JPH0687089B2 - Method for producing single crystal fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention provides an oxide material such as LiNbO ₃ directly from a raw material melt.
The present invention relates to a method for growing an ultrafine fiber single crystal having a diameter of 50 μmφ or less.

[Prior Art] In recent years, the "single crystal fiber" combines the pure and anisotropic physical properties peculiar to single crystals and the unique effects derived from the shape.
A new use of crystalline materials has been proposed mainly in the field of optics, and Nd: YAG and N have been aimed at micro solid-state lasers to date.
Single crystal fibers such as d: Al ₂ O ₃ and single crystal fibers such as alkali halides for flexible infrared transmission lines have been actively grown. But recently, especially LiNbO ₃
Non-linear optical materials such as single crystal fibers have been attracting new attention.

A light wave traveling in a thin waveguide such as a fiber has peculiar propagation characteristics such as a mode peculiar to the waveguide, a high optical electric field density, and a strong interaction with a waveguide material. Therefore, if a single crystal fiber of a nonlinear optical material can be produced, a large nonlinear effect can be generated in the fiber with a low optical power input, and it is possible to realize a so-called functional fiber in which the fiber itself has a function, Applications to various new optical devices can be expected. For example, optical multiplication and optical mixing due to the nonlinear optical effect promise a realization of a small visible short wavelength laser, and a short-crystal fiber of a nonlinear optical material is particularly desired.

Conventionally, a known production method for growing a single crystal fiber includes an extrusion method (TJBridges et al .: Opt. Let.
Vol.5, p85, 1980), reduction method (Y. Mimura et a
l.:Jpn J. Appl. Phys. Vol. 19, pL267, 1980), EFG method (HELabelle, Jr. et al .: Mat.Res.Bull.Vol.6, p571,
1971), laser pedestal method (eg CA Burrus et.
al .: Appl. Phys. Lett. Vol.26, p318, 1975), micro-pulling method (Onishi: Japanese Patent Application No. 61-024763), etc., but not for fiber production, but a single crystal growth method related to the present invention. Method (eg P. Hartman: Crystal Growth
1, p212, North-Holland Pub. Co., 1973).

Among these, the extrusion method and the pulling-down method are methods devised mainly for the purpose of growing infrared fibers, the materials to be handled are generally low melting points, and the obtained fiber diameter is several hundred to ten.
It is relatively thick with 00 μmφ.

The EFG method is a method for directly growing a single crystal having a specific shape such as a cylinder, a cylinder, or a prism from a melt, and is characterized by using a die having a capillary tube. That is, the lower end of the die is immersed in the raw material melt melted in the crucible and the melt is carried to the upper end surface of the die by capillary action, and the melt is regulated by the edge of the upper end surface and pulled up, the same as the upper end surface. Crystallize into a cross-sectional shape. Crystals of various shapes can be grown depending on the shape of the top surface of the die. An example of growing a sapphire single crystal fiber having a diameter of 250 μm by this method has been reported. (JTAPo
llock:... J Mater Sci Vol.7, p631,1972) micro pulling method, especially in LiNbO ₃ or LiTaO ₃ of fiber the devised assuming method, melt the raw material in the heating element having a microprojection Then, the surface of the single crystal fiber is grown by wetting the surface and pulling up the melt at the protrusions on a minute scale. So far, fibers with diameters down to 100 μmφ have been grown.

The laser pedestal method is a method in which laser light is focused on the tip of a rod-shaped raw material to melt its microscopic region, and a seed crystal is immersed in the melt to perform microscale pulling. This method is applicable to a wide range of materials without being contaminated from crucible or die materials and being restricted by their melting points, and is particularly effective for forming end-crystal fibers of high melting point materials. Using this method, single crystal fibers with a diameter of 35 to 250 μmφ such as Nd: YAG and Nd: Al ₂ O ₃ aiming for a small solid-state laser and LiNbO ₃ fibers with a diameter of 20 μmφ for the nonlinear optical effect were grown. ing. (For example MMFejer et al .: Rev. Sci. Ins
Vol.55, p1791,1984) [Problems to be solved by the invention] A single crystal fiber intended to utilize the nonlinear optical effect has technical difficulties in terms of growing temperature and fiber diameter. Nonlinear optical materials such as LiNbO ₃ are generally oxides, and their single crystals are grown from a high temperature melt of 1000 ° C or higher in an oxidizing atmosphere. There are only a few other materials than platinum such as crucibles and dies that can be used under such growing conditions, and their use is greatly restricted in terms of temperature range, workability, mechanical strength at high temperature, corrosiveness, etc., This greatly limits the method of making fibers. In addition, since the nonlinear optical fiber requires a single propagation mode and a large nonlinear effect at a low optical power input, an extremely fine single crystal fiber having a diameter of 50 μm or less is required.

