JP2006030426A - Stacked light branching waveguide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a branching loss by eliminating a gap at a branch point which causes increase of loss in an optical branching circuit. <P>SOLUTION: A quartz stacked optical branching waveguide in which a lower clad layer 12 is present on a substrate 11 and an input waveguide 111 formed on the lower clad layer 12 is branched into two branched waveguides 113, 114 at least one of which is bent, is characterized in that the input waveguide 111 is constituted of two or more core layers stacked in a direction vertical to the substrate 11, and any of the branched waveguides 113, 114 is constituted of at least one of the stacked core layers, and no gap is present at a branch point 112 to the input waveguide 111 of the branched waveguides 113, 114. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a laminated optical branching waveguide used for multi-branching an optical transmission signal in optical communication. Specifically, the present invention provides an optical branching waveguide that reduces branching loss and has low loss in an optical branching circuit.

In response to the recent increase in traffic on the Internet, the development of optical fiber networks has been rapidly advanced.
Among these, a network that can cover a wide area at low cost by sharing one optical fiber transmission line among a plurality of users is desired.

The 8-branch element, 16-branch element, and 32-branch element that play an important role in such a communication network are called splitters.
Considering the expansion of the optical fiber communication network in the near future, a large-scale optical splitter having a branch number of 100 or more is required.
Splitters can be roughly classified into bulk type, fiber type, and planar lightwave circuit type.

In particular, the planar lightwave circuit type is constituted by an optical waveguide on a substrate and has high reliability.
The manufacturing method has the advantage that it can be mass-produced on a flat substrate by using the microfabrication technology cultivated in the semiconductor industry in recent years such as optical waveguide film deposition, photolithography, dry etching, etc. Furthermore, it has reproducibility. It is widely used as a splitter because it has advantages such as small size integration possibility.

Conventionally, a Y-branch type is known as a planar lightwave circuit type splitter.
In this structure, Y branch waveguides are connected in multiple stages, and the configuration is simple and easy to design.
FIG. 6A is a plan view of a conventional planar Y-branch waveguide as viewed from the upper surface (vertical direction of the substrate), and FIG. 6B is an enlarged view of a two-dot chain line portion A surrounding the branch point. This is shown (see Patent Document 1).

In the conventional planar branch, as shown in FIG. 6A, the input waveguide 1 is branched into two curved branch waveguides 2 and 3 at a branch point 4.
Here, in the manufacturing process, the gap 5 always exists at the branch point 4 as shown in FIG. 6B due to the problem of the resolution at the time of mask production around the branch point, the mask exposure limit, and the processing accuracy.

The gap 5 causes radiation of light to the cladding layer other than the core at the branch point 4 and is a major cause of an increase in branch loss.
When the splitters are arranged in multiple stages as two or more branching splitters, the loss in the gap 5 further accumulates to generate a large loss.
Therefore, it is strongly desired to reduce these branching losses by minimizing the gap 5.
JP-A-5-11130

  An object of the present invention is to provide a laminated optical branching waveguide having a small branching loss by eliminating a gap at a branching point that has caused an increase in loss in the conventional optical branching circuit described above.

  The laminated optical branching waveguide according to claim 1 of the present invention that solves the above-described problem has a lower clad layer on a substrate, and the input waveguide formed on the lower clad layer has two curved at least one of them. In the quartz-based laminated optical branching waveguide that branches into the branching waveguide, the input waveguide comprises a core layer in which N layers (N is a natural number of 2 or more) are laminated in a direction perpendicular to the substrate, and the branching waveguide is formed. Each of the waveguides includes at least one core layer of the laminated core layers, and there is no gap at a branch point of the branch waveguide with respect to the input waveguide.

  The laminated optical branching waveguide according to a second aspect of the present invention for solving the above-mentioned problems is that, in the first aspect, the refractive index of at least one core layer of the laminated core layers is different from the refractive index of the other core layers. It is characterized by that.

