JPH08136754A - Production of optical waveguide - Google Patents

Abstract

PURPOSE: To produce an optical waveguide having excellent polarizing characteristics with little deformation. CONSTITUTION: The dopant added to the clad layer has an effect to change the coeff. of thermal expansion of glass. By this method, the density of the dopant to be added to the upper clad layer 31 is controlled to obtain the coeff. of thermal expansion of the upper clad layer 31 almost the same as that of the substrate 1. Thus, the upper clad layer 31 is formed as a glass layer having <=1.5×10<7> N.m<-2> stress. By this method, the inner stress of the upper clad layer 31 is sufficiently decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an optical waveguide using a flame deposition method.

[0002]

2. Description of the Related Art A conventional method for manufacturing an optical waveguide using a flame deposition method is described in JP-A-58-105111. In this method, first, S supplied from the flame burner
A porous glass fine particle layer (SiO ₂ + B ₂ O ₃ + P ₂ O ₅ ) to be a lower cladding layer is deposited on a silicon substrate with iCl ₄ , BBr ₃ and POCl ₃ . Next, SiCl ₄ , GeCl ₄ , B supplied from the burner
By Cl ₃ and POCl ₃ , a porous glass fine particle layer (SiO ₂ + GeO ₂ ) serving as a core is formed on the lower cladding layer.
₂ + B ₂ O ₃ + P ₂ O ₅ ) is deposited. Subsequently, these two glass fine particle layers are sintered and then gradually cooled to obtain transparent vitrification. Next, the core thus formed is subjected to an appropriate patterning process to form a desired optical waveguide pattern. Then, a glass fine particle layer to be an upper clad layer is deposited on the core in the same manner as the lower clad layer, and then the glass fine particle layer is sintered to form an upper clad layer. In this way, the glass waveguide layer including the core and the clad layer is formed on the substrate, and the optical waveguide is completed.

[0003]

According to the conventional manufacturing method,
When the glass waveguide layer and the substrate have different coefficients of thermal expansion like the above-mentioned quartz glass and silicon, non-uniform stress is generated inside the glass layer (mainly the upper clad layer) when the glass fine particle layer is made into transparent glass. appear. As a result, the refractive index becomes non-uniform inside the glass layer, resulting in a problem that the transmission characteristics of the TE mode and the TM mode are affected and the polarization characteristics are deteriorated. Further, since the optical waveguide is deformed due to the generation of stress, when an optical fiber is connected to this optical waveguide by using an optical connector or the like, a positional deviation easily occurs between the core of the optical waveguide and the core of the optical fiber, Connection loss tends to increase.

The present invention has been made in order to solve the above problems, and reduces the stress generated inside the glass waveguide layer to produce an optical waveguide with less deformation and excellent polarization characteristics. The purpose is to

[0005]

In order to solve the above problems, an optical waveguide manufacturing method according to the present invention comprises a lower clad layer formed on a substrate and a lower clad layer formed on the lower clad layer. A first step of preparing an optical waveguide substrate having a core; and a step of spraying glass fine particles produced in a flame onto the optical waveguide substrate while adding a dopant to form a glass fine particle layer to be an upper clad layer. The second step and the third step of subjecting the glass fine particle layer to transparent vitrification to form the upper clad layer by heat-treating the glass fine particle layer, and the internal stress of the upper clad layer is 1.5 × 10 5. It is characterized in that a dopant having a concentration of ⁷ N · m ⁻² or less is added in the second step.

In the first step, glass fine particles produced in a flame are sprayed onto a substrate to form a glass fine particle layer to be a lower clad layer, and then glass fine particles produced in a flame are formed on the glass fine particle layer. To form a glass fine particle layer to be a core by spraying, after that, these glass fine particle layer is subjected to a heat treatment to transparentize the glass fine particle layer to form a lower clad layer and a core, and subsequently, It may be a step of producing an optical waveguide substrate by subjecting this core to a patterning process to form a predetermined optical waveguide pattern. In addition, the first step is
In the process of producing the optical waveguide substrate, the glass fine particle layer to be the lower clad layer is heat-treated to be transparent vitrified, the glass fine particle layer to be the core is formed, and then heat-treated to be transparent vitrified. It may be.

