JPS59116149A - Optical fiber for infrared rays and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture an optical fiber for infrared rays with a small loss due to scattering by coating a core of ZrF4 glass having a specified composition with a layer of fluoride glass having a specified composition and by carrying out drawing at the m.p. of the core or above. CONSTITUTION:ZrF4 glass 2 having a composition consisting of, by mole, 50- 70% ZrF4, 25-40% BaF2, 0-10% LnF3 (Ln is Y or a rare earth element), 0- 8% AlF3 and 0-8% one or more among LiF, NaF and PbF2 and fluoride glass 1 consisting of 25-50% AlF3, 30-60% one or more among BaF2, SrF2, CaF2 and MgF2, 0-25% LnF3 (Ln is Y or a rare earth element) and 0-10% one or more among PbF2, LiF and NaF are put in a crucible 5 so that a core of the glass 2 is coated with a layer of the glass 1, and they are heated with a heater 6 to the m.p. of the core 2 or above at which the layer 1 shows viscosity suitable for drawing. Drawing is then carried out, and the resulting fiber is wound around a winding drum 8 through a capstan 7.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a J11.1 optical fiber for transmitting infrared light and a J11.1 optical fiber made therefrom. It is about the method.

The composition range is fluoride/ruconium as a glass forming agent.
ZrF in mole percent, 50-70% BaF
,, 25-40% LnFs (
Ln=Y or rare earth element) 0-10%AtF'3
．． A multi-component fluoride with a low content of 0-8% LiF, NaF, Yen) F2 (both 0-8% one J: Rinaro component (the sum of more than 100%)) Glass (hereinafter referred to as ZrF4 glass) has excellent transmission characteristics for infrared light, and theoretically it is possible to create fibers with extremely low loss of 0.1 dB/Km or less.However, at present, , the lowest fiber loss value experimentally obtained is 12d.
B/Km, which is more than 100 times the theoretical value -1 = 4?
J loss is big. This is mainly due to the large absorption loss due to impurity ions such as transition metals contained in the fiber and the large scattering loss due to fine crystal grains precipitated in the glass phase.

Therefore, in order to bring the fiber loss close to the theoretical value, it is essential to eliminate these two causes. It is possible to reduce absorption loss due to impurities by using sufficiently purified glass raw materials, as seen in the example of silica-based glass fibers, but microcrystals precipitate in the glass, causing scattering loss. This phenomenon is a problem specific to fluoride glasses, and currently no solution has been found for reducing scattering loss. ZrF4
The problem of precipitation of microcrystals in glass fibers is closely related to the thermal properties of this glass and the method of manufacturing the fiber.

FIG. 1 shows a differential thermal analysis curve of a typical ZrF-based glass. In the figure, Tg is glass transition temperature, Tc is crystallization temperature,
Tm indicates the melting point, and in most ZrF-based glasses, Tg
Th 320℃, TcTh 390℃, Tm:! 5] 0℃
It is.

As can be seen from the figure, this glass changes from glass to crystals at Tc of around 390°C, so in order to prevent crystal formation, it is necessary to handle the glass at a lower temperature than Tc of 390°C. is necessary.

However, in the usual manufacturing method of ZrF-based glass fiber, a method is used in which a preform rod is created and the rod is heated and drawn using ring heat VJ2.・In order to obtain a suitable viscosity for wire drawing, the preform rod is heated at a temperature close to 390°C above Tc.
As a result, microcrystals precipitate. That is, for ZrF-based glasses, the crystallization temperature and the viscosity (10°
~104 voids) are close in temperature, which causes microcrystals to form. Therefore, in order to prevent crystal precipitation, it is necessary to draw the line at the melting point Tm2 or at a temperature much lower than the crystallization temperature Tc, but in the former case, the viscosity is too low. 1. In the latter case, it was impossible to draw a line due to the high viscosity.

1-1 of the present invention is capable of being wired at a temperature higher than the melting point Tm of ZrF4 glass, and as a result, there is little precipitation of microcrystals (an infrared optical fiber with low scattering loss and a method for manufacturing the same). It is about providing.

J. Shimogi's invention will be explained in detail.

As mentioned above, in order to prevent the precipitation of microcrystals in ZrF-based glass fibers, it is sufficient to draw at a temperature higher than Trr + 510°C, but the viscosity is too low for normal drawing. A possible method for drawing low-temperature liquids is not to draw the liquid directly, but to enclose it in a coating material with an appropriate viscosity and draw it together with the coating material.Normally, such coating materials are Glasses such as quartz glass, Pyrex glass, and soda glass, and plastics such as nylon and Teflon can be used, but none of these materials can be used as a coating material for Z r F4 glass fibers. In other words, the conditions for the coating material that can be applied to ZrF-based glass fibers are: 1. It must have an appropriate viscosity for drawing at 0500 to 600°C, 2. It should not be corroded by fluoride, 2. It should have good infrared transmission characteristics, and 2. Z r F.

The essential conditions are that the refractive index is lower than that of glass, and that it has good weather resistance, but none of the above-mentioned coating materials satisfies all of these conditions, and due to the lack of such a coating phase, It can also be said that melt drawing of the Z r F type glass was not performed. Therefore, as a result of conducting various studies on coating materials that satisfy the above conditions, it was found that fluoride glass or heptanophosphate glass having the following composition satisfies the conditions.

(mol%) AtF325~50 LnF"3 (L+1: Y or rare earth element) O~2
5 However, the total of each component is 100 moles, and each component is within the following composition range.

