JPH09133824A - Optical waveguide and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the increase in transmission loss by precipitation of crystals in a glass film in forming a core layer. SOLUTION: Channel waveguides 3a are formed on a quartz substrate 1 and the surface thereof is covered with a clad glass layer 4. The respective channel waveguides 3a have upper and lower two-layered structures. The lower core glass layer 2 have 0.1 to 2μm thickness and contains at least >=2 kinds of additives among the respective additives of germanium, boron, phosphorus and titanium. The total content of the respective additives added thereto is regulated within a range of 13 to 20wt.%.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an optical waveguide used in an optical communication system and a method for manufacturing the same.

[0002]

2. Description of the Related Art FIG. 8 shows a flow of a typical method of manufacturing a conventional optical waveguide. First, a glass particle layer 102 ′ is deposited on a substrate 101 such as quartz or silicon by a flame deposition method (FIG. 10A), and then this is heated at a temperature of 1200 ° C. or higher to remove the deposited glass particle layer. The lower clad layer 102 is formed into a transparent glass (FIG. 2B / glass composition: SiO ₂ —B ₂ O ₃ —P ₂ O ₅ ). Next, a glass fine particle layer 103 ′ for a core is deposited on the lower clad layer 102 by the flame deposition method ((c) in the same figure), and thereafter, the glass fine particle layer is heated again at a temperature of 1200 ° C. or higher. 103 'and transparent glass to form the core layer 103 (FIG. (d) / glass composition: SiO ₂ -B ₂ O ₃ -
P ₂ O ₅ -GeO _2). Next, a mask pattern is formed on the core layer 103 by a photolithography technique, and then etching is performed using this as a mask to form an optical waveguide 103a having a desired pattern ((e) in the figure). Then, the glass fine particle layer 10 is again formed thereon by the flame deposition method.
After depositing 4 ′ (FIG. 6 (f)), the glass is transparentized to form the upper cladding layer 104 (FIG. 4 (g) / glass composition: SiO ₂ —B ₂ O ₃ —P ₂ O ₅ ).

[0003]

However, in the case where the silica glass optical waveguide is formed in this way, when the core layer is formed, crystals are deposited in the glass film that will be the core layer, resulting in a transmission loss. There was a problem of deterioration.

There are two types of crystal precipitation, homogeneous nucleation and heterogeneous nucleation. Heterogeneous nucleation is likely to occur on the surfaces and interfaces of liquids and solids, or on interfaces with impurities and foreign substances. The precipitation mechanism of this crystal is considered as follows. Glass transition temperature (Tg) or higher, crystallization temperature (T
x) When quartz glass is heat-treated in the temperature range of the following, crystal nuclei grow and the crystals (cristobalite) grow. When impurities such as Na, K, Ca, and Fe are attached to the surface of the glass, crystals are deposited so as to surround the impurities, and the growth rate of the crystals is 10 times or more due to the presence of the impurities. Grow at a rate (heterogeneous nucleation).

When forming a core glass for a silica glass optical waveguide, a heat treatment is required, and this heat treatment passes through the above temperature range. For example,
When the glass fine particle layer deposited by the flame deposition method is turned into transparent glass, heat treatment is performed at 1400 ° C. for 10 hours. At this time, if impurities adhere to the substrate on which the glass fine particle layer is deposited, crystals of 100 μm or more are deposited.
This crystal is much larger than the core width of the optical waveguide,
It becomes a scattering source of the optical signal and causes deterioration of transmission loss.

Therefore, in order to improve such a transmission loss, it is necessary to remove the crystal, but impurities such as Na, K, Ca, and Fe, which cause the generation, are completely removed from the glass film manufacturing atmosphere. It is extremely difficult to remove it.

The present invention has been made to solve such a problem, and an object thereof is an optical waveguide capable of sufficiently suppressing the precipitation of such a crystal and sufficiently reducing the transmission loss, and an optical waveguide thereof. It is to provide a manufacturing method.

[0008]

To suppress the generation of crystals even if impurities are present on the substrate, the crystallization temperature (T
It is most effective to widen the temperature difference of x) -glass transition temperature (Tg). Therefore, in the present invention, by adding a network-forming oxide by an additive (boron, phosphorus, titanium, germanium) that promotes the network structure of glass to the first glass fine particle layer between the substrate and the core portion, Suppress precipitation of crystals.

