JPH0980244A - Branch and confluence optical waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a branch and confluence optical waveguide which has one main optical waveguide and >=2 branch waveguides formed on a substrate and makes light branch off and meet together. SOLUTION: This branch and confluence optical waveguide consisting of the main optical waveguide 1 formed on the substrate, a tapered part 2 which is expanded gradually in width about the center axis of the main optical waveguide 1, and a group of optical waveguides (two branch waveguides 3 and 4) which are arranged opposite the tapered part 2 and as wide as each other has a shift of a specific interval (δX) between the center axis of the whole optical waveguide group and the center axis of the main optical waveguide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a branching and merging optical waveguide having one main optical waveguide formed on a substrate and two or more branching waveguides for branching and merging light. Is.

[0002]

2. Description of the Related Art In an optical integrated circuit, an optical branch circuit and an optical stiffness circuit are indispensable as basic constituent elements. As such a branching / merging optical waveguide circuit, a Y-type branching optical waveguide circuit having two or more branching optical waveguides has been conventionally proposed.

This Y-type branched optical waveguide circuit has the advantage that it has no wavelength dependence as compared with a branch circuit using a directional coupler, and is particularly applicable to 1 × N splitters and optical taps. Is expected. In particular, in the application to the optical tap, it was necessary to design a Y-type branch structure capable of asymmetrically distributing the optical power like 40:60.

FIG. 11 shows an example of this conventional optical waveguide circuit having a Y-type branch structure. In FIG. 11, reference numeral 1 is a main optical waveguide, 2 is a tapered waveguide, 3 and 4 are branched waveguides, 5 is a gap between the branched waveguides 3 and 4, and 6 is a tapered waveguide 2 and a branched waveguide. The gaps between the waveguide 3 and the branching waveguide 4 are shown respectively. Here, in order to realize the asymmetric power branch, the widths of the branch waveguide 3 and the branch waveguide 4 are respectively set to W.
It was designed to be different from ₁ and W ₂ . As disclosed in Japanese Patent Application No. 2179348 (Japanese Patent Application Laid-Open No. 4-70605), the gaps 5 and 6 between the waveguides prevent characteristic deterioration due to an error in making the branching waveguides, and reproducibility. It is provided to improve the

The production of such a branching and merging optical waveguide may be carried out, for example, as disclosed in JP-A-58-105111. That is, SiCl ₄ , GeCl
_Using chlorides of ₄ , ₄ , TiCl ₄ , POCl ₃ , and BCl ₃ as a starting material, for example, as shown in FIG. 13, a clad glass layer 8 and a core glass layer 9 are sequentially deposited on a substrate 7 such as silicon (see FIG. a) to (c)), and then a core portion 9a corresponding to the above-described waveguides 1 to 4 by etching processing.
Other than the core layer 9 is etched (see FIG. 13D),
Finally, the clad glass layer 8 is deposited to fill the waveguide (see FIG. 13E).

FIG. 12 is a graph showing the relationship between the branch ratio and the branch excess loss due to the difference in the widths of the asymmetric Y-shaped branch waveguides 3 and 4 described above. Here, the horizontal axis of FIG. 12 represents the difference δW (μm) between the waveguide widths W ₁ and W ₂ between the branch waveguide 3 and the branch waveguide 4, and the left vertical axis represents the branch waveguide 3 and the branch waveguide 4.
And the branch ratio (%), and the right vertical axis is the branch excess loss (dB)
Is shown.

Here, in FIG. 11, the waveguide has a relative refractive index difference Δ.
Is 0.45%, the waveguide size is 7 μm square (W ₀ = 7 μm), the waveguide gaps Wg and Ws are 1.5 mm, the tapered waveguide length is 1 mm, and the optical signal wavelength is 1.3 μm. Even if the width of the branching waveguide is changed within the range of δW = ± 2 μm, the branching ratio changes by 50 ± 3% at most, while the excess loss is 0.
It can be seen that it increases by 2 dB or more. From the graph shown in FIG. 12, in order to change the branching ratio significantly,
Although it is necessary to set W to a larger value, there is a problem in that the excess loss also increases rapidly.

In view of the above problems, it is an object of the present invention to provide a branching / merging optical waveguide in which the branching ratio can be easily set in a wide range and the excess loss is small.

[0009]

The structure of a first branching / merging optical waveguide according to the present invention which achieves the above object is such that a main optical waveguide formed on a substrate and a central axis of the main optical waveguide are centered. In a branching and converging optical waveguide including a tapered portion whose width is gradually enlarged and a plurality of equal-width optical waveguide groups arranged facing the tapered portion, the central axis of the entire optical waveguide group and the main optical waveguide It is characterized in that it is displaced from the central axis of by a predetermined distance.

A second branching and merging optical waveguide according to the present invention has a main optical waveguide formed on a substrate, a taper portion in which the width of the main optical waveguide is gradually enlarged, and a taper portion opposed to the taper portion. In the branching / merging optical waveguide including a plurality of equal-width optical waveguide groups arranged in parallel, the tapered portion is asymmetric with respect to the central axis of the main optical waveguide.

In the branching / merging optical waveguide, the tapered portion and the optical waveguide group are arranged with a space therebetween.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The contents of the embodiments for carrying out the present invention will be described below with reference to the drawings.

First, a first embodiment of the present invention will be described. FIG. 1 is a schematic diagram according to the first configuration of the present invention. In the figure, reference numeral 1 is a main optical waveguide, 2 is a tapered waveguide continuous from the main optical waveguide, 3 and 4 are branched waveguides, 5 is a branched waveguide gap, and 6 is between the tapered waveguide and the branched waveguide. The respective gaps are illustrated.

The first branching and merging optical waveguide structure of the present invention comprises a main optical waveguide 1 formed on a substrate and a tapered portion 2 having a width gradually expanded about the central axis of the main optical waveguide 1. And a plurality of equal-width optical waveguide groups arranged to face the tapered portion 2 (in the present embodiment, two branch waveguides 3,
In the branched and merged optical waveguide of 4), the central axis of the entire optical waveguide group and the central axis of the main optical waveguide are deviated by a predetermined distance (δX).

The operation of the branching and merging optical waveguide having the above structure can be generally explained by coupling Gaussian beams. Here, for simplification of description, it is assumed that the optical field distribution of the optical waveguide is a Gaussian distribution and its spot size is equal to the waveguide half width. Therefore, if the spot size of the branched optical waveguide is ω, the spot size of the tapered waveguide is 2ω. Further, in order to standardize the width deviation δX, a standardized axis deviation amount Δ = δX / 2ω is defined.

When the x-axis perpendicular to the waveguide is set with the center of the tapered waveguide as the origin, the optical field distribution f (x) of the tapered waveguide is expressed by the following equation (1). To be done.

[Equation 1]

Further, the field g (x) of the branch waveguide 3
Is expressed as shown in the following formula (2).

[Equation 2]

At this time, the tapered waveguide 2 to the branched waveguide 3
The coupling ratio η _{3 to} is the overlap integral of the two Gaussian beams, and is expressed as shown in the equation (3) of “Equation 3” below.

(Equation 3)

Similarly, from the tapered waveguide 2 to the branched waveguide 4
Assuming that the coupling ratio to η ₄ is η ₄ , the branching ratio R is expressed by the following equation (4).

(Equation 4)

FIG. 2 shows the dependence of the branching ratio on the standardized axis deviation amount. When the normalized axis deviation is 0 to 0.4, the branching ratio is 50
It is possible to change almost linearly up to ~ 78%.

On the other hand, also in the case of the conventional structure, the branching ratio characteristic can be similarly obtained. The field distribution h (x) of the branch waveguide 3 shown in FIG.
It is expressed as shown in the equation (5).

(Equation 5) Here, the waveguide width difference δW between the branch waveguide 3 and the branch waveguide 4 is standardized as Δ = δX / 2ω.

