JPH06174952A - Substrate type optical waveguide and its production - Google Patents

Abstract

PURPOSE:To easily produce the smooth optical waveguide having an approximately circular shape in section. CONSTITUTION:This substrate type optical waveguide is constituted by providing the optical waveguide 14 having the approximately circular shape in section on a substrate 12 and providing a base material layer 15 narrower in width than the optical waveguide 14 between the substrate 12 and the optical waveguide 14. The base material layer 15 consists of glass having a high softening point and the optical waveguide 14 consists of glass having the refractive index higher than the refractive index of the base material layer 15 and the softening point lower than the softening point of the base material layer. The base material layer 15 and the optical waveguide layer 14 are successively laminated on the substrate 12. The base material layer 15 and the optical waveguide layer 14 are then selectively etched in such a manner that the width of the base material layer 15 is narrower than the optical waveguide layer 14. The optical waveguide layer 14 is then softened by a heat treatment at the prescribed temp. below the softening point of the base material layer 15, by which the optical waveguide is produced. Then, scattering loss is decreased in a single mode and further, the coupling loss with an optical fiber is decreased as well in the case of a multimode. In addition, the reflection loss of the optical waveguide 14 is decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lossless substrate type optical waveguide used for optical communication, an optical information processing system and the like, and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, in the fields of optical communication systems, optical information processing systems, etc., there is a growing demand for higher speed and smaller size. The demand for smaller size, higher speed, and higher reliability is increasing. And, as one of these optical devices, there is a substrate type optical waveguide 1 as shown in FIG. 5, for example. In this substrate type optical waveguide 1, an optical waveguide 3 having a rectangular cross section is formed on a silicon (Si) substrate 2, and the optical waveguide 3 is embedded by an embedding layer 4. The optical waveguide 3 is made of quartz (SiO ₂ ) glass having a high refractive index, and the embedding layer 4 is made of quartz glass having a lower refractive index than the optical waveguide 3. This substrate-type optical waveguide 1 has excellent compatibility with a silica-based optical fiber that is widely used in optical communication systems, and also has various characteristics such as low loss, high reliability, and small size.

As a method of manufacturing the substrate type optical waveguide 1, a method of forming the optical waveguide 3 on the silicon substrate 2 by the FHD method, LP (Low Pressure) CVD method or the like is generally used. . For example, in order to form the optical waveguide 3 on the silicon substrate 2 by the FHD method, silica glass powder having a high refractive index is flame-deposited on the silicon substrate 2,
Next, the silicon substrate 2 is heated to about 1400 ° C. to sinter the quartz glass powder to form an optical waveguide layer. Then, the optical waveguide layer is patterned by photolithography to form the optical waveguide 3.

Further, the silicon substrate 2 is formed by the LPCVD method.
In order to form the optical waveguide 3 on the silicon substrate 2, in order to improve the adhesion between the silicon substrate 2 and the optical waveguide layer and to obtain a smooth surface, the silicon substrate 2 heated to 300 to 600 ° C. has a high refractive index. Quartz glass is deposited to form an optical waveguide layer. Then, the optical waveguide layer is patterned by photolithography to form the optical waveguide 3.

[0005]

However, in the substrate type optical waveguide 1, since the optical waveguide 3 has a rectangular cross section, scattering loss occurs in the single mode, and in the multimode, the optical fiber 3 is further separated from the optical fiber. There is a problem that coupling loss occurs in the. Further, in the method for manufacturing the substrate type optical waveguide 1, since the optical waveguide layer is patterned by photolithography to produce the optical waveguide 3, the cross-sectional shape of the optical waveguide 3 is not limited to a rectangular shape or a trapezoidal shape. However, there is a problem that a circular or elliptical shape cannot be manufactured.

The present invention has been made in view of the above circumstances, and provides a substrate-type optical waveguide without loss and a method for manufacturing the same by making the cross-sectional shape of the optical waveguide substantially circular. is there.

[0007]

In order to solve the above problems, the present invention adopts the following substrate type optical waveguide and its manufacturing method. That is, the substrate type optical waveguide according to claim 1, wherein an optical waveguide having a substantially circular cross section is provided on the substrate, and a base layer having a width narrower than the optical waveguide is provided between the substrate and the optical waveguide. The base material layer is made of glass having a high softening point, and the optical waveguide is made of glass having a higher refractive index and a lower softening point than the base material layer.

The substrate type optical waveguide according to claim 2 is
The substrate type optical waveguide according to claim 1 is characterized in that an embedded layer made of glass having a lower refractive index and a higher softening point than the optical waveguide is provided around the base material layer and the optical waveguide.

According to a third aspect of the present invention, there is provided a substrate type optical waveguide manufacturing method, wherein a substrate layer made of high softening point glass is provided on a substrate.
An optical waveguide layer made of glass having a higher refractive index and a lower softening point than the base layer is sequentially laminated, and then the base layer and the optical waveguide layer are arranged so that the width of the base layer is narrower than that of the optical waveguide layer. Characterized in that the waveguide layer is selectively etched and then heat-treated at a predetermined temperature not higher than the softening point of the base material layer to soften the optical waveguide layer to form an optical waveguide having a substantially circular cross section. There is.

A method of manufacturing a substrate type optical waveguide according to a fourth aspect is the method of manufacturing a substrate type optical waveguide according to the third aspect, wherein the substrate layer and the optical waveguide have a lower refractive index than the optical waveguide. Rate and high softening point glass is deposited, then
It is characterized in that the deposited glass is heat-treated at a predetermined temperature higher than the softening point of the deposited glass to soften the deposited glass to form an embedded layer.

According to a fifth aspect of the present invention, there is provided a method of manufacturing a substrate type optical waveguide, wherein a substrate layer made of high softening point glass is provided on a substrate.
An optical waveguide layer made of glass having a higher refractive index and a lower softening point than the base layer is sequentially laminated, and then the base layer and the optical waveguide layer are arranged so that the width of the base layer is narrower than that of the optical waveguide layer. The waveguide layer is selectively etched, and then a glass having a lower refractive index and a higher softening point than the optical waveguide layer is deposited around the base layer and the optical waveguide layer, and then the softening point of the deposited glass is deposited. Heat treatment at the following predetermined temperature to soften the optical waveguide layer to form an optical waveguide having a substantially circular cross section, and then heat treatment at a predetermined temperature of the softening point of the deposited glass or higher,
It is characterized in that the deposited glass is softened to form a buried layer.

[0012]

In the substrate type optical waveguide according to claim 1 of the present invention,
By providing an optical waveguide having a substantially circular cross section made of glass having a higher refractive index than the base material layer on the substrate, scattering loss is reduced in the case of single mode, and further in the case of multimode, the optical fiber It also reduces the coupling loss between them.

Further, in the substrate type optical waveguide according to a second aspect of the present invention, an embedded layer made of glass having a refractive index lower than that of the optical waveguide is provided around the base material layer and the optical waveguide.
The reflection loss of the optical waveguide is reduced.

Further, in the method of manufacturing a substrate type optical waveguide according to a third aspect of the present invention, the ridged base material layer and the optical waveguide layer are heat-treated at a predetermined temperature below the softening point of the base material layer, The optical waveguide layer is softened, and due to the surface tension, the optical waveguide has a substantially circular cross section and is smooth.

In the method of manufacturing a substrate type optical waveguide according to a fourth aspect, glass having a lower refractive index and a higher softening point than the optical waveguide is deposited around the base material layer and the optical waveguide, and then this deposition is performed. By heat-treating at a predetermined temperature equal to or higher than the softening point of the formed glass, the deposited glass is softened and becomes an embedded layer.

Further, in the method for manufacturing a substrate type optical waveguide according to a fifth aspect, glass having a higher softening point than the optical waveguide layer is deposited around the base material layer of the ridge and the optical waveguide layer, and then, By heat-treating at a predetermined temperature equal to or lower than the softening point of the deposited glass, the optical waveguide layer is softened to form an optical waveguide having a substantially circular cross section due to surface tension. Then, by heat-treating at a predetermined temperature equal to or higher than the softening point of the deposited glass, the deposited glass is softened to form an embedded layer.

[0017]

1 is a front sectional view showing a substrate type optical waveguide 11 according to an embodiment of the present invention. This substrate type optical waveguide 11
Is provided with a cladding layer 13 on the entire upper surface 12a of the substrate 12, an optical waveguide 14 having a substantially circular cross section is provided on the cladding layer 13, and the optical waveguide is provided between the cladding layer 13 and the optical waveguide 14. 14 is provided with a protruding base material layer 15 having an inverted trapezoidal cross section, and the base material layer 15 and the optical waveguide 14 are provided.
A buried layer 16 is provided around the. Substrate 12 is 1
It is made of a material that can withstand temperatures above 800 ° C.
For example, a silicon substrate, a quartz substrate, a sapphire substrate or the like is preferably used.

The cladding layer 13 is made of silica glass having a low refractive index, the base layer 15 is made of silica glass having a low refractive index and a high softening point, and the optical waveguide 14 is made of silica glass having a high refractive index and a low softening point. The burying layer 16 is made of quartz glass, and is made of quartz glass having a lower refractive index and a higher softening point than the optical waveguide 14. The quartz glass is phosphorus (P),
Addition of aluminum (Al), germanium (Ge), titanium (Ti) or the like increases the refractive index, and addition of boron (B), fluorine (F) or the like decreases the refractive index,
Further, there is a property that the softening point decreases when the total addition amount of these additives increases and the softening point increases when the total addition amount decreases. Therefore, by changing the ratio of the additive for increasing the refractive index and the additive for decreasing the refractive index,
The refractive index of the quartz glass can be a predetermined refractive index. Further, the softening point of the quartz glass can be set to a predetermined softening point by changing the total addition amount of these additives.

In this substrate type optical waveguide 11, the optical waveguide 1
Since the cross section of 4 is substantially circular, the scattering loss is reduced in the case of the single mode, and the coupling loss with the optical fiber is further reduced in the case of the multi mode. Further, by providing the buried layer 16, the reflection loss of the optical waveguide 14 is reduced.

Next, a method of manufacturing the substrate type optical waveguide 11 will be described with reference to FIG. First, the clad layer 13 is formed on the substrate 12, and the FHD method or the L method is performed on the clad layer 13.
The base material layer 21 and the optical waveguide layer 22 are sequentially laminated by the PCVD method ((a) in the same figure). Next, the base material layer 21 and the optical waveguide layer 22 are processed by reactive ion etching (RIE) to form a ridge having an inverted trapezoidal cross section in which the width of the base material layer 21a (15) is narrower than the width of the optical waveguide layer 22a. ((B) of the same figure).
Next, the base material layer 15 and the optical waveguide layer 22a are attached to the base material layer 1
Heat treatment is performed at a predetermined temperature not higher than the softening point of No. 5 to soften the optical waveguide layer 22a to obtain the optical waveguide 14 having a substantially circular cross section due to surface tension (FIG. 7C). Here, the optical waveguide layer 22a is softened and the cross section is deformed into a substantially circular shape by the surface tension, and the optical waveguide 14 having a substantially circular cross section and being smooth is formed.

Next, the base layer 15 and the optical waveguide 14
A glass 23 having a lower refractive index and a higher softening point than the optical waveguide 14 is deposited around the glass. Then this deposited glass 2
Heat treatment is performed at a predetermined temperature equal to or higher than the softening point of No. 3, and the deposited glass 23 is softened to form the embedded layer 16 (FIG. 3D). By the above, the substrate type optical waveguide 11 can be manufactured. According to this method, the optical waveguide layer 22a is heat-treated to easily manufacture the optical waveguide 14 having a substantially circular cross section, and the base material layer 15 and the optical waveguide layer 22a can be manufactured with extremely high accuracy. Since it can be manufactured, the diameter of the optical waveguide 14 also becomes extremely highly accurate.

