KR100591766B1 - Spot-size converter embedded silica planar optical waveguide fabrication method - Google Patents

Abstract

The present invention relates to a method for manufacturing a flat optical waveguide, comprising: a first step of etching a predetermined region of a wafer substrate; and a second step of sequentially laminating a lower clad layer and a waveguide core layer on the etched wafer substrate. And a third step of planarizing an upper portion of the waveguide core layer, a fourth step of forming a waveguide pattern on the waveguide core layer, and a fifth step of stacking an upper clad layer on the waveguide core layer.

Silica, Flat Waveguide, Mode Size Matcher, Optical Communication

Description

Spot-size converter embedded silica planar optical waveguide fabrication method

1A to 1D illustrate a method of manufacturing a flat optical waveguide according to the prior art.

2 is a view showing a relationship between a relative refractive index difference between an optical waveguide core layer and a cladding layer and a connection loss relationship with an optical fiber according to the prior art.

3A to 3B illustrate a waveguide structure for matching a mode size in a planar optical waveguide according to the prior art.

4A to 4G illustrate a method of manufacturing a silica plate type optical waveguide in which a mode size matcher is integrated according to an embodiment of the present invention.

5A to 5F illustrate a method of manufacturing a silica plate type optical waveguide in which a mode size matcher is integrated according to another embodiment of the present invention.

FIG. 6 is a side view of a silicon wafer when the silicon wafer substrate is etched at an angle θ vertically or obliquely. FIG.

{Description of major symbols in the drawing}

201: silicon wafer substrate 202: lower clad layer

203: waveguide core layer 204: upper clad layer

The present invention relates to a method for fabricating a silica flat plate integrated optical waveguide in which a mode size matcher is applicable to an optical communication device. In detail, the difference in relative refractive index between the core layer and the clad layer of the flat plate optical waveguide is greater than 0.75%. In this case, the present invention relates to a method for manufacturing a planar optical waveguide in which a mode size matcher is integrated in order to reduce coupling loss between an optical fiber and a silica flat optical waveguide.

Silica flat plate optical waveguide is an essential element for fabricating integrated optical type optical communication devices, and is suitable for various optical communication such as optical splitter, optical coupler, optical modulator, optical switch, wavelength splitter, wavelength combiner, optical filter, optical attenuator and polarization dependent filter. Used for device fabrication.

A conventional silica flat plate integrated optical waveguide manufacturing process that can be used as an optical communication component is as follows.

Stacking a thermal oxide film or an amorphous silica thin film 202 on the silicon substrate 201; The second step of stacking the waveguide core layer 203 on the thermal oxide film or amorphous silica film 202 and performing a photolithography process and then forming a waveguide pattern and a metal oxide in an amorphous state around the waveguide core 203 The third cladding layer is filled with the upper cladding layer 203.

At this time, the relative refractive index difference between the waveguide core layer and the cladding layer is defined as follows.

(1)

(One)

In Equation (1), n _core is the refractive index of the waveguide core layer, and n _clad is the refractive index of the clad layer.

1A to 1D illustrate a structure and a manufacturing method of a silica flat optical waveguide according to the prior art.

Hereinafter, a description will be given with reference to the respective drawings.

FIG. 1A is a cross-sectional view of a silicon oxide substrate 201 laminated with an amorphous metal oxide film 202 by a thermal oxide film, a flame hydrolysis method, or a chemical vapor deposition method. The lower clad layer 202 has a thickness of 5 to 20 μm.

FIG. 1B is a cross-sectional view of the waveguide core layer 203 stacked on the lower clad layer 202. The waveguide core layer 203 has a refractive index of 0.001 to 0.1 higher than that of the lower clad layer 202. The deposition method is flame hydrolysis method, chemical vapor deposition method, sol-gel method or ion exchange method.

FIG. 1C is a cross-sectional view after forming an optical waveguide pattern to be manufactured on the waveguide core layer 203. Only a portion of the waveguide of the waveguide core layer 203 is selectively left in the mask on which the optical waveguide pattern to be manufactured is engraved using a semiconductor lithography process, and the remaining portion is removed by a wet etching method or a dry etching method. The waveguide line width of the waveguide core layer 203 is formed to be greater than 2 μm.

