JPH0419194B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for growing fiber-like single crystals from a melt.

[Conventional technology]

With the completion of ultra-low-loss silica glass fiber technology, high-density optical communication using optical fiber as a transmission medium has become a reality. If this fiber-forming technology can be developed into crystals of materials with large nonlinear optical effects and electro/acousto-optic effects, such as oxide ferroelectric crystals such as lithium niobate, and single crystal fibers can be grown, optical fibers can be produced. By combining the high optical field strength and long interaction length that are characteristic of crystals with the anisotropy of physical constants characteristic of crystals, unique optical effects can be expected, and the development of new devices is also expected.

For this purpose, advanced technology is required to grow crystals while reducing the diameter of high-melting materials, and currently the micropedestal method (for example, CABurruset
al., Appl. Phys. Lett. vol. 26, p. 318, 1975) is the only known one. However, since this method uses a CO ₂ laser as a heat source, it requires measures to stabilize the laser output and a complicated optical system to uniformly focus the laser light onto a microscopic area, making the equipment large and expensive. Moreover, it is necessary to prepare the crystal base material in advance into a uniform thin rod shape, and when growing the crystal, the diameter must be gradually reduced in several stages.
It is technologically advanced and complex, with non-uniformities in crystal diameters occurring at intermediate stages being carried into the final stage.

The pulling method (also called the Czyochralski method) is well known as a typical method for directly pulling crystals from a melt. (For example, P.
Hartman: Crystal Growth I, 212 pages, North
-Holl and Pub.Co., 1973) This method is aimed at growing large crystals, and the crystal base material is once melted in a crucible and then crystallized while being pulled up. This method generally uses high-frequency heating or resistance heating to set and control the thermal conditions for crystal growth.

[Problem that the invention seeks to solve]

However, with this method, there is an unavoidable time delay in temperature control, and the surface temperature of the melt changes in place and time due to heat convection of the melt in the crucible and air convection around the crucible. Since the temperature always fluctuates irregularly, it is impossible to arbitrarily and delicately control the temperature of a specific area of the melt surface. Therefore, the pulling method cannot be directly applied to growing single crystal fibers.

Another method for growing crystals from melt is the EFG method (Edge
There is also a technique called -defined film-fed growth). (For example, HE Labelle, Jr. et al.: Mat.
(Res. Bull. Vol. 6, p. 571, 1971) However, when this method is applied to single crystal fibers, there is a limit to the diameter reduction due to the structural restriction of the die having a capillary tube.

The present invention was made to solve the above-mentioned problems, and provides a technique that makes it possible to directly pull a target single crystal fiber from a melt of a crystal base material.

[Means for solving problems]

To this end, in the present invention, a heating element having minute convex portions formed on a part of its surface is prepared, the crystal matrix material is brought into contact with the heating element and melted, and the melt wetting the heating element is transferred to the convex portions. A method was taken to crystallize the material while pulling it up nearby.

[Effect]

By the means described above, the amount of melt is limited to a small amount, and since the melt wets the surface of the heating element, the temperature of the melt closely follows the temperature of the heating element, and by controlling the temperature of the heating element, the melting This has the effect of allowing fine control of the liquid temperature. Furthermore, there is a local cooling effect due to a decrease in electrical resistance and an increase in heat dissipation at the convex portion provided on the heating element, and effects such as concentration of melt and fixation of the pulling point due to the influence of surface tension are also produced. The combined effect of these factors has made it possible to grow fiber-like single crystals directly from the melt with relative ease.

