JPH10319263A - Optical waveguide and its production as well as optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide with which the alignment between a single mode optical fiber and a mode film may be easily obtd. and a process for producing the same as well as an optical device. SOLUTION: This optical waveguide has a substrate 1, a clad layer 2 which is formed on this substrate 1 and consists of SiO2 and a core layer 3 which contains at least one kind additives for controlling a refractive index in the SiO2 formed in this clad layer 2. In such a case, the core layer 3 is covered with an intermediate layer 9 consisting of SiO2 added with fluorine, by which the changes in the refractive index and fluorine concn. distribution are substantially not occurred even if the optical waveguide is subjected to a high-temp. heat treatment at 1000 to 1200 deg.C and the optical waveguide remains stable and, therefore, a high specific refractive index difference is obtd. Since the input and output terminals of the optical waveguide 8 may be provided with mode conversion parts for aligning the optical fiber 5 and the mode film, the connection of the optical waveguide with the optical fiber 5 with low loss is made possible and the reflected light from the juncture may be made extremely little.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical waveguide, a method for manufacturing the same, and an optical device.

[0002]

2. Description of the Related Art Research and development of waveguide type optical devices using silica glass have been actively conducted with the aim of reducing the cost, size and function of optical devices.

FIG. 8 is a diagram showing a conventional optical device with a pigtail fiber.

The optical device shown in FIG. 1 has a single mode optical fiber 5 connected to an input end 10 of an optical waveguide 4. The optical waveguide 4 has a structure in which a clad layer 2 is formed on a substrate 1 and a core layer 3 having a substantially rectangular cross section is formed in the clad layer 2. This optical waveguide 4 is
As shown in FIG. 8 (d), the refractive index n ₁ and the cladding layer 2 of high Δ optical waveguide relative refractive index difference Δ is 0.8% or more between the refractive index n ₂ of the core layer 3. Therefore, the width and thickness of the core layer 3 become smaller as the relative refractive index difference Δ becomes higher, usually 5 μm.
It is as follows. The relative refractive index difference Δ between the core (refractive index n _C ) 7 and the cladding (refractive index n ₂ ) 6 of the single mode optical fiber 5 is about 0.3%, and the diameter D _{1 of the} core 7 is about 10 μm.
It is. Therefore, the connection between the optical waveguide 4 and the single-mode optical fiber 5 needs to have mode field matching.

That is, the refractive index distribution in the waveguide section (BB line) of the input end 10 of the optical waveguide 4 must be a diffusion distribution as shown in FIG. This diffusion distribution is S
Ge, Ti, and iO ₂ are used as refractive index controlling dopants.
This is realized by heating the input end 10 of the optical waveguide 4 and diffusing the dopant by adding at least one of P, Zn, Sb, Sn and the like to the core layer 3.

The method for diffusing the dopant is shown in FIG.
As shown in (a schematic diagram of a conventional method for forming a mode converter in an optical waveguide), one end (right end in the figure) of an optical waveguide 4 is held by a sample holder 12 and cooling water is placed in the sample holder 12. Flows in the directions of arrows 13-1 and 13-2,
This is a method of cooling by flowing out, and heating the other end (left end in the figure) of the optical waveguide 4 by the heater 11. Reference numeral 14 denotes a heat diffusion region, which is a region 4 mm or more from the other end.

[0007]

By the way, the optical waveguide 4
When the relative refractive index difference Δ of the core layer 3 becomes higher than 1.5%, the value of the refractive index n ₁ of the core layer 3 increases, and conversely, the core layer 6
Is reduced to 4 μm or less. When mode field matching is performed between the optical waveguide 4 having such a structure and the single mode optical fiber 5, FIG.
As shown in (c), the dopant in the core layer 3 must be diffused deeply into the cladding layer 2. For this reason, the width and thickness of the core layer 6 become too large.
That is, in the cross section near the input end of the optical waveguide 4 (B-B
Would width and thickness D ₂ of the core layer of the line) is larger than the diameter D ₁ of the core 7, resulting in mode field matching becomes difficult.

As described above, the conventional method of connecting an optical waveguide to a single mode optical fiber has the following problems.

(1) If the relative refractive index difference Δ of the optical waveguide becomes high, it becomes difficult to perform mode field matching with a single mode optical fiber.

(2) When the mode field mismatch occurs,
As the loss at the connection increases, reflection occurs at the connection.

