JP2002311261A - Optical waveguide and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide and a method for manufacturing the optical waveguide in which a grating is efficiently formed by doping the core part with GeO2 in higher density than in the clad part without using TiO2 for doping and the excess loss due to the cladding mode is suppressed. SOLUTION: The optical waveguide 100 has the core 103 where light propagates and a lower clad 102 and an upper first clad 104 surrounding the core and having the refractive index lower than that of the core on a substrate 101. In this waveguide, the composition of the core 103, the lower clad 102 and the upper first clad 104 consists of GeO2 -doped SiO2 and the GeO2 concentration c1 of the core 103, the GeO2 concentration c2 of the lower clad 102 and the GeO2 concentration c3 of the upper first clad 104 are controlled to have the relation of c1>c2 and c1>c3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide type optical device used for optical fiber communication, and more particularly to an optical waveguide type grating optical device.

[0002]

2. Description of the Related Art Conventionally, with the spread of optical communication systems, development of optical components with lower loss and higher reliability has been promoted. In particular, a waveguide-type optical component using a quartz-based material has received the most attention because it has an advantage that a complicated circuit can be collectively formed on a flat substrate in addition to its low loss property. 2. Description of the Related Art In recent years, a wavelength multiplexing / demultiplexing device that multiplexes or demultiplexes light of various wavelengths (Arrayed Waveguide Grade).
NG; AWG), and an ADD-DROP optical circuit that multiplexes light of a certain wavelength into light of multiple wavelengths and demultiplexes light of a certain wavelength from light of multiple wavelengths. Is being developed. As an ADD-DROP optical circuit, a circuit in which a grating having a periodic refractive index distribution is formed in a Mach-Zehnder optical circuit is considered to be promising.

According to this configuration, a periodic refractive index distribution is formed in the traveling direction of light, and only light having a wavelength determined by the equation (1) is reflected, and other light is transmitted.

Λb = 2 × Neff × ∧ (1) λb: black wavelength, Neff: effective refractive index of the waveguide, ∧: grating period Light having a wavelength according to the formula (1) reflected in the Mach-Zehnder optical circuit is DROP. Light, while ADD light is inserted from another input waveguide.

An optical device using this grating is:
It is roughly classified into a fiber grating and a waveguide grating. At present, fiber-type gratings with large price advantages are predominant, but in the future waveguide-type gratings that can be integrated with various optical circuits, eliminating the need for optical circulators by Mach-Zehnder circuits are expected. is there. As a conventional example of the waveguide grating, there is disclosed an invention in which a core region is made of SiO ₂ glass containing Ge and Ti, and a cladding region is made of SiO ₂ glass containing Ge having substantially the same Ge concentration as the core region (Japanese Patent Laid-Open No. 2000-2000). -155230) has been proposed.

FIG. 5 is a sectional view of a waveguide type optical grating according to the present invention. The composition is Ge on the substrate 501.
A lower cladding 502 made of O ₂ —SiO ₂ is formed,
A ridge of the core 503 having a composition of TiO ₂ —GeO ₂ —SiO ₂ is formed thereon, and a composition of GeO 3 is formed thereon.
_This is a structure in which an upper cladding 504 made of _2- SiO ₂ is formed. Core region 503 and cladding regions 502 and 50
The refractive index difference from 4 is controlled to an arbitrary value by the amount of Ti added to the core region 503. Core area 5
3 and the cladding regions 502 and 504 are irradiated with ultraviolet laser light, thereby forming a grating having a periodic refractive index distribution in both the core region 503 and the cladding regions 502 and 504 where the optical signal leaks. The excess loss caused by the cladding mode occurring in the above can be suppressed.

[0007]

However, in the conventional optical waveguide type grating, the T
GeO ₂ is exposed because iO ₂ absorbs ultraviolet laser,
There is a problem that a periodic refractive index distribution cannot be obtained.

Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art, and to efficiently perform grating by doping TiO ₂ without doping TiO ₂ and doping the core with GeO ₂ having a higher density than the cladding. And an optical waveguide in which excessive loss due to a cladding mode is suppressed, and a method for manufacturing the same.

[0009]

According to the first aspect of the present invention,
In an optical waveguide including a core through which light propagates on a substrate, and a lower cladding and an upper first cladding that cover the periphery of the core and have a lower refractive index than the core, the composition of the core, the lower cladding, and the upper first cladding Is GeO ₂ doped SiO ₂
Made, the GeO ₂ concentration in core c1, if the GeO ₂ concentration of the lower cladding c2, the GeO ₂ concentration in the upper first cladding was c3, and having a relation of c1> c2, c1> c3 .

According to a second aspect of the present invention, in the first aspect, an upper second clad is provided on the upper first clad.

According to a third aspect of the present invention, in the first aspect, an upper second clad having a composition of non-doped SiO ₂ is provided on the upper first clad.

According to a fourth aspect of the present invention, in any one of the first to third aspects, the thickness of the upper first cladding and the lower cladding is formed to be at least larger than the thickness of the core. Features.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects, c2 = c3.

According to a sixth aspect of the present invention, in any one of the first to fourth aspects, a grating having a periodic refractive index distribution is formed in the core, the lower cladding, and the upper first cladding. It is characterized by the following.

According to a seventh aspect of the present invention, there is provided a method of manufacturing an optical waveguide comprising: a core through which light propagates on a substrate; and a lower cladding and an upper first cladding which cover the periphery of the core and have a lower refractive index than the core. In the above, the composition is GeO ₂ doped Si
Comprising forming a core consisting of O _2, the steps of the composition to form a lower cladding made of GeO ₂ doped SiO _2, and forming an upper first cladding composition consisting GeO ₂ doped SiO _2, the core If the GeO ₂ concentration c1, the GeO ₂ concentration of the lower cladding c2, the GeO ₂ concentration in the upper first cladding was c3, c1> c2, c1> c
3 is established.

According to an eighth aspect of the present invention, in the seventh aspect, the GeO ₂ -doped SiO ₂ film of the core, the lower clad, and the upper first clad is formed by a sputtering method or a plasma-excited chemical vapor deposition method. It is characterized by doing.

The ninth aspect of the present invention is the seventh or eighth aspect.
In the above description, when the GeO ₂ -doped SiO ₂ films of the core, the lower clad, and the upper first clad are formed by a sputtering method, independently controlled RF high-frequency power is applied to the GeO ₂ -doped SiO ₂ target. In addition, a separate and independent RF high-frequency power is applied to the substrate.

According to a tenth aspect of the present invention, there is provided the method according to any one of the seventh to ninth aspects, further comprising an upper second cladding on the upper first cladding, wherein the upper second cladding is a plasma-excited chemical vapor phase. It is characterized by being formed by a growth method.

The invention according to claim 11 is the invention according to claims 7 to 10.
Wherein the thickness of the upper first cladding and the lower cladding is formed at least larger than the thickness of the core.

The invention according to claim 12 is the invention according to claims 7 to 11
Wherein c2 = c3.

The invention according to claim 13 is the invention according to claims 7 to 12
Wherein the grating having the periodic refractive index distribution is formed on the core, the lower cladding, and the upper first cladding.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical waveguide according to the present invention and a method for manufacturing the same will be described below with reference to the accompanying drawings.

As shown in FIG. 1A, an optical waveguide 100 according to the present embodiment includes a lower clad 102 of low concentration GeO ₂ -doped SiO ₂ on a quartz substrate 101, a core 103 of high concentration GeO ₂ -doped SiO ₂ , GeO ₂ doped Si
An upper first clad 104 made of O _{2 and} an upper second clad 105 made of non-doped SiO ₂ are provided. The composition and film thickness of each layer are as follows.

