JP2001272562A - Method for manufacturing quartz-base optical waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a quartz-base optical waveguide capable of manufacturing the quartz-base optical waveguide having a good upper clad film which prevents the remaining of air bubbles in the slight spacings between adjacent core waveguides of the optical waveguide in which the plural core waveguides are adjacent to each other with high productivity. SOLUTION: The method for manufacturing the quartz-base glass waveguide which forms a porous glass layer consisting of quartz glass containing a dopant on a quartz substrate formed with the core waveguides on the surface, then forms the upper clad layer vitrified to transparent glass by sintering the porous glass layer consists in forming the porous glass layer in such a manner that its bulk density attains a range of 0.05 to 0.15 g/cm3 and sintering the porous glass layer under conditions of 1,250 to 1,350 deg.C in sintering temperature and 30 to 120 minutes sintering time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a silica-based optical waveguide, and more particularly to an optical waveguide having a plurality of core waveguides adjacent to each other, such as an optical circuit having an optical branching and optical multiplexing / demultiplexing function.
The present invention relates to a method of manufacturing a silica-based optical waveguide having a good upper clad film with no bubbles remaining in a minute gap portion between adjacent core waveguides, with high productivity.

[0002]

2. Description of the Related Art In the technical field of an optical communication device using an optical fiber as an optical transmission line, an optical waveguide core is formed on a quartz glass substrate, and a glass soot serving as an upper cladding layer is formed over the optical waveguide core. Then, an optical waveguide is used in which the soot layer is heated and melted to form a transparent upper clad layer. In the manufacturing process of such an optical waveguide, the upper cladding layer usually has a thickness of 25 to 50 μm.
In order to form an upper clad layer of this thickness, it is necessary to form a porous glass layer having a thickness of 250 to 600 μm and sinter it. In addition, deformation of the substrate and generation of bubbles due to shrinkage of the porous glass,
There were problems such as residue.

[0003] In order to cope with such a problem, various improvement methods have been proposed. For example, Japanese Patent Application Laid-Open No. 7-1206
Japanese Patent Publication No. 32 (1995) discloses that, when depositing porous glass on a substrate, another oxyhydrogen burner that does not supply a glass source gas is arranged next to the porous glass forming burner, and the substrate is formed by the porous glass forming burner. Porous glass deposited on top,
The bulk density (0.2 g / cm ³ ) of the porous glass deposited on the substrate by heat treatment with the above another oxyhydrogen burner
(According to the embodiment, the bulk density is 0.2 g / cm ³ when no oxyhydrogen burner for heat treatment is provided, but 0.7 g / c
is set to m ^3), how to minimize shrinkage during vitrification is disclosed by the subsequent sintering process.
In addition, as a method for preventing the generation and remaining of bubbles at the time of sintering, in a soot layer to be an upper clad layer, a dopant material that lowers a melting point in a lower layer portion close to an optical waveguide core than a portion in an upper layer is used. Add more so that the vitrification by heating occurs near the upper part of the optical waveguide core before the upper layer, and the gas contained therein escapes into the upper unmelted soot layer and vitrifies. For preventing air bubbles from remaining in the formed cladding layer (Japanese Unexamined Patent Publication No.
No. 319842), a method of eliminating bubbles in the clad glass by changing the pressure in the sintering furnace when sintering the porous glass, that is, performing degassing when melting the glass by reducing the pressure, Thereafter, a method of eliminating bubbles remaining in the clad glass by applying pressure (Japanese Patent Application Laid-Open No. 8-62444) has been proposed.

[0004]

SUMMARY OF THE INVENTION Bubbles during the above sintering
Of methods to prevent the generation and residue of
-In the case of adding punts, dope to lower the melting point
-P as a punt_TwoO_FiveAnd B_TwoO_ThreeIs used. Moth
P in the lath_TwoO_FiveIncreases the refractive index and B_TwoO_ThreeIs the refractive index
Has the effect of lowering. Lower layer close to optical waveguide core
In the soot layer of P _TwoO_FiveAnd B_TwoO_ThreeAdd a lot of
When the amount of addition is gradually reduced in the layer direction
In the case, the refractive index distribution tends to fluctuate in the thickness direction of the clad.
It will get worse. As a result, the optical characteristics of the optical waveguide
Problem that controllability and stability are easily impaired
There is. In the method of changing the pressure during sintering,
Air-tight chamber equipment equipped with
Heat resistance so that the airtightness does not change even during high temperature heating
Is required. For this reason, the conventionally used purge
Compared to sintering equipment with only gas supply and heater
There is a problem that the equipment cost is high, and
Relatively complicated operations and operations of pressure adjustment are required.

