JPH1164652A - Waveguide to the core of which fluorine is added and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waveguide which is formed by adding fluorine to a core having a waveguide of a high specific refractive index difference Δ, is substantially free of absorption peaks from a wavelength 1.3 μm band to a wavelength 1.6 μm band, is extremely low in loss and facilitate refractive index control and a process for producing the same. SOLUTION: When the fluorine is added into the core of an oxide co-added with at least one kind of additives to enhance the refractive index, the hydrogen of the OH group, Si-H group or N-H group and fluorine existing in the clad layer 21 and the core 22 react to form gaseous HF which may be released outside the core 22. Consequently, the core 22 substantially free of the OH group, Si-H group or N-H group may be embodied. As a result, the waveguide which is extremely low in loss is obtd. As the amt. of the fluorine to be added into the core 22 is larger, the effect is higher. If the fluorine is added into the intermediate layer and the clad layer 21 as well, the waveguide having the lower loss is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide having a core doped with fluorine and a method for manufacturing the same.

[0002]

2. Description of the Related Art Research and development of a high Δ type glass waveguide having a large relative refractive index difference Δ between a core and a cladding layer has been actively conducted in order to reduce the cost and size of an optical device.

FIG. 10 is a schematic perspective view of a high Δ waveguide proposed by the present inventors.

In the waveguide shown in FIG. 1, a lower refractive index lower cladding layer (SiO ₂ ) 2 is formed on a substrate 1, and a high refractive index core layer (Si) having a substantially rectangular cross section is formed on the lower cladding layer 2.
ONH) 3 and the lower clad layer 2 and the core layer 3 are covered with an upper clad layer (SiO ₂ ) 4.

In the high Δ waveguide shown in FIG. 10, since SiONH is used for the core layer 3, it is possible to make the refractive index extremely high by controlling the content of nitrogen N as shown in FIG. There is an advantage that you can. FIG. 11 shows SiOx
It is a figure which shows the relationship between the nitrogen content in a NyHz film | membrane, and a refractive index, and a horizontal axis | shaft shows nitrogen content and a left vertical axis | shaft shows a refractive index.

[0006] By the way, TiO _2, Al on SiO _2
When a refractive index controlling dopant such as ₂ O ₃ , GeO ₂ or P ₂ O ₅ is added, the refractive index cannot be increased as shown in FIG. FIG. 12 is a diagram showing the relationship between the additive concentration and the refractive index, where the horizontal axis represents the additive concentration,
The vertical axis indicates the refractive index.

Next, the SiON of the high Δ waveguide shown in FIG.
The H core 3, the lower Si cladding layer 2, and the upper SiO ₂ cladding layer 4 are formed using a plasma CVD apparatus shown in FIG. FIG. 13 is a conceptual diagram of a plasma CVD apparatus used for manufacturing a conventional waveguide.

An upper electrode 7 and a lower electrode 8 are arranged opposite to each other in a reaction vessel 6 which is evacuated by an evacuation apparatus 5, and a high frequency voltage is applied between the electrodes 7 and 8 by a high frequency power supply 9. The substrate 1 is disposed on the lower electrode 8, and a voltage is applied from a DC power supply 12 to a heater 11 provided on the lower electrode 8 to heat the heater 11 in a range of 150 ° C. to 450 ° C.

Next, Ar gas (arrow 1) is applied between the electrodes 7 and 8.
(In three directions) to generate a plasma 14 between the electrodes 7 and 8. In this state, the glass raw material gas is supplied by the arrow 15-.
It flows into the plasma 14 from one direction in the direction of arrow 15-2.
Also, N ₂ gas flows into the plasma 14 from the direction of arrow 13. Lower SiO ₂ cladding 2 on substrate 1 (see FIG. 10)
Is flowed from the direction of arrow 15-1 to form SiH ₄ gas and O ₂ gas.

After forming the lower SiO ₂ cladding 2 on the substrate 1, arrows 15-
SiH ₄ gas, NH ₃ gas and O ₂ gas are flowed from one direction.

