JPH1054964A - Optical control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical control device capable of eliminating a limit imparted to resistance of a conductive film for suppressing temp. drift, also suppressing the temp. drift and CD drift and obtaining a low driving voltage. SOLUTION: Electrodes 4a, 4b are formed on an optical circuit 5 consisting of two channel type optical waveguides 2a, 2b formed on a surface of a LiNbO3 , substrate 1 and the optical waveguides 2a, 2b through a buffer layer 3. Further, the conductive film 6 is formed in the vicinity of the electrodes 4a, 4b. The conductive film 6 doesn't conduct between the electrodes 4a, 4b, and parts 7 insulated in the vicinity of the electrodes 4a, 4b exist.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical control device for modulating an optical wave, switching an optical path, and filtering an optical wavelength, and more particularly to an optical control device for performing control using an optical waveguide formed on a substrate having a pyroelectric effect. The present invention relates to a corrugated light control device.

[0002]

2. Description of the Related Art With the practical use of optical communication systems, higher-capacity, multifunctional advanced systems have been demanded, and new functions such as higher-speed generation of optical signals, switching of optical transmission paths, and switching have been proposed. Is required. An optical switch is used as a means for obtaining a function of switching an optical transmission path or a network. Optical switches currently in practical use are those that switch the optical path by mechanically moving a prism, mirror, fiber, etc., and have a low speed.
There is a disadvantage that the shape is large and the matrix formation is unsuitable.

As a means for solving this problem, a waveguide type optical switch using an optical waveguide has been developed, and has features such as high speed, integration of many elements, and high reliability. In particular, a device using a ferroelectric material such as lithium niobate (LiNbO ₃ ) has features such as low light absorption and low loss, and high efficiency due to a large electro-optic effect. In addition, various types of optical control devices such as a directional coupler optical switch, a Mach-Zehnder optical switch, a balanced bridge optical switch, and a total reflection optical switch have been reported.

In recent years, research and development on high-density integration of a waveguide type optical switch using a directional coupler formed in a LiNbO ₃ electro-optic crystal substrate has been actively conducted. According to the Institute of Electronics, Information and Communication Engineers, OQE 88-147, an 8 × 8 matrix optical switch in which 64 directional coupler optical switches are integrated using a Z-plate LiNbO ₃ substrate is obtained. On the other hand, research and development of devices including a single optical switch element such as an external optical modulator are also actively pursued. The characteristic items of such an optical waveguide device include operation stability, switching voltage (power), crosstalk, extinction ratio, loss, switching speed, and the like.

[0005]

Among the above-mentioned characteristic items, stability of operation and reduction of switching voltage (power) are the most important issues. Here, the prior art is shown in FIGS. 5, 6 and 7, and the problem to be solved will be described.
FIG. 5 shows LiNbO ₃ or LiTiO ₃ having a pyroelectric effect.
The two optical waveguides (2a) (2) formed on the substrate (1)
It is sectional drawing which shows the structure of the waveguide type optical control device using the directional coupler (5) consisting of b).

As shown in FIG. 5, a buffer layer (3), which is an optically transparent film, is provided with guided light by electrodes (4a) and (4b) to which an external control signal for controlling the guided light is applied. This is used as an optical buffer layer for preventing absorption of SiO2, and SiO ₂ is usually used for the optical buffer layer (3). This is because SiO ₂ hardly absorbs light and the refractive index is sufficiently smaller than that of the LiNbO ₃ substrate or the LiTiO ₃ substrate. Electrodes (4a) (4b)
Usually, a metal or the like having a small volume resistivity is used so that high-speed operation can be performed, and electrodes (4a) and (4b) are arranged near the optical waveguides (2a) and (2b). Various optical waveguide type optical control devices, such as optical switches and optical modulators, having such a configuration are being studied, but due to the pyroelectric effect, electric charge is generated when there is a temperature change, and the electric charge is generated. There is a reliability problem of temperature drift in which the operating point voltage fluctuates due to localization.

As a method for solving this, an optical control device as shown in FIG. 6 has been proposed. This conventional light control device is disclosed in Sawaki et al., Japanese Patent Application Laid-Open No. Sho 62-73207.
According to Japanese Unexamined Patent Application Publication No. 62-173428 and Japanese Patent Application Laid-Open No. 62-173428, at least one pair of electrodes (4a) and (4b) formed on a substrate (1) having a pyroelectric effect is conducted by a conductive film (6). Let it be done. It has been reported that the localization of the electric charges at the time of temperature generation is thereby uniformed, thereby suppressing the temperature drift.

However, in order to avoid malfunction due to a leak current between the electrodes, the electrodes (4a) and (4)
The resistance of b) needs to be 10 ⁷ to 10 ¹⁰ Ω. Therefore, it is necessary to add a manufacturing process such as heat treatment in which temperature control is strict in order to control the resistance value for realizing this, and there are disadvantages that the manufacturing process becomes complicated and the device yield is deteriorated. Since the electrodes (4a) and (4b) are electrically connected, the electrodes (4a) and (4b) are required to operate the device.
When a potential difference is externally applied between (a) and (4b), carriers such as impurities are formed on the surface of the conductor film (6) or the interface with the layer in contact with the conductor film (6) in the conductor film (6). Move easily. When carrier movement occurs, the electrodes (4a) (4
The applied voltage from the outside is canceled between b). That is, when a DC voltage is continuously applied, the light output
There is a drawback that a reliability problem called DC drift occurs in which the applied voltage characteristic shifts.

On the other hand, a method of reducing the driving voltage when the electrodes are electrically connected by a conductive film is described in Kiyono et al., JP-A-1-302325. FIG. 7 shows a sectional structure of the light control device. That is, 2
A buffer layer (3) is formed just above the optical waveguides (2a) and (2b), and the buffer layer (3) is formed as a conductor film (6).
And two optical waveguides (2a) via the conductor film (6).
A method of giving a potential difference between (2b) has been reported.

However, the potential difference generated between the two optical waveguides (2a) and (2b) that determine the drive voltage is caused by the potential difference between the electrodes (4).
In the case where the conductive film (6) conducts between a) and (4b), the voltage is determined by the respective voltage drops in the vertical and horizontal directions with respect to the substrate (1) due to the conductive film (6). That is, in the structure of FIG. 7, the potential difference generated between the two optical waveguides (2a) and (2b) is a value obtained by subtracting two vertical voltage drops from the externally applied voltage. It is obvious that the voltage drop in the vertical and horizontal directions is simply determined by the ratio of the vertical and horizontal lengths of the conductor film (6) between the electrodes (4a) and (4b).

Therefore, the potential difference generated between the two optical waveguides (2a) and (2b) in the structure of FIG. 7 is the difference between the vertical and horizontal voltage drops caused by the buffer layer (3).
5 and 6, where the potential difference between the two optical waveguides (2a) and (2b) is substantially determined by two vertical voltage drops from the externally applied voltage. Has the disadvantage that the drive voltage is hardly reduced. SUMMARY OF THE INVENTION It is an object of the present invention to eliminate a limitation imposed on the resistance of a conductor film for suppressing a temperature drift, suppress a DC drift as well as a temperature drift, and obtain an optical control device capable of obtaining a lower driving voltage. Is to give.

[0012]

According to the present invention, there is provided an optical control device comprising: an optical waveguide formed on a surface of a substrate having a pyroelectric effect; at least one pair of electrodes formed near the optical waveguide; A film body formed between the substrate and the electrode, and a conductive film having higher conductivity than the film body and covering the vicinity of the pair of electrodes, wherein the conductive film is in the vicinity of the pair of electrodes. It is characterized by being insulated.

[0013] The light control device of the present invention comprises an optical waveguide formed on a surface of a substrate having a pyroelectric effect, at least one pair of electrodes formed near the optical waveguide, and at least a portion between the substrate and the electrode. And a conductive film having a higher conductivity than the film body and covering the vicinity of the pair of electrodes, wherein the conductive film is insulated near the optical waveguide. I do.

The light control device according to the present invention is characterized in that the conductor film is formed at least between the pair of electrodes.

In the light control device of the present invention, the thickness of the film formed between the pair of electrodes is formed to be smaller than the thickness of the film formed in another portion up to the vicinity of the pair of electrodes. And the conductive film is insulated on the thinly formed film body.

According to another aspect of the present invention, there is provided an optical control device comprising: an optical waveguide formed on a surface of a substrate having a pyroelectric effect; at least one pair of electrodes formed near the optical waveguide; A formed film, an insulating material formed on the substrate and between the pair of electrodes and having higher insulating property than the film, and a conductive film formed on the insulating material and having higher conductivity than the film. Wherein the conductive film is insulated in the vicinity of each of the pair of electrodes.

An optical control device according to the present invention comprises an optical waveguide formed on a surface of a substrate having a pyroelectric effect, at least one pair of electrodes formed in the vicinity of the optical waveguide, and between at least the substrate and the electrodes. A formed film body, an insulating material formed on the substrate and between the pair of electrodes, and having higher insulating property than the film body, and covering the vicinity of the pair of electrodes, which has higher conductivity than the film body. A conductive film, wherein the conductive film is formed on the insulating material between the pair of electrodes, and is insulated near the electrodes.

An optical control device according to the present invention includes an optical waveguide formed on a substrate surface having a pyroelectric effect, at least one pair of electrodes formed in the vicinity of the optical waveguide, and between at least the substrate and the electrodes. A formed film body, an insulating material formed on the substrate and between the pair of electrodes, and having higher insulating property than the film body, and covering the vicinity of the pair of electrodes, which has higher conductivity than the film body. A conductive film, wherein the conductive film is formed on the insulating material between the pair of electrodes, and is insulated near the optical waveguide. In the present invention, a substrate having a pyroelectric effect is one in which electric charges are generated in a portion where the temperature of the substrate fluctuates due to a change in the temperature of the atmosphere, for example, LiNbO ₃ or LiTib.
This is a substrate made of O ₃ .

In the light control device according to the present invention, the conductor film is insulated at only a part between the electrodes, but at this time, localization of charges generated by the pyroelectric effect does not occur, and no temperature drift occurs. Was found. As a result, the restriction imposed on the resistance of the conductive film can be eliminated, and an optical control device with improved production yield can be obtained. Further, since the insulation is performed in the vicinity of the electrode, the drop of the externally applied voltage occurs in the insulated portion, and the voltage applied to the conductor film decreases. Therefore, the amount of movement of carriers such as impurities on the surface of the conductive film or the interface with the layer in contact with the conductive film in the conductive film is reduced, and an optical control device capable of suppressing DC drift can be obtained.

Further, since each insulated portion is set in the vicinity of the electrode, that is, in the vicinity of the two optical waveguides, the two optical waveguides (2a) and (2b) for the externally applied voltage that determines the driving voltage. Can be made larger than the conventional structure. Therefore, a light control device driven at low voltage can be obtained.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings.

Embodiment 1 FIG. 1 is a sectional view showing a structure of a light control device according to one embodiment of the present invention.
The light control device shown in FIG. 1 is a LiNbO ₃ substrate (1)
Channel optical waveguides (2a) formed on the surface of
An optical circuit (5) comprising (2b) and an optical waveguide (2a)
An electrode (4a) on (2b) via a buffer layer (3)
(4b) is formed. The electrodes (4a) and (4b)
, A conductor film (6) is formed.

The conductive film (6) is not electrically connected between the electrodes (4a) and (4b), and is insulated at a position near the electrodes (4a) and (4b) (7) (hereinafter referred to as "insulating part"). Call it)
There is. The optical circuit (5) is a directional coupler, a Mach-Zehnder type, a balance bridge type, or the like. The role of the buffer layer (3) is to prevent absorption of guided light by the electrodes (4a) and (4b) by using a material that is optically transparent and has a lower refractive index than that of the substrate. 4b)
When a microwave is applied to the substrate, there is a role of adjusting the speed of the microwave propagating through the electrodes (4a) and (4b) by using the dielectric constant and the thickness of the buffer layer (3).

As a material that fulfills these two roles, an SiO ₂ -based material is mainly used, but any material may be used as long as it has lower conductivity than the conductor film (6), that is, a material having higher insulation. Also ITO (InO ₃ -SnO)
_{2), Al2O 3, MgF 2} , SiON, Si 3 N 4,
SiO ₂ doped with phosphorus (P), titanium (Ti), boron (B), germanium (Ge), or the like is used, and a CVD method, a sputtering method, an evaporation method, or the like is used as a deposition method. As a material of the electrodes (4a) and (4b), A
Various conductive substances such as u, Al, Mo, Cu, WSi, ITO, ZnO-based materials, and conductive polymers are used.

In the present embodiment, the conductor film (6) has S
i, but Au, Al, Mo, Cu, WS
metal materials such as i, ITO, ZnO-based, conductive polymer,
A conductive material such as a semiconductor material such as Si and Si is used. Further, the insulating portion (7) in this embodiment is formed without the conductor film (6), and the insulation between the electrodes (4a) and (4b) is obtained by the buffer layer (3). Note that the insulating portion (7) was formed using a normal photolithography method. The substrate used is LiNbO.
Obviously, any substrate having a pyroelectric effect, such as LiTiO ₃ , may be used instead of the _three substrates. It is apparent that the same effect can be obtained even if the number of insulating portions is not two but more.

In the embodiment of the present invention, if the insulation between the electrodes (4a) and (4b) of the conductor film (6) is only one part, the pyroelectric effect which causes the temperature drift is caused. The generated charges are not localized, and the charges are transferred to the substrate (1).
Was found to be uniformly distributed on the surface and no temperature drift occurred. Therefore, in the conventional structure, the electrodes (4a) (4
b), the resistance between the electrodes (4a) and (4b) by the conductor film (6) is set to 10
^7-10 should be ¹⁰ Omega, necessary to add a production process, such as temperature control severe heat treatment in order to perform or restricted to the material of the conductive film (6), the control of the resistance value in order to achieve this As a result, the manufacturing process is complicated, and the yield of devices is also deteriorated. According to the present invention, it is possible to eliminate restrictions imposed on the material and the resistance of the conductive film, and to obtain a light control device with improved production yield.

In the structure shown in FIG. 1, the drop of the externally applied voltage is small in the conductor film (6) and small in the insulation portion (7) because of the relationship between the resistance values of the conductor film (6) and the insulating portion (7). It is obvious that it is great. Therefore, of the conductive film (6) in which carriers such as impurities are easily moved by an applied voltage that causes DC drift, a layer in contact with the surface of the conductive film (6) or the conductive film (6). The voltage at the interface with is smaller than that of the conventional structure. Therefore, it is possible to obtain an optical control device in which carrier movement is suppressed and DC drift is small.

[Embodiment 2] FIG. 2B is a sectional view showing the structure of a light control device according to another embodiment of the present invention. In FIG. 2B, two insulating portions (7) are formed in the vicinity of the electrodes (4a) and (4b).
Part of the buffer layer (3) between a) and (4b) is thinner than the thickness of the buffer layer (3) in the other part. FIG.
In (b), the effects related to the temperature drift, the DC drift, and the low voltage driving can be further reduced as compared with the embodiment shown in FIG.

2 for the application of an external voltage that determines the drive voltage
The potential difference generated between the two optical waveguides (2a) and (2b) is such that when the electrodes (4a) and (4b) are electrically connected by the conductive film (6), the substrate (1) formed by the conductive film (6) is used. ) Is determined by the respective voltage drops in the vertical and horizontal directions. However, in the present invention, since almost no voltage is applied to the conductor film (6) in the horizontal direction with respect to the substrate (1),
Voltage drops in the vertical and horizontal directions with respect to the substrate (1) are made in the buffer layer (3).

In FIG. 2 (b), the buffer layer (3) between the electrodes (4a) and (4b) is thinner than the thickness of the buffer layer (3) in the other part, and two insulating layers are provided. Department (7)
Are formed on the thinned buffer layer (3) near the electrodes (4a) and (4b). At this time, the electrode (4a)
Since a part of the buffer layer (3) between (4b) is thin, the resistance value in the horizontal direction increases, and the horizontal voltage drop of the externally applied voltage increases. With this structure, the voltage drop in the vertical direction with respect to the substrate (1) is substantially determined by the conductive film (6) having a smaller resistance value than the buffer layer (3), and the voltage in the horizontal direction with respect to the substrate (1) is reduced. The drop is determined by the thinned buffer layer (3) having a large resistance value. Therefore, lower voltage driving can be obtained.

In the embodiment of the present invention, SiO ₂ is used for the buffer layer (3), and a part of the buffer layer (3) is thinned by a usual photolithography method. Also,
Substrate (1), optical waveguides (2a) (2b), conductor film (6)
The same one as in the embodiment shown in FIG. 1 was used.

[Embodiment 3] FIG. 3B is a sectional view showing the structure of a light control device according to another embodiment of the present invention. In FIG. 3B, two insulating portions (7) are formed in the vicinity of the electrodes (4a) and (4b).
A part of the buffer layer between a) and (4b) is removed, and a material (8) having higher insulating properties than the buffer layer (3) (hereinafter referred to as “insulating material”) is formed in that part. Since the resistance in the horizontal direction with respect to the substrate (1) can be easily increased as compared with the structure of FIG. 2B in which the thickness of the buffer layer (3) is reduced, low voltage driving can be easily obtained. .

That is, in FIG. 3B, the electrode (4a)
The buffer layer (3) between (4b) is removed, an insulating material (8) is formed there, and two insulating portions (7) are formed near the electrodes (4a) and (4b). Is formed on. With this structure, the voltage drop in the vertical direction with respect to the substrate (1) is substantially determined by the conductive film (6) having a smaller resistance value than the buffer layer (3), and the voltage in the horizontal direction with respect to the substrate (1) is reduced. The drop is determined by the insulating material (8) having a large resistance value. Therefore, a lower voltage drive can be obtained as compared with the comparative example shown in FIG. Further in FIG. 3, the buffer layer with phosphorus SiO ₂ doped with (P) (hereafter referred to as "PSG"), SiO ₂ (hereafter referred to as "NSG") nothing is doped in the insulating material. By selecting the concentration of phosphorus (P), PSG can reduce the resistance value from about 1/5 to about 1 / 10,000,000 compared to NSG. That is, the potential difference in the horizontal direction with respect to the substrate (1) can be made as large as possible with the externally applied voltage. Therefore, low voltage driving becomes possible.

For removal of a part of the buffer layer (3) and formation of the insulating material (8), a usual photolithography method was used. Further, the optical waveguides (2a) and (2b) and the conductor film (6)
The same material and the same forming method as those of the embodiment shown in FIG. The combination of the materials of the buffer layer (3) and the insulating material (8) is such that the buffer layer (3) and the insulating material (8) are less conductive than the conductor film (6), and the insulating material (8) is a buffer. Obviously, any material can be used as long as it has a higher insulating property than the layer (3).

[Embodiment 4] FIG. 4B is a sectional view showing the structure of a light control device according to another embodiment of the present invention. In FIG. 4B, the buffer layer (3) of the electrodes (4a) and (4b) has been removed, and two insulating portions (7) are provided on the substrate (1) near the electrodes (4a) and (4b). Is formed on the surface. Therefore, according to this structure, the voltage drop in the vertical direction with respect to the substrate (1) is entirely determined by the conductive film (6), and the voltage drop in the horizontal direction with respect to the substrate (1) is usually higher than that of the buffer layer (3). It is determined by the substrate (1) having a large resistance value.