That is, the optical waveguide according to claim 1 is
Substrate, first core glass part formed on the substrate and having a thickness of 0.5 to 2 μm, second core glass part formed on the first core glass part, and first and second core glass A clad glass part formed on the substrate so as to cover the part, and the first core glass part comprises germanium, boron,
Among the respective additives of phosphorus and titanium, at least two or more kinds of additives are contained, and the total amount of the respective additives added to the first core glass part is set to a range of 13 to 20 wt%. Further, in the optical waveguide according to claim 2, this substrate is made of a quartz substrate.

A method of manufacturing an optical waveguide according to claim 3 is
At least two or more kinds of additives of germanium, boron, phosphorus, and titanium are supplied to the flame burner to deposit the first glass fine particle layer for the core on the substrate, and the first step is performed. A second step of depositing a second glass fine particle layer for a core on the first glass fine particle layer, a third step of sintering the first and second fine particle layers on the substrate to form a transparent glass, and a transparent glass A fourth step of patterning the converted first and second fine particle layers into a predetermined core shape, and a fifth step of depositing a third glass fine particle layer for cladding on the patterned first and second fine particle layers A. Sintering the deposited third glass fine particle layer to form a transparent glass
And a process. Then, in the first step, the total amount of each additive added to the first glass fine particle layer is in the range of 13 to 20 wt%, and the thickness of the first glass fine particle layer after sintering is 0.5 to 2 μm. It is characterized in that the supply flow rate of each additive supplied to the flame burner and the deposition time of the first glass fine particle layer are controlled so as to fall within the range.

As a result of the research conducted by the present inventor, the following facts have become clear. In such an optical waveguide, the total amount of each of the above additives added to the first glass fine particle layer is 13 w.
If it is less than t%, crystals will be precipitated if impurities are present at the substrate interface, and if the total addition amount exceeds 20 wt%, B2O3 will be generated when heated at a temperature near 1400 ° C.
Alternatively, a P2O5 rich phase separation occurs. Further, when the thickness of the first glass fine particle layer becomes thinner than 0.5 μm, crystals are precipitated in the presence of impurities at the substrate interface, and when the thickness becomes thicker than 2 μm, when heated at around 1400 ° C., the high-concentration glass layer is formed. As a result, atoms are diffused into the second glass fine particle layer and the core glass is deformed. Therefore, the total amount of each additive in the first glass fine particle layer is 13 to 2
The thickness was defined as 0 wt% and the thickness was in the range of 0.5 to 2 μm.

It is to be noted that among the additives of germanium, boron, phosphorus and titanium, it is decided to use at least two or more kinds of additives, since only one of them is used, a desired relative refractive index is obtained. This is because the rate difference (Δn) cannot be obtained.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

<Example> Hereinafter, a method of manufacturing an optical waveguide will be described step by step with reference to FIG.

First, a shape of φ3 inc is obtained by the flame deposition method.
On the quartz substrate 1 of h × t1 mm, a glass fine particle layer 2 ′ for a core containing SiO ₂ as a main component was deposited for 3 minutes (FIG. 1).
(A)). At this time, the flame burner 20 has SiCl ₄ , BC
l ₃ , POCl ₃ , GeCl ₄ , H ₂ , O ₂ , and Ar were supplied at the flow rates shown in the column 1-a (Fig. 5) of the chart. Continued
The glass fine particle layer 3 ′ for core was deposited for 19 minutes at the flow rate shown in the column (b) of FIG. 1 (FIG. 5) (FIG. 1 (b)).

Next, the glass fine particle layers 2 ′ and 3 ′ for each core deposited on the quartz substrate 1 were heat-treated at 1400 ° C. for 4 hours to be transparent vitrified (FIG. 1C). .
The core glass layer 2 corresponding to the glass fine particle layer 2 ′ has a thickness of 2 μm, and B ₂ O ₃ , P ₂ O ₅ , Ge in the core glass layer 2 are contained.
The total amount of O ₂ added was 16.8 wt%. On the other hand, the thickness of the core glass layer 3 corresponding to the glass fine particle layer 3 ′ is 6 μm.
m, and B ₂ O ₃ , P ₂ O ₅ , Ge in the core glass layer 3
The total amount of O ₂ added was 11.0 wt%. At this time, the number of crystals of 5 μm or more deposited in the core glass layer 3 is 7 /
It was mm ² .

