JP2001074959A - Embedded type optical waveguide and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deformation of cores due to heating to form an over clad layer in an embedded-type optical waveguide having cores and an over clad layer on a substrate. SOLUTION: The embedded type optical waveguide has cores 2 having a rectangular or square cross section and an over clad layer 3 on a substrate 1. Thin film layers 4 made of an oxynitride glass having a refractive index nearer to the refractive index of the core 2 than to that of the over clad layer 3 are formed in the longitudinal direction of the core in the part including two side faces 2a, 2b of the core standing at least on the face 1a of the substrate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a buried optical waveguide having a core having a rectangular or square cross section and an overcladding layer covering the core on a substrate.

[0002]

2. Description of the Related Art A buried optical waveguide used for optical communication is provided with a core made of quartz glass serving as a thin film circuit on a substrate made of silicon, quartz, or the like, and overlaid with a quartz glass to cover them. It is formed by providing a clad layer and embedding the core in the over clad layer. In forming a core on a substrate, first, a core layer of a quartz glass thin film serving as a base of the core is formed on the substrate. In forming the core layer, the substrate is placed on a turntable in a muffle, and a combustion gas such as hydrogen and oxygen and a raw material gas such as silicon tetrachloride and germanium tetrachloride are supplied from a burner, and the glass fine particles are subjected to flame hydrolysis. Is generated and deposited on the substrate, and then the substrate on which the glass fine particles are deposited is heated to make the glass fine particles transparent and vitrified to form a core layer.

Thereafter, a mask pattern is formed on the core layer by photolithography, and reactive ion etching is performed using the mask pattern as a mask layer to obtain a core having a desired core pattern from the core layer. Then
A member with a core formed on a substrate is placed on a rotating table in a muffle, and a combustion gas and a raw material gas are supplied from a burner to generate glass fine particles by flame hydrolysis and deposited on the substrate. The body is heated to be vitrified to form an overcladding layer.

Usually, a dopant such as GeO ₂ , P ₂ O ₅ , B ₂ O ₃ is added to SiO ₂ in order to increase the refractive index of the core layer and to vitrify the glass particles at a temperature at which the substrate is not deformed. Therefore, the softening temperature is considerably lower than that of SiO ₂ . When forming the over cladding layer on the substrate and the core, it is necessary to heat the glass fine particle deposit to be the over cladding layer to make the glass viscous,
The heating may cause the previously formed core to soften and deform. FIG. 5 is a cross-sectional view illustrating an example of a modification of the core, in which 6 is a substrate, 7 is a core, and 8 is an over cladding layer. If the core 7 is normal, the core 7 has a rectangular or square cross section. However, as shown in FIG. 5, the core 7 is deformed due to the rounding of the corner or the falling of the core due to heating during the formation of the over cladding layer. Since the deformation of the core has an adverse effect on the light transmission characteristics, the heating temperature during the vitrification of the overcladding layer is higher than the temperature at which the core deforms so that the core does not deform even when heating during the formation of the overcladding layer. Must be lower.

Therefore, in the method disclosed in Japanese Patent Application Laid-Open No. 3-75606, a considerably large amount of P ₂ O ₅ and B ₂ O ₃ is added to the overcladding layer to soften the overcladding layer more than the softening temperature of the core. The temperature is lowered by 200-450 ° C. Japanese Patent Application Laid-Open No. 63-124006 discloses a method for preventing core deformation without lowering the softening temperature of the over cladding layer by using a material having a softening temperature higher than that of the core and having the same refractive index as quartz. A method is disclosed in which a thin film cladding layer having a thickness of about 2 μm is provided by RF sputtering or CVD, and an over cladding layer is provided thereon.

[0006]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Laid-Open Publication No. Hei 3-7
In the method disclosed in Japanese Patent No. 5606, P ₂ O ₅ and B ₂ O ₃ are added in a large amount, but such a composition is unstable as a glass composition, and B ₂ O _{3 and the} like are aggregated and phase separated. easy. for that reason,
The composition range in which the core is not deformed, does not undergo phase separation, and the over cladding layer does not crack due to the difference in thermal expansion coefficient is extremely limited, and there is a problem that it is difficult to select a composition.

