Abstract: An optical fiber characterized by a cutoff wavelength of 1310 nm or less, a transmission loss of 0.40 dB/km or less at the wavelength of 1385 nm before hydrogen ageing, a transmission loss of 0.40 dB/km or less in the wavelength range of 1310 nm to 1625 nm after hydrogen ageing, and an electron spin density of the Non-Bridging Oxygen Hole Center of 1×10 13 spins/g or less measured by the electron spin resonance method after the diameter of the optical fiber is made to be about 50 &mgr;m by etching in diluted hydrofluoric acid, that having high reliability of hydrogen-proof characteristic suitable for WDM transmission in 1310 nm to 1625 nm and the method of evaluating the optical fiber are offered.

Abstract: The optical fiber which enables the optical fiber transmission stabilized in the wavelength range of the pump light also, which is not used conventionally, and suppresses the non-linear effect on the occasion of WDM transmission is offered. The optical fiber for WDM transmission has at least three or more layers wherein the first core doped with germanium is located at the center and surrounded by the second core having a refractive index lower than the first core, and cladding having a refractive index lower than the first core and higher than second core surrounds the second or last core layer.

Abstract: An optical fiber for forming an optical transmission line suitable for the wavelength division multiplexing transmission by connecting to a positive dispersion optical fiber is provided. Outside a first glass layer (1), a second glass layer (2), a third glass layer (3) and a fourth glass layer (4) are sequentially disposed. The fourth glass layer (4) is to be a reference layer for a standard of a refractive index. A relative refractive indexdifference &Dgr;1 of the first glass layer to the reference layer is set 1.6% to 2.6%, inclusive, a relative refractive index difference &Dgr;2 of the second glass layer is set −0.65% to −0.4%, inclusive, and a relative refractive index difference &Dgr;3 of the third glass layer is set 0.15% to 0.5%, inclusive. A relationship among an outer diameter d1 of the first glass layer, an outer diameter d2 of the second glass layer and an outer diameter d3 of the third glass layer is set 2.5≦(d2/d1)≦3.0, and 1.5≦(d3/d2)≦3.0.

Abstract: Provided are a process for producing an optical fiber preform by depositing glass soot on the periphery of a glass rod and then sintering the glass soot to form a new transparent glass layer and also a process for producing an optical fiber preform by repeating the above procedures, wherein bubble is prevented from occurring in glass layers and interfaces between them. The process includes the steps of forming a glass soot layer by depositing glass soot on the periphery of a glass rod formed by undergoing a sintering heat treatment; and carrying out subsequently another heat treatment for the glass soot to carry out sintering thereof and transform the glass soot layer into a glass layer; wherein, provided that the glass soot is treated at a sintering temperature T′(° C.) and that the glass rod is formed at a sintering temperature T(° C.

Abstract: In a single mode optical fiber formed of a silica-based glass and including a glass part having a central core and a cladding region, the density of non bridging oxygen hole center in the glass part is not higher than 1.0×1014 spins/g in terms of the spin density measured by an electron spin resonance method.

Abstract: An optical fiber for forming an optical transmission line suitable for the wavelength division multiplexing transmission by connecting to a positive dispersion optical fiber is provided. Outside a first glass layer (1), a second glass layer (2), a third glass layer (3) and a fourth glass layer (4) are sequentially disposed. The fourth glass layer (4) is to be a reference layer for a standard of a refractive index. A relative refractive index difference &Dgr;1 of the first glass layer to the reference layer is set 1.6% to 2.6%, inclusive, a relative refractive index difference &Dgr;2 of the second glass layer is set −0.65% to −0.4%, inclusive, and a relative refractive index difference &Dgr;3 of the third glass layer is set 0.15% to 0.5%, inclusive.

Abstract: An optical fiber for forming an optical transmission line suitable for the wavelength division multiplexing transmission by connecting to a positive dispersion optical fiber is provided. Outside a first glass layer (1), a second glass layer (2), a third glass layer (3) and a fourth glass layer (4) are sequentially disposed. The fourth glass layer (4) is to be a reference layer for a standard of a refractive index. A relative refractive index difference &Dgr;1 of the first glass layer to the reference layer is set 1.6% to 2.6%, inclusive, a relative refractive index difference &Dgr;2 of the second glass layer is set −0.65% to −0.4%, inclusive, and a relative refractive index difference &Dgr;3 of the third glass layer is set 0.15% to 0.5%, inclusive. A relationship among an outer diameter d1 of the first glass layer, an outer diameter d2 of the second glass layer and an outer diameter d3 of the third glass layer is set 2.5≦(d2/d1)≦3.0, and 1.5≦(d3/d2)≦3.0.