As described above, according to the substrate type optical waveguide 11 of the above embodiment, since the optical waveguide 14 having a substantially circular cross section is provided on the substrate 12, the scattering loss is reduced in the single mode. In the case of multimode, the coupling loss with the optical fiber can be further reduced. Further, since the embedding layer 16 is provided around the base material layer 15 and the optical waveguide 14, the reflection loss of the optical waveguide 14 can be reduced.

Further, according to the method of manufacturing the substrate type optical waveguide 11 of the above embodiment, the ridged base layer 15 and the optical waveguide layer 2 are provided.
Since 2a is heat-treated at a predetermined temperature equal to or lower than the softening point of the base material layer 15, the optical waveguide 14 having a substantially circular cross section and being smooth can be easily manufactured. In addition, the base material layer 15
Further, a glass 23 having a lower refractive index and a higher softening point than the optical waveguide 14 is deposited around the optical waveguide 14, and then heat-treated at a predetermined temperature equal to or higher than the softening point of the deposited glass 23. The buried layer 16 can be easily formed around the layer 15 and the optical waveguide 14.

FIG. 3 is a diagram showing another embodiment of the method for manufacturing the substrate type optical waveguide 11. In this method,
The clad layer 13 is formed on the substrate 12, and the clad layer 1 is formed.
The base material layer 21 and the optical waveguide layer 22 are sequentially laminated on the substrate 3 by the FHD method or the LPCVD method (FIG. 7A). Then R
The base material layer 21 and the optical waveguide layer 22 are processed by IE to form a ridge having an inverted trapezoidal cross section in which the width of the base material layer 21a (15) is narrower than the width of the optical waveguide layer 22a (FIG. 2B). Then
Around the base layer 15 and the optical waveguide layer 22a, a glass 23 having a lower refractive index and a higher softening point than the optical waveguide layer 22a is deposited (FIG. 7C).

Next, heat treatment is performed at a predetermined temperature below the softening point of the deposited glass 23, and the optical waveguide layer 22a is formed.
Is softened to form an optical waveguide 14. Here, the optical waveguide layer 22a is softened and the cross section is deformed into a substantially circular shape by the surface tension, and the optical waveguide 14 having a substantially circular cross section is formed. Further, the embedded glass 1 is heat-treated at a predetermined temperature equal to or higher than the softening point of the deposited glass 23 to soften the deposited glass 23.
6 ((d) in the figure). An example of this temperature profile is shown in FIG.

Through the above steps, the substrate type optical waveguide 11 can be manufactured. Also in this method, the same actions and effects as those of the manufacturing method of the above embodiment can be obtained. Moreover, by incorporating a program for holding the glass 23 at a temperature below the softening point and a temperature above the softening point for a certain period of time into one temperature profile, it is possible to perform a plurality of heat treatments with one temperature profile. Target.

[0027]

As described above, according to the substrate type optical waveguide of the first aspect of the present invention, the optical waveguide having a substantially circular cross section is provided on the substrate, and the space between the substrate and the optical waveguide is provided. A base layer having a width narrower than that of the optical waveguide is provided, the base layer is made of glass having a high softening point, and the optical waveguide is made of glass having a higher refractive index and a lower softening point than the base layer. Therefore, the scattering loss can be reduced in the single mode, and the coupling loss with the optical fiber can be further reduced in the multimode.

Further, according to the substrate type optical waveguide of claim 2, an embedding layer made of glass having a lower refractive index and a higher softening point than the optical waveguide is provided around the base material layer and the optical waveguide. Therefore, the reflection loss of the optical waveguide can be reduced.

Further, according to the manufacturing method of the substrate type optical waveguide of the third aspect, the base material layer and the optical waveguide layer of the ridge are heat-treated at a predetermined temperature below the softening point of the base material layer. ,
It is possible to easily manufacture a smooth optical waveguide having a substantially circular cross section.

Further, according to the method of manufacturing a substrate type optical waveguide of claim 4, glass having a lower refractive index and a higher softening point than the optical waveguide is deposited around the base layer and the optical waveguide.
Then, since the heat treatment is performed at a predetermined temperature equal to or higher than the softening point of the deposited glass, the embedding layer can be easily formed around the base material layer and the optical waveguide.

Further, according to the method of manufacturing a substrate type optical waveguide of claim 5, glass having a lower refractive index and a higher softening point than the optical waveguide layer is provided around the ridge base material layer and the optical waveguide layer. Since they are deposited and then heat-treated at a predetermined temperature equal to or lower than the softening point of the deposited glass, an optical waveguide having a substantially circular cross section and a smooth cross section can be easily manufactured. Moreover, since the deposited glass is heat-treated at a predetermined temperature equal to or higher than the softening point, an embedding layer can be easily formed around the base material layer and the optical waveguide. Moreover, since two heat treatments can be performed with one temperature profile,
It is efficient.

[Brief description of drawings]

FIG. 1 is a front sectional view showing a substrate type optical waveguide according to an embodiment of the present invention.

FIG. 2 is a process drawing showing a method for manufacturing a substrate type optical waveguide of the present invention.

FIG. 3 is a process drawing showing another method for manufacturing the substrate type optical waveguide of the present invention.

FIG. 4 is a diagram showing an example of a temperature profile of another manufacturing method of the present invention.

FIG. 5 is a front sectional view showing a conventional substrate type optical waveguide.

[Explanation of symbols]

11 ... Substrate type optical waveguide, 12 substrate, 12a upper surface, 13 clad layer, 14 optical waveguide, 15 base material layer, 16 embedding layer, 2
1 base material layer, 22 optical waveguide layer, 23 low folding rate and high softening point glass.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Wada 1440 Rokuzaki, Sakura-shi, Chiba Fujikura Co., Ltd.Sakura factory (72) Ryozo Yamauchi 1440 Rokuzaki, Sakura-shi, Chiba Fujikura Sakura Co., Ltd.

Claims (5)

[Claims] 1. An optical waveguide having a substantially circular cross section is provided on a substrate, and a base layer having a width narrower than that of the optical waveguide is provided between the substrate and the optical waveguide, and the base layer has a high softening point. Substrate optical waveguide, wherein the optical waveguide is made of glass having a higher refractive index and a lower softening point than the base material layer. 2. The substrate type optical waveguide according to claim 1, wherein an embedded layer made of glass having a lower refractive index and a higher softening point than the optical waveguide is provided around the base material layer and the optical waveguide. A substrate-type optical waveguide characterized by: 3. A substrate layer made of glass having a high softening point and an optical waveguide layer made of glass having a higher refractive index and a lower softening point than the substrate layer are sequentially laminated on a substrate, and then the substrate layer The base material layer and the optical waveguide layer are selectively etched so that the width is narrower than the width of the optical waveguide layer, and then heat treated at a predetermined temperature not higher than the softening point of the base material layer, A method of manufacturing a substrate-type optical waveguide, comprising softening a layer to form an optical waveguide having a substantially circular cross section. 4. The method for manufacturing a substrate type optical waveguide according to claim 3, wherein glass having a lower refractive index and a higher softening point than the optical waveguide is deposited around the base material layer and the optical waveguide, and then, A method for manufacturing a substrate-type optical waveguide, comprising heat-treating at a predetermined temperature equal to or higher than the softening point of the deposited glass to soften the deposited glass to form an embedded layer. 5. A base material layer made of glass having a high softening point and an optical waveguide layer made of glass having a higher refractive index and a lower softening point than the base material layer are sequentially laminated on a substrate, and then the base material layer is formed. The base material layer and the optical waveguide layer are selectively etched so that the width is narrower than the width of the optical waveguide layer, and then the refractive index around the base material layer and the optical waveguide layer is lower than that of the optical waveguide layer. And a glass having a high softening point is deposited, and then heat-treated at a predetermined temperature equal to or lower than the softening point of the deposited glass to soften the optical waveguide layer to form an optical waveguide having a substantially circular cross section, and then, A method for manufacturing a substrate-type optical waveguide, comprising heat-treating at a predetermined temperature equal to or higher than the softening point of the deposited glass to soften the deposited glass to form an embedded layer.