That is, the lower clad 102 has a composition of GeO ₂ : 10 mol% -SiO ₂ : 90 mol% and a thickness of 6 μm, and the core 103 has a composition of GeO ₂ : 1:
8 mol% -SiO ₂ : 82 mol%, and the film thickness is 6 μm
The upper first cladding 104 has a composition of GeO ₂ :
10 mol% -SiO ₂ : 90 mol 1%, thickness 6 μm
m, and the upper second cladding 105 has a composition of Si
O ₂ : 100 mol%, and the film thickness is 15 μm.

In this embodiment, the core GeO ₂ concentration (=
18 mol%), the lower clad GeO ₂ concentration (= 10 mol%) is c2, and the upper first clad GeO.
_{2 When} c3 is the concentration (= 10 mol%), c1> c
2, and the relationship of c1> c3 holds. The lower cladding 102 has a thickness of 6 μm, the core 103 has a thickness of 6 μm, and the upper first cladding 104 has a thickness of 6 μm.
m, the upper second cladding 105 has a thickness of 15 μm, and the upper first cladding 104 and the lower cladding 10
2 is formed to be thicker than at least the thickness of the core 103. In this embodiment, the lower cladding 102 and the upper first cladding 104 have the same composition (c2 =
c3). Therefore, the lower cladding 102 and the upper first
The cladding 104 has the same refractive index.

As shown in FIG. 1B, the refractive index of each layer is 1. cladding 102 and upper first cladding 104.
4696, the core 103 is 1.4807, and the upper second cladding 105 is 1.4585.

The relative refractive index difference, the lower clad 102 and the upper first cladding 104 is a Deruta0.76% as compared to the non-doped SiO ₂ of the second upper cladding 105 (delta
0.76% = (1.4696-1.4585) /1.4
696 × 100), and the core 103 is Δ1.50% as compared with the non-doped SiO ₂ (Δ1.50% = (1.48)
07-1.4585) /1.4807×100), which is also Δ0.75% compared to the lower cladding 102 and the upper first cladding 104 (Δ0.75% = (1.48)
07-1.4696) /1.4807×100).

FIG. 2 is a perspective view showing the configuration of an RF sputtering apparatus used for manufacturing the optical waveguide 100. This RF sputtering apparatus is provided with a box-shaped chamber 301 and
A substrate holder 307 consisting of a dome rotating around 5;
A vacuum pump 302 for evacuating the chamber 301 is provided. Targets 303-1 to 30-4 described later are arranged on four inner walls of the chamber 301,
Independently controlled RF high frequency power supplies 304-1 to 304-4 are individually connected. The substrate holder 307 is connected to a separately controlled RF high-frequency power supply 308.

Next, a method for manufacturing an optical waveguide will be described.

As shown in FIG. 3A, a composition having a composition of GeO ₂ : 10 mol% -SiO ₂ : 90 mo is formed on a quartz substrate 101.
1%, 6 μm thick, low concentration GeO ₂ -doped SiO ₂
Is formed by an RF sputtering method. In this case, the RF sputtering apparatus shown in FIG. 2 is used.

The substrate holder 30 of the RF sputtering device
7, a quartz substrate 101 is disposed, and a target 303 is provided.
The composition of -1 to 4 is the same as the desired film composition of the lower clad film 102, that is, GeO ₂ : 10 mol% -SiO ₂ : 90
mol%. Then, Ar and O ₂ were introduced into the chamber 301 at 100 sccm and 5 sccm, respectively, and the substrate holder 307 was moved at 4 rpm around the central axis 305.
m, and apply 1.2k to RF high frequency power supplies 304-1 to 304-4
W power is applied and the RF high frequency
To start film formation.

Since the deposition rate is 100 A / min,
It takes about 600 minutes to form a 6 μm film. After film formation,
Heat treatment is performed to stabilize the refractive index. Heat treatment conditions are 11
00 ° C, 02: 1.5 L / min, 3 h. According to this, the independently controlled RF high-frequency power supply 308 is connected to the substrate holder 307 separately from the RF high-frequency power supplies 304-1 to 30-4 connected to the targets 303-1 to 30-4. Can be controlled with high accuracy.

