JPH1138253A - Optical waveguide device and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide device, in which the bending loss does not increase even though the size is reduced, and to provide a manufacturing method of the device. SOLUTION: In the device, clad glass layers 2a and 2b, which are to become the clad, are provided on a substrate 3 and the optical waveguide, into which a core 1 having a refractive index higher than the refractive index of the clad glass, is buried. The core 1 of the optical waveguide is bent with prescribed radii of curvatures Ra and Rb . In a first region I, the ratio of the differences of the refractive indexes of the core 1 and the layers 2a and 2b has a prescribed value. In a second region II, the core 1 is bent with a radius of curvature Rc , which is larger than the radius of curvature of the region I, and a straight shape portion exists in which the ratio of the differences of the refractive indexes of the core and the clad is smaller than the one in the region I and the portion is continuously formed on both sides of the region I.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide device capable of miniaturizing an optical circuit element and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, with the development of optical fiber communication, network complexity and multiplexing of signal wavelengths have been advanced, and the system configuration has been advanced. In such an optical fiber communication system, the importance of an optical circuit element is increasing. The optical waveguide device as one of the optical circuit elements has advantages such as small size and small insertion loss. For example,
As shown in FIG. 7, the optical branching circuit 5 provided on the substrate 52
0, an optical transmission line 5 for guiding the signal light to the optical branching circuit 50
1 is known.

[0003]

As shown in FIG. 7, when the optical transmission line 51 has a bent portion with a radius of curvature R, the minimum radius of curvature R _min is required to prevent the transmission loss of the optical transmission line 51 from increasing. (Approximately 30 mm), and providing such a radius of curvature is against the purpose of miniaturization. On the other hand, as a means for reducing the bending loss, it is effective to increase the relative refractive index difference between the core and the clad. However, when the relative refractive index difference between the core and the cladding is increased, the field distribution mismatch between the core and the cladding increases, and the connection loss between the optical waveguide and the optical fiber increases. As described above, in the prior art, when realizing a small optical waveguide, it is difficult to achieve both a reduction in bending loss and a reduction in connection loss with an optical fiber.

SUMMARY OF THE INVENTION An object of the present invention is to solve such a problem and to provide an optical waveguide device which does not increase bending loss even if it is miniaturized, and a method of manufacturing the same.

[0005]

An optical waveguide device according to the present invention comprises an optical waveguide device having a clad glass layer to be a clad provided on a substrate and a core having a higher refractive index than the clad glass embedded in the clad glass layer. In the optical waveguide device including the waveguide, the optical waveguide is bent at a predetermined radius of curvature, and a first region in which a relative refractive index difference between the core and the clad has a predetermined size, and a radius of curvature larger than the first region. A core that is bent or linear and has a smaller relative refractive index difference between the core and the cladding than the first region, and has a second region continuously formed on both sides of the first region. And

According to the optical waveguide device of the present invention, the relative refractive index difference between the core and the clad in the first region is formed larger than the relative refractive index difference between the core and the clad in the second region disposed on both sides thereof. Therefore, even if an optical waveguide having a small bending radius is formed in the first region having a large relative refractive index difference, an increase in loss due to bending can be suppressed, and at the same time, a small optical waveguide device can be obtained. .

Further, according to the optical waveguide device of the present invention, it is possible to input and output signal light through the second regions arranged on both sides of the first region, and the relative refractive index difference of the second region is equal to the second region. Since it is not as large as the relative refractive index difference in one region, even if an optical fiber or the like is connected to the end of the second region, reflection due to the relative refractive index difference can be prevented.

In the optical waveguide device of the present invention, the relative refractive index difference between the core and the cladding in the first region is increased by irradiating the core in the first region with X-rays to increase the refractive index of the core. It is preferable that the difference be larger than the relative refractive index difference between the core and the clad in the region. Since the refractive index of the core or the clad is proportional to the dose of X-rays, a desired relative refractive index difference can be obtained by adjusting the dose of X-rays.

