Patent ID: 7142755

Claim:
A method of evaluation of an optical fiber comprising: measuring an electron spin density of a Non-Bridging Oxygen Hole Center 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; and estimating an amount of loss increase of the optical fiber at a wavelength of 1385 nm after hydrogen ageing, based upon said electron spin density of the Non-Bridging Oxygen Hole Center, wherein said loss increase 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 a transmission loss before hydrogen ageing, and in open atmosphere for more than 14 days.