Next, the core glass layer 2 and the core glass layer 3 which has been made into a transparent glass by photolithography are used.
Was patterned to form a plurality of channel waveguides 3a (FIG. 1 (d)). Therefore, each channel waveguide 3a
Is formed by the core glass layer 2 and the core glass layer 3.

Next, in order to embed the entire formed channel waveguide 3a, the flame burner 20 is filled with SiCl ₄ , BC.
l ₃ , POCl ₃ , H ₂ , O ₂ , and Ar were supplied at the flow rates shown in the column 1-c of FIG. 1 (FIG. 5) to deposit the glass fine particle layer 4 ′ (FIG. 1 (e)). Thereafter, the glass fine particle layer 4 ′ is subjected to heat treatment at 1250 ° C. for 4 hours to be transparent,
The upper clad glass layer 4 was formed (FIG. 1 (f)). The waveguide structure was synthesized so that the core cross-sectional shape was 8 × 8 μm and the relative refractive index difference was 0.3% (FIG. 2).

The waveguide loss of the linear optical waveguide manufactured through the above steps was 0.06 ± 0.03 dB / cm.
When a single mode fiber array was connected to both ends of the fabricated waveguide and measured, the connection loss at each port was
It was 0.90 ± 0.03 dB, and relatively good characteristics were obtained.

<Comparative Example 1> An optical waveguide was manufactured in the same manner as in the above-described Example, but in Comparative Example 1, the core glass layer 2 was used.
The core glass layer 3 was formed directly on the quartz substrate 1 without forming. Here, an example in which the substrate is contaminated with impurities is shown.

First, a shape of φ3 inc was obtained by the flame deposition method.
A glass fine particle layer 3 ′ containing SiO ₂ as a main component was deposited on a quartz substrate 1 of h × t1 mm for 22 minutes. At this time, the flame burner 20 is covered with SiCl ₄ , BCl ₃ , POCl ₃ , Ge.
The _{Cl 4, H 2, O 2} , Ar were supplied at a flow rate shown in Figure 2-a column (Fig. 6).

Next, the glass fine particle layer 3'deposited on the quartz substrate 1 was heat-treated at 1400 ° C. for 4 hours to be transparent vitrified to form the core glass layer 3. The thickness of the formed core glass layer 3 is 8 μm, and the total addition amount of B ₂ O ₃ , P ₂ O ₅ , and Ge0 _{2 in} the core glass layer 3 is 1 μm.
It was 1.0 wt%. At this time, the number of crystals of 5 μm or more deposited in the core glass layer 3 was 560 / mm ² .

Next, the transparent vitrified core glass layer 3 was patterned by a photolithography technique to form a plurality of channel waveguides 3a. Next, in order to embed the entire formed channel waveguide 3a, the flame burner 20
SiCl ₄ , BCl ₃ , POCl ₃ , H ₂ , O ₂ , A
r was supplied at the flow rate shown in the column (b) of FIG. 2 (FIG. 6) to deposit the glass fine particle layer 4 ′. After this, the glass fine particle layer 4 '
On the other hand, the upper clad glass layer 4 was formed by heat treatment at 1250 ° C. for 4 hours to make it transparent. The waveguide structure has a core cross-sectional shape of 8 × 8 μm and a relative refractive index difference of 0.3%.
(Fig. 3).

The waveguide loss of the linear optical waveguide manufactured through the above steps is 1.53 ± 0.72 dB / cm, which is much worse than that of the above-mentioned embodiment. It can be considered that the cause of the deterioration of the waveguide loss is that light is scattered by the cristobalite crystals deposited in the core glass layer 3. Crystals are deposited using the impurities adhering to the surface of the quartz substrate as nuclei, but it is necessary to remove these impurities in order to improve the waveguide loss. However, from the viewpoint of obtaining stable quality, it is ideal if impurities attached to all substrates can be completely removed, but it is extremely difficult to completely remove impurities in this way.

