JPS6311902A - Crystalline optical fiber and its manufacturing method - Google Patents

Abstract

PURPOSE:To strongly lock light in the core of an optical fiber, by extruding a double-structure preform which is specific silver halide mixed crystals with an extruding device under a specific condition so as to form the optical fiber in a triple structure of the core, inner clad, and outer clad. CONSTITUTION:The crystalline optical fiber of this invention is composed of a core-inner clad part which is made of mixed crystals of AgBr:AgCl=1:x and constituted of a core and inner clad, with the crystal size of the central core being smaller than that of the surrounding inner clad and an interface X being formed between the core and inner clad, and an outer clad which is made of mixed crystals of AgBr:AgCl=y:1 or AgBr:AgCl=1:u and covering the outside of the core-inner clad part with an interface Y in between. The (x), (y), and (u) are respectively set in the following manner: 0.1wt%<=x<=10wt%, 0wt%<=y<=10wt%, 0.1wt%<=u<=10wt%, and x<u. Such crystalline optical fiber can be manufactured by an extruding process by combining such specific conditions as crystalline material of AgBr-AgCl mixed crystals, 80-200 deg.C extruding temperature,, and 5-30mm/min extruding speed.

Description

DETAILED DESCRIPTION OF THE INVENTION (7) Technical Field The present invention relates to a crystalline optical fiber for infrared light having a core-clad structure and a method for manufacturing the same.

Silica glass fibers are widely used as optical fibers for optical communications, and have already had a sufficient track record.

There are two types of silica glass fibers: step index type and graded index type.

The step-index type has a two-layer structure: a central core and a surrounding cladding.

Silica glass fiber has extremely low loss and excellent properties. However, visible light and near-infrared light (~1.5μ
It can only be used for m). Light with longer wavelengths cannot pass through.

CO2 laser light has a wide range of uses in medical and industrial applications because it is easy to obtain strong power. However, since the wavelength is as long as 10.6 μm, there is no glass fiber that can pass all of this with sufficiently low loss.

There are several fibers that have been developed for use with CO2 laser light. Both have fairly high losses and are only used over short distances. Fiber lengths from 1 m to several meters are used.

However, since C02 laser light is often used as a power source, even a short optical fiber is sufficiently useful.

Glass fibers and crystalline fibers are available as fibers that can pass CO2 laser light.

Examples of glass fiber include chalcogenide glass and fluoride glass.

Some crystalline optical fibers are called metal halide crystals.

There are roughly three types of these.

(1) Silver halide crystals AgBr, AgCl, Agr and mixed crystals thereof (1
1] Thallium halide crystals TlBr, TβCβ, TβI and mixed crystals thereof 01D
In addition to alkali halide crystals CsI, CsBr, and their mixed crystals, any crystalline optical fibers such as Zn5e, 5ZnS, and Z can be used as infrared optical fibers.

The present invention relates to improvements in optical fibers made of silver halide crystal among these fiber materials.

Methods for producing crystalline fibers include an extrusion method starting from a preform, a pulling method starting from a melt, and a pulling method.

In the extrusion method, a single crystal preform is placed in a full die, heated to soften it, compressed, and extruded through a narrow hole to form a thin fiber.

This allows the creation of polycrystalline fibers.

On the other hand, there is also a method of placing crystalline material in a crucible and heating it with a heater to melt it into a liquid. This liquid is called raw material melt. The pulling method is a method in which a seed crystal is immersed in the raw material melt and pulled up from the top of the crucible. This method is the same as the normal crystal growth method.

The pull-down method involves drilling a hole in the bottom of the crucible into which the raw material melt is to be placed, and then pulling the crystal down through the hole.

Starting from a raw material melt, it is easy to obtain a single crystal fiber. However, the growth rate is slow and productivity is poor.

The extrusion method starting from a preform has good productivity because the extrusion speed is quite high.