The SiONH core 3 is patterned into a substantially rectangular cross section by a photolithography and dry etching process. Then, patterned SiON
In order to cover the surface of the H core 3 with the upper SiO ₂ cladding layer 4, SiH ₄ and O ₂ gas are flowed from the direction of arrow 15-1, similarly to the lower SiO ₂ cladding layer 2.

Next, the loss wavelength characteristic of the high Δ waveguide shown in FIG. 10 will be described.

FIGS. 14A and 14B are diagrams showing the relationship between the wavelength and the loss of the high Δ waveguide shown in FIG. 10, wherein the horizontal axis represents the wavelength and the vertical axis represents the loss.

FIG. 14A shows a core 3 and a cladding layer 2.
4 is about 2%, and the size of the core 3 is 5 μm in width.
9 shows measurement results of loss wavelength characteristics of a waveguide having a thickness of 2.5 μm and a thickness of 2.5 μm. This loss includes the propagation loss (absorption loss and scattering loss) of the high Δ waveguide, and the connection loss between the high Δ waveguide and the single mode fiber (two portions on the input side and the output side of the waveguide). . The loss was very low from a wavelength of 0.6 μm to a wavelength of 1.35 μm.

However, the absorption loss due to the OH group at a wavelength of 1.39 μm and the Si—H group (or N
-H group).

Then, as a result of heat-treating this high Δ waveguide at 1000 ° C., as shown in FIG.
The absorption loss due to the OH group near 9 μm was almost eliminated.

However, the absorption loss near the wavelength of 1.5 μm could not be reduced. This is an absorption loss caused by the fact that the core 3 of the high Δ waveguide contains N and H components due to the reaction between SiH ₄ , O ₂ , NH ₃ and N _2, and becomes SiONH. Conceivable.

[0018]

However, the conventional high Δ waveguide has several problems as described above.

(1) The wavelength of the SiONH core is 1.39 μm.
Absorption loss due to an OH group having an absorption peak at a wavelength of 1.5 nm and a Si—H group having an absorption peak at a wavelength of 1.5 μm (or N
-H group). Therefore, the loss is large in the communication wavelength band in the wavelength range of 1.3 μm to 1.6 μm. The absorption loss at a wavelength of 1.39 μm can be reduced by heat-treating the high Δ waveguide at a temperature of about 1000 ° C., but the absorption loss at a wavelength of about 1.5 μm needs to be subjected to a high-temperature heat treatment at 1300 ° C. or higher. It cannot be reduced. However, when a high-temperature heat treatment at 1300 ° C. or more is performed, the high Δ waveguide is softened and warped, or the end face of the waveguide is deformed.

(2) Lower SiO ₂ cladding layer and upper Si
The O ₂ cladding layer also contains OH groups, which causes absorption loss.

Therefore, an object of the present invention is to solve the above-mentioned problems, and has almost no absorption peak in the wavelength band from 1.3 μm to 1.6 μm, ultra-low loss, easy control of the refractive index, and high resolution. An object of the present invention is to provide a waveguide in which fluorine is added to a core having a waveguide having a relative refractive index difference Δ and a method for manufacturing the same.

[0022]

According to the present invention, there is provided a waveguide in which a core is doped with fluorine to achieve the above object. The waveguide has a substantially rectangular cross section in a low refractive index intermediate layer or a cladding layer formed on a substrate. In a waveguide in which a high-refractive-index core having a shape is embedded, fluorine and an oxide obtained by co-adding at least one kind of an additive for increasing the refractive index are used in the core.

In addition to the above structure, the waveguide of the present invention in which fluorine is added to the core is made of S as an oxide base material for the core.
Preferably, iO ₂ or SiON is used.

In addition to the above structure, the waveguide of the present invention in which fluorine is added to the core is made of SiO 2 as an intermediate layer or a cladding layer.
_{2. It} is preferable to use SiO ₂ to which fluorine has been added, or SiO ₂ to which at least one type of additive for controlling the refractive index has been added.

