Disclosed is a low bend loss optical fiber including: a core; an inner layer disposed at outside of the core, which has a refractive index lower than a refractive index of the core, the refractive index of the inner layer gradually decreasing as it becomes farther from the core; and a trench layer disposed at outside of the inner layer, which has a lowest refractive index. An apparatus operable to perform the aforesaid method is also provided. The diagonal parity sets are then grouped into two groups of diagonal parity setsGroup 1 and Group 2such that each data strip is a member of a unique diagonal parity set in Group 1 and a unique diagonal parity set in Group 2. The photo luminescent material is loaded into a low density material such as a xerogel or an aerogel which is adjacent the source of exciting radiation.