(3) With the conventional optical waveguide structure, an optical device having a refractive index and a core layer structure that matches the refractive index and the diameter of the core layer of a single mode optical fiber with a small degree of design freedom is realized. It is difficult.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide an optical waveguide which is easy to achieve mode field matching with a single mode optical fiber, a method for manufacturing the same, and an optical device.

[0013]

Means for Solving the Problems An optical waveguide of the present invention in order to achieve the above object, a substrate and, a clad layer made of SiO ₂ is formed on the substrate, SiO ₂ is formed in its cladding layer And a core layer containing at least one kind of additive for controlling refractive index, wherein the core layer is covered with an intermediate layer made of SiO ₂ to which fluorine is added.

In the method of manufacturing an optical waveguide according to the present invention, an upper electrode and a lower electrode are arranged in parallel in a vacuum-evacuated reaction chamber, and a high-frequency power RF is applied between the two electrodes. The substrate is placed, the substrate is heated to a predetermined temperature T by a heater provided on the electrode, and the vapor of metal alkoxide, fluorine gas such as C ₂ F ₆ and O _{2 A} gas is sprayed in the form of a shower, an SiO ₂ film to which fluorine is added is formed on the substrate while maintaining a certain degree of vacuum P, and a core layer is formed on the SiO ₂ film, and again, so as to cover the core layer. Forming a SiO ₂ film to which fluorine is added, and setting the temperature T in a range of 400 ° C. to 600 ° C .;
The high frequency power RF is set to 350 W or more, and the degree of vacuum P is set to 0.
The film is formed by keeping the growth rate of the SiO ₂ film to which fluorine is added at 1000 Å or less per minute while maintaining the pressure at 5 Torr or less.

In the method of manufacturing an optical waveguide according to the present invention, in addition to the above structure, the SiO ₂ film to which fluorine is added is heat-treated at a high temperature of 1000 ° C. to 1200 ° C., and the change in the refractive index of the film is smaller than before the heat treatment. It is preferable that the content be 0.3% or less.

[0016] The method for manufacturing an optical waveguide in addition the present invention to the above structure, the refractive index of the SiO ₂ film added with fluorine and SiO ₂
The relative refractive index difference from the refractive index of the film is preferably at least greater than 0.5% and less than 1.23%.

[0017] The optical device of the present invention includes a substrate, a cladding layer formed on the substrate made of SiO _2, including at least one refractive index-controlling additives SiO ₂ is formed in its cladding layer An optical waveguide having a core layer;
An optical device comprising: an optical fiber connected to an input / output end of an optical waveguide;
It is covered with an intermediate layer consisting of _two .

In addition to the above configuration, in the optical device of the present invention, it is preferable that the refractive index controlling additive contained in the core layer of the optical waveguide is diffused into the intermediate layer near the connection between the optical waveguide and the optical fiber. .

In addition to the above configuration, in the optical device of the present invention, it is preferable that the optical fiber and the optical waveguide are fused by irradiating a CO ₂ laser beam.

According to the present invention, fluorine is substantially uniformly added to a very dense SiO ₂ film, and this film is heated at a high temperature (100 ° C.).
Even if the heat treatment is performed at 0 ° C. to 1200 ° C.), a film having a small oxygen deficiency and a small fluorine concentration gradient can be realized.

In order to reduce the loss of the optical waveguide (lower absorption loss and lower scattering loss), a high-temperature heat treatment of the fluorinated SiO ₂ film is required.
Since the refractive index of the O ₂ film changes only up to 0.3% compared to before the heat treatment even when the high-temperature heat treatment at 1000 ° C. to 1200 ° C. is performed, it is possible to obtain good characteristics by using the film for the optical waveguide. it can.

According to the present invention, the relative refractive index difference Δ between the core layer and the intermediate layer can be increased to a maximum of 2.83% by using the fluorine-added SiO ₂ film as the intermediate layer of the optical waveguide. . This is because the relative refractive index difference Δ between the intermediate layer and the cladding layer can be larger than 0.5% and lower than 1.23%.

According to the present invention, by using a fluorine-added SiO ₂ film for the intermediate layer of the optical waveguide, a large dispersion value can be obtained as the optical waveguide. Also, the mode field diameter has a greater degree of freedom and can control a wide range of values as compared with the conventional single clad type including a core layer and a clad layer. Further, the optical power distribution of the optical waveguide can be controlled quite freely over a wide range.

