Meeting the impending challenge of parallel data transmission using fiber optics places severe demands on timing skew between the channels. Often, re-clocking electronics is used to automatically deskew the data at the receive end. However, this technique can only be used up to a certain limit, which can be easily exceeded in long fiber links where the fiber ribbon skew can build up to significant levels. Consequently, fiber experts within the Telecommunications Industry Association (TIA) fiber-optic working groups have for some time highlighted the potential need for tight skew specification limits on the ribbon fibers and standards for its measurement. No skew measurement procedure currently exists within TIA's extensive range of fiber-optic test procedures (FOTPs).
Anticipating this need, a recent informal meeting of TIA's Working Group FO-4.2.1, held in conjunction with the September 2002 National Institute of Standards and Technology (NIST) Symposium on Optical Fiber Measurements in Boulder, CO, considered the preparation of a procedure to measure ribbon fiber skew. At this meeting, it was decided to set up a team of experts to begin work on a suitable measurement procedure document in late 2002/early 2003, pending approval within the FO-4.2 subcommittee and the normal TIA balloting process.
In addition to describing applicable techniques such as time-of-flight, phase shift, and OTDR-based methods, the proposed document will examine technical issues, including skew testing in multimode as well as singlemode ribbons, using 1300-nm measurements to predict 850-nm skew for Gigabit Ethernet and multimode-fiber launch conditions.
Many of these issues have been addressed in recent presentations at the NIST Symposium by members of the editing team. The lead author will be yours truly, and anyone interested in participating in this effort should contact me at [email protected].
Arthur Barlow is technology and development manager at PerkinElmer Optoelectronics in the United Kingdom. He is a member of the Telecommunications Industry Association's FO-4 committee as well as the International Electrotechnical Commission's (IEC) SC86 committee.