JPH06235842A - Optical coupler and mutually connectable star coupler - Google Patents

Abstract

PURPOSE:To obtain an optical coupler of a single mode without any confluent loss by serially connecting a Y-shaped branching path with an evanescent optical coupler. CONSTITUTION:The optical coupler shown by a figure is the optical coupler in which the asymmetrical Y-shaped branched path is in series connected with an evanescent optical coupler 4. On a boundary surface between a connecting part 3 and the evanescent optical coupler 4, an optical path difference is adjusted so that the phases of two optical waveguide are in phase that is, a phase matching condition is satisfied. In a single mode optical waveguide, a light is made incident from one optical waveguide 5b of a branching part 4, and in the evanescent optical coupler 4, the light of an optical waveguide 4b is mode-connected on an optical waveguide 4a side and branched, and the branched lights are made confluent again at the asymmetrical Y-shaped branched path 2. At that time, when the phases of the two branched lights are opposite, they are cancelled and the loss is generated. In this case, the optical difference is adjusted so that the phase matching condition can be satisfied and the loss can not be generated. This is applicable to the light made incident from the other optical waveguide 5a of the branching part 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical coupler for branching and multiplexing guided light, and more particularly to an optical coupler having a single-mode guided mode. The present invention also relates to the configuration of a star coupler used in an optical LAN,
In particular, it relates to a star coupler which can be used by being connected to each other in a single mode. It also relates to a star coupler having substantially the same function as a single mode circulator.

[0002]

2. Description of the Related Art Hitherto, there have been proposed star couplers that can be used by connecting them to each other (see, for example, Ohta “Interconnectable Star Coupler”, Spring Institute of Electronics, Information and Communication Engineers B910 (1991), 1991). . In addition, an optical communication network has been proposed in which interconnectable star couplers are connected via an optical amplifier (for example, Takeshi Ota: “Coupled St”).
ar Network: A New Config
ation for Optical Local A
rea Network "IEICE Trans.
Commun. Vol. E75-B, No. 2, p67
-P75 (1992)).

Furthermore, an interconnectable star coupler in which an input terminal and an output terminal are integrated is proposed (for example, Ohta "Coupled Star Network" 19).
1992 Spring Institute of Electronics, Information and Communication Engineers B1020 (1992)). In the single-mode optical waveguide, it is necessary to use an evanescent optical coupler (directional coupler) as the unequal optical branch (for example, see Japanese Patent Application No. 3-158614 filed by the present applicant). Therefore, the conventional example (4 terminals) of a single mode interconnectable star coupler in which the input terminal and the output terminal are combined is shown in FIG.
The structure is as shown in FIG.

An optical signal S input from a terminal having a four-terminal star coupler shown in FIG. 16 is an evanescent light (ev).
an optical) optical coupler (directional coupler) 15a
Is split into two waveguides at a ratio of 0.414: 0.586. One of them (the one with the smaller branching ratio) goes to the opposite terminal, and the other (the one with the larger branching ratio) goes to the remaining two terminals after being equally branched by the evanescent optical coupler (directional coupler) 12. . FIG.
Since each terminal of the star coupler of is symmetrical, the optical signal is not distributed to its own terminal for the input of any terminal,
The optical signal is equally distributed to the terminals other than the own terminal.

By the way, the evanescent optical coupler has a problem that there is a merging loss as shown in FIG. For example, in the evanescent optical coupler 15b, a signal of 0.414S and a signal component of 0.172S and 0.
It is divided into a loss component of 242S, and the loss component is larger than the signal component.

In an evanescent optical coupler (directional coupler), two relatively long optical waveguides (hundreds of wavelengths: several hundreds of microns) are arranged close to each other at a short distance (several wavelengths: several microns). However, a Y-shaped optical branch having a structure in which the optical waveguide is branched has the same function.
Moreover, the Y-shaped optical branching path does not have the merging loss as seen in the evanescent optical coupler. In a multimode Y-shaped optical branch having a plurality of guided modes, the branching ratio is the cross-sectional area ratio of two branched optical waveguides, and a branching ratio of any desired value can be manufactured. On the other hand, in a Y-shaped optical branching path of a single mode with a single guided mode, an optical branching path with a branching ratio of 1: 1 is relatively often used. There are almost no examples of fabrication of unequal optical branches. This is because it is difficult to control the branching ratio of the single mode optical nonuniform branching path. That is, in the single-mode asymmetric Y-shaped optical branch path, most of the two branched optical waveguides flow into the optical waveguide side with a large propagation constant, and almost no light enters the optical waveguide with a small propagation constant. It does not flow (for example, W. K. Burns et al., IEEE).
J. Quantum Elestron. , QE-1
1, p32 (1975) (referred to as document (1) below). To be more precise, the branching ratio greatly changes with a slight difference in the propagation constants of the two branched optical waveguides. This means that the fabrication of a single mode optical iso-branch path itself is more difficult than the evanescent optical coupler. That is, the branching ratio is greatly changed by a slight loss of the symmetry of the optical branch path due to a manufacturing error.

The asymmetric Y-shaped optical branching path referred to here is one in which two optical waveguides whose cross-sectional shapes are not equal are branched at the same angle with respect to the original optical waveguide, and an optical waveguide whose cross-sectional shape is the same. Is a general term for those branching at different angles with respect to the optical waveguide, or those for which two optical waveguides whose cross-sectional shapes are not equal branch at different angles with respect to the original optical waveguide. In short, Y except for the symmetrical Y-shaped optical branch
It is a letter-shaped optical branch.

In a single mode Y-shaped asymmetrical optical branching path as shown in FIG. 17, there is an example in which the branching ratio is calculated and the asymmetrical optical branching path is actually manufactured to obtain the branching ratio (Negami, Haga, Yamamoto, "Waveguide Optical Wavelength Filter Using Y-Branch," IEICE 70th Anniversary General Conference (1987), 972, p4-134 (1987)
(Hereinafter referred to as reference (2)) and Negami, Haga, Yamamoto, "Optical wavelength demultiplexer using Y branch waveguide", Showa 63.
IEICE Fall National Congress, C-187 (198
8) (referred to as document (3) below). 18 is shown in FIG.
7 is a sectional view taken along line XX ′ in FIG. In the above reference (2), FIG.
8 (b), d ₁ = 4.2 μm, w ₁ = 3.
5 μm, d ₂ = 3.3 μm, w ₂ = 4.0 μm, θ =
When set to 0.002 rad (-0.12 °), the wavelength λ
It is described that the light incident from the optical waveguide P _{0 of} = 1.25 μm is branched into energy of only −25 dB (about 1/300) from the P ₂ side to the P ₁ side.
Further, although the configuration of the reference (3) is slightly different from the configuration of the reference (2), a Y-shaped asymmetrical optical branch path is actually manufactured to obtain a result almost in theory. It should be noted from the above results that the slight asymmetry of the Y-shaped optical branch path causes an extremely large difference in branching ratio. Documents (2) and (3) aim at making an optical wavelength demultiplexer, as can be seen from its title. That is, an optical wavelength demultiplexer is made by giving wavelength dependence to the magnitude relationship of the propagation constants of two branched optical waveguides. Therefore, the sectional structure is as shown in FIG. According to the document (2), the above branching ratio is λ = 1.0.
At 7 μm, P ₁ and P ₂ are equally distributed. At λ = 0.80 μm, on the other hand, P ₂ side is -30 dB (about 1/1) to P ₁ side.
It is calculated that the branching ratio changes depending on the wavelength, such that only 000) is branched. As described in Reference (2), in the cross-sectional structure as shown in FIG. 18A, the magnitude relationship of the propagation constants of the two optical waveguides does not change much depending on the wavelength, but it is caused by the difference in the propagation constants. A difference in branching ratio occurs. Therefore, an optical wavelength demultiplexer cannot be made with the sectional structure of FIG.

[0009]

As described above, in order to construct an interconnectable star coupler, an unequal-branch optical coupler is required. However, when the guided mode is a single mode, there is a problem that the evanescent optical coupler causes a coupling loss and it is difficult to control the branching ratio in the Y-shaped optical branching path. Further, the conventional example shown in FIG. 16 has a problem that it is difficult to reduce the size of the star coupler because an arcuate optical waveguide is included in the circuit.

Therefore, an object of the present invention is to realize a single-mode optical coupler (optical unequal branch path) with no merging loss. Another object of the present invention is to realize an interconnectable star coupler with little excess loss by adopting this optical coupler in a circuit. Still another object of the present invention is to miniaturize an optical integrated circuit of interconnectable star couplers.

[0011]

To achieve the above object, the optical coupler of the present invention is characterized in that a Y-shaped branch path and an evanescent optical coupler are connected in series. Especially Y
The character-shaped branch path is an asymmetric Y-shaped branch path. Further, the optical coupler of the present invention is characterized by satisfying a phase matching condition. Further, the optical coupler of the present invention is characterized in that the optical path difference of the optical waveguide branched in order to satisfy the phase matching condition is eliminated. The interconnectable star coupler of the present invention is characterized by including the above-mentioned optical coupler as a component in a circuit. Further, the interconnectable star coupler of the present invention is characterized in that a reflection means is provided in the optical waveguide circuit and the optical path of the light guided by the reflection means is changed. Furthermore, in a star coupler in which N (N ≧ 3) optical couplers are connected in a polygon, at least one of the optical couplers is an asymmetric Y-shaped branch path.

[0012]

The optical coupler of the present invention has an asymmetric Y-shaped branch path and an evanescent optical coupler connected in series,
The evanescent optical coupler controls the branching ratio, and the asymmetric Y-shaped branching path can prevent the generation of multiplexing loss. The interconnectable star coupler of the present invention can reduce loss by including the above-mentioned optical coupler as a constituent element in the circuit. Further, the interconnectable star coupler of the present invention can be downsized by providing a reflecting means in the optical waveguide circuit and changing the optical path of the light guided by the reflecting means.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The features of the present invention will be specifically described below based on embodiments with reference to the drawings. The optical waveguides in the following examples are all single mode optical waveguides.

FIG. 1 is a plan view of an embodiment of the optical coupler of the present invention. The optical coupler shown in FIG. 1 is an optical coupler in which an asymmetric Y-shaped branch 2 and an evanescent optical coupler 4 are connected in series. The asymmetric Y-shaped branch path is, as described above, one in which two optical waveguides whose cross-sectional shapes are not equal are branched at the same angle with respect to the original optical waveguide, and an optical waveguide whose cross-sectional shape is equal. Is a general term for those branching at different angles with respect to the optical waveguide, or those for which two optical waveguides whose cross-sectional shapes are not equal branch at different angles with respect to the original optical waveguide. In the asymmetric Y-shaped branch 2 of the embodiment shown in FIG. 1, the optical waveguide 2b is linear with the optical waveguide of the common portion 1, and the waveguide cross-sectional area is the optical waveguide 2b.
Is larger than the optical waveguide 2a. In the evanescent optical coupler 4, the two optical waveguides 4a and 4b are the same, so that the waveguide cross-sectional area of the optical waveguide 3a in the connection portion 3 increases from the left to the right in FIG.
At the interface between the connecting portion 3 and the evanescent optical coupler 4, the optical path difference is adjusted so that the two optical waveguides have the same phase, that is, the phase matching condition is satisfied. The phase matching condition will be described later.

In the single mode optical waveguide, as shown in FIG. 2, most of the light incident from the common portion 1 propagates to the optical waveguide 2b side and hardly propagates to the optical waveguide 2a side in the asymmetric Y-shaped branch 2. . In the evanescent optical coupler 4, the light of the optical waveguide 4b is mode-coupled and branched to the optical waveguide 4a side. Therefore, the optical coupler shown in FIG. 1 functions as an unequal optical branch path.

As shown in FIG. 3, the light incident from the optical waveguide 5b on one side of the branching portion 5 is branched by the evanescent optical coupler 4 while the light of the optical waveguide 4b is mode-coupled to the optical waveguide 4a side. The rays of light rejoin at the asymmetric Y-shaped branch path 2. In this case, if the phases of the two split lights at the time of merging are opposite to each other, they cancel each other and a loss occurs. In this embodiment, since the optical path difference is adjusted so as to satisfy the phase matching condition, no loss occurs.

As shown in FIG. 4, the light incident from the other optical waveguide 5a of the branching portion 5 is branched by the evanescent optical coupler 4 while the light of the optical waveguide 4a is mode-coupled to the optical waveguide 4b side. The branched light is an asymmetric Y-shaped branch 2
And join again. Also in this case, since the optical path is adjusted so as to satisfy the phase matching condition, no loss occurs.

FIG. 5 schematically shows the relationship of the optical paths of the optical coupler of FIG. In the asymmetric Y-shaped branch path 2, an optical path difference is generated by δ = rsin θ. However, r is the optical waveguide spacing of the evanescent optical coupler 4,
θ is a branch angle of the asymmetric Y-shaped branch path 2. The phase matching condition is satisfied when the optical path difference δ is an integral multiple of the wavelength of the propagating light. Therefore, the phase matching condition changes depending on the wavelength of the propagating light, and the optical coupler of FIG. 1 needs to be designed according to the wavelength used.

FIGS. 6 and 7 show another embodiment constructed by modifying the optical coupler shown in FIG. In these two embodiments, the optical path difference δ between the two optical waveguides that are branched is designed to be 0, so that the wavelength dependence of the phase matching condition does not occur.

The embodiment shown in FIG. 6 has an asymmetric Y-shaped branch path 6 in which optical waveguides having different cross-sectional areas are branched substantially symmetrically at branch angles ω ₁ and ω ₂ . In FIG. 6, the cross-sectional area of the optical waveguide 6a is smaller than that of the optical waveguide 6b. Also, the original optical waveguide 1
With respect to ω ₁ ≈ ω ₂ .
An optical waveguide having a smaller cross-sectional area has a smaller effective refractive index and thus a higher propagation velocity of light, and if ω ₁ = ω ₂ , the phase matching condition cannot be satisfied. Therefore, the optical path difference δ is set to 0 by slightly increasing ω ₁ .

In the embodiment shown in FIG. 7, an asymmetric Y-shaped branch path 7 and an optical path difference adjusting section 8 are provided, which branch the optical waveguides 7a and 7b having the same cross-sectional area with an asymmetric branch angle with respect to the original optical waveguide 1. As a result, the optical path difference δ is set to 0. The optical path 7a that has proceeded straight through the asymmetric Y-shaped branch path 7 has its optical path bent by the optical path difference adjusting unit 8, and the optical path difference δ is 0 in the evanescent optical coupler 4.

Since it is known that the coupling characteristics of the evanescent optical coupler also have wavelength dependence, it is necessary to take this into consideration when designing the actual optical coupler.

As explained above, FIG. 1, FIG. 6 and FIG.
The optical coupler of (1) functions as an unequal optical branch path without merging loss.

FIG. 8 is a plan view of one embodiment of the interconnectable star coupler of the present invention. The interconnectable star coupler shown in FIG. 8 is an evanescent optical coupler 15a to 15d of the conventional star coupler shown in FIG.
The optical couplers 11a to 11d shown in FIG. 1, FIG. 6 or FIG.
Is replaced with. When the optical couplers 11a to 11d are used, the merging loss is not impaired, so that it is possible to realize an interconnectable star coupler with less excess loss.

FIG. 9 shows an embodiment constructed by modifying the interconnectable star coupler of FIG. In the star coupler shown in FIG. 9, the reflection means 25 is provided in the optical waveguide circuit, and thereby the bent portion 14 is formed by bending the optical waveguide at a substantially right angle. Therefore, the arc-shaped optical waveguide shown in FIGS. 16 and 8 is eliminated, the substrate area required for the optical integrated circuit can be reduced, and the star coupler can be miniaturized. In addition, in the configuration of FIG.
Although the branch having a small branching ratio of 11d is connected to the opposite terminal, the branch having a small branching ratio is connected to the adjacent terminal in FIG. Also, in the configuration of FIG. 9, instead of the evanescent optical coupler 12 of FIG.
, Which is an evanescent optical coupler 1
It may be 2. On the contrary, an X-shaped optical branch 13 may be used instead of the evanescent optical coupler 12 shown in FIG.

An enlarged view of the evanescent optical coupler 12 is shown in FIG. 10 (a), and an enlarged view of the X-shaped optical branch path 13 is shown in FIG.
FIG. 10C is an enlarged view of the bent portion 14 in FIG.
, Respectively.