In order to remove a part of the buffer layer (3), a usual photolithographic method was used. Further, the same material and forming method as those of FIG. 1 were used for the substrate (1), the optical waveguides (2a) and (2b), and the conductor film (6).

In FIG. 4B, the same substrates as in FIG. 1 are used for the substrate (1), the optical waveguides (2a) and (2b) and the conductor film (6), but the volume resistivity of the LiNbO ₃ substrate (1) is used. The rate is S
₂ to 10 times the volume resistivity of the iO ₂ buffer layer (3)
00 times larger. Therefore, a lower voltage drive can be obtained as compared with the comparative example shown in FIG.

[0038]

As described above, according to the present invention, the restriction imposed on the resistance of the conductor film for suppressing the temperature drift is eliminated, and the DC drift as well as the temperature drift is suppressed. This has the effect of providing a highly reliable and low driving voltage light control device capable of obtaining a low driving voltage.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a structure of a light control device according to one embodiment of the present invention.

FIG. 2 is a sectional view showing the structure of a light control device according to another embodiment of the present invention.

FIG. 3 is a sectional view showing the structure of a light control device according to another embodiment of the present invention.

FIG. 4 is a sectional view showing the structure of a light control device according to another embodiment of the present invention.

FIG. 5 is a cross-sectional view showing the structure of a conventional light control device.

FIG. 6 is a sectional view showing the structure of a conventional light control device.

FIG. 7 is a sectional view showing the structure of a conventional light control device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2a, 2b Optical waveguide 3 Buffer layer 4a, 4b Electrode 5 Optical circuit 6 Conductive film 7 Insulating part 8 Insulating material

Claims (7)

[Claims] An optical waveguide formed on a surface of a substrate having a pyroelectric effect, at least one pair of electrodes formed near the optical waveguide, and a film formed at least between the substrate and the electrodes. And a conductive film that covers the vicinity of the pair of electrodes and has higher conductivity than the film body, and the conductive film is insulated near the respective electrodes of the pair of electrodes. Light control device. 2. An optical waveguide formed on the surface of a substrate having a pyroelectric effect, at least one pair of electrodes formed near the optical waveguide, and a film formed between at least the substrate and the electrodes. And a conductive film that covers the vicinity of the pair of electrodes and has higher conductivity than the film body, wherein the conductive film is insulated near the optical waveguide. 3. The light control device according to claim 1, wherein said conductor film is formed at least between said pair of electrodes. 4. The light control device according to claim 1, wherein the thickness of the film formed between the pair of electrodes is formed in another portion up to the vicinity of the pair of electrodes. A light control device, wherein the light control device is formed thinner than the thickness of the film body, and the conductor film is insulated on the thinly formed film body. 5. An optical waveguide formed on a surface of a substrate having a pyroelectric effect, and at least one optical waveguide formed near the optical waveguide.
A pair of electrodes, at least a film body formed between the substrate and the electrode, an insulating material formed on the substrate and between the pair of electrodes, and having a higher insulating property than the film body; And a conductive film having higher conductivity than the film body, wherein the conductive film is insulated near each of the pair of electrodes. 6. An optical waveguide formed on the surface of a substrate having a pyroelectric effect, and at least one optical waveguide formed near the optical waveguide.
A pair of electrodes, a film formed at least between the substrate and the electrode, an insulating material formed on the substrate and between the pair of electrodes, and having a higher insulating property than the film; A conductive film having greater conductivity and covering the vicinity of the pair of electrodes, the conductive film being formed on the insulating material between the pair of electrodes, and being insulated near the electrodes. A light control device. 7. An optical waveguide formed on a surface of a substrate having a pyroelectric effect, and at least one optical waveguide formed near the optical waveguide.
A pair of electrodes, a film formed at least between the substrate and the electrode, an insulating material formed on the substrate and between the pair of electrodes, and having a higher insulating property than the film; A conductive film having higher conductivity and covering the vicinity of the pair of electrodes, the conductive film being formed on the insulating material between the pair of electrodes, and insulated near the optical waveguide. A light control device characterized in that: