JP2013079990A - Optical waveguide element and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide element which stabilizes DC drift, does not complicate a manufacturing process, and controls product characteristics accurately, and to provide a method of manufacturing the same.SOLUTION: An optical waveguide element comprises a substrate 1 having an electro-optical effect, an optical waveguide 2 formed on the substrate, a buffer layer 5 formed on the optical waveguide and having SiOas main material, and modulation electrodes 3,4 formed on the buffer layer and modulating light waves propagating through the optical waveguide. On the substrate side of the buffer layer, an area 6 is formed so that the content of Li becomes 1×10(atoms/cm) or more.

Description

  The present invention relates to an optical waveguide device and a method for manufacturing the same, and more particularly, to an optical waveguide device having a stabilized DC drift in an optical waveguide device in which an optical waveguide, a buffer layer, and a modulation electrode are formed on a substrate having an electro-optic effect, and a method for manufacturing the same. About.

  In the optical communication field and the optical measurement field, an optical waveguide device such as a light intensity modulator in which an optical waveguide and a modulation electrode are formed on a substrate having an electro-optic effect such as lithium niobate (LN) is widely used. FIG. 1 is a cross-sectional view showing a part of an optical waveguide element. An optical waveguide 2 is formed by forming a thermal diffusion portion such as Ti on a substrate 1 having an electro-optic effect. A signal electrode 3 and a ground electrode 4 are arranged in the vicinity of the optical waveguide 2 as modulation electrodes for applying an electric field to the optical waveguide.

  In an optical waveguide element manufactured using a substrate having an electro-optic effect such as LN, when a DC voltage for bias control is applied, a so-called DC drift phenomenon occurs in which the bias point shifts. In order to use an optical waveguide element in an optical communication system, it is necessary to realize long-term stable driving, and stabilization of DC drift, such as reduction of the DC drift phenomenon, has been an issue.

  With respect to such a problem, in Patent Document 1, it is conceivable that Li from the substrate becomes a mobile ion in the buffer layer as a cause of the DC drift phenomenon, and a film that suppresses the diffusion of Li is formed between the substrate and the buffer. It has been proposed to stabilize the properties by inserting it between the layers.

  Patent Document 2 proposes a method of forming a protective film on the buffer layer in order to prevent the contamination source from entering the buffer layer, considering that the contamination source enters from the outside of the optical waveguide element.

  Further, in Patent Document 3, annealing is performed in an oxygen dry gas atmosphere to control the amount of OH in the substrate and the buffer layer and stabilize the DC drift characteristics.

  However, in the techniques according to Patent Document 1 and Patent Document 2, a diffusion suppression layer and a protective film layer are used in order to prevent impurities from entering, which can be mainly movable ions from the substrate or the outside. In order for these films to exhibit their effects, it is necessary to use a material having a small diffusion coefficient and hardly causing ionic polarization. For this reason, metals and semiconductors are mainly used as these materials. When such a material is laid between the substrate on which the optical waveguide is formed and the buffer layer above it, characteristics such as optical loss and extinction ratio in the optical waveguide element due to the refractive index and light absorption of the material. Cause deterioration.

  Similarly, when it is laid on the buffer layer, there is a possibility that signal propagation loss such as signal electrodes and electric field application efficiency may be lowered, and the characteristics of the optical waveguide element are deteriorated. In addition, in order to suppress the deterioration of characteristics, measures such as partial laying may be considered, but in this case, it is necessary to perform pattern formation using a lithography technique or the like, resulting in poor productivity. Cause problems.

  In addition, there is a method of injecting impurities into the buffer layer in order to lower the resistance value of the buffer layer or to control the film quality. However, with such a technique, the balance with the substrate and the electrode becomes a problem, and as a substantial device When stabilizing the characteristics, it is necessary to strictly control the characteristics, and it is substantially difficult to stabilize the characteristics.

JP 7-64126 A JP 2001-133743 A JP-A-7-128624

  An object of the present invention is to provide an optical waveguide element that solves the above-described problems, stabilizes DC drift, does not complicate the manufacturing process, and can control the product characteristics with high accuracy, and a manufacturing method thereof.

In order to solve the above-mentioned problems, an invention according to claim 1 is directed to a substrate having an electro-optic effect, an optical waveguide formed on the substrate, and a buffer mainly composed of SiO ₂ formed on the optical waveguide. In an optical waveguide device having a layer and a modulation electrode that is formed on the buffer layer and modulates a light wave propagating through the optical waveguide, the Li content is 1 × 10 ²¹ on the substrate side of the buffer layer. It is characterized by being (atoms / cm ³ ) or more.

