Optical fiber and optical transmission path

An optical fiber which is made mainly from a silica glass having a layer of core and two layers of cladding with a refractive index in an outer layer of cladding higher than a refractive index in an internal layer of cladding, wherein;

• a formula −2.5×10−7/° C.≦α1−α2≦1.0×10−7/° C. is satisfied;
• and
• a polarization mode dispersion is 0.03 ps/km0.5 or lower;
• under condition α1 is a thermal expansion coefficient of glass which forms the layer of core and α2 is a thermal expansion coefficient of glass which forms the layer of cladding having the lowest thermal expansion coefficient of said two layers of cladding.

An optical fiber which is made mainly from a silica glass member having three layers of core and two layers of cladding, with a refractive index in an outer layer of cladding equal to or greater than a refractive index in an internal layer of cladding, and a refractive index in a central layer of core higher than a refractive index in an intermediate layer of core, and a refractive index in the intermediate layer of core lower than a refractive index in an outer layer of core, and a refractive index in the outer layer of core higher than a refractive index of at least the internal layer of cladding of said two layers of cladding, wherein:

• a formula −2.5×10−7/° C. ≦α1−α2≦1.0×10−7/° C. is satisfied;
• and
• a polarization mode dispersion is 0.03 ps/km0.5 or lower;
• under condition that a coefficient of thermal expansion of a glass member which forms the layer of core having the highest coefficient of thermal expansion of said three layers of core is α1 and a coefficient of thermal expansion of a glass member which forms the layer of core having the lowest coefficient of thermal expansion of said three layers of core is α2.

An optical fiber which is made mainly from a silica glass member having four layers of core and two layers of cladding, with a refractive index in an outer layer of cladding equal to or greater than a refractive index in an internal layer of cladding, and a refractive index in a central layer of core lower than a refractive index in an inner-intermediate layer of core, and a refractive index in the inner-intermediate layer of higher than a refractive index in an outer-intermediate layer of core, and a refractive index in the outer-intermediate layer of core lower than a refractive index in an outer layer of core, and a refractive index in the outer layer of core higher than a refractive index in at least the internal layer of cladding of said two layers of cladding, wherein;

• a formula −2.5×10−7/° C.≦α1−α2≦1.0×10−7/° C. is satisfied;
• and
• a polarization mode dispersion is 0.03 ps/km0.5 or lower;
• under condition that a coefficient of thermal expansion of the glass member which forms the layer of core having the highest coefficient of thermal expansion of said four layers of core is α1 and a coefficient of thermal expansion of a glass member which forms the layer of cladding having the lowest coefficient of thermal expansion of said two layers of cladding is α2.