The present invention has been made in view of the state of the prior art as described above, and is an optical waveguide in which a plurality of core waveguides are adjacent to each other, such as an optical circuit having an optical branching and optical multiplexing / demultiplexing function. It is an object of the present invention to provide a method of manufacturing a silica-based optical waveguide that can produce a silica-based optical waveguide having a good upper clad film without leaving air bubbles in a small gap portion with high productivity.

[0006]

The present invention includes the following aspects (1) to (5) as means for solving the above-mentioned problems. (1) On a quartz substrate having a core waveguide formed on a surface thereof, a porous glass layer made of quartz glass containing a dopant is formed by a flame deposition method so as to cover the core waveguide, and then the porous glass layer is formed. In the method for manufacturing a quartz glass waveguide in which an upper clad layer is formed by sintering a transparent glass to form a transparent glass, the porous glass layer has a bulk density of 0.05 to 0.1.
15 g / cm ³ of formed so as to range, and the sintering temperature is 1250 to 1350 ° C., the production method of silica-based glass waveguides sintering time is characterized by sintering under the conditions of 30 to 120 minutes . (2) After forming a core glass film made of quartz glass to which a refractive index increasing dopant is added on the substrate, the core waveguide is formed in a rectangular cross section by photolithography and reactive ion etching. (1) The method for manufacturing a silica-based glass waveguide according to (1) above, wherein (3) The porous glass layer formed by the flame deposition method has P ₂ O ₅ of 0.9 to ₂ wt% and 0.9 to ₂ wt%.
Method for producing a silica-based glass waveguide of said (1) or (2) to the B ₂ O _3, characterized in that it comprises as a dopant. (4) The formation of the porous glass layer by the flame deposition method
The above (1) to (3), wherein the heating is performed by heating the substrate to 100 to 400 ° C. and controlling the H ₂ / O ₂ flow ratio in the oxyhydrogen flame to 0.25 to 0.50.
The manufacturing method of any one of the silica-based glass waveguides. (5) The method for manufacturing a quartz-based glass waveguide according to (4), wherein the heating of the substrate is performed by a heater provided below the substrate.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION On a quartz substrate having a core waveguide formed on its surface, a porous glass layer made of quartz glass containing a dopant is deposited on the quartz substrate by a flame deposition method so as to cover the core waveguide. After the formation, the porous glass layer is sintered to form a transparent vitrified upper cladding layer. In the case of manufacturing a silica glass waveguide, usually, a minute (1 to 2 μm) between adjacent core waveguides is small. Air bubbles are likely to remain in the gap. As a method of forming the core waveguide, for example, after forming a core glass film made of silica glass to which a refractive index increasing dopant is added on a substrate on which an under cladding layer is formed as necessary, the core glass film is formed. A general method is to form a core waveguide having a rectangular cross section by processing by photolithography and ion etching.

FIG. 1 shows the state of the porous glass layer formed near the core waveguide before sintering. Usually, the porous glass layer 3 formed on the surface of the quartz substrate 1 on which the core waveguide 2 is formed is not filled in the root portion of the core waveguide 2 or the narrow gap 4 between the core waveguides 2. Is deposited on the upper part of the core waveguide 2 with the gap 4 left. Thereafter, at the time of sintering, the porous glass on the upper part of the core waveguide 2 softens and flows and fills the gap 4 to form an upper clad glass layer.

Here, as schematically shown in FIG. 2, if the degree of aggregation of the glass particles 5 constituting the porous glass layer 3 is too high, that is, if the gap between the glass particles 5 is too small, firing is performed. During the sintering process, the glass particles 5
At the time of integration, bubbles existing between the core waveguides 2 become difficult to pass between the glass microparticles 5, and as a result, bubbles are likely to remain in minute (1 to 2 μm) gaps between the core waveguides 2. . On the other hand, as shown in FIG. 3, when the degree of aggregation of the glass particles 5 constituting the porous glass layer 3 is low,
When the gap between the glass particles 5 is large to some extent, bubbles existing between the core waveguides 2 easily pass through the glass particles 5 when the glass particles 5 are aggregated and integrated in the sintering process, and the bubbles remain. do not do.