On the other hand, the cladding in the second region is irradiated with X-rays to increase the refractive index of the cladding, thereby reducing the relative refractive index difference between the core and the cladding in the second region. May be smaller than the relative refractive index difference.

A method of manufacturing an optical waveguide device according to the present invention includes an optical waveguide in which a clad glass layer to be a clad is formed on a substrate, and a core having a higher refractive index than the clad glass is embedded in the clad glass layer. A first region bent in the clad glass layer at a predetermined radius of curvature, and a first region bent at a radius of curvature larger than the first region, or a straight line, and formed on both sides of the first region. A first step of forming an optical waveguide by embedding a core composed of a second region continuously formed in the first region, and irradiating the core of the first region with X-rays to increase the refractive index of the core,
The second is to increase the relative refractive index difference between the core and the cladding in the region.
And a process.

[0011] According to the production method of the present invention, the first step comprises:
The core composed of the first region and the second region is embedded in the clad glass layer on the substrate, and the refractive indices of both are formed substantially uniform. Can be used without doing.

The second step is a method of irradiating the core of the first region with X-rays to increase the refractive index of the core in this portion and forming the relative refractive index difference of the first region larger than that of the second region. is there.
Since the required amount of X-rays can be irradiated to the core of the required portion, the relative refractive index difference between the core and the clad can be adjusted to a predetermined value.

Another method for manufacturing an optical waveguide device according to the present invention is directed to an optical waveguide device in which a clad glass layer to be a clad is formed on a substrate, and a core having a higher refractive index than the clad glass is embedded in the clad glass layer. In the method for manufacturing an optical waveguide device comprising: a first region bent in the clad glass layer with a predetermined radius of curvature, and a first region bent or bent linearly with a radius of curvature larger than the first region. A first step of forming an optical waveguide by embedding a core composed of a second region continuously formed on both sides of the cladding, and irradiating the cladding around the core in the second region with X-rays to increase the refractive index of the cladding. And forming a second step of reducing the relative refractive index difference between the core and the clad in the second region.

According to another manufacturing method of the present invention, in the first step, the core composed of the first region and the second region is embedded in the cladding glass layer on the substrate, and the refractive indexes of both are substantially equal. Because it is formed uniformly, the conventional technology is
It can be used without introducing technology.

In the second step, the cladding in the second region is irradiated with X-rays to increase the refractive index of the cladding, and the relative refractive index difference between the core and the cladding in the second region is reduced by the relative refractive index of the first region. This is a method of forming a layer smaller than the difference in rate. Since the required amount of X-rays can be applied to the required portion of the clad, the relative refractive index difference between the core and the clad can be adjusted to a predetermined value.

[0016]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

FIG. 1 is a perspective view showing the structure of the optical waveguide device according to the present embodiment, and FIG. 2 is a graph showing the refractive index distribution of the optical waveguide device shown in FIG. In FIG. 1, a lower clad layer 2a mainly composed of quartz glass to be a clad and an upper clad layer 2b are formed on a substrate 3, and a quartz having a higher refractive index than the clad is provided between the clad layers 2a and 2b. This is an optical waveguide device including an optical waveguide in which a core 1 mainly composed of glass is arranged.

The core 1 embedded in the optical waveguide bends at predetermined radii of curvature R _a and R _b , and a first region I having a relative refractive index difference between the core and the clad having a predetermined magnitude Δn ₁ is provided. ,
Bent at a large curvature radius R _c from the first region, or a linear, the relative refractive index difference between the core and the clad than the first region I [Delta] n ₂ is small, continuously formed on both sides of the first region I And the second region II. An optical circuit such as an optical coupler and an optical splitter is formed in the first region, and a waveguide such as an optical fiber for inputting and outputting signal light to and from the optical waveguide device is connected to the second region.

