JP2000266951A - Waveguide passage type polarizer and forming method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain a metal film from peeling from a buffer layer by providing a metal film continuously formed extending over the upper face and/or the bottom face of a stereostructure part and the side parts of the stereostructure part, so as to include a part acting as a polarizer. SOLUTION: A resist pattern is lifted off, and a Ti mask opening a rectangular territory over a light waveguide passage 12 is formed. A buffer layer exposed in the opening part is removed by dry etching, and after exposing the surface of a X base plate 10, the Ti mask is removed by chemical etching, and the X base plate 10 having a buffer layer 14a forming a metal film forming scheduled territory part into a rectangular opening is obtained. Thereafter, photoresist is spread on the whole surface, a resist pattern having a rectangular opening formed so as to include a recessed part therein by photolithography is formed as a polarizer pattern, an Al film as a metal film is formed on the whole surface by a sputtering method, and the resist pattern is removed to obtain a waveguide passage type polarizer provided with the metal film 20a covering a square pillar like recessed part is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide polarizer and a method of forming the same, and more particularly, to a waveguide polarizer used in an optical waveguide modulator or the like to eliminate the influence of polarization fluctuation.

[0002]

2. Description of the Related Art An optical waveguide type modulation device formed by connecting an optical fiber to a chip formed by forming an optical waveguide, a buffer layer, and a traveling-wave electrode on a substrate having an electro-optical effect such as lithium niobate. Optical devices such as optical devices have been developed as key devices in long-distance, broadband optical communication systems, and have been introduced into actual systems.

In an optical waveguide type modulator used as such an optical device, usually, only one of the oscillating wave components of the light wave propagating through the optical waveguide, which vibrates only vertically or horizontally with respect to the substrate, is used. Select and use. For this reason, a polarization maintaining fiber is often provided on the incident side of the optical waveguide type modulator to selectively input linearly polarized light oscillating vertically or horizontally to the substrate.

However, when stress is applied to the polarization maintaining fiber from the outside, or when the incident light is not linearly polarized light, there arises a problem that the extinction ratio in the fiber on the output side decreases.

To solve such a problem, Japanese Unexamined Patent Publication No. 4-282608 discloses a method in which a superpolarizer is attached to an end face of an input waveguide or both end faces of an input / output waveguide to reduce an extra polarization component. It has been proposed to cut to prevent the extinction ratio from decreasing.

In Japanese Patent Application Laid-Open No. 62-99913, a film having a refractive index equal to (or substantially equal to) the transmission refractive index of guided light is arranged near an optical waveguide, and this film is used as an optical waveguide. It is disclosed to operate and selectively take out one of two types of light waves propagating through the optical waveguide.

By the way, in a waveguide type polarizer for selecting one of two types of light waves propagating through an optical waveguide, the simplest configuration is shown in FIG. There is a metal-loaded waveguide polarizer having a configuration in which a rectangular metal film 30 is loaded above.

This metal-loaded waveguide polarizer utilizes the difference in the absorption efficiency of a metal film with respect to the polarization direction of light. Suematsu et. Al: Appl. Phys. Lett., Vol. , No
6 (1972) shows the principle.

Briefly, a metal film loaded on an optical waveguide vibrates horizontally (hereinafter referred to as T
It is called E-mode light. ) And selectively absorbs a vertically oscillating polarized wave (hereinafter, referred to as TM mode light), and has a simple structure and a relatively high extinction ratio. It has the feature of.

[0010] This metal-loaded waveguide polarizer is generally constructed by loading a rectangular metal film above an optical waveguide parallel to the surface of a substrate. Since a loaded waveguide polarizer always absorbs TM mode light, an optical waveguide modulator using X-cut lithium niobate using TE mode light as a substrate (hereinafter, referred to as an X substrate). Etc. are used.

The waveguide type polarizer having such a configuration is TM
It does not act as a polarizer for an optical waveguide type modulator using a Z-cut lithium niobate substrate (hereinafter, referred to as a Z substrate) using mode light. So, for example,
In Japanese Patent Publication No. 6-85006, as shown in FIG. 16, a groove 50 having a wall surface in a direction perpendicular to the Z substrate 11 is formed adjacent to the optical waveguide 12, and only the wall surface of the groove is formed in the optical waveguide. A light-absorbing substance having a filter function of absorbing undesired light that propagates, that is, a light-absorbing substance having a rectangular metal film 30 has been proposed.

