Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
1999-06-25
2001-08-28
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C428S034600, C428S212000, C385S124000, C385S126000, C385S127000, C359S341430
Reexamination Certificate
active
06280850
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of optical fibers and optical fiber manufacturing, and more particularly to optical fiber preforms which minimizing the diffusion of OH from the substrate tube to the core of an optical fiber.
2. Description of the Related Art
A single mode optical fiber is made by depositing a cladding layer and a core layer. In a DC-SM (depressed cladding-single mode) type, a cladding layer is deposited by doping SiO
2
with P
2
O
5
, GeO
2
, and F to lower the deposition temperature and the refractive index, a core layer for transmitting light is deposited by doping SiO
2
with GeO
2
to increase the refractive index, and then an optical fiber preform is manufactured through a collapsing and closing process.
In a process for manufacturing an optical fiber preform using modified chemical vapor deposition (MCVD), self-collapse of a substrate tube occurs during deposition as the deposition layer becomes thicker, resulting in an increase in the thickness of the tube. Also, a high temperature burner is required to sinter and consolidate a thick deposition layer, and the time for the collapsing and closing process becomes longer, so that a substrate tube becomes exposed to a high temperature over a long period of time.
In this process, when a very small amount of water (H
2
O) (generally about several ppm) contained in the substrate tube diffuses into the deposition layer, diffused water is combined with P
2
O
5
or SiO
2
deposited in the cladding region, thus forming P—O—H or Ge—O—H bonds. OH which diffuses to the core region is combined with SiO
2
or GeO
2
deposited in the core layer, thus forming Si—O—H or Ge—O—H bonds while dissolving Si—O or Ge—O bonding. O—H or P—O—H bonds formed in the combination with water in each deposition region as described above result in additional optical loss due to absorption bands at specific wavelength regions. In the case of a single mode optical fiber, wavelength bands in which serious optical loss occurs are the 124 &mgr;m-1.385 &mgr;m band due to the O—H bond combination, and the 1.2-1.8 &mgr;m band due to the P—O—H bond combination. When OH is diffused into the core region, it forms a non-bridging oxygen (NBO), and the structural homogeneity of glass material of the core layer is thus locally deteriorated, which causes density fluctuation of the core layer. Consequently, scattering loss is increased.
The inside and outside diameters of a tube contract with an increase in the thickness of the deposition layer during sintering performed simultaneously with deposition, so that it is difficult to obtain an appropriate diameter ratio (that is, cladding diameter/core diameter=D/d). Therefore, a distance sufficient to prevent diffusion of OH cannot be secured, thus greatly increasing loss due to OH.
In the prior art, a method of thickening the cladding layer is used to prevent OH from diffusing from the substrate tube to the core layer. However, when a large-aperture preform is manufactured by this method, contraction of the tube makes it difficult to secure an appropriate diameter ratio, and a burner of a higher temperature is required during deposition of the core layer since the efficiency of transmitting heat to a core layer is degraded due to an increase in the thickness of the tube layer. Thus, the tube is exposed to high temperature for a long time, thus increasing loss due to OH.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an improved optical fiber preform and method of manufacturing the preform.
It is also an object of the present invention to provide an optical fiber preform with lower optical loss due to OH and POH absorption bands.
It is a further object of the present invention to provide an optical fiber preform with lower scattering loss.
It is a yet further object of the present invention to provide an optical fiber preform which avoids the problem of diffusion of OH to the core.
It is a still further object of the invention to provide an optical fiber preform which allows easier control over the cladding/core diameter ratio.
To achieve the above objectives, the present invention provides an optical fiber preform capable of effectively reducing loss due to OH while lowering the diameter ratio by forming a barrier layer for blocking or remarkably alleviating diffusion of OH between a substrate tube and a core layer in order to prevent OH from diffusing from the substrate tube into the core layer. The present invention also provides a method of manufacturing an optical fiber preform having an OH barrier.
Accordingly, to achieve the objectives, there is provided an optical fiber preform having a substrate tube, a cladding layer and a core layer, the optical fiber preform further including a first barrier layer deposited by a material having a low OH diffusion coefficient between the substrate tube and the cladding layer, wherein the first barrier layer is for substantially preventing OH contained in the substrate tube from being diffused into the cladding layer.
It is preferable that the optical fiber preform further comprises a second barrier layer formed by depositing a material having a low OH diffusion coefficient between the cladding layer and core layer, for substantially preventing OH which has been diffused into the cladding layer from the substrate tube from being diffused further into the core layer.
There is also provided another optical fiber preform having a substrate tube, a cladding layer and a core layer, the optical fiber preform further comprising a first barrier layer deposited by a material having a low OH diffusion coefficient between the substrate tube and the cladding layer, wherein the first barrier layer is for substantially preventing OH contained in the substrate tube from being diffused into the cladding layer, wherein the refractive index of the core layer is greater than the refractive index of the cladding layer and gradually increases in the direction from the outside of the core layer to the center of the core layer.
It is preferable that this optical fiber preform further comprises a second barrier layer deposited by a material having a low OH diffusion coefficient between the cladding layer and core layer, wherein the second barrier layer is for substantially preventing OH diffused into the cladding layer from being diffused further into the core layer.
To achieve the second objective, there is provided a method of manufacturing an optical fiber preform having a substrate tube, a cladding layer and a core layer, the method comprising the steps of: forming a first barrier layer by depositing a material having a low OH diffusion coefficient; forming a cladding layer by doping a material suitable for lowering a process temperature and increasing deposition efficiency; and forming a core layer being a region through which an optical signal is transmitted.
It is preferable that a second barrier layer is further formed by depositing a material having a low OH diffusion coefficient, before the core layer is formed after the cladding layer is formed. Also, it is preferable that the core layer is formed so that the refractive index gradually increases in is the direction from the outside to the center of the core layer.
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Do Mun-Hyun
Oh Sung-Koog
Seo Man-Seok
Yang Jin-Seong
Bushnell , Esq. Robert E.
Jones Deborah
McNeil Jennifer
Samsung Electronics Co,. Ltd.
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