Optical waveguides – Having particular optical characteristic modifying chemical... – Of waveguide core
Reexamination Certificate
2000-07-19
2004-02-24
Cherry, Euncha (Department: 2872)
Optical waveguides
Having particular optical characteristic modifying chemical...
Of waveguide core
Reexamination Certificate
active
06697562
ABSTRACT:
CLAIM OF PRIORITY
This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from my application DISPERSION CONTROL FIBER AND A LARGE SIZE PREFORM MANUFACTURE METHOD THEREOF filed with the Korean Industrial Property Office on Jul. 22, 1999 and there duly assigned Ser. No. 29828/1999.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical fiber and a manufacturing method thereof, and more particularly to a dispersion control fiber and a method of manufacturing a large size preform thereof.
2. Description of the Related Art
Optical fibers as widely used as new media for transmitting information are largely classified into a single mode fiber and a multi mode fiber, according to the transmitting mode. The single mode fiber is also classified into a single mode fiber and a dispersion control fiber.
The dispersion control fiber comprises a dispersion shifted fiber with a zero dispersion wavelength band shifted to a wavelength band of 1.5 &mgr;m, a dispersion flattened fiber with a constant dispersion value in a wide wavelength band of 1.3~1.6 &mgr;m, and a non-zero dispersion shifted fiber with a low dispersion value in a wavelength band of 1.5~1.6 &mgr;m. The dispersion shifted fiber is disclosed in U.S. Pat. No. 5,721,800 issued to Kato, et al., and the dispersion flattened fiber is disclosed in U.S. Pat. No. 5,675,690 issued to Nouchi, et al.
While the optical fibers have been made directly from raw materials, most of them generally have been made from a separate preform heated above a softening point within a furnace.
The length of an optical fiber capable of being drawn from the preform is dependent upon the diameter of the preform. In particular, since the drawing amount of the optical fiber is proportional to the preform diameter, methods of manufacturing a large size preform have been proposed. The size enlargement of preforms can be achieved by enlarging the diameter of a first preform formed by the deposition and collapse, and by enlarging the diameter of a tube for over-cladding.
FIG. 1
is a flow chart showing the process of manufacturing a general optical fiber As shown in
FIG. 1
, the general method of manufacturing the optical fiber includes the steps of forming a preform (step
10
), drawing the optical fiber (step
20
), coating a sheath around the outer periphery of the optical fiber (step
30
), and winding the optical fiber (step
40
). Generally, the steps of drawing and coating are continually performed within a fiber drawing apparatus.
The step
10
is a process of forming a base preform to draw the optical fiber. The method of forming the preform includes a vapor-phase axial deposition (VAD) method, an outer chemical vapor-phase deposition (OCVD) method, a plasma chemical vapor-phase deposition (PCVD) method, and a modified chemical vapor-phase deposition (MCVD) method, the MCVD method being widely used.
The process of manufacturing the preform by the MCVD method will hereinafter be explained in detail. Gas such as SiCl
4
or GeCl
4
is introduced in a deposition tube rotated at a constant speed, and a burner movable left and right heats the outer periphery of the tube. Particles are deposited on the inner surface of the deposition tube. The deposited particles are sintered, collapsed and closed by the heat of the burner to form a first preform with a core layer and a cladding layer. The first preform is treated by over-cladding to form a resultant preform.
The refractive difference between the core and cladding can be selected by adjusting components of gas supplied into the deposition tube, and the process of manufacturing the preform by using the MCVD method is disclosed in U.S. Pat. Nos. 4,389,230 and 5,397,372 in detail.
The drawing and coating steps
20
and
30
are continually performed in the optical fiber apparatus provided with a furnace and a coating machine to draw the optical fiber from the preform. When the preform is heated above a softening point in the furnace, the optical fiber is drawn through a drawing hole provided on the lower end of the furnace. Then, the optical fiber is coated by passing through the coating machine, and cooled by passing through a cooling machine.
In the winding step
40
, the optical fiber is applied with a stress by a capstan, and is wound around a spool.
FIG
2
is a cross sectional view illustrating the structure of a general single mode fiber, and
FIG. 3
is a cross sectional view illustrating the structure of a conventional dispersion control fiber. The shown optical fibers mainly consist of SiO
2
.
As shown in
FIGS. 2 and 3
, the general single mode fiber and the conventional dispersion control fiber include a core
110
or
210
, a cladding
120
or
220
, and a sheath
130
or
230
, respectively.
SiO
2
is a main component of the core
110
or
210
, and GeO
2
is added to adjust the refractive index distribution. The cladding
120
or
220
includes GeO
2
, P
2
O
5
and Freon to adjust the refractive index distribution or reduce the deposition temperature, in addition to SiO
2
. While the claddings
120
and
220
are shown in a single layer to be easily understood, a multi-layered cladding formed by over-cladding may be adopted.
Generally, the single mode fiber
100
has a core diameter of 8~12 &mgr;m and a relative refractive index of 0.35, and the dispersion control fiber
200
has a core diameter of 5~8 &mgr;m and a relative refractive index of 0.7~0.15. In other words, the core
210
of the dispersion control fiber
200
has a diameter smaller than that of the general single mode fiber
100
, but has a refractive index higher than that of the single mode fiber. The relative refractive index is expressed by (n1
2
-n2
2
)/(2n1
2
)*100, wherein n1 is a maximum refractive index of the core, and n2 is a minimum refractive index.
The sheaths
130
and
230
function as inner protective layers for preventing the cores
110
and
210
and the claddings
1
20
and
220
from mechanical or chemical damage. The sheaths
130
and
230
are made of a plastic material such as a thermosetting resin.
Table 1 shows a variation of the optical characteristics of the general single mode fiber and the prior dispersion control fiber. In Table 2, the variation of the optical characteristics and the deformation of the deposition tube are indicated in dependence on the diameter increment of the preform and the drawing temperature. In Table 1, S represents SiO
2
, G represents GeO
2
, P represents P
2
5
, and F represents Freon.
TABLE 1
Variation of optical characteristics
Example
Diameter of
Composition
Zero dispersion
Mode field
Dispersion
Shrink
of
preform
Composition
of
wavelength
diameter
slope
deformation of
Prior Art
(mm)
Class
of core
cladding
(nm)
(&mgr;m)
(ps
m
2
km)
deposition tube
1
50
S.M.F.
S + G
S + G + P + F
0~2
0~0.5
0~0.0001
No
2
66
S.M.F.
S + G
S + G + P + F
0~2
0~0.2
0~0.0001
No
3
50
D.C.F.
S + G
S + G + P + F
1~3
0~0.2
0~0.0001
No
4
66
D.C.F.
S + G
S + G + P + F
20~40
0.2~0.5
0.004~0.009
No
Variation of drawing temperature depending on the increasing diameter of preform: 20° C., diameter of core: 8~8 &mgr;m,
Relative refractive index ratio(%): 0.35
S.M.F. represents a single mode fiber, and D.C.F. represents a dispersion control fiber.
As can be seen from the examples 1 and 2, even though in the case of a general single mode fiber, it is drawn at an increased drawing temperature, there is no or little variation in the photo characteristics, such as the zero dispersion wavelength, the mode field diameter, and the dispersion slope in so far as the drawing of the fiber is carried out under the condition in which the preform used has a size enlarged from 50 mm to 66 mm, as compared to the case using a preform involving no size enlargement.
However, as seen from the examples 3 and 4, even though in the case of a dispersion control fiber, it is draw
Do Mun-Hyun
Lee Ji-Hoon
Bushnell , Esq. Robert E.
Cherry Euncha
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