JP3048740B2 - Single crystal growth method and single crystal growth furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single crystal growing method and a single crystal growing furnace for growing an organic material such as a nonlinear optical element in a capillary in a single crystal.

[0002]

2. Description of the Related Art Recently, 2-methyl-4-nitroaniline (M
Optical waveguides such as thin film waveguides and optical fiber waveguides made of organic nonlinear optical materials such as NA) have been developed.

[0003] Such a nonlinear optical element can convert the writing wavelength of an optical disk from 780 nm to 390 nm, for example, and can improve the writing efficiency. In particular, the optical fiber type has a high optical energy. The use of a Cerenkov-type phase matching that can obtain a density enables phase matching to be performed relatively easily, and has the advantage that a large crystal is not required.

As a single crystal growth method for such an optical fiber waveguide, there are a conventional Bridgman-Stockberger method, a reverse Bridgman-Stockberger method, a zone melt method and the like. In such a single crystal growth method, a melt of a non-linear optical material such as MNA melted in a heating furnace is introduced into a glass capillary having a length of, for example, about 10 cm using capillary action, and the capillary is pulled up (down). ) While cooling, the nonlinear optical material is crystallized. Here, a temperature gradient in a pulling (down) direction required for single crystal growth is formed where the capillary exits the heating furnace.

[0005]

However, the optical fiber waveguide obtained by the conventional single crystal growth method is
1) The orientation of the crystal is not oriented so that an effective nonlinear susceptibility can be used. 2) The quality of the crystal is poor. 3) The selection of the cladding material is poor. Is being avoided by refining the material and computer calculation, but it was difficult to control the crystal orientation in 1). That is, the organic non-linear optical materials used for optical fiber waveguides are mainly low-molecular organic materials, and these organic materials easily crystallize in a specific direction in the capillaries constituting the cladding. The orientation is not effective for wavelength conversion. For this reason, there is a method of controlling the orientation by applying an electric field with a slab-type electrode during the crystal growth. However, this method does not provide satisfactory results such as an increase in the size of the apparatus and poor probability.

A fiber in which an MNA core 11 is formed on an elliptical capillary (cladding) 100 having an elliptical hole as shown in FIG. 6 has also been proposed (Electron).
Letter 10 (22), P.449 (1974), J. Cryst.
7, P.116 (1977)). In this method, the crystal orientation is controlled by utilizing the temperature gradient caused by the difference in the thickness of the clad glass, but it is difficult to obtain a fiber having a preferable diameter, in which both the core and the clad are not circular. There is a disadvantage that it is.

[0007] The present invention solves such conventional difficulties,
It is an object of the present invention to provide a single crystal growth method capable of easily controlling a crystal orientation and producing a crystal core fiber having a desired diameter and shape. Another object of the present invention is to provide a single crystal growth furnace to which such a single crystal growth method is applied.

[0008]

According to the single crystal growth method of the present invention which achieves the above object, a single crystal is grown while introducing an organic material into a capillary in a heating furnace or by moving the heating furnace or the capillary after the introduction. In the method for growing a crystal,
The relative traveling direction of the capillary is inclined with respect to the side surface of the heating furnace.

Further, the single crystal growth furnace of the present invention has a hole through which a crystal material passes, two heating means provided with the hole interposed therebetween, each of which can be set to a different temperature, and And a heat-resistant spacer for separating the means.

[0010]

A temperature gradient is formed in a direction (sectional direction) orthogonal to the axial direction of the capillary by heating two heating means provided with a hole through which a crystal material passes through to different temperatures. . The capillary is regulated by this temperature gradient, the crystal orientation is controlled, and by moving the capillary so as to be inclined with respect to the side of the heating furnace, the temperature gradient at the end face of the heating furnace is formed oblique to the capillary. Is done. Thus, the crystal orientation is controlled by the temperature gradient inclined with respect to the wall surface of the capillary.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the single crystal growth method of the present invention will be described below in detail with reference to the drawings.

FIGS. 1 to 3 show a single crystal growth furnace 1 by a horizontal Bridgman-Stockberger method to which a single crystal growth method of the present invention is applied, through which a capillary 2 containing a crystal material such as an organic optical material passes. The organic material in the capillary 2 is cooled and solidified from one end of the heating furnace 1 to form a single crystal by moving either the heating furnace 1 or the capillary 2. Here, a temperature gradient as shown in FIG. 1 is formed at the outlet of the heating furnace, whereby a single crystal grows.

