Wideband multimode co-doped optical fiber employing GeO
The wideband multimode co-doped optical fiber has a silica core co-doped with GeO 2 and Al 2 O 3 . The GeO 2 concentration is maximum at the fiber centerline and monotonically decreases radially out to the core radius. The Al 2 O 3 concentration is minimum at the centerline and monotonically increases radially out to maximum concentration at the core radius. The cladding has an inner cladding region of relative refractive index Δ2, an intermediate cladding region having a relative refractive index Δ3, and an outer cladding region having a relative refractive index Δ4, wherein Δ3<Δ2, Δ4. The optical fiber has a bandwidth BW≥5 GHz·km with a peak wavelength λ P within a wavelength range of 800 nm to 1200 nm and over a wavelength band Δλ of at least 100 nm.
1. A method of forming a wideband multimode co-doped optical fiber, comprising:
a) forming a preform, the preform comprising:
i) a preform co-doped core having a preform core outer edge and comprising silica and co-doped with a first radially varying concentration of GeO 2 that decreases with the radial coordinate r out to the preform core outer edge and a second radially varying concentration of Al 2 O 3 that increases with the radial coordinate r out to the preform core outer edge;
ii) a preform cladding immediately surrounding the preform co-doped core and comprising silica, the preform cladding having an inner preform cladding region of relative refractive index Δ2, an intermediate preform cladding region having a relative refractive index Δ3 with a minimum value Δ3 MIN , and an outer preform cladding region having a relative refractive index Δ4, wherein the intermediate cladding region comprises a moat and wherein Δ3 MIN <Δ2, Δ4; and
b) drawing the preform to form the wideband multimode co-doped optical fiber comprising a co-doped fiber core defined by the preform co-doped core and having a fiber core outer edge and a diameter in a range from 20 microns to 70 microns and having the first and second radially varying concentrations of GeO 2 and Al 2 O 3 out to the fiber core outer edge, and a fiber cladding surrounding the co-doped fiber core and defined by the preform cladding and having a fiber inner cladding region having the relative refractive index Δ2, a fiber intermediate cladding region having the relative refractive index Δ3 with the minimum value Δ3 MIN , and a fiber outer cladding region having the relative refractive index Δ4, wherein the fiber intermediate cladding region comprises a moat and wherein Δ3 MIN <Δ2, Δ4; and
c) wherein the wideband multimode co-doped optical fiber has a wavelength band Δλ of at least 100 nm having a peak wavelength λ P in a wavelength range from 800 nm to 1200 nm and a bandwidth BW≤5 GHz·km.
2. The method according to claim 1 , further comprising forming the preform using a deposition process selected from the group of deposition processes comprising: outside vapor deposition, modified chemical vapor deposition, and plasma chemical vapor deposition.
3. The method according to claim 1 , wherein the co-doped fiber core has a radial concentration of GeO 2 defined by a first alpha value α 1 in the range from 2.0≤α 1 ≤2.2 and a radial concentration of Al 2 O 3 defined by a second alpha value α 2 in the range from 2.0≤α 2 ≤2.6.
4. The method according to claim 1 , wherein the wavelength band Δλ is a range from 100 nm to 300 nm.