JPH06230233A - Production of single crystal optical fiber and its apparatus - Google Patents

Abstract

PURPOSE:To provide the process and apparatus for production of the single crystal optical fiber having decreased crystal defects and excellent light transmission characteristics. CONSTITUTION:The part near the solid-liquid boundary of a heated and molten part 11 and the single crystal optical fiber 9 is heated to the temp. below the m.p. of the single crystal optical fiber 9 by a part of a laser beam 7 to be used for heating and melting or another laser beam, thereby, the temp. distribution of the solid-liquid boundary is uniformalized and the rapid cooling of the grown single crystal optical fiber 9 is released in the process for production of the single crystal optical fiber 9 by heating and melting a base material with the laser beam 7, bringing a seed crystal into contact with the base material and moving the seed crystal together with the base material in the same direction. As a result, the good-quality single crystal optical fiber 9 having the decreased crystal defects and the excellent light transmission characteristic is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for manufacturing a single crystal optical fiber used for optical signal processing or storage elements.

[0002]

2. Description of the Related Art FIG. 2 is an explanatory view showing a conventional method for manufacturing a single crystal optical fiber. In the figure, an upper portion of a base material 2 which is a raw material of a single crystal optical fiber is heated by a heating laser beam 1 to form a fusion zone 5. Next, after adhering the seed crystal 4 to the melting part 5, the seed crystal 4 is moved upward and the base material 2 is also moved in the same direction, whereby the single crystal optical fiber 3 is manufactured. Here, assuming that the moving speed of the base material is V ₁ , the moving speed of the seed crystal is V ₂ , and the diameter of the base material is D ₁ , the diameter D ₂ of the single crystal optical fiber to be produced is It is represented by a formula. D ₂ = D ₁ × √ (V ₁ / V ₂ ) ... (Equation 1) Therefore, by adjusting the moving speed V ₂ of the seed crystal and the moving speed V _{1 of the} base material, single crystal light having a desired diameter can be obtained. Fibers can be made. Further, the crystal orientation of the single crystal optical fiber 3 matches the crystal orientation of the seed crystal 4, and the composition becomes almost the same as the composition of the base material 2. In this conventional method for producing a single crystal optical fiber, the temperature around the fusion zone 5 is about room temperature. On the other hand, the temperature of the fusion zone 5 is equal to or higher than the melting point of the base material, and for example, S produced by this method is used.
155 in the case of BN (Sr _0.6 Ba _0.4 Nb ₂ O ₆ ) crystal
It will be over 0 ℃. Therefore, the produced single crystal optical fiber 3 is rapidly cooled in the process of solidifying from the fusion zone 5,
There is a problem that strain occurs in the crystal. Further, in the vicinity of the solid-liquid interface where the single crystal optical fiber 3 is formed from the fusion zone 5, the temperature is higher toward the center and a temperature gradient is generated in the radial direction of the single crystal optical fiber 3, so that the optical fiber to be produced is produced. There was a problem in that the cooling rate was different in the radial direction, and strain also occurred in the crystal due to this. The diameter of the single crystal optical fiber 3 manufactured by this method is about 0.1 to 1 mm, but the above problem becomes larger when a single crystal optical fiber having a larger diameter is manufactured, and the conventional diameter is 0 mm. .5 mm
In the above cases, a good quality single crystal optical fiber could not be obtained. That is, the strain in the optical fiber single crystal generated during the cooling process appears as a crystal defect such as a dislocation and significantly deteriorates the light transmission characteristics. As a conventional technique, for example, US Pat. No. 4,421,721 can be cited.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method for producing a single crystal optical fiber having few crystal defects and excellent light transmission characteristics, and a method thereof. To provide a device.

[0004]

In order to achieve the above object of the present invention, one end of a base material of a single crystal optical fiber is heated and melted by laser light, and a seed crystal is brought into contact with the heated and melted portion, In the method of manufacturing a single crystal optical fiber by moving the base material in the direction of the seed crystal and moving the seed crystal in the same direction as the base material, a part of the laser light or a laser different from the laser light is used. The light is used as a heating source different from that for forming the heating / melting section, and the vicinity of the solid-liquid interface between the heating / melting section and the single crystal optical fiber is set to a temperature below the melting point at which the grown single crystal optical fiber does not melt. By heating, the temperature distribution in the vicinity of the solid-liquid interface is made uniform, and the step of reducing the rapid cooling of the grown crystal is included. In the conventional method for manufacturing a single crystal optical fiber,
The heating laser light is used only for melting the base material, and no other heating source is used. On the other hand, in the method for manufacturing a single crystal optical fiber of the present invention, a part of the heating laser light or another laser light is used. Laser light is used as a heating source different from the heating source for melting the base material to make the temperature distribution at the solid-liquid interface uniform and suppress the generation of strain due to rapid cooling of the single crystal optical fiber. Is.

[0005]