In conventional extrusion processing of crystalline fibers, the mold temperature was 250°C or higher. In particular, most of the temperatures were 300°C or higher.

The extrusion speed was often 101 minutes or less, especially 54 minutes or less.

The present invention relates to improvements in manufacturing crystalline optical fibers by extrusion.

B) Prior Art These optical fibers for infrared light usually consist of only a core. It lacks the part corresponding to the cladding.

The core material is simply inserted into a polymer tube and used as an optical fiber. Therefore, the air existing between the core crystal and the tube acts as a cladding.

There is a difference in refractive index between the core and air. Therefore, infrared light propagates into the core while being totally reflected at the interface. It is called an air clad structure.

It is said that air plays the role of cladding, but this is extremely unstable and cladding.

The core surface plays an extremely important role in optical transmission.
Depending on the environment and conditions in which the optical fiber is placed, it can become contaminated or completely damaged.

If the core surface becomes contaminated or has water droplets attached to it, the refractive index difference between the core and cladding changes, causing strong absorption.

Since the C02 laser light is a powerful light, it generates a lot of heat due to absorption. Sometimes optical fibers are destroyed.

In particular, light leakage is significant at the output end and input end of the optical fiber, and thermal damage is likely to occur at the ends.

Thus, the air clad structure has several drawbacks.

All that is required is to attach a cladding to the infrared optical fiber.

An overview will be given of an infrared optical fiber with a cladding.

A proposal was made to vacuum-deposit a metal coating around the outer periphery of an infrared optical fiber core, thereby protecting the optical fiber core and preventing leakage of infrared light from the surface (Japanese Patent Laid-Open No. 1983-1992).
-132301. (Released on October 26, 1981).

For example, 1 μm thick gold is vacuum deposited around an optical fiber. Since gold reflects infrared light well, it is possible to effectively confine all infrared light within the core.

However, the gold-coated original fiber has the following drawbacks.

It is difficult to deposit gold evenly on the outer periphery of an optical fiber with a circular cross section. There is also a lot of waste of gold materials.

Furthermore, it is not possible to apply a thick gold layer. 1μ at most
It can only be made as thin as a meter. When it is thin like this, it lacks the ability to physically protect the entire core. The effect of completely confining light within the core is also insufficient.

Gold is not transparent to infrared light. Therefore, infrared light that enters the gold layer is strongly absorbed and generates heat. For this reason, there is also the drawback that the entire gold layer cannot be made very thick.

As in the case of fused silica fibers, the cladding is
The material should be highly transparent to light at that wavelength.

Furthermore, a method of manufacturing a crystalline fiber consisting of a core and a cladding made of an infrared crystal material has been proposed, but this method has the drawbacks of requiring a large number of man-hours and making the manufacturing process complicated.

(b) Purpose: In the next step, the entire cladding is formed on the outside of the pre-fabricated core.
A first object of the present invention is to provide a method for manufacturing a crystalline optical fiber having a core-clad structure.

Improvement of AgBr-AgCl mixed crystal fiber,
A second object of the present invention is to provide a fiber that has a double core-cladding interface and can more strongly confine the light beam of the CO□ laser in the core.

B) Method of the present invention The present invention combines AgBr and AgCl to provide an infrared optical fiber having a triple structure consisting of a double cladding and a core.

For light with a wavelength of 10.6 μm, AgBr has a higher
It has a higher refractive index than C[. Therefore, AgBr and Ag(J
Combine them to suit the core and cladding.

However, as described later, the core material is divided into a core and an inner cladding depending on the extrusion conditions.

Because of this, the materials for the core are limited.

The core must not be pure AgBr.

However, since the cladding material does not separate into two layers,
Such a limit may be less than 10% AgCd.

There is such an asymmetry in the required properties of the core and cladding. Therefore, there is an asymmetry in the selection of AgBr and AgCl. You have to make complex combinations and choices.

FIG. 1 is a sectional view of a crystalline fiber extrusion apparatus for carrying out the manufacturing method of the present invention.