In the waveguide of the present invention in which fluorine is added to the core in addition to the above-described structure, an oxide such as GeO ₂ , P ₂ O _5, or TiO ₂ is used as a high-refractive-index additive co-doped in the core. Is preferred.

Further, according to the method of the present invention for producing a waveguide in which fluorine is added to a core, an intermediate layer or a clad layer having a low refractive index is formed on a substrate, and a substantially rectangular cross-sectional shape is formed in the intermediate layer or the clad layer. In a method of manufacturing a waveguide in which a core having a high refractive index is embedded, an oxide obtained by co-adding fluorine and at least one additive for increasing the refractive index to the core is used, and the waveguide is heat-treated in a temperature range of 500 ° C. to 1350 ° C. Things.

In the method of manufacturing a waveguide of the present invention in which fluorine is added to the core in addition to the above structure, it is preferable that the intermediate layer or the cladding layer and the core are formed by low-pressure plasma CVD.

In the method of manufacturing a waveguide of the present invention in which fluorine is added to the core in addition to the above structure, the cladding layer is preferably formed by a flame deposition method.

(1) Here, the reduced pressure plasma C
When the clad and core layers were formed by the VD method, OH groups, Si-H groups, or NH groups were mixed into the clad and core layers, resulting in absorption loss.

Therefore, according to the present invention, when fluorine is co-added to the core of an oxide to which at least one additive for increasing the refractive index is co-added, the fluorine is present in the OH group, Si It reacts with hydrogen of -H group or NH group to become HF gas, which can be released outside the core. As a result, a core layer having few groups such as an OH group, a Si—H group, and an NH group can be realized.
Thereby, an ultra-low loss waveguide can be obtained. still,
The greater the amount of fluorine added to the core, the greater the low loss effect. Further, by adding fluorine to the intermediate layer and the cladding layer, a waveguide with lower loss can be obtained.

(2) Fluorine-doped waveguide at 500 ° C.
To 1350 ° C., the reaction between the OH group, Si—H group, and N—H group present in the waveguide and the fluorine is further promoted to become HF gas to efficiently out of the waveguide. , The loss can be easily reduced.

(3) By using SiON to which fluorine is added for the core, a high Δ waveguide can be obtained without substantially lowering the softening temperature. Can be used. That is, the flame deposition method, after forming a soot-like porous film,
Although the core film is sintered at a high temperature of about 1350 ° C to make the core glass transparent, the core withstands high temperature and does not deform, so that an optical multiplexing / demultiplexing circuit, an optical coupling / separating circuit, an optical filter circuit, etc. A waveguide component having excellent optical characteristics (wavelength separation characteristics, optical isolation characteristics, etc.) can be obtained.

[0033]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a schematic perspective view showing one embodiment of a waveguide in which fluorine is added to a core according to the present invention.

The waveguide shown in FIG. 1 is made of a fluorine-doped Si formed on a substrate 20 made of quartz glass (or Si).
Fluorine-doped Si having a rectangular cross section in the O ₂ cladding layer 21
It has a structure in which the ON core 22 is embedded.

FIG. 2 is a graph showing the relationship between the fluorine concentration and the refractive index of the fluorine-added SiO ₂ film used in the waveguide shown in FIG. 1, where the horizontal axis represents the fluorine concentration and the vertical axis represents the refractive index. Is shown.

FIG. 2 shows that fluorine can be added up to a concentration of 4.5%. That is, it is possible to obtain a high Δ waveguide having a higher relative refractive index difference Δ,
Si-H groups and N-H groups can be more effectively reduced. The relationship between the nitrogen concentration of SiONH of the core and the refractive index is shown in FIG. 11 described above, and when fluorine is added to the core, the refractive index becomes lower than the value shown in FIG.
It has been found that the degree of this decrease is substantially in proportion to the fluorine concentration. For example, if 2.7% of fluorine is added to a SiONH film to which 5 atomic% of nitrogen is added, the refractive index of the fluorine-added SiON core becomes about 1.475 (wavelength 0.63).
μm). Si with 2.7% fluorine added
O ₂ clad layer (refractive index 1.444) and fluorine
7% added SiON core (N: 5 atomic% added)
And a waveguide having a relative refractive index difference Δ of about 2.1%
An O ₂ substrate was used), and then heat-treated at 1000 ° C. in a nitrogen atmosphere for about 3 hours. FIG. 3 is a diagram showing the relationship between the wavelength and the propagation loss of the waveguide shown in FIG.
The horizontal axis indicates the wavelength, and the vertical axis indicates the propagation loss.

