CA1206755A - Method for producing optical multiple fiber - Google Patents
Method for producing optical multiple fiberInfo
- Publication number
- CA1206755A CA1206755A CA000437246A CA437246A CA1206755A CA 1206755 A CA1206755 A CA 1206755A CA 000437246 A CA000437246 A CA 000437246A CA 437246 A CA437246 A CA 437246A CA 1206755 A CA1206755 A CA 1206755A
- Authority
- CA
- Canada
- Prior art keywords
- silica glass
- preforms
- fiber
- optical
- support layer
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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- Manufacture, Treatment Of Glass Fibers (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
In a method for producing an optical multiple fiber wherein a multiplicity of optical fibers are fused together with each other and each optical fiber comprises a core made of pure silica glass and a cladding layer made of a silica glass containing a dopant disposed on the core, by bundling a multiplicity of preforms corresponding to the optical fibers and drawing the bundle at a high temperature, an improvement which comprises using, as said optical fiber preforms, preforms having a three-layer construction wherein a support layer made of a silica glass having a drawable temperature of at least 1,800°C. is further disposed on the cladding layer, and drawing the bundle of the preforms to give a multiple fiber wherein the support layer of each optical fiber has a thickness of 0.01 to 1 µm, in order to produce a multiple fiber in which the cladding layer of each optical fiber has a sufficient thickness to fulfill the function as a cladding layer and which has an excellent image-transmitting capacity.
In a method for producing an optical multiple fiber wherein a multiplicity of optical fibers are fused together with each other and each optical fiber comprises a core made of pure silica glass and a cladding layer made of a silica glass containing a dopant disposed on the core, by bundling a multiplicity of preforms corresponding to the optical fibers and drawing the bundle at a high temperature, an improvement which comprises using, as said optical fiber preforms, preforms having a three-layer construction wherein a support layer made of a silica glass having a drawable temperature of at least 1,800°C. is further disposed on the cladding layer, and drawing the bundle of the preforms to give a multiple fiber wherein the support layer of each optical fiber has a thickness of 0.01 to 1 µm, in order to produce a multiple fiber in which the cladding layer of each optical fiber has a sufficient thickness to fulfill the function as a cladding layer and which has an excellent image-transmitting capacity.
Description
~J6';~5.'j B~CKGROUND_OF THE INVENTION
The present invention relates to a method for producing an optical multiple fiber (hereinafter referred to as "multiple fiber") having a construction that a multiplicity of silica glass optical fibers are fused together with each other, and more particularl~ to a method for producing a multiple ~iber, each constituent optical ~iber of which consists of a core of pure silica glass and a cladding layer thereon made of a silica glass containing a dopant and having a lower refractive index than pure silica glass.
The above-mentioned multiple fiber which consists of optical ibers each having a core of pure silica glass retains desirable properties such as excellent heat resistance and radiation resistance inherent in pure silica glass, and is useful as an image-guide for monitoring the inside of a high temperature furnace, a nuclear reactor 9 and the like.
It is known that addition of a dopant to pure silica glass results in a sharp decrease of softening or deformation point. Thus, whereas the softening or deformation point of pure silica glass is as high as at least about 1,800C., that of a silica glass containing a sufficient amount of a dopant to-serve as a cladding layer i5 not more than 1,500C. or in some cases, not more than 1,000C., though it varies depending on the kind and amount of the dopant. Moreover, there also is a large difference in deformation resistance in softened state between pure silica glass and a dopant-containing silica glass. The dopant-containing silica glass has a very low deformation resistance as compared with pure silica glass.
Çenerally, a multiple fiber of silica glass is produced by bundling a multiplicity of optical fiber preforms or those obtained by drawing the preform to reduce it in diameter (the abo~e-mentioned optical fiber preform and those obtained b~ drawing the preform to reduce it in diameter are included in the scope o~ "preform" intended in the present inveniton) and drawing the resulting bundle _ 3 - ~Z~6~5 at a high temperature. When the core of each preform is made of pure silica glass and the cladding layer thereon is made of a silica glass containing a dopant, the cladding layer begins to be fluidized and deformed before the core is softened and deformed in the drawing step, and the cladding material tends to separate from the core and flow into portions of low flow resistance, which results in the formation of a defective multiple fiber wherein the cores of adjacent optical fibers are brought abnormally near to each other or into direct contact with each other in some places. This pro~lem i5 apt to occur when the average thickness of cladding layers after drawing is small. Such a multiple fiber, of course, is deficient in image-transmitting capacity.