The preform 1 is a high quality single crystal consisting of a core 1b and a cladding 1a. Both core and cladding are AgBr
It is a crystal that has a combination of components: and Ag(J).However, since the composition ratio is different, a difference occurs between the core and the cladding.

Regarding the combination of core material and cladding material, please refer to the following 5.
Two cases are possible.

(I):17 is mainly AgBr f, with 0 AgCl
．． It is a mixed crystal added with 1 to 10 W#. The amount added is x v muscle.

The cladding is a mixed crystal of 100% AgGg. Simply written, Core AgBr: AgCl= 1: x Cladding AgBr: AgCl= O: 10.11
Bin ≦X≦lQi secret (1):! 7 is AgBr @ main body, AgCl=z
It is a mixed crystal containing 0.1 wt% to 10 wt%.

The cladding is mainly made of AgCl, AgBr f Ow
It is a mixed crystal added at a rate of 10 mm/min. The total amount of AgBr added is written as y. To write a simple formula, Core AgBr: AgCl= 1: x Cladding AgBr: AgC[= y: IQ,
l■彬≦X≦to”=rts o<y≦LOW The relationship in magnitude between x and y is arbitrary.

■ The core is mainly composed of AgBr f, with 0 AgCl,
It is a mixed crystal when added in an amount of 1 wt% to 10 wt%. The cladding is also mainly composed of AgBr, with 0 and 1 wt of AgCl.
It is a mixed crystal with 0.01% addition. However, Ag in the core
The content of Cl is lower than the content of AgC,5 in the cladding. Simply written, core AgBr: AgC[= 1: X cladding AgBr: AgCl= 1: uQ,
1wt%≦x<u≦l0wti (dish) core is AgC
l as the main body, AgBr f:Q. 1wt% ~10
It is a mixed crystal with W streaks added. The cladding is a mixed crystal mainly composed of AgCl with addition of AgBr t-Qv# to lQw#. However, the AgBr content in the core is greater than the AgBr content in the cladding.

:27 AgBr: AgCl=Z: 1 Clad AgBr: AgCl1= 7: 1
o<y≦l0wt% 0.1w muscle≦2≦I Qvr muscle y (z (V): tA is mainly composed of AgC#, AgBr
It is a mixed crystal to which f Q is added in an amount of 1 wt% to 10 Wt/i.

The cladding is 100% AgCl.

Core AgBr: AgCl=z: 1 Clad AgBr: AgCl= O: 1O-IW
Strain ≦2≦l 0WVJ As described above, there are five cases in the combination of core and cladding components of AgBr and AgCl.

It is very easy to understand, so I will explain it using a composition diagram.

FIG. 4 is a graph of the composition ratio of the core and cladding.

This is not a commonly used phase diagram. This is a composition ratio graph specially devised by the present inventor in order to accurately express the present invention.

Consists of square 0PQR. The horizontal direction indicates the composition of the core. The vertical axis direction indicates the composition of the cladding.

Both the core and the cladding are based on 100% AgBr, and each time the ratio of AgCl increases, the value of the coordinate η increases.

The origin O represents 100% AgBr in both the core and cladding. Point P indicates that the core is 100% AgCl and the cladding is 100% AgBr.

In other words, for the core, the straight line OR is AgBr1
00%, and the straight line PQ shows 100% AgCl. Let the composition ratio variable of the core be η. η takes a value between 0 and 1. In the straight line OR, η is 0. In straight line PQ, η is assumed to be 1.

That is, η is the weight ratio of AgC2 to the entire core.

The variable X in 1, l, l[ is η = (1) for η 1+X There is a relationship between

Variable 2 in plate ■ has the relationship η = −(2) 1+z with respect to η. This is simply a matter of rewriting the expression of the ratio into a fractional expression.

1. In L l, regarding the core composition, x = 001w
The striations and the 10W striations provide the boundaries. On the plate, z=0
, 1wt% and 1(lvt%) give the boundaries.