Therefore, even if some impurities are attached to the surface of the substrate, if chemically stable glass is formed thereon,
Crystal precipitation can be reduced. When an additive (boron or the like) that promotes the network structure of glass is added to quartz glass, chemically stable glass can be formed. The additive concentration at which crystals do not precipitate is 13 wt% or more, and if a glass layer (lower glass layer 2) having a thickness of 0.5 μm or more is formed between the substrate and the core glass layer, the crystals of the core glass will not be precipitated. It can be reduced.

In Comparative Example 1, since the additive concentration in the glass layer was less than 13%, it is considered that crystals were deposited in the core glass layer as nuclei of impurities on the substrate surface and the transmission loss was deteriorated. . On the other hand, in the above-mentioned embodiment, the thickness is 2 μm and the additive concentration is 13 on the quartz substrate 1.
Since the glass layer (lower glass layer 2) of not less than wt% was formed, the precipitation of crystals having impurities as nuclei on the substrate surface could be reduced, and the transmission loss was good.

<Comparative Example 2> An optical waveguide was manufactured in the same manner as in the above-mentioned Example, but in Comparative Example 2, the glass fine particle layer 2'for forming the core glass layers 2 and 3 was formed in comparison with Example 1. The manufacturing was performed with different deposition times of 3 '.

First, a shape of φ3 inc is obtained by the flame deposition method.
On the quartz substrate 1 of h × t1 mm, a glass fine particle layer 2 ′ for a core containing SiO ₂ as a main component was deposited for 11 minutes. At this time, the flame burner 20 is coated with SiCl ₄ , BCl ₃ , POCl
_3, a _{GeCl 4, H 2, O 2} , Ar were supplied at flow rates shown in Figure 3-a column (Fig. 7). Subsequently, the glass fine particle layer 3 ′ for the core is set to 1 at the flow rate shown in the column (b) of FIG.
It was deposited for 1 minute.

Next, the glass fine particle layers 2 ′ and 3 ′ for each core deposited on the quartz substrate 1 were subjected to heat treatment at 1400 ° C. for 4 hours to obtain transparent vitrification. The core glass layer 2 corresponding to the glass fine particle layer 2 ′ had a thickness of 4 μm, and the total amount of B ₂ O ₃ , P ₂ O ₅ , and GeO ₂ added to the core glass layer 2 was 16.8 wt%. On the other hand, glass particle layer '3
The thickness of the core glass layer 3 corresponding to 4 μm was 4 μm, and the total amount of B ₂ O ₃ , P ₂ O ₅ and GeO ₂ added in the core glass layer 3 was 11.0 wt%. At this time, the number of crystals of 5 μm or more deposited in the core glass layer 3 was 5 / mm ² .

Next, the core glass layer 2 was patterned together with the transparent vitrified core glass layer 3 by a photolithography technique to form a plurality of channel waveguides 3a.

Next, in order to embed the entire formed channel waveguide 3a, the flame burner 20 is filled with SiCl ₄ , BC.
l ₃ , POCl ₃ , H ₂ , O ₂ , and Ar were supplied at the flow rates shown in column (c) of Fig. 3-c (Fig. 7) to deposit the glass fine particle layer 4 '. Then, 1250 to the glass fine particle layer 4 '.
The upper clad glass layer 4 was formed by heat treatment at 4 ° C. for 4 hours to make it transparent. The waveguide structure was synthesized so that the core cross-sectional shape was 8 × 8 μm and the relative refractive index difference was 0.3% (FIG. 4).

The waveguide loss of the linear optical waveguide manufactured through the above steps was 0.31 ± 0.08 dB / cm.
When a single mode fiber array was connected to both ends of the fabricated waveguide and measured, the connection loss at each port was
The value was 0.22 ± 0.07 dB, which was deteriorated as compared with the above-mentioned embodiment.

