Optical waveguides – Optical fiber waveguide with cladding – Utilizing multiple core or cladding
Reexamination Certificate
2003-01-28
2004-02-24
Robinson, Mark A. (Department: 2872)
Optical waveguides
Optical fiber waveguide with cladding
Utilizing multiple core or cladding
C385S142000, C385S144000
Reexamination Certificate
active
06697559
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical fiber having a ring core portion, and a favorable method of making the same.
2. Related Background Art
Dispersion-shifted optical fibers have a zero-dispersion wavelength, where their chromatic dispersion value becomes zero, in the wavelength range of 1.55 &mgr;m. Known as one kind thereof are those of a ring-shaped structure in which a ring core region having a higher refractive index and a cladding region having a lower refractive index are disposed concentrically around a center core region. A dispersion-shifted optical fiber having such a ring-shaped structure of refractive index profile is manufactured by drawing an optical fiber preform having a similar refractive index profile.
The refractive index profile of this optical fiber preform can be realized by employing silica glass as a main ingredient, adding F (fluorine) element to a center core portion which is to become the center core region of the optical fiber, and adding GeO
2
(germanium dioxide) to a ring core portion which is to become the ring core region. This optical fiber preform is subjected to melt spinning, i.e., so-called drawing, an optical fiber having a desirable refractive index profile may be obtained.
SUMMARY OF THE INVENTION
However, upon drawing, the optical fiber preform is heated and, at this time, the F element added to the center core portion diffuses into its surrounding regions, whereas Ge added to the ring core portion diffuses into the center core portion and the outer cladding region. Due to this mutual diffusion, transmission loss would increase. Also, when Ge and F mingle with each other, then GeF
4
or GeO may be produced in a heating and unifying process, so as to generate bubbles, which deteriorate the quality of the optical fiber to be made. As a result, there has been a problem that desirable fiber characteristics may not be obtained.
In order to overcome the above-mentioned problem, it is an object of the present invention to provide an optical fiber of a ring-shaped structure having a region doped with F element and a region doped with Ge, which can be manufactured stably and has a desirable refractive index profile; and a method of making the same.
For overcoming the above-mentioned problem, the optical fiber in accordance with the present invention is composed of silica glass, having a center core region doped with F element and a ring core region doped with GeO
2
, wherein a buffer layer made of undoped SiO
2
(silicon dioxide) or SiO
2
doped with both or one of P (phosphorus) and Cl (chlorine) is disposed between the center core region and the ring core region.
The optical fiber in accordance with the present invention can be made by drawing an optical fiber preform having a cross-sectional profile similar to that of this optical fiber. Namely, the optical fiber preform also has a buffer layer made of undoped SiO
2
or SiO
2
doped with one or both of P and Cl. When this optical fiber is drawn, the mutual diffusion of F and Ge between the ring core region and the center core region is suppressed due to the existence of buffer layer. The fact that this buffer layer exists in the resulting optical fiber indicates that the mutual dispersion suppressing effect sufficiently functions, so as to maintain fiber characteristics.
Preferably, the thickness of the buffer layer is at least 0.01 &mgr;m but not greater than 5 &mgr;m. If the buffer layer is thinner than the lower limit of this range, there is a possibility of the mutual diffusion of Ge and F occurring beyond the buffer layer. On the other hand, if the buffer layer is thicker than the upper limit of the range, the bending loss occurring when the optical fiber is bent may become unfavorably large.
Alternatively, the optical fiber in accordance with the present invention is composed of silica glass, having a center core region, a ring core region doped with GeO
2
(germanium dioxide), and an inner cladding region doped with F (fluorine) element which are arranged concentrically, wherein a buffer layer made of undoped SiO
2
or SiO
2
doped with both or one of P and Cl is disposed between the ring core region and the inner cladding region.
The mutual diffusion of F and Ge between the ring core region and the inner cladding region when drawing an optical fiber preform having a similar structure is suppressed due to the existence of buffer layer in this case as well. Similarly, the fact that this buffer layer exists in the resulting optical fiber indicates that the mutual dispersion suppressing effect sufficiently functions, so as to maintain fiber characteristics.
In this case, the thickness of the buffer layer is preferably 0.01 &mgr;m or greater. It is because of the fact that there is a possibility of the mutual diffusion of Ge and F occurring beyond the buffer layer if the buffer layer is thinner than this lower limit. On the other hand, the change in bending loss occurring upon bending the optical fiber depending on the thickness of the buffer layer in this case is smaller than that in the case where the buffer layer is formed between the ring core region and the center core region, whereby the buffer layer can be made thicker.
Alternatively, the optical fiber in accordance with the present invention is comprised of silica glass, having a center core region doped with F element and a ring core region doped with GeO
2
; wherein, letting a [&mgr;m] be the radius of the center core region, and C
G
(r) [wt %] be the concentration of GeO
2
in the ring core region at a position separated from the center by a radius r [&mgr;m], the concentration gradient Y
G1
[wt %·&mgr;m
2
] of GeO
2
in a boundary portion of the ring core region with respect to the center core region defined by:
y
G1
=
∫
a
a
+
1
(
rC
G
(
r
)
exp
(
a
-
r
)
)
ⅆ
r
(
1
)
is set to 100 wt %·&mgr;m
2
or less; or, letting C
F
(r) [wt %] be the concentration of F element in the center core region at a position separated from the center by a radius r [&mgr;m], the concentration gradient y
F1
[wt %·&mgr;m
2
] of F element in a boundary portion of the center core region with respect to the ring core region defined by:
y
F1
=
∫
a
-
1
a
(
rC
F
(
r
)
exp
(
r
-
a
)
)
ⅆ
r
(
2
)
is set to 18 wt %·&mgr;m
2
or less.
Alternatively, the optical fiber in accordance with the present invention is composed of silica glass, having a center core region, a ring core region doped with GeO
2
, and an inner cladding region doped with F element which are arranged concentrically; wherein, letting b [&mgr;m] be the radius of the ring core region, and C
G
(r) [wt %] be the concentration of GeO
2
in the ring core region at a position separated from the center by a radius r [&mgr;m], the concentration gradient Y
G2
[wt %·&mgr;m
2
] of GeO
2
in a boundary portion of the ring core region with respect to the inner cladding region defined by:
y
G2
=
∫
b
-
1
b
(
rC
G
(
r
)
exp
(
r
-
b
)
)
ⅆ
r
(
3
)
is set to 180 wt %·&mgr;m
2
or less; or, letting C
F
(r) [wt %] be the concentration of F in the inner cladding region at a position separated from the center by a radius r [&mgr;m], the concentration gradient Y
F2
[wt %·&mgr;m
2
] of F element in a boundary portion of the inner cladding region with respect to the ring core region defined by:
y
F2
=
∫
b
b
+
1
(
rC
F
(
r
)
exp
(
b
-
r
)
)
ⅆ
r
(
4
)
is set to 30 wt %·&mgr;m
2
or less.
The diffusion velocity of the above-mentioned mutual diffusion of Fe and Ge generated upon drawing results from the concentration gradient in the boundary portion between the region doped with F element and the region doped with GeO
2
. The inventors have found that, when the radial distribution of doping amount of GeO
2
or F element in each region is set such that the weighted concentr
Hirano Masaaki
Onishi Masashi
Yokoyama Yoshio
Amari Alessandro
McDermott & Will & Emery
Robinson Mark A.
Sumitomo Electric Industries Ltd.
LandOfFree
Optical fiber and method of making the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical fiber and method of making the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical fiber and method of making the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3340647