JP2809517B2 - Branch and multiplex optical waveguide circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a branching and multiplexing optical waveguide circuit, and is expected to provide a low-loss circuit which facilitates the manufacture of a waveguide and has excellent reproducibility.

[0002]

2. Description of the Related Art In an optical integrated circuit, an optical branch circuit and an optical multiplexing circuit are indispensable as basic components.
Such a branching and multiplexing optical waveguide circuit has conventionally been 2
A Y-branch optical waveguide having more than two branch optical waveguides is known. In particular, the Y-branch waveguide circuit is expected to be applied to a 1 × N splitter optical circuit or the like since it has a lower wavelength dependency than a directional coupler.

FIGS. 15 and 16 show the structure of a conventional Y-branch waveguide circuit. As shown in both figures, the Y branch waveguide circuit is an optical waveguide in which the main waveguide 4, the tapered waveguide 8, and the branch waveguides 5 and 6 are connected in order. A branch point 7 is interposed between them. As shown in FIGS. 17 and 18, each of the branch waveguides 5 and 6 has an inflection point a, and is a curved waveguide curved with a radius of curvature R in opposite directions before and after the inflection point a. is there. Further, the branch waveguides 5 and 6 are respectively connected to the output waveguide c. The width W ₅ of the width W ₄ and the branch waveguides 5 and 6 of the main waveguide 4,
It is equal to W _6, and the width between the branch waveguides 5 and 6 at the branch point 7 (hereinafter referred to as round width) has an ideal shape of zero.

[0004] To manufacture this Y-branch waveguide circuit, Si
Starting from chlorides such as Cl ₄ , Ge Cl ₄ , Ti Cl ₄ , Po Cl ₃ , and BCl ₃ , for example, as shown in FIGS. 19 to 23, a cladding layer 2 and a core glass layer 3 are formed on a silicon substrate 1.
Are sequentially deposited, the core glass layer 3 other than the core portion is removed by etching, and the main waveguide 4, the branch waveguides 5, 6, and the tapered waveguide 8 are formed as waveguides through which light propagates. This is done by depositing layer 2.

[0005]

Conventionally, in order to reduce the loss of the Y-branch waveguide circuit, first, it is necessary to increase the radius of curvature of the branch waveguides 5 and 6 which are curved in an arc shape. It is important that the branch point 7 be ideally sharp, that is, the rounding width be zero. However, there are the following problems in achieving the above two items.

First, in order to increase the radius of curvature of the branch waveguides 5 and 6, it is necessary to increase the circuit size.
In reality, since the circuit size is restricted by the size of the substrate, there is a limit in increasing the radius of curvature. Also, 1 ×
In a circuit constituted by multi-stage branch waveguides such as an N optical splitter, since a waveguide having a small radius of curvature is used, there is a problem that the insertion loss necessarily increases.

Second, in realizing an ideal sharp branch point 7, the sharp branch point 7 is not formed as shown in FIG. width W _B of the branching waveguides 5,6 at 7 when it is created without becoming zero will result in a large branch losses.

Next, there is a problem in the variation of the branching ratio of the Y-branch waveguide.

First, in the conventional structure, since the shape of the branch point 7 is delicate, when the branch point 7 has an asymmetric shape as shown in FIG. 25, a large branch loss is generated and the branch ratio is reduced. Variations will occur. Also, the reproducibility is not good.

Secondly, in a circuit composed of multi-stage branch waveguides such as a 1 × N optical splitter, light passing through the preceding branch waveguide is transmitted through its output waveguide, that is, the subsequent input waveguide. Since the field distribution fluctuates, the branching ratio varies.

Third, when mounting the input / output fiber to the 1 × N optical splitter or the like, the input fiber and the input linear waveguide of the optical circuit are caused by the tool accuracy of the jig and the mechanical accuracy of the alignment device. May cause axial misalignment. In this case, a higher mode and a radiation mode other than the fundamental mode are excited in the waveguide, and as a result, the branching ratio varies.

SUMMARY OF THE INVENTION The present invention has been made in view of the above prior art, and has as its object to provide a low-loss optical branching / multiplexing circuit which has solved the problems of branch loss, branch ratio variation and reproducibility. Is what you do.

[0013]

In order to achieve the above object, according to the structure of the present invention, a tapered waveguide is connected to a main waveguide, and a plurality of branch optical waveguides having inflection points are provided at branch points of the tapered waveguide. Connected, further in the branch multiplexed optical waveguide circuit formed by connecting an output waveguide to each of the branch optical waveguides,
An axis deviation is provided at an inflection point of the branch optical waveguide and a connection point with the output waveguide, and a gap is provided between the branch waveguides at a branch point of the tapered waveguide.

Further, it is more preferable that a constricted portion is provided as a mode stabilizing region in the input linear waveguide connected to the main waveguide.

[0015]

1 to 3 show a first embodiment of the present invention.
In this embodiment, the present invention is applied to a Y-branch optical waveguide. That is, the Y-branch optical waveguide is formed by connecting the main waveguide 4, the tapered waveguide 8, and the branch waveguides 5 and 6 in this order, and the branch between the taper waveguide 8 and the branch waveguides 5 and 6. Point 7 is interposed. In the branch point 7, between the branching waveguides 5,6, clearance d ₁ is provided. Each of the branch waveguides 5 and 6 has an inflection point a.
Are curved waveguides that are curved in opposite directions before and after.
The inflection point a of the branch waveguides 5 and 6 is provided with an axis deviation d ₂ , and the branch waveguides 5 and 6 are connected to the output waveguide c, and the connection point b has an axis deviation d 2. _Three are provided.

Here, as shown in FIG. 4, the peak of the field distribution of the linear waveguide exists at the center of the waveguide, but the field distribution of the curved waveguide becomes smaller as the radius of curvature becomes smaller. The peak moves outward. For this reason, if connection is made without an axial deviation at the connection point between the input waveguide and the branch waveguide, the inflection point a of the branch waveguide, and the connection point b between the branch waveguide and the output waveguide c, as in the prior art, Since the positions of the peaks of the field distribution are different, a loss due to the field distribution mismatch occurs. Further, due to the perturbation due to the field distribution mismatch, the output waveguide c
The field distribution fluctuates from side to side, causing a variation in the branching ratio. As shown in FIG. 5, the outward direction perpendicular to the tangential direction z of the curved waveguide is defined as the positive direction of the x-axis.

On the other hand, in this embodiment, at the inflection point a of the branch waveguides 5 and 6 and the connection point b between the branch waveguides 5 and 6 and the output waveguide c, the axial deviations d ₂ and d _{3 are obtained.} Is provided to match the position of the peak of the field distribution, it is possible to suppress an increase in loss and a variation in the branching ratio due to the field distribution mismatch. FIG. 6 shows the relationship between the gap d ₁ between the branch waveguides 5 and 6 at the branch point 7 and the insertion loss. As shown in the figure, the value of the gap d ₁ that minimizes the insertion loss is not 0, but about 1 μm. Therefore, branch point 7
Than the conventional case without a gap (d ₁ = 0μm) between the branching waveguides 5,6 in, prefer to therebetween a gap of about 1μm to d _1, so that the insertion loss is reduced.
However, in FIG. 6, it was assumed that d ₂ = d ₃ = 0 μm.

FIG. 7 shows the relationship between the axis shift d _{2 at} the inflection point a of the branch waveguides 5 and 6 and the insertion loss.
As shown in the figure, the value of the gap d ₂ of the insertion loss and the minimum rather than 0, it can be seen that exist between the 0.2 to 0.5 [mu] m. Therefore, the structure according to the present invention can reduce the insertion loss as compared with the conventional structure in which no axial deviation is given. However, in FIG. 7, it is assumed that d ₃ = 2d ₂ and d ₁ = 0 to ₃ μm. FIG. 8 shows the relationship between the presence / absence of axial deviations d ₂ and d ₃ of the branch waveguide and the perturbation of the field distribution in the output waveguide c. The horizontal axis z indicates the distance from the connection point b between the branch waveguides 5 and 6 and the output waveguide c, and the vertical axis xo indicates the position where the field distribution is maximum. In the case where the axis deviations d ₂ and d ₃ are provided, as shown by black circles in the figure, the axis deviations d ₂ and d shown by white circles
Compared to the case where ₃ is not provided, it can be seen that the misalignment of the field distribution is eliminated and the perturbation of the output waveguide c is suppressed by the effect of the axis shift. Since higher-order modes and radiation modes other than the fundamental mode excited in the waveguide due to the misalignment between the input fiber and the optical circuit have weak confinement effects, mode stabilization of long linear waveguides, curved waveguides, constrictions, etc. It can be removed by providing a region. As a result, perturbation of the field distribution of the waveguide is suppressed, and good characteristics without variation in the branching ratio are obtained.