Further, a silicon wafer is used as a substrate, quartz glass particles are sprayed as glass particles, and B ₂ O ₃ , P ₂ O ₅ , TiO ₂ and GeO are used as dopants.
_At least one or more of ₂ and F may be added. For example, 7.5 to 14.5 wt% as a dopant
B ₂ O ₃ and 2.0 to 11.0 wt% P ₂ O ₅ are preferably added.

[0008]

The dopant added to the clad layer in the method of manufacturing the optical waveguide has a function of changing the thermal expansion coefficient of the glass. The method for producing an optical waveguide of the present invention utilizes this, by controlling the concentration of the dopant added to the upper clad layer according to the substrate material and the type of glass formed on the substrate, the upper clad layer is It should have a coefficient of thermal expansion close enough. As a result, the internal stress of the upper clad layer is sufficiently low at 1.5 × 10 ⁷ N · m ⁻² or less. Therefore, the optical waveguide manufactured by the method of the present invention is little deformed and exhibits good polarization characteristics.

When a silicon wafer is used as the substrate and a quartz glass fine particle layer is formed as the glass fine particle layer, 7.5 to 14.5 wt% of B ₂ O is used as a dopant.
_{When 3} and 2.0 to 11.0 wt% of P ₂ O ₅ are added, the internal stress of the upper clad layer is 1.5 × 10 ⁷ N · m.
^-2 or less. As a result, an optical waveguide having a small amount of deformation and exhibiting good polarization characteristics is manufactured.

[0010]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

1 to 7 are process diagrams showing a method of manufacturing the optical waveguide of this embodiment. In this embodiment, a silicon wafer having a diameter of 3 inches and a thickness of 0.5 mm is prepared as a substrate, and a core and a clad layer made of silica glass are formed on the wafer by the flame deposition method.

First, as shown in FIG. 1, a silicon wafer 1
A first glass fine particle layer 10 serving as a lower clad layer is formed thereon. Using an oxyhydrogen flame burner 50, while feeding a raw material gas such as SiCl _{4 which} is a raw material of the glass fine particles 10 into the oxyhydrogen flame together with a fuel (O ₂ , H ₂ ),
It is carried out by directly spraying fine particles of quartz glass generated in a flame onto the silicon wafer 1 (FIG. 1). At this time, the burner 50 repeatedly moves on the silicon wafer 1. Next, the second glass fine particle layer 20 serving as a core is formed on the first glass fine particle layer 10 by the same method (FIG. 2).

When forming the first glass fine particle layer 10, the gases of BCl ₃ and POCl ₃ which are dopant raw materials are sent into the oxyhydrogen flame together with SiCl ₄ which is a glass raw material. When forming the second glass fine particle layer 20,
In addition to BCl ₃ and POCl ₃ , GeCl ₄ is fed as a raw material gas for a dopant for increasing the refractive index of the core.

Next, after heating the silicon wafer 1 on which the glass fine particle layers 10 and 20 are formed in a sintering furnace,
The glass fine particle layers 10 and 20 are gradually cooled to be transparent vitrified. As a result, the lower clad layer 11 (SiO ₂ + B ₂ O ₃ + P ₂ O ₅ ) and the core layer 21 (SiO ₂ + GeO ₂ + B ₂ O ₃ + P ₂ O ₅ ) are formed on the silicon wafer 1.
Are formed (FIG. 3).

Next, in order to pattern the core layer 21, a photoresist 60 having a predetermined optical waveguide pattern is formed on the upper surface of the core layer 21 by using a photolithography technique (FIG. 4). After that, the core layer 21 is subjected to reactive ion etching to sequentially provide Y.
1 x 8 branches into 1 to 8 waveguides by branching
The branch core 22 is formed (FIG. 5).

Next, a third glass fine particle layer 30 serving as an upper clad layer is formed on the optical waveguide substrate manufactured as described above. This is the first glass fine particle layer 10
Similarly to the above, the gas of BCl ₃ and POCl _{3 as} the dopant raw materials is fed into the oxyhydrogen flame together with SiCl ₄ , and the glass fine particles generated in the flame are blown onto the upper surfaces of the core 22 and the lower cladding layer 11 ( (Figure 6).

After that, the glass fine particle layer 30 is heated in a sintering furnace and then gradually cooled to form a transparent glass, and the upper clad layer 31 (SiO ₂ + B ₂₎ to which a dopant is added is formed.
O ₃ + P ₂ O ₅ ) is formed. This upper clad layer 31
Combine with the lower cladding layer 11 to form one cladding, which surrounds the core 22 (FIG. 7).

