JP3849996B2 - Method for manufacturing single crystal optical element - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a KNbO ₃ single crystal optical element used for wavelength conversion, light modulation, and the like, and a method for manufacturing the same.
[0002]
TECHNICAL BACKGROUND OF THE INVENTION
Potassium niobate (KNbO ₃ ) single crystal has been attracting attention as a piezoelectric material as a nonlinear optical material or as an electro-optical material. In particular, laser light, which is monochromatic light near 860 nm or 980 nm, has a half harmonic. Since it has high SHG (Second Harmonic Generation) characteristics for conversion, it has been attracting attention as a nonlinear optical material.
[0003]
This KNbO ₃ single crystal is produced by T.W. FUKUDA, Y.M. UEMATU, J.A. J. et al. A. P. 11 (1973) 163, a powdered mixture of potassium carbonate and niobium oxide (Nb ₂ O ₅ ) is heated and melted to a temperature of 1050 ° C. or higher, and seed crystals are immersed in the resulting melt. The temperature of the melt can be gradually lowered to grow. When the thus obtained KNbO ₃ single crystal is cooled, a structural phase transition occurs from a cubic system to a tetragonal system at about 420 ° C., and a structural phase transition from a tetragonal system to an orthorhombic system occurs at about 210 ° C. At room temperature, an orthorhombic and multi-domain KNbO ₃ single crystal is obtained.
[0004]
Such a KNbO ₃ single crystal has orthorhombic symmetry at room temperature. For example, in SHG of 860 nm, when polarized light having a polarization plane parallel to the b-axis is incident on the incident surface of the a-plane, c An SHG wave having a plane of polarization parallel to the axis is obtained. If the incident laser polarization direction is tilted from the b-axis direction, the conversion efficiency decreases. For this reason, the incident laser and the crystal axis need to match the incident direction and the polarization direction with a specific crystal orientation.
[0005]
Conventionally, when a KNbO ₃ single crystal is used as an optical element such as a wavelength conversion element, as shown in FIG. 3, the normal directions of the mirror-polished laser beam incident surface 11 and the exit surface 11 ′, and the side surfaces 12, 13 has a specific crystal orientation. For example, in the 860 nm SHG application, the laser light incident / exit surfaces 11 and 11 'are a-planes, and the other surfaces 12 and 13 are b-plane and c-plane.
[0006]
In order to distinguish the crystal orientation between the incident and exit surfaces of the laser beam and other surfaces, a mark is made on the side surface of the crystal element, or a corner of the crystal element is scraped with sandpaper, etc. Methods such as varying the length of have been performed.
[0007]
However, the method of marking the side of the crystal element and the method of cutting the corner of the crystal element are effective when the size of the crystal element is about 10 × 10 × 10 mm and the amount of the crystal element to be processed is small. Although it is a means, when the crystal element becomes a size of about 3 × 3 × 3 mm, or when the processing amount of the crystal element is large, there is a problem that the work is complicated and inefficient. . In addition, the method of marking the side of the crystal element has drawbacks such as the paint material evaporating and disappearing during the optical coating, or it may evaporate when the device is used and contaminate the surrounding environment. .
[0008]
Further, in the method of changing the length of the crystal element, the difference in the element length of at least about 0.3 to 0.5 mm is necessary for visual judgment. There were problems such as the need for measuring instruments such as meters. In addition, the number of crystals that can be taken from the limited crystal is reduced, and the profitability is not good.
[0009]
OBJECT OF THE INVENTION
The present invention is to solve the above-mentioned problems of the prior art, and provides a KNbO ₃ single crystal optical element having a pattern that can easily identify the crystal orientation of the KNbO ₃ single crystal optical element, and a method for manufacturing the same. It is intended to provide.
[0010]
Summary of the Invention
KNbO ₃ single crystal optical element according to the present invention is to prepare a KNbO ₃ single crystal plate cut the KNbO ₃ single crystal was treated single poling, mirror polished laser beam entry and exit surface of the KNbO ₃ single crystal plate After that, the laser light incident / exit surface of the KNbO ₃ single crystal plate is cut so as to form a pattern in which the crystal orientation can be confirmed at the side edge of the laser light incident / exit surface.
[0011]
The pattern is preferably a domain pattern or chipping formed when a KNbO ₃ single crystal optical element is manufactured by cutting a KNbO ₃ single crystal plate.
[0012]
The width of the pattern is preferably 0.5 mm or less.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the single crystal optical element and the manufacturing method thereof according to the present invention will be specifically described.
[0014]
[KNbO ₃ single crystal optical element]
First, the KNbO ₃ single crystal optical element according to the present invention will be specifically described with reference to the drawings.
[0015]
For example, as shown in FIG. 1, the KNbO ₃ single crystal optical element according to the present invention has an a-plane 2 where the a-plane 2 of the KNbO ₃ single-crystal is the laser light incident / exit surface and the side surfaces are the b-plane 3 and c-plane 4, respectively. 2 has a pattern 6 on which the crystal orientation can be confirmed.
[0016]
The KNbO ₃ single crystal used in the KNbO ₃ single crystal optical element according to the present invention, for example prepared by TSSG (Top Seeded Solution Growth) method, KNbO ₃ single crystal was cut into a predetermined crystal orientation is used. As such a KNbO ₃ single crystal, one subjected to a single domain treatment is usually used.
[0017]
In the present specification, a plurality of domains in which domains having different polarization directions are adjacent to each other are referred to as multidomains, and a state in which such multidomains are formed is referred to as a multidomain state. Moreover, making a single crystal in this multi-domain state into a mono-domain state in which the domain directions are uniformly aligned is referred to as single-domain processing.
[0018]
The pattern 6 on the side edge portion 5 is preferably a domain pattern or chipping formed when a KNbO ₃ single crystal plate is cut to manufacture a KNbO ₃ single crystal optical element.
[0019]
The domain pattern is formed by changing the KNbO ₃ single crystal close to the cut surface into a multi-domain state when the KNbO ₃ single crystal plate is cut.
Further, chipping is a lack of a cut surface formed when a KNbO ₃ single crystal plate is cut.
[0020]
For example, in the case of the KNbO ₃ single crystal optical element shown in FIG. 1, the pattern has a line shape parallel to the edge at the side edge of the c-plane 4 and a line shape perpendicular to the edge at the side edge of the b-plane 3. Become. The width of such a pattern is, _0. 5 mm or less, preferably at most _0. 3 mm or less.
[0021]
In the single crystal optical element according to the present invention, a surface other than the a-plane of the KNbO ₃ single crystal can be used as the laser light incident / exit surface.
For example, as shown in FIG. 2, a 60 ° ab surface 7 having a perpendicular to the direction of 60 ° from the a axis in the ab axis surface is a laser light incident / exit surface, and a 30 ° ab surface 8 and a c surface 9 are side surfaces. You can also
[0022]
In this case, the pattern has a triangular shape at the side edge 10 on the c-plane, and no pattern is formed on the side edge 10 on the 30 ° ab plane.
As described above, the single crystal optical element according to the present invention has a pattern in which the crystal orientation can be confirmed at the side edge of the laser light incident / exit surface. (For example, the b surface and the c surface) can be easily identified.
[0023]
[Method for producing KNbO ₃ single crystal optical element]
Next, a method for manufacturing the KNbO ₃ single crystal optical element according to the present invention will be described.
First, in the present invention, a single-domain KNbO ₃ single crystal is cut to produce a KNbO ₃ single crystal plate.
[0024]
Incidentally, the single poling treatment of KNbO ₃ single crystal, the c plane of the KNbO ₃ single crystal, or applying a conductive paste containing conductive powder such as silver powder or carbon powder, or the like by depositing gold The positive electrode and the negative electrode can be formed, and then an electric field of 1 kV / cm or higher is applied at 200 ° C. between the positive and negative electrodes of the KNbO ₃ single crystal. In such a single domain treatment, a semi-insulating material layer may be provided between the KNbO ₃ single crystal and the electrode.
[0025]
The method for cutting the KNbO ₃ single crystal is not particularly limited, and for example, a rotary blade in which diamond is embedded can be used.
Next, the obtained KNbO ₃ single crystal plate is mirror-polished to form a laser light incident / exit surface.
[0026]
Mirror polishing is performed using a pitcher cloth as a surface plate and fine particles such as cerium oxide, alumina or silica as an abrasive.
The mirror-polished KNbO ₃ single crystal plate cuts the laser light incident / exit surface to form a KNbO ₃ single crystal optical element so that a crystal orientation can be confirmed on the side edge of the laser light incident / exit surface. Make it.
[0027]
The method for cutting the KNbO ₃ single crystal plate is not particularly limited. For example, the cutting is performed using a rotary blade in which diamond is embedded. At this time, it is preferable to cut the laser light incident / exit surface so that a pattern having a width of 0.5 mm or less is formed from the cut portion.
[0028]
The obtained KNbO ₃ single crystal optical element may be washed as necessary.
[0029]
【The invention's effect】
According to the KNbO ₃ single crystal optical element according to the present invention, the crystal orientation can be easily identified. For this reason, at the time of assembling the device, it is possible to reduce the defect rate due to an incorrect crystal orientation. In particular, when the alignment of elements is automated, the crystal orientation can be confirmed by pattern recognition of the side edges of the elements, which is suitable for mass production.
[0030]
According to the method of manufacturing a KNbO ₃ single crystal optical element according to the present invention, the pattern creation process can be performed in the same manner as the cutting process of the KNbO ₃ single crystal optical element.
[0031]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.
[0032]
[Example 1]
The KNbO ₃ single crystal was grown by the TSSG method. That is, an excess potassium KNbO ₃ powder was put into a platinum crucible having an average diameter of 80 mm and a depth of 80 mm, and the KNbO ₃ powder was melted by resistance heating. Next, seeding was performed on the surface of the melt to grow a KNbO ₃ single crystal. From the 40 × 40 × 20 mm KNbO ₃ single crystal thus obtained, a crystal block having a size of 10 × 10 × 10 mm was cut out and subjected to a single domain treatment. In the single domain treatment, gold is deposited on the c-plane of a KNbO ₃ single crystal to form a positive electrode and a negative electrode, and then an electric field of 1 kV / cm is applied between the positive and negative electrodes of the KNbO ₃ single crystal at 200 ° C. went. After the single domain treatment, the deposited gold was removed by lightly mirror-polishing the c-plane.
[0033]
A 10 × 10 × 3 mm a-plane plate (10 × 10 mm surface is a-plane) was cut out from the single-divided crystal block, and both surfaces of the a-plane plate were mirror-polished. After mirror polishing, the mirror polished surface was cut to 3 × 3 mm to produce a KNbO ₃ single crystal optical element.
[0034]
When the domain and chipping of the nine mirror-side edges of the obtained elements were observed with a 50 × optical microscope, it was found that the c-plane and b-plane of the KNbO ₃ single crystal optical element could be easily distinguished.
[0035]
[Example 2]
From the 10 × 10 × 10 mm single crystal block produced in Example 1, the incident / exit surface normal direction is 60 ° from the a axis in the ab axis plane, and 3 mm A crystal plate was cut out in thickness. Both surfaces of the cut crystal plate were mirror-polished, then cut to 3 × 3 mm and washed to produce a KNbO ₃ single crystal optical element.
[0036]
When the domain and chipping of the nine mirror elements on the mirror surface side were observed with a 50 × optical microscope, it was found that the c-plane and ab-plane of the KNbO ₃ single crystal optical element could be easily distinguished.
[Brief description of the drawings]
FIG. 1 is a drawing for explaining an example of a KNbO ₃ single crystal optical element according to the present invention.
FIG. 2 is a drawing for explaining another example of the KNbO ₃ single crystal optical element according to the present invention.
FIG. 3 is a drawing for explaining the outline of a KNbO ₃ single crystal optical element according to the present invention.
[Explanation of symbols]
2 ... Laser light incident / exit surface (a surface)
3 ... b surface 4, 9 ... c surface 5 ... side edge 6, 10 ... pattern 7 ... laser light incident / exit surface (60 ° ab surface)
8 ... 30 ° ab surface 11 ... Laser light incident / exit surfaces 12, 13 ... side surfaces

Claims (3)

To prepare KNbO ₃ single crystal plate cut the KNbO ₃ single crystal was treated single poling, after mirror polishing the laser light incident and exit surfaces of the KNbO ₃ single crystal plate, the laser beam entering the KNbO ₃ single crystal plate A method of manufacturing a KNbO ₃ single crystal optical element, wherein the emission surface is cut so as to form a pattern whose crystal orientation can be confirmed at a side edge of the laser beam incident / exit surface. 2. The KNbO ₃ single crystal optical element according to claim 1, wherein the pattern is a domain pattern or chipping formed when a KNbO ₃ single crystal optical element is manufactured by cutting a KNbO ₃ single crystal plate. _3. Manufacturing method. The method for producing a KNbO ₃ single crystal optical element according to claim 1 or 2, wherein the width of the pattern is 0.5 mm or less.

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