Here, as a quantitative parameter that reflects the degree of aggregation of the glass fine particles constituting the porous glass layer, a bulk density defined by total weight / (substrate area × thickness of the porous body) can be considered. A low bulk density indicates that the degree of aggregation of the glass particles constituting the porous glass layer is low, and a high bulk density indicates that the degree of aggregation of the glass particles constituting the porous glass layer is high. Represents In order to examine the effect of the bulk density of the porous glass layer formed on the surface of the quartz substrate on which the core waveguide was formed on the rate of residual bubbles generated between the core waveguides during sintering, a width of 7 μm and a height of 7 μm were investigated. 7 μm,
A porous glass layer containing 1.3 wt% of P ₂ O ₅ and 0.9 wt% of B ₂ O ₃ as dopants was formed on a quartz substrate on which core waveguides having a length of 1 mm were formed at intervals of 2 μm. Changed and formed. This porous glass layer is heated at 1300 ° C.
At 60 ° C. for 60 minutes and the state of bubbles remaining between adjacent core waveguides was examined.

[0011] The bulk of the porous glass layer thus determined
The relationship between the density and the residual bubble generation ratio in the core space
As shown in FIG. Here, generation of residual air bubbles in the core space
The ratio is 20 adjacent cores arranged in a 4 inch quartz substrate.
A shows a bubble generation ratio remaining between the waveguides. FIG.
From the bulk density of the porous glass layer is 0.05 to 0.15 g /
cm^ThreeIn the range, almost no residual air bubbles are generated.
Also good, no cracks in the porous glass
Quality upper clad layer
The bulk density of the glass layer is 0.15 g / cm^ThreeBeyond
It was found that the bubble generation ratio increased. Also, the bulk density is
0.05g / cm^ThreeBelow, the porous glass layer is cracked
Occurred, and the defect of peeling off from the quartz substrate occurred frequently. I
Therefore, air bubbles remain between adjacent core waveguides with a narrow gap.
To make a good upper clad
, The bulk density of the porous glass layer is 0.05 to 0.15 g
/ Cm ^ThreeIs appropriate.

As dopants to be added to the porous glass layer, there are P ₂ O ₅ and B ₂ O ₃ . P ₂ O ₅ , B
If the added concentration of ₂ O ₃ is too high, the difference in the coefficient of thermal expansion from the quartz substrate becomes large, and the polarization dependence is deteriorated. If the addition concentration of P ₂ O ₅ or B ₂ O ₃ is too low, the porous glass layer remains unsintered even if the sintering temperature is increased within a range where the quartz substrate is not deformed, and light scattering is large. turn into. At the same time, if the addition concentration of P ₂ O ₅ or B ₂ O ₃ is too low, crystals tend to be generated at the interface between the core and OC (overcladding). In order to manufacture an optical waveguide having good polarization dependence and excellent light transmittance, P
The added concentration of ₂ O ₅ and B ₂ O ₃ is 0.9 to ₂ respectively.
A range of wt% is appropriate.

The parameters for determining the bulk density of the porous glass layer include the addition concentration of P ₂ O ₅ and B ₂ O ₃ in the porous glass and the temperature of the porous glass deposition surface. Here, in the above-mentioned P ₂ O ₅ and B ₂ O ₃ addition concentration region, even if the concentration changes, the change in the bulk density is not large, and the bulk density is determined mainly by the temperature of the porous glass deposition surface. Further, the temperature of the porous glass deposition surface depends on the temperature of the deposition surface in the oxyhydrogen flame and the substrate surface temperature when the porous glass is deposited. The temperature of the deposition surface in the oxyhydrogen flame can be adjusted by the H ₂ / O ₂ flow rate, and the substrate surface temperature can be adjusted by a heater installed below the table on which the substrate is placed.

Therefore, the bulk density of the porous glass layer is 0.0
H ₂ in an oxyhydrogen flame of ⁵ to 0.15 g / cm ³
The / O ₂ flow rate and the substrate surface temperature heated by the heater were examined.
As a result, as shown in FIG.
_{When the 2} / O ₂ flow ratio is 0.25 to 0.50 and the temperature of the heated substrate is 100 to 400 ° C., the bulk density of the porous glass layer is 0.05 to 0.15 g / cm ³ . Turned out to enter the area. If the substrate temperature is less than 100 ° C,
Cracks were easily generated in the porous glass layer. Also,
When the substrate temperature exceeds 400 ° C., it takes time (60 minutes or more) to raise the temperature by heating the heater, which is considered to be disadvantageous in terms of productivity.