Up to now, the laser pedestal method has been the only manufacturing method that can meet these requirements. However, this method requires a special device that stabilizes the output of the laser that serves as a heat source, a complicated optical system for uniformly focusing the laser light, etc., and the device is large-scale and economically expensive. is there. Moreover,
It is necessary to prepare the crystal raw material in advance into a uniform thin rod shape,
When growing a crystal, the diameter must be gradually reduced in several steps, and moreover, a high-level and complicated growing technique is required, such as non-uniformity of the diameter in the middle step being brought to the final step.

Assuming that LiNbO ₃ is specifically used as the nonlinear optical material, platinum can be used in terms of temperature, and if this is used as the material for the crucible and die, it seems that the pulling method and EFG method can be applied to fiber growth. . However, with the EFG method, the diameter is 5
When trying to grow a thin single crystal fiber of 0 μmφ or less, it is necessary to process the upper end surface of the die to a fiber diameter as small as possible, and to make a capillary tube through the die. Will be needed. In addition, if the capillaries become thin to some extent or more, the transport of the melt due to capillarity is suppressed, so that the crystallization rate must be extremely slowed down. In such a case, especially when pulling a small-diameter crystal, abnormal growth often occurs and the fiber shape is largely impaired (Ohnishi: 47th Society of Applied Physics 28pG2, 1986), and it becomes impossible to grow a uniform fiber. On the other hand, in the pulling method, irregular temperature fluctuations in terms of location and time always occur due to the thermal convection of the melt in the crucible, and it is still possible to grow a long single crystal in the micron unit without any means. difficult.

To date, the simplest growth method for LiNbO ₃ single crystal fibers is the micro-pulling method, and it is relatively easy to obtain single crystal fibers with a diameter as small as 100 μmφ. However, if this method is extended to single crystal fibers of 50 μmφ or less, the situation becomes extremely difficult. In the pulling method, the diameter of the normally grown crystal depends on both the pulling rate and the melt temperature, but in the case of the micro-pulling method, the pulling rate is slow from the high temperature melt with low viscosity, and the low temperature melt Since then, they are growing at a high pulling rate. However, as the crystal diameter becomes smaller, the amount of melt that adheres to the pulled crystal and rises above the melt surface gradually decreases, and the force acting on it becomes predominantly the adhesive force due to wetting.
Therefore, an abnormal solid-liquid interface, which has not been experienced by the conventional pulling method, is formed, and it becomes extremely difficult to control the shape and diameter of the growing crystal. Therefore, if the melt temperature is lowered to increase the viscosity in order to improve the controllability, then the melt fluidity will decrease and the melt supply will be suppressed, and the fiber diameter during growth will be reduced or cut. This makes it difficult to make the diameter uniform and lengthen it. After all, as the diameter becomes smaller, the temperature condition becomes more severe, and it becomes difficult to grow the fiber.

The present invention has been made for the purpose of solving the above problems, and provides a new technique for directly producing a desired single crystal fiber from a melt of a crystal base material.

[Means for Solving Problems] In order to solve the above problems, the present invention takes the following means. That is, an electric heating element is made of a stranded platinum wire, and a platinum pipe having a capillary tube is erected on a part thereof. A minute projection is formed in advance on a part of the end surface of the platinum pipe. The raw material is melted by the devised heating element and the surface is wetted with the melt, and the melt is transported to the upper end surface by utilizing the capillarity by the capillary of the pipe, and the shape of the upper end surface is regulated. Without pulling, the protrusion is crystallized while pulling up on a minute scale.

[Operation] By utilizing the wetting in the above means, the melt is limited to a very small amount, and thermal convection, that is, irregular temperature fluctuation due to it is suppressed, and moreover, the melt and the heating element are brought into close contact with each other. Therefore, the melt temperature sensitively follows the temperature of the heat generating element, and the melt temperature can be finely adjusted by controlling the energizing current of the heat generating element. Furthermore, by moving the crystallization point to the upper end surface of the pipe, the melt temperature around the heating element and the melt temperature at the crystallization point can be made independent, and the viscosity of the melt can be selected quite freely, As a result, the growing conditions were relaxed. The protrusion provided on the upper end surface of the pipe has the effect of fixing the crystallization point by the action of surface tension when pulling the fiber, in addition to the concentration of the melt there, the promotion of the heat dissipation effect, etc. It has become possible to grow thin fibers.