These correspond to the following values of η from equations (1) and (2), respectively.

! = 0.1W%J 77 = 0.001 (
Straight line a)! = 10wt% 77 = 0.0
91 (straight line b)” = IQv sister 77 == 0-91
(Straight line C) z = 0.1vt% 77 =
0.999 (Straight line d) Vertical lines a, b, c in Figure 4
, d correspond to these values of η. Regarding the core composition, 1%l, H is in a Nb, dish, ■
For more information, see c Nd.

The above was an explanation of the horizontal axis regarding the core composition η. Next, the composition ζ of the cladding will be explained.

The horizontal straight line OP indicates that the cladding is 100% AgBr. The horizontal straight line RQ indicates that the cladding is 100% AgCl. The compositional variable ζ of the cladding is defined as the weight ratio of AgCA to the entire cladding.

ζ=0 corresponds to OP, and ζ=1 corresponds to RQ.

In I and V, the cladding is 100% AgCt.

This means that G = 1, and if the straight line of ζ;l is called i, it can be said that I and V are on the straight line i (same as the straight line RQ).

I lies between a Nb with respect to the core composition and on i with respect to the cladding. After all, ■ is equivalent to the area indicated by line segment AB.

■ is between cNd in terms of core composition and on i in terms of cladding. After all, ■ is equivalent to the area indicated by the line segment MN.

(2) states that the weight ratio U of AgCt to AgBr in the cladding is 0.1w~tovr. (2) and dish state that the weight ratio y of AgBr to AgCt in the cladding is 0 wt% to 10 wt%. These can be rewritten as the weight ratio ζ of AgCA to the whole using the formula ζ = −(3) 1+u. Each limit value corresponds to the following.

u = = Q, l4 Takashi ζ = 0.001 (straight line e)
u == 10W line ζ=0.091 (straight line)' = 10! #ζ=0.91 (Straight line g) The straight line e1f1g drawn horizontally in FIG. 4 corresponds to this above value.

For l, the range of “,’/ is limited and x.

The magnitude relationship of y itself is not defined. In other words, it is sufficient for the core to be between aNb and for the cladding to be between gNi. After all, the eyes correspond to the area indicated by the rectangle CDBA.

Regarding ■, it is more complicated. For the core aN
b, and the cladding is between +5 Nf'.

Moreover, there is an inequality X(u), which is expressed by equation (1),
From (3), we have η. η=This graph is the straight line OQ. η×ζ means the upper left of OQ. Therefore, ■ is surrounded by triangle IGH (line segment IG
It can be seen that it corresponds to the area (excluded).

Regarding plates, there are similar complications. For the core it is between cwd and for the cladding it is between 8 and 1.

Furthermore, there is a condition that y<z.

This means ζ × η. It is on the upper left of straight line OQ.

Eventually, the dish corresponds to the area indicated by the scalene trapezoid JKNM.

The core/cladding composition of 1 to V is written as η and ζ as follows. This is equivalent to the representation in FIG.

1 0.001≦η≦0.091 ζ=11 0.0
01≦η≦0.091 0.91≦ζkull1l O,
001≦η×60.091 dishes 0.91 ≦η ≦
0.999 ζ 0.91≦ζ くIV
O,91≦η≦0.999 ζ=1. However, I
, If can be combined into one. In ■, the cladding is said to be a "mixed crystal", and in I, the cladding is AgCl.
Since it is expressed as 100% crystal, like this, 2
It can be divided into

However, the mixed crystal ratio AgBr:AgCl=y:1
When defining 0≦y≦lQW7%, I, l
will be included. It is strange to call y = Q wt% a mixed crystal, but if this is also called a mixed crystal, I and l
can be combined into one.

The plate and V can also be combined into one if 0≦y≦lQW.

Preparation of a preform having such a composition is necessary as a preparation for carrying out the present invention.

