JPS593030A - Manufacture of base material for infrared optical fiber - Google Patents

Abstract

PURPOSE:To manufacture a base material for an infrared optical fiber having a core-clad waveguide structure, by erecting a fine wire at the center of a casting mold, pouring a melt for a clad, pulling out the wire, and filling molten glass for a clad into the resulting small cavity. CONSTITUTION:A casting mold is composed of an outer frame 1 divided into a plurality of parts 2, 2', 2'' and a ring 3 for clamping the frame 1. A fine metallic wire 6 of platinum or the like is erected at the center of the inner hollow 5 of the mold with a bottom cover 4 in-between, and molten glass for a clad is poured into the hollow 5. The wire 6 is heated beforehand by directly supplying an electric current or by other method, and it is pulled out immediately after pouring the molten glass. Molten glass for a core is filled into the resulting small cavity and annealed so as to prevent the production of stress. After finishing the molding, the parts 2, 2', 2'' are detached to obtain a base material for an infrared optical fiber. By this method, a fluoride glass base material for an optical fiber capable of transmitting infrared rays having about 2-6mum wavelengths can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a base material for a heptadide glass optical fiber capable of transmitting infrared rays in the 2-6 μm band.

Conventional optical fiber base materials mainly consist of silicon dioxide (Sin) glass, but this glass material
It has infrared absorption due to vibration of i-0 bond. For this reason, the low-loss wavelength range that exists between Rayleigh scattering loss and infrared absorption loss is from the visible range to the near-infrared range (wavelengths from 0.6 to
1.7 μm), and it was not possible to obtain a low-loss optical fiber in a wavelength region longer than that.

On the other hand, according to existing technical knowledge, Rayleigh scattering decreases in inverse proportion to the fourth power of the wavelength. If it is possible to form a preform (reform), it is possible to further reduce loss by drawing such a preform to create an optical fiber.On the other hand, long-distance transmission must be performed using a single mode optical fiber. At that time, if infrared light with a wavelength longer than 2 μm is to be transmitted, the core diameter of the fluoride-based single-mode optical fiber should be set to at least twice the core diameter of the conventional silica-based single-mode optical fiber. This makes coupling between the fibers extremely easy.

Therefore, there is a need for a method for forming a single mode optical fiber preform that is optimal for infrared transmitting materials.

Optical fibers for communications have a waveguide structure in which a core with a high refractive index is covered with a cladding with a lower refractive index, and currently, optical fibers with a waveguide structure for infrared transmission are known. As for cladding and A by hgat
Combination with core by g(07Br), T/(BrI
) There are polycrystalline optical fibers made by combining a core with a plastic cladding, etc. However, in the case of these polycrystalline optical fibers, it is difficult to create ultra-low loss optical fibers due to the influence of grain boundary scattering loss. Essentially impossible. Also O,
at4 liquid core and 810. Optical fibers with cladding are also known, but there are major problems in producing long optical fibers and connecting them.

In addition, heptamide glass is attracting attention as a material that eliminates the drawbacks of the various fiber materials mentioned above and has a high possibility of realizing ultra-low loss optical fibers in the infrared wavelength range of 2 to 6 μm. Regarding the manufacturing method of optical fiber preforms, there is a slight introduction to the production of multimode optical fibers (S., Mitaohi, e.
tal: Jpn, J, Appl, Phys・1 (198
1), LaB5. S, Mitaohi, etal: El
eotron, Letters 17 (1981), 59
1) There is no particular introduction to the manufacturing method of single mode optical fiber. In addition, compared to silicon dioxide glass, fluoride glass generally exhibits a rapid viscosity change near the glass deformation temperature. It is clear that it cannot be applied as is.

The present invention has been made in view of the above-mentioned current situation, and its purpose is to solve the shortcomings of the prior art, to create a fluoride glass that can transmit infrared rays with a wavelength of 2 to 6 μm, and has an extremely low loss. An object of the present invention is to provide a method for manufacturing an infrared fiber base material made of.

In order to achieve such an object, in the method for manufacturing an infrared optical fiber preform according to the present invention, a mold having a vertical crack structure that can be divided into a plurality of pieces has a cylindrical hollow part inside the mold, and the cylindrical hollow part is formed inside the mold. A thin wire is positioned in the center of the hollow part of the shape, and the molten glass melt for the cladding is poured around the thin wire.The thin hollow part created by pulling out this thin wire is filled with the glass melt for the core to guide the Q core cladding. The present invention is characterized by obtaining a preform for an infrared optical fiber having a wave structure.

