Patent ID: 6931185

Claim:
An optical fiber comprising: a core; and a cladding which is disposed around the core, wherein the core comprises at least two or more layers having different refractive indexes, the at least two or more layers comprising an innermost layer, wherein the innermost layer comprises a lower photosensitivity layer, the lower photosensitivity layer having a non-zero photosensitivity to a change of refractive index by a light radiation, wherein the photosensitivity of the lower photosensitivity layer is lower than a photosensitivity of one of the at least two or more layers, wherein the cladding comprises at least two or more cladding layers having different refractive indexes, the at least two or more cladding layers comprising an innermost cladding layer which contacts the core, wherein the innermost cladding layer comprises a higher photosensitivity layer, the higher photosensitivity layer having a photosensitivity to a change of refractive index by a light radiation that is higher than a photosensitivity of one of the at least two or more cladding layers.