JPH0695045A - Optical control element and its production - Google Patents

Abstract

PURPOSE:To lessen the temp. rise of a crystal plate and to lessen light loss, phase deviation and waveform distortion by connecting coupling electrodes to signal electrodes provide on an optical waveguide and connecting an introducing electrode to the coupling electrodes. CONSTITUTION:The main surface of a Z-cut crystal plate 1 consisting of lithium niobate is provided thereon with the optical waveguides 2 of Mach-Zehunder type. The one optical waveguide 2 is provided therein with a grounding electrode 3 consisting of gold (Au) of 3mum thickness and the other optical waveguide 2 is provided thereon with the signal electrode 4 consisting of gold. The optical waveguides 2 are formed by depositing titanium by evaporation on the parts corresponding to the optical waveguides 2 on the main surface of the crystalline plate 1 by a photolithography method, then subjecting these parts to a thermal diffusion treatment at 1050 deg.C in an oxygen atmosphere. Five pieces of the coupling electrodes 11 consisting of gold and having 20mum length X 10mum width X 3mum thickness are provided in connection to this signal electrode 4 and further the introducing electrode 12 consisting of gold and having 20mum length X 27mum width X 3mum thickness are provided in connection to the coupling electrodes 11. Then, the internal impedance of the signal electrode is lowered without changing the impedance between the signal electrode and the grounding electrode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical control element used in a broadband communication system using an optical fiber and a manufacturing method thereof.

[0002]

2. Description of the Related Art FIG. 1 shows a conventional light control element of this type.
1 and shown in FIG.

FIG. 11 shows a light control element for light modulation.
Is a crystal plate exhibiting an electro-optical effect, a Mach-Zehnder type optical waveguide 2 is provided on the main surface of the crystal plate 1, a ground electrode 3 is provided on one side of the optical waveguide 2, and a signal electrode is provided on the other side. 4 was provided. In the optical waveguide 2, an element having a larger refractive index than that of the crystal plate 1 is vapor-deposited on the main surface of the crystal plate 1 by a lithographic method on a portion corresponding to the optical waveguide 2 and subjected to thermal diffusion treatment. As shown in the cross-sectional view of FIG. 11B taken along the line B, the vapor-deposited element was diffused in the depth direction to form the Mach-Zehnder type optical waveguide 2. Light propagates in the X-axis direction of the crystal plate 1, and an electric field is applied in the Y-axis direction. Since the refractive index of the optical waveguide 2 is larger than that of the crystal plate 1, light propagates in the optical waveguide 2 without leaking to the outside. In such a light control element for light modulation, when an optical signal from the left optical fibers 5 to 6 is put into the left optical waveguide 2, it is divided into two at the branch point and propagates through the branch portion. When a modulation signal voltage is applied to the signal electrode 4 from the drive power source 7 during this time, a phase difference occurs between the two optical signals branched by the electro-optical effect of the crystal plate 1 at the branch portion. When the two optical signals are merged by the right optical waveguide 2 and received by the right optical fiber 8, a modulated signal such as 9 can be taken out. Reference numeral 10 is a terminating resistor.

As shown in FIG. 12, an optical control element for an optical switch has one or more sets of optical waveguides 2 on the main surface of a crystal plate 1.
And the ground electrode 3 is provided between the pair of optical waveguides 2, and the signal electrode 4 is provided at a position opposed to the ground electrode 3 via the optical waveguide 2. With such a configuration, an optical signal is input from the optical fiber 5 on the left side, and the driving power source 7 is applied to the signal electrode 4.
When a modulation signal voltage is applied from, a switch signal is obtained by the right optical fiber 8 due to the electro-optic effect of the crystal plate 1.

[0005]

However, when a high frequency signal is applied to the signal electrode 4 in the above-described conventional light control element for distributed constant operation, a current flows through the signal electrode 4 at the same phase velocity as the optical signal. Heat is generated due to Joule loss and the signal electrode 4
The temperature of the lower optical waveguide 2 is increased. Then, there is a problem that an electromotive force is generated on the main surface of the crystal plate 1 due to the pyroelectric effect and stable modulation or switch characteristics cannot be obtained.

Further, since the optical waveguide 2 is formed by the thermal diffusion method, the refractive index is highest on the surface of the substrate and the Gaussian distribution is semicircular toward the inside of the substrate. For this reason, there are problems such as optical loss, phase shift, and waveform distortion.

