JP2001056415A - Quartz based optical waveguide and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a quartz based optical waveguide and its production which can decrease the connection loss with another optical waveguide or optical fiber and which has a structure with good reproducibility. SOLUTION: In the production method, an upper core layer 14A is formed by disposing a mask 16 as floated above a substrate 11 on which a lower clad layer 12 and a lower core layer 13A are formed, and then the lower core layer 13A and the upper core layer 14A are simultaneously patterned into a waveguide. Then the upper clad layer 15 is formed. Thus, an upper core 13 having such a structure that the film thickness near the input and output ends is gradually increased to the input and output ends is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a silica-based optical waveguide capable of reducing a connection loss with another optical waveguide or an optical fiber, and a method of manufacturing the same.

[0002]

2. Description of the Related Art With the rapid progress of optical communication, there is an increasing demand for a quartz-based optical waveguide circuit itself to have a large scale and to improve mass productivity by downsizing the optical circuit. To achieve this, the confinement of light in the core may be increased. That is, the bending radius of the optical waveguide can be reduced by strengthening confinement, and the distance between adjacent cores can be reduced. As a result, since individual circuit elements can be made smaller, a large-scale optical circuit in which they are integrated can be manufactured, and the number of optical waveguide circuits that can be manufactured in one process can be increased.

[0003] However, if the confinement of light in the optical waveguide circuit is increased, the coupling loss with other optical components such as optical fibers increases.

A practically promising method for reducing the coupling loss is a spot size conversion structure using a two-layer taper as shown in FIG. 1 (for example, RS Fan and R.A.).
B. Hooker, "Taper Polymer
Single-Mode Waveguides fo
r Mode Transformation ”, IE
EEJ. Lightwave Technology
y, vol. 17, 1999 pp. 466-474
reference).

In FIG. 1, a lower core 3 and an upper core 4 are formed on a lower cladding layer 2 deposited on a substrate 1, and they are buried by an upper cladding layer 5.

In this structure, first, the light confinement is gradually expanded in the horizontal direction in the portion a of the lower core 3, and then the light confinement is gradually expanded in the vertical direction in the portion b of the upper core 4. Thereby, the spot size of light at the input / output end of the waveguide and the spot size of other optical components typified by the optical fiber are made to match, thereby reducing the connection loss between the two.

However, of the parts a and b, the part b
In the above structure, the spot expansion in the vertical direction of light is equivalently realized by changing the width of the waveguide in the horizontal direction.
It is necessary to set the region where the waveguide width changes to be sufficiently long over 1 mm or more.

[0008]

FIG. 2 shows a connection loss histogram between an optical waveguide and a single mode optical fiber according to the conventional structure described above. 0.3 dB as an average value
Although a numerical value of the order is obtained, it can be seen that the value varies greatly and the reproducibility is poor. This is because the conventional structure has the following two manufacturing error factors.

The first factor is due to the structure itself. That is, since the structure of the portion b extends over 1 mm or more, the tip c is sharp and thin. However, in practice, the tip c is rounded instead of an acute angle, or falls or bends during processing. And cannot always reproduce the same structure.

The second factor is a pattern shift between the lower core 3 and the upper core 4. That is, since a two-stage reactive ion etching process must be performed to produce a two-layer tapered structure, when the waveguide pattern of the upper core 4 is formed by photolithography, it completely matches the pattern of the lower core 3. I have to do it. However, since the core expansion width is only about 10 μm, a pattern shift occurs when patterning is actually performed, which causes a variation in connection characteristics.

Both of these two drawbacks result in the problem that it is difficult to fabricate a structure in which the thickness of the core gradually increases in the vertical direction. That is, if the film thickness is gradually increased in the first place in the portion b in FIG. 1, it is not necessary to process the upper core 4 at an acute angle, and the upper and lower cores can be formed into a predetermined waveguide pattern by one etching. Can be made into a structure.

An object of the present invention is to provide a silica-based optical waveguide having a structure that can reduce connection loss with another optical waveguide or an optical fiber and has a good reproducibility, and a method of manufacturing the same.

[0013]

According to the present invention, a lower cladding layer formed on a substrate is provided.
A quartz optical waveguide comprising a lower core, an upper core, and an upper cladding layer, the quartz optical waveguide having an upper core having a structure in which a film thickness near an input / output end gradually increases toward an input / output end. suggest.

According to the present invention, a sharp pointed structure in the upper core for realizing the vertical spot expansion of light equivalently by changing the waveguide width in the horizontal direction as in the prior art is not required. Since the upper and lower cores can be patterned by one etching, it is not necessary to perform pattern matching of the upper and lower cores. That is, according to the structure of the present invention, manufacturing errors can be significantly reduced.

In the present invention, a step of forming a lower clad layer on a substrate, a step of forming a lower core layer, and a step of setting a mask so as to float on the substrate on which the lower clad layer and the lower core layer are formed. Forming an upper core layer, forming an upper core and a lower core by simultaneously patterning the upper core layer and the lower core layer with a waveguide, and forming an upper clad layer. A manufacturing method is proposed.

According to the present invention, a mask having a predetermined shape is provided so as to be floated on the substrate on which the lower clad layer and the lower core layer are formed, and the upper core layer is deposited. In place, the upper core layer wraps slightly below the mask. As a result, the boundary portion has a structure in which the film thickness decreases as it goes deeper into the mask, and after the mask is removed, an upper core layer whose film thickness gradually increases toward the input / output end is obtained. That is, according to the present invention, good connection characteristics can be realized with better reproducibility than before.

[0017]

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

In the following embodiment, a case where a quartz glass film other than the upper core layer is formed by using a flame deposition method will be described. However, the present invention is not limited to a method of manufacturing a glass film, and the invention is not limited thereto. A part or all of the parts can be replaced with a sputtering method, a CVD method, or the like. Also,
Although the case of using the sputtering method is described for the production of the upper core layer, it can also be produced by another vapor phase glass film formation method such as a CVD method.

FIG. 3 shows an embodiment of a silica-based optical waveguide having a spot size conversion structure according to the present invention, in which 11 is a substrate, 12 is a lower cladding layer, 13
Is a lower core, 14 is an upper core, and 15 is an upper cladding layer.

FIG. 4 shows a procedure of a method of manufacturing the quartz optical waveguide of the present invention shown in FIG.

First, a lower cladding layer 12 containing SiO ₂ as a main component is deposited on a silicon or quartz substrate 11 by a flame deposition method (A), and then SiO ₂ containing GeO ₂ as a dopant is used as a main component. After the lower core layer 13A was deposited (B), it was vitrified in an electric furnace. The thickness of the lower cladding layer 12 is 20 μm, and the thickness of the lower core layer 13A is 5 μm.

Next, a mask 16 having a predetermined shape is placed on the substrate 11 on which the lower clad layer 12 and the lower core layer 13A are deposited so as to be floated at a distance of 1 mm from the substrate 11 (C). The upper core layer 14A having the same refractive index as the lower core layer 13A
(D). At this time, the upper core layer 14A slightly goes under the mask 16 at a location corresponding to the boundary of the mask 16. As a result, the thickness of the mask 1 is
6 is reduced as it goes deeper.

Then, upper and lower core layers 13A and 14A are simultaneously patterned into a waveguide by reactive ion etching to produce lower core 13 and upper core 14 (E).

Finally, an upper clad layer 15 having the same refractive index as that of the lower clad layer 12 was deposited (F), and vitrification was performed, thereby producing a spot size conversion structure shown in FIG.

The specifications of the optical waveguide used in the present circuit are that the relative refractive index difference between the core and the clad of both the lower core 13 and the upper core 14 is 0.75%, and the cross-sectional dimension is the lower core 13. Has a width of 5 μm × height of 5 μm and the upper core 14 has a width of 5 μm.
μm × 6 μm in height. The width of each of the upper and lower cores at the input and output ends is increased to 11 μm.

FIG. 5 shows the connection loss between the optical waveguide having the spot size conversion structure manufactured as described above and a single mode optical fiber. It can be seen that the reduction in fabrication error has reduced the variation in loss.

In the present invention, the cross section of the core has a width of 5 μm.
m × 5 μm high optical waveguide 11 μm wide × 11 μm high
The purpose of the present invention is to propose and manufacture a spot size enlargement (conversion) structure in which the film thickness gradually increases. It goes without saying that the present invention is applicable even if the cross-sectional size of the optical waveguide structure to be connected is different from that of the present embodiment.

The length of the region where the film thickness increases can be adjusted by changing the distance between the mask and the substrate when depositing the upper core layer. Further, since the present invention relates to the structure of the input / output unit of the optical waveguide, it is not limited to the type of optical waveguide circuit to be manufactured. That is, the present invention can be applied to input / output units of all optical waveguide circuits that require the structure of the present invention.

[0029]

As described above, according to the quartz optical waveguide of the present invention, the upper core having the structure in which the film thickness near the input / output end gradually increases toward the input / output end is provided. Since the sharp tip structure of the conventional upper core is not required, a manufacturing error due to the deformation of the tip structure disappears. Further, since the upper core and the lower core can be simultaneously processed so as to have a predetermined waveguide pattern, pattern matching between the upper and lower cores is not required, and a manufacturing error due to a pattern shift is eliminated.

According to the manufacturing method of the present invention, a mask having a predetermined shape is provided so as to float on the substrate on which the lower clad layer and the lower core layer are formed, and the upper core layer is deposited. It is possible to produce a spot size conversion structure in which the core thickness required by the proposed structure gradually increases. That is, according to the present invention, it is possible to reduce the variation in connection loss characteristics due to the manufacturing error found in the conventional structure, and to realize good connection characteristics as a whole with higher reproducibility than before.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an optical waveguide having a conventional spot size conversion structure.

FIG. 2 is a diagram showing a connection loss histogram between a conventional optical waveguide and a single mode optical fiber.

FIG. 3 is a diagram showing an example of an embodiment of a silica-based optical waveguide according to the present invention.

FIG. 4 is a view showing a procedure of a method for manufacturing a silica-based optical waveguide according to the present invention.

FIG. 5 is a diagram showing a connection loss histogram between the silica-based optical waveguide of the present invention and a single-mode optical fiber.

[Explanation of symbols]

11: substrate, 12: lower cladding layer, 13: lower core,
13A: lower core layer, 14: upper core, 14A: upper core layer, 15: upper cladding layer, 16: mask.

Claims (2)

[Claims] 1. A quartz optical waveguide comprising a lower cladding layer, a lower core, an upper core, and an upper cladding layer formed on a substrate, wherein a film thickness near an input / output end gradually increases toward the input / output end. A quartz optical waveguide comprising an upper core having an increasing structure. 2. A step of forming a lower clad layer on a substrate, a step of forming a lower core layer, and a step of setting a mask so as to float on the substrate on which the lower clad layer and the lower core layer are formed. Forming an upper core layer and a lower core layer at the same time by forming an upper core layer and a lower core layer into a waveguide pattern, and forming an upper clad layer. Manufacturing method.