First, the core portion is grown as a single crystal using a pulling method or a port method. This is cylindrically ground to form a cylindrical single crystal.

For the cladding, a single crystal is similarly grown. The inside is removed and ground into a cylindrical shape. This cladding and core are combined to form a preform.

In this way, the preform is made of a mixed crystal of AgBr and AgCt, and has a core and a cladding portion formed in advance.

Furthermore, other trace elements may be added for purposes such as improving mechanical properties to the extent that optical properties are not impaired.

Since a preform is thus prepared, the present invention uses it as a starting material.

Once the preform is extruded according to the invention,
The core part becomes the core and inner crust.

This part is called the core/inner cladding part.

The cladding portion is the outermost cladding. This part is called the outer cladding part.

In FIG. 1, the mold 4.4 forms a cylindrical space into which the preform 1 is placed.

At the tip of this space, there is an extrusion die 2 with a thin hole.
is the provision. The softened preform is extruded to the outside from here.

A heater 5 is provided around the mold 4.4 to uniformly heat the mold and preform.

A thermocouple (not shown) is provided within the mold to monitor the temperature of the mold. Return to the temperature reading of this 1-'
The mold and preform are maintained at a predetermined temperature.

The ram 3 is provided so as to be able to move forward and backward in the cylindrical space. This extrudes a preform 1 from an extrusion die 2.

The configuration of an extrusion device as shown in FIG. 1 is known.

The present invention is characterized by the composition of the preform, extrusion temperature, and extrusion speed of the preform as described above. By specially setting these conditions νζ, the core material is divided into two layers: the core and the inner Clara Y.

As already mentioned, in conventional extrusion processing of crystalline optical fibers, the mold temperature is 250° C. or higher, and in most cases 300° C. or higher. The extrusion speed was often below 10 m/min, especially below 5IIIZ min.

However, in the present invention, (1) Mold temperature 80°C to 200°C (11)
Extrusion speed: 5-30 g+m/min Compared to conventional methods, the extrusion conditions of the present invention have a lower temperature range and faster extrusion speed.

A double-structured preform made of silver halide mixed crystal as described above is placed in a cylindrical inner space of a mold 4, sealed with a ram 3, and heated to 80°C to 200°C with a heater 5. At this temperature the preform does not melt, but softens.

Appropriate mechanical force is applied to the ram 3 to extrude the polycrystalline fiber 6 from the extrusion die 2 at a speed of 5 to 30 m/min.

In this way, thin polycrystalline fibers 6 will be manufactured continuously.

Figure 2(b) shows an enlarged cross-sectional view of the manufactured polycrystalline fiber.
It is shown in

The part indicated by the thick line is the core-cladding interface. The preform has a core-clad dual structure, and this interface is what remains after being formed into a fiber. Therefore, this interface Y originally existed in the preform.

In the cross-sectional view, thin lines indicate grain boundaries.

The size of crystal grains appearing in the fiber cross section is not uniform.

This is the most important feature of the present invention. The grains are extremely small at the center and extremely thick at the periphery. Such differences clearly occur at the core.

According to actual measurements, the ratio DI/D2 between the diameter D2 of the crystal grains in the center and the diameter Dl of the crystal grains in the peripheral part is 5 times or more.

Although the shape and size of the crystal grains are undefined, there is a significant difference in the size of the crystal grains in the center and the periphery.

Moreover, the difference in grain size does not occur continuously or randomly, but rather, this change occurs along the same circle. This is the important point.

A new interface X is generated due to the difference in grain size. This interface X occurs naturally through extrusion molding. This interface or the outer circumference of the fiber is approximately concentric.

Thus, the method of the invention creates two interfaces in the optical fiber. There is an interface X due to a difference in crystal grain size, and an interface Y due to a difference in composition.

The crystal grains are generally large inside and outside the interface Y, and there is no difference in grain size. However, since the composition is changed when manufacturing the preform, differences in composition exist inside and outside the interface Y.