As can be seen from the figure, OH groups, Si--H
And a low-loss waveguide having no absorption loss due to the NH group.

FIG. 4 is a schematic perspective view showing another embodiment of the waveguide in which fluorine is added to the core of the present invention. Note that the same members as those of the waveguide shown in FIG.

The difference from the waveguide shown in FIG.
The fluorinated SiON core 22 is embedded in the fluorinated SiO ₂ intermediate layer 23 formed on the
The point is that the SiO ₂ clad layer 24 is formed on the iO ₂ intermediate layer 23. In this waveguide, the effective core area is increased by widening the power distribution propagating through the waveguide, and the nonlinear effect (the change in the refractive index due to the change in the optical power with the increase in the optical power) is suppressed. It is a wave path, and is particularly effective in realizing an optical circuit such as an optical filter for high-density wavelength division multiplexing transmission and an optical multiplexer / demultiplexer.

FIG. 5 is a schematic perspective view showing another embodiment of a waveguide in which fluorine is added to a core according to the present invention.

The difference from the waveguide shown in FIG.
This is the point where the fluorine-added SiON core 22 covered with the fluorine-added SiO ₂ intermediate layer 23 is embedded in the SiO ₂ clad layer 24 formed on the substrate 0, and has a W-type refractive index distribution. Such a waveguide has the same effect as the waveguide shown in FIG.

FIG. 6 is a schematic perspective view showing another embodiment of a waveguide in which fluorine is added to a core according to the present invention.

The difference from the waveguide shown in FIG.
This is the point that the fluorine-added SiO ₂ —GeO ₂ core 25 is embedded in the fluorine-added SiO ₂ clad layer 21 formed on the “0”. This GeO ₂ is an additive that increases the refractive index. Incidentally, even if GeO ₂ is added to SiO ₂ , the refractive index cannot be so increased as shown in FIG. When fluorine is added, the refractive index decreases. Therefore,
By using SiO ₂ to which fluorine is added at a high concentration for the fluorine-added SiO ₂ cladding layer 21, the Δ is increased (Δ ≧ 2
%).

FIG. 7 is a schematic perspective view showing another embodiment of the waveguide in which fluorine is added to the core of the present invention.

The difference from the waveguide shown in FIG. 6 is that P ₂ O ₅ is used instead of GeO ₂ as a co-additive in the core.

This fluorine-added SiO ₂ —P ₂ O ₅ core 2
Also in the case of the waveguide using GaN, the fluorine-added SiO ₂ cladding layer 21 is made of SiO ₂ doped with fluorine, and the core 26
Relative refractive index difference Δ between the fluorine-added SiO ₂ cladding layer 21 and
Is configured to be large.

FIG. 8 is a schematic perspective view showing another embodiment of the waveguide in which fluorine is added to the core of the present invention.

The difference from the waveguide shown in FIG.
The SiO ₂ cladding layer 27 is formed on the 0, the fluorine-added SiON core 22 is patterned on the SiO ₂ cladding layer 27, SiO ₂ so as to cover the entire patterned surface
This has a structure in which the clad layer 24 is formed, and is easy to manufacture.

FIG. 9 is a conceptual view of a plasma CVD apparatus used for manufacturing the waveguide of the present invention. Note that FIG.
The same reference numerals are used for members similar to those shown in FIG.

