JPS6347706A - Preparation of single crystal fiber - Google Patents

Abstract

PURPOSE:To permit direct prepn. of an objective single crystal fiber from the melt of a crystal base material by providing a microprojection to a part at the top end face of a pipe having a capillary, transferring the melt to the top end part of the pipe by capilarity and pulling up part of the melt in the microprojection. CONSTITUTION:The platinum pipe 5 is erected at approximately the center of a main heater 3. The microprojection 7 is formed on the cut face at the time of cutting out the pipe. Both sides of the pipes are held open and the pipe with the projection 7 faced upward is erected in substantial proximity to the groove of a twisted wire in such a manner that the bottom end of the pipe is dipped in the melt 12 when said melt wets the main heater 3 at the time of mounting the pipe. A raw material LiNbO3 is attached to the front end of a vertical driving mechanism 10 and is brought into contact with the main heater 3 by which the material is melted and the surface thereof is wetted. A seed crystal 11 which is LiNbO3 having a desired crystal orientation is then mounted in place of the raw material and the top end is brought into contact with the top end of the pipe so that said crystal is partly melted back to set the projection 7 and to fuse the melt thereof with the raw material melt 12 sucked by the capillarity. The temp. conditions are thereafter set at a desired fiber diameter and while the melt is puled up in the projection 7, the melt is crystallized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for growing an oxide material such as LiNbO3 directly from a raw material melt into an ultrafine fibrous single crystal with a diameter of 50 μm or less.

[Prior art] In recent years, "single crystal fiber" has been developed, which combines the pure and anisotropic physical properties characteristic of single crystals with the unique effects derived from their shape.
New uses of Nd crystalline materials have been proposed mainly in the optical field, and to date, Nd has been used with the aim of producing microsolid-state lasers:
Light waves traveling through thin waveguides such as single crystal fibers such as YA, Nd:Al2O3, and flexible infrared transmission paths are characterized by modes unique to the waveguides.
It has unique propagation characteristics such as high optical field density and strong interaction with the waveguide material. Therefore, if a single crystal fiber of nonlinear optical material can be fabricated, a large nonlinear effect can be generated within the fiber with low optical power. It is possible,
The fiber itself has a function. It is possible to create so-called functional fibers, and it is expected to be applied to a variety of new optical devices. For example, optical multiplication and optical mixing due to nonlinear optical effects promise the realization of compact visible short-wavelength lasers, and the production of single-crystal fibers from nonlinear optical materials is particularly eagerly awaited.

Conventionally, known production methods for the purpose of growing single crystal fibers include the extrusion method (T, J, Bridges et al.
al,: Opt, Lett, Vol, 5. p85
．． 1980), lowering method (Y, Mimura at
aL,: Jpn J, Appl, Phys, V
ol.

19, pL2G7.1980), E F G method (H
, E., Labelle, Jr.

et al,: Mat, Res, Bull, Vol, 6
．． p571. 1971), the pulling method (for example, P. Hartman: Crys
taL Grovfthl, p212. Nort
h-Ho1land Pub.

Co., 1973).

Among these, the extrusion method and the pull-down method are methods devised mainly for the purpose of growing infrared fibers, and the materials used generally have a low melting point, and the resulting fiber diameter is several too large.
-too μmφ and relatively thick.

The EFG method is a method of growing single crystals with specific shapes such as cylinders, cylinders, and prisms directly from melt.

It is characterized by using a die with a capillary tube.

That is, the lower end of the die is immersed in the raw material melt melted in the crucible, the melt is carried to the upper end surface of the die by capillary action, and the melt is pulled up while being defined by the edge of the upper end surface. Crystallize into shape.

'1972) The same micro-pulling method is particularly useful for LiNbO3 and LiTa.
This method was devised with the idea of turning O3 into fibers, and uses a heating element with microscopic protrusions to melt the raw material and wet its surface.
Single crystal fibers are grown by pulling up the melt on a microscopic scale at the projections. Up to now, fibers with diameters down to 100 μmφ have been grown.