In the above method, each glass fine particle layer is formed in the reaction vessel 40 as shown in FIG.
A rotatable turntable 41 (diameter 600 mm) is provided inside the reaction container 40, and a plurality of silicon wafers 1 on which glass particles from the burner 50 are to be deposited are placed on the turntable 41. . A heater 42 is provided under the turntable 41,
Silicon wafer 1 placed on turntable 41
Heat evenly. The glass particles and the exhaust gas not deposited on the silicon wafer 1 are sucked into the exhaust pipe 43 and discharged to an exhaust treatment device (not shown).

Burner 50 while supplying the raw material gas and fuel
Is repeatedly moved along the radial direction of the turntable 41 and the glass particles are sprayed, whereby a glass particle layer can be uniformly formed on the silicon wafer 1. In this example, the first to third glass fine particle layers are produced by this method.

The lower clad layer 11 has a layer thickness of 40 μm, the upper clad layer 31 has a layer thickness of 40 μm, and the core 22 has a thickness of 8 μm.
It is formed so as to have a cross section of × 8 μm. This allows
A glass waveguide layer having a layer thickness of about 80 μm is formed on the silicon wafer 1. Further, the dopant concentration of the core and the clad layer is set so that the relative refractive index difference of the optical waveguide becomes 0.3%.

In the method of this embodiment, the upper cladding layer 31
The coefficient of thermal expansion of the upper cladding layer 31 is made close to that of the silicon wafer 1 by controlling the concentration of the dopant added to the above to an appropriate value. This will be described below in comparison with the conventional method.

In the conventional method for producing an optical waveguide, when the glass fine particle layer is heated in a sintering furnace and then gradually cooled, silicon as a substrate material is more preferable than silica-based glass constituting the waveguide layer. Since the coefficient of thermal expansion is large, the silicon wafer 1 contracts strongly. As a result, stress is generated inside the glass waveguide layer along the laminated surface of the waveguide layer. In the method of forming the lower clad layer and the core and then forming the upper clad layer, this stress is mainly generated in the upper clad layer 31, and the magnitude thereof increases as it approaches the surface of the waveguide layer.

Generally, when stress is generated inside the glass,
The photoelastic effect increases the refractive index of the stress generating portion. Since the magnitude of the stress inside the glass waveguide layer is larger as it is closer to the surface of the waveguide layer, the increase amount of the refractive index of the upper cladding layer 31 is also larger as it is closer to the surface of the waveguide layer. As a result, the core 22
Since the difference in refractive index between the upper clad layer 31 and the upper clad layer 31 is reduced, the effect of confining light is weakened and the radiation loss is increased.

As described above, in the upper clad layer 31, the amount of increase in the refractive index changes along the layer thickness direction, so that the TE mode and the TM mode, which are waveguide modes, have different effects of the change in the refractive index. As a result, the amount of increase in radiation loss differs between the TE mode and the TM mode. Therefore, the difference in transmission loss between the two modes, that is, the polarization characteristic becomes large. If the transmission characteristics differ depending on the polarization direction, it is not preferable for communication. Therefore, an increase in the transmission characteristics difference depending on the polarization direction can be translated into deterioration of the polarization characteristics.

On the other hand, in the manufacturing method of the present embodiment, the difference in thermal expansion coefficient between the upper clad layer 31 and the silicon wafer 1 is controlled by controlling the concentrations of B ₂ O ₃ and P ₂ O ₅ added to the upper clad layer 31. Is reduced, the stress generated when the upper cladding layer 31 is gradually cooled is reduced. That is, the dopant added to the silica-based glass has the effect of changing the thermal expansion coefficient of the silica-based glass, and if the dopant of an appropriate concentration is added to the cladding layer, the difference in the thermal expansion coefficient can be reduced. Is.

FIG. 9 is a graph showing the relationship between the concentration of various dopants added and the coefficient of thermal expansion of silica glass.
Further, FIG. 10 is a graph showing the relationship between the addition concentrations of various dopants and the refractive index of silica glass. By considering the influence of various dopants on the thermal expansion coefficient and the refractive index of the silica-based glass, the dopant concentration is appropriately controlled to obtain a predetermined relative refractive index difference (0.3% in this embodiment).
It is possible to reduce the difference in coefficient of thermal expansion between the substrate and the glass layer while realizing the above.