〔Example〕

FIGS. 1a and 1b are a side sectional view and a partially enlarged view of the main parts of a typical embodiment of an apparatus showing the contents of the present invention. A vertical electric furnace for a fore heater 12 and an after heater 13 is installed in a lifting device equipped with two movable upper and lower drive shafts 9 and 10, and a heating element 1 according to the present invention is installed in the center thereof. The heating element 1 is formed by winding a platinum wire 2 with a diameter of 0.5 to 1.0 mmφ into a coil with 5 to 10 turns to a diameter of 3 to 10 mmφ, and a thin platinum wire 3 with a diameter of 0.1 to 0.3 mmφ is wrapped around a part of the upper end of the coil. It is made to protrude upward by 0.7 mm and welded to form a minute convex portion 4. The heating element 1 is heated by electricity, and the crystal matrix material 5 attached to the lower drive shaft 10 is brought into contact with it from below to melt it, and the heating element 1 is filled with melt 6 to wet the heating element 1 and the convex portion 4. . Next, the seed crystal 7 is freely attached to the drive shaft 9 of the pulling device via the chain 11 and lowered, and the tip of the seed crystal 7 wets the convex part 4 with the melt, or if the wetting is insufficient, the convex part The fiber crystal 8
The growth conditions are controlled at a growth rate of 0.5 to 2 mm/min while controlling the temperature. The growth temperature is controlled by the current applied to the heating element while observing the growth state, and the fiber is thermally stabilized at the desired fiber diameter. In order to continuously supply the crystal matrix material 5 to the heating element 1, the lower part of the heating element coil 1 is wound more closely to increase the temperature.

FIGS. 2 and 3 show another embodiment of the convex structure formed on the surface of the heating element. In addition to the above-mentioned thorn-like protrusions, the platinum wire 2 of the heating element has a diameter of 0.3 to 0.6 mmφ.
Similarly, a structure in which a convex portion is formed by winding one or two thin platinum wires 3 of about 100 mL (as shown in the second figure), and a structure in which a plurality of thin platinum wires 3 form a barb as shown in FIG. It is valid.

FIG. 4 shows another embodiment of the heat generating structure. If the size of the crystal fiber to be grown is within about 300 μmφ×100 mm, continuous supply of raw material melt is not required. At this time, the diameter is 0.3 as shown in Figure 4.
A conical basket-shaped heating element made of multiple stranded platinum wires 15 with a diameter of ~0.6 mm is particularly effective.
A crystal base material is filled into the basket, heated and melted, and then pulled up at a convex portion provided at the upper end of the basket. Note that twisting the platinum wires forming the heating element can be effectively applied in all cases.

As a heating method, in addition to the above-mentioned electrical heating, high frequency heating and infrared heating can also be applied, and there are no particular restrictions depending on these.

〔Effect of the invention〕

By the method described above, for LiNbO ₃ the diameter
Single-crystal fibers up to about 100 μm in diameter can be grown directly from the melt relatively easily, and there are no restrictions in principle on further reductions in diameter. Furthermore, metals other than platinum can be used for the material of the heating element, which is the main part of the present invention, and if the material of the crystal fiber to be grown does not chemically react with the heating element and its melt wets the heating element. There are no restrictions. Commercially available vertical electric furnaces can be used for the pulling device, fore heater, and after heater.

As a result of the above, it has become possible to grow a fiber-like single crystal directly from the melt with relative ease.

[Brief explanation of drawings]

Figures 1a and b are side sectional views and partially enlarged views of the main parts of a typical embodiment of the apparatus for explaining the method of the present invention, and Figures 2a and b are formed on a part of the platinum heating element. FIGS. 3a and 3b are cross-sectional views and side views of still another example of minute convex portions formed on a part of a platinum heating element, FIGS. 4a and 4b are a side sectional view and a partially enlarged view of a conical basket type heating element formed of multiple lines. In the figure, 1 is a heating element, 2 is a platinum wire forming the heating element 1, 3 is a thin platinum wire forming a convex portion, 4 is a minute convex portion formed by the thin platinum wire 3, 5 is a crystal matrix material, 6 is a melt, 7 is a seed crystal, 8 is a grown single crystal fiber, 9 is a pulling drive shaft, 10 is a drive shaft for supplying crystal base material, 11 is a chain, 12 is a fore heater, 13 is an after heater, 14 1 is a heating wire of the heater, and 15 is a platinum twisted wire.

Claims (1)

[Claims] 1 Form a minute convex part on a part of the heating element, heat and melt the crystal matrix material with this heating element, and pull up the melt while wetting the surface of the heating element with the melt, and remove the convex part of the heating element. 1. A method for growing a single-crystal fiber, characterized by crystallizing a melt in the vicinity of a shaped part.