JPS62182188A - Process for growing single crystal fiber - Google Patents

Abstract

PURPOSE:To enable direct and ready growth of a single crystal fiber from molten liquid, by contacting a crystal matrix to a heater having a minute protrusion at a part of the surface and pulling up the molten liquid formed near the protrusion to effect the crystallization of the material. CONSTITUTION:A platinum wire 2 is wound to a coil of 5-10 turns to form a heater 1. A thin platinum wire 3 is welded to a part of the upper end of the coil in a manner slightly protruded from the top upward to form a minute protrusion 4. The heater 1 is heated by electric current and a crystal matrix 5 attached to a lower driving shaft 10 is made to contact with the heater 1 from beneath until the heater 1 and the protrusion 4 is wet with the molten liquid 6 filled in the heater 1. A seed crystal 7 freely attached to a driving shaft 9 of a pulling-up device through a chain 11 is lowered until the tip of the crystal is brought into contact with the molten liquid wetting the protrusion 4 to effect partial melting of the seed crystal. The crystal is pulled up at a prescribed growth rate while controlling the temperature to the condition for the growth of a fiber crystal 8. In order to continuously supply the crystal material 5 to the heater 1, the lower part of the heater coil 1 is wound at higher winding density to raise the temperature at the lower part.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for growing a fiber l-shaped single crystal 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.・Crystals of substances with large acousto-optic effects,
For example, if a single crystal fiber can be grown by developing an oxide ferroelectric crystal such as lithium niobate, it would be possible to combine the high optical field strength and long interaction length that are characteristic of optical fibers with the physical property constants unique to crystals. With the addition of directionality, 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 substances.
p 7t, law (e.g., C, A, BurruSet
al,, Appl, Ph1s, Lett, 2
Vol. 6, p. 318, 1975) is the only known publication. However, since this method uses a C(h laser) as a heat source, it requires measures to stabilize the laser output and a complicated optical system to uniformly focus the laser beam onto a microscopic area, making the equipment large and expensive. In addition, it is necessary to prepare the crystal matrix material in advance into a uniform thin rod shape, and during crystal growth, the diameter must be gradually reduced over several stages, and in addition, non-uniformity of crystal diameter at intermediate stages. is brought to the final stage, etc.
Technically advanced and complex.

The pulling method (also called the Czochralski method) is well known as a typical method for directly pulling crystals from a melt. (For example, P.

Hartman: Crystal Growth
I, page 212, North-Hollzna
Pub, Co., 1973) This method is aimed at growing large crystals, and involves once melting a crystal matrix material in a crucible and crystallizing it while being pulled up. This method generally uses high-frequency heating or resistive heating, which sets and controls the thermal conditions for crystal growth.

[Problem that the invention attempts to solve]

However, with this method, there is an unavoidable time delay in temperature control, and the surface temperature of the melt varies depending on location and time due to heat convection of the melt within 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 (Edg, e-define), which transports the melt to the upper end surface of the die by capillary action and pulls up a crystal with the same cross-section as the upper end surface.
There is also a device called d Film-fed Growth). (e.g. H, E, Labelle, J.
r, etal, : Mat, Res, Bull
, Vol. 6, p. 571, 1971) However, when this method is applied to a single crystal fiber, 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 with the aim of solving 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]

For this purpose, in this Qll, we prepare a heating element with a minute convex part formed on a part of its surface, bring the crystal base material into contact with this heating element and melt it, and the melt that wets the heating element is shaped into a convex shape. A method was taken to crystallize the material while pulling it up in the vicinity of the part.

[Effect]

By the above-mentioned means, the amount of melt is limited to the evening view, and since the melt wets the surface of the heating element, the melt temperature closely follows the temperature of the heating element. This has the effect of allowing fine control of the liquid temperature. Furthermore, there is a local cooling effect due to a reduction in electrical resistance and an increase in heat dissipation at the convex part provided on the heating element, as well as effects such as concentration of melt and fixation of the pulling point due to the influence of surface tension. Due to the comprehensive action of these factors, it has become possible to grow a fibrous single crystal directly from the melt with relative ease.