Even if the same preform is extruded, the temperature is 200℃.
When the temperature exceeds ℃, the grain size becomes almost the same in both the center and the periphery. There is almost no difference in particle size. This results in a collection of uniform crystal grains with large grain sizes, resulting in a cross section as shown in FIG. 2(a).

A device having the cross section shown in FIG. 2(a) will be described below as a comparative example using the conventional method. In this case, only the core-cladding interface Y (indicated by a thick line) exists due to the difference in composition.

Only when the mold temperature is lowered to 200°C does a small portion of crystal grains appear in the center of the fiber.

As the temperature is further lowered, the small crystal grains in the center begin to expand. In other words, the part that corresponds to the central core is expanding. On the contrary, the cladding portion decreases.

Simply put, lower temperatures result in thinner cladding, and higher temperatures result in thicker cladding. The cladding here refers to the outside of the interface X. The core is the area inside the interface X.

When the temperature drops below 80° C., the entire cross section of the fiber becomes fine crystals. In other words, the structure is such that the portion inside the interface X in FIG. 2(b) is expanded throughout. Therefore, the core-cladding structure defined by the interface
l<7xru.

Diagrammatically speaking, when the temperature exceeds 200℃, the core disappears,
When the temperature drops below 80°C, the cladding disappears. For this reason, 8
At extrusion temperatures below 0°C or above 200°C, the double structure is 'lx<72.

As already mentioned, the grain size Dl of the inner cladding part
The value DI/D2, which is the ratio of the size D2 of the crystal grains in the core portion, is preferably 5 or more.

As described above, when there is a difference in particle size, the difference in refractive index between the core portion and the inner rad portion with respect to the C02 laser beam becomes approximately 2% or more.

The difference in refractive index allows light to be confined in the core.

In order for the core to be able to effectively confine light, the cladding must be fairly thick (not thin, at least 5% or more of the core diameter).

Measure the particle size by microscopic observation. The size of the crystal grains in the center was several μm. The size of the crystal grains in the peripheral area is 3
It was about 0 to 100 μm.

The crystal grain size also depends on the size of the fiber diameter.

When the fiber diameter was 1 m, the size of the surrounding crystal grains was about 50 to 100 μm. .

When the fiber diameter was 0.7 m, the size of the surrounding crystal grains was about 40 to 70 μm.

The present invention is a crystal material made of Ag, Br-AgCt mixed crystal, an extrusion temperature of 80°C to 200°C, an extrusion speed of 5 m/
By a combination of specific conditions, from 30 minutes to 30 minutes/minute,
A crystalline fiber having a core-clad double structure characterized by an interface X, in which the crystal grain size differs between the center and the periphery, is manufactured by extrusion processing.

The reason for the double structure is presumed as follows.

When the preform is pressed under strong pressure and emerges from the die as a thin fiber, the crystal grains that make up the fiber become finer. After passing through the die, the fine grains become larger and consolidated. Recrystallization occurs.

During recrystallization, the recrystallization speed of fine crystal grains in the center and periphery of the fiber differs due to non-uniform stress within the fiber during fiber extrusion. It is speculated that this difference in crystal grain size between the center and the periphery and the difference in refractive index due to stress distribution within the fiber are caused.

What is important is that this core-clad structure creates a refractive index difference and has the effect of confining light in the core.

The composition of the core is a mixed crystal of A, HBr and AgCt,
The mixed crystal ratio η of AgCl is 0.001 to 0.091 and 0
．． It is limited to those between 91 and 0.999. If the composition is other than this, a double structure of core and inner cladding will not occur.

If the core is 100% AgBr, no double structure will occur. So the 100% AgBr core is excluded.

Why does extrusion molding create a double structure of core and inner cladding? That being said, it can be thought of as follows.