[Embodiment] FIG. 1 is a view for explaining an embodiment of the present invention. FIG. 1 is a side view of a heating element structure which is a main part thereof, and FIG. 2 is an enlarged view of a platinum pipe portion during fiber growth. Indicates. Diameter 0.4
Platinum wire 1 of -0.77mmφ forms a platinum stranded wire 2 of about 25cm, the middle 5-9mm is directly used as the main heater 3, and the platinum stranded wire at the other ends is placed above and below the main heater 3. Each sub-heater 4 has a structure in which it is wound in a vertical coil shape. A platinum pipe 5 having an outer diameter of 200 μmφ, an inner diameter of 100 μmφ and a length of about 500 μm is tied up with a platinum thin wire 6 and installed upright at approximately the center of the main heater 3. When cutting the pipe, make a cut leaving a part of the circumference, and pull it to cut to form a minute projection 7 (second illustration) on the cut surface. The protrusions 7 were placed upright at the openings, and when the melt 12 wetted the main heater 3, the lower end of the pipe was sufficiently close to the groove of the stranded wire so as to be immersed in it. As shown in FIG. 3, the heating element 14 thus constructed is stored in a growth furnace 9 whose circumference is kept warm by a heat-resistant material 8 and is added to a vertical drive mechanism 10 having a moving speed of 0.01-3 mm / min. did.

Next, specific growth of the single crystal fiber will be described below. First, the raw material of LiNbO ₃ is attached to the tip of the up-and-down drive mechanism 10 and brought into contact with the main heater 3 which is being energized to be melted to wet the surface. Then, a seed crystal 11 of LiNbO ₃ having a desired crystal orientation was attached in place of the raw material, the tip of the seed crystal 11 was brought into contact with the upper end surface of the pipe, and part of it was melted back to wet the protrusion 7 and was sucked up by the capillary phenomenon. It is fused with the raw material melt 12. After that, the temperature condition was set to a desired fiber diameter, and the protrusion was crystallized at the protrusion 7.

This manufacturing method differs from the EFG method in that the fiber diameter can be pulled up sufficiently thin independently of the pipe diameter, and the pipe end face does not require flatness like the die top face. In particular,
In order to grow a fiber having a diameter as small as about 50 μmφ, it was possible to positively utilize a slight convex portion remaining on the end face of the pipe instead of the minute protrusion, the edge of the pipe attached at an angle. Also, instead of a pipe,
Other structures having a capillarity, such as superposition of platinum foil plates and twisted wires, are also available.

The material of the heating element and the pipe is a metal that does not chemically react with the raw material melt, has a melting point sufficiently higher than that of the raw material, and is not restricted as long as it is wet with the melt, and conversely,
Materials other than LiNbO ₃ can be applied as the crystal raw material as long as they meet the above conditions.

By the methods described above [Effect of the invention], in the case of LiNbO _3, directly from the single crystal fiber melt was reduced in diameter until a diameter of about 50Myuemufai, yet has become possible relatively easily grown. This method has a great technical and economic advantage over the conventional method. The heating element structure, which is the main part of the present invention, can have a wide range of structures satisfying the principle of the present invention, and the single crystal fiber to be grown can also have a diameter of 50 μmφ or less by improving the performance of the vertical drive mechanism. Moreover, it can be applied to a wide range of materials other than LiNbO ₃ that satisfy the growth conditions.

[Brief description of drawings]

FIG. 1 is a side view of a heating element structure according to an embodiment of the present invention,
FIG. 2 is an enlarged view of a platinum pipe portion during growth of a single crystal fiber according to the present invention, and FIG. 3 is a cross-sectional view of a fiber growth device associated with a heating element. In the figure, 1 is a platinum wire, 2 is a platinum wire twisted wire, 3 is a main heater part, 4 is a sub-heater part, 5 is a platinum pipe, 6 is a platinum thin wire, 7 is a minute protrusion, 8 is a heat-resistant material, and 9 is a growth material. A furnace, 10 is a vertical drive mechanism, 11 is a seed crystal, 12 is a raw material melt, 13 is a melt transported by capillary action, 14 is a heating element, 15 is a monitoring magnifying glass, and 16 is a power source.

Claims (1)

[Claims] 1. A molten liquid in which a minute projection is provided on a part of an upper end surface of a pipe having a capillary tube, and the pipe is erected at a part of an electric heating element at openings at both ends, and the crystal raw material is directly melted by the heating element. A method for producing a single crystal fiber characterized in that the surface of the heating element is wetted with, the melt is transported to the upper end of the pipe by a capillary phenomenon, and a part of the melt is pulled up at the minute protrusions.