ITU-T recommendation G.657 published on December 2006 had only two versions of Single mode fibers categorized as G.657.A and G.657.B. The difference between these fibers was in the permissible bending radius.
Bend insensitive optical fibers are being produced to support the fiber to the home applications. FTTH is growing and the demand for optical fibers suitable for transmission at 1550nm to utilize the DWDM application spectrum is increasing in the back bone networking. 1550nm is sensitive to bending and now a days the trend is to use smaller cabinets and fiber storage mediums in order to reduce the installation space. If back bone cables are sensitive to bending, the fiber optic cables will show increase in attenuation over a period of time under small bends.
To overcome these problems, optical fiber manufacturers have come up with bend insensitive optical fiber that can be used in the feeder cables as well as back bone cabling network. The trend in the FTTH scenario is moving towards further small bends and the demand from FTTH installation fields reaches upto 5 millimeter.
Single mode optical fibers complying with ITU-T G.657A was developed with the purpose of using at FTTx sites. G.657A category fibers are therefore compliant with G.652 category fibers also. This back compatibility makes the G.657A category fibers suitable for access networks used for FTTx. The other category, G.657.B does not need to be compliant with G.652 fibers. Therefore G.657.B category fibers are mostly used in indoor fiber optic cables that are installed with field installable optical connectors.
To make the things clear let us summarize as follows;
ITU-T G.657.A fibers were developed to be bend tolerant upto 15mm radius
ITU-T G.657.B fibers were developed to be bend tolerant upto 7.5mm radius
The recent trends and the announcements from Industry leaders shows that single mode optical fibers that is bend insensitive upto 10mm bending radius is categorized as G.657.A1 fibers. Fibers that are bend insensitive for bending radius upto 7.5mm are called G.657.A2 fibers. Both are compliant with G.652 recommendations as well.
On the other hand, G.657.B.2 fibers can tolerate bending radius upto 7.5mm. The industry leaders have announced new versions of high performance bending insensitive fibers that are categorized as G.657.B.3. These fibers can tolerate a bending radius of 5mm!
The technology is growing and we already have hole assisted fibers etc, that are yet to put into economical mass production in order to find their way for massive deployment in cabling.