In the method described in Japanese Patent Application Laid-Open No. 63-124006, the thin film cladding layer has a thickness of about 2 μm, the center arrangement interval between the cores is narrow, and the gap between the core surfaces is 5 μm or less. In the case of such a narrow optical waveguide,
It is difficult to form a thin-film clad layer having a uniform thickness up to the groove bottom between the cores. SUMMARY OF THE INVENTION The present invention provides a buried optical waveguide and a method for manufacturing the same, which solve the above-mentioned problems of the prior art.

[0008]

According to the present invention, there is provided a buried optical waveguide in which a core having a rectangular or square cross section made of quartz glass and an overcladding layer made of quartz glass covering the core are provided on a substrate. Type optical waveguide, wherein a thin film layer made of oxynitride glass having a composition whose refractive index is closer to the core than the overcladding layer includes a portion including two side surfaces of the core standing upright with respect to the surface of the substrate. It is provided along the longitudinal direction of the core.

Thus, the softening temperature of the oxynitride glass (about 1500 ° C. to 1700 ° C.) is higher than the softening temperature (about 1200 ° C. to 1500 ° C.) of a core obtained by adding a dopant such as GeO ₂ to SiO ₂ which is usually used. Therefore, even if the heating temperature during the vitrification of the overcladding layer is slightly higher than that of the prior art, if the temperature is sufficiently lower than the deformation temperature of the oxynitride glass, the core does not deform. In the case where there is no thin film layer made of oxynitride glass, the softening temperature of the over cladding layer needs to be about 850 ° C. to 1100 ° C. The softening temperature of the layer is 850 ° C. to 130
The temperature can be set to about 0 ° C., and the material composition of the over cladding layer can be easily selected.

In addition, if the refractive index of the thin film layer made of oxynitride glass is made equal to or close to the refractive index of the core, and the thin film layer also has an optical transmission function as a part of the core, the core + The size of the thin film layer can be the same as the size of the core without the thin film layer. In this case, the core can be reduced by an amount corresponding to the thickness of the thin film layer. Accordingly, the gap between the surfaces of adjacent cores can be increased by an amount corresponding to twice the thickness of the thin film layer, so that the work of forming the thin film layer can be easily performed.

[0011] Further, it is possible to form a buried optical waveguide without deformation of the core by providing the entire core with oxynitride glass without providing a thin film layer of oxynitride glass along the core. Can be done.

[0012]

FIG. 1 is a cross-sectional view showing an embodiment of a buried optical waveguide according to the present invention.
a is a surface of the substrate, 2 is a core, 2a and 2b are two side surfaces of the core standing upright with respect to the surface of the substrate, 2c is an upper surface of the core, 3 is an over cladding layer, and 4 is a thin film layer.

First, the FHD method (Frame Hydro)
A core layer made of silica-based glass is formed on a substrate 1 made of silicon, quartz, or the like by a lysis deposition method. That is, SiO ₂ is produced by flame hydrolysis.
To form glass fine particles to which dopants such as GeO ₂ , B ₂ O ₃ , and P ₂ O ₅ are added, and deposit them on the substrate 1, and heat them to form a transparent glass, thereby forming a core layer on the substrate 1. .
A mask pattern is formed on the core layer by a photolithography technique using a mask material, and a core 2 having a rectangular or square cross section is formed from the core layer by reactive ion etching.

Next, on the two side surfaces 2a and 2b of the core 2 standing upright with respect to the surface 1a of the substrate 1, a 1 μm thick oxynitride glass is formed by plasma CVD.
The thin film layer 4 is provided. The thin film layer 4 can be formed by the method described below, but is not limited to the following method. The mask layer remaining on the upper surface 2c of the core 2 when forming the core 2 from the core layer is left as it is, and a mask layer is also provided on the exposed surface 1a of the substrate 1. The mask layer on the surface 1a of the substrate can be formed by using a different mask material from the mask material used for forming the mask pattern on the core layer.

