JP3575342B2 - Method for manufacturing silica glass optical waveguide - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a silica glass optical waveguide having a wide range of applications in the field of optical communication components, and more particularly to a method for manufacturing a silica glass optical waveguide capable of reducing polarization dependence.
[0002]
[Prior art]
FIG. 3 shows the structure of a conventional silica glass optical waveguide.
[0003]
As shown in FIG. 3, in the conventional silica glass optical waveguide, a plurality of core waveguides 11 formed on a silica glass substrate 10 are covered with a cladding layer 12 made of SiO ₂ glass to which B and P are added. Embedded structures are common.
[0004]
The manufacturing method will be described with reference to FIGS.
[0005]
First, as shown in FIG. 4A, a quartz glass substrate 20 is prepared, and as shown in FIG. 4B, a core of a composition SiO ₂ —TiO ₂ is formed on the quartz glass substrate by an electron beam evaporation method. A film 21 is formed. Next, as shown in FIG. 4C, a plurality of core waveguides 22 are formed on the core film by photolithography and reactive ion etching, and further, as shown in FIG. around, depositing _{SiO 2 -B 2 O 3 -P 2} O 5 based porous glass layer by flame hydrolysis deposition. Next, it was moved into an electric furnace and subjected to a heat treatment in a He gas atmosphere, and as shown in FIG. 4 (e), it was made transparent and made of SiO ₂ —B ₂ O ₃ —P ₂ O ₅ -based glass. The clad layer 24 is formed. The temperature of the heat treatment at this time is 1340 ° C. Here, the dopants of B ₂ O ₃ and P ₂ O ₅ are added for the purpose of lowering the temperature of the transparent glass, and the refractive index of the cladding layer 24 is different from that of the silica glass substrate 20, ie, silica, in terms of optical characteristics. The amounts of B and P are adjusted so as to be equivalent.
[0006]
[Problems to be solved by the invention]
As described above, when the plurality of core waveguides 22 formed on the quartz glass substrate 20 are embedded with the cladding layer 24, the porous glass layer 23 to which B and P are added is formed on the core waveguide 22 by the flame deposition method. In general, a method of subjecting this to a heat treatment to form a transparent glass is provided.
[0007]
In this case, in order to reduce the polarization dependence, which is an important characteristic of the quartz glass optical waveguide, it is desirable to minimize the amounts of B and P contained in the cladding layer 24.
[0008]
However, in order to cover and embed between the plurality of core waveguides 22 with no gap by the flame deposition method, a certain amount or more of the added amount of B and P and a certain amount or more of the heat treatment temperature of the porous glass layer are required. Specifically, a temperature of 1300 ° C. or more is absolutely necessary, and this temperature exceeds a temperature at which thermal deformation of the quartz glass substrate 20 as a substrate occurs.
[0009]
In view of these, in the case where a glass waveguide for wavelength division multiplexing and optical multiplexing / demultiplexing is manufactured, the shift amount of the center wavelength due to polarization (hereinafter, defined as "polarization dependence") is set to 0.05 nm or less. Was impossible.
[0010]
Further, a waveguide-type optical splitter of 2 inputs × 16 outputs was prototyped by the manufacturing method shown in FIG. 4, and light was supplied to V-grooves formed at a predetermined pitch in 16 output ports of the waveguide-type optical splitter. When an optical fiber array in which the ends of the fibers were fixed was connected, there were many optical fiber arrays with extremely large connection losses, and the yield was extremely poor.
[0011]
As a result of studying the cause, the pitch between the core waveguides significantly shrinked from the design value due to the high temperature treatment during the manufacturing process, causing the axis deviation between the core waveguide and the optical fiber of the optical fiber array. Turned out to be a factor.
[0012]
Therefore, an object of the present invention is to solve the above-mentioned drawbacks of the prior art, to greatly reduce the polarization-dependent or polarization-dependent loss, and to enable high-precision connection between an optical waveguide and an optical fiber. An object of the present invention is to provide a method for manufacturing a silica glass optical waveguide that can achieve an improvement in yield and lower cost.
[0013]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention according to claim 1 relates to a method for manufacturing a silica glass optical waveguide in which a plurality of core waveguides formed on a silica glass substrate are embedded with a cladding layer having a lower refractive index than the core waveguide. After forming a SiO ₂ film to which a metal element for increasing the refractive index is added, heat treatment is performed at a temperature in the range of 1000 ° C. to 1200 ° C. to form a core glass film. From the core glass film, photolithography and reaction are performed. forming a core waveguide of multiple using sex ion etching, around the core waveguide, and heat-treated at a temperature in the range of from 1000 ° C. to 1200 ° C. after forming the SiO ₂ glass containing no dopant This is a quartz glass optical waveguide forming a cladding layer.
