A microbend is a fiber imperfection. Microbends cause an increase in cable loss. This loss can result in an excessively large loss in excess of 100 dB/km in some cases. A major cause of this loss occurs during cable manufacture. It is related to axial distortions that invariably occur during cabling when the fiber is pressed against a surface that is not perfectly smooth.
Microbend-induced loss is a function of mode-field diameter, cable design, and cable construction. Losses due to microbend-induced attenuation consistently decrease with mode-field diameter.
A macrobend refers to the specified minimum bending radius. The cable manufacturer should specify the minimum bending radius. When fiber is on reels, of course it is bent around the reel. When it is installed, particularly in buildings, fiber cable must be bent around corners. The installer must not exceed the specified minimum bending radius by making a still sharper bend than the specification calls for.
We might expect a typical bending radius of a fiber optic cable to be between 10 cm (4 inch) and 30 cm (11 inch), depending to a certain degree on the fiber count in the cable. Bending a fiber optic cable tighter than the specified bending radius can cause damage, even break the fiber carried in the cable. It can also cause a dramatic increase in fiber attenuation.