It is an object of the present invention to provide a method for producing a multiple fiber having an excellent image-transmitting capacity in which the cladding layer of each optical fiber has a sufficient thickness to fulfill the function as a cladding layer.
This and other objects of the present invention will become apparent from the description hereinafter.
SUMMARY OF THE INVENTION
The present invention provides a method for producing a multiple fiber wherein a multiplicity of optical fibers are fused together with each other and each optical fiber comprises a core made of pure silica glass and a cladding layer made of a silica glass containing a dopant and disposed on the core, by bundling a multiplicity of preforms corresponding to the optical fibers and drawing the bundle at a high temperature, the method being improved in that preforms having a three-layer construction wherein a support layer made of a silica glass having a drawable temperature of at least 19 800C. is further disposed on the cladding layer are used as said optical fiber preforms, and the bundle of the preforms is drawn to give a multiple fiber wherein the support layer of each optical fiber has a thickness of ~Z~16~5S
0.01 to 1 ~m.
In the present invention, the drawable temperature of the support layer means the temperature of the constituent material thereoE that permits drawing by a conventional method. More particularly, it is defined as follows: A pipe made of the same material as that to be used for forming the support layer and having an inner diameter of 23 mm. and an outer diameter of 26 mm. is drawn to reduce the pipe in diameter, giving a pipe having an inner diameter of 2.3 mm. and an outer diameter of 2.6 mm. The drawable temperature means the lowes-t temperature that permits to take up the pipe of the reduced diameter at a rate of ~.5 m./min. with a drawing tension of not more than 500 g.
DETAILED DESCRIPTION
.. . . _ In the present invention~ the multiple fiber is produced by bundling a multiplicity of preforms having the three-layer construction corresponding to optical fibers having the three-layer construction and drawing the bundle. The above-mentioned support layer of high-softening silica glass located on the outside of the cladding layer of each preform helps prevent an excessive fluidization of the cladding layer during drawing to thereby eliminate the problem that the cores of some adjacent optical fibers come into direct contact with each other.
The silica glass as the constituent material of the support layer may be any of natural silica glasses and synthetic silica glasses only if its drawable temperature is at least 1,800C. Preferred is a silica glass having a drawable temperature of at least 1,850C., particularly at least l,900C. Such a high-softening silica glass has a sufficient deformation resistance in softened state which is comparable to that of pure silica glass.
If the support layer of each optical fiber is too small in thickness, it does not provide a sufficient - 5 ~ 6755 property to prevent the excessive fluidization of the cladding layer. Therefore, in terms of "the thickness of the support layer" as defined hereinafter, it is preferable that the support layer has a thickness of at least 0.01 ~m., especially at least 0.1 ~m.
On the other hand, the research undertaken by the present inventors has shown tha-t the light incident on the support layers of the optical fibers included in a multiple fiber during the transmission of an image with the multiple fiber exerts the bad influence of blurring the transmitted image, that is to say, the support layer functions as a path of stray light. The degree of such bad influence is much higher with an increasing thickness of the support layer. Therefore, it is preferable that the thickness of the support layer of each optical fiber is not more than 1 ~m., particularly not more than 0.5 ~m.
By ensuring such a small thickness for the support layer of each optical fiber, the degree of the bad influence due to the stray light can be reduced.
Definition of the thickness of the support layer:
In most of the optical fibers in a multiple fiber produced by bundling and drawing a multiplicity of preforms having the three-layer construction, the cladding layer and the support layer are deformed so that their outer shapes are hexagonal in cross section, with the support layers of adjacent optical fibers being fused together with each other. Therefore, the thickness of the support layer for single optical fiber is defined to be one-second of the total thickness of two fused support layers between two adjacent optica~ fibers.
The multiple fiber wherein each support layer of the optical fibers contained ther~in has the above-mentioned thickness can be easily produced by taking into consideration the thickness of the support layer of optical fiber preforms used and the drawing ratio. The drawing temperature is usually from 1,800 to 2,200C., preEerably from 19900 to 29100C. The outer diameter of each optical fiber included in the final multiple fiber (the distance between the diametrically opposite two sides of the support layer having the above-mentioned hexagonal outer shape) is usually from 10 to 50 ~m.
