Multimode optical fibers are typically tested at 850 nm and 1300 nm, with OM5 fibers also supporting additional wavelengths for WDM applications.

Standard Test Wavelengths

Multimode fibers (MMF) are designed to operate primarily at 850 nm and 1300 nm. These wavelengths correspond to the peak performance of LEDs and VCSELs used in multimode systems and are the standard wavelengths for measuring insertion loss and attenuation in the field, ensuring compatibility with network equipment and calibration standards (FOA, Fluke Networks) .

• 850 nm: Used for short-reach applications, typically within data centers or campus networks. It is the primary wavelength for LED and VCSEL sources in OM1, OM2, OM3, and OM4 fibers.
• 1300 nm: Used for longer multimode links, providing lower attenuation and slightly reduced modal dispersion compared to 850 nm. For OM5 fibers, which are designed for wideband multimode applications and support shortwave WDM (SWDM), additional wavelengths such as 880 nm, 910 nm, and 940 nm are used for simultaneous multiple-channel transmission. However, field testing of OM5 still generally uses 850 nm and 1300 nm to verify link performance according to TIA standards .

Practical Considerations

• LED vs. Laser Sources: LEDs produce a broader spectral width, which can increase modal dispersion, while VCSELs provide a narrower, more coherent light source, improving performance over longer multimode links .
• Calibration: Optical power meters and test equipment are calibrated at these standard wavelengths to ensure accurate loss measurements .
• Standards Compliance: Testing at 850 nm and 1300 nm aligns with TIA-568, ISO/IEC 11801, and other industry standards for multimode fiber certification .

Summary

For most multimode fiber testing, 850 nm and 1300 nm are the standard wavelengths. OM5 fibers, while capable of supporting additional WDM wavelengths, are still tested at these two primary wavelengths to ensure compliance and reliable network performance. Choosing the correct test wavelength is critical to accurately measure fiber loss, verify link integrity, and maintain network reliability .