Generally, such a metal-loaded waveguide polarizer is monolithically integrated with an optical waveguide modulator using a traveling-wave electrode or the like. In order to achieve this, an optical waveguide modulator having a configuration in which a buffer layer is formed on a substrate surface has been proposed.

[0013]

However, a metal-loaded waveguide polarizer has a structure in which a rectangular metal film is loaded on an optical waveguide formed on a substrate usually made of a dielectric material. As shown in Japanese Patent Publication No. 6-85006, the configuration is such that a rectangular metal film is loaded on the wall surface of the groove provided near the optical waveguide. Since the adhesive force is weak, the rectangular metal film may be peeled off in a subsequent process.

For example, in an optical waveguide modulator having a metal-loaded waveguide polarizer, a rectangular metal film acting on an optical waveguide is formed on the substrate surface, and then the substrate is cleaned with ultrasonic waves or the like. An electrode is formed by electroplating or the like, and the electrode is formed. However, the rectangular metal film may be peeled off during cleaning by ultrasonic waves or the like performed after the formation of the rectangular metal film.

A substrate on which a rectangular metal film is adhered;
Alternatively, since the buffer layer formed on the substrate and the rectangular metal film are made of different materials, there is a difference in thermal stress. Therefore, there is a possibility that the metal film may be separated from the substrate due to a difference in thermal stress due to a large temperature change occurring after the formation of the rectangular metal film.

In order to eliminate such a fear, in the case of a high-speed type optical waveguide type modulator having a buffer layer, a structure in which a metal film acting on the optical waveguide is formed and then the buffer layer is formed. Is also conceivable.

However, in general, the buffer layer is made of Si
After forming a dielectric such as O _2, it is necessary to anneal at a high temperature of about 600 ° C. for the purpose of improving the mechanical strength of the film and compensating for oxygen in the oxygen-deficient portion, and the like. Another problem arises in that the metal film provided therebetween is oxidized and deteriorates, and the extinction ratio is deteriorated. Of course, at present, there is no solution for an optical waveguide modulator without a buffer layer.

Further, when a rectangular metal film is formed on the wall surface of a groove as in Japanese Patent Publication No. 6-85006, there is a problem that high-precision patterning is required and the manufacturing efficiency is low.

From the above, the present invention provides a waveguide type polarizer which can be manufactured relatively easily, and in which a metal film acting on an optical waveguide is hardly peeled off from a substrate or a buffer layer formed on the substrate surface. It is an object to provide a forming method.

[0020]

According to one aspect of the present invention, there is provided a waveguide polarizer including a substrate having an electro-optic effect and an optical waveguide formed on the substrate. Wherein the three-dimensional structure portion includes a three-dimensional structure portion provided near the optical waveguide such that a surface is formed on at least one of the upper side and the side surface of the optical waveguide, and a portion that functions as a polarizer. And a metal film formed continuously on at least one of the upper surface or the bottom surface and the side surface portion of the three-dimensional structure.

That is, according to the first aspect of the present invention, the three-dimensional structure is formed near the optical waveguide such that a surface is formed at least on one side or the upper side of the optical waveguide. Since the metal film formed so as to include the portion acting as a child is formed continuously on the side surface portion of the three-dimensional structure portion and the upper surface portion or the bottom surface portion of the three-dimensional structure portion, the adhesive force to the substrate Are applied from at least two different directions, and are hardly peeled off.

The metal film acts only on one of the portion covering the side surface of the three-dimensional structure portion and the portion covering the top surface or the bottom surface of the three-dimensional structure portion. As a result, the area of the region that adheres to the substrate increases, and the adhesion to the substrate becomes stronger.

As described in claim 2, the thickness of the metal film at the portion covering the side surface of the three-dimensional structure is smaller than the thickness at the portion covering the top or bottom surface of the three-dimensional structure. In this case, since the thermal stress is smaller in the thinner portion than in the thicker portion, the thermal stress of the entire metal film is reduced, and the metal film becomes more difficult to be peeled off.

In the waveguide polarizer of the second aspect, the thickness of the portion covering the side surface of the three-dimensional structure is made smaller than the thickness of the portion covering the top or bottom surface of the three-dimensional structure. It suffices if there is a metal film continuously formed on the side surface portion of the three-dimensional structure portion and the upper surface portion or the bottom surface portion of the three-dimensional structure portion, and a portion where this metal film is continuously formed in another region is used. You may have.