When the preform is pressed under strong pressure and emerges from the die as a thin fiber, the grains that make up the fiber become finer. After passing through the die, recrystallization occurs in which the fine grains are consolidated into larger sizes. At this time, due to the non-uniformity of stress within the seven fibers during fiber extrusion processing, the recrystallization speed of fine crystal grains in the center and peripheral parts of the fiber differs. Since the strain stress is greater in the peripheral area, recrystallization is faster.

This is probably why the crystal grains inside and outside are different.

At the same time, there will likely be a difference in refractive index between the inside and outside.

This is due to the high extrusion speed and low temperature.

It also depends on the mixed crystal ratio of the core. This does not happen with 100% AgBr. Most of the particles are large in size.

When AgBr:AgCL=50%:50%, the crystal grains become too small overall. Therefore, the mixed crystal ratio is
It becomes possible to create regions with different crystal grain sizes in the range between 0 and 1 wt% to tovts, which is between these.

There are relatively few restrictions on the composition ratio for the outer cladding.

However, depending on the material between the core and Clara Y (Y interface),
Since there must be a refractive index difference, the cladding AgBr
The mixed crystal ratio must be less than that of AgBr in the core.

This means that the composition ratio value exists on the upper left of the straight line OQ in FIG.

(a) Function The crystalline optical fiber manufactured according to the present invention has a triple structure. The core inside the interface X, the interface and the interface Y
It has a triple structure of an inner cladding between the two and an outer cladding outside the interface Y.

As shown in FIG. 1, since the preform originally had a double structure, it becomes a triple structure.

When light from a CO2 laser passes through it, the light is confined within the core due to the difference in refractive index. Measurements have shown that a difference in refractive index occurs between the core and the inner cladding by about 2 to 1%. With such a large difference in refractive index, light can be confined efficiently. Since the light components leaking from the surface of the optical fiber are reduced, the transmittance is substantially increased. In particular, leakage of light at the output end and the input end, which is a serious problem with infrared fibers, can be effectively prevented.

Furthermore, even if the surface of the fiber is damaged, the transmittance decreases less. This is because the cladding protects the core.

Furthermore, it is easier to obtain a smaller beam spot. This is because the light energy is localized in the core. The spread of the beam diameter can be measured using an evaluation device as shown in FIG. When the beam diameter was measured from the acrylic burn pattern, it was found that the optical fiber of the present invention had a smaller spot diameter.

(2) Effects A crystalline fiber with a triple structure of core, inner cladding, and outer cladding can be manufactured by simply extruding the preform using an extrusion device.

This fiber consists of a core that collects and propagates the C02 laser light, and a double cladding that mechanically protects the core and reflects the C02 laser light at the interface. Become. Therefore, the overall transmittance is higher than that of an optical fiber consisting only of a core.

When the transmittance was measured, the transmittance of the optical fiber of the present invention with a length of 1 m and a diameter of 0.7 sn was 68%. In a comparative example with the same diameter and length (shown in Figure 2 (a)), the transmittance was 55.
%Met. There was a difference of 13%. From this result, it can be seen that the light of the C02 laser can be propagated extremely effectively.

Also, since the laser light is localized more narrowly, Zn5e
77 Any lens can be used to focus the beam into a smaller spot.

Using the evaluation apparatus shown in FIG. 8, the beam spread of C02 laser light was measured for the fibers of the present invention and the comparative example.

The light from the crystalline optical fiber is focused by a Zn5e lens and applied to an acrylic plate. The acrylic plate will burn out depending on the beam diameter. The shape of the burnt part is called a burn pattern. The beam diameter can be determined from the burn pattern.

The burn pattern when using the optical fiber of the present invention is 0.
It was 3 snφ. The burn pattern of the comparative example is 0.6+
It was mφ.

Table 1 is a table showing the measurement results of the beam spot diameter and transmittance of the crystalline fibers according to the present invention and the comparative example (conventional example) when CO□ laser light is passed through them.