Next, as shown in FIG. 3B, on the lower cladding 102, the composition is GeO ₂ : 18 mol% -Si.
O ₂ : 82 mol%, 6 μm thick, high concentration GeO ₂
The core film 103A of doped SiO ₂ is formed by the RF sputtering method. The device configuration and manufacturing conditions in this case are almost the same as those for manufacturing the lower clad 102. However, the composition of the target is
GeO ₂ : 18 mol% -SiO ₂ : 8 same as the film composition of No. 3
The deposition rate is 120 A / min, and the deposition time is 500 min. After forming the core film, heat treatment is performed to stabilize the refractive index. The heat treatment conditions are 1100 ° C., 02: 1.
5 L / min, 3 h.

Next, as shown in FIG. 3C, the WSi film 204 serving as a mask material is
Form 0.6 μm on 03A. Then, as shown in FIG. 3D, photolithography is performed on the WSi film 204 to form a resist pattern 205. Further, as shown in FIG. 3E, using the resist pattern 205 as a mask, the WSi film is patterned by dry etching, and as shown in FIG.
SiO ₂ -GeO ₂ core film 103A using the i film as a mask
Is patterned by a dry etching method to form a core ridge 103. Next, the core ridge 103 is heat-treated to stabilize the film composition and the refractive index. Heat treatment conditions are 12
00 ° C, 02: 1.5 L / min, 3 h.

Next, as shown in FIG. 3G, an upper first cladding film 104 is formed on the core ridge 103 by the same RF sputtering method. The device configuration and manufacturing conditions are the same as those for manufacturing the lower clad 102 described above. Heat treatment conditions: 1100 ° C, 02: 1.5 L / mi
n and 3h.

Then, as shown in FIG. 3H, the upper second cladding 105 is formed by a plasma enhanced chemical vapor deposition method (plasma CVD method).

The illustration of the apparatus for plasma CVD is omitted. In the plasma CVD method, a raw material gas is sent between two electrode plates,
In this method, a raw material gas is plasma-decomposed between the electrode plates to form highly reactive ions or radicals, and the ions and radicals are reacted on the substrate to form a film. A feature of the plasma CVD method is that not only the controllability of the film thickness and the refractive index is good, but also it is possible to obtain a clad film in which particles are suppressed as much as possible.

Since the composition of the upper second cladding 105 was non-doped SiO ₂ , SiH ₄ ,
O ₂ and Ar were used.

Since the deposition rate is 500 A / min,
It takes 300 min to form a 15 μm film. After film formation,
Heat treatment is performed to stabilize the refractive index. Heat treatment conditions are 11
00 ° C, 02: 1.5 L / min, 3 h.

Next, a grating is formed by irradiating the optical waveguide manufactured through the manufacturing process shown in FIG. 3 with ultraviolet rays.

First, prior to irradiating the optical waveguide with ultraviolet light,
A hydrogenation treatment is performed. This hydrogenation treatment is performed in order to promote a change in the refractive index of the core due to ultraviolet light irradiation. Specifically, the optical waveguide is set at 100 to 300 atm, about 50 ° C.
This is achieved by holding in a hydrogen pressurized vessel adjusted to about 1 week.

FIG. 4 shows an ultraviolet irradiation device.

In this apparatus, ultraviolet light 40 having a wavelength of 248 nm emitted from a light source (KrF excimer laser) 401 is used.
2 is a mirror 403 made of a material that totally reflects the ultraviolet light.
The direction of travel is bent 90 degrees by the
Through the phase mask 405 to irradiate the optical waveguide 100 vertically.