In the first and second aspects of the present invention, the three-dimensional structure provided near the optical waveguide such that a surface is formed on at least one of the upper side and the side of the optical waveguide is defined as the claim As in the invention described in 3, the concave portion having the surface formed above the optical waveguide as a bottom surface, as in the invention described in claim 5, so as to include the optical waveguide therein, and
A convex portion formed along the longitudinal direction of the optical waveguide such that the opposing side surface is located on the side of the optical waveguide. One side is located on the side of the optical waveguide as in the invention described in claim 6. A concave portion provided along the longitudinal direction of the optical waveguide, a step formed along the longitudinal direction of the optical waveguide with the upper region of the optical waveguide as the upper stage, and a longitudinal portion of the optical waveguide with the upper region of the optical waveguide as the lower stage. All three-dimensional structures such as steps formed along the direction are included.

Further, as in the third aspect of the present invention,
In the case where the three-dimensional structure portion is a concave portion having a bottom surface on the surface formed above the optical waveguide, if a metal film is formed on the bottom surface and side surfaces of the concave portion, there is an advantage that the three-dimensional structure portion can be formed by a simple manufacturing process. .

According to a third aspect of the present invention, as in the fourth aspect, the substrate is an electro-optic crystal substrate having a buffer layer on the surface, and the recess is partially formed so that the surface of the electro-optic crystal substrate is exposed. The configuration with the removed portions results in a waveguide-type polarizer usable for a high-speed optical waveguide-type modulator, which is preferable.

When an X substrate is used as the substrate,
As described in the third aspect, the structure may be such that the TM mode light is absorbed by causing the metal film portion covering the bottom surface of the concave portion formed above the optical waveguide to act on the optical waveguide.

When a Z substrate is used as the substrate,
A metal film formed on at least one of the opposing side surfaces of a convex portion formed along the longitudinal direction of the optical waveguide so as to include the optical waveguide therein, as described in claim 5. By acting on the optical waveguide,
It is configured to absorb the mode light, or as described in claim 6, a concave portion is formed along the longitudinal direction of the optical waveguide so that a surface is formed on the side of the optical waveguide, and at least the concave portion is formed. The metal film formed on the side surface on the side of the optical waveguide makes T
What is necessary is just to comprise so that E mode light may be absorbed.

Further, in the case of the structure described in claim 5, a metal film may be formed on the upper surface of the convex portion in the manufacturing process, but the upper surface portion of the convex portion is made of, for example, SiO _2.
Since the buffer layer is provided, the metal film on the upper surface can be prevented from acting on the optical waveguide. Further, in the case of the configuration as described in claim 5, since the metal film acting on the optical waveguide can be formed on both sides of the optical waveguide, the TE mode light can be efficiently absorbed, and the conductive film with good performance can be obtained. There is also an advantage that a waveguide polarizer can be obtained.

According to a seventh aspect of the present invention, in the method of forming a waveguide type polarizer, the optical waveguide is formed such that a surface is formed on at least one of an upper side and a side of the optical waveguide formed on the electro-optic crystal substrate in advance. Forming a three-dimensional structure in the vicinity of the three-dimensional structure, forming a polarizer pattern so that at least one of the top surface or side surface of the three-dimensional structure is exposed, the thickness of the metal film formed on the side surface of the three-dimensional structure is After forming the metal film so as to be thinner than the thickness of the metal film formed on the upper surface or the bottom surface of the three-dimensional structure, the method includes a step of removing the polarizer pattern.

That is, according to the method of forming a waveguide type polarizer of the present invention, the three-dimensional structure is formed near the optical waveguide such that the surface is formed at least on one side or above the optical waveguide. By forming a metal film on the surface of the three-dimensional structure after formation, the waveguide polarizer according to any one of claims 1 to 6 can be manufactured relatively easily.

The method for forming the three-dimensional structure in the vicinity of the optical waveguide so that a surface is formed on at least one of the upper side and the side of the optical waveguide is not particularly limited, but is preferably formed by shaving the substrate. Alternatively, another layer such as a buffer layer formed in advance on the surface of the substrate may be shaved off. In the case where the optical waveguide is formed by shaving the substrate, the optical waveguide may be formed at a deep position in advance.

At this time, if the three-dimensional structure is formed by dry etching, the surface of the formed three-dimensional structure is roughened at the atomic level, so that the metal film formed on the surface of the three-dimensional structure in a later step is three-dimensional. An anchor effect is generated in that the structure portion is intricately entangled with the rough portion of the surface of the structure to increase the adhesion. Therefore, there is an advantage that the adhesive force between the metal film and the surface of the three-dimensional structure part becomes stronger.