This apparatus comprises a reaction vessel 6, an exhaust device 5 for evacuating the reaction vessel 6, an upper electrode 7 disposed horizontally above the reaction vessel 6, and an opposing arrangement below the upper electrode 7. Lower electrode 8, high-frequency power supply 9 connected between both electrodes 7, 8, and heater 1 provided below lower electrode 8.
1, a DC power supply 12 connected to a heater 11, and a reaction vessel 6 through a gas outlet formed below the upper electrode 7.
A gas supply pipe 28 for supplying a predetermined gas into the inside, and heaters 29-1 and 29 provided around the gas supply pipe 28
-2, DC power supplies 30-1 and 30-2 connected to the heaters 29-1 and 29-2, respectively, and a gas supply pipe 31 for directly supplying gas into the reaction vessel 6.

By using the apparatus shown in the figure, films such as a fluorine-added SiO ₂ cladding layer 21, a fluorine-added SiO ₂ intermediate layer 23, and a fluorine-added SiON core 22 are formed on a substrate 20.

The reaction vessel 6 is evacuated by the exhaust device 5. The substrate 20 placed on the lower electrode 8 is a heater 1
Heating is performed in the temperature range of 100 ° C. to 500 ° C. by the energization of 1. A high-frequency voltage is applied between the upper electrode 7 and the lower electrode 8. Glass source gas, oxidizing gas, inert gas, and the like are fed into the upper electrode 7 from the direction of the arrow 32-1 to the direction of the arrow 32-2. Arrow 33
C ₂ F ₆ (or a fluorine-based gas such as CF ₄ ) can be fed between the electrodes 7 and 8 from the direction. Arrow 32-
The gas sent in the direction of arrow 32-2 from one direction is heated by applying a DC voltage to the heaters 29-1 and 29-2.

In order to form the above-mentioned film using the apparatus shown in FIG.
Ar gas is supplied from one direction to generate a plasma 14 between the electrodes 7 and 8. Next, a gas such as SiH ₄ , O ₂ , C ₂ F ₆ , Ar or the like is flowed from the direction of arrow 32-1 to form a SiO ₂ film to which fluorine is added. To form a SiON core film to which fluorine has been added, arrows 32-
This is performed by flowing SiH ₄ , O ₂ , NH ₃ , and C ₂ F ₆ gases from one direction. SiO ₂ —GeO ₂ further doped with fluorine
To form a core film, Si
H ₄ , GeH ₄ , O ₂ , C ₂ F ₆ and Ar gas are flowed. The film of the clad layer is formed by using a flame deposition method to form a soot-like porous film in addition to the low pressure plasma CVD method.
A method of sintering while flowing He gas in (before and after) to make it transparent can be used.

As described above, according to the present invention, the following effects can be obtained.

(1) When a clad layer and a core are formed by a low pressure plasma CVD method as in the prior art, an OH group, a Si—H group, or an NH group is mixed in the clad layer and the core, and the absorption by these groups is caused. Although loss occurs, when fluorine is co-added in the core of the oxide in which at least one additive for increasing the refractive index is co-added as in the present invention, the fluorine reacts with hydrogen in the group to form HF gas, It can be released outside the core. As a result, a core layer having almost no OH group, Si—H group or N—H group can be realized. Thereby, an ultra-low-loss waveguide can be obtained.
The effect increases as the amount of fluorine added to the core increases. Further, when fluorine is added to the intermediate layer and the cladding layer, a waveguide with lower loss can be obtained.

(2) Fluorine-doped waveguide at 500 ° C.
, The OH group, the Si-H group, and the NH group in the waveguide are further promoted to react with fluorine, and are released as HF gas outside the waveguide. Therefore, it is easy to reduce the loss.

(3) When SiON with fluorine added to the core is used, a high Δ waveguide can be obtained without substantially lowering the softening temperature. Therefore, a film formed by the flame deposition method, which can be easily made thick, is used as the cladding layer. Can be used. That is, the flame deposition method, after forming a soot-like porous film,
The film is sintered at a high temperature of about 1350 ° C. to vitrify the film, but since the core withstands the high temperature and does not deform, the optical multiplexing / demultiplexing circuit, the optical coupling / separating circuit, the optical filter A waveguide component having excellent optical characteristics (wavelength separation characteristics, optical isolation characteristics, etc.) such as a circuit can be obtained.