After the above-described hydrogenation treatment is performed, when ultraviolet irradiation is performed through an ultraviolet irradiation device, the optical waveguide 1
At 00, the core 103 of the portion irradiated with ultraviolet light
Only the refractive index increases. Therefore, if the ultraviolet irradiation is changed periodically, a grating 408 in which the refractive index of the core 103 changes periodically is formed. In the case where the ultraviolet irradiation is changed periodically, for example, the ultraviolet light 40 is moved while the mirror 403 is moved in the longitudinal direction of the optical waveguide (the direction of arrow A).
2 and the speed of moving the ultraviolet light 402 and the irradiation time at each irradiation position may be changed.

In this embodiment, the grating 408 having a good reflection and transmission spectrum can be formed by controlling the refractive index modulation.

As another embodiment, the upper first clad 1
04 and the thickness of the lower cladding 102
Can be formed to be thicker than the thickness. According to this, light can be effectively confined, and propagation loss is reduced.

The GeO ₂ -doped SiO ₂ films of the core 103, the lower cladding 102, and the upper first cladding 104 may be formed by a plasma CVD method. In this case, the source gas may be a combination of SiH ₄ , GeH ₄ , O ₂ ,
Alternatively, Si (O (C ₂ H ₅ ) ₄ ), Ge (O (C
A combination of H ₃ ) ₄ ) and O ₂ is used. Plasma C
According to the VD method, similarly to the sputtering method, the refractive index and the film thickness can be controlled with high accuracy. Plasma C
A further merit of the VD method is that the refractive index can be easily controlled by controlling the flow rate of the raw material gas, so that feedback is possible. In the sputtering method, the composition is almost determined by the target, so that it is not easy to feed back the refractive index.

In this embodiment, the following effects are obtained.

[0049] The GeO ₂ concentration in core 103, because of the higher than GeO ₂ concentration of the lower cladding 102 and the upper first cladding 104, without doping the Ti in the core 103, by doping only the high concentration of GeO ₂ , Eliminate the problem of light absorption, and
By doping 2104 with GeO ₂ at a low concentration, excessive loss due to the cladding mode can be suppressed.

The first upper portion made of GeO ₂ -doped SiO ₂
On top of the cladding 104, a non-doped SiO ₂
Since the upper second cladding 105 is formed, light can be effectively confined, and propagation loss can be reduced.

Since the upper first cladding 104 and the lower cladding 102 have a thickness larger than at least the thickness of the core 103, light can be effectively confined as described above, and the propagation loss can be reduced. can do.

[0052] By equal composition of GeO ₂ concentration of GeO ₂ concentration and the upper first cladding 104 of the lower clad 102, it is possible to equalize the refractive index in the lower and upper core 103, reducing the polarization dependence Therefore, the propagation loss can be reduced.

By irradiating the core 103, the lower clad 102, and the upper first clad 104 with an ultraviolet laser beam, a grating having a periodic refractive index distribution is formed, so that the grating can be formed in the light traveling direction. Excess loss due to the cladding mode can be suppressed.

By forming the GeO ₂ -doped SiO ₂ films of the core 103, the lower clad 102, and the upper first clad 104 by a sputtering method or a plasma CVD method, the refractive index and the film thickness can be controlled with high precision.

When a GeO ₂ -doped SiO ₂ film is formed by a sputtering method, independently controlled RF high-frequency power is individually applied to the GeO ₂ -doped SiO ₂ target, and separately independent RF high-frequency power is applied to the substrate. By doing so, not only the refractive index and the film thickness but also the film stress can be controlled with high accuracy.

The upper second clad 105 is plasma-CV
By forming by the method D, not only the controllability of the film thickness and the refractive index can be improved, but also a clad film in which particles are suppressed as much as possible can be obtained.

Although the present invention has been described with reference to one embodiment, it is apparent that the present invention is not limited to this.

[0058]

According to the present invention, TiO ₂ is not doped,
By doping the core with GeO ₂ having a higher density than the cladding, a grating was efficiently formed, and excess loss due to the cladding mode could be suppressed.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of an optical waveguide according to the present invention.