The method of forming the metal film includes, for example, a sputtering method and a vapor deposition method. The metal film formed on at least the side surface of the three-dimensional structure portion (that is, the surface substantially perpendicular to the substrate surface) can be used. The thickness of the metal film formed on the top surface or bottom surface of the three-dimensional structure portion (the bottom surface if the three-dimensional structure portion is a concave portion, or the top surface if the three-dimensional structure portion is a convex portion; that is, a surface parallel to the substrate surface). What is necessary is just to be able to form so that it may become thinner than thickness.

When the substrate is an X substrate, an optical waveguide is formed at a deep position in advance, and a concave portion formed by shaving the substrate so that the upper side of the optical waveguide is a bottom surface, or a buffer layer is previously formed on the surface of the substrate. May be formed by etching the buffer layer until the surface of the substrate above the optical waveguide is exposed. The buffer layer only needs to be made of a material that blocks the function of the metal film, and for example, a dielectric material such as SiO ₂ can be used.

When the substrate is a Z substrate, the substrate is dry-etched by masking the upper surface along the longitudinal direction of the optical waveguide until the substrate reaches at most the depth of the optical waveguide, and the optical waveguide is formed therein. After forming the convex portion including the mask and removing the mask, the polarizer pattern is formed so that at least the side surface along the longitudinal direction of the optical waveguide of the convex portion is exposed, and after forming the metal film on the entire surface, the polarizer pattern is removed. It is formed so that

That is, this forming method is the same as the above-described claim 5.
In this case, a buffer layer is formed on the surface of the substrate in advance, and the metal film formed on the upper surface of the projection has a polarizer action on the optical waveguide. Should be prevented.

As another forming method when the substrate is a Z-substrate, a concave portion is formed at a position along the longitudinal direction of the optical waveguide until the concave portion reaches at least the same depth as the optical waveguide. A polarizer pattern is formed so that at least the bottom surface of the concave portion and the side surface on the optical waveguide side are exposed, and after forming a metal film on the entire surface, the polarizer pattern is removed.

That is, this forming method is the same as in claim 6 above.
In this case, a method of manufacturing a waveguide-type polarizer as described in the above, in this case, the concave portion is located at a position along the optical waveguide at a depth of at most the same as the depth of the optical waveguide, formed on the surface Except that the formed metal film is left on at least the bottom surface of the concave portion and the side surface on the optical waveguide side, the description is omitted because it is the same as above.

The recesses described in all of the above-mentioned claims are those whose inner surface shape includes, for example, polygonal pillars such as quadrangular pillars, grooves, and the like, and the protrusions described in all the above claims. The section has, for example, a rectangular shape or a trapezoidal shape in cross section.

[0042]

FIG. 1 is a block diagram showing an embodiment of the present invention.
This will be described with reference to FIG.

(First Embodiment) FIG. 1 is a flow chart showing a manufacturing process of a waveguide polarizer according to a first embodiment. Hereinafter, the first embodiment will be described with reference to FIG. In the first embodiment, an X-cut lithium niobate substrate (X substrate) 10 is used.

First, a buffer layer 14 made of SiO ₂ having a thickness of 0.1 mm is formed on the surface of the X substrate 10 having the optical waveguide 12 formed on the substrate surface by thermally diffusing Ti by sputtering.
It is formed so as to have a thickness of 5 μm, and is annealed at 600 ° C. for 5 hours.

Next, after a photoresist is applied to the entire surface of the substrate, patterning is performed by photolithography so that the photoresist above the optical waveguide 12 remains in a rectangular shape.
A rectangular resist pattern 16a is formed to cover a region where a metal film is to be formed as a polarizer on the substrate surface. Thereafter, Ti is deposited to form a Ti film 18 on the entire surface of the X substrate 10 (FIG. 1A).

Thereafter, the resist pattern 16a is lifted off, and a Ti mask 18 having an opening in a rectangular region (ie, a region where a metal film is to be formed) above the optical waveguide 12 is formed.
a is formed (FIG. 1B).

ECR (Electron cyclotron resonance)
The buffer layer exposed at the opening is removed by dry etching using a plasma source to expose the surface of the X substrate 10, and then the Ti mask 1 is removed by chemical etching.
Remove 8a. Thus, the X substrate 1 provided with the buffer layer 14a having a rectangular opening in the region where the metal film is to be formed is formed.
0, in other words, an X substrate 10 having a quadrangular prism-shaped concave portion whose bottom surface is the region where the metal film is to be formed is obtained (FIG. 1).
(C)).

Thereafter, a photoresist is applied to the entire surface, and a resist pattern 16 having a rectangular opening formed therein so as to include a concave portion is formed by photolithography.
b is formed as a polarizer pattern (FIG. 1D).