According to the knowledge of the present inventors, the stress generated inside the upper cladding layer 31 is 1.5 × 10 ⁷ N · m ^−2.
If it is below, deterioration of the polarization characteristics of the obtained optical waveguide can be sufficiently suppressed.

FIG. 11 shows that the internal stress of the upper cladding layer 31 is B ₂ O ₃ and P such that the internal stress is 1.5 × 10 ⁷ N · m ⁻² or less.
It is a figure which shows the addition concentration range of ₂ O ₅ . In this figure, the area 100 surrounded by the solid line has an internal stress of 1.5 × 1.
It is a region of 0 ⁷ N · m ⁻² or less, and the dotted line 110 in the region 100 indicates that the thermal expansion coefficient of the silica glass to which B ₂ O ₃ and P ₂ O ₅ are added is equal to that of silicon.

As shown in this figure, in order to reduce the internal stress of the upper cladding layer 31 to 1.5 × 10 ⁷ N · m ⁻² or less, the concentration of B ₂ O ₃ added to the upper cladding layer 31 is reduced. Is about 7.5 to about 14.5 wt% and the concentration of P ₂ O ₅ is about 2.0 to about 11.0 wt%. Incidentally, such a numerical value hardly depends on the thickness of the substrate.

In view of the above facts, in this embodiment, 9.4 wt% of B ₂ O ₃ and 4.1 was added to the upper cladding layer 31.
wt% P ₂ O ₅ is added. Further, the core 22 contains 3.6 wt% B ₂ O ₃ and 1.2 wt% P.
₂ O ₅ , and _{5. to make} the relative refractive index difference 0.3%.
4 wt% GeO ₂ is added. Lower clad layer 1
1 contains 7.6 wt% B ₂ O ₃ and 3.2 wt% P.
₂ O ₅ is added.

The inventors measured the magnitude of stress generated in the upper cladding layer 31 of the optical waveguide manufactured by the method of this example. This can be calculated by measuring the amount of warpage of the silicon wafer 10 caused by the difference in coefficient of thermal expansion between silicon and quartz glass and using the following formula. ^{σ = (Δδ / r 2)} × (E S / 3 (1-ν)) × (d S
² / d _F ) where σ: internal stress of the upper clad layer Δδ: amount of substrate warp after formation of the upper clad layer−substrate warp amount before formation of the upper clad layer E _S : Young's modulus of silicon wafer ν: Poisson's ratio d _S : Layer thickness of the glass waveguide layer d _F : Thickness of the silicon wafer r: Radius of the silicon wafer In this embodiment, the warp amount Δδ of the silicon wafer is 93 μ.
m, and using this, the internal stress σ of the upper cladding layer 31 is found to be 1.1 × 10 ⁷ N · m ⁻² .

When the fluctuation range of the refractive index in the upper clad layer 31 of the optical waveguide manufactured in this example was measured, it was as small as 0.05%. Also, 1 × 8
When the polarization characteristics, that is, the difference in transmission loss between the TE mode and the TM mode, is examined for each optical path of the branch waveguide,
Good results were obtained with a maximum of 0.5 dB and a minimum of 0.1 dB. Thus, according to this embodiment, it is possible to manufacture an optical waveguide having sufficiently low polarization characteristics.

Further, in the manufacturing method of this embodiment, the stress generated in the upper cladding layer 31 is sufficiently reduced, and as a result, the deformation of the manufactured optical waveguide is reduced. There is also an advantage that positional deviation is less likely to occur during connection, and connection loss is reduced.

The method of this embodiment is different from the conventional method in that the dopant (B ₂
Since the concentrations of O ₃ and P ₂ O ₅ ) are high, the glass fine particle layer formed on the silicon wafer is easily peeled off.
However, this point is that when the glass fine particles are blown by the burner 50 using the apparatus of FIG.
It can be improved by increasing the rotation speed of (1) above the normal rotation speed (about 10 rpm).

The present invention is not limited to the above embodiment, but various modifications can be made. For example, even when the substrate material or the type of glass forming the waveguiding layer is different from that of this embodiment, the concentration of the dopant added to the glass is appropriately controlled according to the type of the substrate material or the glass, and the difference in the coefficient of thermal expansion is It is possible to fabricate an optical waveguide exhibiting good polarization characteristics by reducing the deformation.