Then, only the two side surfaces 2a and 2b of the core 2 standing upright with respect to the surface 1a of the substrate 1 are exposed, and the oxynitride glass having a thickness of about 1 μm is formed thereon by plasma CVD. Thin film layer 4
Is provided. The oxynitride glass forming the thin film layer 4 is adjusted to have the same refractive index as the core 2 or the refractive index of the core 2 more than the refractive index of the over clad layer 3 by adjusting the amount of nitrogen added. It can be close.

Thereafter, the upper surface 1c of the core and the surface 1a of the substrate
Removing the upper mask layer to expose the substrate 1 and the core 2;
The over cladding layer 3 is provided on the exposed surfaces of the substrate 1, the core 2, and the thin film layer 4. The formation of the over cladding layer 3 includes:
This is performed by the FHD method, and a layer made of a material in which a dopant such as B ₂ O ₃ or P ₂ O ₅ is added to SiO ₂ is formed as the over cladding layer 3.

FIGS. 2 and 3 are cross-sectional views showing another embodiment of the buried optical waveguide of the present invention, and the same reference numerals as those in FIG. 1 denote the same components. In the example of FIG. 2, the two side surfaces 2a and 2b and the upper surface 2c of the core 2 are covered with the thin film layer 4 made of oxynitride glass, and the method is the same as that of the embedded optical waveguide shown in FIG. After the core 2 is formed from the core layer by reactive ion etching, the mask layer remaining on the upper surface 1c of the core 2 is removed, and then the thin film layer 4 is formed. The formation of the thin film layer 4 and the formation of the over cladding layer 3 can be performed by the same manufacturing procedure as in FIG.

The example of FIG. 3 shows two side surfaces 2 of the core 2.
a, 2b, the upper surface 2c, and the thin film layer 4 formed on the exposed portion of the surface 1a of the substrate 1. After the core 2 is formed as in the case of FIG. 1, the mask layer is removed and the surface 1a of the substrate 1 is removed.
The thin film layer 4 is provided by a plasma CVD method or the like without providing a new mask layer on the exposed portion of the substrate. And
FHD is applied to the over cladding layer 3 so as to cover the entire thin film layer 4.
By forming by the method, the embedded optical waveguide of FIG. 3 can be manufactured.

The embedded optical waveguides shown in FIGS. 1, 2 and 3 each have at least a core 2 standing upright on the surface 1 a of the substrate 1.
The thin film layer 4 made of oxynitride glass is provided on the two side surfaces 2a and 2b. At least core 2
Are protected by the thin film layer 4 made of oxynitride glass having a softening temperature higher than the softening temperature of the core 2, so that the over cladding layer 3
The core 2 can also be heated by the transparent vitrification process during the formation.
Can be prevented from falling down, and core deformation can be prevented.

In the buried optical waveguide shown in FIG. 3, a thin film layer 4 is also provided on the interface between the substrate 1 and the over cladding layer 3 except for the side surface of the core 2. Since the refractive index of the thin film layer 4 is closer to the refractive index of the core 2 than the refractive index of the over cladding layer 3, a part of the light transmitted through the core 2 is part of the interface between the substrate 1 and the over cladding layer 3. However, since the thickness of the thin film layer 4 is as thin as about 1 μm, there is almost no effect on transmission loss, and there is no practical problem. Even in the case of a buried optical waveguide in which a plurality of cores are provided and a function as a coupler is provided between the cores, the branching ratio of the coupler can be designed in consideration of light leakage due to the thin film layer 4. Since it is possible, there is no problem in practice if the thin film layer 4 is present at the boundary between the substrate 1 and the over cladding layer.

FIG. 4 is a cross-sectional view showing another embodiment of the embedded optical waveguide of the present invention, and the same reference numerals as those in FIG. 1 denote the same components. Reference numeral 5 denotes a core made of oxynitride glass. In this example, since the entire core 5 is made of oxynitride glass having a high softening temperature, the core 5 is not deformed even by heating when the overcladding layer 3 is formed.