The laser pedestal method is a method in which a laser beam is focused on the tip of a rod-shaped raw material to melt a microscopic area, and a seed crystal is immersed in the melt to perform microscale pulling. This method is applicable to a wide range of materials without contamination from crucible or die materials or limitations due to their melting points, and is particularly effective in converting high-melting-point materials into single-crystal fibers. Using this method, Nd:YAG and Nd:A can be used to create microsolid-state lasers.
Single crystal fibers such as l2O3 with a diameter of 35 to 250 μmφ, and LiN with a diameter of 20 μmφ aimed at nonlinear optical effects.
bO3's Phi No Ku- is being cultivated. (For example, Ah,
M, Fejer etal, :Rev, Sci, ■
nstrum, Vol. 55. p1791.198
4) [Problems to be Solved by the Invention] Single-crystal fibers intended to utilize nonlinear optical effects have technical difficulties regarding growth temperature and fiber diameter. Nonlinear optical materials such as LiNbO3 are generally oxides, and their single crystals are in an oxidizing atmosphere.

It is grown from a high-temperature molten liquid at a temperature of too many degrees Celsius or higher. In addition to platinum, there are only a few other materials for crucibles and dies that can be used under these growth conditions, and their use is severely restricted in terms of temperature range, workability, mechanical strength at high temperatures, corrosivity, etc. This greatly limits the methods for making fibers. Furthermore, since nonlinear optical fibers require single propagation modes and large nonlinear effects with low optical power, single crystal fibers with extremely small diameters of 50 μm or less are particularly required.

Until now, the only manufacturing method that can meet these demands has been the laser pedestal method. However, this method requires special equipment to stabilize the output of the laser, which is the heat source, and a complicated optical system to uniformly focus the laser light, making the equipment large-scale and economically expensive. be. On top of that,
It is necessary to prepare the crystal raw material in advance into a uniform thin rod shape,
When growing a crystal, it must be divided into several stages and the diameter must be successively reduced, and the non-uniformity of the diameter at intermediate stages is carried over to the final stage, requiring advanced and complex growth techniques.

Specifically assuming LiNbO3 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 likely that the pulling method and EFG method can be applied to fiber growth. However, E.F.
If you try to grow a thin single-crystal fiber with a diameter of 50 μm or less using the G method, you will have to process the upper end of the die to be as thin as the fiber diameter, and then drill a capillary tube through the die, which requires extremely sophisticated and fine processing. This requires advanced processing technology. Moreover, if the capillary tube becomes smaller than a certain degree, transport of the melt by capillarity is suppressed, and therefore the crystallization rate must be extremely slowed down. In such cases, especially when pulling small-diameter crystals, abnormal growth often occurs and the fiber shape is severely damaged (Onishi:
47th Japan Society of Applied Physics 28pG2, 1986), it becomes impossible to grow uniform fibers. On the other hand, in the pulling method, irregular temperature fluctuations always occur in place and time due to thermal convection of the melt in the crucible, and it is difficult to grow long single crystals on the micron scale without some kind of ingenuity. difficult.

Up to now, the simplest method for growing LiNb0z single crystal fibers is the micro-pulling method, with a diameter of 100 μm.
Single crystal fibers with diameters as small as φ can be obtained relatively easily. However, if we try to extend this method to single crystal fibers with a diameter of 50 μm or less.

Things become extremely difficult. In the pulling method, the diameter of the crystal grown usually depends on both the pulling speed and the melt temperature, but in the case of the micro-pulling method as well, the pulling speed is slow from a high-temperature melt with low viscosity, and from a low-temperature melt. From then on, the adhesion force that develops at a high pulling speed becomes dominant. This results in the formation of an abnormal solid-liquid interface that has not been experienced in conventional pulling methods, making it extremely difficult to control the shape and diameter of the growing crystal. Therefore, when the melt temperature is lowered and the viscosity is increased with the aim of improving controllability, the fluidity of the melt decreases and the supply of the melt is suppressed, causing the diameter of the fiber being grown to become thinner or cut. This makes it difficult to make the diameter uniform and make it longer. Ultimately, as the diameter becomes smaller, temperature conditions become more severe and fiber growth becomes more difficult.

The present invention has been made to solve the above-mentioned problem, and provides a new technique for directly producing the desired single-crystal fiber from a melt of a crystal base material.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the following measures were taken in the present invention. First, an energized heating element is made of twisted platinum wire, and a platinum pipe having a capillary tube is crystallized while being pulled up to a minute scale at the protrusion without being partially removed.

