Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
1999-07-28
2001-10-23
Kelly, Cynthia H. (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S375000, C428S392000, C065S414000, C065S421000, C065S422000, C385S124000, C427S163200
Reexamination Certificate
active
06306500
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to porous optical fiber base materials, optical fiber base materials and methods for producing them. In particular, the present invention relates to a porous optical fiber base material with improved weight of fine glass powder deposited on a member contained in the material, or improved fine glass powder deposit efficiency, and a porous optical fiber base material capable of affording a reduced number of air bubbles in a sintered body which is obtained by vitrifying deposited fine glass powder by fusion, and the present invention further relates to optical fiber base materials that can be obtained from the aforementioned porous base materials, and methods for producing them.
2. Description of the Related Art
A porous optical fiber base material has conventionally been produced by, for example, as in the outside chemical vapor deposition, depositing fine glass powder on a circumferential surface of axially rotating member of porous optical fiber base material.
In order to deposit the fine glass powder on the circumferential surface of the member, for example, the member is placed in an apparatus, called chamber, which covers the both ends of the member along its axial direction, and fine glass powder is produced around the member with flame formed from fuel gas and material gas thrown from a flame burner provided at a front part of the chamber so that the fine glass powder should be deposited on the member. The chamber is also provided with a mechanism for exhausting unreacted gases, gases generated from reactions, fine glass powder not deposited and the like from an exhaust port provided on the side opposite to the flame burner in the chamber.
A porous optical fiber base material produced by depositing fine glass powder on a member as described above has excellent purity and other-various excellent qualities. That is, in the field of the porous optical fiber base material production, marked progress has been achieved as for quality in recent years.
SUMMARY OF THE PRESENT INVENTION
The first object of the present invention is to further improve such a porous optical fiber base material having the various kinds of excellent qualities as described above, thereby obtaining a porous optical fiber base material with improved weight of fine glass powder deposited on the member per batch, or improved fine glass powder deposit efficiency, which may greatly contribute to improvement of production ability and reduction of production cost.
By the way, a conventional sintered body produced by vitrifying such a porous optical fiber base material as mentioned above by fusion (optical fiber base material) may internally contain bright spots. Such bright spots may remain even after the material is made into an optical fiber, and thus they may be a cause of light transmission loss. It is considered that the cause of the bright spots is exogenous contaminants or air bubbles contained in the material.
Therefore, the second object of the present invention is to further improve a conventional porous optical fiber base material to provide a porous optical fiber base material which can markedly decrease air bubbles in an optical fiber base material after the fusion vitrification, and an optical fiber base material substantially free from bright spots, which can be obtained from the porous optical fiber base material.
The inventors of the present invention earnestly conducted studies to achieve the first object of the present invention. As a result, it was found that, in order to increase the deposition weight of the fine glass powder on the member, without mentioning the enhancement of strength of the member, it is necessary to improve the strength of the deposited fine glass powder itself. That is, when the weight of the deposited fine glass powder is increased, the strength of the member can be enhanced by using a larger diameter. However, as for the deposited fine glass powder, if the deposition amount is simply increased, it inevitably causes its breakage during handling for the transfer to a subsequent step. That is, the deposited fine glass powder is transferred to the subsequent step by, for example, carrying it by a hand truck provided with a cushioning material. However, in spite of the use of the cushioning material, the bottom of the deposited fine glass powder may be broken of its own weight. Thus, the strength of the deposited fine glass powder itself should be required.
The present invention has been-accomplished in order to solve the above problem, and provides a porous optical fiber base material comprising a member on which fine glass powder is deposited, characterized in that the deposited fine glass powder has a controlled pore size.
By controlling the pore size of the deposited fine glass powder as in the aforementioned material, the strength of the deposited fine glass powder can be improved, and thus the weight of the deposited fine glass powder on the member can be increased.
In a preferred embodiment of the aforementioned porous optical fiber base material of the present invention, mode of the pore size of the deposited fine glass powder is controlled to be 0.1 to 1 &mgr;m.
A porous optical fiber base material whose pore size is controlled so that its mode should be in the above defined range can have, in particular, a long length and large diameter, i.e., it can have heavier deposited fine glass powder, and can be made into an optical fiber exhibiting excellent optical properties.
Further, during the earnest studies aiming at achieving the aforementioned first object, the inventors of the present invention found that there was correlation between deposit efficiency of the fine glass powder and physical properties of the deposited fine glass powder, in particular, a total amount of absorbed H
2
O amount and OH group amount on the fine glass powder per square meter of fine glass powder surface area, which is calculated based on specific surface area of the fine glass powder determined by the BET method.
That is, the present invention also provides a porous optical fiber base material comprising a member on which fine glass powder is deposited, characterized in that a total amount of absorbed H
2
O amount and OH group amount on the fine glass powder per square meter of fine glass powder surface area is 3.5×10
−5
to 7.5×10
−5
g.
If the total amount of absorbed H
2
O amount and OH group amount on the fine glass powder per square meter of the fine glass powder surface area is in the above-defined range, the porous optical fiber base material can have a high deposit efficiency of the fine glass powder to the center base material.
The present invention also provides an optical fiber base material which is obtained by vitrifying by fusion the aforementioned porous optical fiber base material having an increased weight of the deposited fine glass powder as a result of the control of the pore size, or the aforementioned porous optical fiber base material having an improved fine glass powder deposit efficiency.
By vitrifying by fusion the aforementioned porous optical fiber base material having an increased weight of the deposited fine glass powder as a result of the control of the pore size, an optical fiber base material having a long length and large diameter can be produced, and thus it can be made into an optical fiber exhibiting excellent optical properties.
Further, by using the aforementioned porous optical fiber base material having an improved fine glass powder deposit efficiency, a large-sized optical fiber base material having excellent optical characteristics can be produced at low cost.
The present invention also provides a method for producing a porous optical fiber base material comprising depositing fine glass powder on a rotating member, characterized in that pore size of the deposited fine glass powder is controlled.
By controlling the pore size of the deposited fine glass powder as in the aforementioned method, the strength of the deposited fine glass powder
Hirasawa Hideo
Kuwabara Haruyoshi
Shimada Tadakatsu
Gray J. M.
Hogan & Hartson L.L.P.
Kelly Cynthia H.
Shin-Etsu Chemical Co. , Ltd.
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