The organic material is appropriately selected depending on the single crystal to be produced. Examples of the organic nonlinear optical material include 2-methyl-4-nitroaniline (MNA), 4-dimethylamino-4'-nitrosostilbene (DAN), Piperonylidene cyano acetate (PCA-ethly), 3
-Methyl-4-nitropyridin-1-oxide (PO
M), 4'-dimethylamino-N-methyl-4-stilbazolium methyl sulfate (DMSM) and the like are used.

The capillary 2 is made of a cladding material such as quartz or glass and has a hole having a circular cross section.

The heating furnace further comprises a set of copper blocks 5, 5 'incorporating heaters 4, 4' as shown in FIGS.
Interposes two heat-resistant spacers 6 to form the capillary 2
Are fixed so as to form a hole 3 for moving. The heaters 4 and 4 'of the copper blocks 5 and 5' can be set to different temperatures by a power supply circuit (not shown), and a temperature gradient is formed between the copper blocks 5 and 5 'as shown in FIG. You. The heat-resistant spacer 6 can be made of a metal such as a ceramic plate, a Teflon sheet, copper, or stainless steel. When the melting point of the organic material is high, for example, in the case of DAN having a melting point of about 180 ° C., the spacer 6 is made of a metal such as copper or stainless steel having a high thermal conductivity in order to obtain a temperature gradient between the copper blocks 5 and 5 ′. It is preferable that the copper block 5
A hole may be provided between the 5's to increase the cooling effect through gas or liquid to form a larger temperature gradient.

In order to monitor the temperature near the center of the hole 3, between each copper block 5, 5 'and the heater 4, 4', as shown in FIG. A thermocouple 7 is provided. It is desirable that two thermocouples 7 are provided for each of the copper blocks 5, 5 ', one for temperature control and one for monitoring. It is desirable that such a heating furnace 1 be provided with a heat insulating cover (not shown) on the outside.

In such a configuration, the organic material is heated and melted in the heating furnace 1 and introduced into the capillary 2, and the single crystal of the organic material is formed in the capillary 2 while moving the capillary 2 at a predetermined speed. Let it grow. On this occasion,
At the tip of the capillary 2 on the moving side, there is a region having a temperature gradient where the capillary 2 exits the heating furnace 1, and single crystal growth is promoted in this region. on the other hand,
In the heating furnace 1, there is a temperature gradient in the cross-sectional direction of the capillary 2.
If so, control is performed so that [001] is oriented in the Z direction (the direction of crystal growth).

Next, another embodiment of the present invention will be described.

FIGS. 4 and 5 are views showing a crystal growth furnace 10 to which the single crystal growth method of the present invention is applied. The crystal growth furnace 10 shown in the drawing has substantially the same configuration as the crystal growth furnace of FIGS. 1 to 3, and a set of copper blocks 50, 50 ′ containing heaters 40, 40 ′ has two sets. The capillaries 20 are fixed so that the holes 30 through which the capillaries 20 move are formed with the heat-resistant spacer 60 interposed therebetween. A temperature sensor 70 similar to the heating furnace of FIG.
Is provided. For the copper blocks 50 and 50 ', the heaters 40 and 40', the spacer 60, and the temperature sensor 70, those having the same material and configuration as those used in the crystal growth furnace 1 can be used.

The hole 30 formed by the spacer 60
Is inclined at a predetermined angle θ with respect to an axis 10b orthogonal to the side surface 10a of the heating furnace 10, as shown in FIG. Is preferably about 10 ° to 40 °. The above-mentioned crystal material such as the above-mentioned organic optical material is introduced into the capillary 20, and either the heating furnace 10 or the capillary 20 is moved to cool and solidify the organic material in the capillary 20 from one end of the heating furnace 10 to form a single crystal. I do. Here, a temperature gradient similar to the temperature gradient shown in FIG. 1 is formed at the outlet of the heating furnace, but the hole 30 through which the capillary 20 moves is inclined with respect to the side surface 10a of the heating furnace 10 as described above. Therefore, the crystal material in the capillary 20 passes through the portion of the temperature gradient while the elliptical surface crosses the portion. That is, a plane perpendicular to the temperature gradient is an ellipsoid. Therefore, the same effect as when an elliptical capillary having an elliptical hole is used is obtained, and the orientation of the crystal along the temperature gradient is controlled, and a single crystal grows.

In such a configuration, the capillary 20
Is moved, strings of aramid fiber or the like are connected to both ends of the capillary 20, and a certain weight is applied to one of the strings, for example, and a certain tension is applied to the other string. At a speed of, for example, 1 to 10 mm / hour to move the capillary 20 horizontally. The furnace temperature of the heating furnace 10 may be controlled separately for the upper limit block, or may be set to the same temperature. In any case, the furnace temperature is set higher than the melting point (Tm) of the material, but is preferably set to Tm + 10 ° C. or lower so as not to be too high.