Next, the sintering conditions (temperature,
Time), the degree of residual bubble generation in the core interval
We also looked at how it would change. As shown in FIG.
Quartz base forming the same core waveguide used in the test
P on the plate as a dopant _TwoO_Five1.3 wt% and
B_TwoO_ThreeContains 0.9wt%, bulk density is 0.08g / c
m^ThreeTo form a porous glass layer of sintering temperature and time
The sintering was performed while changing, and the generation state of the residual air bubbles was examined. result
At a sintering temperature of 1200 ° C. or less, as shown in FIG.
Rather than performing sintering with a sintering time of 120 minutes or more, 1250
Sintering at a sintering temperature of at least 90 ° C for a sintering time of 90 minutes or less
However, it was found that the residual bubbles were reduced. Low temperature / long time
High-temperature, short-time sintering is better than porous glass
It is estimated that the fluidity of the layer increases and it is easy to enter the core gap.
Was. When the sintering temperature exceeds 1350 ° C, the quartz substrate
Deformation also increases, which is disadvantageous in the characteristics of the optical waveguide.
You. The sintering conditions for reducing the residual bubbles include the sintering temperature
1250-1350 ° C, sintering time 30-120 minutes is appropriate
It was considered.

[0016]

The present invention will now be described in more detail with reference to the following examples.
Explain, but the invention is not limited to these examples
is not. (Example 1) Outer diameter 4 inches (10.16 cm), thickness
Plasma CVD on 0.5mm quartz glass substrate
So GeO_Two-SiO_TwoWas formed. Core membrane
Are characterized by a relative refractive index difference of 0.75% from the quartz substrate and a film thickness of 6 μm
m. Next, photolithography, reactive ions
By etching, the core film should have a minimum core spacing of 2 μm
Optical circuit of multiplexer / demultiplexer (20 pieces) composed of directional coupling unit
It was processed into a shape (see FIG. 7). Light having a shape indicated by reference numeral 6 in FIG.
Turn the quartz glass substrate 1 on which the circuit core is formed
Heated to 300 ° C. on the _Two
-B_TwoO_Three−P_TwoO_FiveSooting of upper clad layer of composition
(Formation of a porous glass layer) was performed.

H ₂ / O ₂ in the oxyhydrogen flame at this time
The flow rate is 1.8 (liter / minute) / 6 (liter / minute)
(Flow rate ratio: 0.3), and the bulk density of the porous glass layer (thickness: about 850 μm) after soaking was evaluated.
08 g / cm ³ . The quartz substrate on which the porous glass layer was formed was heated at a sintering temperature of 1300 ° C. for 1 hour to produce an optical waveguide having a transparent and uniform clad glass film (30.0 μm thick). When the degree of residual bubble generation in a directional joint having a minimum core spacing of 2 μm was evaluated by a microscope,
No air bubbles were generated. A part of the manufactured optical waveguide substrate was cut, and the SiO ₂ -B ₂ O ₃ -P ₂ O ₅ concentration analysis in the thickness direction of the upper cladding layer was performed. As a result, the P ₂ O ₅ concentration was 1.3 wt. %, The B ₂ O ₃ concentration was 0.9 wt%. When the optical characteristics of the optical waveguide chip of the multiplexing / demultiplexing optical circuit were evaluated, good values were obtained with an excess loss of 1 dB or less and a polarization dependent loss of 0.1 dB or less.

Comparative Example 1 In the same manner as in Example 1, a quartz glass substrate having a multiplexing / demultiplexing optical circuit was prepared. The substrate was heated to 300 ° C. on a turntable, and the upper clad layer was sooted as in Example 1. However, the H ₂ / O ₂ flow rate in the oxyhydrogen flame was 3.6 (liter / liter).
Min) / 6 (liter / min) (flow rate ratio 0.6). When evaluating the bulk density of the porous glass layer after sooting,
It was 0.20 g / cm ³ . Then, sintering temperature 130
Heat at 0 ° C. for 1 hour to obtain a transparent clad glass film (30.
0 μm thick). Microscopic evaluation of the degree of residual air bubbles generated in the directional joints having a minimum core spacing of 2 μm revealed that bubbles remained in about 15 out of the 20 directional joints.

Comparative Example 2 A core was formed in the same manner as in Example 1.
Film and optical circuit processing are performed, and SiO_Two-B _TwoO_Three
−P_TwoO_FiveAn upper clad layer having a composition was sooted.
Next, heating at 1200 ° C. for 5 hours,
A glass substrate (30.0 μm thick) was produced. Smallest core
The degree of residual air bubbles generated at the directional joint with a spacing of 2 μm
When evaluated with a microscope, there were 20 directional coupling sections.
In other words, almost all of the bubbles showed residual bubbles.

(Comparative Example 3) Core film formation and optical circuit processing were performed in the same manner as in Example 1, and a turntable temperature of 300 ° C.
The composition of SiO ₂ —B ₂ O ₃ —P ₂ O ₅ was obtained under the condition that the H ₂ / O ₂ flow rate in the oxyhydrogen flame was 1.2 (liter / minute) / 6 (liter / minute) (flow rate ratio: 0.2). The upper clad layer was sooted. The resulting porous glass layer had a thickness of about 1600 μm and a bulk density of 0.04 g / cm ³ , however, soot peeling occurred and sintering was impossible.