[0059]

In summary, according to the present invention, the following excellent effects are exhibited.

By using fluorine and an oxide in which at least one additive for increasing the refractive index is co-added to the core, there is almost no absorption peak in the wavelength band of 1.3 μm to 1.6 μm, and the core has an extremely low loss. In addition, it is possible to provide a waveguide in which the refractive index is easily controlled and a core having a waveguide with a high relative refractive index difference Δ is doped with fluorine, and a method for manufacturing the same.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing an embodiment of a waveguide in which fluorine is added to a core of the present invention.

FIG. 2 shows a fluorine-doped S used for the waveguide shown in FIG.
FIG. 4 is a diagram showing the relationship between the fluorine concentration and the refractive index of an iO ₂ film.

FIG. 3 is a diagram illustrating a relationship between a wavelength and a propagation loss of the waveguide illustrated in FIG. 2;

FIG. 4 is a schematic perspective view showing another embodiment of a waveguide in which fluorine is added to a core according to the present invention.

FIG. 5 is a schematic perspective view showing another embodiment of a waveguide in which fluorine is added to a core according to the present invention.

FIG. 6 is a schematic perspective view showing another embodiment of a waveguide in which fluorine is added to a core according to the present invention.

FIG. 7 is a schematic perspective view showing another embodiment of a waveguide in which fluorine is added to a core according to the present invention.

FIG. 8 is a schematic perspective view showing another embodiment of a waveguide in which fluorine is added to a core according to the present invention.

FIG. 9 is a conceptual diagram of a plasma CVD apparatus used for manufacturing the waveguide of the present invention.

FIG. 10 is a schematic perspective view of a high Δ waveguide proposed by the present inventors.

FIG. 11 is a diagram showing a relationship between a nitrogen content in a SiOxNyHz film and a refractive index.

FIG. 12 is a graph showing a relationship between an additive concentration and a refractive index.

FIG. 13 is a conceptual diagram of a plasma CVD apparatus used for manufacturing a conventional waveguide.

FIGS. 14A and 14B are diagrams showing the relationship between the wavelength and the loss of the high Δ waveguide shown in FIG. 10;

[Explanation of symbols]

Reference Signs List 20 substrate 21 clad layer (SiO ₂ clad layer) 22 core (fluorine-added SiON core)

Claims (7)

[Claims] In a waveguide having a high refractive index core having a substantially rectangular cross section embedded in a low refractive index intermediate layer or a cladding layer formed on a substrate, the core increases the refractive index with fluorine. A waveguide in which fluorine is added to a core, wherein an oxide containing at least one additive is co-added. 2. The waveguide according to claim 1, wherein SiO ₂ or SiON is used as a base material of the oxide for the core. 3. An Si layer as an intermediate layer or a cladding layer.
_{3. The} waveguide according to claim 1, wherein O ₂ , SiO ₂ to which fluorine is added, or a material obtained by adding at least one kind of an additive for controlling the refractive index to said SiO ₂ is used. 4. The core according to claim 1, wherein an oxide such as GeO ₂ , P ₂ O ₅ or TiO ₂ is used as an additive having a high refractive index which is co-added in the core. A waveguide to which is added. 5. A method of manufacturing a waveguide, comprising forming an intermediate layer or a clad layer having a low refractive index on a substrate and embedding a core having a substantially rectangular cross section and a high refractive index in the intermediate layer or the clad layer. Manufacturing an oxide in which a core is doped with fluorine by using an oxide obtained by co-adding at least one kind of an additive for increasing the refractive index with fluorine and heat treating the waveguide in a temperature range of 500 ° C. to 1350 ° C. Method. 6. The method according to claim 5, wherein the intermediate layer or the clad layer and the core are formed by a low pressure plasma CVD method. 7. The method according to claim 5, wherein the cladding layer is formed by a flame deposition method.