JPH03245107A - Branching/multiplexing optical waveguide circuit - Google Patents

Abstract

PURPOSE:To improve productivity and reproducibility by respectively specifying the radius of curvature in the bending part of branch waveguides, the specific refractive index difference between the respective waveguides and clad and the dull width at the branch point. CONSTITUTION:This circuit has the optical waveguides of a quartz glass formed on a silicon substrate and is formed in the clad and>=2 branch waveguides 12, 13 are communicated with one waveguide 11. The bending part of the branch waveguides 12, 13 is formed to an arc of >=40mm radius R of curvature and the specific refractive index difference between the waveguide 11 and the wave grides 12, 13 and the clad is 0.22 to 0.30%; in addition, the dull width WB at the branch point 14 is <=2.0mum. The branching loss at 1.3mum, 1.55mum wavelength is suppressed to <=0.2dB. The improved productivity and reproducibility and the decreased loss are attained.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a low-loss branching/combining optical waveguide circuit in which the waveguide is easy to manufacture and has excellent reproducibility.

<Prior art> In an optical integrated circuit (35), an optical branching circuit and an optical multiplexing circuit Z are indispensable as elements of the base 111. *A Y-branch optical waveguide circuit having the above-mentioned branch leading waveguide is known□,
) Ruco's Y-branch optical guide e, @ path; Well, compared to a directional coupler, there is no wavelength dependence and the variation in branching ratio is small), so it is expected to be especially applied to ]XN splitters, etc. There is. .

Here, a schematic diagram of an example of a Y-branch optical waveguide circuit is shown in FIG. In the figure, 11 is the main waveguide, ]2゜13 is the branch waveguide,
14 represents these branching points, and 15 represents the Taber portion. This Y
In the branch optical waveguide circuit, the radius of curvature of the branch waveguide 12.13 is R.
The width W of the first main waveguide 11 and the radiation W of the branch waveguides 12 and 13
, 2. W, , are all equal, and near the branch point 14,
The convergence of the wedge-shaped tip surrounded by the branch waveguide 12.13 (
It has an ideal shape in which the round width (hereinafter referred to as round width) is zero. Note that the main waveguide 11 and branch waveguides 12 and 13 are
As shown in FIG. 8, which shows a cross section, it is formed by a core 3 formed in a cladding 2 on a substrate 1.

Such a branching/combining optical waveguide may be fabricated as disclosed in, for example, Japanese Patent Laid-Open No. 105111/1983. That is, 5iCj, , GeCl4. TlC1
4, POCl3. BCj.

chloride as a starting material, for example, as shown in Figure 9,
A cladding glass layer 2 and a core glass layer 3 are sequentially deposited on a substrate 1 made of silicon or the like (a) to (ell), and then etched to form a core part 3a corresponding to the above-mentioned waveguides 11, 12, 13, 15. Etch the core layer 3 of (
d)) Finally depositing the cladding glass layer 2.

<Problems to be Solved by the Invention> Conventionally, there have been no design guidelines regarding structural parameters for reducing the loss of the Y-branch optical waveguide circuit as described above. In particular, it has been thought that the sharper the shape of the branch point 14 is ideally, that is, the closer the rounded radius W8 is to zero, the lower the loss will be. However, in reality, due to reasons such as patterning and etching accuracy, the branch point 14 is fabricated with a finite radius W6 with variations, as shown in FIG. In some cases, the points 14 were made to have an asymmetrical shape. That is, in the past, large branching losses or variations in branching ratios occurred.

In view of these circumstances, it is an object of the present invention to provide a branching/combining optical waveguide with improved manufacturability and reproducibility and low loss.

Means for Solving the Problems〉 The branching/combining optical waveguide according to the present invention that achieves the above object is formed in a cladding on a substrate, and has a branching waveguide double above one waveguide. In the branching/combining optical waveguide circuit in which the branching waveguides are in communication, the bent portion of the branching waveguide is an arc having a radius of curvature of 40+m+ or more, and the relative refractive index difference between the waveguide and the branching waveguide and the cladding is is 0.22 to 0430%, and the rounded width of the branch point is 240 μm or less.

FIG. 1 shows a schematic diagram of an example of the branching/combining optical waveguide circuit of the present invention. In the figure, 11 is the main waveguide, 12 and 13 are branch waveguides, ] 4 is a branch point, and 15 is a tapered part.
By setting the relative refractive index difference between 11°12.13 and the cladding and the rounding radius W of the branching point 14 within the above ranges, fabrication and reproducibility are improved, and a branching/combining optical guide with low loss can be achieved. A wave circuit can be obtained, and the problem of variations in branching ratios can also be solved.

In the present invention, the radius of curvature R of the bending portion of the branch waveguide 12, 13 is set to 40 m or more, thereby reducing the branch loss to 0.
．． This is because it can be suppressed to 1 dB or less. That is, as the radius of curvature R becomes larger, the radiation loss is suppressed and the branching loss monotonically decreases. As shown in FIG. 2, when R is 40 m or more, the branching loss becomes 0.1 dB or less. Muo,
In Figure 2, the width and height of the waveguide are 8 μm, and the relative refractive index difference △ is 0.
．． In the case of 25%, it is displayed.

In addition, in the present invention, the relative refractive index difference △ between the waveguide and the cladding can be reduced to 0.
．． The reason for setting it to 22 to 0.30% is because it is necessary to minimize branch loss.

FIG. 3 shows the relationship between the relative refractive index difference Δ and the branching loss when the radius of curvature R is 50++s, but when the relative refractive index Δ is 0.
The change in branch loss between 22 and 0.30% is 0.2
The optimal value of the relative refractive index △ that can be suppressed to dB or less and at each wavelength, the branching loss is the minimum value 0.1 dB or less is 0.
．． It is shown that it exists between 22 and 0.30%.

Further, in the present invention, the rounding width W8 is set to 2.0 μm or less because within this range, branch loss changes little, and beyond this range, large branch loss increases monotonically. FIG. 4 shows the relationship between the rounding width W and the branching loss when the radius of curvature R is 50w+ and the relative refractive index Δ is 0.25%, and this result also follows the above-mentioned tendency.

Therefore, as described above, by setting the radius of curvature R to 40 m or more, the relative refractive index difference Δ to 0.22 to 030%, and the rounding width of the branch point to within 2.0 μm, for example, wavelengths of 1, 3
μm, 1.55 μm It is clear that the branch loss can be suppressed to 0.2a or less.

<Example> Hereinafter, the present invention will be explained based on examples.

FIG. 5 shows a 1×8 splitter optical circuit using the Y-branch optical waveguide of the present invention. As shown in the figure, this circuit consists of 7
It has a structure using seven molecules in three stages. In the figure, 20 is an input boat, 21 to 28 are eight output boats, and 29 to 3 are eight output boats.
5 and 7 Y-branches.

The manufacturing procedure of such an optical circuit will be explained.

First, a cladding layer with a composition of 5in2 was deposited on a silicon substrate with a diameter of 3mm and a thickness of 700μm using a flame deposition method.
-P2O3-B20. A porous glass film with a composition of Sin2-Gem2-P2O3-B is then deposited as a core layer.
20. of porous glass and then at a temperature of 1390
Heat treatment was carried out for 2 hours in a mixed atmosphere of He and 0□ at ℃.

Next, the entire optical waveguide pattern as described above was formed by reactive di-sodching, and then a cladding layer similar to that described above was formed to cover this core layer. As a result, a 1.times.8 splitter optical circuit having a light guide path shown in FIG. 5 was completed. In addition, each Y branch part 29-35 has a radius of curvature R of the bending part of 40 m or more, and a relative refractive difference Δ of 0.22 to 0.
．． 30%, accented convergence W at the branch point.

is within 20 μm.

Kakaro 1>8 Amazing, Tsuta - Light with a wavelength of 155 μm is introduced from the input port 20 of the optical circuit, and each output port 21 to 28
Figure 6 shows the results of measuring the insertion loss between the two.

As is clear from this result, each output boat 21~
Insertion loss variation in 28! It is ±0.3dB, and the loss in the input/output section and the Y branch are connected in three stages.
! I1. Taking this into account, the branching loss per stage of branching was 016B, which was a very low loss and had little variation.

Although this embodiment shows an example of a branch circuit, it goes without saying that the present invention can also be applied to a multiplexing circuit.

Further, in the above embodiments, a silica-based glass waveguide has been described, but the present invention can also be applied to other waveguides such as semiconductor waveguides.
-, 1NbO, waveguide, B:I + . In addition, the branching/coupling leading circuit according to the present invention can be manufactured under specific conditions, and has high manufacturability and reproducibility.
This is layered and has low loss.

[Brief explanation of drawings]

Figure 1! 4 An explanatory diagram showing the Y-branch optical guide system according to the present invention,
Figure 2 is a graph showing the relationship between branching loss and radius of curvature R, and Figure 3 is a graph showing the relationship between branching loss and specific analysis rate △.
Seraph Figure 4; Mabu @ loss and t'ih convergence W. Graph showing which relationship, 1 large 8 sub 1i according to the bar example in Fig. 5
. . . An explanatory diagram showing the T77 optical circuit. Figure 6 shows the insertion loss of each output port. Figures 7 and 8:
An explanatory diagram showing the entire configuration of a Y-branch optical waveguide according to the prior art,
FIG. 9C is an explanatory diagram showing the other manufacturing steps, and FIGS. 1O and 11 are explanatory diagrams showing the configuration of other Y-branch optical waveguides. In the drawing, 11 is a main waveguide, 12 and 13 are branch waveguides, 14 is a branch point, 15 is a taper portion, 20 is an input port, 20 to 28 are output ports, and 29 to 35 are Y branch portions.

Claims (2)

[Claims] (1) In a branching/multiplexing optical waveguide circuit formed in a cladding on a substrate and in which two or more branching waveguides communicate with one waveguide, the bending portion of the branching waveguide has a radius of curvature. It is based on a circular arc of 40 mm or more, and the relative refractive index difference between the waveguide and branch waveguide and the cladding is 0.22 to 0.30%, and the rounded width of the branch point is 2.0 μm or less. A branching/combining optical waveguide circuit characterized by the following. (2) The branching/combining optical waveguide circuit according to claim 1, wherein the waveguide is a silica-based glass single optical waveguide formed on a silicon substrate.