JPS6011239A - Manufacture of optical fluoride fiber - Google Patents

Abstract

PURPOSE:To manufacture an optical fluoride fiber with a very small loss by removing transition metals as impurities from starting materials for an optical fluoride fiber in a quartz pipe, melting the refined starting materials by heating, and carrying out drawing. CONSTITUTION:Starting materials for an optical fluoride fiber are refined. In case of a fluoride having <=1,300 deg.C b.p. under ordinary pressure, it is refined by sublimation under reduced pressure in a quartz pipe lined optionally with a platinum plate or a gold plate. In case of a fluoride having >=1,300 deg.C b.p. under ordinary pressure, it is put in said quartz pipe and heated to >=1,000 deg.C under reduced pressure to remove transition metals as impurities by sublimation. The refined starting materials are charged into crucibles 18, 19 from tanks 14 through weighing pipes 15 and a rotating stirring pipe 17. The crucibles 18, 19 are moved to an electric furnace 21 with a sliding plate 20, and the starting materials are melted by heating. This melt is cast in a casting mold to form a preform for an optical fiber, and the perform is drawn to obtain an optical fluoride fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing ultra-low loss optical fibers (fluoride optical fibers that are considered promising as materials).

Conventional optical fibers whose main constituent material is 5in2 have so far achieved a low loss value of 0.2 C1f3/Km, which is comparable to the theoretical limit. This low loss value is determined by the ultraviolet absorption edge, infrared absorption edge, and Rayleigh scattering loss, and these essential loss factors cannot be removed. Therefore, in order to realize an optical fiber with even lower loss, it was necessary to use a material that is transparent at long wavelengths and has lower Rayleigh scattering loss.

From this point of view, fluoride glass has attracted attention as a material that is transparent in the infrared region, and is expected to have a low loss value of 10 to 1 O-3 (iB/Km).

Conventional fluoride raw materials contain several ppm or more of connected metal ions such as ye, au, etc. Therefore, the effect of the blotting edge caused by these blotting around 1 μm appears at 2 to 8 μm, making it possible to significantly reduce loss. It was a hindrance.

Since fluoride raw materials generally die at a high temperature of around 1000° C. or higher, it has been extremely difficult to separate these raw materials and transition metal fluorides in a gas phase. Furthermore, there was no method for producing a fiber base material using these purified raw materials while avoiding contamination with impurities.

The present invention is characterized by removing transition metals from fluoride raw materials for fluoride optical fibers by sublimation purification, which has not been successful in the past, and then continuously weighing, mixing, and melting the metals in a purified atmosphere. The aim is to create ultra-low loss fluoride optical fibers.

The present invention will be described below with reference to Examples, but the present invention is not limited in any way by the Examples.

Figure 1 shows an example of a sublimation purification apparatus, where 1 indicates the raw material z rF.
,,2 is sublimation ZrF4.8 is electric furnace, scratch is ArN2 is K
OH dehydration pipe, 6 is liquid nitrogen trap, 7 is vacuum pump,
8 is a Teflon pipe, 9 is a three-way cock, and 10 is a quartz tube. Using this, sublimation purification of ZrF was carried out as follows.

Commercially available ZrF was placed in a sublimation purification apparatus as shown in FIG. 1, and purified by sublimation at 90° C. in a dry argon atmosphere of 1 to 3 mm Hg. Sublimation rate is 0.8 g/mi
n.

100 g of sublimation-purified ZrF was obtained from starting material 1501.

Example 2 As shown in Fig. 2, a sublimation purification apparatus (
11 is gold plate lining), 25g of AIF.

was introduced and purified by sublimation at 950° C. under a dry argon atmosphere of 1 to 8 mm Hg to obtain sublimated AlF3 of 7J9.