According to the present invention, a mode converter for achieving mode field matching with an optical fiber can be provided at the input / output end of the optical waveguide, so that the optical fiber can be connected to the optical fiber with low loss. The reflected light from the connection portion can be extremely reduced.

According to the present invention, the reflected light from the connection between the optical waveguide and the optical fiber can be extremely reduced, and the connection can be fused and the core layer of the optical waveguide can be irradiated by CO ₂ laser beam irradiation. Can be diffused into the intermediate layer, and mode field matching with the optical fiber can be realized.

[0026]

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

FIG. 1A is a front sectional view showing an embodiment of the optical waveguide of the present invention, and FIG.
It is a right view of (a). Note that the same members as those of the conventional example shown in FIG.

The optical waveguide shown in FIGS. 1 (a) and 1 (b) has a structure in which the intermediate layer 9 is made of SiO ₂ in which fluorine which is a feature of the present invention is added.
A film (a fluorine-added SiO ₂ film having a heat treatment temperature characteristic of a refractive index indicated by a curve LC in FIG. 4 described later) is used.

As the substrate 1, a SiO ₂ substrate, a ceramic substrate, or the like can be used. Cladding layer (refractive index n ₂₂₎ 2 is formed on the substrate 1. The cladding layer 2 usually has SiO ₂ (n ₂₂ at a wavelength of 0.63 μm is approximately 1.4).
58) is used and the cladding (Si
Preferably, the refractive index is the same as that of O ₂ ). Clad layer 2
The core layer 3 covered with the intermediate layer 9 is formed therein. The value of the refractive index n ₉ of the intermediate layer 9 can be controlled in a range from 1.440 to 1.455 (a value at a wavelength of 0.63 μm) in accordance with the amount of fluorine added. Rate n ₉ is in the range of 1.440 to 1.452,
There is a feature in this point.

The core layer (refractive index n ₃ ) 3 is made of SiO ₂ to which at least one kind of refractive index controlling additive such as Ge, Ti, P, Zn, Ta or the like is added, or a material such as SiON. The value of the refractive index n _{3 is in} the range of 1.458 to 1.482 (value at a wavelength of 0.63 μm). The value of the refractive index n ₃ and index of refraction n ₉ Metropolitan relative refractive index difference delta ₃₉ resulting from a range of 0.21% 2.83%.

That is, in the case of the conventional optical waveguide, FIG.
As shown (d), the when trying to enlarge the core layer 3 and the relative refractive index difference delta ₁₂ of the cladding layer 2, had to be increased refractive index n ₁ of the core layer 3. Further, in order to single-mode transmission optical waveguide has to reduce the width or thickness D ₃ of the core layer 3 in the order of several [mu] m, the thickness of the core layer the larger the relative refractive index difference delta ₁₂ I had to make it smaller. In this state, as shown in FIG. 8 (c) even tries to mode field matching between the optical waveguide 4 and the optical fiber 5 becomes larger width or thickness D ₂ of the core layer 3 is, the optical fiber 5 A mode field mismatch has occurred.

[0032] In contrast, in the present invention, the relative refractive index difference of the optical waveguide 8 is large relative refractive index difference by reducing the value of the refractive index n ₉ without increasing the value of the refractive index n ₃ can do. Therefore, mode field matching with the optical fiber 5 is easy as described later.

FIG. 2A is a front sectional view showing another embodiment of the optical waveguide of the present invention, and FIG.
It is a right view of (a).

This embodiment also uses an SiO ₂ film in which fluorine is added to the intermediate layer 9, but differs from the embodiment shown in FIG. 1 in that the entire upper surface of the cladding layer 2-1 is formed. The point is that the intermediate layer 9 of the SiO ₂ film to which fluorine is added is formed. As described above, it is necessary to form SiO ₂ to which fluorine is added on the entire upper surface of the cladding layer 2-1.
This is advantageous in easily manufacturing the optical waveguide of FIG. That is, in the optical waveguide shown in FIG. 1, the intermediate layers 9-1 and 9-
It is necessary to add a step of removing the area 2
This is because the step of removing the regions of the intermediate layers 9-1 and 9-2 becomes unnecessary in the optical waveguide shown in FIG. In the step of removing the regions of the intermediate layers 9-1 and 9-2, the surfaces of the cladding layer 2-1 and the core layer 3 are roughened by the etching gas, causing scattering loss. In such a case, there is no problem of such roughness and scattering loss.

Next, a method for manufacturing an optical waveguide according to the present invention will be described.

FIG. 3 is a schematic view of a plasma CVD apparatus to which the method for manufacturing an optical waveguide according to the present invention is applied.

In the plasma CVD apparatus 15, two parallel plate-like upper electrodes 16 and lower electrodes 17 are provided.
A high-frequency power source (high-frequency power R
F) A high frequency voltage is applied from 22. The inside of the device 15 is evacuated to a vacuum by a vacuum exhaust device 25 (vacuum degree P). The substrate 1 on which the clad layer 2-1 is formed is provided on the lower electrode 17, and is heated to a temperature T by applying a DC voltage 21 to a heater 20 provided below the lower electrode 17. . The upper electrode 16 has an arrow 19-1.
The gas sent from the direction is supplied to the upper electrode 16 and the lower electrode 1.
A shower electrode structure for uniformly ejecting the air between the shower electrode and the shower head is used. The upper electrode 16 having the shower structure is insulated from the device 15 by the insulator 23. Arrow 19
Gas fed in the arrow 19-2 direction from -1 direction in the apparatus _{15, Si (OC 2 H 5)} 4, Si (OCH 3) and steam metal alcoholate oxides such as _4, fluorine-based, such as C ₂ F ₆ that conveys the gas an O ₂ gas is used. In addition, C ₂
F ₆ may alternatively be fed into the device 15 in the direction of arrow 24.

Next, characteristics of the fluorine-added SiO ₂ film formed by using the apparatus 15 shown in FIG. 3 will be described.

[0039]

【Example】

(Comparative Example 1) Si (OC ₂ H ₅ ): 12 SCCM O ₂ : 100 SCCM C ₂ F ₆ : 11 SCCM Heater temperature T: 350 ° C. High frequency power RF: 300 W Vacuum degree P: 0.6 Torr A fluorine-added SiO ₂ film is formed thereon (film formation rate: 2100 Å / min), and thereafter, the Si substrate 1 is divided into 5 parts, each of the divided substrates is placed in an electric furnace, and N ₂ is flowed at 5 liters per minute. While
Each heat treatment temperature 500 ℃ 、 800 ℃ 、 1000 ℃
And a heat treatment at 1200 ° C., and the refractive index of each film was measured. The result is shown by a curve LA in FIG.

When the heat treatment temperature is increased, the refractive index increases, and the refractive index of SiO ₂ (1.458)
Lower values could not be achieved. This is presumably because the density of the fluorine-added SiO ₂ film was low, and the high-temperature heat treatment resulted in an oxygen-deficient film, which increased the refractive index. It was also found that fluorine was diffused together with oxygen vacancies. still,
FIG. 4 is a diagram showing the heat treatment temperature dependence of the refractive index of the fluorine-added SiO ₂ film formed by using the apparatus shown in FIG. 3, in which the horizontal axis shows the heat treatment temperature and the vertical axis shows the refractive index. .

Comparative Example 2 Si (OC ₂ H ₅ ) ₄ : 12 SCCM O ₂ : 100 SCCM C ₂ F ₆ : 350 ° C. High frequency power RF: 300 W Vacuum degree P: 0.6 Torr To form a fluorine-added SiO ₂ film at a film formation rate of about 2200 angstroms per minute.
Thereafter, as in Comparative Example 1, the Si substrate 1 was divided, and each substrate was heat-treated at a desired temperature, and the refractive index was evaluated. The refractive index characteristic in this case is shown by a curve LB in FIG.

From the curve LA, the refractive index is low because the amount of added fluorine is large, but as the heat treatment temperature is increased, the refractive index becomes higher than that of SiO ₂ . That is, this film is also a fluorine-doped Si for the optical waveguide of the present invention.
It turned out that it cannot be used as an O ₂ film.

(Example 1) Si (OC ₂ H ₅ ) ₄ : 12 SCCM O ₂ : 100 SCCM C ₂ F ₆ : 11 SCCM Heater temperature T: 400 ° C. High frequency power RF: 350 W Vacuum degree P: 0.4 Torr Then, a fluorine-added SiO ₂ film is formed on the Si substrate 1 (deposition speed of 940 Å / min), and thereafter, the Si substrate 1 is divided similarly to Comparative Example 1, and each substrate is heat-treated at a desired temperature. The refractive index was evaluated. The refractive index characteristic in this case is shown by a curve LC in FIG. A value lower than the refractive index of SiO ₂ could be realized. this is,
This is achieved by forming a very dense and stable film by increasing the heating temperature of the substrate, increasing the output of the high-frequency power RF, and increasing the degree of vacuum. Therefore, even if the high-temperature heat treatment was performed, oxygen in the film was not released, thereby suppressing the diffusion of fluorine and making it difficult to move through the film, and as a result, a film having a refractive index that was difficult to change was obtained. It seems to be.