The present invention solves the above problems, and an object of the present invention is to provide an optical control element in which the temperature rise of a crystal plate is small, optical loss, phase shift, and waveform distortion are small, and a manufacturing method thereof.

[0008]

In order to achieve the above object, the light control element of the present invention has an electrode structure in which a coupling electrode is connected to a signal electrode and an introduction electrode is connected to the coupling electrode, or tantalum is used. An epitaxial crystal layer of lithium niobate doped with one or more of titanium, iron, zinc, copper and silver is provided on the main surface of a crystal plate of lithium oxide or lithium niobate, and the epitaxial crystal layer is subjected to optical etching by an ion etching method. A structure with a waveguide is provided.

[0009]

According to the present invention, the internal impedance of the signal electrode can be lowered without changing the impedance between the signal electrode and the ground electrode and the heat dissipation can be increased by the coupling electrode and the introduction electrode. The distribution of the refractive index in the optical waveguide is concentric. Further, if the epitaxial layer is processed by the ion etching method, it is 100 to 200.
Since it can be processed at ℃, it can form an optical waveguide with fewer defects such as dislocation (dislocation) and composition change than the thermal diffusion method.

[0010]

【Example】

(Embodiment 1) A first embodiment of the present invention will be described below with reference to FIG.

This embodiment is different from the conventional example of FIG. 11 in that the coupling electrode 11 is connected to the signal electrode 4 and the coupling electrode 11 is connected.
This is the point at which the introduction electrode 12 was connected to. Further specifically explaining this embodiment, 1 is lithium niobate (LiNb)
O ₃ ) Z-cut crystal plate, length 40 mm x width 3 mm
× Thickness is 1 mm. A Mach-Zehnder type optical waveguide 2 is provided on the main surface of the crystal plate 1. On the one optical waveguide 2, a ground electrode 3 of gold (Au) having a thickness of 3 μm,
A signal electrode 4 of Au is provided on the other optical waveguide 2. For the optical waveguide 2, titanium (Ti) was vapor-deposited on the main surface of the LiNbO ₃ crystal plate 1 in a portion corresponding to the optical waveguide 2 by a photolithography method in an amount of 700 Å, and was placed in an oxygen atmosphere.
A Mach-Zehnder type optical waveguide 2 is formed by thermal diffusion treatment at 0 ° C. and diffusing Ti to a depth of about 5 μm as shown in the cross-sectional view of FIG. 1B taken along the line AB of FIG. did. The size of the signal electrode 4 was 20 mm in length × 9 μm in width × 3 μm in thickness, and its DC resistance was 20Ω. The distance between the branched portions of the optical waveguide 2 was set to about 1 mm. The terminating resistance 10 was 50Ω. The above-mentioned configuration is the same as that of the conventional example of FIG. 11, but in the present example, it is connected to the signal electrode 4 and has a length of 20 μm and a width of 10 μm.
Five Au coupling electrodes 11 of m × thickness 3 μm are provided and connected to the coupling electrodes 11 and the length is 20 mm × width 27 μm × thickness 3 μ.
An m introduction electrode 12 of Au was provided.

When driven under the same conditions as in the conventional example with the above-mentioned configuration, the temperature rise was smaller than in the conventional example and stable modulation characteristics were exhibited.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG.

The present embodiment is different from the conventional example of FIG. 12 in that the coupling electrode 11 is connected to the signal electrode 4 and the coupling electrode 11 is connected.
This is the point at which the introduction electrode 12 was connected to. The structure of each of these electrodes was the same as that in Example 1, but the ground electrode 3 had a length of 2 mm.
Au of 0 mm × width 30 μm × thickness 3 μm was provided between the optical waveguides 2.

When driven under the same conditions as in the conventional example with the above-mentioned structure, the temperature rise was smaller than in the conventional example and stable switching characteristics were exhibited.

(Embodiment 3) Next, a third embodiment of the present invention will be described with reference to FIG.

This embodiment is different from Embodiment 1 in FIG. 1 in that lithium tantalate (LiTaO ₃ ) is used as the crystal plate 13 instead of the crystal plate 1 of LiNbO ₃ , and the main surface thereof is doped with Ti. The epitaxial crystal layer 14 of LiNbO ₃ is formed, and the Mach-Zehnder type optical waveguide 15 is formed on the epitaxial crystal layer 14 by the ion etching method.
Is the point that formed. The structure of each electrode is the same as that of the first embodiment.

When driven under the same conditions as in the conventional example with the above-mentioned configuration, the temperature rise is smaller than in the conventional example, and the optical loss, phase shift,
The modulation characteristics with little waveform distortion are shown.