The cause of the deterioration of the waveguide loss can be considered as follows. Usually, the softening deformation of the core glass is prevented by adjusting the addition amount of the additive so that the softening temperature of the core glass is 100 ° C. or more higher than the softening point temperature of the upper clad glass layer 4. However, the softening temperature of the core glass layer of Comparative Example 2 (column in Figure 3-a) is only 50 ° C. higher than that of the upper clad glass layer. Like the core glass layer of Comparative Example 2, the core glass having a large amount of the additive added is
It is considered that the softening deformation occurred at the temperature when the upper clad glass layer was formed, and therefore the loss was caused by the mismatch of the mode field patterns of the single mode fiber and the straight waveguide.

From Comparative Example 2, it is understood that when the amount of boron and phosphorus added to the core glass layer 2 is increased, the core glass is softened and deformed by heat when the upper clad glass is formed.

[0034]

As described above, according to the optical waveguide or the method for manufacturing an optical waveguide according to each claim, an additive capable of promoting a glass network structure is contained between the substrate and the core portion. Therefore, in the manufacturing process of the optical waveguide substrate, the crystallization temperature (Tx) -glass transition temperature (Tg)
It is possible to widen the temperature difference between the two and thereby to suppress the generation of crystals even if impurities are present on the substrate. Thereby, it becomes possible to sufficiently suppress the precipitation of crystals and sufficiently reduce the transmission loss of the optical waveguide.

[Brief description of the drawings]

1A to 1F are process diagrams sequentially showing a method of manufacturing an optical waveguide according to the present embodiment.

FIG. 2 is a side view showing an optical waveguide according to the present embodiment.

FIG. 3 is a side view showing an optical waveguide according to Comparative Example 1.

FIG. 4 is a side view showing an optical waveguide according to a comparative example 2.

FIG. 5 is a chart showing a flow rate and a deposition time of a source gas supplied to a flame burner when forming each layer of the optical waveguide according to the example.

FIG. 6 is a diagram illustrating the process of forming each layer of the optical waveguide according to Comparative Example 1,
It is a chart showing the flow rate and deposition time of the source gas supplied to the flame burner.

FIG. 7 is a diagram showing a case where each layer of the optical waveguide according to Comparative Example 2 is formed,
It is a chart showing the flow rate and deposition time of the source gas supplied to the flame burner.

8A to 8G are process diagrams sequentially showing a conventional method for manufacturing an optical waveguide.

[Explanation of symbols]

1 ... Quartz substrate, 2 '... Glass fine particle layer (first glass fine particle layer), 2 ... Lower glass layer (first core glass part), 3'
... Glass fine particle layer (second glass fine particle layer), 3 ... Core glass layer (second core glass part), 4 '... Glass fine particle layer (third glass fine particle layer), 4 ... Upper clad glass layer (clad glass part) .

Claims (3)

[Claims] 1. A substrate, a first core glass part formed on the substrate and having a thickness of 0.5 to 2 μm, a second core glass part formed on the first core glass part, A clad glass part formed on the substrate so as to cover the first and second core glass parts, wherein the first core glass part is at least 2 of each additive of germanium, boron, phosphorus and titanium. An optical waveguide containing at least one kind of additive, and the total amount of each additive added to the first core glass part is in the range of 13 to 20 wt%. 2. The optical waveguide according to claim 1, wherein the substrate is a quartz substrate. 3. A first step of supplying at least two or more kinds of additives of germanium, boron, phosphorus and titanium to a flame burner and depositing a first glass fine particle layer for a core on a substrate. And a second core layer on the deposited first glass fine particle layer.
A second step of depositing a glass fine particle layer, a third step of sintering the first and second fine particle layers on the substrate to form transparent vitrification, and a predetermined step of forming the transparent vitrified first and second fine particle layers. A fourth step of patterning into a core shape, a fifth step of depositing a third glass fine particle layer for cladding on the patterned first and second fine particle layers, and the deposited third glass fine particle layer And a sixth step of forming a transparent glass by sintering, wherein in the first step, the total amount of each additive added to the first glass fine particle layer is in the range of 13 to 20 wt%,
Moreover, the thickness of the first glass fine particle layer after sintering is 0.5.
A method for manufacturing an optical waveguide, characterized in that the supply flow rate of each additive supplied to the flame burner and the deposition time of the first glass fine particle layer are controlled so as to fall within a range of ˜2 μm.