(Example 2) Si (OC ₂ H ₅ ) ₄ : 12 SCCM O ₂ : 100 SCCM C ₂ F ₆ : 31 SCCM Heater temperature T: 450 ° C. High frequency power RF: 380 W Vacuum degree P: 0.4 Torr or more Forming a fluorine-added SiO ₂ film on the Si substrate (at a deposition rate of 900 angstroms per minute),
The Si substrate was divided in the same manner as in Example 2, and each substrate was heat-treated at a desired heat treatment temperature, and the refractive index was evaluated. FIG.
Curve LD shows the refractive index characteristics.

In this case as well, a value significantly lower than the refractive index of SiO ₂ could be realized. Further, the film was a stable film whose refractive index hardly changed even after high-temperature heat treatment.
This seems to have been achieved because the substrate was heated at a higher temperature and the output was higher than the high frequency power, resulting in a more dense film.

The concentration distribution of fluorine in the film was examined by secondary ion mass spectrometry (SIMS) of fluorine. The movement of fluorine in the film was from the surface of the film to a depth of more than 10 tens of nm. Has only a slight concentration distribution.

From the above Examples and Comparative Examples, to obtain a fluorine-added SiO ₂ film in which the change in the refractive index due to the high-temperature heat treatment is small and the gradient distribution of the fluorine concentration in the film is small, the heating during the film formation is required. The temperature is maintained in the range of 400 ° C. to 600 ° C., the high-frequency power RF is set to 350 W or more, the degree of vacuum P is set to 0.5 Torr or less, and the film formation rate of the fluorine-added SiO ₂ film is 1000 Å / min or less. I knew I had to do it.

FIG. 5A is a cross-sectional view of the optical device of the present invention, FIG. 5B is a refractive index distribution diagram in a cross section taken along line DD, and FIG. Refractive index distribution diagram in Fig. 5
(D) is a refractive index distribution diagram in a cross section taken along line FF.

This optical device has a structure in which the single mode optical fiber 5 is connected to the input end of the optical waveguide 8.

The first characteristic of the optical waveguide 8 shown in FIG.
A clad layer 2 is formed on a substrate 1, and the clad layer 2
It has a structure in which a substantially rectangular core layer 3 covered with an intermediate layer 9 is provided therein.

The relative refractive index difference Δ of the optical waveguide 8 is shown in FIG.
As shown in (d), the refractive index n ₃ of the core layer ₃ and the intermediate layer 9
And the refractive index n ₉ . Refractive index n ₉ of intermediate layer ₉
Can be controlled in the range of 1.440 to 1.455, so that the refractive index n ₃ of the core layer 3 is considerably lower than the refractive index n ₁ of the core layer 3 of the conventional optical waveguide shown in FIG. can do. For example, 1.440 as the refractive index n ₉
When the relative refractive index difference Δ between the core layer 3 and the intermediate layer 9 is set to 2%, the refractive index n ₃ may be set to 1.469, and the relative refractive index between the core layer 3 and the cladding layer 2 may be adjusted. The difference Δ is about 0.
75%. Assuming that the relative refractive index difference Δ between the core layer 3 and the cladding layer 2 of the conventional optical waveguide 4 shown in FIG. 8 is 2%, the width and thickness D ₁ of the core layer 3 must be about 3 μm as described above. There was no Banara, width and thickness D ₃ of the core layer 3 of the optical waveguide 8 of the present invention may be a value close to 2 times the thickness D _1. Thus, since the value of the thickness D ₁ can be increased, it is possible to reduce the connection loss of the optical fiber 5, moreover can be easily connected.

The second characteristic of the optical waveguide shown in FIG. 5 is that the refractive index distribution in the cross section taken along line EE in FIG. 5C is obtained by melting the optical fiber 5 and the optical waveguide 8 by irradiating a CO ₂ laser. When the connection is made, an excessive CO ₂ laser beam is applied to the input end 1 of the optical waveguide 8.
By irradiating near 0, the dopant for controlling the refractive index of the core layer 3 is diffused and moved into the intermediate layer 9, and the core layer 3 of the optical waveguide 8 is substantially equal to the diameter D _f of the core 7 of the optical fiber 5. The point is that the width and thickness can be set, and the refractive index can be made substantially equal to the refractive index of the core 7. That is, it is possible to realize a configuration in which mode field matching is achieved between the optical fiber 5 and the input end of the optical waveguide 8.

The third characteristic of the optical waveguide shown in FIG. 5 is that the dispersion value of the optical waveguide is determined by the refractive indices n ₃ , n ₂ and n ₉ , the thickness D ₃ of the core layer of the optical waveguide, and the thickness t of the intermediate layer. That is, it can be controlled and a large value can be obtained. In other words, the optical waveguide shown in the figure has a greater degree of freedom in designing the dispersion value than the conventional optical waveguide.

The fourth feature of the optical waveguide shown in FIG. 5 is that the mode field diameter can also be controlled by the refractive indices n ₃ , n ₂ and n ₉ , the thickness D _{3 of the} core layer and the thickness t of the intermediate layer. That is, the degree of freedom in design is great.

FIG. 6 is an explanatory diagram for explaining a method of forming a mode converter in the optical device according to the present invention. This figure shows an embodiment of a method of fusion splicing an optical waveguide and an optical fiber with a CO ₂ laser beam and diffusing a refractive index controlling dopant in a core layer of the optical waveguide into an intermediate layer. .

With the end face of the optical fiber 5 pressed against the input end 10 of the optical waveguide 8, the connection surface is irradiated with the CO ₂ laser beam 27 condensed by the condensing lens 26 and fusion spliced. By irradiating the CO ₂ laser beam 27 for a short time (about 1 to 10 seconds), the dopant for controlling the refractive index in the core layer 3 is diffused into the intermediate layer 9. When the CO ₂ laser beam 27 irradiates a continuously oscillating output,
The range from several W to several tens of watts is preferable. The diameter of the CO ₂ laser beam 27 is preferably in the range of 100 μm to several hundred μm.

Next, the results of trial production using the optical waveguide of the present invention and its manufacturing method will be described.

An optical waveguide having the same structure as the optical waveguide shown in FIG. That is, the SiO ₂ substrate 1
_{2 The} cladding layer 2-1 is formed to a thickness of 2 μm by a plasma CVD method.
An intermediate layer 9 of a SiO ₂ film to which a film is formed and then fluorine is added
Was formed in a thickness of 2 μm by the method described in Example 1. However, in Example 1, the flow rate of C ₂ F ₆ was 37 SCCM. Then, a 5 μm-thick SiON core layer 3 to which N was added was formed on the intermediate layer 9 by a plasma CVD method. This S
The iON layer was formed in a plasma atmosphere by supplying SiH ₄ , NH _3, and O ₂ gas between the electrodes of the plasma CVD apparatus shown in FIG. 3 (the heater temperature during the film formation was 400 ° C.). . Thereafter, heat treatment was performed at 1000 ° C. in an O ₂ atmosphere for 3 hours. Next, the core layer 3 and the cladding layer 9 to which fluorine is added are formed into a substantially rectangular shape (width 6 μm) by dry etching.
Was patterned. Then, the above-mentioned fluorine-added SiO ₂ film was again formed on the entire patterned surface by 2 μm.
Formed. Finally, the cladding layers 2-2 of SiO ₂ to 8μm formed on the SiO ₂ film added with the fluorine. As a result of evaluating the propagation loss of the optical waveguide in a wavelength range of 1.1 μm to 1.6 μm, as shown in FIG. 7, it was 0.15 dB / cm or less in a wavelength range of 1.3 μm to 1.6 μm. In addition, there was no absorption loss due to the OH group near the wavelength of 1.39 μm or absorption loss due to the Si—H or NH group near the wavelength of 1.5 μm. That is, a flat loss wavelength characteristic with almost no absorption group in the above-mentioned wavelength band could be realized. FIG. 7 is a loss wavelength characteristic diagram of the optical waveguide of the present invention, in which the horizontal axis represents wavelength and the vertical axis represents propagation loss.
The relative refractive index difference Δ of the optical waveguide is equal to the SiO ₂ cladding layer 2-1.
The relative refractive index difference between (2-2) and the fluorine-doped SiO ₂ intermediate layer 9 is about 2%, and the core layer 3 and the SiO ₂ clad layer 2
The relative refractive index difference from -1 (2-2) was about 0.8%.
Here, usually, OH is contained in the SiON core layer 3.
Groups, Si-H groups and N-H absorbing groups are mixed,
Among them, the OH group was almost completely evaporated by the heat treatment at 1000 ° C., but the Si—H group and the N—H group could not be easily removed unless the temperature was 1200 ° C. or higher. On the other hand, these absorbing groups could be removed by the structure of the present invention. This is 1000 ° C
During the heat treatment, the fluorine ions in the intermediate layer 9 react with the O—H, Si—H, and N—H groups in the core layer 3, and the reacted HF groups evaporate. And O in the core layer 9
It is considered that low loss was realized as a result of removing the -H group, the Si-H group, and the NH group.

As described above, the core layer 3 and the cladding layer 2-1
It was confirmed that by providing a SiO ₂ layer to which fluorine was added between (2-2) and performing high-temperature heat treatment, low loss could be achieved. This is a remarkable feature as a new effect of the present invention. In addition, if the high-temperature heat treatment is further performed after forming the cladding layer 2-2, the loss can be further reduced.

The present invention is not limited to the above embodiments or examples. In FIG. 3, the substrate 1 is
Alternatively, various gases may be blown out from the shower electrode structure provided on each electrode from below the lower electrode 17. In that case, the substrate 1 is heated by a heater attached to the upper electrode 16 side. The plasma CVD apparatus 15 shown in FIG. 3 can be used not only for forming an intermediate layer but also for forming a clad layer and a core layer.
Further, as the optical fiber 5 used in the optical device shown in FIG. 5, a dispersion shift fiber, a dispersion compensation fiber, a non-zero dispersion shift fiber, or the like may be used in addition to a normal single mode fiber. In FIG. 5, as a connection method other than the fusion splicing, the optical fiber 5 and the optical waveguide 8 may be arranged such that the optical fiber is abutted on the end face of the optical waveguide and the vicinity of the abutted portion is fixed with an adhesive. In that case, it is preferable to interpose a refractive index matching agent between the optical fiber and the optical waveguide. The mode field matching section near the end face of the optical waveguide is connected after being formed beforehand by irradiation with a CO ₂ laser beam.

The optical waveguide shown in FIGS. 1 and 2 is manufactured at a stage during the manufacture of the optical waveguide (after forming the cladding layer and the intermediate layer,
Or after forming a cladding layer, an intermediate layer and a core layer, or after patterning the core layer into a substantially rectangular shape by photolithography and dry etching, etc.), or performing a heat treatment at a high temperature of 1000 ° C. to 1200 ° C. To reduce the loss of the optical waveguide.

As described above, according to the present invention, (1) an intermediate layer between a core layer and a clad layer of an optical waveguide includes:
A high relative refractive index difference can be realized by using a stable fluorine-added SiO ₂ film in which the refractive index and the fluorine concentration distribution hardly change even when a high-temperature treatment at 1000 ° C. to 1200 ° C. is performed.

[0063] (2) relative refractive index difference delta _ci between the core layer and the intermediate layer of the optical waveguide, it is possible to obtain 1.23%
The relative refractive index difference delta _WC between the core layer and the cladding layer has the advantage that it is possible to match the relative refractive index difference between the core layer and the cladding of the optical fiber (0.3% usually). Further, the optical waveguide of the present invention can be adjusted to the relative refractive index difference (usually 0.3%) between the core layer and the clad layer of the optical fiber.
In the conventional high relative refractive index difference waveguide, it must be the relative refractive index difference delta _WC between the core layer and the cladding layer to 1% or more,
As described above, mode matching with an optical fiber has been difficult.

(3) The fluorine-added SiO ₂ film is formed at 1000 ° C.
And 1200 ° C. high-temperature heat treatment. Therefore, by subjecting the optical waveguide itself to high-temperature heat treatment, impurities (OH groups, C atoms) contained in the core layer, the cladding layer, and the intermediate layer are contained.
It is possible to reduce the absorption loss due to the absorption difference between the H group and the Si-H group. In addition, since each of the above layers can be densified, scattering loss due to minute non-uniform structure can be reduced. Further, structural irregularities between the respective layers can be reduced, and the scattering loss due to this can also be reduced.

(4) Since mode field matching can be obtained from both the refractive index and the structure of the optical fiber, the loss at the connection can be greatly reduced.

(5) Designing the mode field diameter, optical power distribution, dispersion characteristics, and the like using the parameters of the refractive indexes n ₃ , n ₂ , and n ₉ , the thickness D ₃ of the core layer of the optical waveguide, and the thickness t of the intermediate layer. Therefore, the degree of design freedom is greater than that of the conventional optical waveguide.