Although Ti has been described as the doping element in this embodiment, iron (Fe) may be used instead of Ti.
The same effect can be obtained by using one or more of zinc (Zn), copper (Cu), and silver (Ag).

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described with reference to FIG.

The present embodiment is different from the conventional example of FIG. 12 in that LiTaO ₃ is used as the crystal plate 13 instead of the crystal plate 1 of LiNbO ₃ , and the main surface thereof is doped with Ti to form an epitaxial crystal of LiNbO ₃ . The layer 14 is formed, the optical waveguide 15 is formed on the epitaxial crystal layer 14 by the ion etching method, and the optical waveguide 15 is connected to the signal electrode 4 to form the coupling electrode 1.
1 is provided, and the introduction electrode 12 is provided by connecting to the coupling electrode 11.

When driven under the same conditions as in the conventional example with the above-mentioned configuration, the temperature rise is smaller than in the conventional example, and optical loss, phase shift,
It showed switching characteristics with little waveform distortion.

Although Ti was described as a doping element in the examples, Fe, Zn, C may be used instead.
Similar effects can be obtained by using at least one of u and Ag.

(Fifth Embodiment) Next, a fifth embodiment of the present invention will be described with reference to FIG.

The embodiment of FIG. 5 is different from the embodiment 1 of FIG. 1 in that the silicon oxide (S) having a thickness of 3000 Å is formed on the optical waveguide 2.
The point is that the buffer layer 16 of iO ₂ ) is provided. As a result, similar to the first embodiment, the temperature rise is smaller than that of the conventional example, stable modulation characteristics are shown, and the optical loss is lower than that of the first embodiment.

(Sixth Embodiment) Next, a sixth embodiment of the present invention will be described with reference to FIG.

The embodiment of FIG. 6 is different from the embodiment 3 of FIG. 3 in that a buffer layer 16 of SiO ₂ having a thickness of 3000 Å is provided on the optical waveguide 15. As a result, similar to the third embodiment, the temperature rise is smaller than that of the conventional example, the modulation characteristics with less optical loss, phase shift, and waveform distortion are exhibited, and the optical loss is lower than that of the third embodiment.

(Embodiment 7) Next, a seventh embodiment of the present invention will be described with reference to FIG.

The embodiment of FIG. 7 differs from the embodiment 2 of FIG. 2 in that a buffer layer 16 of SiO ₂ having a thickness of 3000 Å is provided on the optical waveguide 2. As a result, similar to the second embodiment, the temperature rise is smaller than that of the conventional example, stable switching characteristics are exhibited, and the optical loss is lower than that of the second embodiment.

(Embodiment 8) Next, an eighth embodiment of the present invention will be described with reference to FIG.

The embodiment of FIG. 8 is different from the embodiment 4 of FIG. 4 in that a buffer layer 16 of SiO ₂ having a thickness of 3000 Å is provided on the optical waveguide 15. As a result, similar to the fourth embodiment, the temperature rise is smaller than that of the conventional example, the switching characteristics with less optical loss, phase shift, and waveform distortion are exhibited, and the optical loss is lower than that of the fourth embodiment.

(Embodiment 9) In this embodiment, Embodiment 3 is used.
A method of manufacturing the light control element having the LiNbO ₃ epitaxial crystal layer described in (FIG. 3) will be described with reference to FIGS. 9 and 10.

FIG. 9 shows an apparatus for producing an LiNbO ₃ epitaxial crystal layer. First, at least one flux of lead oxide (PbO), bismuth oxide (Bi ₂ O ₃ ), and boron oxide (B ₂ O ₃ ) is placed in the platinum crucible 17 and heated in the electric furnace 18 to melt the flux. Next, niobium oxide (Nb ₂ O ₅ ), lithium carbonate (Li ₂ CO ₃ ) and titanium oxide (TiO ₂ ) are added to produce a melt 19. Next, the melt 19 is brought into a supercooled state of 600 to 700 ° C. Next, the crystal plate 13 of LiTaO ₃ (the crystal of LiNbO ₃ is LiT
Since it has the same crystal structure as aO ₃ , it is epitaxially grown on the crystal plate of LiTaO ₃ . ) The rotating shaft 20
It is attached to the substrate holder 21 fixed to the tip of the and is put into the melt 19. When the LiTaO ₃ crystal plate 13 is rotated at a constant speed by the rotating shaft 20, a titanium-doped LiNbO ₃ crystal is epitaxially grown. In the figure, 22 is a stirring plate and 23 is a heat insulating material.
Predetermined thickness of the epitaxial crystal layer formed after flux removal, epitaxial LiNbO ₃ doped with Ti on the main surface of the crystal plate 13 of LiTaO ₃ as shown in FIG. 10 (a) When annealing the crystal plate 13 A substrate on which the crystal layer 14 is formed is obtained. Next, the epitaxial crystal layer 14
By masking the top and forming the optical waveguide 15 by the ion etching method, a substrate as shown in FIG. 10B is obtained. Finally, masking necessary for forming each electrode is performed and Au is vapor-deposited by a vacuum vapor-deposition method.
It is possible to manufacture a light control element for light modulation in which the Mach-Zehnder type optical waveguide 15 in which 2 is formed is formed.

Although the light control element of the third embodiment (FIG. 3) has been described in this embodiment, the fourth embodiment (FIG. 4), the sixth embodiment (FIG. 6) and the eighth embodiment (FIG. 4) are manufactured by the same manufacturing method. The light control element of FIG. 8) can be manufactured.

Further, the light control element having the SiO ₂ buffer layer 16 described in Example 5 (FIG. 5), Example 6 (FIG. 6), Example 7 (FIG. 7) and Example 8 (FIG. 8) was used. As the manufacturing method, after forming the optical waveguide 2 or 15, the sputtering method or the vacuum deposition method is used.

Further, although the epitaxial crystal layer 14 is formed by the liquid phase epitaxial method in this embodiment, it may be formed by the sputtering method instead.

[0037]

As is apparent from the above description, according to the light control element and the method of manufacturing the same of the present invention, the following effects can be obtained.

(1) It is possible to obtain an optical control element having a stable modulation or switch characteristic with less temperature rise than the conventional example.

(2) An optical control element having a modulation or switch characteristic with less optical loss, phase shift and waveform distortion can be obtained as compared with the conventional example.

[Brief description of drawings]

FIG. 1A is a perspective view of a light control element according to a first embodiment of the present invention, and FIG. 1B is a sectional view taken along line AB of FIG.

FIG. 2A is a perspective view of a light control element according to a second embodiment of the present invention, and FIG. 2B is a sectional view taken along line AB of FIG.

FIG. 3A is a perspective view of a light control element according to a third embodiment of the present invention, and FIG. 3B is a sectional view taken along line AB of FIG.

FIG. 4A is a perspective view of a light control element according to a fourth embodiment of the present invention, and FIG. 4B is a sectional view taken along line AB of FIG.

FIG. 5A is a perspective view of a light control element according to a fifth embodiment of the present invention, and FIG. 5B is a sectional view taken along line AB of FIG.

FIG. 6A is a perspective view of a light control element in a sixth embodiment of the present invention, and FIG. 6B is a sectional view taken along the line AB of FIG.

FIG. 7A is a perspective view of a light control element according to a seventh embodiment of the present invention, and FIG. 7B is a sectional view taken along the line AB of FIG.

FIG. 8A is a perspective view of a light control element according to an eighth embodiment of the present invention, and FIG. 8B is a sectional view taken along the line AB of FIG.

FIG. 9 is a sectional view of an epitaxial crystal layer manufacturing apparatus according to the present invention.

FIG. 10 is a perspective view of the manufacturing process of the optical waveguide according to the present invention.

11A is a perspective view of a light control element in a conventional example, and FIG. 11B is a sectional view taken along the line AB of FIG.

FIG. 12A is a perspective view of a light control element in another conventional example, and FIG. 12B is a sectional view taken along the line AB of FIG.

[Explanation of symbols]

 1, 13 Crystal Plate 2, 15 Optical Waveguide 3 Earth Electrode 4 Signal Electrode 11 Coupling Electrode 12 Introduction Electrode 14 Epitaxial Layer 16 Buffer Layer

Claims (10)