[0014]
The invention according to claim 2 is a method for manufacturing a quartz glass optical waveguide in which the metal element added to SiO ₂ forming the core glass film is Ti or Ge.
[0015]
The invention according to claim 3 is a method for manufacturing a quartz glass optical waveguide in which the absolute value of the film forming temperature difference between the core glass film and the cladding layer is 50 ° C. or less.
[0016]
The invention according to claim 4 is that, after the core glass film is formed at a temperature of 500 ° C. or less by using an electron beam evaporation method, a sputtering method, or a plasma CVD method, 1000 ° C. is used so that the refractive index becomes a desired value. This is a method for manufacturing a quartz glass-based optical waveguide formed by performing a heat treatment at a temperature in the range of 1 to 1200 ° C.
[0017]
The invention according to claim 5 is that the cladding layer is formed at a temperature of 500 ° C. or less by a sputtering method or a plasma CVD method, and then has a refractive index in a range of 1000 ° C. to 1200 ° C. so as to have a desired value. This is a method for manufacturing a silica glass optical waveguide formed by heat treatment in step (a).
[0018]
The invention according to claim 6 is a method for manufacturing a quartz glass optical waveguide, wherein the quartz glass substrate is a synthetic quartz substrate made of pure SiO ₂ glass.
[0019]
According to the above configuration, since the cladding layer is made of pure SiO ₂ , the linear expansion difference from the quartz glass substrate is equal, and the generation of internal stress on the core waveguide is substantially eliminated. Alternatively, a silica glass optical waveguide having extremely small polarization dependent loss can be manufactured. Further, since the heat treatment temperature of the core glass film and the cladding layer is set to a maximum of 1200 ° C. or less, the pitch shrinkage of the core waveguide due to the shrinkage of the quartz glass substrate is eliminated, and the waveguide and the optical fiber can be connected with high accuracy. be able to.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.
[0021]
FIG. 2 shows a cross-sectional view of a silica glass optical waveguide manufactured according to the present invention.
[0022]
As shown in FIG. 2, this quartz glass-based optical waveguide is formed on a quartz glass substrate 1 having an outer diameter of 4 inches and a thickness of 1 mm, a core conductor having a height h ₁ and a width w ₁ of 6 × 6 μm and a square cross section. The two waveguides 2, 2 are formed in parallel, and the distance d between the side surfaces of these two core waveguides 2, 2 is formed to be 9 μm. That is, the aspect ratio ( d / h ₁ ) is set to 1.5.
[0023]
Further, a cladding layer 3 is formed around the core waveguides 2 and 2 with a thickness of 30 μm from above the quartz glass substrate 1.
[0024]
The quartz glass substrate 1 is made of a synthetic quartz substrate made of pure SiO ₂ , and the core waveguide 2 is made of SiO ₂ to which one kind of metal element having a higher refractive index than that of the quartz glass substrate 1 is added. As this metal element, for example, Ti or Ge is used. The cladding layer 3 is made of SiO ₂ glass containing no dopant, that is, pure SiO ₂ like the quartz glass substrate described above.
[0025]
Next, a method for manufacturing a silica glass optical waveguide according to the present invention will be described with reference to FIG.
[0026]
When manufacturing a silica glass optical waveguide, as shown in FIG. 1A, for example, a quartz glass substrate 30 having an outer diameter of 4 inches and a thickness of 1 mm is prepared, and as shown in FIG. A TiO ₂ —SiO ₂ core glass film 31 is formed on a quartz glass substrate 30 by an electron beam evaporation method. At this time, the film formation temperature is 350 ° C. Thereafter, heat treatment is performed in an oxygen atmosphere at 1100 ° C. in order to set the refractive index of the core glass film 31 to a desired value. Thereby, thermal ion exchange is performed, and the core glass film 31 whose refractive index is adjusted is formed.
[0027]
Further, as shown in FIG. 1C, the core glass film is processed by using photolithography and reactive ion etching to form a plurality of core waveguides 32.
[0028]
Then, as shown in FIG. 1D, pure SiO ₂ is formed by a plasma CVD method on the quartz glass substrate on which the core waveguides 32, 32 are formed. At this time, the film formation temperature is about 400 ° C. Thereafter, heat treatment is performed in an oxygen atmosphere at 1100 ° C. in order to make the pure SiO ₂ glass have a desired refractive index. Thus, a cladding layer having a controlled refractive index is formed by performing thermal ion exchange, and a silica glass optical waveguide is manufactured.