Next, a second embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. In this embodiment, the present invention is applied to a 1 × 8 splitter optical circuit. That is, this 1 ×
The 8-splitter optical circuit has seven Y-branch optical waveguides 18 to 25 connected in three stages, and further has an input port 9 and output ports 10 to 17 connected thereto. Each of the Y branch optical waveguides 18 to 24 has a structure in which the tapered waveguide 8 and the branch waveguides 5 and 6 are separated by cladding as shown in FIG. This is for uniformly introducing the clad material into the narrow gap between the branch waveguides 5 and 6. An optical circuit having such a configuration is created by the following procedure. First, a porous glass film is deposited by a flame deposition method on a silicon substrate having a diameter of 3 inches and a thickness of 700 μm. The deposition order is as follows. First, the composition is SiO ₂ —P ₂ as a cladding layer.
A porous glass film of O ₅ -B ₂ O ₃ was deposited, and then a porous glass film having a composition of SiO ₂ -GeO-P ₂ O ₅ was deposited as a core layer. The substrate on which the porous glass film was deposited was heated to a temperature of 1
Heat treatment was performed at 390 ° C. in a mixed atmosphere of He and O ₂ for 2 hours. Next, an optical waveguide pattern was formed by reactive ion etching. Further, a clad layer is formed so as to cover the core layer. As a result, the optical waveguide shown in FIG. 9 is formed, and the fabrication of the 1 × 8 splitter optical circuit is completed. However, the dimensions of the core are 8 μm × 8 μm, d ₁ = 1 μm, d ₂ =
0.4 μm and d ₃ = 0.2 μm. As a result, the variation of the insertion loss of the output ports 10 to 17 was ± 0.3 dB, and the branch loss per one stage of the Y branch waveguide was very low at 0.1 dB, and the variation was small.

FIG. 11 shows a third embodiment of the present invention. In this embodiment, a 1 × mode stabilizing region is provided.
It relates to a two-splitter optical circuit. That is, a long input linear waveguide (15 mm) 26 is connected to the main waveguide of the Y-branch waveguide 25 as a mode stabilizing region. By providing such a long input linear waveguide 26, basic confinement with weak confinement is achieved. Modes other than the mode were attenuated, and the characteristic that the dispersion of the branching ratio was small with respect to the displacement of the input fiber was obtained. The Y-branch waveguide of this circuit was the same as in the second embodiment.

FIG. 12 shows a fourth embodiment of the present invention. The present embodiment relates to a 1 × 2 splitter optical circuit provided with a curved waveguide that curves in an S-shape as a mode stabilizing region. In other words, the main waveguide of the Y-branch waveguide 27 is connected to the curved waveguide 28 which is curved in an S-shape as a mode stabilizing region, and providing such a curved waveguide 21 causes a perturbation. Higher-order mode and radiation mode light are removed by the curved waveguide 28, and the variation of the branching ratio with respect to the displacement of the input fiber is reduced. The Y-branch waveguide 27 of this circuit was the same as in the second embodiment.

FIG. 13 shows a fifth embodiment of the present invention. The present embodiment relates to a 1 × 2 splitter optical circuit in which a constriction is formed in an input linear waveguide as a mode stabilizing region. That is, the input linear waveguide 30 is connected to the main waveguide of the Y-branch waveguide 29, and the input linear waveguide 30 is provided with a narrow portion 31 having a narrow width as shown in FIG. . By forming the constricted portion 31 in the input linear waveguide 30 in this manner, light of a higher-order mode and a radiation mode that causes perturbation is confined to the constricted portion 31.
And the dispersion of the branching ratio with respect to the displacement of the input fiber was reduced. The Y-branch waveguide 29 of this circuit was the same as in the second embodiment.

In this embodiment, the constricted portion 31 is provided in the input linear waveguide 30 as a mode stabilizing region. Therefore, when the curved waveguide 28 curved in an S-shape is provided as in the fourth embodiment. A design optimized by comparison is possible. That is,
In the design of a curved waveguide, it is difficult to optimize so as to achieve both low insertion loss in the fundamental mode over a wide wavelength range and high insertion loss in the cutoff wavelength region of the higher-order mode. On the other hand, in the design of the waveguide in the constricted portion, it is possible to make both the insertion loss in the fundamental mode cut-off wavelength region high and the insertion loss high in the cutoff wavelength region of the higher-order mode while reducing the insertion loss in the fundamental mode over a wide wavelength range.

Although the second, third, fourth, and fifth embodiments have been described with reference to a silica glass waveguide, the present invention is not limited to such a waveguide. The present invention can be applied to other waveguides. Furthermore, Ti diffusion Li Nb O ₃ waveguide, a proton exchange waveguide, even when the refractive index distribution is the distribution function, such as ion-exchange waveguide, in which the present invention can be applied.

[0025]

As described above in detail with reference to the embodiments, according to the present invention, the inflection point of the branch optical waveguide and the connection point with the output waveguide are provided with an axis shift, and the branch of the tapered waveguide is provided. Since the gap is provided between the branch waveguides at the points, the deviation of the peak of the field distribution in the curved waveguide can be compensated. For this reason, the manufacturability of the waveguide is facilitated, and a low-loss branched multiplexed optical waveguide circuit having excellent reproducibility can be provided.
Furthermore, when a mode stabilizing region is provided in the input waveguide, higher-order modes and radiation modes that cause perturbation can be removed, and the variation in the branching ratio can be reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a Y-branch waveguide according to one embodiment of the present invention.

FIG. 2 is an enlarged explanatory view showing the vicinity of an inflection point of the branch waveguide in the Y-branch waveguide shown in FIG.

FIG. 3 is an explanatory diagram showing an enlarged view of the vicinity of a connection point between a branch waveguide and an output waveguide in the Y-branch waveguide shown in FIG. 1;

FIG. 4 is a graph showing field distribution in a straight waveguide and a curved waveguide.

FIG. 5 is an explanatory diagram showing coordinates in a field distribution.

FIG. 6 shows a branch waveguide 5 at a branch point of a tapered waveguide section.
6 is a graph illustrating a relationship between a gap d1 of _No. 6 and an insertion loss.

FIG. 7 is a graph showing a relationship between an axis shift d ₂ and an insertion loss at an inflection point of a branch waveguide.

FIG. 8 is a graph showing a perturbation of a field distribution depending on the presence or absence of an axis shift.

FIG. 9 is a plan view of a 1 × 8 splitter optical circuit according to a second embodiment of the present invention.

FIG. 10 is an explanatory diagram showing an enlarged Y branch waveguide of the 1 × 8 splitter optical circuit in FIG. 9;

FIG. 11 is an explanatory view showing a third embodiment of the present invention.

FIG. 12 is an explanatory view showing a fourth embodiment of the present invention.

FIG. 13 is an explanatory view showing a fifth embodiment of the present invention.

FIG. 14 is an explanatory diagram showing the constricted portion shown in FIG. 5 in an enlarged manner.

FIG. 15 is an explanatory diagram showing a configuration of a conventional Y-branch waveguide.

FIG. 16 is a sectional view taken along a line AB in FIG.

FIG. 17 is an enlarged explanatory view showing the vicinity of the inflection point of the branch waveguide in the Y-branch waveguide of FIG. 15;

FIG. 18 is an enlarged explanatory view showing the vicinity of a connection point between a branch waveguide and an output waveguide in the Y-branch waveguide of FIG.

FIG. 19 is an explanatory view showing a manufacturing process of a conventional Y-branch waveguide.

FIG. 20 is an explanatory view showing a manufacturing process of a conventional Y-branch waveguide.

FIG. 21 is an explanatory view showing a manufacturing process of a conventional Y-branch waveguide.

FIG. 22 is an explanatory view showing a manufacturing process of a conventional Y-branch waveguide.

FIG. 23 is an explanatory view showing a manufacturing process of a conventional Y-branch waveguide.

FIG. 24 is an explanatory diagram showing a state where a gap is formed between branch waveguides at a branch point of a Y-branch waveguide.

FIG. 25 is an explanatory diagram showing a state where a branch point of a Y-branch waveguide is formed asymmetrically.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Cladding 3 Core 4 Main waveguide 5 Branch waveguide 6 Branch waveguide 7 Branch point 8 Taper waveguide 9 Input port 10 Output port 11 Output port 12 Output port 13 Output port 14 Output port 15 Output port 16 Output port 17 Output Port 18 Y-branch waveguide 19 Y-branch waveguide 20 Y-branch waveguide 21 Y-branch waveguide 22 Y-branch waveguide 23 Y-branch waveguide 24 Y-branch waveguide 25 Y-branch waveguide 26 Input linear waveguide 27 Y-branch waveguide Waveguide 28 Input linear waveguide 29 Y-branch waveguide 30 Input linear waveguide 31 Neck

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiroshi Takahashi 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (58) Field surveyed (Int.Cl. ⁶ , DB name) G02B 6 / 12

Claims (3)

(57) [Claims] 1. A tapered waveguide is connected to a main waveguide, a plurality of branch optical waveguides having an inflection point are connected to a branch point of the tapered waveguide, and an output waveguide is connected to each of the branch optical waveguides. In the branched multiplexed optical waveguide circuit, the inflection point of the branched optical waveguide and the connection point with the output waveguide are provided with an axis shift, and a gap is provided between the branched waveguides at the branch point of the tapered waveguide. A multiplexed optical waveguide circuit. 2. A mode stabilizing region in an input linear waveguide connected to the main waveguide.
The multiplexed optical waveguide circuit described in the above. 3. A branching and multiplexing optical waveguide circuit according to claim 2, wherein a constricted portion is provided as said mode stabilizing region.