I’d like to bend your ear a bit today on the topic of bend insensitive multimode optical fiber (BIMMF). When bend insensitive multimode fiber made its debut a few years ago, we urged end-users to use caution if they were going to adopt it in their data centers.
Since the existing fiber and measurement procedures were not designed to accommodate the intentional improvements in BIMMF’s performance nor the unintentional side-effects caused by the revised fiber design, the providers of BIMMF could have differences in how they define what BIMMF is and how they measure the various parameters of the fiber. Our concerns centered on whether differences in how the various providers of BIMMF measured its numerical aperture, core diameter, and Differential Mode Delay (DMD) would cause compatibility issues if BIMMF were used with non-BIMMF.
Since then, the International Electrotechnical Commission Subcommittee on Fibres and Cables (IEC SC 86A) have been working diligently at updating the standards that define a MMF’s numerical aperture, core diameter, and Differential Mode Delay (DMD), as well as developing a common standard for BIMMF. Although I don’t expect final ratification of the updates to the specifications and a standard for BIMMF until sometime time next year, it appears the agreements that have been made among the committee’s membership will result in a standards compliant BIMMF that is compatible with non-BIMMF.
Now that there are upcoming standards for bend insensitive multimode fiber that address the compatibility issues, we at Panduit feel it is acceptable to use BIMMF in the data center and to mix-n-match with non-BIMMF. That being said, I still recommend using the same cable management standards and techniques to ensure a long life span for your infrastructure. Even though there may be standards compliant BIMMF, it is constructed with the same glass as non-BIMMF, so although BIMMF increases the optical performance of a link, it does nothing to increase its mechanical reliability. In essence, BIMFF has the same reliability characteristics as non-BIMMF and over time, may fracture in tight bend conditions.
Therefore, I still recommend that BIMMF cables are not bent tighter than 10 times the cable diameter because they still have the same failure probability of non-BIMMF.