(6) A mode converter can be easily provided at the optical fiber connection on the input / output end side of the optical waveguide.

[0068]

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

It is possible to realize an optical waveguide which can be easily subjected to mode field matching with a single mode optical fiber, a method of manufacturing the same, and an optical device.

[Brief description of the drawings]

FIG. 1A is a front sectional view showing one embodiment of an optical waveguide of the present invention, and FIG. 1B is a right side view of FIG.

FIG. 2A is a front sectional view showing another embodiment of the optical waveguide of the present invention, and FIG. 2B is a right side view of FIG.

FIG. 3 is a schematic view of a plasma CVD apparatus to which the method for manufacturing an optical waveguide of the present invention is applied.

FIG. 4 is a diagram showing the dependence of the refractive index of a fluorine-added SiO ₂ film formed by using the apparatus shown in FIG. 3 on the heat treatment temperature.

5A is a cross-sectional view of the optical device of the present invention, FIG. 5B is a refractive index distribution diagram in a DD line cross-section, and FIG. 5C is a refractive index distribution in a EE line cross-section. FIG. 3D is a refractive index distribution diagram in a cross section taken along line FF.

FIG. 6 is an explanatory diagram for explaining a method of forming a mode converter in the optical device of the present invention.

FIG. 7 is a loss wavelength characteristic diagram of the optical waveguide of the present invention.

FIG. 8A is a cross-sectional view of a conventional optical device with a pigtail fiber, and FIG. 8B is a cross-sectional view taken along line AA of FIG.
(C) is a refractive index distribution diagram in a cross section taken along the line BB in (a), and (d) is a refractive index distribution diagram in a cross section taken along a line CC.

FIG. 9 is a schematic view of a conventional method for forming a mode converter on an optical waveguide.

[Explanation of symbols]

 Reference Signs List 1 substrate (Si substrate) 2 clad layer 3 core layer 5 optical fiber 8 optical waveguide 9 intermediate layer

Claims (7)

[Claims] 1. A substrate and SiO ₂ formed on the substrate.
And a core layer formed in the cladding layer and containing at least one type of a refractive index control additive in SiO ₂ , wherein the core layer is made of SiO ₂ in which fluorine is added. An optical waveguide characterized by being covered with an intermediate layer. 2. An upper electrode and a lower electrode are arranged in parallel in a vacuum-evacuated reaction chamber, a high-frequency power RF is applied between the two electrodes, and a substrate is arranged on one of the electrodes. The substrate is heated to a predetermined temperature T by the provided heater, and vapor of metal alkoxide, fluorine gas such as C ₂ F ₆ and O ₂ gas are sprayed from the other electrode side toward one electrode side in a shower shape, the SiO ₂ film added with fluorine kept constant degree of vacuum P is formed on a substrate, a core layer was formed on the SiO ₂ film, a SiO ₂ film added again fluorine so as to cover the core layer And temperature T is 400 ° C.
To 600 ° C and the high frequency power RF is 350W
A method of manufacturing an optical waveguide, comprising: maintaining the vacuum degree P at 0.5 Torr or less, and forming the SiO ₂ film to which fluorine is added at a growth rate of 1000 Å / min or less. 3. The SiO ₂ film to which fluorine has been added is 1
3. The method of manufacturing an optical waveguide according to claim 2, wherein the heat treatment is performed at a high temperature of from 000 ° C. to 1200 ° C. so that a change in the refractive index of the film is 0.3% or less as compared with before the heat treatment. 4. A relative refractive index difference between a refractive index of the SiO ₂ film to which fluorine is added and a refractive index of the SiO ₂ film is at least larger than 0.5% and lower than 1.23%.
Or the manufacturing method of the optical waveguide of 3. 5. A substrate and SiO ₂ formed on the substrate.
An optical waveguide having a cladding layer made of: a core layer formed in the cladding layer and containing at least one type of a refractive index control additive in SiO ₂ ; and light connected to the input / output end of the optical waveguide. An optical device comprising a fiber, wherein the core layer is covered with an intermediate layer made of SiO ₂ doped with fluorine. 6. The optical device according to claim 5, wherein a refractive index control additive contained in a core layer of the optical waveguide is diffused into an intermediate layer near a connection portion between the optical waveguide and the optical fiber. 7. The optical fiber and the optical waveguide are CO
₂ laser according to claim is fused by the beam irradiation 5 or 6
An optical device according to claim 1.