FIG. 1D is a cross-sectional view of the upper cladding layer 204 filled around the waveguide pattern region formed in the waveguide core layer 203. The upper clad layer 204 is laminated with an amorphous metal oxide film or polymer material, and the refractive index is lower than that of the waveguide core layer 203. The upper clad layer 204 has a thickness of 10 ~ 100 ㎛.

In order to increase the degree of integration of the optical waveguide device in the silicon wafer substrate, Δn between the waveguide core layer and the cladding layer should be increased.

2 shows that the connection loss between the silica plate optical waveguide and the optical fiber increases as Δn increases. As DELTA n increases, the size of the optical device to be manufactured decreases and the degree of integration of the optical device increases, but the connection loss with the optical fiber increases.

3A to 3B illustrate a method of reducing a connection loss with an optical fiber by forming a waveguide pattern structure in the waveguide core layer 203 and widening the propagation mode of the waveguide in order to overcome the above disadvantages.

FIG. 3A is a structure in which the size of the waveguide is thermally increased in the transverse direction (hereinafter, an up-tapered structure), and FIG. 3B is a structure in which the waveguide is thermally reduced in the transverse direction (hereinafter, a down-tapered structure).

In the above embodiment, the size of the propagation mode can be matched in the lateral direction, but there is a limit in reducing the connection loss because mode size matching is impossible in the longitudinal direction.

An object of the present invention is to reduce the connection loss with the optical fiber by integrating the mode size matcher with the flat optical waveguide in order to solve the problems of the prior art as described above.

Another object of the present invention is to reduce the splicing loss with the optical fiber in the case of a flat optical waveguide having a relative refractive index difference between the waveguide core layer and the cladding layer greater than 0.75%, and in both the transverse direction and the longitudinal direction of the mode size matcher. It is to provide an optical waveguide that can completely match the mode size with the optical fiber by changing the size.

In order to achieve the above object, a method of manufacturing a flat optical waveguide of the present invention includes a first step of etching a predetermined region of a wafer substrate, and sequentially forming a lower clad layer and a waveguide core layer on the etched wafer substrate. A second step of laminating, a third step of planarizing an upper portion of the waveguide core layer, a fourth step of forming a waveguide pattern on the waveguide core layer, and a fifth step of laminating an upper clad layer on the waveguide core layer Include.

In the present invention, the method of laminating the lower clad layer and the waveguide core layer in the second step is preferably made to have a uniform thickness.

In the present invention, the horizontal axis length of one end of the waveguide pattern is preferably different from the horizontal axis length of the waveguide pattern end formed in the center portion of the waveguide pattern.

In the present invention, the longitudinal axis length of one end of the waveguide pattern is preferably different from the longitudinal axis length of the waveguide pattern end formed in the center portion of the waveguide pattern.

In the present invention, the refractive index of the waveguide core layer is preferably 0.001 to 0.1 higher than the refractive index of the lower clad layer.

In the present invention, the etching method in the first step is preferably used one method selected from a dry wet method or a wet wet method.

In the present invention, the method of laminating the lower clad layer in the second step is preferably using flame hydrolysis.

In the present invention, the method of stacking the waveguide core layer in the second step is preferably used by one method selected from flame hydrolysis deposition, chemical vapor deposition, plasma ion deposition, sputtering, sol-gel, and rotary coating.

In the present invention, the method of planarizing the waveguide core layer of the third step preferably uses a chemical-mechanical polishing process.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings. In describing the present invention, detailed descriptions of related well-known functions or configurations are omitted in order not to obscure the subject matter of the present invention.

4A to 4G illustrate a method of manufacturing a silica plate type optical waveguide in which a mode size matcher is integrated according to an embodiment of the present invention.

In this embodiment, the optical waveguide includes a substrate layer 201, a lower cladding layer 202, a waveguide core layer 203, and an upper cladding layer 204.

The embodiment schematically illustrates a process of forming a concave etch and stacking the inside of the substrate layer.

In order to match the size of the propagation mode of the silica plate optical waveguide and the mode size of the optical fiber, the size of the waveguide must be adiabatic in the longitudinal direction as well as in the transverse direction.

4A is a view showing a plan view and a side view of a silicon wafer substrate used in the present invention.

4B is a side view of the silicon wafer substrate 201 after vertically etching the desired portion by depth D. FIG. Preferably, the etching of the silicon substrate 201 uses a dry wet method, and the vertical etching depth D is formed to be 1 to 10 µm.