The method for manufacturing the base material according to the present invention basically involves placing a thin metal wire in the center of the mold, and
Preheat to around temperature, pour the cladding melt here,
Pull out the thin metal wire immediately.

At this time, it is effective to draw out the thin metal wire by direct heating by passing an electric current through it. Next, a core glass melt is poured into the pores formed by drawing out the thin wire and annealed, thereby obtaining a base material for an infrared optical fiber having a core clad waveguide groove structure from the mold.

The mold used in the present invention will be explained with reference to the drawings. Figure 1 shows a side view of the mold, Figure 2 shows the x in Figure 1.
A cross-sectional view of the mold along the -x' line is shown.

The outer frame 1 of the mold is an outer frame divided body 2゜2' shown in Fig. 2.
, 2' (eight in the example in Figure 2)
It has a vertical cracking structure that can be divided into two outer frame divided bodies 2 and 2'.
, ring 8 tightening 2', outer frame divided body 2'2'
, ! It consists of a bottom cover 4 that accommodates the lower end of the thin wire 6 and holds the thin wire 6 vertically, and the outer frame divided body 2.2' is
, 2' are tightened to form a hollow portion 5. In addition to the eight divided bodies shown in FIG. 2, the outer frame divided bodies may be two or four or more divided bodies as appropriate. These divided bodies 2, 2', 2 forming the outer frame 1
' can be made of metal, for example brass, or non-metallic, for example carbon electrode, and must have corrosion resistance against fluoride glass and good mold releasability.

A case will be described in which the present invention is implemented using the mold shown in FIGS. 1 and 2.

A gold wire or platinum wire is vertically placed in the center of the cylindrical hollow part of the brass mold shown in FIGS. 1 and 2 and preheated to around the glass transition temperature. At the same time, in a gold crucible, we produced 7-hide glass for the core and 7-hide glass for the cladding.
Melting tsulfide glass. First, the cladding melt is cast between the hollow part of the brass mold and the platinum wire in the center, and the gold wire or platinum wire placed in the center is quickly pulled out downward. At this time, it is extremely effective to apply an electric current in advance to heat the gold wire or platinum wire to prevent the cladding melt from solidifying and adhering to the gold wire.

While drawing the platinum wire, a core melt is poured from above to obtain a base material having a core clad waveguide structure having a thin core portion. This is annealed to prevent the generation of stress, and after the molding is completed, the outer frame divisions 2, 2', and 2' are removed to form a light beam consisting of a core glass part and a cladding glass part as shown in Figure C4B. Obtain a base material for fiber.

Next, the present invention will be explained with reference to examples thereof, but the present invention is not limited thereto.
%Le%BaF.

(18,759)-8,8 mol% GdF, <2.049
)-6 mol% JiJF.

10y of 11 (4F-HF) was weighed and mixed into a cladding mixture consisting of C0,9859), and the mixture was ground and mixed in a mortar.

This was introduced into a metal crucible, and heated and melted at 400°C for 80 minutes using an electric furnace. In parallel with this, the composition is 6
1.7%/l/% ZrF, (25 g) -132-4 mol% BaF.

(18,8 g)-8,9 mol% GdF, (2 g)-2 mol% AIF8 (o, s2 g)
09 NH, F and HF were weighed and mixed and ground and mixed in a mortar.

This was introduced into a metal crucible and heated at 400°C for 80 minutes using an electric furnace to completely fluorinate the raw material, and then
The mixture was heated and melted at 00°C for 2 hours.

2.5 in the center of the mold as shown in Figures 1 and 2.
A gold wire of φ was placed vertically and heated in advance at 800°C, into which a glass melt for cladding was first poured. Immediately thereafter, the core melt was cast while quickly pulling out the gold wire, and the central part was filled with the glass melt for the core. At this time, it was found that if the gold wire was rotated at high speed, it could be easily pulled out.

This is followed by an 80 hour annealing followed by a 24 hour annealing.
It took some time to return to room temperature. As a result, the outer diameter of the clad glass was 9 mm, the core diameter was Q, 5 mm. A base material having a length of tmφ of 120 mm was obtained.

The relative refractive index difference between the core and cladding of the optical fiber obtained by drawing this base material was 0.38%, and the cladding-core diameter ratio was 8.6. material was obtained.

Example 2 Composition is 59.2% ZrF4(259)-81,
0 mol% BaF.

(18,759)-8,8 mol%GdF (LO49)
-6 mol% A! 109 NH and F-HF were weighed and mixed into a cladding mixture consisting of F8 (0,9859), and the mixture was ground and mixed in a mortar. This was introduced into a metal crucible and heated at 400°C for 80 minutes using an electric furnace to completely fluorinate the raw material, and then heated at 900°C for 80 minutes to melt it. In parallel with this, the composition is 60.48% ZrF
, (2f+9)-81,68 mol% BaF (IL8g
)-8,8+ %le%GdF8(29)-4mol%A
4F, 10g in a core mixture consisting of (0,6449)
NH4F-HF was weighed, ground and mixed in a mortar, introduced into a metal crucible, and heated at 400°C for 80°C using an electric furnace.
Complete fluorination of the medium material is achieved by heating for 900 min.
The mixture was heated and melted at °C for 2 hours.

As shown in Figures 1 and 2, 1.
A platinum wire with a diameter of 2 mm was erected vertically and was preheated at 800°C, into which a glass melt for cladding was first poured. At this time, an electric current was applied to the platinum wire to heat it, and the core melt was cast while being pulled out, so that the center portion was filled with the core glass melt. Thereafter, it was annealed for 30 hours and returned to room temperature for 24 hours.

As a result, a base material was obtained in which the outer diameter of the clad glass was 9 mm, the core diameter was 1.2 mm, and the length was 120 mm.

The core diameter of the optical fiber obtained by drawing this base material is 20μ
m, the cladding diameter is 150 μm, and the relative refractive index difference is 0.17.
%, and a fluoride optical fiber base material was obtained which had a single mode in the 25 μm band.

Application Example 1 The base materials obtained in Example 1 and Example 2 were coated with Teflon FEP coated tubes, and rod drawing was performed using normal zone melting to obtain an outer diameter as shown in Figures 8 and 4. 200 μm 1 cladding diameter 150 μm, core diameter 4
2 μ course, multimode optical fiber with relative refractive index difference of 0.88%, outer diameter 200 μM, cladding diameter 150 μm 1 core diameter 2
A single mode optical fiber (cutoff wavelength 2.2 μm) with a relative refractive index difference of 0 μm1 of 0.17% was obtained. All of these 7-eye lights have a wavelength band of 2.6 μm, and 1. O
It was an optical fiber for infrared transmission with a low loss window of dB^ or less. This indicates that the interface between the core clad and the core clad is optically smoothly fused, and the scattering loss caused by the irregularity of the far clad interface, which is a problem, is reduced, resulting in a low-loss optical fiber.

By using the manufacturing method of the present invention, the core diameter can be freely controlled by changing the diameter of the gold wire or platinum wire erected at the center. A compound optical fiber has been fabricated.

As explained above, according to the method for manufacturing an infrared optical fiber preform of the present invention, a waveguide structure can be formed with the core-clad interface in an optically smooth state, and the relative refractive index difference, cladding diameter/ The core diameter ratio can also be set within any range. Therefore, it is extremely easy to manufacture base materials of heptadide optical fibers for multi-mode and single-mode infrared transmission with a step-type refractive index distribution, and as a result, they can be used for temperature sensors, image transmission, etc. using infrared rays. However, it has the advantage that it is easy to manufacture a single mode optical fiber with a large core diameter, and it can be applied to long-distance transmission where fibers can be easily coupled.

[Brief explanation of drawings]

#! IFIfJ is a side view showing a specific example of a mold used in carrying out the present invention, FIG. 2 is a sectional view taken along the line x-x' in FIG. 1, and FIGS. FIG. 1 is a cross-sectional view showing an example of a base material obtained by the method and a diagram showing a refractive index distribution. l... Outer frame, 2, 2', 2'... Outer frame division body, 8... Ring, 4... Bottom cover, 5... Hollow part, 6
Kawasaki wire or gold wire, 1.10... Preform cross section, 8.11... Position on preform corresponding to refractive index distribution, 9... Multimode fiber obtained in Example 1 Refractive index distribution, 12...Refractive index distribution of the single mode fiber obtained in Example 2. Figure 1 Figure 3 Figure 4

Claims (1)

[Claims] 1. A mold with a vertical crack structure that can be divided into multiple pieces has a cylindrical hollow part inside it, a thin wire is placed in the center of this cylindrical hollow part, and the molten glass melt for cladding is poured around the thin wire. An infrared optical fiber preform, characterized in that a thin hollow formed by drawing out this thin wire is filled with core glass melt to obtain an infrared optical fiber preform having a core-clad waveguide structure. manufacturing method.