In FIG. 1, in order to reduce the size of the optical circuit formed in the first region, it is necessary to incorporate an optical waveguide having a small radius of curvature. By the way, the signal light propagating through the optical waveguide travels while repeating total reflection at the interface between the core and the clad. However, when propagating in a core having a curvature, the angle of incidence on the boundary surface increases, so that some power penetrates into the cladding, causing loss.
Therefore, if the relative refractive index difference between the core and the clad is increased, the transmission loss due to bending does not increase even if the radius of curvature of the optical waveguide is reduced, so that a compact optical waveguide device can be formed. Therefore, the relative refractive index difference of the entire first region of the optical waveguide on which the optical circuit is formed may be increased, or the relative refractive index difference of only the bent portion may be increased. The relative refractive index difference Δn ₁ of the first region I is selectively determined as needed.

On the other hand, the second region is located near the end face of the substrate and is connected to an optical fiber or the like to input and output signal light. Accordingly, if the relative refractive index difference of the second region is different from the relative refractive index difference of the optical fiber, reflection occurs, so that the value is set as good as possible. The relative refractive index difference Δn _{2 in} the second region II is about 0.2 to 0.4%, which is substantially the same as the relative refractive index difference of a commonly used optical fiber.

FIG. 2 is a graph showing a state where different relative refractive index differences exist in one optical waveguide device. FIG. 2 (a) shows a core and a clad in a first region and a second region. Is formed substantially uniformly, and thereafter, the core in the first region is irradiated with X-rays to increase the refractive index (portion indicated by an arrow), and the relative refractive index between the core and the clad in the first region is increased. It is a graph which shows the state which made the difference large. On the other hand, FIG.
In (b), after the refractive indices of the core and the cladding in the first and second regions are formed substantially uniformly, the cladding in the second region is irradiated with X-rays to increase the refractive index of the cladding (indicated by an arrow). (Shown portion), a graph showing a state in which the relative refractive index difference between the core and the clad in the second region is reduced.

When the refractive indices of the core and the clad in the first region and the second region are formed to be substantially uniform first, the structure is simple and the formation can be performed without introducing new equipment and technology. it can. In addition, since a required amount of X-rays can be applied to a required portion of the core or the clad, the relative refractive index difference between the core and the clad can be adjusted to a predetermined value.

Next, a method of manufacturing the optical waveguide device according to the present embodiment will be described with reference to FIGS. FIG. 3 is a cross-sectional view for explaining the first step in this manufacturing method, and shows an example of a method of forming a core and a clad having a substantially uniform refractive index on a substrate.

In FIG. 3A, a silica glass substrate 1
Core layer 1 of silica glass doped with germanium on 1
2 are formed. The core layer 12 is obtained, for example, by depositing glass fine particles generated by flame hydrolysis of silicon tetrachloride and germanium tetrachloride, and heating the fine particle layer to a high temperature to convert it to a transparent glass layer.

In FIG. 3B, on the core layer 12,
Resist pattern 1 having a pattern corresponding to an optical circuit
3 is formed using photolithography.

In FIG. 3C, the resist pattern 1
Using the mask 3 as a mask, the core layer 12 is etched using reactive ion etching to form a core ridge 12a corresponding to the optical circuit pattern.

In FIG. 3D, glass fine particles of silicon tetrachloride generated by the flame hydrolysis method are deposited so as to cover the core ridge 12a having a pattern corresponding to the optical circuit, and the upper clad layer 14 is formed. You. As a result, an optical waveguide having a core and a clad optical circuit having a uniform refractive index is completed.

Next, the second method of the manufacturing method according to the present embodiment will be described.
The steps will be described. FIG. 4 is a cross-sectional view of an apparatus for irradiating the optical waveguide formed in the first step with X-rays to form a desired refractive index distribution.

In FIG. 4, X-rays having a wavelength of 0.12 nm to 0.7 nm are emitted from a synchrotron radiation device (not shown), and are formed through the X-ray intensity modulation mask 31 in the first step described above. The irradiated optical waveguide device 30 is irradiated. The X-ray mask 31 is a support film 31 that transmits X-rays.
a and an X-ray shield layer 31b formed thereon by patterning so as to cover portions other than the core of the first region I.