FIG. 4C is a side view after laminating a lower clad layer 202 made of an amorphous metal oxide film material by a flame hydrolysis method on the vertically etched silicon wafer substrate 201.

The lower clad layer 202 has a thickness of 5 ~ 20 ㎛. The laminated lower clad layer has a gentle bend in a direction parallel to the silicon substrate (hereinafter, a horizontal axis direction), and the height difference due to the bend has a vertical etching depth D of the silicon substrate.

4D is a side view after laminating the optical waveguide core layer 203 on the curved lower clad layer 202.

The core layer 203 is preferably deposited using a chemical vapor deposition method or a plasma ion deposition method, the refractive index is 0.001 ~ 0.1 higher than the lower clad layer 202. The waveguide core layer has a curvature in the horizontal axis like the curved lower clad layer 202.

4E is a side view of the curved waveguide core layer 203 after surface polishing and planarization.

The optical waveguide region designated by A is a portion to be connected to the optical fiber, and the region designated by B represents the point where the region of the waveguide core layer 203 without change in thickness starts. The planarization method is preferably a chemical-mechanical polishing (CMP) method. The difference between the thickness of the waveguide core layer 203 at the point A and the thickness of the waveguide core layer 203 at the region indicated by B is the vertical etching depth D of the silicon substrate.

4F is a side view of the flattened waveguide core layer 203 after forming a waveguide pattern of an optical device to be manufactured using a semiconductor lithography process, and a cross-sectional view of the waveguide formed at points A and B. FIG.

Mode size matching in a direction perpendicular to the silicon substrate 201 (hereinafter, referred to as the longitudinal axis direction) is performed by the curved waveguide core layer 203, and mode size matching in the horizontal direction is formed by an up-tapered waveguide pattern. Therefore, the waveguide core layer 203 becomes thinner in the longitudinal axis direction and wider in the horizontal axis direction as the waveguide core layer 203 gradually increases, so that the waveguide mode layer gradually increases toward the point A, thereby increasing the mode size of the optical fiber. Will be matched.

4G is a side view of the upper cladding layer 204 stacked on the waveguide core layer 203 having the waveguide pattern formed thereon.

The upper clad layer 204 is laminated with an amorphous metal oxide film or a polymer material, and the refractive index is smaller than that of the waveguide core layer 203. The upper clad layer 204 has a thickness of 10 ~ 100 ㎛.

5A to 5F illustrate a silica plate optical waveguide fabrication process in which a mode size matcher is integrated according to another embodiment of the present invention.

The embodiment illustrates a process of etching the outer portion of the silica substrate to form protrusions on the inside of the silica substrate, and stacking each layer thereon.

Referring to the drawings, FIG. 5A is a side view of the silicon wafer substrate 201 after vertically etching an undesired region by the depth D on the silicon wafer substrate 201.

That is, the shape of the silicon substrate 201 is opposite to that of FIG. 4B. The etching of the silicon substrate 201 preferably uses a dry wet method, and the vertical etching depth D is 1 to 10 µm.

FIG. 5B is a side view after laminating the lower clad layer 202 made of an amorphous metal oxide film material by flame hydrolysis on the vertically etched silicon wafer substrate 201.

The lower clad layer 202 has a thickness of 5 ~ 20 ㎛. The laminated lower clad layer has a gentle curvature in the horizontal axis direction and the height difference due to the curvature has a vertical etching depth D of the silicon substrate.

FIG. 5C is a side view after laminating the optical waveguide core layer 203 on the curved lower clad layer 202.

The waveguide core layer 203 is preferably deposited using a chemical vapor deposition method or a plasma ion deposition method, the refractive index is 0.001 ~ 0.1 higher than the lower clad layer 202. The waveguide core layer has a curvature in the horizontal axis like the curved lower clad layer 202.

FIG. 5D is a side view of the curved waveguide core layer 203 after surface polishing and planarization.

The optical waveguide region designated by A is the portion to be connected to the optical fiber, and the region designated by B represents the point where the region where there is no change in the thickness of the waveguide core layer 203 starts. The planarization method is preferably a chemical-mechanical polishing (CMP) process method. The difference between the thickness of the waveguide core layer 203 at the point A and the thickness of the waveguide core layer 203 at the region indicated by B is the vertical etching depth D of the silicon substrate.