[0022]

EXAMPLE 1 As Example 1, an embedded optical waveguide shown in FIG. 1 was manufactured in the following manner. First, GeO ₂ and B ₂ were added to SiO ₂ on a substrate made of quartz glass by the FHD method.
Forming a core layer made of a material to which O ₃ and P ₂ O ₅ are added;
From the core layer, two parallel rectangular cores having a cross section of 6 μm and a width of 4 μm were formed by photolithography and reactive ion etching. The center distance between the two cores was 8 μm.

Thereafter, the mask layer remaining on the upper surface of the core is left as it is, and a mask layer made of a different mask material from the mask layer on the upper surface of the core is provided on the exposed substrate. On the two side surfaces of each of the cores, a thin film layer of oxynitride glass having a thickness of 1 μm was formed by a plasma CVD method. The amount of nitrogen added to the oxynitride glass was 0.8 at. %, And the refractive index was adjusted to the refractive index of the core. As a result, the core + thin film layer became a square having a cross section of 6 μm each in the vertical and horizontal directions, and the gap between the thin film layers formed on the side surface of the adjacent core was 2 μm. In addition,
at. % Indicates the ratio of the number of nitrogen atoms to the total number of atoms in the composition. % Means that in the case of oxynitride glass in which N is added to SiO ₂ , 33.5 Si, 65.7 O, N
Refers to those made of 0.8 pieces.

Thereafter, the mask layer is removed, and an overcladding layer made of a material obtained by adding B ₂ O ₃ and P ₂ O ₅ dopants to SiO ₂ is formed on the exposed core, thin film layer, and substrate.
It was formed by the HD method. When the light was transmitted to the completed embedded optical waveguide, the cross section was 6 μm each in the vertical and horizontal directions.
Light transmission similar to that of the embedded optical waveguide having m cores was possible. In addition, when the embedded optical waveguide was cut in the cross-sectional direction and observed with an electron microscope, no deformation of the core was observed.

Next, as Example 2, an embedded optical waveguide shown in FIG. 2 was manufactured in the following manner. First, Example 1
A core layer was formed in the same manner as described above, and two parallel rectangular cores having a cross section of 5 μm and a width of 4 μm were formed from the core layer by photolithography and reactive ion etching. The center distance between the two cores was 8 μm.

Thereafter, the mask layer remaining on the upper surface of the core is removed, a mask layer is provided on the exposed substrate surface, and the three side surfaces of each of the two cores standing upright on the substrate surface are provided.
A 1 μm thick thin film layer made of oxynitride glass was formed by a plasma CVD method. The material of the oxynitride glass was the same as in Example 1. as a result,
The core + thin film layer has a square cross section of 6 μm each in the vertical and horizontal directions, and the gap between each thin film layer formed on the side surface of the adjacent core is 2 μm.
m.

Thereafter, the mask layer was removed, and an overcladding layer was formed in the same manner as in Example 1. When light was transmitted to the completed buried optical waveguide, the same optical transmission as that of the buried optical waveguide having a core having a cross section of 6 μm in each of vertical and horizontal directions was possible. Also, this embedded optical waveguide was cut in the cross-sectional direction and observed with an electron microscope.
No deformation of the core was observed.

Next, as Example 3, a buried optical waveguide shown in FIG. 4 was manufactured in the following manner. First, a core layer made of oxynitride glass is formed on a substrate made of quartz glass by a plasma CVD method, and a cross section of 6 μm square is formed from the core layer by photolithography and reactive ion etching. Two cores were formed. The center distance between the two cores is 8 μm,
The gap between the two cores was 2 μm. The amount of nitrogen added to the oxynitride glass was 0.8 at. %.
The relative refractive index difference between the core and quartz was 0.75%.