Further, an Al film 20 is formed as a metal film on the entire surface by a sputtering method (FIG. 1E), and by removing the resist pattern 16b, a waveguide provided with a metal film 20a covering a rectangular column-shaped concave portion is formed. A polarizer is obtained (FIG. 1 (f)).

In the obtained waveguide type polarizer, as shown in FIG. 2, the portion covering the bottom surface of the concave portion of the metal film 20a adheres to the X substrate 10, and the portion covering the side surface of the concave portion is the buffer layer 1.
4A, it is characterized in that it is less likely to be peeled off than a conventional flat polarizer.

Further, since the metal film 20a covering the concave portion is formed by the sputtering method, the thickness of the side portion is smaller than that of the bottom portion. In other words, since the thermal stress of the entire metal film is reduced by forming the film thickness of the side surface portion to be thin, it is more difficult to peel off.

In the first embodiment, the buffer layer formed on the substrate is shaved to form a concave portion having the substrate surface as the bottom surface, and the waveguide provided with the metal film 20a covering the inner surface of the concave portion. Although the type polarizer has been described, for example, as shown in FIG. 3, a waveguide type polarizer including a metal film 20 a that is formed by shaving the substrate itself to form a concave portion and cover the inner surface of the concave portion can also be used. In addition, the case where the inner surface shape of the concave portion is a square pillar shape has been described, but the inner surface shape of the concave portion is not particularly limited to the square pillar shape. Is also good.

Further, in the first embodiment, the shape of the metal film 20a covering the concave portion is described as being concave. However, the present invention is not particularly limited to this shape, and the side surface of the three-dimensional structure may be formed. It is only necessary that the thickness of the metal film to be covered be smaller than the thickness of the metal film to cover the top or bottom surface.

For example, as shown in FIGS. 4 and 5, a waveguide-type polarizer including a metal film 20b having a substantially L-shaped cross section that covers a step formed on the surface of the substrate may be used.
The step can be formed by forming a buffer layer on the substrate surface and shaving the buffer layer 14a as shown in FIG. 4 or by shaving the substrate 10 itself as shown in FIG.

The resist pattern 1 is formed so that the alignment accuracy at the time of manufacturing is increased so that only the inner surface of the concave portion is exposed.
6b and a waveguide polarizer including a metal film 20c that covers only the inner surface of the concave portion as shown in FIGS. In this case, since the thickness of the outer edge portion of the metal film 20c becomes thin, the degree of freedom of expansion and contraction due to thermal stress increases, which is preferable. Of course, similarly, in the case of forming by a step, it is also possible to use a metal film having an L-shaped cross section configured to reduce the thickness of the outer edge portion.

In the first embodiment, the Al film is formed by the sputtering method. However, even when the Al film is formed by the evaporation method, the thickness of the side portion is smaller than that of the bottom portion. Good.

(Second Embodiment) FIG. 8 is a flow chart showing a manufacturing process of a waveguide polarizer according to a second embodiment. Hereinafter, the second embodiment will be described with reference to FIG. In the second embodiment, a Z-cut lithium niobate substrate (Z substrate) 11 is used.

First, a buffer layer 14 made of SiO ₂ is formed to a thickness of 0.5 μm on a surface of a Z substrate 11 in which an optical waveguide 12 is formed on the substrate surface by thermally diffusing Ti, by vapor deposition. Anneal at 600 ° C. for 5 hours.

Next, after a photoresist is applied to the entire surface of the substrate, patterning is performed by photolithography so that the photoresist above the optical waveguide 12 is removed in a rectangular shape, thereby forming a resist pattern 17a having a rectangular opening. And then deposit Ti on the entire surface of the Z substrate 11
A film 18 is formed (FIG. 8A).

After that, the resist pattern 17a is lifted off to form a rectangular Ti mask 18b that covers a region above the optical waveguide 12 on the surface of the Z substrate 11 in a rectangular shape (FIG. 8B).

ECR (Electron cyclotron resonance)
After the buffer layer not covered with the Ti mask 18b and the substrate thereunder are etched to a depth substantially at which the optical waveguide 12 is formed by dry etching using a plasma source, the Ti mask 1 is etched by chemical etching.
Remove 8b. As a result, the Z substrate 11 including the optical waveguide 12 and having a convex portion having a rectangular cross section is obtained (FIG. 8C).

Thereafter, a photoresist is applied to the entire surface, and a resist pattern 17b having a rectangular opening including a region where a metal film is to be formed is formed by photolithography.
Is formed as a polarizer pattern.