[0036]

As described above in detail, in the method of manufacturing the optical waveguide of the present invention, the concentration of the dopant added to the upper clad layer is controlled so that the upper clad layer has a thermal expansion coefficient sufficiently close to that of the substrate. To have. Therefore, according to the present invention, as a result of the internal stress of the upper clad layer being sufficiently low, it is possible to manufacture an optical waveguide exhibiting a good polarization characteristic with little deformation.

When the substrate is a silicon wafer and a silica-based glass fine particle layer is formed as the glass fine particle layer, the upper clad layer is made of 7.5 to 14.5 wt% B ₂ O.
By adding ₃ and 2.0 to 11.0 wt% of P ₂ O ₅ , the internal stress of the upper cladding layer can be easily made sufficiently low.

Since the optical waveguide manufactured by the above method has a small deformation, it can be connected to the optical fiber for communication with low loss and its polarization characteristics are good, so that it can be suitably used in the optical communication field. is there.

[Brief description of drawings]

FIG. 1 is a first process chart showing a method for manufacturing an optical waveguide of an example.

FIG. 2 is a second process chart showing the method of manufacturing the optical waveguide of the example.

FIG. 3 is a third process chart showing the method of manufacturing the optical waveguide of the example.

FIG. 4 is a fourth process chart showing the method of manufacturing the optical waveguide of the example.

FIG. 5 is a fifth process chart showing the method of manufacturing the optical waveguide of the example.

FIG. 6 is a sixth process chart showing the method for producing the optical waveguide of the example.

FIG. 7 is a seventh process chart showing the method of manufacturing the optical waveguide of the example.

FIG. 8 is a diagram showing an apparatus used for forming a glass fine particle layer.

FIG. 9 is a graph showing the relationship between the addition concentration of various dopants and the coefficient of thermal expansion of silica glass.

FIG. 10 is a graph showing the relationship between the added concentrations of various dopants and the refractive index of silica-based glass.

FIG. 11 shows that the internal stress of the upper clad layer is 1.5 × 10 ^7.
Is a diagram showing the addition concentration range of N · m is ^-2 or less B ₂ O ₃ and P ₂ O _5.

[Explanation of symbols]

1 ... Silicon wafer, 10 ... First glass fine particle layer,
11 ... Lower clad layer, 20 ... Second glass fine particle layer,
21 ... Core layer, 22 ... 1 × 8 branched core, 30 ... Third glass fine particle layer, 31 ... Upper clad layer, 40 ... Reaction vessel, 41 ... Turntable, 42 ... Heater, 43 ... Exhaust pipe, 50 ... Oxyhydrogen flame burner, 60 ... Photoresist.

Claims (4)

[Claims] 1. A lower clad layer formed on a substrate,
A first step of preparing an optical waveguide substrate having a core formed on the lower clad layer, and glass fine particles generated in a flame are sprayed onto the optical waveguide substrate while adding a dopant, A second step of forming a glass fine particle layer to be a clad layer; and a third step of subjecting the glass fine particle layer to a transparent vitrification to form an upper clad layer by heat-treating the glass fine particle layer. , The internal stress of this upper cladding layer is 1.5 × 10 ⁷ N · m
^A method of manufacturing an optical waveguide, characterized in that a dopant having a concentration of ⁻² or less is added in the second step. 2. In the first step, glass fine particles produced in a flame are sprayed onto a substrate to form a glass fine particle layer serving as the lower clad layer, and then the glass fine particle layer is produced on the glass fine particle layer in a flame. The glass fine particles are sprayed to form a glass fine particle layer to be the core, and then these glass fine particle layers are subjected to heat treatment to make these glass fine particle layers transparent vitrified, and the lower clad layer and the core. 2. The production of an optical waveguide according to claim 1, which is a step of producing the optical waveguide substrate by forming a core, and then subjecting the core to a patterning process to form a predetermined optical waveguide pattern. Method. 3. The substrate is a silicon wafer, quartz glass particles are sprayed as the glass particles, and B ₂ O ₃ , P ₂ O ₅ , TiO _{2 are used} as the dopants.
_{3. The} method for producing an optical waveguide according to claim 1, wherein at least one of GeO ₂ and F is added. 4. As the dopant, 7.5 to 14.
5 wt% B ₂ O ₃ and 2.0-11.0 wt% P
_The method for producing an optical waveguide according to claim 3, wherein ₂ O ₅ is added.