(Comparative Examples 4 to 7)
A film formation and optical circuit processing are performed, and SiO_Two-B _Two
O_Three−P_TwoO_FiveSoot the upper cladding layer of the composition
Was. Next, as shown in Table 1, the sintering temperature was outside the range of the present invention.
And sintering by changing the sintering time, the clad glass film (3
0.0 μm thick). As a result, any sample
In this case, crystal formation, substrate deformation, bubble generation, etc. were observed.
As a result, a good quality clad glass film could not be obtained.
For Example 1 and Comparative Examples 1 to 7, sintering conditions and
Table 1 summarizes the evaluation results of the clad glass films
You.

[0022]

[Table 1]

[0023]

According to the method of the present invention, the following effects can be obtained. (1) When forming the upper cladding layer, no bubbles remain in the minute gap between the adjacent core waveguides. (2) In addition to the above effects, good upper clad film quality can be obtained by the flame deposition method. It is possible to manufacture an optical waveguide having no irregularities such as crystals in the film quality and extremely small light scattering. (3) When forming the porous glass layer by the flame deposition method,
By optimizing the ₂ / O ₂ flow ratio and / or the substrate temperature, no air bubbles remain in minute gaps between adjacent core waveguides, and at the same time, an upper clad layer having an extremely smooth surface can be obtained. Thus, an optical waveguide with extremely low light scattering can be manufactured with high productivity.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a state of a porous glass layer formed near a core waveguide.

FIG. 2 is an explanatory view schematically showing a state of a porous glass layer formed of glass particles having a high degree of aggregation formed near a core waveguide.

FIG. 3 is an explanatory view schematically showing a state of a porous glass layer formed in the vicinity of a core waveguide and formed of glass particles having a low degree of aggregation.

FIG. 4 is a graph showing the relationship between the bulk density of a porous glass layer and the rate of occurrence of residual bubbles in a core space.

FIG. 5 is a diagram showing the relationship between the H ₂ / O ₂ flow rate, the substrate surface temperature heated by a heater, and the bulk density of a porous glass layer in an oxyhydrogen flame during soaking.

FIG. 6 is a diagram showing a relationship between a sintering temperature and a sintering time and a bubble remaining state.

FIG. 7 is an explanatory view showing the shape of an optical circuit formed on a quartz glass substrate in Examples and Comparative Examples.

[Explanation of symbols]

Reference Signs List 1 quartz substrate 2 core waveguide 3 porous glass layer 4 gap 5 glass fine particles 6 optical circuit core

Continued on the front page (72) Inventor Nobuhiro Akasaka 1 Tayacho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Sumitomo Electric Industries, Ltd. Yokohama Works F-term (reference) 2H047 KA04 KB04 LA11 PA05 PA14 PA24 QA04 RA08 TA05 TA31 TA42

Claims (5)

[Claims] 1. A porous glass layer made of quartz glass containing a dopant is formed on a quartz substrate having a core waveguide formed on a surface thereof by a flame deposition method so as to cover the core waveguide. In the method for manufacturing a quartz glass waveguide in which an upper clad layer formed by sintering a glass layer to form a transparent glass, the porous glass layer has a bulk density of 0.05.
０．１0.15 g / cm ^3, a sintering temperature of 1250 to 1350 ° C., and a sintering time of 30 to 1
A method for producing a silica glass waveguide, comprising sintering for 20 minutes. 2. After forming a core glass film made of silica glass doped with a refractive index increasing dopant on the substrate, the core glass film is formed into a rectangular cross section by photolithography and reactive ion etching. The method for manufacturing a silica-based glass waveguide according to claim 1, wherein the core-shaped waveguide is formed as described above. 3. The method according to claim _2, wherein the porous glass layer formed by the flame deposition method has a P ₂ O ₅ content of 0.9 to ₂ wt% and a P ₂ O ₅ content of 0.9 to ₂ wt%.
_{3. The} method for manufacturing a silica-based glass waveguide according to claim 1, comprising ₂ wt% of B2O3 as a dopant. 4. The method of claim 1, wherein forming the porous glass layer by flame deposition comprises heating the substrate to 100 to 400 ° C.
The H ₂ / O ₂ flow rate ratio in the oxyhydrogen flame is
2. The method according to claim 1, wherein the control is performed at 0.50.
4. The method for manufacturing a silica-based glass waveguide according to any one of the above-described items. 5. The method according to claim 4, wherein the heating of the substrate is performed by a heater installed below the substrate.