Recently, I am doing some research about OM1 and OM2 fiber. According to the provided information, the OM2 fiber has more loss than OM1, but it doesn't point out the specific reason, just 1 sentence. I suppose that it is related to the source light it used. So does anyone here know some specific reasons?

Any help would be appreciated.

  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide and accept your own answer.
    – Ron Maupin
    Feb 19, 2018 at 17:48

2 Answers 2


Om1 has 62.5um (micron) core diameter

Om2 has 50 um (micron) core diameter

It's basically the way the light travels more "efficiently" with the lasers/leds. Smaller core diameter eliminates modal dispersion and enables tremendous transmission capacity over very long distances. excellent pdf by bicsi

You can get up to 10 times the speed in 50 micron VS 62.5 just because of the effectiveness.

The Differences Although 50-micron fiber features a smaller core, which is the light-carrying portion of the fiber, both 62.5- and 50-micron cable feature the same glass cladding diameter of 125 microns. You can use both in the same types of networks, although 50-micron cable is recommended for premise applications: backbone, horizontal, and intrabuilding connections, and should be considered especially for any new construction and installations. Both types can use either LED or laser light sources. The main difference between 50-micron and 62.5-micron cable is in bandwidth-50-micron cable features three times the bandwidth of standard 62.5-micron cable, particularly at 850 nm. The 850-nm wavelength is becoming more important as lasers are being used more frequently as a light source. Other differences are distance and speed. 50-micron cable provides longer link lengths and/or higher speeds in the 850-nm wavelength.

Side note... If you ever patch 50 and 62.5 together it's kind of like putting two diffrent water pipes together. The data will work pretty good from 50 to the 62.5 but 62.5 to 50 it will have lots of loss. You can patch them to a gbic or adaptor to do the conversion properly. We sometimes use a media converter that looks similar to the fiber to ethernet type but have 2 gbics instead of a gbic and rj45. The gbics work properly with both diameters of fiber.

Reference for most of this link

  • thx, got it. But I still think it is not so comprehensive. Besides, the last two paragraphs has little to do with the theme. anyway, thx!
    – Malikyu
    Aug 25, 2017 at 10:25
  • Your "theme" doesn't really make since. Loss is attenuation loss (a degradation as distance, bends, splices, fiber quality and other light interference happens). Om1 and Om2 use light diffrently because their core diameter reflects light at diffrent angles. If you put 850nm light on Om1 and 1300nm light on OM2 it'll travel the same 550 meters. As far as comprehensive how far do you want to dig in? How does light bounce? How is laser light created.? Your welcome!
    – Fixitrod
    Aug 25, 2017 at 13:06

I think you may be looking at the Return Loss, and the higher the Return Loss, the better the cable. You don't want the power reflected back to the source, so a 100% Return Loss would be ideal.

Multimode fiber shall have a minimum return loss of 20 dB, and return loss for singlemode shall be 26 dB, when measured as per ANSI/TIA/EIA-455-1.07. The minimum return loss for singlemode fiber for CATV applications is 55 dB.

  • no, not the return loss but the fiber loss.
    – Malikyu
    Aug 25, 2017 at 10:25
  • There are types of loss considered in optical fiber, but there is not one called Fiber Loss.. Return Loss is one, You will need to be more specific.
    – Ron Maupin
    Aug 25, 2017 at 13:02

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