〔Example〕

FIG. 1 (αL (b) is a side sectional view and partially enlarged view of the main parts of a typical embodiment of the device expressing the content of the present invention. Two movable upper and lower drive shafts 9 and 10 are shown. A vertical electric furnace for the fore-heater 12 and the after-heater 13 is installed in the pulling device, and the heating element 1 according to the present invention is installed in the center of the furnace.The heating element 1 has a diameter of 0.5 to 1.
．． 0fiφ platinum wire 2 with a diameter of 3~10111jII-φ
A fine platinum wire 3 with a diameter of 0.1 to 0.3 mm is attached to a part of the upper end of the coil.
-0.7 degrees of upward protrusion and welding to form minute convex portions 4. A heating element 1 is heated by electricity, and a lower drive shaft 10 is attached to it.
The crystal matrix material 5 attached to the crystal base material 5 is brought into contact with it from below and melted.
The heating element 1 is filled with the 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 is brought into direct contact with a platinum wire and partially melted (melted back), and the fiber is pulled up at a growth rate of 0.5 to 2 min/min while controlling the temperature to meet the crystal growth conditions.

The growth temperature is controlled by one current applied to the heating element while observing the growth state, and the fiber is thermally stabilized at a 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 projections, there is a structure in which a platinum thin wire 3 with a diameter of about 0.3 to 0.6 ysφ is wound once or twice around the platinum wire 2 of the heating element to form a convex part (as shown in the second figure).
, and a structure in which a plurality of thin platinum wires 3 form barbs as shown in FIG. 3 are similarly effective.

FIG. 4 shows another embodiment of the heating element structure. If the dimensions of the crystal fiber to be grown are within the order of 300μ stirring diameter×100mm, continuous supply of the raw material melt is not required. At this time, a conical basket-shaped heating element formed of multiple twisted platinum wires 15 with a diameter of 0.3 to 0.6 φ as shown in Fig. 4 is particularly effective, and the heating element is filled with a crystal matrix material. The material is heated and melted, and then pulled up through 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.

In addition to the above-mentioned electrical heating, heating methods include high-frequency heating,
Infrared heating can also be applied, and there are no particular restrictions imposed by these.

〔Effect of the invention〕

By the method described above, in the case of LiNbO3, a diameter of 100
Single-crystal fibers up to about μmφ can be grown directly from the melt relatively easily, and there are no restrictions in principle on further reduction 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, foreheater, and afterheater.

As described above, it has become possible to grow a fibrous single crystal directly from a melt with relative ease.

[Brief explanation of drawings]

FIG. 1(eL), <b) is a side sectional view and partially enlarged view of the main parts of the device of a typical embodiment of the present invention, which will not be described in detail, and FIG. 2(tL), (b) is a partial enlarged view. A cross-sectional view and a side view of another embodiment of a minute convex portion formed on a part of a platinum heating element, and FIGS. A sectional view and a side view of still another embodiment, and FIGS. 4(cL) and 4(b) 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, and 3
5 is a crystal matrix material; 6 is a melt; 7 is a digit crystal; 8 is a grown single-crystal fiber; 9 is a thin platinum wire forming a convex portion; 1 is a pulling drive shaft, 10 is a drive shaft for supplying crystal base material, 11 is a chain, 1 is
2 is an after-heater, 13 is an after-heater, 14 is a heating wire of the heater, and 15 is a platinum stranded wire. , ゛－－゛－ ：・ -一り一會□Direction 1 Figure 1 Title Chidoine
8 ￥Ni: f1 fτ droplet fin 5 l-) f iba 7 r,
Fin & 14 Engagement Black Fig. 2 (a) (b) Fig. 3 2: 屓≦茨久NET y 4 Growing mortar 4 tip 8 艮 3: Convex part Σ formation 7 Loop base 6 Day gap 4th Figure 15.

Claims (1)

[Claims] A minute convex part is formed on a part of the heating element, the crystal base material is heated and melted by this heating element, the surface of the heating element is wetted with the melt, and the area near the convex part formed on this heating element is 1. A method for growing a fibrous single crystal, which comprises crystallizing the melt while limiting the solidification point and pulling the melt.