The synchrotron radiation (SR light) is transmitted from the synchrotron radiation device through the SR light introducing pipe 33 to the S
It is led into the R light irradiation chamber 32. Since the irradiation chamber 32 contains helium at atmospheric pressure, the synchrotron radiation device side of the introduction tube 33 is maintained in an ultra-high vacuum.
A diaphragm 34 is provided in the introduction pipe 33.

Support film 31a of X-ray intensity modulation mask 31
Silicon nitride, silicon carbide, diamond, or the like having mechanical strength and X-ray transmitting ability is used. X-ray shield layer 31
b is a tungsten layer capable of shielding X-rays,
A tantalum layer or the like is used.

By irradiating the core of the optical waveguide with X-rays through such an X-ray mask 31, the refractive index of the core increases according to the pattern. As a result, FIG.
As shown in (a), the distribution of the refractive index of the core in the first region is high and the refractive index of the core at the end of the second region is low.

Up to now, the case where the core portion of the first region is irradiated with X-rays to increase the refractive index of this portion has been described. 2B, a refractive index distribution is formed in which the relative refractive index difference in the first region is large and the relative refractive index difference in the second region is small, as shown in FIG.

Embodiment 1 FIG. 5 is a plan view showing an optical waveguide device in which a directional coupler is formed on a substrate by an optical waveguide. In FIG. 5, the directional coupler 40 includes a substrate 41
According to the method shown in the first step described above, a core was prepared by adding germanium to silica glass, and a clad made of silica glass was formed around the core. The cross-sectional dimension of the core is 8 μm × 8 μm, the relative refractive index difference between the core and the clad is Δn ₂ = 0.3%, and the directional coupler 40 has eight bent portions with a radius of curvature R ₁ = 10 mm. ing. The excess loss of the directional coupler 40 thus formed was 0.7 dB at a wavelength of 1.55 μm. Here, the excess loss refers to a total loss of the output optical power from the two output ports of the directional coupler with respect to the input optical power to the directional coupler.

Then, the core portion near the radius of curvature R ₁ is irradiated with X-rays by using the X-ray irradiator shown in FIG. 4, and the relative refractive index difference between the core and the cladding in this portion is Δn ₁ = 0.
Increased to 6%. As a result, the excess loss of the directional coupler 40 was improved to 0.3 dB at a wavelength of 1.55 μm. By thus increasing the refractive index difference of the curvature portion, since the excess loss by reducing the radius of curvature R ₁ is not increased, it was possible to form an optical waveguide device in size.

Embodiment 2 FIG. 6 is a plan view showing an optical waveguide device in which an optical branch is formed on a substrate by an optical waveguide. In FIG. 6, an optical splitter 50 for dividing input light into eight light beams
The optical transmission line 51 connected to the input end of the optical splitter 50 is made of a core made of silica glass with germanium added to the substrate 52 by the method shown in the above-described first step, and silica glass on the outer periphery of the core. It was made by cladding. The cross-sectional dimension of the core is 7 μm × 7 μm, the relative refractive index differences between the core and the clad are all Δn ₂ = 0.6%, and the optical transmission line 51 has two bent portions with a radius of curvature R ₂ = 10 mm. The bent portions are each bent at a right angle. The connection loss when the optical waveguide thus formed is connected to an optical fiber having a relative refractive index difference of 0.6% between the core and the clad is:
At a wavelength of 1.55 μm, the value was 0.3 dB per location.

Next, the X-ray irradiator shown in FIG. 4 is used to irradiate the cladding near the radius of curvature R2 with X-rays, and the relative refractive index difference Δn ₁ between the core and the cladding in this part is obtained.
Reduced to 0.3%. As a result, the connection loss when connecting the optical waveguide and the optical fiber having a relative refractive index difference of 0.6% between the core and the clad is 1 at a wavelength of 1.55 μm.
It has been reduced to 0.1 dB per location.

As described above, the relative refractive index difference at the central portion of the substrate on which the optical component is formed is increased to reduce the radius of curvature R ₂ , and at the same time, the relative refractive index difference between the core and the clad at the peripheral portion is reduced. Adjustment can suppress an increase in connection loss.