In the above description, the horizontal bridgeman
Although described based on the Stockberger method, the single crystal growth method of the present invention can be applied to other known single crystal growth methods such as the reverse Bridgman-Stockberger method and the zone melt method.

Example 1 Each of the vertical and horizontal lengths is 10 cm, and the thickness is 2.4 cm.
2mm thick copper block with built-in silicon heater
The heat furnace shown in FIG. 2 was manufactured by stacking the heat-resistant plates described above so that a 2 mm square hole was formed therebetween. As the heat-resistant plate, a ceramic plate and Teflon were used. On the other hand, the capillary has an outer diameter of 1 mm, an inner diameter of 30 μm, and a length of 10 mm.
A capillary made of a pure quartz tube of cm was used, and MNA was used as an organic nonlinear optical material.

The temperature of the upper block of the heating furnace is set to 130
The temperature of the lower block was set to 120 ° C., and the crystal was grown at a growth rate of 1 to 20 mm / hour to grow a single crystal.

When X-ray analysis was performed on the crystal core fiber manufactured as described above, 50% or more of the samples showed M
The NA of [001] and the fiber axis were parallel within several degrees.

A crystal core fiber was prepared by changing the inner diameter and material of the capillary to DAN, and the same X-ray analysis was performed. The same result was obtained.

Example 2 Two copper blocks with built-in silicon heaters each having a length of 10 cm and a width of 10 cm, and a thickness of 5 cm were prepared with a thickness of 1.2 mm.
The heat-resistant plates shown in FIG. 4 were stacked on top of each other so that a 1.2 mm square oblique hole was formed therebetween. The angle θ between the hole and the heating furnace axis is 0 °, 10 °, 20 °,
30 ° and 40 ° were manufactured respectively. On the other hand, a capillary made of borosilicate glass having an outer diameter of 1 mm, an inner diameter of 1 μm, and a length of 10 cm was used as a capillary, and MNA was used as an organic nonlinear optical material. Kevlar (trade name, aramid fiber) was attached to both ends of the capillary, and was moved in a heating furnace by a motor to grow a single crystal.

The temperatures of the upper and lower blocks of the above-mentioned heating furnace are separately controlled, and each is 5 ° C. higher than the melting point Tm.
The temperature was set at 0 ° C., and the crystal growth rate was 1 mm / hour.

Observation with a polarizing microscope on the crystal core fiber manufactured as described above revealed that the crystal orientation changed according to the angle of the spacer when the angle was given as compared with the case where θ was 0 °. Was confirmed.

[0030]

As is clear from the above embodiments, according to the single crystal growth method and the single crystal growth furnace of the present invention, the heating furnace is inclined by inclining the moving direction of the capillary with respect to the side of the heating furnace. The elliptical surface of the capillary passes through a portion of the outlet where the temperature gradient is present, so that the crystal orientation can be controlled. Further, according to the single crystal growth method of the present invention, it is possible to easily obtain a nonlinear optical element whose crystal orientation is controlled and which has a high nonlinear susceptibility by a conventional manufacturing apparatus.

[Brief description of the drawings]

FIG. 1 is a plan view showing one embodiment of a single crystal growth furnace to which a single crystal growth method of the present invention is applied, and a graph showing a temperature gradient in a moving direction.

FIG. 2 is a cross-sectional view showing the single crystal growth furnace of FIG. 1 and a graph showing a temperature gradient in a direction orthogonal to a moving direction.

FIG. 3 is an exploded perspective view of the single crystal growth furnace of FIG.

FIG. 4 is an exploded perspective view showing another embodiment of the single crystal growth furnace to which the single crystal growth method of the present invention is applied.

FIG. 5 is a plan view of the single crystal growth furnace of FIG.

FIG. 6 is a sectional view of a conventionally used capillary.

[Explanation of symbols]

 1, 10 ... heating furnace (single crystal growth furnace) 2, 20 ... capillary 4, 4 ', 40, 40' ... heater (heating means) 5, 5 ', 40, 40' ... block (heating means) 6, 60 ... spacer

Claims (2)

(57) [Claims] 1. A method for growing a single crystal in a capillary by moving one of the heating furnace and the capillary while introducing or after introducing an organic material into the capillary in the heating furnace, wherein A single crystal growing method, wherein a relative traveling direction is inclined with respect to a side surface of the heating furnace. 2. A hole through which the crystal material passes, and a hole provided between the hole and which can be set at different temperatures.
A single crystal growth furnace, comprising: two heating means; and a heat-resistant spacer for separating the two heating means.