The effect oE the support layer is especially pronounced when the multiple fiber produced by the method of the present invention has an outer diameter of 0.5 to 3 mm. (when the skin layer described hereinafter is present, the outer diameter including the skin layer) and contains 1,000 to 30,000 optical ~ibers.
In the practice of the presen-t invention, a bundle of preforms may be directly drawn but it is more advantageous to insert preforms into a silica glass tube made of synthetic or natural silica glass in an orderly arrangement and draw the bundle of the preforms together with the silica glass tube, the latter method ensuring the production of a multiple fiber having a more uniform outer diameter. In this case, the resulting multiple fiber has a silica glass skin layer derived from the silica glass tube as an outermost layer.
The method of the present invention is explained by means of the following Examples. These Examples are intended to illustrate the invention and not be construed to limit the scope of the invention. It is understood that various changes and modifications may be made in the invention without departing from the spirit and scope thereof.
Examples 1 and 2 and Comparative Example 8,000 three-la~er preforms having clean surfaces and each consisting of a core made of pure silica glass and having an outer diameter of 300 ~m., a cladding layer disposed on the core and made of a silica glass doped with B2O3 and having a thickness of 70 ~m., and a support layer disposed on the cladding layer and made of a natural silica (drawable -temperature: 1,900C.) and having a thickness of 15 ~m. were bundled and encased in a silica glass pipe. While the silica glass pipe was evacuated from the upper end thereof, the pipe was heated at the :~Z&'~i~S~
lower end at a temperature of 2,000C. and drawn from the lower end to give a multiple fiber made up of 8,000 optical fibers each having a support layer of 0.4 ~m. in thickness (Example 1). Microscopic examination of the end surface of the obtained multiple fiber revealed no direct contact between the cores of the optical fibers.
A multiple fiber wherein the support layer of each optical fiber had a thickness of 0.1 ~m. (Example 2) and another multiple fiher wherein the support layer of each optical fiber had a thickness of 2 ~m. tComparative Example) were also produced by changing only the drawing ratio in the procedures of Example 1. While none of the multiple fibers of Examples 1 and 2 and of Comparative Example sbowed a direct contact between the cores oE the optical fibers, the multiple fibers of Examples 1 and 2 were superior to that of Comparative Example in the sharpness of transmitted image when used as image-guides due to the thinness of the support layers.
The present invention relates to a method for producing an optical multiple fiber (hereinafter referred to as "multiple fiber") having a construction that a multiplicity of silica glass optical fibers are fused together with each other, and more particularl~ to a method for producing a multiple ~iber, each constituent optical ~iber of which consists of a core of pure silica glass and a cladding layer thereon made of a silica glass containing a dopant and having a lower refractive index than pure silica glass.
The above-mentioned multiple fiber which consists of optical ibers each having a core of pure silica glass retains desirable properties such as excellent heat resistance and radiation resistance inherent in pure silica glass, and is useful as an image-guide for monitoring the inside of a high temperature furnace, a nuclear reactor 9 and the like.
It is known that addition of a dopant to pure silica glass results in a sharp decrease of softening or deformation point. Thus, whereas the softening or deformation point of pure silica glass is as high as at least about 1,800C., that of a silica glass containing a sufficient amount of a dopant to-serve as a cladding layer i5 not more than 1,500C. or in some cases, not more than 1,000C., though it varies depending on the kind and amount of the dopant. Moreover, there also is a large difference in deformation resistance in softened state between pure silica glass and a dopant-containing silica glass. The dopant-containing silica glass has a very low deformation resistance as compared with pure silica glass.
Çenerally, a multiple fiber of silica glass is produced by bundling a multiplicity of optical fiber preforms or those obtained by drawing the preform to reduce it in diameter (the abo~e-mentioned optical fiber preform and those obtained b~ drawing the preform to reduce it in diameter are included in the scope o~ "preform" intended in the present inveniton) and drawing the resulting bundle _ 3 - ~Z~6~5 at a high temperature. When the core of each preform is made of pure silica glass and the cladding layer thereon is made of a silica glass containing a dopant, the cladding layer begins to be fluidized and deformed before the core is softened and deformed in the drawing step, and the cladding material tends to separate from the core and flow into portions of low flow resistance, which results in the formation of a defective multiple fiber wherein the cores of adjacent optical fibers are brought abnormally near to each other or into direct contact with each other in some places. This pro~lem i5 apt to occur when the average thickness of cladding layers after drawing is small. Such a multiple fiber, of course, is deficient in image-transmitting capacity.
It is an object of the present invention to provide a method for producing a multiple fiber having an excellent image-transmitting capacity in which the cladding layer of each optical fiber has a sufficient thickness to fulfill the function as a cladding layer.
This and other objects of the present invention will become apparent from the description hereinafter.
SUMMARY OF THE INVENTION
The present invention provides a method for producing a multiple fiber wherein a multiplicity of optical fibers are fused together with each other and each optical fiber comprises a core made of pure silica glass and a cladding layer made of a silica glass containing a dopant and disposed on the core, by bundling a multiplicity of preforms corresponding to the optical fibers and drawing the bundle at a high temperature, the method being improved in that preforms having a three-layer construction wherein a support layer made of a silica glass having a drawable temperature of at least 19 800C. is further disposed on the cladding layer are used as said optical fiber preforms, and the bundle of the preforms is drawn to give a multiple fiber wherein the support layer of each optical fiber has a thickness of ~Z~16~5S
0.01 to 1 ~m.
In the present invention, the drawable temperature of the support layer means the temperature of the constituent material thereoE that permits drawing by a conventional method. More particularly, it is defined as follows: A pipe made of the same material as that to be used for forming the support layer and having an inner diameter of 23 mm. and an outer diameter of 26 mm. is drawn to reduce the pipe in diameter, giving a pipe having an inner diameter of 2.3 mm. and an outer diameter of 2.6 mm. The drawable temperature means the lowes-t temperature that permits to take up the pipe of the reduced diameter at a rate of ~.5 m./min. with a drawing tension of not more than 500 g.
DETAILED DESCRIPTION
.. . . _ In the present invention~ the multiple fiber is produced by bundling a multiplicity of preforms having the three-layer construction corresponding to optical fibers having the three-layer construction and drawing the bundle. The above-mentioned support layer of high-softening silica glass located on the outside of the cladding layer of each preform helps prevent an excessive fluidization of the cladding layer during drawing to thereby eliminate the problem that the cores of some adjacent optical fibers come into direct contact with each other.
The silica glass as the constituent material of the support layer may be any of natural silica glasses and synthetic silica glasses only if its drawable temperature is at least 1,800C. Preferred is a silica glass having a drawable temperature of at least 1,850C., particularly at least l,900C. Such a high-softening silica glass has a sufficient deformation resistance in softened state which is comparable to that of pure silica glass.
If the support layer of each optical fiber is too small in thickness, it does not provide a sufficient - 5 ~ 6755 property to prevent the excessive fluidization of the cladding layer. Therefore, in terms of "the thickness of the support layer" as defined hereinafter, it is preferable that the support layer has a thickness of at least 0.01 ~m., especially at least 0.1 ~m.
On the other hand, the research undertaken by the present inventors has shown tha-t the light incident on the support layers of the optical fibers included in a multiple fiber during the transmission of an image with the multiple fiber exerts the bad influence of blurring the transmitted image, that is to say, the support layer functions as a path of stray light. The degree of such bad influence is much higher with an increasing thickness of the support layer. Therefore, it is preferable that the thickness of the support layer of each optical fiber is not more than 1 ~m., particularly not more than 0.5 ~m.
By ensuring such a small thickness for the support layer of each optical fiber, the degree of the bad influence due to the stray light can be reduced.
Definition of the thickness of the support layer:
In most of the optical fibers in a multiple fiber produced by bundling and drawing a multiplicity of preforms having the three-layer construction, the cladding layer and the support layer are deformed so that their outer shapes are hexagonal in cross section, with the support layers of adjacent optical fibers being fused together with each other. Therefore, the thickness of the support layer for single optical fiber is defined to be one-second of the total thickness of two fused support layers between two adjacent optica~ fibers.
