JPH08327836A - Y-branching optical waveguide circuit - Google Patents

Abstract

PURPOSE: To provide a small Y branching optical waveguide circuit of good reproducibility, easy to manufacture, and capable of brancing a light beam with a low loss. CONSTITUTION: Optical waveguides 13a, 13b on the branching side are connected to an optical waveguide 11 on the coupling side in a Y-shaped manner through a tapered waveguide 12 widened on the side of the optical waveguides 13a, 13b so as to form the Y-branch optical waveguide 9. A temple bell-shaped wedge 14 having a lower refractive index than that of the Y-branch optical waveguide 9 is arranged in the branching part of the Y-branch optical waveguide 9. the branching angle p of the optical waveguides 13a, 13b on the branching side is formed to be larger than the opening angle 6 of the tapered waveguide 12 (θ=0.2 deg., β=0.7 deg.) and the optical waveguides 13a, 13b on the branching side have curved waveguides being bent in the direction for increasing a distance between the waveguides.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Y-branch optical waveguide circuit used as an optical branching / multiplexing circuit in an optical communication system.

[0002]

2. Description of the Related Art There is a telephone communication as an example of an optical communication system using an optical fiber, and an optical branching / multiplexing circuit having a function of 1 × N branch and 2 × N branch between a telephone station and a plurality of subscribers is provided. PDS (Passive
A network topology called Double Star) is under consideration.

The optical branching / multiplexing circuit used in this PDS can be roughly classified into a fiber type circuit and an optical waveguide type circuit depending on its form. However, since the fiber type circuit individually manufactures components of the circuit. In addition, there is a problem that not only the productivity is poor, but also the circuit becomes large in size as the number of branches increases. Recently, it has been considered promising to use an optical waveguide type optical branching / multiplexing circuit.

FIG. 5 shows a 1 × N (N = 8) star coupler as an example of the optical branching waveguide circuit. Such a star coupler is, for example, a Y coupler as shown in FIG.
It is formed by connecting Y-branch optical waveguide circuits having a V-shaped structure in multiple stages (three stages in FIG. 5).

An optical waveguide type circuit is formed, for example, on a silicon substrate, and as shown in FIG. 5, a waveguide pattern formed by a core layer and a cladding layer 10 covering the core layer are provided. When forming such an optical waveguide type circuit, for example, as shown in FIG. 9A, the silica glass to be the lower cladding layer 10a is deposited on the silicon substrate 18 by flame deposition. Deposit method, then
As shown in (b) of the same figure, silica glass added with titanium or germanium to be the core layer is deposited, and both layers are made into transparent vitrification. Next, as shown in FIG. 5C, a channel waveguide 19 is formed by photolithography using reactive ion etching using a photomask on which a predetermined optical waveguide pattern is drawn. A waveguide pattern is formed. Then, finally, as shown in FIG. 9D, silica glass to be the upper clad layer 10b is deposited again by the flame deposition method, and this is made into a transparent glass, whereby the embedded optical waveguide is formed. It is formed.

As described above, the optical waveguide type circuit can be mass-produced because a large number of circuits can be collectively manufactured on a flat substrate such as a silicon substrate, and the reproducibility is good. It has advantages such as small size and integration.

As shown in FIG. 7, the Y-branch optical waveguide 9 forming a star coupler or the like has two branch optical waveguides 13a and 13a.
b and one merge-side optical waveguide 11 are connected to the branch-side optical waveguide 13
The a and 13b sides are connected in a Y-shape via a widened tapered optical waveguide 12, and in the conventional Y-branch optical waveguide, each branching angle β of the branching side optical waveguides 13a and 13b is tapered. It is formed to have an opening angle θ of the optical waveguide 12. Also, the tapered waveguides of the branch side optical waveguides 13a and 13b
A triangular wedge 14 having a refractive index lower than that of the Y-branch optical waveguide 9 is provided on the connection end side with the branch-side optical waveguides 13a and 13b.
It is driven in such a manner that it is sandwiched between. This wedge 14 has a triangular apex angle φ of the branch side optical waveguide of the Y branch optical waveguide 9.
It is formed smaller than the branch angle β of 13a, 13b,
For example, when the branch angle β = 0.2 °, the apex angle φ of the wedge 14 =
It is formed at 0.05 °. The wedge 14 may be made of the same material as the clad layer 10.

In this Y-branch optical waveguide circuit, when light is incident from the merging-side optical waveguide 11 of the Y-branch optical waveguide 9,
The field distribution of the light is expanded in the tapered waveguide 12,
Smoothly branching optical waveguide 13a as the light propagation width spreads
And propagates to the 13b side. Further, in the Y branch optical waveguide 9 in which the wedge 14 as shown in FIG. 7 is arranged,
The traveling direction of the propagating light propagating from the tapered waveguide 12 side to the branch side optical waveguides 13a and 13b side is toward the Y branch optical waveguide 9 side where the refractive index is high due to the wedge 14 whose refractive index is smaller than that of the Y branch optical waveguide 9. It is forcibly bent, whereby the propagating light is distributed almost evenly to the branch side optical waveguides 13a and 13b and propagates.

[0009]

However, in the conventional Y-branch optical waveguide circuit, at the branch portion of the Y-branch optical waveguide 9 (the connection end side of the branch-side optical waveguides 13a and 13b with the tapered waveguide 12). The provided wedge 14 is a triangular wedge having a very small apex angle such as an apex angle φ = 0.05 °, and the wedge 14 having such an extremely acute apex angle is used as the branch side optical waveguide 13a. , 13b, it is necessary to make the distance between the branch portions of the branch side optical waveguides 13a, 13b very small. As described above, since the conditions for forming the Y-branch optical waveguide 9 are strict, in the conventional Y-branch optical waveguide circuit,
It is difficult to manufacture the Y-branch optical waveguide 9 exactly as designed and with good reproducibility because the tip side (vertical angle side) of the wedge 14 becomes dull and the position of the tip side of the wedge 14 greatly varies. Met. As a result, a large variation occurs in the characteristics of the 1 × N branch star coupler formed by connecting the Y branch optical waveguides 9 in multiple stages.

Further, conventionally, by driving a wedge 14 into the branch portion of the Y-branch optical waveguide 9, the light from the merging side optical waveguide 11 is forcibly bent and branched to the branch side optical waveguides 13a and 13b side. However, the branch-side optical waveguide of the Y-branch optical waveguide 9 is not examined because no detailed study has been made as to how the shape and size of the wedge 14 should be formed to reduce the loss at the branch portion of the Y-branch optical waveguide 9. Waveguides 13a and 13b
The branch angle β, the opening angle θ of the tapered waveguide 12 and the like, and the size and shape of the wedge 14 are not optimally set. Therefore, in the propagating light that is forcibly bent from the tapered waveguide 12 to the branch side optical waveguides 13a and 13b by the wedge 14, the peak position of the light intensity thereof is at the branch side optical waveguides 13a and 13b.
In this case, the optical axis of the waveguide b does not coincide with the optical axis of the waveguide b, so that not only a connection loss occurs due to a mismatch in matching between the tapered waveguide 12 and the branch-side optical waveguide 13, but also the propagating light propagates into the branch-side optical waveguide. 13 There was a problem of meandering inside.

Then, such a Y-branch optical waveguide 9 is formed.
In a circuit such as a 1 × N star coupler in which multiple stages are connected, since the axis of the incident light is off-axis in the Y-branch optical waveguide circuit of the second and subsequent stages, the light of the incident light that is off-axis is incident. It becomes impossible to equally distribute the intensity to the two branch side optical waveguides 13a and 13b. Therefore, in a circuit such as a 1 × N star coupler, there is a problem that the uniformity of the intensity of light emitted from the emission end (for example, ports 1 to 8 in FIG. 5) between ports is significantly deteriorated. Moreover, the meandering phenomenon of the propagating light is very unstable and is easily affected by the external environment such as the wavelength of the propagating light, temperature and stress. However, it is difficult to obtain an optical branching / multiplexing circuit device having stable characteristics.

For example, in FIG. 8, Y as shown in FIG.
The measurement results of the loss characteristics at each of the ports 1 to 8 on the emission end side of the 1 × 8 star coupler (FIG. 5) configured by connecting the branched optical waveguides 9 in three stages are shown. , The difference in loss characteristics between each port 1-8 is 2.5 dB.
It has become very large. Moreover, the average insertion loss is about 11.2 dB, which is about 2.2 dB larger than 9.0 dB, which is the value of the division loss that occurs in principle. Here, the value of the average propagation loss obtained from the reference pattern of the linear waveguide and the curved waveguide is 0.05 dB / cm.
Based on the above, the propagation loss of a chip length of 3.3 cm was estimated to be 0.165 dB, and it was found that an excess loss of 2.03 dB was generated by connecting the Y branch optical waveguide 9 in three stages.
It can be seen that the excess loss per branched optical waveguide becomes a large value of about 0.678 dB.

Further, in the above Y branch optical waveguide 9, if the branch angle β of the branch optical waveguides 13a and 13b is simply increased, the distance between the branch portions of the two branch optical waveguides 13a and 13b increases. In order to propagate the propagation light to the tapered waveguide 12
Cannot be coupled to the branch side optical waveguides 13a, 13b side with low loss, and a part of the propagating light is radiated at the branch part. Therefore, the branch angle β of the branch side optical waveguides 13a, 13b is extremely reduced. It cannot be formed at a large angle.

Nevertheless, in the conventional Y-branch optical waveguide 9, the branch angle β of the branch-side optical waveguides 13a and 13b matches the opening angle θ of the tapered waveguide 12, and the branch-side optical waveguide Since the waveguides 13a and 13b are straight waveguides, if the distance between the tip ends (emission end sides) of the two branch side optical waveguides 13a and 13b is increased, the total circuit length of the Y branch optical waveguide circuit becomes long. There was a problem that became. For example, when the branch angle β = 0.2 °, a circuit length of about 35.81 mm is required to separate the two branch-side optical waveguides 13a and 13b, which are straight waveguides, by 250 μm.

The present invention has been made in order to solve the above-mentioned conventional problems, and an object thereof is to reduce loss and shorten a circuit length, which is excellent in productivity and reproducibility. It is to provide a Y-branch optical waveguide circuit.

[0016]

In order to achieve the above object, the present invention is constructed as follows. That is, the present invention provides a Y-branch optical waveguide in which two branch-side optical waveguides and one merging-side optical waveguide are connected in a Y-shape on the branch-side optical waveguide side via a tapered waveguide having a wide width. In the Y-branch optical waveguide circuit, a bell-shaped wedge having a lower refractive index than the refractive index of the Y-branch optical waveguide is provided on the branch-side optical waveguide on the connection end side of the branch-side optical waveguide with the tapered waveguide. The branch-side optical waveguides are arranged in a sandwiched manner, and the branch angle of the branch-side optical waveguide is formed larger than the opening angle of the tapered waveguide.

The wedge has a length of about 70 to 150 μm, and the region extending from the base end side to the tip end side of the branch side optical waveguide sandwiching the wedge is two branch side optical waveguides. It is also a characteristic configuration of the present invention that the curved waveguide is formed so as to be curved in a direction of increasing the distance.

[0018]

In the present invention having the above-mentioned structure, for example, the light incident from the merging side optical waveguide is branched into two branching side optical waveguides via the tapered waveguide. Is branched by forcibly changing its traveling direction to the branch side optical waveguide side by a wedge having a refractive index lower than that of the Y branch optical waveguide. In the present invention, since the branch angle of the branch side optical waveguide is formed to be larger than the opening angle of the tapered waveguide, the peak position of the light intensity after branching in which the traveling direction is forcibly changed by the wedge Is almost coincident with the optical axis center of the branch side optical waveguide,
Light hardly leaks from the Y-branch optical waveguide due to branching, and the light propagates in the branch-side optical waveguide without meandering.

Therefore, for example, when the Y-branch optical waveguide circuits of the present invention are connected in multiple stages to form a star coupler circuit or the like, almost all the light incident from the merging side optical waveguide of the first-stage Y-branch optical waveguide circuit leaks. Instead, it propagates to the branch side optical waveguide side. Further, the light propagates along the optical axis of the branch-side optical waveguide evenly and without meandering, and is incident on the merge-side optical waveguide of the merge-side optical waveguide circuit of the second stage Y-branch optical waveguide circuit. By repeating such operation, from the plurality of emission end sides of the star coupler formed by connecting the Y branch optical waveguide circuits of the present invention in multiple stages,
In both cases, light with a substantially uniform light intensity is emitted.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. In the description of the present embodiment, the same reference numerals will be given to the same names as those in the conventional example, and the duplicated description will be omitted.
FIG. 1 shows a main configuration of an embodiment of a Y-branch optical waveguide circuit according to the present invention. In this embodiment as well as the conventional example, two branch side optical waveguides 13a and 13b and a tapered waveguide are provided.
12. A Y-branch optical waveguide circuit provided with a Y-branch optical waveguide 9 composed of a merging-side optical waveguide 11. This embodiment is different from the conventional example in that the branch-side optical waveguides 13a and 13b are tapered. The wedge 14 disposed on the connection end side with the waveguide 12 is a bell-shaped wedge, and the branch angle β of the branch side optical waveguides 13a and 13b is formed larger than the opening angle θ of the tapered waveguide 12.
That is, the branch side optical waveguide has a curved waveguide.

The bell shape in this specification means that the side surfaces 15a and 15b of the wedge 14 are substantially parallel to each other as shown in FIG. 1, or the side surface 15a and the side surface 15a are as shown in FIG.
It is used in a wide concept including a shape close to a trapezoid that is not parallel to 15b.

The branch angle β of the branch side optical waveguides 13a and 13b is branched at the branch portion of the Y branch optical waveguide 9 and is forced by the wedge 14 to the branch side optical waveguides 13a and 13b, respectively. ) Is formed larger than the opening angle θ of the tapered waveguide 12 so that the peak position of the light intensity of the changed light coincides with the center of each optical axis of the branch side optical waveguides 13a and 13b. Is formed with a branch angle β = 0.7 ° for an opening angle θ = 0.2 °. Further, in the present embodiment, the length of the wedge 14 (the branch side optical waveguides 13a, 13a
The length in the longitudinal direction of b) L is 120 μm, and the width W of the wedge is 2.5 μm.
It is formed in m. The wedge 14 is made of quartz glass, which is the same material as the clad layer 10, and the relative refractive index difference Δ between the wedge 14 and the clad layer 10 and the Y-branch optical waveguide 9 is
It is 0.30%.

The curved waveguides of the branch side optical waveguides 13a and 13b are the base side 16 which sandwiches the wedge 14 of the branch side optical waveguides 13a and 31b.
Is formed in a region extending from the to the tip side, and is curved so as to increase the distance between the two branch side optical waveguides 13a and 13b. The radius of curvature R of this curved waveguide is 50 mm.

By the way, in order to specify the Y-branch optical waveguide 9 having the structure shown in FIG.
And the branch-side optical waveguide 13 has a width of 8.0 μm, the branch-side optical waveguides 13a and 13b have a radius of curvature of 50 mm, the wedge 14 has a width W of 2.5 μm, and the Y-branch optical waveguide 9 and the wedge 14 and the clad. The relative refractive index difference Δ with the layer 10 is set to 0.3%, and under the above setting conditions, the length L of the wedge 14, the opening angle θ of the tapered waveguide 12, and the branch angles of the branch side optical waveguides 13a and 13b. β,
Using the wavelength λ of the light incident from the merging-side optical waveguide 11 as a parameter, a simulation of the light intensity emitted from the two branch-side optical waveguides 13a and 13b when light of a constant intensity was incident was performed. Then, the insertion loss of light from the merging side optical waveguide 11 to the branching side optical waveguides 13a and 13b is obtained, and the theoretical division loss is subtracted from this value to calculate the excess loss at the branching portion of the Y branching optical waveguide 9. Sought by. This result is shown in Figure 2.
Is shown in.

As is clear from this calculation result, the length L of the wedge 14 causes the excess loss to be large when the branch angle β of the branch side optical waveguides 13a and 13b is set to any value of 0.2 to 1.2. In contrast, it can be seen that there is a minimum excess loss value at a length L of the wedge 14 of about 120 μm corresponding to the length L of the wedge 14. And this minimum value makes the branch angle β 0.
It was found that the angle becomes the smallest when the angle is set to 7 °, and thus the branch angle β is set to the opening angle θ of the tapered waveguide 12.
It can be seen that the minimum value of excess loss can be reduced by setting a value such as 0.7 ° that is larger than (0.2 ° or 0.4 °).

As is well known, the propagation speed of a light wave propagates in a portion having a low refractive index such as the wedge 14 is faster than the propagation velocity in a portion having a high refractive index such as the core portion. As shown in FIG. 11, when a wedge 14 having a low refractive index is set at a branch portion of an optical waveguide such as the Y-branch optical waveguide 9, the wavefront (the in-phase surface 20) representing the in-phase portion of light has a refractive index. High direction,
That is, it is forcibly directed in the direction of the branch side optical waveguides 13a and 13b. Such an effect is called a phase accelerator (Phase Accelerator) effect. It is considered that the above results shown in FIG. 2 are due to the phase accelerator effect and the relationship between the opening angle θ of the tapered waveguide 12 and the branch angle β of the branch side optical waveguides 13a and 13b.

In other words, the light incident from the merging side optical waveguide 11 side is branched at the branch portion of the Y branch optical waveguide 9, and at this time, the traveling direction (propagating direction) of the light is due to the phase accelerator effect of the wedge 14. Branch side optical waveguide 13a side and 13
The branch side optical waveguides 13a and 13 are forcibly bent to the b side.
However, by setting the branch angle β of the branch-side optical waveguides 13a and 13b larger than the opening angle θ of the tapered waveguide 12, the light from the merge-side optical waveguide 11 is guided by the wedge 14. Forcibly bendable angle and branch side optical waveguide
The branching angles β of the 13a and 13b coincide with each other, whereby the peak position of the light intensity of the light propagating through the branching optical waveguides 13a and 13b coincides with the optical axis center of each of the branching optical waveguides 13a and 13b. . As a result, it is considered that the light hardly leaks from the Y-branch optical waveguide 9 and the light can propagate without meandering, so that the excess loss is suppressed.

The angle at which the light is forcibly bent by the wedge 14 is considered to depend on the length L of the wedge 14, etc., and the length L of the wedge 14 is set to about 100 to 120 μm. Sometimes the wedge 14 forces the light to bend at an angle of about 0.
7 °, and the branch angle β of the branch side optical waveguides 13a and 13b is
By setting it to 0.7, it is considered that the branch angle and the angle at which the light is bent by the wedge 14 match.

In FIG. 3, in order to clarify the dependence of the excess loss at the branch portion of the Y-branch optical waveguide 9 on the length of the wedge 14, only the length L of the wedge 14 is used as a parameter in FIG. The result of optical characteristic evaluation of the Y-branch optical waveguide 9 having the configuration shown is shown. The branch angle β of the branch side optical waveguides 13a and 13b is 0.7 ° and the taper angle θ of the tapered waveguide 12 is θ.
= 0.2 °, and the width W of the wedge 14 is W = 2.5 μm. As is apparent from FIG. 3, when the wavelength λ of the light incident on the merging side waveguide 11 is set to 1.31 μm or 1.55 μm, the length L of the wedge 14 is in the range of about 70 to about 150 μm. It can be seen that the excess loss becomes a small value when
It has been proved that the excess loss becomes the smallest when the length L of the wedge 14 is around 120 μm.

Further, as shown in FIG. 4, according to the calculation,
It is understood that the narrower the width W of the wedge 14, the smaller the excess loss. However, if the width W of the wedge 14 is made extremely small, the apex angle of the triangular wedge 14 is set to be very small. Like the Y-branch optical waveguide circuit, it is difficult to manufacture the Y-branch optical waveguide circuit accurately and with good reproducibility. Therefore, in this embodiment, the width of the wedge 14 is set to 2.5 μm.

As described above, in this embodiment, the wedge 14 provided at the branch portion of the Y-branch optical waveguide 9 is formed in a bell shape, and the length L thereof is 120 μm. When the branch angle β of 13a and 13b is set to 0.7 ° and the opening angle θ of the tapered waveguide 12 is set to be larger than 0.2 °, when the light incident from the merging side optical waveguide 11 side is branched at the branching portion, Each of the branch side optical waveguides 13a, 13 is formed by the wedge 14.
The angle at which the light is forcibly bent to b is set to the branch side optical waveguides 13a, 13
It becomes possible to match the branching angle β of b, thereby suppressing leakage of light that cannot be matched at the branching portion, and the tapered waveguide 12 and the branch-side optical waveguide 13a,
It is possible to prevent meandering propagation due to mismatching between 13b, and it is possible to provide an excellent Y-branch optical waveguide circuit in which loss can be made extremely small.

Further, according to the present embodiment, the branch side optical waveguide
By forming the branch angle β of 13a and 31b larger than the opening angle θ of the tapered waveguide 12, the branch angle β and the opening angle θ are formed equal to each other as in the conventional case, and the Y branch optical waveguide circuit The circuit length can be shortened. For example, the distance between the tip ends of the branch side optical waveguides 13a and 13b is 250 μm.
When separated by m, the conventional Y-branch optical waveguide circuit (β = θ =
0.2 °), the circuit length is about 35.81 mm, but if the branch angle β is set larger than the opening angle θ by setting θ = 0.2 ° and β = 0.7 ° as in this embodiment, the branch side optical waveguide is set. Even if 13a and 13b are composed of linear waveguides,
Its circuit length can be reduced to about 10.23 mm.

Further, according to this embodiment, the region extending from the base end side 16 sandwiching the wedge 14 of the branch side optical waveguides 13a and 13b to the tip side is the distance between the two branch side optical waveguides 13a and 13b. Since the curved waveguide is formed in the expanding direction, the circuit length of the Y-branch optical waveguide circuit can be further shortened. In this embodiment, the branch-side optical waveguides 13a and 13 are provided.
When the distance on the tip side of b is set to be 250 μm apart, the circuit length of the Y-branch optical waveguide circuit becomes about 3.53 mm, and the circuit length can be shortened to about 1/10 of the conventional example. Therefore, the Y-branch optical waveguide circuit of the present embodiment can be a very small circuit, and the cost of the circuit can be reduced.

In FIG. 6, the Y-branch optical waveguide circuit of this embodiment is connected in three stages to form a 1 × 8 star coupler circuit as shown in FIG. Output ports 1 to 1 when light enters from the optical waveguide 11 on the merging side of the circuit
The evaluation results of the insertion loss of each port obtained by measuring the intensity of the emitted light of No. 8 are shown. As is clear from this figure, the insertion loss between ports 1-8 is almost the same, and the uniformity between ports is about 0.9 dB.
It can be seen that the uniformity is much better than that of the star coupler formed by connecting the Y-branch optical waveguide circuits of the conventional example shown in FIG.

The average insertion loss of each port 1-8 is also 9.
It is 7 dB, and it can be seen that there is almost no effect due to the difference in the wavelength of the incident light. From this result, the excess loss generated in one stage of each Y-branch optical waveguide circuit was calculated in the same manner as the conventional one, and it was only about 0.178 dB, which was compared with the excess loss of about 0.678 dB in the conventional Y-branch optical waveguide circuit. Then, it was confirmed that the excess loss of the Y-branch optical waveguide circuit of the present example could be reduced to a small value of about 1/4 of the conventional value.

Further, according to the present embodiment, the wedge 14 has a bell shape, and the width thereof is set to 2.5 μm.
14 is very easy to form, and unlike the conventional Y-branch optical waveguide circuit in which a triangular wedge 14 having an extremely small apex angle is arranged, it is sandwiched between the branch-side optical waveguides 13a and 13b. By disposing the wedge 14, the Y-branch optical waveguide circuit can be manufactured accurately and with good reproducibility.

The present invention is not limited to the above-mentioned embodiment, and various embodiments can be adopted. For example, although the width of the wedge 14 is set to 2.5 μm in the above embodiment, the width of the wedge 14 is not limited to 2.5 μm, the wedge 14 can be easily formed, and the wedge 14 can be manufactured with good reproducibility. If possible, the width of the wedge 14 should be as small as possible as shown in FIG.

In the above embodiment, the wedge 14 has a length of 120.
Although the length of the wedge 14 is not limited to 120 μm, it is set appropriately, for example, about 70 to 150 μm.
Since the excess loss of the Y-branch optical waveguide circuit can be made extremely small by forming the wedge m, it is desirable to form the wedge 14 to have a length of about 70 to 150 μm.

Further, in the above embodiment, the tapered waveguide is used.
The opening angle of 12 is 0.2 °, and the branch side optical waveguides 13a and 13b
Although the branch angle β of the above is set to 0.7 °, the opening angle θ of the tapered waveguide 12 and the branch angle β of the branch side optical waveguides 13a and 13b are not particularly limited, and the branch angle β is smaller than the opening angle θ. By making the Y-branch optical waveguide circuit large, the excess loss of the Y-branch optical waveguide circuit is appropriately set.

Furthermore, in the above embodiment, the merging side optical waveguide is used.
11 and branch side optical waveguides 13a and 13b have a waveguide width of 8 μm
However, the merging side optical waveguide 11 and the branch side optical waveguides 13a, 13
The waveguide width of b is not limited to 8 μm, but may be set as appropriate.

Further, in the above embodiment, the branch side optical waveguide
A region extending from the base end side 16 to the tip end side sandwiching the wedge 14 of 13a is a curved waveguide having a radius of curvature of 50 μm, but the curvature radius of the curved waveguides of the branch side optical waveguides 13a and 13b is not always 50 μm. This is not always the case, but is set appropriately. Further, the branch side optical waveguides 13a and 13b can also be formed by linear optical waveguides. However, the circuit length of the Y-branch optical waveguide circuit is shortened by forming the branch-side optical waveguides 13a and 13b in a curved manner so as to widen the distance between the two branch-side optical waveguides 13a and 13b as in the above embodiment. In addition, the branch side optical waveguide is
It is desirable that 13a and 13b have a curved waveguide.

Further, in the above embodiment, the wedge 14 is made of quartz glass or the like made of the same material as the cladding layer 10.
May be formed of a material different from that of the clad layer 10, and is formed of an appropriate material having a lower refractive index than the Y-branch optical waveguide 9 which is the core layer.

Further, the material and forming method of the Y-branch optical waveguide 9 and the clad layer 10 which form the Y-branch optical waveguide circuit of the present invention are not particularly limited and may be appropriately set.

Further, in the above embodiment, the wavelength λ from the merging side optical waveguide 11 of the Y branch optical waveguide circuit is 1.31 μm or 1.55.
The evaluation was carried out by injecting light of μm, but the wavelength of light incident on the Y-branch optical waveguide circuit is not particularly limited,
It is set appropriately.

Further, in the above embodiment, the Y-branch optical waveguide circuit of the present invention is connected in three stages to obtain the one shown in FIG.
The formation example for forming the × 8 star coupler has been described.
By connecting the Y-branch optical waveguide circuits of the present invention in multiple stages, 1 × N branch circuits and 2
Various circuits such as a × N branch circuit can be configured.

[0046]

According to the present invention, the branch portion of the Y-branch optical waveguide (the side of the branch-side optical waveguide connected to the tapered waveguide).
, A bell-shaped wedge having a refractive index lower than that of the Y-branching optical waveguide is arranged, and the branching angle of the branching-side optical waveguide is formed to be larger than the opening angle of the tapered waveguide. It is possible to substantially match the angle of the light that is forcibly bent to the optical waveguide side with the branching angle, so that the peak position of the distributed light intensity and the center of the optical axis of the branching side optical waveguide are matched. As a result, it is possible to suppress light leakage and light meandering propagation due to mismatching between the tapered waveguide and the branch side optical waveguide.

Moreover, according to the present embodiment, the branch angle of the branch side optical waveguide is made larger than the opening angle of the tapered optical waveguide, so that the circuit length of the entire circuit can be shortened. As a result, in addition to reducing the loss at the branch portion, it is possible to suppress the propagation loss of light, and to provide an excellent circuit that can efficiently branch and propagate light with very low loss. You can
It is possible to reduce the circuit size and cost.

Further, according to this embodiment, the wedge is a bell-shaped wedge, which is different from the case where a triangular wedge having an extremely small apex angle is arranged as in the conventional Y-branch optical waveguide circuit.
It is possible to easily form a wedge, which allows Y
The branched optical waveguide circuit can be manufactured accurately and with good reproducibility.

In particular, according to the present invention, the length of the wedge is about 70 to 150 μm. According to the present invention, the wedge is formed to a length within the range of about 70 to 150 μm. The bent peak position of the light intensity and the optical axis of the branch-side optical waveguide can be more surely aligned with each other, and the above-mentioned effect can be achieved more reliably.

Further, the region extending from the base end side to the tip end side of the branch side optical waveguide sandwiching the wedge is a curved waveguide formed in a direction to increase the distance between the two branch side optical waveguides. According to the invention, the circuit length of the Y-branch optical waveguide circuit can be shortened even when the distance between the two branch-side optical waveguides is set to be wide, which reduces the propagation loss of the circuit and reduces the size of the circuit. And further cost reduction can be achieved.

[Brief description of drawings]

FIG. 1 is a main part configuration diagram showing an embodiment of a Y-branch optical waveguide circuit according to the present invention.

FIG. 2 is a graph showing a simulation result of excess loss obtained by using a wedge length L and a branch angle β of a branch side optical waveguide as parameters in the Y branch optical waveguide circuit having the configuration shown in FIG.

FIG. 3 is a graph showing a measurement result of excess loss obtained by using a wedge length L as a parameter in the Y-branch optical waveguide circuit having the configuration shown in FIG.

FIG. 4 is a graph showing a simulation result of excess loss obtained by using the width of a wedge as a parameter in the Y-branch optical waveguide having the configuration shown in FIG.

FIG. 5 is an explanatory diagram showing a 1 × 8 star coupler formed by connecting Y branch optical waveguide circuits in three stages.

FIG. 6 is a graph showing the measurement results of insertion loss in a 1 × 8 star coupler formed by connecting the Y-branch optical waveguide circuits of the above example as shown in FIG.

FIG. 7 is an explanatory diagram showing a conventional Y-branch optical waveguide circuit.

8 is a graph showing measurement results of insertion loss in a 1 × 8 star coupler formed by connecting the Y-branch optical waveguide circuit of the conventional example shown in FIG. 7 as shown in FIG.

FIG. 9 is an explanatory diagram showing an example of a method of forming a waveguide type optical branch circuit.

FIG. 10 is an explanatory diagram showing another example of forming a bell-shaped wedge.

FIG. 11 is an explanatory diagram of a wedge phase accelerator effect.

[Explanation of symbols]

 9 Y branch optical waveguide 11 Merging side optical waveguide 12 Tapered waveguides 13a, 13b Branch side optical waveguide 14 Wedge θ Opening angle β Branching angle

Claims (3)

[Claims] 1. A Y-branch optical waveguide in which two branch-side optical waveguides and one merging-side optical waveguide are connected in a Y-shape on the branch-side optical waveguide side through a tapered waveguide having a wide width. In the Y-branch optical waveguide circuit, a bell-shaped wedge having a refractive index lower than that of the Y-branch optical waveguide is sandwiched between the branch-side optical waveguides on the connection end side of the branch-side optical waveguide with the tapered waveguide. The Y-branch optical waveguide circuit, wherein the branch-side optical waveguide has a branching angle larger than an opening angle of the tapered waveguide. 2. The Y-branch optical waveguide circuit according to claim 1, wherein the wedge has a length of about 70 to 150 μm. 3. An area extending from a base end side to a tip side of a branch side optical waveguide sandwiching a wedge is formed as a curved waveguide curved in a direction of increasing a distance between two branch side optical waveguides. The Y-branch optical waveguide circuit according to claim 1 or 2.