This document outlines the specifications for ITU-T G. 657 optical fibers, which are designed for improved bending loss performance compared to ITU-T G. Worldwide, technologies for general transport network and broadband access networks are advancing rapidly. It details two main categories: Category A, with subcategories A1 and A2. This paper describes designs of the single mode fibers with both bending loss insensitivity and high strength intensity. This type of fibers has been. Bending losses are a function of the fiber type (SM or MM), fiber design (core diameter and NA), transmission wavelength (longer wavelengths are more sensitive to stress) and cable design. In 2007, a new type of "bend-insensitive" singlemode fiber was introduced, followed by multimode fiber in. In one aspect of the invention, the bend insensitive single-mode optical fiber includes a core layer and cladding layers having an inner cladding layer, a trench cladding layer and an outer cladding layer sequentially formed surrounding the core layer from inside to outside.