According to a second aspect of the present invention, in the optical waveguide device according to the first aspect, the thickness of the region containing 1 × 10 ²¹ (atoms / cm ³ ) or more of Li in the buffer layer is ¼ in the film thickness direction. It is characterized by occupying the above.

  The invention according to claim 3 is the optical waveguide device according to claim 1 or 2, wherein the buffer layer is doped with at least one of In or Ti.

The invention according to claim 4 is a substrate having an electro-optic effect, an optical waveguide formed on the substrate, a buffer layer mainly made of SiO ₂ formed on the optical waveguide, and on the buffer layer In the method of manufacturing an optical waveguide element having a modulation electrode that modulates a light wave propagating through the optical waveguide, at least after the buffer layer is formed, heat treatment is performed at 400 to 1000 ° C. mainly in an oxygen atmosphere. Thus, a region having a Li content of 1 × 10 ²¹ (atoms / cm ³ ) or more is formed on the substrate side of the buffer layer.

  The invention according to claim 5 is the method for manufacturing an optical waveguide element according to claim 4, wherein, in the heat treatment, a material containing Li is heat-treated in the same atmosphere.

The invention according to claim 6 is a substrate having an electro-optic effect, an optical waveguide formed on the substrate, a buffer layer mainly made of SiO ₂ formed on the optical waveguide, and on the buffer layer In the method of manufacturing an optical waveguide device having a modulation electrode that modulates a light wave propagating through the optical waveguide, a material containing Li is used as a film formation material when the buffer layer is formed by a vacuum film formation method. It is characterized by being formed by mixing so that the Li content of the buffer layer is 1 × 10 ²¹ (atoms / cm ³ ) or more.

According to the first aspect of the present invention, a substrate having an electro-optic effect, an optical waveguide formed on the substrate, a buffer layer mainly made of SiO ₂ formed on the optical waveguide, and the buffer layer In the optical waveguide device having a modulation electrode that modulates a light wave propagating through the optical waveguide, the Li content is 1 × 10 ²¹ (atoms / cm ³ ) or more on the substrate side of the buffer layer. Since the Li—O bond becomes strong, the movement of Li due to the electric field is suppressed, and the DC drift can be stabilized, for example, by reducing the DC drift. In addition, since Li is contained by heat treatment, the Li content can be easily controlled by adjusting the temperature, the manufacturing process is not complicated, and the product characteristics can be controlled with high accuracy.

According to the second aspect of the present invention, the thickness of the region containing 1 × 10 ²¹ (atoms / cm ³ ) or more of Li in the buffer layer occupies 1/4 or more in the film thickness direction, thereby stabilizing the DC drift. This can be realized more reliably.

  According to the invention of claim 3, since the buffer layer is doped with at least one of In or Ti, the resistance value of the buffer layer can be lowered, and the DC drift characteristic can be further stabilized. It becomes possible.

According to the invention of claim 4, a substrate having an electro-optic effect, an optical waveguide formed on the substrate, a buffer layer mainly made of SiO ₂ formed on the optical waveguide, and on the buffer layer In the method of manufacturing an optical waveguide element having a modulation electrode that modulates a light wave propagating through the optical waveguide, at least after the buffer layer is formed, heat treatment is performed at 400 to 1000 ° C. mainly in an oxygen atmosphere. Thus, a region where the Li content is 1 × 10 ²¹ (atoms / cm ³ ) or more is formed on the substrate side of the buffer layer, so that the manufacturing process is complicated only by controlling the temperature of the heat treatment. Therefore, it is possible to provide an optical waveguide element in which the content of Li in the buffer layer can be accurately controlled and the characteristics of DC drift are stabilized.

  According to the invention of claim 5, since the material containing Li is heat-treated in the atmosphere together with the heat treatment, an optical waveguide device capable of promoting the penetration of Li from the surface of the buffer layer and stabilizing the DC drift characteristic is obtained. It becomes possible to manufacture efficiently.

According to the invention of claim 6, a substrate having an electro-optic effect, an optical waveguide formed on the substrate, a buffer layer mainly made of SiO ₂ formed on the optical waveguide, and the buffer layer In the method of manufacturing an optical waveguide device having a modulation electrode that modulates a light wave propagating through the optical waveguide, and the buffer layer is formed by a vacuum film formation method, a material containing Li as a film formation material Is formed so that the Li content of the buffer layer is 1 × 10 ²¹ (atoms / cm ³ ) or more, so that Li can be contained in advance when forming the buffer layer, which complicates the manufacturing process. Thus, an optical waveguide device with stabilized DC drift characteristics can be efficiently manufactured.