Example 8 For BaF, ・GdF3, the third plate plated with platinum was used.
In a sublimation purification apparatus M (12 is lined with platinum) as shown in the figure, the mixture was treated in a dry argon atmosphere of 1 to 8 mm l (g) at 1100'C for 5 hours, and the contained 78F8°0uF
M transfer metal impurities 18 such as 2+ NiF2 were removed by sublimation.

Example 4 NH,F-HF was heated for 200'CGC at 1 to 8 mm Hg using the sublimation purification apparatus shown in FIG.
200g NH,F-IF to 150# sublimated NH,
li'-HF was obtained.

Example 5 For SbF, the sublimation purification apparatus shown in Fig. 2 was used.
Heat to 300°C at 1-8% Hg and 200g of SbF.

125 g of sublimed 5bF8 was obtained from

Example 6 Among the raw materials obtained in Examples 1 to 5, NH, F −
) Since the boiling point of IF and 5bF8 is significantly different from that of transition metals such as FeF3.0uF2, it can be expected that the purification will be carried out satisfactorily.

Table 1 shows the melting points and boiling points of fluorides.

Table 1: Melting point and boiling point of fluoride (unit: 2°C) (Note) S is the sublimation point. Also, only NH4 and HF have a boiling point of 1 to 8.
mm Hg, and the others are '160 mm Hg.

10,000, BaF, lGdF3 have higher boiling points and sublimation points than transition metal fluorides, and therefore it was necessary to remove the transition metals by sublimation. Since AlF3 has a boiling point close to that of transition metal fluorides, it was necessary to carefully perform sublimation fractional distillation.

Since ZrF4 sublimates at a low temperature, it can be sufficiently separated from transition metals.

Regarding BaF@GtiF and ZrF4*AIF8, transition metal fluoride was extracted using a 12% HCt solution in order to examine the effect of sublimation. The ultraviolet spectrum of this extracted solution was measured, and by comparison with the stationary ultraviolet spectrum of FeF3, impurity-containing plates in each purified raw material were determined. For comparison, the measurement results for the starting material before purification are also shown in Table 2.

Table-2 Fe8+ concentration in fluoride (1) pm) ZrF,
In n5AIF8, the concentration of each kFf9'' was significantly reduced, indicating that the effect of sublimation purification was fully exhibited.

Embodiment 7 FIG. 4 shows a block diagram of a continuous glass melting apparatus used in the manufacturing method of the present invention, in which 14 is a raw material tank, ]5 is a scale lid tube, and 1
6 is a cock, 17 is a rotary stirrer tube, 18 is a metal crucible for cladding, 19 is a metal crucible for core Pi', 2o is a slide plate, 21 is an electric furnace, 22 is a quartz reaction tube, 28 is a rotary stirrer This is a tube drive motor. Using this, the following procedure was performed to produce an optical fiber preform.

First, the raw material tank 14 shown in FIG. 4 is filled with the refined raw materials of Examples 1 to 6, and the relationship between its weight and volume is determined in advance. According to the phase ratio shown in Table 8 for each raw material, while measuring the amount of movement of the raw material in the weighing tube 15, adjust the filling amount with the cock 6, and place the metal crucible 18.19.
Table 8 Composition of core and cladding (mol%) At this time, the cladding m1 was poured into the metal crucibles 18 and 19 while stirring through the rotary stirrer tube 17 driven by the drive motor 23. Inject the JJA material with the composition for the core. At this time, the raw material Zr
In order to completely fluorinate oxides such as ZrFa(OH) and ZrF2(OH)2 attached to the surface of F + BaF2+ GdF3*AjF8, a predetermined amount (10 to 15 g) of NH4F-HF is also added.

Next, by moving the slide plate 20, the gold crucible 18.1
9 was moved into an electric furnace 21, heated and melted for 2 hours, and the clad melt was cast into a preheated hollow cylindrical brass mold, where it immediately solidified and the center of the insulator was poured. A base material (9 diameter x 100 fins) prepared by casting core melt into the center of the resulting hollow glass tube was coated with a Teflon FEP tube, and a 185 m optical fiber was obtained by band melting.