Thereafter, the mask layer on the core is removed, and the overcladding layer made of a material obtained by adding B ₂ O ₃ and P ₂ O ₅ dopants to SiO ₂ is formed on the exposed core and the substrate.
It was formed by the HD method. When the light was transmitted to the completed embedded optical waveguide, the cross section was 6 μm each in the vertical and horizontal directions.
It was possible to transmit light as in the case of the embedded optical waveguide having a core made of m-quartz glass. Further, when the embedded optical waveguide was cut in the cross-sectional direction and observed with an electron microscope, no deformation of the core was observed.

[0030]

According to the buried optical waveguide of the present invention, a thin film layer made of oxynitride glass is provided along a core provided on a substrate. There is no core deformation such as falling down. Further, by providing the thin film layer made of oxynitride glass, the allowable temperature range of the over cladding layer is widened, so that the composition of the over cladding layer can be easily selected.

Further, the refractive index of the thin film layer made of oxynitride glass is set to be the same as or close to the refractive index of the core, and the thin film layer also functions as a part of the core. The size can be the same as the size of the core without the thin film layer. Therefore, the core can be reduced by an amount corresponding to the thickness of the thin film layer. Accordingly, the gap between the surfaces of the adjacent cores can be increased, so that the work of forming the thin film layer on the side surface of the core between the adjacent cores becomes easy.

Also, a buried optical waveguide without deformation of the core can be manufactured by forming the entire core from oxynitride glass without providing a thin film layer along the core.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a buried optical waveguide of the present invention.

FIG. 2 is a cross-sectional view showing another embodiment of the embedded optical waveguide of the present invention.

FIG. 3 is a cross-sectional view showing another embodiment of the embedded optical waveguide of the present invention.

FIG. 4 is a cross-sectional view showing another embodiment of the embedded optical waveguide of the present invention.

FIG. 5 is a diagram illustrating core deformation of the embedded optical waveguide.

[Explanation of symbols]

1, 6: Substrate 1a: Substrate surface 2, 5, 7: Core 2a, 2b: Two side surfaces of core erecting with respect to substrate surface 2c: Upper surface of core 3, 8: Over cladding layer 4: Thin film layer

Claims (6)

[Claims] 1. A buried optical waveguide having a substrate made of quartz-based glass and having a rectangular or square cross-section made of quartz-based glass and an overcladding layer made of quartz-based glass covering the core, the refractive index of which is higher than that of the overcladding layer. A thin film layer made of oxynitride glass having a composition close to the core is provided along a longitudinal direction of the core at a portion including two side surfaces of the core standing upright with respect to a surface of the substrate. Embedded optical waveguide. 2. The device according to claim 1, wherein the thin film layer is provided on a portion including two side surfaces of the core and an upper surface of the core, the two sides being upright with respect to a surface of the substrate. Embedded optical waveguide. 3. The burying device according to claim 1, wherein the thin film layer is provided over a boundary between the substrate and the over cladding layer and a boundary between the core and the over cladding layer. Type optical waveguide. 4. In a buried optical waveguide in which a core having a rectangular or square cross section and an overcladding layer covering them are provided on a substrate, the core is made of oxynitride glass, and the overcladding layer is made of quartz glass. A buried optical waveguide, comprising: 5. A core layer is provided on a substrate, a mask layer is provided on the core layer, a mask pattern is formed on the core layer, and a core is formed from the core layer by etching. After removal, a thin film layer made of oxynitride glass is provided on at least the portion including the exposed side and top surfaces of the core, and thereafter, an overcladding layer is formed on the exposed surface of the core, the thin film layer and the substrate. And a method of manufacturing a buried optical waveguide. 6. A core layer is provided on a substrate, a mask layer is provided on the core layer, a mask pattern is formed on the core layer, a core is formed from the core layer by etching, and the core is subsequently covered with the mask layer. A thin film layer made of oxynitride glass is provided on at least a portion of the side surface of the core and the surface of the substrate that includes the side surface of the core, and then the mask layer is removed, and the core, the thin film layer, and the substrate are removed. Forming a buried optical waveguide on the exposed surface of the substrate.