Further, an Al film 20 was formed as a metal film on the entire surface by a vapor deposition method (FIG. 8D), and the resist pattern 17b was removed so that the cross-section covered the convex portion having a rectangular shape. A waveguide polarizer including the convex metal film 21a is obtained (FIG. 8E).

Although the above description has been made as a rectangular projection for easy understanding of the description of the production of the metal film portion, the waveguide type polarizer is actually an optical waveguide type modulator or the like. Since the optical waveguide portion is optically connected to other components, it is not cut off by etching or the like. That is, when used as an actual optical waveguide modulator, as shown in FIG. 9A, the buffer layer and the substrate are etched along the optical waveguide so that a surface is formed on the side of the optical waveguide. This results in a configuration cut away.

FIG. 9 is a schematic explanatory view showing a waveguide type polarizer according to the second embodiment. This waveguide type polarizer covers a convex portion 40 having a rectangular cross section. It has the formed convex-shaped metal film 21a.

The metal film 21a is formed on the upper surface of the convex portion 40 formed on the Z substrate 11 and is opposed to the upper surface of the convex portion 40 in parallel with the optical waveguide.
Since it is attached to the side surface, it has a feature that it is less likely to be peeled off than a conventional flat polarizer.

When the metal film 21a is formed by the vapor deposition method, as shown in the cross-sectional view of FIG. Since the thin portion is formed to be thinner than the thickness of the metal film to be coated, the thermal stress of the thin portion is smaller than that of the thick portion. It has good adhesion and is difficult to peel off.

In the second embodiment, a case has been described where a convex portion having a rectangular cross section is formed and the metal film 21a covering the convex portion acts on the optical waveguide. Not limited to the shape, for example, the cross section as shown in FIG. 10 may be configured to have a trapezoidal shape, and the side portion of the metal film (21b in FIG. 10) covering this may be configured to act on the optical waveguide. You can also.

In order to form a convex portion having a trapezoidal cross section, the substrate may be arranged so as to be oblique to the direction in which the plasma is drawn during dry etching when forming the side surface portion of the convex portion. . By forming such a cross section as a trapezoidal convex portion, there is an advantage that loss of light propagating in the optical waveguide can be suppressed low.

Further, in the second embodiment, the configuration in which the metal film is formed on the two opposing side surfaces and the upper surface parallel to the optical waveguide of the convex portion, ie, all the surfaces exposed to the surface has been described. The present invention is not limited to this, and it suffices if it is formed at least on the upper surface where the thick film is formed and on one surface parallel to the optical waveguide of the convex portion where the thin film is formed.

Also, a resist pattern 17b is formed by aligning the side surfaces of the resist pattern 17b so as to be close to the two opposing side surfaces parallel to the optical waveguide of the convex portion.
As shown in FIG. 1 and FIG. 12, it is also possible to adopt a configuration in which convex metal films 21c and 21d covering only the outer surfaces of the convex portions act on the optical waveguide.

In the second embodiment, the Al film is formed by the vapor deposition method. However, the Al film may be formed by the sputtering method as in the first embodiment.

(Third Embodiment) FIG. 13 is a flowchart showing a manufacturing process of a waveguide polarizer according to a third embodiment. Hereinafter, the third embodiment will be described with reference to FIG. In the third embodiment, the Z substrate 11 is used.

First, a buffer layer 14 made of SiO ₂ having a thickness of 0.1 mm is formed on the surface of a Z substrate 11 in which an optical waveguide 12 is formed on the substrate surface by thermally diffusing Ti.
It is formed so as to have a thickness of 5 μm, and is annealed at 600 ° C. for 5 hours.

Next, after a photoresist is applied to the entire surface of the substrate, the photoresist at the position along the optical waveguide 12 is patterned by photolithography so as to remain in a rectangular shape, and a rectangular shape is formed at a position along the optical waveguide 12. A resist pattern 16a is formed. After that, Ti is deposited to form a Ti film 18 on the entire surface of the Z substrate 11 (FIG. 13).
(A)).

Thereafter, the resist pattern 16a is lifted off to form a Ti mask 18c having an opening in a rectangular area along the optical waveguide 12 (FIG. 13).
(B)).

ECR (Electron cyclotron resonance)
The buffer layer exposed in the opening is removed by dry etching using a plasma source, and the Z substrate 11 exposed by the removal of the buffer layer is further etched to approximately the depth of the optical waveguide 12, and then chemically etched. The Ti mask 18c is removed. As a result, a Z substrate 11 having a rectangular column-shaped recess penetrating the buffer layer 14 with the rectangular region located along the optical waveguide 12 as an opening is obtained (FIG. 13C).