The transmission loss spectrum of the optical fiber thus obtained and the results of impurity factor analysis are shown in FIG. The scattering loss curve of the fiber shown by the two-dot chain line in FIG.
, e3 μm, and was approximated as being proportional to the reciprocal of the square of the wavelength. For comparison, a transmission loss curve A of a fluoride optical fiber using a purified raw material and a transmission loss curve B of an optical fiber using an unrefined raw material are also shown.

Due to sublimation purification, the impurity peak in the 1 μm band is 580
significantly decreased from dB/Km to 150 dB/Km,
In particular, the content value of Fe B+ decreased significantly, so that the lowest loss value was 8.5 aB,/xm at 2.12 μm.

Table 4 shows the estimated impurity-containing shellfish in the optical fiber when using unrefined raw materials and when using purified raw materials.

Table-4 Estimated impurity content m (ppm) According to this, the content of Fe2+ decreases to nearly -0 You can see that it's a little done.

Even when 5bF8 was used instead of NH,F-HF, a similar low-loss optical fiber was obtained, demonstrating the effectiveness of purifying raw materials by n1 sublimation purification.

As explained above, in order to highly purify raw materials for fluoride optical fibers, as in the present invention, a sublimation purification method is applied according to the boiling point of each fluoride, and continuous weighing, mixing, and stirring are performed in a clean atmosphere. By doing so, it becomes possible to separate the transition metal impurities and the raw material, and as a result, the method for producing a fluoride optical fiber of the present invention can be said to be an extremely important technology for producing a low-loss optical fiber. .

In addition, this method is not only applicable to the production of fluoride optical fibers.
It has the advantage of being widely applicable to refining raw materials for optical glass.

[Brief explanation of drawings]

1st. Figures 8 through 8 are schematic diagrams of a sublimation purification apparatus used in an embodiment of the present invention, Figure 4 is a block diagram of a continuous glass melting apparatus which is an embodiment of the present invention, and Figure 5 is a schematic diagram of a continuous glass melting apparatus which is an embodiment of the present invention. FIG. 3 is a diagram showing a transmission loss spectrum of a fluoride optical fiber obtained in one example. 1.Ji material ZrF 1'...Raw material AlF3.11
,,・Jix material BaF, 4~ 2...Sublimated ZrF, 2'...Sublimated AlF3.8・
...Electric furnace, 4...Ar (argon), 5...K
OH dehydration pipe, 6...liquid nitrogen trap, ? ...Vacuum pump, 8...Teflon pipe, 9...Three-way hook, ]0...Quartz tube, 11...Gold plate lining, 12...
・Platinum lining, 18...Transition metal impurities, 14...
Raw material tank, 15... Scale pipe, 16... Hook, 1
7... Simultaneous stirring tube, 18... Metal crucible for cladding, 19... Metal crucible for core, 20... Slide plate,
21... Electric furnace slag, 22... Quartz reaction tube, 23...
- Rotating stirrer tube drive motor, A...Transmission loss curve of fluoride optical fiber using purified raw material, B...Transmission loss curve of fluoride optical fiber using unrefined raw material. Patent applicant Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] L Fluoride optical fiber (raw material for which the boiling point is normal pressure 1
Fluorides with a boiling point below 1800°C at normal pressure are purified by sublimation in a quartz tube or a quartz tube lined with a platinum or gold plate under reduced pressure. Alternatively, fluoride is placed in a quartz tube lined with a platinum plate, heated to 1.000°C or higher under reduced pressure to sublimate and remove transition metal impurities, and the raw material purified by the above process is closed in the tube. It is characterized by the process of continuously weighing, mixing, heating and melting in the system, and casting to obtain an optical fiber (preform), and drawing it to create a fluoride optical fiber. A method for producing fluoride optical fibers.