Patent ID: 7376307

Claim:
A multimode long period fiber Bragg grating for a predetermined wavelength band, comprising: a multimode optical fiber core formed of a non-photosensitive material having an initial index of refraction, the multimode optical fiber core includes; a substantially cylindrical surface; a longitudinal core axis; a core radius; and a plurality of index-altered portions having an altered index of refraction different from the initial index of refraction; wherein; each of the plurality of index-altered portions of the multimode optical fiber core has a first transmission surface and second transmission surface substantially parallel to the first transmission surface; and the plurality of index-altered portions are arranged within the non-photosensitive material of the multimode optical fiber core such that the first transmission surface of one portion of the plurality of index-altered portions is substantially parallel to the second transmission surface of a neighboring portion of the plurality of index-altered portions to form a long period Bragg grating structure.