Thereafter, a photoresist is applied to the entire surface, and a resist pattern 16 having a rectangular opening formed therein so as to include a concave portion is formed by photolithography.
c is formed as a polarizer pattern (FIG. 13D).

Further, an Al film 20 is formed as a metal film on the entire surface by sputtering (FIG. 13E), and the resist pattern 16c is removed to form a concave shape formed so as to cover the rectangular column-shaped concave portion. Metal film 2
A waveguide polarizer having 2a is obtained (FIG. 13 (f)).

The concave metal film 22a penetrates the buffer layer 14c and is formed on the Z substrate 11, and the side surface on the optical waveguide 12 side acts on the optical waveguide. Since the metal film 22a of the third embodiment is attached to both the buffer layer 14c and the Z substrate 11 as in the first and second embodiments, the metal film 22a is compared with a conventional flat polarizer. It has the characteristic that it is hard to peel off.

In the third embodiment, similarly to the first embodiment, for example, as shown in FIG. 14, a step perpendicular to the substrate surface is formed on the surface of the substrate to cover the step. A waveguide-type polarizer having a substantially L-shaped metal film 22b may be used. In this case, since a step portion perpendicular to the substrate surface acts on the optical waveguide, it is needless to say that a portion where the optical waveguide is not formed is shaved to form a step.
The step may be formed to a depth at most about the depth of the optical waveguide by forming a buffer layer on the substrate surface as shown in FIG. 14 and shaving the buffer layer and the substrate. The rest is the same as the first embodiment, and the description is omitted.

In all the embodiments described above, A
The metal film such as 1 has a weak adhesion to the dielectric material and thus easily peels off. However, since the concave or convex portions are formed by dry etching, the substrate surface is appropriately roughened, and the roughened portion is loaded. Since an anchor effect is caused between the metal film and the metal film, the metal film is hardly peeled off.

The metal film is provided such that when the three-dimensional structure is a concave portion, the thickness of the metal film on the side surface is smaller than the thickness of the metal film on the bottom surface. When the structural portion is a convex portion, the metal film on the side portion is provided to be thinner than the metal film on the upper surface portion. Since it is smaller than the film portion, even if a large temperature change occurs, it has good adhesion to the substrate and the buffer layer formed on the surface of the substrate, and has the effect of being hardly peeled off.

Further, the metal films in all the embodiments described above can be formed relatively easily on the buffer layer, and have good adhesion to the dielectric material used as the material of the buffer layer. Therefore, it is particularly suitable as a component of a waveguide polarizer used for a high-speed optical waveguide modulator requiring a buffer layer.

In all of the embodiments described above, Al having the highest electric absorptivity is used as the metal constituting the waveguide type polarizer. Absent. For example, Ti, Cr, Ni and P
t or an alloy composed of at least two of Al, Ti, Cr, Ni and Pt can be used.

In particular, when high-power light is incident on the optical waveguide, the electric field component absorbed by the metal film is likely to change into thermal energy and degrade the polarizer. In the waveguide-type polarizer described in the embodiment, the attachment area of the loaded metal film to the substrate is larger than that of the waveguide-type polarizer having the conventional configuration, so that the heat radiation efficiency is improved. That is, even if the absorbed electric field component is converted into heat energy, heat can be efficiently radiated, so that the possibility of deterioration due to heat energy can be reduced.

Further, according to the method of manufacturing the waveguide type polarizer described in the first to third embodiments, fine patterning is unnecessary, and the waveguide type polarizer having good performance even if alignment accuracy is low. Can be formed, so that the manufacturing efficiency and the manufacturing yield are improved, and there is also an advantage that it is preferable.

[0088]

As described above, according to the first and second aspects of the present invention, a waveguide type polarized light in which a metal film acting on an optical waveguide is hardly peeled off from a substrate or a buffer layer formed on the surface of the substrate. There is an effect that a child can be obtained.

Further, according to the third to sixth aspects of the present invention, there is an effect that a waveguide type polarizer which is difficult to peel off can be obtained with a relatively simple structure.

According to the invention of claim 7, there is an effect that fine patterning is unnecessary and a waveguide type polarizer having good performance can be formed even if alignment accuracy is low.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a manufacturing process of a waveguide polarizer according to a first embodiment.

FIG. 2A is a perspective view schematically showing a waveguide polarizer according to the first embodiment, and FIG. 2B is a cross-sectional view taken along line AA of FIG.