FIG. 2 is a diagram illustrating an RF sputtering apparatus.

FIGS. 3A to 3H are diagrams illustrating a manufacturing process of an optical waveguide.

FIG. 4 is a diagram showing a grating forming apparatus.

FIG. 5 is a diagram showing a conventional optical waveguide.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 optical waveguide 101 quartz substrate 102 lower cladding 103 core 104 upper first cladding 105 upper second cladding

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Akifumi Hongo 5-1-1, Hidaka-cho, Hitachi City, Ibaraki Prefecture Inside the Opto-System Research Laboratory, Hitachi Cable, Ltd. (72) Inventor Seiichi Kashimura Hidaka-cho, Hitachi City, Ibaraki Prefecture 5-1-1, Hitachi Cable, Ltd., Opto-System Laboratory (72) Inventor Hiroaki Okano 5-1-1, Hidaka-cho, Hitachi, Ibaraki F-term, Hitachi Cable, Ltd., Opto-System Laboratory (reference) 2H047 KA01 KA04 LA02 PA04 PA05 PA21 PA24 PA30 QA04 TA31 TA41

Claims (13)

[Claims] 1. An optical waveguide comprising a core through which light propagates on a substrate, and a lower cladding and an upper first cladding that cover the periphery of the core and have a lower refractive index than the core. The composition of the first clad is Ge
O ₂ doped SiO ₂ , and the core GeO ₂ concentration is c
1, when the GeO ₂ concentration of the lower cladding c2, the GeO ₂ concentration in the upper first cladding was c3, c1> c2, c
An optical waveguide having a relationship of 1> c3. 2. The optical waveguide according to claim 1, further comprising an upper second clad on the upper first clad. 3. The optical waveguide according to claim 1, further comprising an upper second clad having a composition of non-doped SiO ₂ on the upper first clad. 4. The optical waveguide according to claim 1, wherein the thickness of the upper first cladding and the lower cladding is formed to be at least larger than the thickness of the core. 5. The optical waveguide according to claim 1, wherein c2 = c3. 6. The optical waveguide according to claim 1, wherein a grating having a periodic refractive index distribution is formed on the core, the lower clad, and the upper first clad. A core light to 7. A substrate propagates, in the manufacturing method of the optical waveguide and a lower cladding and upper first cladding having a refractive index lower than that of the core covers the periphery of the core, the composition is GeO ₂ Forming a core made of doped SiO ₂ , forming a lower clad having a composition of GeO ₂ doped SiO ₂ , and forming a core of GeO ₂ doped Si ₂
And forming an upper first cladding consisting of O _2, the GeO ₂ concentration in core c1, the lower clad GeO ₂
When the concentration is c2 and the GeO ₂ concentration of the upper first cladding is c3, the relationship of c1> c2 and c1> c3 is satisfied. 8. The optical waveguide according to claim 7, wherein the GeO ₂ -doped SiO ₂ film of the core, the lower clad, and the upper first clad is formed by a sputtering method or a plasma-excited chemical vapor deposition method. Production method. 9. When a GeO ₂ -doped SiO ₂ film of a core, a lower clad and an upper first clad is formed by a sputtering method, independently controlled RF high-frequency power is applied to a GeO ₂ -doped SiO ₂ target. 9. The method according to claim 7, wherein an independent RF high-frequency power is applied to the substrate. 10. The method according to claim 7, wherein an upper second clad is provided on the upper first clad, and the upper second clad is formed by a plasma-excited chemical vapor deposition method. The manufacturing method of the optical waveguide. 11. The method of manufacturing an optical waveguide according to claim 7, wherein the upper first clad and the lower clad are formed to be thicker than at least the core. 12. The method of manufacturing an optical waveguide according to claim 7, wherein c2 = c3. 13. The method of manufacturing an optical waveguide according to claim 7, wherein a grating having a periodic refractive index distribution is formed on the core, the lower cladding, and the upper first cladding.