[0039]

According to the optical waveguide device of the present invention, since an optical component having a small radius of curvature is formed in the second region where the relative refractive index difference between the core and the clad is large, an increase in loss due to the curvature can be suppressed. At the same time, a small optical waveguide device can be obtained. Further, the optical waveguide device of the present invention has a structure in which the second region having a small relative refractive index difference between the core and the clad is connected to the optical fiber for inputting and outputting the signal light, and therefore, the optical waveguide device has a relative refractive index difference at the connecting portion. An increase in reflection loss can be prevented.

According to the manufacturing method of the present invention, a necessary amount of X-rays is applied to a required portion of the core or clad.
The relative refractive index difference between the core and the clad can be adjusted to a desired value.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating a configuration of an optical waveguide device according to an embodiment.

FIG. 2 is a graph showing a refractive index distribution of the optical waveguide device of FIG.

FIG. 3 is a cross-sectional view for explaining the method for manufacturing the optical waveguide device.

FIG. 4 is a cross-sectional view illustrating a configuration of an X-ray irradiation device.

FIG. 5 is a plan view illustrating a configuration of an optical waveguide device including the directional coupler according to the first embodiment.

FIG. 6 is a plan view illustrating a configuration of an optical waveguide device including an optical splitter according to a second embodiment.

FIG. 7 is a plan view showing a conventional optical waveguide device provided with an optical splitter.

[Explanation of symbols]

1, 12 ... core, 2, 14 ... clad layer, 3, 11,
41, 52: substrate, 13: resist, 30: optical waveguide device, 31: X-ray mask, 32: irradiation chamber, 33 ...
Introduction tube, 34 ... diaphragm, 40 ... directional coupler, 50 ...
・ Optical splitter, 51 ・ ・ ・ Optical transmission line, 53 ・ ・ ・ Optical fiber, 5
4 ... coupling member, R ... radius of curvature, Δn ... relative refractive index difference,
I: first area, II: second area

Claims (5)

[Claims] 1. An optical waveguide device comprising: an optical waveguide in which a clad glass layer to be a clad is provided on a substrate, and wherein a core having a higher refractive index than the clad glass is embedded in the clad glass layer. Is bent at a predetermined radius of curvature, and a first region having a relative refractive index difference between the core and the clad having a predetermined size, and bent at a radius of curvature larger than the first region, or linearly. And a core having a smaller relative refractive index difference between the core and the cladding than the first region, and a second region continuously formed on both sides of the first region. Optical waveguide device. 2. irradiating the core of the first region with X-rays,
The optical waveguide device according to claim 1, wherein the refractive index of the core is formed to be larger than the refractive index of the core in the second region. 3. The method according to claim 1, wherein the cladding in the second region is irradiated with X-rays, and the refractive index of the cladding is formed larger than the refractive index of the cladding in the first region. 3. The optical waveguide device according to claim 1. 4. A method for manufacturing an optical waveguide device comprising an optical waveguide in which a clad glass layer to be a clad is formed on a substrate and a core having a higher refractive index than the clad glass is embedded in the clad glass layer. A first region bent at a predetermined radius of curvature in the clad glass layer, and bent at a radius of curvature larger than the first region;
A first step of forming an optical waveguide by embedding a core that is linear and composed of a second region continuously formed on both sides of the first region; and forming an X-ray on the core of the first region. Irradiating the core to increase the refractive index of the core, and increasing the relative refractive index difference between the core and the clad in the first region. 5. A method for manufacturing an optical waveguide device having an optical waveguide in which a clad glass layer to be a clad is formed on a substrate and a core having a higher refractive index than the clad glass is embedded in the clad glass layer. A first region bent at a predetermined radius of curvature in the clad glass layer, and bent at a radius of curvature larger than the first region;
Or a first step of forming an optical waveguide by embedding a core that is linear and composed of a second region continuously formed on both sides of the first region; and forming a clad around the core in the second region. A second step of irradiating X-rays to increase the refractive index of the cladding and reduce the relative refractive index difference between the core and the cladding in the second region;
A method for manufacturing an optical waveguide device, comprising: