JP2001091772A - Waveguide type optical circuit and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waveguide type optical circuit, in which connection loss to an optical fiber is greatly reduced, and its manufacturing method. SOLUTION: A waveguide type optical circuit has a optical waveguide 10 consisting of a core 4 which has input output sections 2 and 3 on a substrate that are connected to the core of an optical fiber and clad which covers the core 4. In the manufacturing method of the circuit, a first core film is heaped up on the substrate, the film is formed into a waveguide pattern, the pattern is etched for several times so as to leave the portions that become the sections 2 and 3 and to form a step section, and a second core film is heaped up to cover the step section. Then, the second core film is etched to make the waveguide pattern so as to form a tapered section 4h on the core 4 of the sections 2 and 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type optical circuit used for an element for an optical transmission module and a method of manufacturing the same, and more particularly, to a waveguide type optical circuit in which an input / output unit core is formed in a tapered shape. The present invention relates to the manufacturing method.

[0002]

2. Description of the Related Art A conventional waveguide type optical circuit will be described with reference to FIGS.

FIG. 6 shows a plan view of a conventional waveguide type optical circuit.

As shown in FIG. 6, this waveguide type optical circuit is formed by laminating a silica-based glass as a core and a silica-based glass as a clad on a glass substrate 11 so as to cover the core. In addition, a branched waveguide 20 branched in three stages is formed.

One input port (input section) 12 is formed at one end of the branch source of the branch waveguide 20, and eight output ports (output sections) 1 are formed at the other end of the branch destination.
3 are formed.

FIG. 7 is an enlarged perspective view of a region A in which the input / output units 12 and 13 are formed.

As shown in FIG. 7, each of the input / output sections 12 and 13 of the waveguide type optical circuit has a connection loss with the optical fiber as the relative refractive index difference increases when the optical fiber and the element are mounted. In order to reduce the connection loss, the core 14 is formed in a tapered shape that becomes wider toward the input / output section end face in the width direction of the core 14.

[0008]

However, in the waveguide type optical circuit, the height direction of the core 14 is greatly different from the core diameter of the optical fiber only by forming the core 14 in a tapered shape in the width direction thereof. Therefore, there is a limit in reducing the connection loss.

SUMMARY OF THE INVENTION An object of the present invention is to provide a waveguide type optical circuit and a method for manufacturing the same, which can greatly reduce the connection loss with an optical fiber.

[0010]

According to a first aspect of the present invention, there is provided an optical waveguide comprising: a core having an input / output portion connected to a core of an optical fiber on a substrate; and a cladding covering the core. In the waveguide type optical circuit for an optical transmission module in which a wave path is formed, the input / output portion of the core is formed in a tapered shape that becomes wider toward the end face of the input / output portion in both the width direction and the height direction.

According to a second aspect of the present invention, the core width and the core height other than the input / output section are formed to be smaller than the core diameter of the connection section of the optical fiber connected to the input / output section. .

According to a third aspect of the present invention, the angle of the taper is in the range of 0.3 ° to 1 °.

According to a fourth aspect of the present invention, there is provided a method of manufacturing a waveguide type optical circuit, wherein an optical waveguide comprising a core having an input / output portion connected to a core of an optical fiber and a clad covering the core is formed on a substrate. After depositing a first core film on the substrate, the first core film is formed in a waveguide pattern, and the waveguide pattern is etched a plurality of times so that a portion serving as an input / output portion remains, and the step is performed. After forming a stepped portion having a shape of a circle and depositing a second core film so as to cover the stepped portion, the core of the input / output portion is etched by etching the second core film so as to form the waveguide pattern. This is a method of forming a tapered shape.

According to a fifth aspect of the present invention, the first core film comprises:
This is a stepwise etching method in which the angle between the length direction and the height direction of the core is in the range of 0.3 ° to 1 °.

According to a sixth aspect of the present invention, the second core film comprises:
The mode field mismatch loss with the optical fiber is 0.
This is a method of depositing a core having a thickness of less than 1 dB / 1.

According to the above configuration, the core width and the core height of the input / output portion of the waveguide are equal to the core diameter of the optical fiber, and the core cross-sectional shape of the waveguide is close to the core cross-sectional shape of the optical fiber. Become. As a result, the mode field diameter increases, and the connection loss with the optical fiber is reduced.

[0017]

Next, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a plan view of a waveguide type optical circuit according to the present invention.

As shown in FIG. 2, the waveguide type optical circuit is formed by laminating a core and a clad on the glass substrate 1 so as to cover the core, and also has a branch shape branched in three stages. Waveguide 10 is formed.

The core of the waveguide 10 has a refractive index of 1.4 so that the relative refractive index difference between the core and the clad is 0.5%.
The cladding is made of quartz glass having a refractive index of 1.458.

One input port (input section) 2 is formed at one end of the branch source of the branch waveguide 10, and eight output ports (output sections) 3 are formed at the other end of the branch destination. Are formed.

FIG. 1 is an enlarged perspective view of a region A in which the input / output units 2 and 3 are formed.

As shown in FIG. 1, the core width and the core height of the core 4 other than the input / output sections 2 and 3 of the waveguide 10 are the same as those of the connection section of the optical fiber connected to the input / output sections 2 and 3. It is formed narrower according to the diameter. For example, for single mode transmission, the core film and the core height are 6 μm.
Formed. The mode field diameter at this time is 7.28
μm.

Each of the input / output units 2 and 3 of the waveguide type optical circuit
When mounting the optical fiber and the element, the connection loss with the optical fiber increases as the relative refractive index difference increases, so that the connection loss is reduced in the width direction and the height direction of the core 4. The tapered portions 4h and 4w are formed so as to become wider toward the input / output unit end faces 2a and 3a. The angle of this tapered portion ranges from 0.3 ° to 1 °.

Next, the manufacturing method of the present invention will be described together with the operation in FIG.
This will be described with reference to FIGS. 4A to 4E and FIGS.

FIGS. 3A to 3E are plan views of a substrate to be a waveguide type optical circuit according to the present invention, and FIG.
FIG. 4E is a side view of a substrate serving as a waveguide type optical circuit according to the present invention.

In this embodiment, the relative refractive index difference is 0.5
%, A case where an optical waveguide type optical circuit having a core diameter (width, height) of 6 μm smaller than the core diameter of a general optical fiber by 2 μm will be described.

In manufacturing the waveguide type optical circuit according to the present invention, first, a first core film made of quartz glass is deposited to 2 μm on a glass substrate (first core film formation). Then, a mask pattern (waveguide pattern) for forming a tapered portion in the width direction of the core is formed, and FIG.
As shown in (a), the core film deposited on the glass substrate 31 is etched to form a core 32 having a tapered portion 32w in the width direction.

Thereafter, the glass substrate 31 shown in FIG.
The 2 μm core 32 formed above is masked with tungsten silicide or the like so that the input / output side core part (several hundred μm in length) 32 a is not etched as shown in FIG. 4B, and the remaining core part 32 b Is etched by 0.5 μm. Thereby, as shown in FIG. 3B, the tapered portion 32w in the width direction of the core 32 is etched only in the height direction without being changed.

Further, as shown in FIG. 3C, the input / output side core portion 32a and the core portion 32b etched by 0.5 μm are formed.
Is masked with tungsten silicide or the like to a length of about 50 μm from the end face of the input / output section to prevent etching, and then etched again by 0.5 μm.

Similarly, as shown in FIG. 3D, the input / output side core portion 32a and the core portions 32b and 32c etched by 0.5 μm in two stages are subsequently inserted as shown in FIG. 3E. The output side core part 32a and the core parts 32b to 32d etched at 0.5 μm in three stages are masked with tungsten silicide or the like so as not to be etched, and are sequentially etched in 0.5 μm steps until the glass substrate 31 is exposed. A step-like step portion 33 is formed.

As shown in FIG. 4C, the stairs 33
Is etched so that the angle θ (the angle of the asymptote of the stepped core) between the length direction and the height direction of the core is in the range of 0.3 ° to 1 °. That is, the length 32l of the stepped core portion is formed to be about 100 times the height 32h of the stepped core.

After the step-shaped core is formed, FIG.
As shown in (d), a second core film 34 made of quartz glass having the same refractive index as that of the stepped core (stepped portion 33) is deposited to a thickness of 6 μm (second core film formation). After that, the second core film 34 is etched so as to have the above-described waveguide pattern, and the input / output portion has a tapered core 30.
To form

According to the above process, the waveguide type optical circuit has a height H of the input / output section of 8 μm and a height H of 6 μm except the input / output section.
A μm core 30 can be obtained.

The core 30 thus formed has an asymptote angle θ between the input / output portion and the connection portion of the other cores of 0.3.
Since the taper has a gentle taper of from 1 ° to 1 °, the radiation loss at this tapered portion can be ignored.

Finally, as shown in FIG. 4E, an over clad 40 is deposited on the core 30 to complete the manufacture of the waveguide type optical circuit.

FIG. 5 shows the mode field mismatch loss value with respect to the core diameter of the thus manufactured waveguide type optical circuit.

The core diameter of a general optical fiber is about 8 μm, and the mode field diameter at a wavelength of 1.3 μm is about 9.5 μm. When this optical fiber and the waveguide type optical circuit are connected, the mode field mismatch loss between the optical fiber and the waveguide core is 0.30 dB per location.

On the other hand, as shown in FIG. 5, when the width direction of the core of the input / output portion of the waveguide type optical circuit is tapered to 8 μm, the mode field diameter becomes 7.78 μm.
The mode field mismatch loss between the optical fiber and the waveguide core can be reduced to 0.17 dB per location.

Further, when the height direction of the core of the input / output portion of the waveguide type optical circuit is tapered to 8 μm, the mode field diameter becomes 8.40 μm, and the mode field mismatch loss between the optical fiber and the waveguide core becomes 1 0 per location.
It can be greatly reduced to 08 dB.

As described above, according to the present invention, the mode field mismatch loss with the optical fiber is 0.1%.
It is possible to manufacture a waveguide type optical circuit having a low loss of less than dB and a small radiation loss of the optical circuit.

In this embodiment, an element formed by laminating quartz glass on a glass substrate has been described. However, the present invention is also applicable to an element formed by laminating quartz glass on a Si substrate. It is possible, and the same effects as in the present embodiment can be obtained.

[0043]

In summary, according to the present invention, not only the width direction of the waveguide type optical circuit core but also the height direction of the core are expanded to the same as the mode field diameter of the optical fiber, so that the mode with the optical fiber can be improved. Field mismatch loss can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is an enlarged perspective view of an input / output unit of a waveguide type optical circuit according to the present invention.

FIG. 2 is a plan view of a waveguide type optical circuit showing one embodiment of the present invention.

FIG. 3 is a diagram for explaining a method of manufacturing a waveguide type optical circuit according to the present invention.

FIG. 4 is a diagram for explaining a method of manufacturing a waveguide type optical circuit according to the present invention.

FIG. 5 is a diagram showing the magnitude of mode field mismatch loss with respect to the core diameter.

FIG. 6 is a plan view of a conventional waveguide type optical circuit.

FIG. 7 is a partially enlarged perspective view of the waveguide type optical circuit of FIG. 6;

[Explanation of symbols]

 2 input port (input section) 3 output port (output section) 4 core 4h taper section 10 waveguide

Claims (6)

[Claims] In a waveguide type optical circuit for an optical transmission module, an optical waveguide comprising a core having an input / output unit connected to a core of an optical fiber and a clad covering the core is formed on a substrate. Wherein the input / output section is formed in a tapered shape which becomes wider toward the end face of the input / output section in both the width direction and the height direction. 2. The waveguide type according to claim 1, wherein a core width and a core height other than the input / output section are formed smaller than a core diameter of a connection section of an optical fiber connected to the input / output section. Optical circuit. 3. The waveguide type optical circuit according to claim 1, wherein the angle of the taper is in a range of 0.3 ° to 1 °. 4. A method for manufacturing an optical waveguide circuit, comprising: forming an optical waveguide comprising a core having an input / output portion connected to a core of an optical fiber on a substrate and a clad covering the core; After depositing the first core film, the first core film is formed into a waveguide pattern, and the waveguide pattern is etched a plurality of times so that a portion serving as an input / output portion remains to form a stepped step portion. After forming and depositing a second core film so as to cover the step portion, the second core film is etched so as to have the waveguide pattern, thereby forming the core of the input / output portion in a tapered shape. A method for manufacturing a waveguide-type optical circuit, comprising: 5. The method according to claim 4, wherein the first core film is etched stepwise so that an angle between a length direction and a height direction of the core is in a range of 0.3 ° to 1 °. A method for manufacturing a waveguide type optical circuit. 6. The waveguide type optical circuit according to claim 4, wherein the second core film is deposited to a thickness such that a mode field mismatch loss with the optical fiber is less than 0.1 dB / 1. Manufacturing method.