JPH0310281B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to an image fiber and a method for manufacturing the same. <Prior Art> Conventionally, it has been difficult to obtain a conduit type image fiber in which pixel fibers are fused together, especially a silica-based glass image fiber, in which the roundness of the core or the distance between the cores is maintained uniform. If the core shape is deformed and the distance between the cores is not constant, uneven brightness or color tends to occur in the transmitted image, making it impossible to obtain a high-quality transmitted image. In general, image fibers consist of a core with a higher refractive index and a cladding surrounding it, which are bundled together in a large number and housed in a glass tube. (referred to as collapse) to form a preform, which is further heated and melted and drawn to form a conduit-type image fiber. In this case, if the viscosity of the core material at the temperature of the molten pixel is lower than that of the cladding material, the shape of the core 1 will be deformed and will no longer be a perfect circle, as shown in Figure 4a, and conversely, the viscosity of the cladding material will decrease. If it is low, as shown in Figure 4b, the spacing between the cores will be
There was a problem that t ₁ , t _{2 ,} etc. were disturbed. The present invention has been made in view of the deficiencies of the prior art, and it is an object of the present invention to provide an image fiber that does not cause deformation in pixel shape or disorder in pixel arrangement, and a method for manufacturing the same. <Means for Solving the Problems> The structure of the image fiber according to the present invention that achieves the above object includes a core portion of high refractive index silica-based glass made by adding additives to silica, and a low refractive index surrounding the core portion. A large number of pixels consisting of a cladding part of silica glass, and a material filling between these pixels, whose refractive index is lower than the refractive index of the cladding part, and whose viscosity at the coalescence temperature of the many pixels is higher than the viscosity of the core part and the cladding part. It is characterized by consisting of a glass layer with a low fluorine content. Such an image fiber of the present invention includes, for example,
A core portion of high refractive index glass, a cladding portion of low refractive index glass surrounding the core portion, and a refractive index provided surrounding the outer periphery of the cladding portion are lower than the refractive index of the cladding portion, and the softening point is lower than that of the cladding portion. A step of bundling a large number of fiber wires made of a jacket portion of glass whose softening points are lower than the softening points of the core and cladding portions in parallel, a step of inserting the bundle of fiber wires into a cylindrical glass tube, a step of inserting the fiber wire bundle into a cylindrical glass tube, and a step of inserting the fiber bundle into a cylindrical glass tube. It is manufactured through a process of heating together with a wire bundle and collapsing to form a multifiber preform, and a process of heating and melting the multifiber preform and drawing it to form an image fiber. <Example> An example of the image fiber according to the present invention is as follows:
This will be explained with reference to the drawings. To manufacture the image fiber according to this example, first, a glass rod for the core made of GeO ₂ -doped SiO ₂ is formed by a VAD method or the like. Next, the core glass rod is placed coaxially within a pure quartz tube for the cladding, and heated and melted while rotating around the quartz tube, collapsing to form a rod-shaped body in which the core and cladding are integrated. A deposited layer of F-doped SiO ₂ glass is formed on the outer periphery of the rod-shaped body according to the plasma outer dimensions. F addition
The deposited layer of SiO ₂ is further heated and melted to form a jacket layer of F-doped SiO ₂ glass on the core-clad rod to form a fiber preform. This preform is then heated and drawn to form a fiber having a wire diameter of 150 μm, for example. Next, the fiber strands are cut to a predetermined size, for example, about 20 cm, and arranged in parallel to form a bundle of fiber strands, which is stuffed into a quartz tube without disturbing the arrangement. Next, the quartz tube is held horizontally and rotated while heating its outer periphery and collapsing it to form a multifiber preform. The multifiber preform can then be hot drawn to form a conduit-shaped image fiber. In the image fiber according _to the present invention described _above , as shown in FIG _.
The jacket part 3 is made of F-doped _SiO2 , the core part 1 is made of high refractive index glass, the cladding part 2 is made of low refractive index glass, the jacket part 3 has a refractive index lower than that of the cladding part, and has a temperature lower than that of the molten amalgam of the pixel. The F-added glass layer has a lower viscosity than the core portion 1 and the cladding portion 2. In addition, clad part 2
As a guideline for the viscosity difference between the jacket portion 3 and the jacket portion 3, it is preferable that the temperature difference at the softening point (4.5×10 ⁷ poise) is 50° C. or more. Further, the reason why the refractive index of the jacket portion 3 is set to be lower than the refractive index of the cladding portion 2 is to prevent the degree of concentration of light in the core portion from deteriorating. If the refractive index of the jacket portion 3 is made higher than the refractive index of the cladding portion 2, light from the core portion will easily seep into the jacket portion, reducing the contrast of image transmission. FIG. 2 shows a cross-sectional structure of an image fiber obtained by the method of manufacturing an image fiber of the present invention.
As shown in FIG. 2, the feature of the image fiber of the present invention is that the shape of the core portion 1 of the pixel is a perfect circle and does not deform, and the distance t between pixels is constant. Also,
A partially enlarged view of the image fiber according to the invention shown in FIG. 2 is shown in FIG. As shown in FIG. 3, in the image fiber manufacturing process, when a large number of pixel fibers are inserted into a circular tube and the pixels are melted and fused together to form a conduit-shaped image fiber preform, the jacket temperature increases at the temperature of the molten fiber. Since the viscosity of part 3 is kept low compared to the viscosity of core part 1 and clad part 2,
It can be seen that the jacket part 3 flows easily and fills the gap between the highly viscous core and clad parts. Due to such a viscosity difference in the temperature of the molten material, the roundness of the core portion 1 is maintained and the pixel interval t is maintained constant. Since the image fiber described above is composed of silica glass pixels, it is possible to obtain a bright image with very little light transmission loss during image transmission. It also has excellent heat resistance and strength. Furthermore, since the cladding material is pure silica glass, it is relatively inexpensive and has good productivity. The concentration of fluorine added to the jacket portion 3 is preferably 1 to 5 wt%. When the amount exceeds about 5 wt%, SiF ₄ evaporates from the pixel surface when the pixels are fused together, making it easy to generate bubbles on the pixel surface and between the pixels.
Moreover, if it is less than 1wt%, there is almost no effect on manufacturing. Table 1 shows specific examples of desirable configurations of each part of the image fiber in the present invention.