Therefore, from the tapered waveguide 2 to the branched waveguide 3
The coupling rate η ₃ is expressed by the overlap integral of the two Gaussian beams shown in the equation (6) below, and the branching ratio R
Is expressed as shown in the following equation (7).

(Equation 6)

(Equation 7)

FIG. 3 shows the branching ratio characteristic of the conventional structure. From FIG. 3, even if the standardized waveguide width difference Δ is changed to 0.4, the branching ratio changes only up to about 62%, and the branching ratio change amount is half or less of the case of the present invention.

As described above, the analysis based on the coupling of Gaussian beams has revealed that the structure of the present invention is suitable for obtaining a large change in branching ratio. In order to obtain a more accurate branching ratio and insertion loss, it is necessary to further rely on numerical calculation, but the tendency of branching ratio characteristics does not change this approximate analysis.

In the fabrication of the branching and merging optical waveguide of the present embodiment shown in FIG. 1, a silicon substrate having a diameter of 4 inches and a thickness of 1 mm is first formed by a flame deposition method, and the composition of the cladding layer is SiO ₂ -P _{2 first.} A porous glass film of O ₅ -B ₂ O ₃ is deposited and then the composition of the core layer is SiO ₂ -G.
was deposited eO ₂ -P ₂ O ₅ porous glass membrane -B ₂ O _3. After that, heat treatment was performed for 2 hours in a mixed atmosphere of He and O _{2 at} a temperature of 1300 ° C. Next, an optical waveguide pattern as described above is formed by reactive ion etching,
Then, a clad layer having the same composition as that described above was formed so as to embed the core layer.

Here, by adjusting the GeO ₂ concentration, it becomes possible to fabricate branched and merged optical waveguides having various relative refractive index differences Δ.

FIGS. 4, 5 and 6 show the axial deviation δX, the branching ratio and the branch excess loss in the branching / merging optical waveguides having the relative refractive index differences Δ of 0.3%, 0.45% and 0.75%. Shows the relationship. Here, the relative refractive index difference Δ is 0.3%,
The waveguide dimensions for 0.45% and 0.75% are 8 × 8 μm, 7 × 7 μm, and 6 × 6 μm, respectively. Also, in each case, the waveguide gaps Wg and Ws
Is 1.5 μm, the length of the tapered waveguide 2 is 1 mm, and the optical signal wavelength is 1.3 μm. Regardless of the relative refractive index difference Δ, when the axis deviation amount δX is 0 to 2 μm, the branching ratio is 5
It has been found that it is possible to make a substantially linear change in the range of 0 to 68%.

Further, the branch excess loss in this range has a fluctuation of about 0.1 dB depending on the case of 0.75%, but the increase itself of the branch excess loss is as small as 0.1 dB or less and can be almost ignored. .

Next, a second embodiment of the present invention will be described. FIG. 7 is a schematic view of a branching / merging optical waveguide according to a second embodiment of the present invention. In the figure, reference numeral 1 is a main optical waveguide,
Reference numeral 2 is a taper waveguide continuous from the main optical waveguide, 3 and 4 are branch waveguides, 5 is a branch waveguide gap, and 6 is a gap between the taper waveguide and the branch waveguide. In addition, the waveguide expansion amount of the tapered waveguide 2 is set to D ₁ , D _{2 as} shown in FIG.
And the asymmetry is expressed as δY = D ₁ −D ₂ .

FIGS. 8, 9 and 10 show the asymmetry δY of the tapered waveguide 2 in the branching and merging optical waveguides having relative refractive index differences Δ of 0.3%, 0.45% and 0.75%. The relationship between the branch ratio and the branch excess loss is shown. Here, the waveguide dimensions for the relative refractive index difference Δ of 0.3%, 0.45%, and 0.75% are 8 × 8 μm, 7 × 7 μm, and 6 ×, respectively.
It is 6 μm. In each case, the waveguide gaps Wg and Ws are set to 1.5 μm, the length of the tapered waveguide 2 is set to 1 mm, and the optical signal wavelength is 1.3 μm. It has been found that it is possible to change the branching ratio substantially linearly in the range of 50 to 68% when the asymmetry δY is 0 to 2 μm, regardless of the relative refractive index difference Δ. Further, it was found that the increase in branch excess loss in this range was as small as 0.1 dB and could be almost ignored.

In the branching / merging waveguide in the above embodiment, Japanese Patent Application No. 2-179378 (Japanese Patent Application Laid-Open No. 4-7060).
Since it has the waveguide gap shown in No. 5), it also has the feature of high reproducibility of circuit production.

In this embodiment, the branching / merging waveguide using the glass-based waveguide has been described as an example.
The present invention is not limited to this. For example, an organic material-based waveguide,
It is applicable regardless of the waveguide material such as a semiconductor material type waveguide.

Further, in the present embodiment, the relative refractive index difference of 0.
The case of 3%, 0.45%, and 0.75% waveguides has been shown, but the present invention is not limited to this, and is also applicable to waveguides having different relative refractive index or different waveguide dimensions. Needless to say, the present invention can be applied only by changing the design.

[0034]

As described above, according to the present invention, the branching ratio can be set in a wide range with a simple branching waveguide structure, and the branching excess loss is small. .

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a first embodiment of a branching / merging waveguide according to the present invention.

FIG. 2 is a graph showing the relationship between the normalized axial deviation amount of the branching ratio and the branching ratio according to the present invention.

FIG. 3 is a graph showing the relationship between the normalized waveguide width difference of the branching ratio and the branching ratio according to the present invention.

FIG. 4 is a branch / merging waveguide (relative refractive index difference of 0.3
Is a graph showing the relationship between the branching ratio of (%) and excess loss.

5 is a branch / merging waveguide shown in FIG.
5B) is a graph showing the relationship between the branching ratio (5%) and the excess loss.

FIG. 6 is a branch / merging waveguide shown in FIG.
5B) is a graph showing the relationship between the branching ratio (5%) and the excess loss.

FIG. 7 is an explanatory diagram showing a second embodiment of a branching / merging waveguide according to the present invention.

FIG. 8 is a branch / merge waveguide shown in FIG.
Is a graph showing the relationship between the branching ratio of (%) and excess loss.

9 is a branch / merging waveguide shown in FIG.
5B) is a graph showing the relationship between the branching ratio (5%) and the excess loss.

FIG. 10 shows the branching / merging waveguide shown in FIG.
(75%) is a graph showing the relationship between the branching ratio and excess loss.

FIG. 11 is a configuration diagram of a branching / merging waveguide according to a conventional technique.

12 is a graph showing the relationship between the branching ratio and the excess loss of the branching / merging waveguide shown in FIG.

FIG. 13 is an explanatory diagram showing a manufacturing process of the branching / merging waveguide circuit.

[Explanation of symbols]

 1 main optical waveguide 2 taper waveguide continuous from the main optical waveguide 3, 4 branch waveguide 5 branch waveguide gap 6 gap between taper waveguide and branch waveguide

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Kazuyuki Moriwaki 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation

Claims (3)

[Claims] 1. A main optical waveguide formed on a substrate, a taper portion whose width is gradually expanded about a central axis of the main optical waveguide, and a plurality of etc. arranged facing the taper portion. A branching / merging optical waveguide comprising a group of optical waveguides having a width, wherein a central axis of the entire optical waveguide group and a central axis of the main optical waveguide are displaced from each other by a predetermined distance. 2. A main optical waveguide formed on a substrate, a taper portion in which the width of the main optical waveguide is gradually expanded, and a plurality of equal-width optical waveguide groups arranged so as to face the taper portion. In the branched and merged optical waveguide, the tapered portion is asymmetric with respect to the central axis of the main optical waveguide. 3. The branched / merged optical waveguide according to claim 1, wherein the tapered portion and the optical waveguide group are arranged with a space therebetween.