JPS60221705A - Manufacture of image guide of double-layer structure - Google Patents

Abstract

PURPOSE:To obtain the flexible image guide with a small external diameter by removing a port layer from an optical fiber base material of three-layer structure obtained by a rod-in tube method and forming two-layer structure, and forming the quartz glass image guide of two-layer structure by using said two- layer structure. CONSTITUTION:A core, clad, and support are laminated concentrically by the rod-in tube method successively from inside to manufacture the base material. Then, the supporting layer is removed and the resulting material is drawn to form a preform of two-layer structure consisting of the core and clad. Then numbers of preforms are bundles and drawn. The supporting layer is removed by using fluoric acid.

Description

[Detailed Description of the Invention] In more detail, the support layer is removed from the Hikari 7 IPA base material, which has a three-layer structure produced by the four-in-tube method, to obtain a two-layer structure, and this is used. The p-tud-in-tube method, which is one of the methods for manufacturing an optical fiber base material, is a method for manufacturing a two-layer structure quartz glass image guide. /4 and B? This method involves passing a mixed gas of 3 and 02 to form a fluorine-doped clad on the inner surface of the pipe, and then inserting a quartz glass rod into the pipe and collapsing it.The quartz glass rod (core)
The only optical fiber base material that can be obtained is a three-layer optical fiber base material: fluorine-doped quartz glass (cladding) and quartz glass pipe (support).

In an optical fiber manufactured from a three-layer base material obtained by such a rod-in-tube method, the supports present in the outermost layer are not the same in use. However, in image guides manufactured by fusing multiple optical fibers, the material of the support is almost the same as that of the core, so the support becomes an optical transmission path just like the core, resulting in stray light that is transmitted. The clarity of the image decreases. Furthermore, the presence of the support increases the outer diameter of the image guide accordingly, reducing its flexibility.

The present inventors have conducted intensive research to develop a method for manufacturing a two-layered image guide from a three-layered optical fiber base material obtained by the Rondo-in-tube method. When manufacturing an image guide using a base material with a two-layer structure by dissolving it with hydrofluoric acid or removing it by fire polishing, it is important to note that the image guide can be replaced with a two-layer structure without a support. The present invention has been completed.

In the present invention, in order to remove the support using the 7-year boring method, 02-H! A method is adopted in which the support layer is scattered under the high heat of the flame.The temperature of the sprayed flame is approximately 2000-2200°a, preferably 2050-2150°a.The time required for removal depends on the material and thickness of the support. The removal of the support can also be carried out using hetamine, which usually takes 4 to 5 hours, although it varies greatly depending on the flame temperature and other factors. When using hydrofluoric acid, a method is generally adopted in which the outermost support layer is dissolved and removed by immersing the preform in a hydrofluoric acid solution filled in an acrylic container for an appropriate time.The concentration of the hydrofluoric acid used is It is preferably 10 to 30%, and the immersion time is 1 to 10 hours, and the temperature is 10 to 40°C, but is not particularly limited to a narrow range.

A two-layer preform for manufacturing an image guide is produced from the two-layer optical fiber base material thus obtained, and a large number of preforms, for example 5,000 to 50.
There are no particular limitations on the manufacturing method of the 0 preform, in which a two-layer structure image guide can be changed by bundling 000 pieces and drawing at about 1900 to 2100° a, and the method of drawing the preform on the east side, and conventionally known methods can be adopted. . Alternatively, a bundle of preforms may be wire-drawn after only the -H cladding is heat-fused to each other.

The quartz glass image guide having a two-layer structure obtained by the manufacturing method of the present invention has no support, so it does not generate stray light, and has a small outer diameter and is highly flexible.

Next, the manufacturing method of the present invention will be explained based on Examples, but the present invention is not limited to these Examples.

Example 1 [Preparation of a base material with a five-layer structure using the p-tud-in-tube method] A quartz glass pipe with an inner diameter of 23 mm and an outer diameter of 26 mm, whose surface was cleaned, was moved back and forth at a speed of 2 mm/sec for 300 seconds per round trip. , 1600~18 with an oxyhydrogen burner from the outside.
Heated to 00°0. 8 in this heated pipe
Mixed Gabe Sin of 1074, BIF3 and oxygen! 4:B
73:07l=1:1.3:S, O, molar ratio) was introduced for 300 minutes at a flow rate of 7oo/min to form 5102 soot doped with fluorine and boron on the inner surface of the pipe, and then 1600 to 180rJoO The soot was vitrified to form a cladding.

Next, a pure silica glass rod with an outer diameter of 12 mm, which will serve as the core, was inserted into Hype and heated to 2050 to 2150°0 to collapse, producing an optical fiber base material consisting of three layers: support, cladding, and core. The base material was core outer diameter 21mm, cladding thickness 3-5mm.
The support thickness was 7.5'mm.

[Removal of support by fire polishing method] 7 When removing the support layer by fire polishing method,
Set the preform on a glass lathe and turn it at a speed of 10 to 60 minutes per minute.
rpm and heated to 2000-2300°0 with an oxyhydrogen burner moving at a speed of 5-50 mm/win to evaporate and remove the outermost layer of quartz glass.

[Manufacture of two-layer structure image guide] From the obtained two-layer structure base material, a core diameter of 240
An image guide precursor fiber with a thickness of 60 μm and a cladding thickness of 60 μm was fabricated.

Next, 10,000 of these image guide precursor fibers were arranged and filled in a pure silica glass skin pipe with a length of 320 mm, an outer diameter of 39 mm, and an inner diameter of 38 mm without any gaps.
Tummy pipes were then connected to both ends of the skin pipe to create a bundle assembly. This assembly was set vertically in a high-temperature drawing device, the lower end was sealed with a silicone rubber stopper, and the upper end was connected to a vacuum pump to reduce the pressure inside the assembly to 0.2 atmospheres. The electric furnace was then heated to 1450° C., the assembly was lowered at a rate of 5 mm/min, and once all the bundle portions had passed through the heating zone, the assembly was raised at the same temperature. Perform this operation 3
When the bundle assembly was observed after repeating the process several times, it was found that all the spaces between the precursor fibers in the bundle assembly had disappeared, resulting in a perfectly cylindrical precursor fiber bundle without any bubbles. Set it in a drawing device and draw it under the conditions of a furnace temperature of about 2000%, a precursor fiber bundle feed temperature of 2 mJlnin s, and a σ1 scraping speed of 1.8 m/win of the image guide.
A two-layer image guide with an outer diameter of 1.25 m111 was manufactured. The core outer diameter was 8 μm and the core occupancy was 44%.

Example 2 The three-layered optical fiber base material prepared in Example 1 was immersed in a 30-50% hydrofluoric acid solution filled in an acrylic container for more than ten hours to dissolve and remove the outermost support layer◇ A two-layer image guide was manufactured in the same manner as in Example 1 from the obtained two-layer base material.

The obtained image guide had an outer diameter of 1.25 mm, 5 cores with an outer diameter of 8 μm, and 1 core occupancy rate of 44%.

Comparative Example A three-layer image guide for comparison with the same number of cores and core outer diameter as the image guide obtained in Example 1 was manufactured by a conventional method from the three-layer optical fiber base material produced in Example 1. did. The obtained image guide has an outer diameter of 1.
It was 40 mm and had a core occupation rate of 36%.

Next, the clarity and flexibility of the two-layer structure image guide and the three-layer structure image guide manufactured in Example 1 and Comparative Example were examined.

(Resolution test) An eyepiece lens is placed at one end of a 5 m long image guide, and an objective lens with a viewing angle of 20 degrees (focal length 4 mm) is placed at the other end. A, T Test chart A is placed and a color viewer (DNPmolel-V
, (lamp used I'l+-100WX4)) were arranged and lines that could be visually identified were examined.

As a result, the resolution of the image guide of the present invention obtained in Examples 1 and 2 was 600 lines/560 m, respectively.
m55so lines/560 mm, but the resolution of the comparative example image guide was only 400 lines/360 mm.

(Flexibility) The image guides obtained in Example 1 and Comparative Example were bent into a loop shape, and the diameter of the loop was gradually reduced.
We investigated the diameter of the loop when the image guide broke.◎ As a result, the image guide obtained in the comparative example was 30 mm.
However, the image guide obtained in Example 1 did not break until it reached a diameter of 25 mm.

Patent applicant: Dainichi Nippon Electric Cable Co., Ltd.

Claims (1)

[Claims] 1. Produced using the rod-in-tube method. A base material is prepared in which the core, cladding, and support are laminated concentrically from the inside. Then, the support layer is removed, and this is made into a wire! A preform 2 with a two-layer structure consisting of a core and a cladding is prepared by stirring, and a large number of these preforms are bundled together. A method for manufacturing a quartz glass image guide with a two-layer structure characterized by a single layer. 2. The manufacturing method according to claim 1, wherein the support layer is removed using hydrofluoric acid. 3. Manufacturing method 0 according to claim 1, in which the support layer is removed by a 7-eye boring method.