[0029]
As described above, the heat treatment temperature of the core glass film 31 and the clad layer 33 is set in the range of 1000 ° C. to 1200 ° C., and the absolute value of the heat treatment temperature difference between the core glass film 31 and the clad layer 33 is set to 50 ° C. or less. The quartz glass substrate 30 is also heated during the heat treatment, but does not melt because the melting point of the quartz glass substrate 30 is about 1300 ° C., and the pitch shrinkage of the core waveguide 32 due to the shrinkage of the quartz glass substrate 30 is achieved. Is also eliminated. As a result, it is possible to connect the waveguide and the optical fiber with high precision, and it is possible to achieve an improvement in manufacturing yield and a reduction in cost.
[0030]
Further, since the clad layer 33 is made of pure SiO ₂ , the silica glass optical waveguide has the same linear expansion difference as the quartz glass substrate 30, and substantially no internal stress is generated on the core waveguide 32. According to the invention, it is possible to manufacture a silica glass optical waveguide having extremely small polarization-dependent or polarization-dependent loss due to polarization.
[0031]
Next, a glass waveguide for wavelength multiplexing / demultiplexing was manufactured from the silica glass-based optical waveguide described in the present embodiment, and its optical characteristics were examined.
[0032]
As a result, the polarization dependence due to polarization was 0.001 nm or less, which was about 1/50 of that produced by the conventional manufacturing method, and it was confirmed that the polarization dependence due to polarization could be completely eliminated.
[0033]
Next, a prototype optical waveguide splitter having 2 inputs × 16 outputs was fabricated, and the ends of the optical fibers were fixed to V-grooves formed at a predetermined pitch at 16 output ports of the waveguide optical splitter. An optical fiber array was connected.
[0034]
As a result, the connection loss was 0.2 dB or less for all ports, and extremely good results were obtained.
[0035]
【The invention's effect】
In short, according to the present invention, the following excellent effects are exhibited.
[0036]
(1) A silica glass-based optical waveguide having extremely small polarization-dependent or polarization-dependent loss due to polarized light can be manufactured.
[0037]
(2) Pitch shrinkage of the core waveguide due to shrinkage of the quartz glass substrate is eliminated, and highly accurate connection between the waveguide and the optical fiber can be made possible.
[0038]
(3) It is possible to improve the production yield and reduce the cost.
[Brief description of the drawings]
FIG. 1 is a manufacturing process diagram for explaining the present invention.
FIG. 2 is a cross-sectional view of a silica glass optical waveguide manufactured according to the present invention.
FIG. 3 is a cross-sectional view of a silica glass optical waveguide manufactured according to the related art.
FIG. 4 is a manufacturing process diagram for explaining a conventional technique.
[Explanation of symbols]
Reference Signs List 30 quartz glass substrate 31 core glass film 32 core waveguide 33 clad layer

Claims (6)

In a method for manufacturing a quartz glass optical waveguide in which a plurality of core waveguides formed on a quartz glass substrate are embedded with a cladding layer having a lower refractive index than the core waveguide, SiO ₂ added with a metal element for increasing the refractive index is used. after forming, to form a core glass film was heat-treated at a temperature in the range of 1200 ° C. from 1000 ° C., from the core glass film, forming a core waveguide of several by photolithography and reactive ion etching And forming a clad layer by forming a SiO ₂ glass containing no dopant around the core waveguide and then performing a heat treatment at a temperature in a range of 1000 ° C. to 1200 ° C. Waveguide manufacturing method. _{2. The method according} to claim 1, wherein the metal element added to the SiO ₂ forming the core glass film is Ti or Ge. 2. The method according to claim 1, wherein the absolute value of the film forming temperature difference between the core glass film and the cladding layer is 50 ° C. or less. After the core glass film is formed at a temperature of 500 ° C. or less by using an electron beam evaporation method, a sputtering method, or a plasma CVD method, the refractive index is in a range of 1000 ° C. to 1200 ° C. so that the refractive index becomes a desired value. 2. The method for manufacturing a quartz glass optical waveguide according to claim 1, wherein the optical waveguide is formed by heat treatment. The cladding layer is formed by sputtering or plasma CVD at a temperature of 500 ° C. or less, and then heat-treated at a temperature in the range of 1000 ° C. to 1200 ° C. so that the refractive index becomes a desired value. Item 4. The method for producing a silica glass optical waveguide according to Item 1. _{2. The method according} to claim 1, wherein the quartz glass substrate is a synthetic quartz substrate made of pure SiO2 glass.

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