5E is a side view of the flattened waveguide core layer 203 after forming a waveguide pattern of an optical device to be manufactured using a semiconductor lithography process, and a cross-sectional view of the waveguide formed at points A and B. FIG.

Mode size matching in the longitudinal direction is made by the curved waveguide core layer 203, and mode size matching in the transverse direction is formed by the up-tapered waveguide pattern. Therefore, since the waveguide core layer 203 becomes wider in the longitudinal and transverse directions in the longitudinal axis direction toward the point A, the mode size of the waveguide gradually increases in the direction of the point A so as to match the mode size of the optical fiber. .

5F is a side view after the upper cladding layer 204 is stacked on the waveguide core layer 203 on which the waveguide pattern is formed.

The upper clad layer 204 is laminated with an amorphous metal oxide film or a polymer material, and the refractive index is smaller than that of the waveguide core layer 203. The upper clad layer 204 has a thickness of 10 ~ 100 ㎛.

FIG. 6 is a side view of the silicon substrate when the silicon substrate is vertically wet-wetted and when it is wet obliquely.

In the above two embodiments, the silicon substrate is vertically etched by the depth D. However, even when the silicon is wet-etched at an angle Θ, the mode size matching with the optical fiber may be achieved in the same process as in the above embodiment.

In the above two embodiments, although the up-tapered waveguide is used, the mode size matching with the optical fiber can be achieved by the same process as in the above embodiment using the down-tapered waveguide structure.

In addition, although the two embodiments use the up-tapered waveguide, the mode size matching with the optical fiber can be achieved by the same process as in the embodiment using the down-tapered waveguide structure.

As described above, although described with reference to the preferred embodiment of the present invention, those skilled in the art will be variously modified without departing from the spirit and scope of the invention described in the claims below. And can be changed.

As described above, according to the present invention, the connection loss with the optical fiber can be reduced to improve the insertion loss characteristic of the optical device.

In addition, since the mode size matcher is integrated in the silica plate type optical waveguide, there is no need for a very cumbersome process of preparing a separate mode size matcher and inserting it between the optical fiber and the silica plate type waveguide.

In particular, when Δn of the silica plate optical waveguide is larger than 0.75%, connection loss with the optical fiber can be reduced, and thus the size of the optical device to be manufactured without increasing the insertion loss even when the silica optical waveguide with Δn larger than 0.75% is used. By reducing the density, the density and production yield can be increased.

Claims (11)

In the method of manufacturing a planar optical waveguide comprising a lower clad layer on a silicon wafer substrate and a core layer and an upper clad layer on the lower clad layer, A first step of etching a predetermined region of the wafer substrate; A second step of sequentially laminating a lower clad layer and a waveguide core layer on the etched wafer substrate; A third step of planarizing an upper portion of the waveguide core layer; A fourth step of forming a waveguide pattern in the waveguide core layer; and And a fifth step of stacking an upper clad layer on the waveguide core layer. The optical waveguide manufacturing method according to claim 1, wherein the longitudinal surfaces of the portions etched on the wafer substrate are at right angles. delete delete The optical waveguide manufacturing method according to claim 1 or 2, wherein the horizontal axis length of one end of the waveguide pattern is different from the horizontal axis length of the waveguide pattern end formed in the center portion of the waveguide pattern. The optical waveguide manufacturing method according to claim 1 or 2, wherein the longitudinal axis length of one end of the waveguide pattern is different from the longitudinal axis length of the waveguide pattern end formed in the center portion of the waveguide pattern. The optical waveguide manufacturing method according to claim 1 or 2, wherein the refractive index of the waveguide core layer is 0.001 to 0.1 higher than that of the lower clad layer. The method of manufacturing an optical waveguide according to claim 1 or 2, wherein the etching method in the first step uses one method selected from a dry wet method and a wet wet method. The method of manufacturing an optical waveguide according to claim 1 or 2, wherein the method of laminating the lower clad layer in the second step uses a flame hydrolysis method. The method of claim 1 or 2, wherein the method of stacking the waveguide core layer in the second step is one selected from flame hydrolysis deposition, chemical vapor deposition, plasma ion deposition, sputtering, sol-gel and rotary coating. An optical waveguide manufacturing method characterized by using a method. 3. The method of claim 1 or 2, wherein the method of planarizing the waveguide core layer in the third step uses a chemical-mechanical polishing process.

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