It is sectional drawing which shows an example of the conventional optical waveguide element. It is sectional drawing which shows the optical waveguide element of this invention. It is a graph which shows the distribution condition of Li when heat processing temperature is 200 degreeC. It is a graph which shows the distribution condition of Li when heat processing temperature is 500 degreeC. It is a graph which shows the distribution condition of Li when heat processing temperature is 600 degreeC. It is a graph which shows the distribution condition of Li when heat processing temperature is 700 degreeC. It is a graph which shows the change of DC drift of an optical waveguide element when not heat-treating and when heat-treating at 300 ° C or 600 ° C.

The optical waveguide device of the present invention will be described in detail below.
As shown in FIG. 2, the optical waveguide device of the present invention includes a substrate 1 having an electro-optic effect, an optical waveguide 2 formed on the substrate, and SiO ₂ formed on the optical waveguide as main materials. In the optical waveguide device having the buffer layer 5 that is formed and the modulation electrode (3, 4) that is formed on the buffer layer and modulates the light wave that propagates through the optical waveguide, The region 6 having a content of 1 × 10 ²¹ (atoms / cm ³ ) or more is formed.

A region in which the Li content is 1 × 10 ²¹ (atoms / cm ³ ) or more is formed in the buffer layer, and Li—O bonding is strengthened, so that Li is moved by an electric field such as a modulation signal or a DC bias bias. Is suppressed, the DC drift is reduced, and the characteristics of the DC drift can be stabilized. In addition, since the Li content can be easily controlled by controlling the temperature of the heat treatment, the manufacturing process is not complicated, and the product characteristics can be controlled with high accuracy.

  As the substrate used in the present invention, a substrate using a material having an electro-optic effect can be used. For example, lithium niobate, lithium tantalate, PLZT (lead lanthanum zirconate titanate), and quartz-based materials, A substrate combining these materials can also be used. In particular, when Li is contained in the buffer layer by heat treatment, a substrate rich in Li such as lithium niobate (LN) crystal is preferably used.

  As a method of forming the optical waveguide on the substrate, it can be formed by diffusing Ti or the like on the substrate surface by a thermal diffusion method or a proton exchange method. It is also possible to use a ridge-shaped waveguide having a convex portion corresponding to the optical waveguide, such as etching a substrate other than the optical waveguide or forming grooves on both sides of the optical waveguide. In the case of the ridge shape, since the electric field efficiency in the vicinity of the waveguide is high and Li is likely to move, the present invention can be applied more suitably.

  In the optical waveguide device, modulation electrodes such as a signal electrode 3 and a ground electrode 4 are formed on a substrate 1. Such an electrode can be formed by forming a Ti / Au electrode pattern, a gold plating method, or the like.

A buffer layer 5 is provided between the optical waveguide 2 and the modulation electrodes (3, 4). For the buffer layer, after forming the optical waveguide, a SiO ₂ film of about 0.5 μm to 1.0 μm is formed by sputtering using a SiO ₂ target mainly by parallel plate type magnetron sputtering. In particular, as the SiO ₂ target, it is possible to use a material in which a small amount of a metal such as In or Ti is doped for the purpose of reducing the resistance value of the film in order to stabilize the DC drift characteristic.

In the optical waveguide device of the present invention, the movement of Li due to the electric field is suppressed by forming a region in which the Li content is 1 × 10 ²¹ (atoms / cm ³ ) or more in the buffer layer. In addition, the thickness of the region containing 1 × 10 ²¹ (atoms / cm ³ ) or more of Li in the buffer layer occupies 1/4 or more in the film thickness direction, so that the stabilization of the DC drift can be realized more reliably. Is possible.

As a method of incorporating Li in the buffer layer, from a lithium niobate substrate which is a substrate having an electro-optic effect, Li can be supplied in abundance, and after forming a buffer layer mainly containing SiO ₂ , the entire substrate is formed. Li can be easily contained in the buffer layer by heat treatment. SiO ₂ which is a material of the buffer layer used in the optical device has a large diffusion coefficient, and Li can easily diffuse.

Further, in controlling the Li content, it can be easily controlled at the heat treatment temperature, and Li can be sufficiently diffused at a temperature in the range of 400 to 1000 ° C. In particular, when thermal diffusion is performed at 600 ° C. or higher, a region containing 1 × 10 ²¹ (atoms / cm ³ ) or higher can be easily formed. The heat treatment temperature is not in the unit of several degrees, and it is possible to control the Li diffusion even with a rougher temperature control.

