| abstract |
A fiber structure with a cross section havingnx-axis and y-axis directions includes an alternatenlamination including a first portion having anrefractive index na and a thickness da and a secondnportion adjacent to the first portion and having anrefractive index nb and a thickness db, wherein whenn1.0 ≦ na < 1.8, 1.3 ≦ nb ≦ 1.8, and 1.01 ≦ nb/na ≦n1.80 , a primary peak wavelength λ 1 which is equal ton2(nada + nbdb) is given by λ 1 ≧ 0.78 or 1.6 (µm). |