5 Not Specified 400* 400m* 150m
* The IEEE in conjunction with the TIA is supporting 10GBASE-SR to 400 m over OM4.

Cautionary note: In ANSI/TIA-568-B.3, the modal bandwidth of 62.5 µm fibre was 160 MHz.km, not the 200 MHz.km found in the current ANSI/TIA-568.3-D. This change was done to harmonize with ISO/IEC 11801 that would reduce the distance for 1000BASE-SX to 220 m and 10GBASE-S to 26 m.

What you can clearly see from the table is that OM4 can transmit longer distances than OM3. There is still some debate about OM4 under 10gig from the above table a figure of 400mtr, in practice with a good quality fibre this could be 550mtrs.


Bandwidth of OM3 vs OM4


This is the main difference between OM4 and OM3. 

Modal bandwidth of OM4 - 4700 MHz per km 
Modal bandwidth of OM3 - 2000 MHz per km

Modal bandwidth indicates a fibre’s ability to transmit a specific amount of information over a certain amount of distance, which means OM4 fibre can send more information within the same distance than OM3 fibre. 

The modal dispersion determines the modal bandwidth in fibre cables. The higher bandwidth available in OM4 means a smaller modal dispersion, allowing the cable links to be longer with lower losses or attenuation.

The following table is provided to illustrate the modal bandwidth differences.

 
                                                              Minimum modal bandwidth MHz-km
 
                   Fibre Type                                                                            Overfilled Launch                       Bandwidth                Effect Laser Launch Bandwidth
 
Fibre Type Core Diameter 850nm 1300nm 850nm
OM1 62.5 µm 200 500 Not Specified
OM2 50 µm 500 500 Not Specified
OM3 50 µm 1500 500 2000
OM4 50 µm 3500 500 4700
OM5 50 µm 3500 500 4700


Speed of OM3 vs OM4


The OM3 fibre specification shows that OM3 fibre was designed for 10 Gb/s transmission speed, but it can also run under 40 Gb/s and 100 Gb/s. As an improvement on OM3 fibre, OM4 fibre was specifically designed for 10G, 40G and 100G Ethernet. 

Both OM3 and OM4 fibres can support 40 Gb/s and 100 Gb/s transmission speeds when they are terminated with 8 or 12-fibre MTP/MPO connectors and 24-fiber MTP/MPO connectors respectively. 

The 40G interfaces are 4x10G channels on four fibres per direction. 
The 100G interfaces are 10x10G channels on ten fibres per direction.


Can we Mix OM3 vs OM4 Fibres?


OM4 is 100% backward compatible with OM3. You can deploy OM4 fibre in any OM3 network with no issues. This is also true in most cases where OM3 is used in an OM4 Link/Network, except for 40 GbE & 100GbE links where the effective distance is limited to 100mtrs on OM3 compared to 150mtrs on OM4.

Note: The maximum performance of the link will ALWAYS be that of the lowest specified fibre/component within the link/network.


Colour identification of OM3 vs OM4 Cables


Both OM3 and OM4 multimode fibres should have an Aqua jacket when used with LC connectors, and so they usually share the same colour. 

To assist technicians in identifying OM3 and OM4 fibre optic cable, especially when viewed from the front of a patch panel or ODF where all the adapters look similar, some manufacturers offer an (Erika) Violet colour for OM4 in Europe and America. 

OM3 and OM4 cable terminated with MTP/MPO connector almost always use an aqua jacket for OM3 and Erika Violet jacket for OM4.

You can find out about the range of fibre products available from CMW by clicking here. You can also speak to the team by emailing sales@cmwltd.co.uk