Patent ID: 6944381

Claim:
An optical fiber characterized by: a cutoff wavelength of 1310 nm or less; a transmission loss of 0.40 dB/km or less at a wavelength of 1385 nm before hydrogen ageing; a transmission loss of 0.40 dB/km or less in a wavelength range of 1310 nm to 1625 nm after hydrogen ageing, wherein said transmission loss after hydrogen ageing is measured after exposing the optical fiber to an atmosphere containing hydrogen of about 0.01 atmospheres at room temperature until an increase of a transmission loss of 0.03 dB/km or more at a wavelength of 1240 nm compared with said transmission loss before hydrogen ageing, and in open atmosphere for more than 14 days; and an electron spin density of a Non-Bridging Oxygen Hole Center of 1×10 13 spins/g or less, wherein said electron spin density is measured by an electron spin resonance method after the diameter of the optical fiber is made to be about 50 μm by etching in diluted hydrofluoric acid.