[Table] Further, their desirable compositions and structural ratios (area ratio S) are shown in Table 2.

[Table] The area ratio between the core and the cladding depends on the refractive index difference (Δ ₁ ) between the core and the cladding and the pixel density (number of pixels per unit area). In addition, the jacket component may include other components that soften the glass, such as
_P2O5 , _{B2O3 , etc.} may be added. In this case, it is necessary that the refractive index of the jacket glass is lower than the refractive index value of the cladding part due to the addition. It is also possible to add a material that increases light absorption, such as a transition metal such as Fe or Cu, to the jacket 3 so that the jacket also has the function of absorbing stray light. In this case, the closer the refractive index of the jacket is to the refractive index of the cladding, the more effective the effect will be. Specific embodiments of the image fiber according to the present invention will be described below. A silica glass rod containing GeO ₂ (approximately 30 wt%) was synthesized by the VAD method, and this was drawn into a rod with an outer diameter of 10 mm. A quartz glass tube of equal length (outer diameter 20 mm, wall thickness 4.5 mm) is placed coaxially over this glass rod, placed in a glass lathe, and heated strongly with an H ₂ /O ₂ burner to make the rod and tube one piece. was made into Using plasma flame using CCl ₂ F ₂ , SiCl ₄ and O ₂ as raw materials, F-containing SiO ₂ was added to the outer periphery of this rod-shaped structure.
The glass layer was formed to a thickness of 10% of the outer diameter of the cladding. Here, the F concentration of the F-containing SiO ₂ glass is approximately 3wt.
%, the refractive index difference was approximately 0.8% lower than that of SiO ₂ . The fiber preform obtained above was heated in a drawing furnace at approximately 2000°C, and the outer diameter
A 150 μm fiber wire was drawn. These strands were packed in a quartz tube with an outer diameter of 30 mm and a wall thickness of 1.5 mm in a densely arranged parallel arrangement. This fiber bundle was heated and drawn at about 2000° C. together with a quartz tube to form an image fiber with an outer diameter of 2 mm. This image fiber is approximately
It had 30,000 cores, and its structure, as shown in FIG. 2, had constant pixel spacing, and the shape of the pixel core was a perfect circle without deformation. The image transmitted through the image fiber obtained through the above manufacturing process was free of color unevenness, brightness unevenness, and bleeding, and had good image quality. In the example described above, the fusion process of a large number of pixels was performed as a separate process before drawing the pixel bundle, but this step is omitted and the pixels are melted together when drawing the aligned pixel bundle. It may also be made into a melted amalgam. <Effects of the Invention> In the image fiber according to the present invention, the shape of the pixel core was a perfect circle without being deformed, and the intervals between the pixels were constant. Therefore, the image transmitted by the image fiber of the present invention was free from unevenness in brightness and color and was able to provide a good image. Further, according to the present invention, since the viscosity of the jacket part of the fiber wire at the melting and integration temperature of the pixels is lower than that of the core/cladding part, the true circle can be maintained without destroying the shape of the core. In addition, we were able to obtain an image fiber in which the core spacing was kept constant.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a fiber used in the image fiber of the present invention, FIG. 2 is a cross-sectional view of the image fiber according to the present invention, FIG. 3 is a partially enlarged view of the image fiber shown in FIG. Figures a and b are cross-sectional views of conventional image fibers. In the drawings, 1 is a core part, 2 is a clad part, and 3 is a jacket part.

Claims (1)

[Claims] 1. A large number of pixels consisting of a core portion of high refractive index silica-based glass made by adding additives to silica and a cladding portion of low refractive index silica glass surrounding the core portion;
The structure is characterized by comprising a fluorine-doped glass layer that fills the space between these pixels and has a refractive index lower than that of the cladding part and a viscosity at the temperature at which a large number of pixels are combined is lower than the viscosity of the core part and the cladding part. image fiber.