(mol %) BaF20-30 SrF20-30 CaF2 0-50 MgF2 0-30 PbF, 0-10 LiF O-1O NaF O-10 In addition, the two phosphorus compound components are, for example, AAFs→AtP
It is also possible to substitute with a phosphate, such as O4r BaF, -+ Ba3(PO4)2. In this case, the amount of substitution is within a range where the refractive index nD is smaller than the refractive index nD of the core glass, usually within 50% of the molar ratio of fluoride and phosphate. - By way of example, the characteristics of the coating glass and core glass in the fiber of the invention are shown below.

40 [(]-x)AlF3+xklPo]-20B
aF2-25CaF2-15YF3 (coated glass) 6
2ZrF4-30BaF28LaF, (core glass) where no is the refractive index and η is the viscosity at 550°C.

9- As shown above, the coated glass has a lower refractive index than the core glass, a suitable viscosity for drawing at temperatures above the melting point Tm of the core glass, and excellent infrared light transmission properties. In addition, the corrosion resistance against fluorides and weather resistance 471 were also good, and all the above-mentioned conditions were satisfied. Therefore, in the fiber of the present invention, which combines such a coated glass and a core glass, by encapsulating the core glass within the coated glass,
It is possible to draw at temperatures above the melting point of the core glass. Therefore, microcrystals do not precipitate during drawing, and a fiber with low scattering loss can be obtained.

The fiber of the present invention, as shown in the cross section of the fiber in FIG.
In addition to the two-layer structure of FAL with a core 2 made of glass, there is also a core 2 and cladding layer made of ZrF and glass of a somewhat different composition;
(and the outside thereof is covered with a coating glass 1 having the above composition range, or tb+, the core 2 is formed of ZrF4 glass,
The cladding layer 4 and the coating layer 1 outside the cladding layer 1 are coated with glass having slightly different compositions within the above composition range. By constructing the glass with a certain type of glass, it is easy to match the linear expansion coefficient and the infrared transmission wavelength range.

Next, FIGS. 3 and 4 will be explained regarding the method of manufacturing the fiber of the present invention.
Based on this. Figure 3(a) shows a two-layer fiber;
(bl indicates a method for producing a fiber with a three-layer structure by crucible drawing. In the figure, 1, 2, and 3 indicate the materials of corresponding parts, 5 is a crucible, 6 is a heating element, 7 is a heater, and 7 is a crucible.
8 indicates a capstan, and 8 indicates a winding drum. In the fiber of the present invention, since the above-mentioned specific coating glass is used as the outermost coating, it is possible to draw the fiber at a temperature higher than the melting point of the core glass, which was previously impossible.

FIG. 4 shows a method of drawing a preform rod colored fiber prepared in advance. In the figure, 9 indicates a preform rod feeding mechanism. Also in this case, since the above-mentioned coating glass is used for the outermost coating layer, drawing can be performed at a temperature higher than the melting point of the core glass.

As explained above, the fiber of the present invention can be drawn at a temperature higher than the melting point of the ZrF-based glass that forms the core. Can prevent precipitation of microcrystals,
Therefore, it is possible to realize an infrared glass fiber with low scattering loss (less than ] db/Km). As described above, since the fiber of the present invention can eliminate essential loss factors, the infrared fiber has an extremely low loss (11 losses) close to the theoretical loss value.
I can do that.

[Brief explanation of drawings]

FIG. 1 is a characteristic diagram showing the differential thermal analysis curve of the glass used in the present invention, FIG. 2 is a cross-sectional view showing an example of the present invention, and FIGS. 3 and 4 are system diagrams for explaining the manufacturing method according to the present invention. It is. 1... Test glass, 2... ZrF4-based glass (
core), 3.4... Crucible layer, 5... Crucible, 6... Heater, 7... Capstan,
8... Winding drum, 9... Preform rod feeding mechanism. Figure 3 (0) (b) Flash 4 2, (0) (b)

Claims (2)

[Claims] (1) In mole percent Z r F450-70% BaF2 25-40% IJnF
3 (Ln-Y or (・1 rare earth element) 0-10%A
tF3 0-8%LiF, NaF
', a component consisting of at least 0 to 8% of PbF2 (the sum of the components of L is 10 (1%)), with a core of glass having a composition range of 10 (1%), At1i"3 with 1 mole percent 25 to 50 %1,
nF3 (I, n;: Y or rare earth element) 0-25
% (the grinding of the following components is 100%), and the composition range of the 51st component is BaF20-30% S r F20-30% CaF2 0-50% Mg
F20-30% pbp2o-10% Nal5O-10% LiFO-10 1
The side covered layer (infrared optics with - reduced scattering loss) - Eyeva. (2) Molversen] Z r F4 50-70%11
aF, 25-40% LnF,
(Ln=Y or rare earth element) 0-10%A, tF
, 0-8% Li1i”, Na
Glasses with a composition range of at least 0 to 8% of F, pbF2 - 25 to 50% of AlF2 in mole percent L
n F3 (Ln = y or rare earth element) 0 to 2
5% (however, the ratio of the second component is 100%),
Among them, the composition range of the following components is BaF20-30% 5rF20-30% CaF2 0-50% MgFz O-30% PbF20-10% NaF 0-10% 1, J + F 0-10% , lath, or phosphoric acid glass in which a portion of each of the above components is replaced with a corresponding phosphate, as the outermost coating layer, and the coating layer exhibits a viscosity suitable for drawing at a temperature equal to or higher than the melting point of the core. A method for manufacturing an infrared optical fiber, which is characterized by drawing at a temperature.