Table 1 Beam spot diameter and transmittance of the fibers of the present invention and the conventional example The fiber of the comparative example also has a core-clad structure, as shown in Figure 2 (a), so the beam diameter at the exit surface is smaller than that of the fiber. Narrower than the outer diameter (0.7m=φ), 0.61φ
It becomes. Also, the transmittance is good.

However, the optical fiber of the present invention is even more superior in spot diameter and transmittance.

The C02 laser light can be propagated efficiently and can be focused into a narrower beam at the output end.

Therefore, if the optical fiber of the present invention is used to guide the light of the C02 laser, it is possible to concentrate the light with a strong energy density onto the workpiece.

By using the optical fiber of the present invention, the usefulness of industrial processing machines and medical treatment machines using CO2 lasers can be further improved.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a crystalline optical fiber manufacturing apparatus of the present invention. FIG. 2(a) is a cross-sectional view of a conventional crystalline fiber in which the crystal grain size is approximately the same throughout the entire cross section of the fiber. 2) is a cross-sectional view of a crystalline fiber according to the present invention. FIG. 3 is a block diagram of a device for evaluating beams. Figure 4 is a graph showing the mixed crystal ratio of the core and cladding. 1 ... Preform 1a ... Preform cladding 1b ...
Preform core 2... Extrusion die 3... Ram 4...
・・・Mold 5 ・・・・・・ Hi-Taro ・・・
...Polycrystalline fiber inventor Ken Takahashi
-Yoshi 1) Noriyuki

Claims (8)

[Claims] (1) It is a mixed crystal of AgBr:AgCl=1:x and consists of a core and an inner cladding, and the crystal grain size of the core in the center is smaller than the crystal grain size of the inner cladding in the periphery. A core/inner cladding portion where an interface
The outer cladding is in contact with the outside of the inner cladding part at the interface Y, and 0.1wt%≦x≦10wt%, 0wt%≦
y≦10wt%, 0.1wt%≦u≦10wt%, x<
A crystalline optical fiber characterized by being u. (2) The crystalline optical fiber according to claim (1), wherein the thickness of the intracrystalline cladding is 5% or more of the diameter of the core. (3) The crystalline material according to claim (1) or (2), wherein the grain size of the crystalline core is 1/5 or less of the crystal grain size of the intracrystalline cladding. optical fiber. (4) It is a mixed crystal of AgBr:AgCl=z:1 and consists of a core and an inner cladding, and the crystal grain size of the core in the center is smaller than the crystal grain size of the inner cladding in the periphery. It consists of a core/inner cladding portion in which an interface , 0wt%≦y≦10wt%, 0.1w
A crystalline optical fiber characterized in that t%≦z≦10wt% and y<z. (5) The crystalline optical fiber according to claim (4), wherein the thickness of the intracrystalline cladding is 5% or more of the diameter of the core. (6) The crystal according to claim (4) or (5), wherein the grain size of the crystalline core is 1/5 or less of the grain size of the intracrystalline cladding. quality optical fiber. (7) A core that is a mixed crystal of AgBr:AgCl=1:x and a core that is a mixed crystal of AgBr:AgCl=y:1 or Ag
A preform combining a cladding which is a mixed crystal of Br:AgCl=1:u, 0.1wt%≦x≦10
wt%, 0.1wt%≦u≦10wt%, 0wt%≦y
A preform with a composition of ≦10wt% and x<u is 8
A method for manufacturing a crystalline optical fiber, which comprises heating to 0°C to 200°C and extruding at a processing speed of 5 to 30 mm/min. (8) A preform that combines a core that is a mixed crystal of AgBr:AgCl=z:1 and a cladding that is a mixed crystal of AgBr:AgCl=y:1, where 0wt%≦y≦1
A preform having a composition of 0 wt%, 0.1 wt%≦z≦10wt%, and y<z is heated to 80 ° C. to 200 ° C.,
A method for manufacturing a crystalline optical fiber, characterized by extrusion processing at a processing speed of 5 to 30 mm/min.