[Action Co. By utilizing wetness in the above means.

The melt is limited to a small amount, suppressing thermal convection, or irregular temperature fluctuations caused by it, and since the liquid 7a and the heating element are in close contact, the temperature of the melt is equal to the temperature of the heating element.

It is now possible to sensitively track the temperature of the melt and make delicate adjustments to the temperature of the melt by controlling the current flowing through the heating 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, allowing the viscosity of the melt to be selected quite freely. As a result, the growing conditions were relaxed. The protrusion provided on the upper end surface of the pipe not only concentrates the melt there, promotes the heat dissipation effect, etc. Figure 2 shows an enlarged view of the platinum pipe during fiber growth. Diameter 0
．． 4-0.7! A platinum stranded wire 2 of about 25c1 is formed on a platinum wire of lllTlφ, and the middle part 5-9 is used straight as the main heater 3, and the remaining platinum stranded wires at both ends are vertically connected to the top and bottom of the main heater 3, respectively. A structure is adopted in which the subheater 4 is formed by winding it into a coil shape. Approximately in the center of the main heater 3 is an outer diameter of 200 μmφ and an inner diameter of 100 μmφ.
A platinum pipe 5 with a length of about 500 μm is tied up with a thin platinum-gold wire 6 and set up. When cutting the pipe, make a cut leaving a part of one circumference, and by pulling and cutting it, a minute protrusion 7 (shown in the second figure) is formed on the cut surface, and the upper and lower parts have the same cutting speed as the pipe. It was added to the drive mechanism 10.

Next, specific growth of single crystal fiber will be explained below. First, the raw material L1Nbo3 is attached to the tip of the vertical drive mechanism 10, and the main heater 3 is heated with electricity.
melt on contact and wet the surface. Next, a seed crystal 11 of LiNbO3 having a desired crystal orientation is used instead of the raw material.
is attached, and its tip is brought into contact with the upper end surface of the pipe, and a portion thereof is melted back to wet the protruding portion 7 and fuse with the raw material melt 12 sucked up by capillary action. After that,
The temperature conditions were set to a desired fiber diameter, and the fiber was crystallized while being pulled up at the protrusion 7.

In this manufacturing method, the fiber diameter can be made sufficiently thin completely independently of the pipe diameter, and the edges of the pipe, which are attached to the EFG method, are rather actively modified by overlapping metal foil plates, twisting wires, etc., and using capillary effects. Other structures with .

The materials for the heating element and pipes are not subject to any restrictions as long as they do not chemically react with the raw material melt, have a sufficiently higher melting point than the raw material, and can be wetted by the melt.
As the crystal raw material, materials other than LiNbO3 can be used as long as they meet the above-mentioned conditions.

[Effect of the invention] By the above method, in the case of LiNbO3, a diameter of 50 μm
Single-crystal fibers with a diameter as small as φ can now be grown directly from the melt, and relatively easily. This method has significant technical and economical advantages over conventional methods. The heating element structure, which is the main part of the present invention, can have a wide range of structures that satisfy the principles of the present invention, and the single crystal fiber grown also improves the performance of the vertical drive mechanism.
It is thought that it is possible to reduce the diameter to 50 μm or less, and it is also applicable to a wide range of materials other than t'6' L 1Nbo3 that satisfy the growth conditions.

(blank below)

[Brief explanation of the drawing]

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 sectional view of a fiber growth apparatus associated with a heating element. In the figure, 1 is a platinum wire, 2 is a platinum wire strand, 3 is a main wire,
4 is a part of the sub-heater, 5 is a platinum mirror, and 16 is a power source. Figure 1 2vA

Claims (1)

[Claims] A small protrusion is provided on a part of the upper end surface of a pipe having a capillary tube,
A part of the heating element is erected at both ends of the pipe, and the crystal raw material is directly melted by the heating element, the surface of the heating element is wetted with the melt, and the melt is applied to the upper end of the pipe by capillary reduction. A method for producing a single-crystal fiber, characterized by transporting the melt to a part and pulling up a part of the melt at the minute protrusion.