JPH0727936A - Production of periodic inversion type photorefractive waveguide - Google Patents

Abstract

PURPOSE:To provide a process for production of a periodic inversion type photorefractive waveguide which decreass man-hour for mending by preventing the generation of crack and lowering a defective rate during working, makes it possible to execute poling regardless of the sizes and dimensional ratios of crystals, easily produces periodic inversion waveguides at a low cost and facilitates formation of the finer polarization patterns thereof. CONSTITUTION:Plural electrodes 11 periodically arranged on a pair of the surfaces of a BaTiO3 single crystal 10 worked to be a prescribed shape are brought into contact with the single crystal 10 so as to hold the single crystal therebetween. All the polarities of the electrodes on the one surface are set positive and the polarities of the electrodes on the other surface negative. A uniform electric field is impressed to the single crystal 10 to monopolarize the single crystal. The inverted polarizations are thereafter partially generated in the single crystal by inverting the polarities of the arbitrary electrodes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a function of amplifying an optical signal by a photo-refractive effect and is also used for image processing such as hologram recording.
The present invention relates to an O ₃ ) optical single crystal, and more particularly to a method for manufacturing a period-inverted photorefractive waveguide having a structure in which the polarization direction is periodically inverted, which is composed of the barium titanate optical single crystal.

[0002]

2. Description of the Related Art In recent years, photorefractive (hereinafter referred to as P
Researches on optical amplification, hologram recording, and the like, which apply the (R) effect, have been actively conducted. Among them, a periodic polarization inversion type waveguide has been devised as a PR waveguide, which has a long effective working length and improves efficiency. In a LiNbO ₃ single crystal, such an inversion structure is obtained at an arbitrary inversion period by selectively diffusing an impurity in a part of the crystal by utilizing the property that polarization is inverted by diffusion of impurities and defects. be able to.

In BaTiO ₃ single crystal as well, there is a report that a waveguide having a periodically poled structure was produced by applying a spatially inverted electric field during poling (Ito et al. Appl. Phys. Lett. Vol.60, No.7, 1
992).

Conventionally, such a polarization-inverted waveguide of BaTiO ₃ single crystal has been produced by the following process by combining mechanical poling and electrical poling, as shown in FIG. First, the BaTiO ₃ single crystal 1 formed into a predetermined size has a 90 ° domain 2 and a 180 ° domain 3 as shown in the upper diagram of FIG. 3, so uniaxial compression is applied to this single crystal. In addition, 90 ° domain 2 is removed (mechanical poling).

As shown in the middle diagram of FIG. 3, only 180 ° domains 5 remain in the crystal 4 after mechanical poling, but the crystals are arranged in the direction of the light propagation direction of this crystal. The plurality of electrodes 6 are brought into contact with each other with the crystal sandwiched therebetween, and a high voltage power source is connected so that the polarities of the adjacent electrodes are reversed. In this way, by applying to the crystal an electric field that is alternately inverted in the light propagation direction, a crystal 7 having a domain structure in which the polarization direction is inverted according to the direction of the electric field can be created (lower diagram of FIG. 3).

[0006]

[Problems to be Solved by the Invention] However, BaT
Since the iO ₃ single crystal is a brittle material, it is easily broken during machining, and special attention is required especially in mechanical poling applying a large stress. Conventionally, when mechanical poling of a crystal with a size of several mm square is performed, cracks 8 are generated in about half of the crystals as shown in FIG. 4. Therefore, after poling, polishing is performed to polish cracks 8 Was being scraped off.

The occurrence of such a crack may cause a fatal defect when the waveguide becomes thinner. If the ratio of the long side to the short side of the single crystal exceeds 10: 1, it becomes difficult to apply compressive stress 9 along the axis of the crystal 1 as shown in FIG. You will not be able to remove the domain. Therefore, conventionally, it is necessary to first form a crystal to a large size (thickness) so that the size ratio is less than 10: 1, perform mechanical poling, and then re-polish it to the final size, which is very difficult to manufacture a waveguide. Was spending a lot of time.