Li is also an ion that moves in SiO ₂ , and the resistivity and capacitance value of the buffer layer are also controlled by the amount of Li. Li enters the buffer layer even without heat treatment or at a low temperature of about 200 ° C., but Li has different mobility in the buffer layer depending on the density of the buffer layer and the bonding state between Li and oxygen. In the present invention, by performing heat treatment in an oxygen atmosphere at 400 to 1000 ° C., preferably 600 ° C. or higher, the Li—O bond is strengthened and the buffer layer itself is dense. As a result, the mobility of Li can be reduced, and the movement of Li due to the electric field that becomes an element that deteriorates the DC drift can be suppressed.

3 to 6 show that an SiO ₂ buffer layer of about 0.6 to 0.8 μm formed on an LN substrate is heat-treated at 200 ° C., 500 ° C., 600 ° C. and 700 ° C. It is the graph which measured distribution of content of Li.

FIG. 3 shows a case where heat treatment is performed at 200 ° C., but the Li content in the buffer layer is 1 × 10 ¹⁹ (atoms / cm ³ ) or less. FIG. 4 shows a case where heat treatment is performed at 500 ° C., and the Li content in the buffer layer is such that the thickness of a region of 1 × 10 ²¹ (atoms / cm ³ ) or more is about 0.4 μm. FIG. 5 shows a case where heat treatment is performed at 600 ° C. The Li content in the buffer layer is about 0.6 μm in the thickness of a region of 1 × 10 ²¹ (atoms / cm ³ ) or more. Furthermore, FIG. 6 shows a case where heat treatment is performed at 700 ° C., and the content of Li in the buffer layer is about 0.8 μm in the thickness of a region of 1 × 10 ²¹ (atoms / cm ³ ) or more. Spread in the layers.

  FIG. 7 is a graph showing the state of DC drift in a temperature environment of 150 ° C. for an optical waveguide element that is not heat-treated and an optical waveguide element that is heat-treated at 300 ° C. or 600 ° C. Compared with optical waveguide elements that have not been heat-treated and optical waveguide elements that have been heat-treated at 300 ° C., optical waveguide elements that have been heat-treated at 600 ° C. have reduced DC drift under the same test environment, and their characteristics have been stabilized. Is easily understood. Similarly, as a result of experiments, when heat treatment was performed at 400 ° C. or higher, a decrease in DC drift was observed, and in particular, at 600 ° C. or higher, almost the same result was obtained. When the temperature exceeds 1000 ° C., there is no difference in the effect of Li diffusion. Rather, the optical waveguide is formed by Ti thermal diffusion, which causes problems such as Ti diffusion progressing.

As a method of incorporating Li into the buffer layer, further, in the heat treatment, infiltration of Li from the surface of the buffer layer is promoted by heat-treating a material rich in Li such as LiCl or Li ₂ O in the same atmosphere. In addition, an optical waveguide element with stabilized DC drift characteristics can be efficiently manufactured.

Further, after the optical waveguide is formed on the substrate, a buffer layer containing SiO ₂ as a main material is formed thereon by a vacuum film forming method such as sputtering, vapor deposition or CVD. In particular, it is preferably formed by a sputtering method. When forming this buffer layer, a film forming material, for example, a sputtering target is mixed with a material containing Li such as Li ₂ O, and the content of Li in the buffer layer is 1 × 10 ²¹ (atoms / cm ³ ). It is also possible to form it as described above. When the buffer layer is formed, Li can be contained in advance, and the optical waveguide element with stabilized DC drift characteristics can be efficiently manufactured without complicating the manufacturing process.

  As described above, according to the present invention, it is possible to provide an optical waveguide element that stabilizes DC drift, does not complicate the manufacturing process, and can accurately control product characteristics, and a manufacturing method thereof. .

DESCRIPTION OF SYMBOLS 1 Substrate having electro-optic effect 2 Optical waveguide 3 Signal electrode 4 Ground electrode 5 Buffer layer 6 Li-containing region

  The present invention relates to an optical waveguide device and a method for manufacturing the same, and more particularly, to an optical waveguide device having a stabilized DC drift in an optical waveguide device in which an optical waveguide, a buffer layer, and a modulation electrode are formed on a substrate having an electro-optic effect, and a method for manufacturing the same. About.

  In the optical communication field and the optical measurement field, an optical waveguide device such as a light intensity modulator in which an optical waveguide and a modulation electrode are formed on a substrate having an electro-optic effect such as lithium niobate (LN) is widely used. FIG. 1 is a cross-sectional view showing a part of an optical waveguide element. An optical waveguide 2 is formed by forming a thermal diffusion portion such as Ti on a substrate 1 having an electro-optic effect. A signal electrode 3 and a ground electrode 4 are arranged in the vicinity of the optical waveguide 2 as modulation electrodes for applying an electric field to the optical waveguide.

  In an optical waveguide element manufactured using a substrate having an electro-optic effect such as LN, when a DC voltage for bias control is applied, a so-called DC drift phenomenon occurs in which the bias point shifts. In order to use an optical waveguide element in an optical communication system, it is necessary to realize long-term stable driving, and stabilization of DC drift, such as reduction of the DC drift phenomenon, has been an issue.

  With respect to such a problem, in Patent Document 1, it is conceivable that Li from the substrate becomes a mobile ion in the buffer layer as a cause of the DC drift phenomenon, and a film that suppresses the diffusion of Li is formed between the substrate and the buffer. It has been proposed to stabilize the properties by inserting it between the layers.

  Patent Document 2 proposes a method of forming a protective film on the buffer layer in order to prevent the contamination source from entering the buffer layer, considering that the contamination source enters from the outside of the optical waveguide element.

  Further, in Patent Document 3, annealing is performed in an oxygen dry gas atmosphere to control the amount of OH in the substrate and the buffer layer and stabilize the DC drift characteristics.

  However, in the techniques according to Patent Document 1 and Patent Document 2, a diffusion suppression layer and a protective film layer are used in order to prevent impurities from entering, which can be mainly movable ions from the substrate or the outside. In order for these films to exhibit their effects, it is necessary to use a material having a small diffusion coefficient and hardly causing ionic polarization. For this reason, metals and semiconductors are mainly used as these materials. When such a material is laid between the substrate on which the optical waveguide is formed and the buffer layer above it, characteristics such as optical loss and extinction ratio in the optical waveguide element due to the refractive index and light absorption of the material. Cause deterioration.

  Similarly, when it is laid on the buffer layer, there is a possibility that signal propagation loss such as signal electrodes and electric field application efficiency may be lowered, and the characteristics of the optical waveguide element are deteriorated. In addition, in order to suppress the deterioration of characteristics, measures such as partial laying may be considered, but in this case, it is necessary to perform pattern formation using a lithography technique or the like, resulting in poor productivity. Cause problems.

  In addition, there is a method of injecting impurities into the buffer layer in order to lower the resistance value of the buffer layer or to control the film quality. However, with such a technique, the balance with the substrate and the electrode becomes a problem, and as a substantial device When stabilizing the characteristics, it is necessary to strictly control the characteristics, and it is substantially difficult to stabilize the characteristics.

JP 7-64126 A JP 2001-133743 A JP-A-7-128624

  An object of the present invention is to provide an optical waveguide element that solves the above-described problems, stabilizes DC drift, does not complicate the manufacturing process, and can control the product characteristics with high accuracy, and a manufacturing method thereof.

In order to solve the above-mentioned problems, an invention according to claim 1 is directed to a substrate having an electro-optic effect, an optical waveguide formed on the substrate, and a buffer mainly composed of SiO ₂ formed on the optical waveguide. In an optical waveguide device having a layer and a modulation electrode that is formed on the buffer layer and modulates a light wave propagating through the optical waveguide, the Li content is 1 × 10 ²¹ on the substrate side of the buffer layer. A region of (atoms / cm ³ ) or more is formed, and the thickness of the region occupies 1/4 or more in the film thickness direction .

The invention according to claim 2 is the optical waveguide element according to claim 1 , wherein the buffer layer is doped with at least one of In and Ti.

According to a third aspect of the present invention, there is provided a substrate having an electro-optic effect, an optical waveguide formed on the substrate, a buffer layer mainly made of SiO ₂ formed on the optical waveguide, and on the buffer layer In the method of manufacturing an optical waveguide element having a modulation electrode that modulates a light wave propagating through the optical waveguide, at least after the buffer layer is formed, heat treatment is performed at 400 to 1000 ° C. mainly in an oxygen atmosphere. Thus, on the substrate side of the buffer layer, an area where the Li content is 1 × 10 ²¹ (atoms / cm ³ ) or more occupies 1/4 or more in the film thickness direction. It is formed as follows.

According to a fourth aspect of the present invention, in the method for manufacturing an optical waveguide element according to the fourth aspect, in the heat treatment, a material containing Li is heat-treated in the same atmosphere.

The invention according to claim 5 is a substrate having an electro-optic effect, an optical waveguide formed on the substrate, a buffer layer mainly made of SiO ₂ formed on the optical waveguide, and on the buffer layer In the method of manufacturing an optical waveguide device having a modulation electrode that modulates a light wave propagating through the optical waveguide, a material containing Li is used as a film formation material when the buffer layer is formed by a vacuum film formation method. mix, characterized in that the content of Li in the buffer layer is a region to be a ^{1 × 10 21 (atoms / cm} 3) or more, the thickness of the region, is formed so as to occupy more than a quarter the thickness direction And

According to the first aspect of the present invention, a substrate having an electro-optic effect, an optical waveguide formed on the substrate, a buffer layer mainly made of SiO ₂ formed on the optical waveguide, and the buffer layer In the optical waveguide device having a modulation electrode that modulates a light wave propagating through the optical waveguide, the Li content is 1 × 10 ²¹ (atoms / cm ³ ) or more on the substrate side of the buffer layer. preparative are regions ing formation, the thickness of the region may occupy 1/4 or more in the thickness direction, because the binding of Li-O is increased, the movement of Li reduces the DC drift is suppressed by the electric field For example, DC drift can be stabilized. In addition, since Li is contained by heat treatment, the Li content can be easily controlled by adjusting the temperature, the manufacturing process is not complicated, and the product characteristics can be controlled with high accuracy.

According to the second aspect of the present invention, since the buffer layer is doped with at least one of In and Ti, the resistance value of the buffer layer can be lowered and the DC drift characteristic can be further stabilized. It becomes possible.

According to the invention of claim 3 , a substrate having an electro-optic effect, an optical waveguide formed on the substrate, a buffer layer mainly made of SiO ₂ formed on the optical waveguide, and the buffer layer In the method of manufacturing an optical waveguide element having a modulation electrode that modulates a light wave propagating through the optical waveguide, at least after the buffer layer is formed, heat treatment is performed at 400 to 1000 ° C. mainly in an oxygen atmosphere. Thus, a region where the Li content is 1 × 10 ²¹ (atoms / cm ³ ) or more is formed on the substrate side of the buffer layer, so that the manufacturing process is complicated only by controlling the temperature of the heat treatment. Therefore, it is possible to provide an optical waveguide element in which the content of Li in the buffer layer can be accurately controlled and the characteristics of DC drift are stabilized.

Further, according to the invention of claim 3, Li in the buffer layer is reduced to 1 × 10. ²¹ (Atoms / cm ³ ) When the thickness of the above-described region occupies ¼ or more in the film thickness direction, it is possible to more reliably realize stabilization of DC drift.

According to the invention of claim 4 , since the material containing Li is heat-treated in the atmosphere together with the heat treatment, an optical waveguide element that can promote the penetration of Li from the surface of the buffer layer and stabilize the DC drift characteristics. It becomes possible to manufacture efficiently.

According to the invention of claim 5 , a substrate having an electro-optic effect, an optical waveguide formed on the substrate, a buffer layer mainly made of SiO ₂ formed on the optical waveguide, and on the buffer layer In the method of manufacturing an optical waveguide device having a modulation electrode that modulates a light wave propagating through the optical waveguide, and the buffer layer is formed by a vacuum film formation method, a material containing Li as a film formation material Is formed so that the Li content of the buffer layer is 1 × 10 ²¹ (atoms / cm ³ ) or more, so that Li can be contained in advance when forming the buffer layer, which complicates the manufacturing process. Thus, an optical waveguide device with stabilized DC drift characteristics can be efficiently manufactured.

Furthermore, according to the invention of claim 5, Li in the buffer layer is reduced to 1 × 10. ²¹ (Atoms / cm ³ ) When the thickness of the above-described region occupies ¼ or more in the film thickness direction, it is possible to more reliably realize stabilization of DC drift.

It is sectional drawing which shows an example of the conventional optical waveguide element. It is sectional drawing which shows the optical waveguide element of this invention. It is a graph which shows the distribution condition of Li when heat processing temperature is 200 degreeC. It is a graph which shows the distribution condition of Li when heat processing temperature is 500 degreeC. It is a graph which shows the distribution condition of Li when heat processing temperature is 600 degreeC. It is a graph which shows the distribution condition of Li when heat processing temperature is 700 degreeC. It is a graph which shows the change of DC drift of an optical waveguide element when not heat-treating and when heat-treating at 300 ° C or 600 ° C.

The optical waveguide device of the present invention will be described in detail below.
As shown in FIG. 2, the optical waveguide device of the present invention includes a substrate 1 having an electro-optic effect, an optical waveguide 2 formed on the substrate, and SiO ₂ formed on the optical waveguide as main materials. In the optical waveguide device having the buffer layer 5 that is formed and the modulation electrode (3, 4) that is formed on the buffer layer and modulates the light wave that propagates through the optical waveguide, The region 6 having a content of 1 × 10 ²¹ (atoms / cm ³ ) or more is formed.

A region in which the Li content is 1 × 10 ²¹ (atoms / cm ³ ) or more is formed in the buffer layer, and Li—O bonding is strengthened, so that Li is moved by an electric field such as a modulation signal or a DC bias bias. Is suppressed, the DC drift is reduced, and the characteristics of the DC drift can be stabilized. In addition, since the Li content can be easily controlled by controlling the temperature of the heat treatment, the manufacturing process is not complicated, and the product characteristics can be controlled with high accuracy.

  As the substrate used in the present invention, a substrate using a material having an electro-optic effect can be used. For example, lithium niobate, lithium tantalate, PLZT (lead lanthanum zirconate titanate), and quartz-based materials, A substrate combining these materials can also be used. In particular, when Li is contained in the buffer layer by heat treatment, a substrate rich in Li such as lithium niobate (LN) crystal is preferably used.

  As a method of forming the optical waveguide on the substrate, it can be formed by diffusing Ti or the like on the substrate surface by a thermal diffusion method or a proton exchange method. It is also possible to use a ridge-shaped waveguide having a convex portion corresponding to the optical waveguide, such as etching a substrate other than the optical waveguide or forming grooves on both sides of the optical waveguide. In the case of the ridge shape, since the electric field efficiency in the vicinity of the waveguide is high and Li is likely to move, the present invention can be applied more suitably.

  In the optical waveguide device, modulation electrodes such as a signal electrode 3 and a ground electrode 4 are formed on a substrate 1. Such an electrode can be formed by forming a Ti / Au electrode pattern, a gold plating method, or the like.

A buffer layer 5 is provided between the optical waveguide 2 and the modulation electrodes (3, 4). For the buffer layer, after forming the optical waveguide, a SiO ₂ film of about 0.5 μm to 1.0 μm is formed by sputtering using a SiO ₂ target mainly by parallel plate type magnetron sputtering. In particular, as the SiO ₂ target, it is possible to use a material in which a small amount of a metal such as In or Ti is doped for the purpose of reducing the resistance value of the film in order to stabilize the DC drift characteristic.

In the optical waveguide device of the present invention, the movement of Li due to the electric field is suppressed by forming a region in which the Li content is 1 × 10 ²¹ (atoms / cm ³ ) or more in the buffer layer. In addition, the thickness of the region containing 1 × 10 ²¹ (atoms / cm ³ ) or more of Li in the buffer layer occupies 1/4 or more in the film thickness direction, so that the stabilization of the DC drift can be realized more reliably. Is possible.

As a method of incorporating Li in the buffer layer, from a lithium niobate substrate which is a substrate having an electro-optic effect, Li can be supplied in abundance, and after forming a buffer layer mainly containing SiO ₂ , the entire substrate is formed. Li can be easily contained in the buffer layer by heat treatment. SiO ₂ which is a material of the buffer layer used in the optical device has a large diffusion coefficient, and Li can easily diffuse.

Further, in controlling the Li content, it can be easily controlled at the heat treatment temperature, and Li can be sufficiently diffused at a temperature in the range of 400 to 1000 ° C. In particular, when thermal diffusion is performed at 600 ° C. or higher, a region containing 1 × 10 ²¹ (atoms / cm ³ ) or higher can be easily formed. The heat treatment temperature is not in the unit of several degrees, and it is possible to control the Li diffusion even with a rougher temperature control.

Li is also an ion that moves in SiO ₂ , and the resistivity and capacitance value of the buffer layer are also controlled by the amount of Li. Li enters the buffer layer even without heat treatment or at a low temperature of about 200 ° C., but Li has different mobility in the buffer layer depending on the density of the buffer layer and the bonding state between Li and oxygen. In the present invention, by performing heat treatment in an oxygen atmosphere at 400 to 1000 ° C., preferably 600 ° C. or higher, the Li—O bond is strengthened and the buffer layer itself is dense. As a result, the mobility of Li can be reduced, and the movement of Li due to the electric field that becomes an element that deteriorates the DC drift can be suppressed.

3 to 6 show that an SiO ₂ buffer layer of about 0.6 to 0.8 μm formed on an LN substrate is heat-treated at 200 ° C., 500 ° C., 600 ° C. and 700 ° C. It is the graph which measured distribution of content of Li.

FIG. 3 shows a case where heat treatment is performed at 200 ° C., but the Li content in the buffer layer is 1 × 10 ¹⁹ (atoms / cm ³ ) or less. FIG. 4 shows a case where heat treatment is performed at 500 ° C., and the Li content in the buffer layer is such that the thickness of a region of 1 × 10 ²¹ (atoms / cm ³ ) or more is about 0.4 μm. FIG. 5 shows a case where heat treatment is performed at 600 ° C. The Li content in the buffer layer is about 0.6 μm in the thickness of a region of 1 × 10 ²¹ (atoms / cm ³ ) or more. Furthermore, FIG. 6 shows a case where heat treatment is performed at 700 ° C., and the content of Li in the buffer layer is about 0.8 μm in the thickness of a region of 1 × 10 ²¹ (atoms / cm ³ ) or more. Spread in the layers.

  FIG. 7 is a graph showing the state of DC drift in a temperature environment of 150 ° C. for an optical waveguide element that is not heat-treated and an optical waveguide element that is heat-treated at 300 ° C. or 600 ° C. Compared with optical waveguide elements that have not been heat-treated and optical waveguide elements that have been heat-treated at 300 ° C., optical waveguide elements that have been heat-treated at 600 ° C. have reduced DC drift under the same test environment, and their characteristics have been stabilized. Is easily understood. Similarly, as a result of experiments, when heat treatment was performed at 400 ° C. or higher, a decrease in DC drift was observed, and in particular, at 600 ° C. or higher, almost the same result was obtained. When the temperature exceeds 1000 ° C., there is no difference in the effect of Li diffusion. Rather, the optical waveguide is formed by Ti thermal diffusion, which causes problems such as Ti diffusion progressing.

As a method of incorporating Li into the buffer layer, further, in the heat treatment, infiltration of Li from the surface of the buffer layer is promoted by heat-treating a material rich in Li such as LiCl or Li ₂ O in the same atmosphere. In addition, an optical waveguide element with stabilized DC drift characteristics can be efficiently manufactured.

Further, after the optical waveguide is formed on the substrate, a buffer layer containing SiO ₂ as a main material is formed thereon by a vacuum film forming method such as sputtering, vapor deposition or CVD. In particular, it is preferably formed by a sputtering method. When forming this buffer layer, a film forming material, for example, a sputtering target is mixed with a material containing Li such as Li ₂ O, and the content of Li in the buffer layer is 1 × 10 ²¹ (atoms / cm ³ ). It is also possible to form it as described above. When the buffer layer is formed, Li can be contained in advance, and the optical waveguide element with stabilized DC drift characteristics can be efficiently manufactured without complicating the manufacturing process.

  As described above, according to the present invention, it is possible to provide an optical waveguide element that stabilizes DC drift, does not complicate the manufacturing process, and can accurately control product characteristics, and a manufacturing method thereof. .

DESCRIPTION OF SYMBOLS 1 Substrate having electro-optic effect 2 Optical waveguide 3 Signal electrode 4 Ground electrode 5 Buffer layer 6 Li-containing region

Claims (6)

A substrate having an electro-optic effect; an optical waveguide formed on the substrate; a buffer layer made mainly of SiO ₂ formed on the optical waveguide; and an optical waveguide formed on the buffer layer, In an optical waveguide device having a modulation electrode for modulating a propagating light wave,
An optical waveguide device characterized in that the Li content is 1 × 10 ²¹ (atoms / cm ³ ) or more on the substrate side of the buffer layer. 2. The optical waveguide device according to claim 1, wherein a thickness of a region containing 1 × 10 ²¹ (atoms / cm ³ ) or more of Li in the buffer layer occupies 1/4 or more in the film thickness direction. Optical waveguide element.   3. The optical waveguide device according to claim 1, wherein the buffer layer is doped with at least one of In or Ti. A substrate having an electro-optic effect; an optical waveguide formed on the substrate; a buffer layer made mainly of SiO ₂ formed on the optical waveguide; and an optical waveguide formed on the buffer layer, In a method of manufacturing an optical waveguide device having a modulation electrode that modulates a propagating light wave,
At least after the buffer layer is formed, heat treatment is mainly performed in an oxygen atmosphere at 400 to 1000 ° C., so that the Li content is 1 × 10 ²¹ (atoms / cm ³⁾ on the substrate side of the buffer layer. ) A method for manufacturing an optical waveguide device, wherein the region to be described above is formed.   5. The method for manufacturing an optical waveguide element according to claim 4, wherein a material containing Li is heat-treated in an atmosphere together with the heat treatment. A substrate having an electro-optic effect; an optical waveguide formed on the substrate; a buffer layer made mainly of SiO ₂ formed on the optical waveguide; and an optical waveguide formed on the buffer layer, In a method of manufacturing an optical waveguide device having a modulation electrode that modulates a propagating light wave,
When the buffer layer is formed by a vacuum film formation method, a material containing Li is mixed with the film formation material so that the Li content of the buffer layer is 1 × 10 ²¹ (atoms / cm ³ ) or more. An optical waveguide device manufacturing method characterized by the above.

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