Fujikura Limited

Sho Endo

Takayuki Kitamura

Tatsuya Kishi

Ryo Maruyama

The refractive index of the inner core partin a region in contact with the boundary of the outer core partis higher than the refractive index of the outer core part. The refractive index of the outer core partis gradually decreased from the inner circumferential side to the outer circumferential side. The refractive index of the inner cladding partis equal to the refractive index of the outermost circumferential part of the outer core partand not greater than the refractive index of the outer cladding part

Optical fiber

An optical fiber includes a core and a cladding surrounding an outer periphery of the core and has a refractive index profile in which a relative refractive index difference with respect to a distance r from a center of the core is represented by &#x394;(r), where a value of A represented by(&#x394;()&#x2212;&#x394;())(&#x394;()&#x2212;&#x394;())&#x2003;&#x2003;(Formula 1)is 0.3%&#xb7;&#x3bc;m or less, where a unit of r is &#x3bc;m, a unit of a relative refractive index difference &#x394;(r) is %, &#x394;(r)=&#x2212;0.064r+0.494, and MFDis a mode field diameter at a wavelength of 1.31 &#x3bc;m.

Optical fiber and method of manufacturing the same

An optical fiber including a core and a cladding including an inner cladding layer and an outer cladding layer is provided. The refractive index of the core &#x394;1, the refractive index of the inner cladding layer &#x394;2, and the refractive index of the outer cladding layer &#x394;3 have a relationship denoted by the following expressions: &#x394;1max&#x3e;&#x394;2min and &#x394;1max&#x3e;&#x394;3, and 0.01%&#x3c;|&#x394;2min&#x2212;&#x394;3|&#x3c;0.03%. An outer circumference radius r1 of the core, an outer circumferential radius r2 of the inner cladding layer, and an outer circumferential radius r3 of the outer cladding layer have a relationship denoted by the following expressions: r1&#x3c;r2&#x3c;r3, and 0.2&#x2266;r1/r2&#x2266;0.5. A cable cut-off wavelength &#x3bb;cc 1260 nm or less. A mode field diameter at a wavelength of 1310 nm is 8.6 &#x3bc;m or more and 9.5 &#x3bc;m or less.

An optical fiber includes a core, and a clad surrounding an outer circumference of the core, in which a first relative refractive index difference &#x394;1a is greater than 0, a second relative refractive index difference &#x394;1b is greater than 0, the first relative refractive index difference &#x394;1a is greater than the second relative refractive index difference &#x394;1b, the first relative refractive index difference &#x394;1a and the second relative refractive index difference &#x394;1b satisfy a relationship denoted by the following expression: 0.20&#x2266;(&#x394;1a&#x2212;&#x394;1b)/&#x394;1a&#x2266;0.88, and a refractive index profile &#x394; of the core in an entire region of a section of 0&#x2266;r&#x2266;r1 as a function &#x394;(r) of a distance r from a center of the core in the radial direction is denoted by the following expression: &#x394;(r)=&#x394;1a&#x2212;(&#x394;1a&#x2212;&#x394;1b)r/r1.

Optical fiber and manufacturing method thereof

A muffle tube inspection method inspects a muffle tube used for dehydrating and sintering a silica glass-based optical fiber preform, the muffle tube includes a sintering furnace provided with a furnace body covering a heater disposed around a periphery of the muffle tube. The method detects a crack generated at the muffle tube by measuring a pressure inside the furnace body while varying a pressure inside the muffle tube.

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Sakura, Japan

Sho Endo