The present invention has been made in view of the above problems, and prevents the occurrence of cracks during processing to reduce the defective rate, thereby reducing the number of repair steps and the size and size ratio of crystals. To provide a method for manufacturing a period-inverted photorefractive waveguide which can perform poling regardless of the above, can easily produce a period-inverted waveguide at low cost, and can easily miniaturize its polarization pattern. With the goal.

[0009]

A method of manufacturing a periodic reversal type photorefractive waveguide according to the present invention is directed to a pair of BaTiO ₃ single crystals processed into a predetermined shape so as to sandwich the single crystal. Applying a uniform electric field to the single crystal by contacting a plurality of electrodes arranged periodically on one surface with all electrodes on one surface having a positive polarity and the electrodes on the other surface having a negative polarity. And a step of forming a single domain, and a step of inverting the polarity of any of the electrodes to partially generate an inversion domain in the single crystal.

[0010]

In the present invention, a BaTiO ₃ single crystal is processed into a predetermined waveguide shape, and then electrodes arranged periodically are brought into contact with a pair of surfaces of the single crystal. And the first
In the electrical poling step, a uniform electric field is applied to the single crystal by setting all the polarities of the electrodes on one surface as + and all the polarities of the electrodes on the other surface as −. This gives 9
The 0 ° and 180 ° domains are removed. Next, in the second electric poling step, the polarity of the electrode of a particular electrode is reversed, and an electric field in which the polarity direction is partially reversed is applied to the single crystal. As a result, an inversion domain (180 ° domain) is generated and a desired polarization inversion structure is formed.

In this way, only a 180 ° domain is generated by the second electric poling in the single crystal divided into the single domains by the first electric poling, and a crystal having a desired periodic inversion domain structure can be obtained. it can. This eliminates the need for mechanical poling, and eliminates the restrictions on the crystal size caused by the occurrence of cracks and processing accuracy. Further, although the electric poling is performed twice, since the electrode need only be arranged once on the single crystal, a fine polarization pattern can be formed with high precision with a small number of steps.

[0012]

EXAMPLES Examples of the present invention will be specifically described below in comparison with comparative examples. Example 1 A 0.5 mm × 0.5 mm × 6 mm prismatic crystal 10 was cut out from the grown BaTiO ₃ single crystal along a crystal main axis perpendicular to the crystal, as shown in FIG. However, the present invention can be applied even if it is tilted within 30 ° from the crystal plane (100) plane or (001) plane forming the prism. The single crystal 10 is a material for the waveguide, and in the state before poling as it was cut out, there was a fine domain structure in the crystal and the crystal was opaque.

Next, as shown in FIG. 1B, a pattern electrode 1 having a desired domain-inverted structure is drawn so that the crystal 10 is sandwiched between a pair of opposed front and back surfaces of the cut crystal 10.
1 was formed by applying a silver paste. This electrode pattern has, for example, a width of the electrode 11 along the longitudinal direction of the crystal.
1.3mm, 2.6mm, 1.3mm, the gap between electrodes 11 is 0.4mm
Is. As a means for forming the electrode 11, in addition to the application of the silver paste, there are means for applying another conductive paste, printing, and depositing a conductive material by a thin film forming technique. And each of these 3
The lead wire 12 was connected to the divided electrode 11.

The crystal with the lead wire thus connected was placed in a constant temperature bath and heated to 140 ° C., and then the three electrodes 11 on one side of the crystal were all set to the same potential as the + pole. And all three electrodes on the opposite side are
A direct current power source was connected to each lead wire 12 so that the potentials of the poles were the same, and a uniform electric field 13 was applied to the crystal. Applied voltage is
It is 250V.

After maintaining this state for a while, the temperature of the constant temperature bath was gradually lowered to 120 ° C. while applying the voltage, and then the applied voltage was lowered to zero. At this stage, all the domains in the crystal disappeared and the crystal became transparent, as shown in FIG. 1 (c).

Next, as the second polling, as shown in FIG.
As shown in (a), the electrodes 11 adjacent to each other on one crystal plane
The connection between the lead wire and the power source was changed so that the polarities of the two were reversed, and a voltage of 100 V was applied to generate a periodically inverted electric field in the crystal. And in this state 120 ℃
The temperature was maintained for 10 hours.