[Claims] 1. A Mach-Zehnder type optical waveguide having a larger refractive index than that of the crystal plate is provided on the main surface of the crystal plate exhibiting the electro-optical effect, a ground electrode is provided on one of the optical waveguides, and the other optical waveguide is provided on the other optical waveguide. A light control element for light modulation, wherein a signal electrode is provided in the light control element, and a coupling electrode is connected to the signal electrode, and an introduction electrode is connected to the coupling electrode. 2. One or more sets of optical waveguides having a refractive index higher than that of the crystal plate are provided on the main surface of the crystal plate exhibiting the electro-optical effect, and a ground electrode is provided between the one set of optical waveguides. In a light control element for an optical switch in which a signal electrode is provided at a position opposed to the ground electrode via an optical waveguide, a coupling electrode is connected to the signal electrode, and an introduction electrode is connected to the coupling electrode. Optical control element for optical switch. 3. One of titanium, iron, zinc, copper and silver on the main surface of a crystal plate of lithium tantalate or lithium niobate.
An epitaxial crystal layer of lithium niobate doped with at least one seed is provided, a Mach-Zehnder type optical waveguide is provided by the ion etching method on the epitaxial crystal layer, a ground electrode is provided on one optical waveguide, and a signal is provided on the other optical waveguide. An electrode is provided, and a coupling electrode is connected to the signal electrode,
A light control element for light modulation in which an introduction electrode is connected to the coupling electrode. 4. One of titanium, iron, zinc, copper and silver on the main surface of a crystal plate of lithium tantalate or lithium niobate.
An epitaxial crystal layer of lithium niobate doped with at least one seed is provided, one or more sets of optical waveguides are provided in the epitaxial crystal layer by an ion etching method, and a ground electrode is provided between the one set of optical waveguides. An optical control element for an optical switch, in which a signal electrode is provided at a position opposed to the ground electrode via a connection electrode, a coupling electrode is connected to the signal electrode, and an introduction electrode is connected to the coupling electrode. 5. The light control element for light modulation according to claim 1, wherein a buffer layer is provided on the optical waveguide, and a ground electrode and a signal electrode are provided on the buffer layer. 6. A buffer layer provided on the optical waveguide.
Alternatively, the light control element for an optical switch according to the item 4. 7. One of titanium, iron, zinc, copper and silver on the main surface of a lithium tantalate or lithium niobate crystal plate.
An epitaxial crystal layer of lithium niobate doped with at least one species is formed by a liquid phase epitaxial method or a sputtering method, and then a Mach-Zehnder type optical waveguide is formed on the epitaxial crystal layer by an ion etching method.
Next, a ground electrode is provided on one of the optical waveguides, a signal electrode is provided on the other optical waveguide, then a coupling electrode is provided by connecting to the signal electrode, and an introducing electrode is provided by connecting to the coupling electrode. Item 4. A method of manufacturing a light control element for light modulation according to Item 3. 8. One of titanium, iron, zinc, copper and silver on the main surface of a crystal plate of lithium tantalate or lithium niobate.
An epitaxial crystal layer of lithium niobate doped with at least one seed is formed by a liquid phase epitaxial method or a sputtering method, and then one or more sets of optical waveguides are formed on the epitaxial crystal layer by an ion etching method. A ground electrode is provided between the optical waveguides, a signal electrode is provided at a position facing the ground electrode through the optical waveguide, a connecting electrode is provided by connecting to the signal electrode, and a connecting electrode is provided by introducing the connecting electrode. The method for manufacturing a light control element for an optical switch according to claim 4, wherein an electrode is provided. 9. Titanium, iron, zinc, copper, silver 1 on the main surface of a crystal plate of lithium tantalate or lithium niobate.
An epitaxial crystal layer of lithium niobate doped with at least one species is formed by a liquid phase epitaxial method or a sputtering method, and then a Mach-Zehnder type optical waveguide is formed on the epitaxial crystal layer by an ion etching method.
Next, a buffer layer is provided on the surface on which the optical waveguide is provided, then a ground electrode is provided on the buffer layer on one optical waveguide, and a signal electrode is provided on the buffer layer on the other optical waveguide. The method for manufacturing a light control element for light modulation according to claim 5, wherein a coupling electrode is provided in connection with the signal electrode, and an introduction electrode is provided in connection with the coupling electrode. 10. An epitaxial crystal layer of lithium niobate doped with one or more of titanium, iron, zinc, copper and silver is formed on a main surface of a crystal plate of lithium tantalate or lithium niobate by a liquid phase epitaxial method or sputtering. Method, and then one or more sets of optical waveguides are formed on the epitaxial crystal layer by an ion etching method, then a buffer layer is provided on the optical waveguides, and then a ground is provided between the one set of optical waveguides. 7. An electrode is provided, a signal electrode is provided at a position opposed to the ground electrode via the optical waveguide, a coupling electrode is provided in connection with the signal electrode, and an introduction electrode is provided in connection with the coupling electrode. Manufacturing method of light control element for optical switch of.