FIG. 3 is a cross-sectional view showing another embodiment in the first embodiment.

FIG. 4 is a cross-sectional view showing another embodiment in the first embodiment.

FIG. 5 is a cross-sectional view showing another embodiment in the first embodiment.

FIG. 6 is a cross-sectional view showing another embodiment in the first embodiment.

FIG. 7 is a cross-sectional view showing another embodiment in the first embodiment.

FIG. 8 is a flowchart showing a manufacturing process of the waveguide polarizer of the second embodiment.

9A is a perspective view schematically showing a waveguide polarizer according to a second embodiment, and FIG. 9B is a cross-sectional view taken along line AA of FIG. 9A.

FIG. 10 is a cross-sectional view showing another embodiment in the second embodiment.

FIG. 11 is a cross-sectional view showing another embodiment in the second embodiment.

FIG. 12 is a cross-sectional view showing another embodiment in the second embodiment.

FIG. 13 is a flowchart showing a manufacturing process of the waveguide polarizer of the third embodiment.

FIG. 14 is a cross-sectional view showing another embodiment in the third embodiment.

FIG. 15 is a perspective explanatory view showing an example of a conventional metal-loaded polarizer used for an X substrate.

FIG. 16 is a cross-sectional view illustrating an example of a conventional metal-loaded polarizer used for a Z substrate.

[Explanation of symbols]

REFERENCE SIGNS LIST 10 X substrate 11 Z substrate 12 optical waveguide 14 buffer layer 14 a to 14 c patterned buffer layer 16 a to 16 c, 17 a, 17 b resist pattern 18 Ti film 18 a to 18 c Ti mask 20 metal film 20 a to 20 c, 22 a, 22 b concave shape Metal film 21a to 21d Metal film of convex shape 30 Metal film of rectangular shape 40 Convex part 50 Groove

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Hirotoshi Nagata 585 Tomimachi, Funabashi-shi, Chiba F-term in the New Technology Research Laboratory, Sumitomo Osaka Cement Co., Ltd. 2H047 LA21 QA03 TA21 2H079 AA13 BA02 CA08 DA03 DA22 DA25 DA26 EA01 HA22

Claims (7)

[Claims] 1. A waveguide polarizer including a substrate having an electro-optic effect and an optical waveguide formed on the substrate, such that a surface is formed on at least one of an upper side and a side of the optical waveguide. A three-dimensional structure provided in the vicinity of the optical waveguide; and a part continuous with at least one of the top surface or the bottom surface of the three-dimensional structure and a side surface of the three-dimensional structure so as to include a portion acting as a polarizer. A waveguide polarizer comprising a metal film formed by: 2. The metal film is formed such that a thickness of a portion covering a side surface of the three-dimensional structure is smaller than a thickness of a portion covering an upper surface or a bottom surface of the three-dimensional structure. 2. The waveguide polarizer according to 1. 3. The concave portion having a surface formed above the optical waveguide as a bottom surface, and the metal film is formed on a bottom surface and a side surface of the concave portion. 3. The waveguide polarizer according to 1. 4. The substrate is an electro-optic crystal substrate provided with a buffer layer on the surface, and the recess is a portion where one portion of the buffer layer is removed so that the surface of the electro-optic crystal substrate is exposed. The waveguide type polarizer according to claim 3. 5. The three-dimensional structure part is a convex part formed so as to include the optical waveguide inside and a side surface facing the longitudinal direction of the optical waveguide. The waveguide polarizer according to claim 1, wherein the waveguide polarizer is formed on at least one of an upper surface of the portion and the side surface facing the portion. 6. The concave portion provided along the longitudinal direction of the optical waveguide such that a surface is formed on a side of the optical waveguide. The metal film is a bottom surface of the concave portion. The waveguide type polarizer according to claim 1, wherein the waveguide type polarizer is formed on at least a side surface on an optical waveguide side. 7. A three-dimensional structure is formed in the vicinity of the optical waveguide such that a surface is formed above or at least on one side of the optical waveguide previously formed on the electro-optic crystal substrate, and an upper surface of the three-dimensional structure is formed. Alternatively, a polarizer pattern is formed such that at least one of the side surfaces is exposed, and the thickness of the metal film formed on the side surface of the three-dimensional structure portion is greater than the thickness of the metal film formed on the top surface or the bottom surface of the three-dimensional structure portion. A method of forming a waveguide-type polarizer, comprising a step of removing a polarizer pattern after forming a metal film so as to be thinner.