1 is a schematic view showing an example of the structure in the vicinity of a crystal growth chamber of an apparatus for producing a single crystal optical fiber according to the present invention.
In the figure, the heating laser beam 7 introduced into the crystal growth chamber 6 is a donut-shaped mirror 12 having an angle of 45 degrees.
Mirror 1 which is reflected in the upward direction and is arranged concentrically
Incident on 3 and 14. Here, the heating laser light 7 may be light from one laser light source, or light from two or more laser light sources may be coaxially arranged. For example, the laser light incident on each of the mirror 13 and the mirror 14 may be light from different laser light sources. The mirror 13 has a parabolic surface, and the laser light reflected by the mirror 13 heats and melts the upper portion of the base material 8. After adhering the seed crystal 10 to the fusion zone 11, the seed crystal 10 is moved at a speed V ₂ and the base material 8 is moved at a speed V ₁ , whereby the single crystal optical fiber 9 is manufactured. The diameter D ₂ of the single crystal optical fiber 9 is determined by the equation (1) described above. On the other hand, the laser light reflected by the mirror 14 irradiates the vicinity of the solid-liquid interface between the fusion zone 11 and the single crystal optical fiber 9. The laser light reflected by the mirror 14 is weaker than the laser light reflected by the mirror 13, and the mirror 14 has an elliptical surface.
It is not as focused as the laser light reflected by 3. Therefore, it is possible to heat to a temperature at which the vicinity of the solid-liquid interface does not melt, and the temperature distribution is kept uniform. Therefore, rapid cooling of the manufactured optical fiber is suppressed, and the cooling rate in the radial direction of the single crystal optical fiber 9 can be made uniform. Next, specific examples will be described. C
SBN (Sr _0.6 ) doped with 0.02 wt%
Using a Ba _0.4 Nb ₂ O ₆ ) crystal as a base material, a single crystal optical fiber was produced using the above-described apparatus for producing a single crystal optical fiber of the present invention. A CO ₂ laser was used as the heating laser beam 1, and the number of light sources was one. The pulling shaft of the optical fiber was a-axis, the pulling speed was 0.5 mm / min, the diameter was 0.5 mm, and the length was 5 cm. The obtained SBN
The crystal defects of the single crystal optical fiber were measured by micro X-ray topography, but no crystal defects could be detected. The SBN crystal has a photorefractive property in which the refractive index changes by light irradiation, and can be used as a hologram recording medium by using this. Here, the produced SBN single crystal optical fiber was evaluated as a hologram recording medium. The produced optical fiber was cut into a length of 5 mm, both end faces were polished, and then the optical fiber was mounted on a hologram recording / reproducing system using an Ar laser (wavelength 514.5 nm) to evaluate the recording / reproducing characteristics. As a result, the diffraction efficiency of the hologram is 10% or more, and the reproduction resolution of the recorded image is 100 lp / mm (line pair / mm).
Met. On the other hand, the SBN single crystal optical fiber produced by the conventional apparatus for producing a single crystal optical fiber has a diffraction efficiency of about 10%, but the reproduction resolution is about 10 lp / mm. It was found that the reproduction resolution of the single crystal optical fiber manufactured in the example was significantly improved. This indicates that the single crystal optical fiber thus produced had few crystal defects and was excellent in uniformity without being repaired. Further, although the SBN single crystal optical fiber has been described in the above-mentioned embodiment, by using the single crystal optical fiber manufacturing apparatus of the present invention, for example, potassium niobate, lithium niobate, KTN (KTa _1-x Nb) can be obtained.
_x O ₃ ), YAG, Al ₂ O _{3 and} other oxide optical crystals, and Nb
Alternatively, it can be easily inferred that the method and apparatus for producing a single crystal optical fiber of the present invention is also used to improve the quality of a single crystal fiber made of a Cu-based oxide superconducting material.

[0006]

As described above, according to the method and apparatus for manufacturing a single crystal optical fiber of the present invention, a good quality single crystal optical fiber having few crystal defects and excellent light transmission characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic view showing a configuration in the vicinity of a crystal growth chamber of a manufacturing apparatus for a single crystal optical fiber illustrated in an embodiment of the present invention.

FIG. 2 is a schematic view showing a conventional method for manufacturing a single crystal optical fiber.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Laser light for heating 2 ... Base material 3 ... Single crystal optical fiber 4 ... Seed crystal 5 ... Melting part 6 ... Crystal growth chamber 7 ... Laser light for heating 8 ... Base material 9 ... Single crystal optical fiber 10 ... Seed crystal 11 … Melting part 12, 13, 14 ・ ・ ・ Mirror D ₁・ ・ ・ Diameter of base material D ₂・ ・ ・ Diameter of needle-like single crystal V ₁・ ・ ・ Movement speed of base material V ₂・ ・ ・ Movement speed of seed crystal

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yokohama To Chiyoda-ku, Tokyo 1-6, Uchisaiwaicho Nihon Telegraph and Telephone Corporation

Claims (2)

[Claims] 1. A single crystal optical fiber, wherein one end of a base material is heated and melted by laser light, and a seed crystal is brought into contact with the heated and melted portion,
Along with moving the base material in the direction of the seed crystal, in the method for producing a single crystal optical fiber by moving the seed crystal in the same direction as the base material, a part of the laser light used for the heating and melting, or By using a laser beam different from the laser beam used for heating and melting, the vicinity of the solid-liquid interface between the heating and melting portion and the single crystal optical fiber is heated to a temperature equal to or lower than the melting point of the grown single crystal optical fiber, A method for producing a single crystal optical fiber, which comprises a step of uniformizing a temperature distribution at a liquid interface and a step of relaxing rapid cooling of the grown single crystal optical fiber. 2. A means for condensing a laser beam on one end of a base material of a single crystal optical fiber to heat and melt the base material, and a seed crystal is brought into contact with the heating / melting portion to direct the base material to the direction of the seed crystal. In the crystal growth chamber of the single crystal optical fiber manufacturing apparatus equipped with at least a means for growing the single crystal optical fiber by moving the seed crystal in the same direction as the base material, the heating and melting part and the single crystal light. In the vicinity of the solid-liquid interface of the fiber, a part of the laser beam is branched and a means for irradiating by adjusting the focusing degree of the laser beam, or the focusing degree of the laser beam from another laser light source is adjusted. Arrange means for irradiating,
An apparatus for producing a single crystal optical fiber, characterized in that means for controlling heating of the vicinity of the solid-liquid interface near the melting point of the single crystal optical fiber substantially evenly is provided.