Understand the Wide Band Multimode Fiber (WBMMF)

Recently, there has been some buzz about Wide Band Multimode Fiber (WBMMF). The 2016 edition of document TIA-492AAAE, released on June 1, is available. This document/standard is the detailed specification for 50 μm graded index multimode optical fiber with laser optimized bandwidth characteristics specified for wavelength division multiplexing. So, from an installed cabling testing perspective, what is the difference between WBMMF and other multimode fiber and how should you test it in the field?

The optical fiber cable transmission performance requirements for factory acceptance testing, as given in draft 8 of TIA-568.3-D for cable type, wavelength, and maximum attenuation is given as (note OM3, OM4, and WBMMF all have the same specification except WBMMF introduces attenuation at 953 nm):

¹ OM3 and OM4 are designations defined in ISO/IEC 11801, the international structured cabling standard.
² The values for maximum attenuation apply to cabled fiber, not bare fiber which is normally lower.

Since the new WBMMF can transmit at multiple wavelengths between 850 nm and 953 nm, a factory performance parameter is specified at 953 nm. Also, WBMMF does not yet have an ISO/IEC designator (i.e. OMx); that is under discussion in the ISO/IEC subcommittee 25. What may influence the naming of WBMMF is the additional minimum modal bandwidth specification for 953 nm at 2470 MHz∙km. This implies that WBMMF has increased bandwidth which historically increases the designator in numerical value (i.e. OM3 to OM4).

Test results

Fluke Networks conducted measurements of WBMMF to develop a perspective on field testing. Testing samples were provided by two vendors. Links were measured at 850 nm, 950 nm and 1300 nm using a light source and power meter. The light source was encircled flux compliant for all three wavelengths. The 1-cord method was used. Connector attenuation was measured at 850 nm and 1300 nm using an encircled flux compliant OTDR. The links were tested with and without “defects” (contaminated connectors and fiber bends). Various link configurations and lengths were tested (1 km, 30 m + 100 m, 30 m + 100 m + 100 m). Connector and fiber attenuations were measured using a combination of the light source/power meter and OTDR.

Examination of the data leads to the conclusion that attenuation measurements at 950 nm, with or without defects such as dirty connectors or fiber bends, do not reveal any vital information. Testing at 950 nm did not reveal more information than did testing at 850 nm; as expected attenuation at 950 nm was slightly lower that at 850 nm. Given that no vital information is revealed by testing at 950 nm we conclude that traditional testing at 850 nm and 1300 nm continues to be the preferred method.