Multimode fiber is typically tested at 850 nm and 1300 nm wavelengths, with OM5 fibers also supporting additional wavelengths for wideband applications.

Standard Test Wavelengths

For most multimode fibers (OM1, OM2, OM3, OM4), testing is performed at 850 nm and 1300 nm, which correspond to the primary operating windows for short- and medium-range multimode transmission . These wavelengths are sufficient to verify fiber performance, including insertion loss, attenuation, and modal bandwidth, without needing to test every possible operating wavelength. OM5 fiber, also known as Wide Band Multimode Fiber (WBMMF), is designed to support Short Wavelength Division Multiplexing (SWDM) across four wavelengths: 850 nm, 880 nm, 910 nm, and 940 nm . However, according to the TIA 492AAAE standard, testing OM5 is still only required at 850 nm and 1300 nm, as these measurements are representative of the fiber's performance across the full SWDM range.

Modal Bandwidth and Measurement

The modal bandwidth of multimode fiber defines the maximum frequency at which data can be transmitted over a given distance. It is measured using the -3 dB bandwidth method, where the frequency at which the optical power drops by 3 dB relative to the baseband is recorded . The units are typically MHz·km, indicating the achievable transmission frequency over one kilometer of fiber. This measurement is critical for ensuring the fiber can support the intended data rates.

Practical Testing Methods

Multimode fiber testing can be performed using several tools:

• Optical Power Meters and Light Sources: Measure insertion loss and verify signal strength at the test wavelengths .
• OTDR (Optical Time Domain Reflectometer): Detects faults, breaks, and reflections along the fiber.
• Visual Fault Locators (VFLs): Use visible laser light to identify breaks or bends.
• MPO Testers: For multi-fiber connectors, automated testers can measure all fibers simultaneously, ensuring correct polarity and loss . For OM5 and other multimode fibers, the same test procedures apply as for standard multimode fibers, with the primary focus on 850 nm and 1300 nm to ensure compliance with standards .

Summary

• Test wavelengths: 850 nm and 1300 nm for all multimode fibers; OM5 supports 850–940 nm for SWDM but only requires 850/1300 nm testing.
• Modal bandwidth: Measured in MHz·km using the -3 dB method.
• Testing tools: Optical power meters, OTDRs, VFLs, and MPO testers.
• Purpose: Verify fiber performance, loss, and bandwidth to ensure reliable high-speed data transmission. This approach ensures that multimode fibers meet performance specifications for both current and future high-speed network applications.