In the conventional optical branch circuit, a gap having a finite length exists at the branch point, and the branch loss is increased.
However, according to the present invention, a branch circuit is constituted by an input waveguide composed of stacked core layers and two branch waveguides in which at least one of the stacked core layers is curved. Thus, branching without a gap can be realized, and an optical branching waveguide with small branching loss can be provided.

  The best mode for carrying out the present invention is the following examples.

A laminated optical branching waveguide according to a first embodiment of the present invention is shown in FIG.
The present embodiment relates to a laminated optical branching waveguide composed of two core layers formed on a flat substrate.
FIG. 1A is a bird's-eye view of a laminated optical branching waveguide according to the present embodiment. FIGS. 1B and 1C are lines AA ′ and BB ′ in FIG. It is sectional drawing. The AA ′ line represents the input side of the branching waveguide, and the BB ′ line represents the output side cross section.

As shown in FIG. 1, a clad layer 20 is provided on a substrate 11, and an input waveguide 111 and branching waveguides 113 and 114 are embedded in the clad layer.
As will be described later, the clad layer 20 includes a lower clad layer 12 (under clad layer) and an upper clad layer (over clad layer) 16 formed thereon.

The input waveguide 111 is formed of a core layer in which N layers (N is 2 in the present embodiment) are stacked in a direction perpendicular to the substrate 11, and each of the branched waveguides 113 is curved (having a certain curvature), Branches to a branch point 112 at 114.
One branching waveguide 113 is composed of a lower layer (layer close to the substrate 11) of the laminated core layer, and the other branching waveguide 114 is composed of an upper layer (layer separated from the substrate 11) of the laminated core layer.

Therefore, in the laminated optical branching waveguide according to this embodiment that branches from the input waveguide 111 to the upper and lower branching waveguides 113 and 114, the gap at the branching point 112 can be made zero. It is possible to greatly reduce the loss due to the gap.
In this embodiment, when viewed from the input waveguide 111 side, the lower branch waveguide 113 is bent in an S shape on the right, and the upper branch waveguide 114 is bent on the left. is there.

However, the branching waveguide in the present invention is not limited to these, and it is sufficient that at least one of the upper and lower branching waveguides is curved.
Further, in the drawing, the core layer composed of upper and lower layers is shown so that the input waveguide 111 is almost equally divided, but the upper and lower ratios are not limited to this.

A fiber was connected to the input and output of the laminated optical branching waveguide according to this example, and the power branching rate was measured.
Except for the coupling loss with respect to the optical fiber, the sum of the power from the two exits was equal to the input power, and no loss at the branching portion could be confirmed.

An example of a method for manufacturing a laminated optical branching waveguide according to an embodiment of the present invention will be described with reference to FIGS. In the following example, a manufacturing method of a branching waveguide in which a laminated core layer branches into two layers is shown.
2A is a plan view of the laminated optical branching waveguide as viewed from above, and FIGS. 2B and 2C are respectively AA ′ and BB ′ in FIG. It is sectional drawing of a line. The same applies to FIGS. 3A, 3B, 3C, 4A, 4B, 4C, and 5A, 5B, and 5C.

First, as shown in FIG. 2, a lower clad layer (under clad) 12 is formed on a substrate 11, and a lower layer core 121 to be a lower layer portion of the input waveguide 111 and a branch waveguide 113 is formed thereon.
In this embodiment, a glass having a relatively low softening temperature is first deposited as a lower clad layer 12 on a silicon substrate 11 by 30 μm, and a lower core 121 (width 9 μm, height is formed by using typical photolithography thereon. 4 μm, difference in refractive index 0.3%).

The produced lower layer core 121 is bent to the right as viewed from the AA ′ plane.
Flame deposition was used for glass deposition. This method is widely used for forming a thick glass thin film.

Next, as shown in FIG. 3, heat treatment was performed on the entire substrate at a temperature (1250 ° C.) at which the lower clad layer 12 positioned below the lower core 121 was sufficiently softened for a predetermined time (3 hours).
The lower core 121 sinks into the cladding layer 12 by this heat treatment.
However, the settlement of the lower core 121 stops at a position where the height of the upper surface of the lower core 121 and the surface of the cladding layer 12 coincide.

This is because the lower core 121 sinks due to surface tension and loses tension when the upper surface of the core and the height of the clad are the same.
As described above, when the lower core 121 is submerged in the lower cladding layer 12, a very flat surface can be obtained without passing through a polishing process or the like.

Subsequently, as shown in FIG. 4, when the upper layer core 122 is deposited thereon, the upper layer portion of the input waveguide 111 of the upper layer core 122 is directly above the lower layer portion of the input waveguide 111 of the lower layer core 121. The upper core 122 was deposited and processed so as to form the same.
The upper core 122 has a width of 9 μm, a height of 4 μm, and a refractive index difference of 0.3%.

Here, the upper and lower layer cores 121 and 122 have the same cross-sectional shape and refractive index difference. However, these are not limited to these values, and may be vertically asymmetric.
When the upper layer core 122 is deposited, the portion that becomes the branching waveguide 114 of the upper layer core 122 is bent to the left as viewed from the AA ′ plane so as not to overlap with the branching waveguide 113 of the lower layer core 121. Was given.

Finally, as shown in FIG. 5, a laminated optical branching waveguide can be manufactured by embedding them in the upper cladding layer 16. The lower clad layer 12 and the upper clad layer 16 constitute the clad layer 20 in FIG.
The laminated branch structure according to the present embodiment uses the subduction phenomenon as compared with the case where the conventional laminated waveguide method using polishing is used, so the laminated optical branch waveguide should be easily produced. Is possible.

That is, in the prior art, after forming the lower layer core 121, the upper layer is subjected to a polishing process in which the lower layer core 121 is buried once in the lower layer branching waveguide and planarized until the upper surface of the lower layer core 121 and the surface of the lower cladding layer 12 coincide. The core 122 must be deposited, which requires an enormous number of processes and leads to an increase in cost.
On the other hand, in the present invention, since the sinking phenomenon is used, such a polishing process is unnecessary, and therefore, the laminated optical branching waveguide can be easily manufactured.

  INDUSTRIAL APPLICABILITY The present invention can be widely used as an optical branching waveguide for branching an optical transmission signal in optical communication. In particular, it can be widely used as a splitter, particularly a large-scale optical splitter, which plays an important role in a rapidly developing optical fiber network.

1A is a bird's-eye view of a laminated optical branching waveguide according to an embodiment of the present invention, and FIGS. 1B and 1C are lines AA ′ and BB ′ in FIG. FIG. It is process drawing which shows the manufacturing method of the lamination | stacking optical branching waveguide which concerns on one Example of this invention. It is process drawing which shows the manufacturing method of the lamination | stacking optical branching waveguide which concerns on one Example of this invention. It is process drawing which shows the manufacturing method of the lamination | stacking optical branching waveguide which concerns on one Example of this invention. It is process drawing which shows the manufacturing method of the lamination | stacking optical branching waveguide which concerns on one Example of this invention. FIG. 6A is a plan view of a conventional optical branch circuit, and FIG. 6B is an enlarged view of a range A surrounded by a two-dot chain line in FIG.

Explanation of symbols

11 Silicon substrate 12 Lower clad layer (under clad layer)
16 Upper clad layer (over clad layer)
20 Cladding layer 111 Input waveguide 112 Branch point 113 Lower branch waveguide 114 Upper branch waveguide 121 Lower core 122 Upper core

Claims (2)

There is a lower clad layer on a substrate, and the input waveguide formed on the lower clad layer is a quartz-based laminated optical branching waveguide that branches into two branched waveguides, at least one of which is curved. Is composed of a core layer in which N layers (N is a natural number of 2 or more) are stacked in a direction perpendicular to the substrate, and each of the branched waveguides is composed of at least one core layer in the stacked core layers, A laminated optical branching waveguide characterized in that no gap exists at a branching point of the branching waveguide with respect to the input waveguide. 2. The laminated optical waveguide according to claim 1, wherein a refractive index of at least one core layer of the laminated core layers is different from a refractive index of another core layer.

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