In this way, the crystal, which had been subjected to the two-stage poling, was taken out from the thermostat and observed with a polarizing microscope. As a result, neither the 90 ° domain remained nor the generation of a new 90 ° domain was observed. When HCl etching was performed to examine the structure of the 180 ° domain, it was confirmed that an inverted structure shown in FIG. 2B, which was clearly divided into three regions, was formed. Therefore, the electrode 11
Was removed, a waveguide having two inversion structure regions was obtained as shown in FIG.

The time required for the poling process in this example was 73.5 hours, of which the time required for the work setup was 2.5 hours. Further, the number of chipping defects caused by the application and removal work of the electrode 11 was 5 out of 1000.

Comparative Example 1 As a first electric poling, a silver paste was used as a crystal 1
The electrodes are uniformly applied to the pair of surfaces to form one electrode on each crystal face, and in the second electrical poling, divided pattern electrodes are formed in the same manner as in the embodiment, and the conditions such as applied voltage are set. In the same manner as in the example, the first poling for removing the 90 ° domain and the 180 ° domain and the second poling for forming the 180 ° inverted domain structure were performed. As a result, the periodically inverted polarization structure was formed, but the time required for poling was 82.5 hours, and the setup time was 4.5 hours. The rate of chipping defects is 9 out of 1000.
It was an individual.

Comparative Example 2 Under the same conditions as in the first electrical poling of the example, only the polarity was reversed from the beginning and an inversion electric field was applied to perform poling. As a result, 90 ° domains and cracks were generated at the electrode ends in the crystal.

Comparative Example 3 The first electric poling was not carried out, but only the second electric poling was carried out under the same conditions as in the embodiment. As a result, 90 ° domains remained in the crystal.

[0022]

As described above, according to the present invention,
1 for BaTiO ₃ single crystal processed into a predetermined shape
The electrodes arranged periodically are brought into contact with the paired surfaces, and all electrodes on one surface are made to have the same polarity of + and the other electrodes are made to have the same polarity of − to make the voltage by the first electrical poling. Since the voltage is applied to make it into a single domain, it can be made into a single domain without performing mechanical poling, and defects due to cracks generated during mechanical poling are eliminated. Further, there is an advantage that there is no restriction due to the size and shape of the crystal that can be poled. Further, in the second poling forming the inversion domain, it is only necessary to partially reverse the polarities of the electrodes,
The present invention can obtain an inversion domain structure with a small number of steps.

[Brief description of drawings]

FIG. 1 is a diagram showing steps of a method according to an embodiment of the present invention in the order of steps.

FIG. 2 is a diagram showing the next step of the method according to the embodiment of the present invention in the order of steps.

FIG. 3 is a diagram showing one step of a conventional method.

FIG. 4 is a diagram for explaining the drawback of the conventional method.

FIG. 5 is a diagram for explaining a drawback of the conventional method.

[Explanation of symbols]

 1,4,7,10; single crystal 2; 90 ° domain 3,5,13; 180 ° domain 6,11; electrode 12; lead wire

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shoji Ajimura 1-5-1, Kiba, Koto-ku, Tokyo Inside Fujikura Ltd. (72) Inventor Akito Kurosaka 1-1-5, Kiba, Koto-ku, Tokyo Fujikura stock company (72) Inventor Haruo Tominaga 1-5-1, Kiba, Koto-ku, Tokyo Stock company Fujikura stock (72) Inventor Kenichi Kitayama 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Incorporated (72) Inventor Fumihiko Ito 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (1)

[Claims] 1. A BaTiO ₃ single crystal processed into a predetermined shape is brought into contact with a plurality of electrodes periodically arranged on a pair of surfaces so as to sandwich the single crystal, and one surface of the BaTiO ₃ single crystal is brought into contact therewith. The polarity of all the electrodes of +, and the polarity of the electrode on the other surface is-to apply a uniform electric field to the single crystal to make a single domain, and reverse the polarity of any of the electrodes. And a step of partially generating an inversion domain in the single crystal. A method of manufacturing a periodic inversion type photorefractive waveguide, comprising: