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50 Micron Multimode Fiber

At one time, the network designer or end user who specified multimode optical fiber for short reach systems had to choose from two fiber types defined by their core size, namely, 50 micron or 62.5 micron.

Now, that choice is slightly different, choose from OM3, OM4, or the new OM5 grade of 50 micron multimode optical fibers.

Today, 62.5 micron OM1 multimode optical fiber is virtually obsolete and is relegated for use with extensions or repairs of legacy, low bandwidth systems. 62.5 micron OM1 fiber supports only 33 meters at 10G, and is not even recognized as an option for faster speeds.

50 micron multimode optical fibers were first deployed in the 1970s for both short and long reach applications.

But as data rates increased, 50 micron reach became limited with the LED light sources used at the time. To resolve this, 62.5 micron multimode optical fiber was developed and introduced in the 1980’s. With its larger core, 62.5 micron optical fiber coupled more signal power than 50 micron optical fiber.

This allowed for longer reach (2 kms) at 10 Mb/s to support campus applications. That was the only time when 62.5 micron fiber offered an advantage over 50 micron optical fiber.

With the advent of gigabit (1 Gb/s) speeds and introduction of the 850 nm VCSEL laser light source in the mid-1990s, we saw a shift back to 50 micron optical fiber, with its inherently higher bandwidth.

Today, 50 micron laser-optimized multimode (OM3, OM4, and OM5) optical fibers offer significant bandwidth and reach advantages for short reach applications, while preserving the low system cost advantages of multimode optical fiber.

Planning for the Future

Industry standards groups including IEEE (Ethernet), INCITS (Fibre Channel), TIA, ISO/IEC and others continue to include multimode optical fiber as the short reach solution for next generation speeds. This reinforces multimode optical fiber’s continued economic advantage for these applications.

IEEE includes multimode optical fiber in its 40G and 100G Ethernet standards as well as its pending 50G, 200G, and 400G standards. In addition, TIA issued a new standard for the next generation of multimode optical fiber called wide band (OM5) multimode optical fiber.

This new version of 50 μm optical fiber can transmit multiple wavelengths using Short Wavelength Division Multiplexing (SWDM) technology, while maintaining OM4 backward compatibility. In this way, end users can obtain greater bandwidth and higher speeds from a single fiber by simply adding wavelengths.