JP2018063455A5 - - Google Patents

Claims (12)

An optical fiber for fusion splicing with CSMF (Conventional Single Mode Fiber),
A core made of quartz glass to which an updopant is added;
An inner clad covering the side surface of the core, the inner clad made of quartz glass to which both an updopant and a downdopant are added;
An outer clad covering the outer surface of the inner clad, and comprising an outer clad made of quartz glass,
The refractive index of the inner cladding is substantially equal to the refractive index of the outer cladding,
The concentration of the updopant in the inner cladding is determined so that the refractive index increase rate by the updopant is 0.25% to 0.5% ,
The concentration of the updopant in the core is determined such that the mode field diameter at a wavelength of 1550 nm is 3.5 μm or more and 6.5 μm or less .
An optical fiber characterized by that. The concentration of the downdopant in the inner cladding is determined so that the absolute value of the relative refractive index difference of the inner cladding with respect to the outer cladding is 0.1% or less.
The optical fiber according to claim 1 . Germanium is added to the core as the updopant,
Fluorine is added to the inner cladding as the downdopant,
The optical fiber according to claim 1 or 2 , wherein One or both of phosphorus and germanium are added as the updopant to the inner cladding,
The optical fiber according to claim 3 . The optical fiber according to claim 3 or 4 , wherein boron is further added to the inner cladding as the downdopant. A pair of stress applying portions disposed symmetrically with respect to the core;
The optical fiber according to any one of claim 1 to 5, characterized in that. The pair of stress applying portions are arranged such that the outer edges thereof are in contact with the outer edges of the inner cladding, or the outer edges are separated from the outer edges of the inner cladding,
The optical fiber according to claim 6 . In at least one end of the optical fiber during or after heat treatment, at least a first region having a relative refractive index difference value lower than that of the inner cladding is present in at least the outer cladding, The second region having a relative refractive index difference value relatively higher than that of the first region is present outside the first region. 8. An optical fiber as described in 1.   At least one region where the concentration of the downdopant is positive exists in the core at least at one end of the optical fiber during or after the heat treatment.
The optical fiber according to claim 1, wherein the optical fiber is an optical fiber.   In at least one end of the optical fiber after the heat treatment, the concentration of the downdopant in the entire interior of the core is positive.
The optical fiber according to claim 9. An optical device comprising: the optical fiber according to any one of claims 1 to 10 ; and the CSMF fused and connected to the other end of the optical fiber. The optical device according to claim 11 , further comprising a semiconductor optical waveguide connected to one end of the optical fiber.