Macrobending loss in Optical Fibers

The loss induced on the fiber, when it is bend by wrapping on a mandrel is known as Macrobending loss. Macrobending loss happes due to the bends at macro level to compare it with the microbend loss. As per ITU-T documentations, macrobending loss varies with wavelength, bend radius and number of turns about a mandrel with a specified radius for singlemode fibers. Therefore, the limit for the macrobending loss is specified in ITU-T Recommendations for defined wavelength(s), bend radius, and number of turns.

The recommended number of turns corresponds to the approximate number of turns deployed in all splice cases of a typical repeater span. The recommended radius is equivalent to the minimum bend-radius widely accepted for long-term deployment of fibers in practical systems installations to avoid static-fatigue failure. For multimode fibers the launch condition is of paramount importance for macrobending loss, in particular the presence of higher order modes which are the most sensitive being stripped off due to bending.

The mode distribution encountered at a specific macrobend may depend on how many macrobends precede it. For example, the first bend might influence the launch condition at the second bend, and the second bend might influence the launch condition at the third bend, etc. Consequently, the macrobending added loss at a given bend might be different than the macrobending added loss at another bend. In particular, the first bend may have the largest influence on following bends. Consequently, the macrobending added loss produced by multiple bends should not be expressed in the units of “dB/bend” by dividing the total added loss by the number of bends, but in dB for the specified number of bends.

A bend diameter of 60 mm is recommended for G.652.D fibers, while for G.657A1 fibers, this bend diameter can go up to 20 mm. and 15 mm for G.657.A2 and G.657.B2 fibers. For G.657.B3 fibers, this bending diameter can go up to 10mm.  Induced loss tolerance is also high for G.657 category fibers compared to G.652 fibers.

Author: chen

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