The multiple fiber wherein each support layer of the optical fibers contained ther~in has the above-mentioned thickness can be easily produced by taking into consideration the thickness of the support layer of optical fiber preforms used and the drawing ratio. The drawing temperature is usually from 1,800 to 2,200C., preEerably from 19900 to 29100C. The outer diameter of each optical fiber included in the final multiple fiber (the distance between the diametrically opposite two sides of the support layer having the above-mentioned hexagonal outer shape) is usually from 10 to 50 ~m.
The effect oE the support layer is especially pronounced when the multiple fiber produced by the method of the present invention has an outer diameter of 0.5 to 3 mm. (when the skin layer described hereinafter is present, the outer diameter including the skin layer) and contains 1,000 to 30,000 optical ~ibers.
In the practice of the presen-t invention, a bundle of preforms may be directly drawn but it is more advantageous to insert preforms into a silica glass tube made of synthetic or natural silica glass in an orderly arrangement and draw the bundle of the preforms together with the silica glass tube, the latter method ensuring the production of a multiple fiber having a more uniform outer diameter. In this case, the resulting multiple fiber has a silica glass skin layer derived from the silica glass tube as an outermost layer.
The method of the present invention is explained by means of the following Examples. These Examples are intended to illustrate the invention and not be construed to limit the scope of the invention. It is understood that various changes and modifications may be made in the invention without departing from the spirit and scope thereof.
Examples 1 and 2 and Comparative Example 8,000 three-la~er preforms having clean surfaces and each consisting of a core made of pure silica glass and having an outer diameter of 300 ~m., a cladding layer disposed on the core and made of a silica glass doped with B2O3 and having a thickness of 70 ~m., and a support layer disposed on the cladding layer and made of a natural silica (drawable -temperature: 1,900C.) and having a thickness of 15 ~m. were bundled and encased in a silica glass pipe. While the silica glass pipe was evacuated from the upper end thereof, the pipe was heated at the :~Z&'~i~S~
lower end at a temperature of 2,000C. and drawn from the lower end to give a multiple fiber made up of 8,000 optical fibers each having a support layer of 0.4 ~m. in thickness (Example 1). Microscopic examination of the end surface of the obtained multiple fiber revealed no direct contact between the cores of the optical fibers.
A multiple fiber wherein the support layer of each optical fiber had a thickness of 0.1 ~m. (Example 2) and another multiple fiher wherein the support layer of each optical fiber had a thickness of 2 ~m. tComparative Example) were also produced by changing only the drawing ratio in the procedures of Example 1. While none of the multiple fibers of Examples 1 and 2 and of Comparative Example sbowed a direct contact between the cores oE the optical fibers, the multiple fibers of Examples 1 and 2 were superior to that of Comparative Example in the sharpness of transmitted image when used as image-guides due to the thinness of the support layers.
Claims (2)
1. In a method for producing an optical multiple fiber wherein a multiplicity of optical fibers are fused together with each other and each optical fiber comprises a core made of pure silica glass and a cladding layer made of a silica glass containing a dopant and disposed on the core, by bundling a multiplicity of preforms corresponding to the optical fibers and drawing the bundle at a high temperature, an improvement which comprises using, as said optical fiber preforms, preforms having a three-layer construction wherein a support layer made of a silica glass having a drawable temperature of at least 1,800°C. is further disposed on the cladding layer, and drawing the bundle of the preforms to give a multiple fiber wherein the support layer of each optical fiber has a thickness of 0.01 to 1 µm.
2. The method of Claim 1, wherein the drawable temperature of the silica glass consitituting the support layer is at least 1,850°C., the thickness of the support layer of each optical fiber included in the obtained multiple fiber is 0.1 to 0.5 µm., the outer diameter of the multiple fiber is 0.5 to 3 mm. and the number of the optical fibers included therein is 1,000 to 30,000.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000437246A CA1206755A (en) | 1983-09-21 | 1983-09-21 | Method for producing optical multiple fiber |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000437246A CA1206755A (en) | 1983-09-21 | 1983-09-21 | Method for producing optical multiple fiber |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1206755A true CA1206755A (en) | 1986-07-02 |
Family
ID=4126133
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000437246A Expired CA1206755A (en) | 1983-09-21 | 1983-09-21 | Method for producing optical multiple fiber |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1206755A (en) |
-
1983
- 1983-09-21 CA CA000437246A patent/CA1206755A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry | ||
| MKEX | Expiry |
Effective date: 20030921 |