In FIG. 10A, the light incident from the optical waveguide 21a is mode-coupled at the coupling portion 23 in which the two optical waveguides are arranged in close proximity to each other, and the optical waveguides 22a and 22b.
Are evenly distributed. Light incident from the optical waveguide 21b is equally distributed to the optical waveguides 22a and 22b.

In FIG. 10B, the light incident from the optical waveguide 21a is equally distributed to the optical waveguides 22a and 22b via the mixing optical waveguide 24. Light incident from the optical waveguide 21b is equally distributed to the optical waveguides 22a and 22b.

In FIG. 10C, the light incident from the optical waveguide 21 is reflected by the reflecting means 25 and the optical path is bent toward the optical waveguide 22. The reflecting means 25 is specifically a total reflection mirror or the like formed by dry etching on the optical integrated circuit substrate. A technique for bending an optical waveguide using a total reflection mirror is already known (for example, Shibata, Oku,
Ikeda, Kadota, "Multistage connectivity of asymmetric Y-branch using total reflection mirror", 1992 IEICE Spring Conference, C
-198 (1992)).

The method of providing the reflecting means in the optical waveguide is effective also in the conventional interconnectable star coupler in terms of miniaturization of the optical integrated circuit.

The present invention can also be applied to a 1 × 3 optical coupler. FIG. 11 shows an example in which a 1 × 3 optical coupler 15 of the present invention is used to form a 4-terminal interconnectable star coupler. Since the 1 × 3 optical branch 17 basically has an asymmetric structure, the 1 × 3 evanescent optical coupler 1
By connecting in series with 8 (three optical waveguides arranged in parallel), a 1 × 3 optical coupler 15 without merge loss can be formed. Therefore, four such 1 × 3 optical couplers 15 can be combined to form a star coupler capable of interconnecting four terminals with a small excess loss. In the orthogonal portion 16 of the optical waveguide, the lights passing through the two orthogonal optical waveguides do not affect each other due to the straightness of the light. The structure itself of the four-terminal interconnectable star coupler shown in FIG. 11 is described in Japanese Patent Application No. 4-187065 filed by the present applicant.

FIG. 12 shows an embodiment of a three-terminal star coupler having substantially the same function as a single-mode circulator, in which asymmetric Y-shaped branch paths 31a to 31c are connected in a triangular shape. In this star coupler, all optical signals input to the terminal 32a are transmitted to the terminal 32b, all optical signals input to the terminal 32b are transmitted to the terminal 32c, and all optical signals input to the terminal 32c are transmitted to the terminal 32a.

FIG. 13 shows an embodiment of a four-terminal star coupler having substantially the same function as a single-mode circulator, in which asymmetric Y-shaped branch paths 31a to 31d are connected in a quadrangular shape. In this star coupler, all optical signals input to the terminal 32a are input to the terminal 32b, all optical signals input to the terminal 32b are input to the terminal 32c, all optical signals input to the terminal 32c are input to the terminal 32d, and optical signals input to the terminal 32 are input. All signals are transmitted to the terminal 32a.

Similarly, a star coupler having substantially the same function as a circulator having five or more terminals can be constructed.

Further, by using the optical coupler shown in FIG. 1 as a part of the N optical couplers connected in a polygonal shape or using a symmetrical Y-shaped branch path, a star having various characteristics other than the above is provided. A coupler can be constructed.

For example, FIG. 14 shows an embodiment of a star coupler that functions as a single mode bidirectional access coupler. The optical couplers 41a and 41b are optical couplers having the configuration shown in FIG. 1, and 42 is a symmetrical Y-shaped branch path. Most of the optical signals input to the terminal 43b (for example, 99
%) Is transmitted to the terminal 43c, and a part (for example, 1%) is transmitted to the terminal 43a. Similarly, most (for example, 99%) of the optical signal input to the terminal 43c is transmitted to the terminal 43b, and part (for example, 1%) is transmitted to the terminal 43a. The optical signals input to the terminal 43a are transmitted to the terminals 43b and 43c half by half. By connecting the bidirectional access couplers 50 shown in FIG. 14 in series, a so-called T (Y) branch network as shown in FIG. 15 can be constructed. In addition, 51 is a station and 52 is a bus (optical fiber).

The optical coupler and the interconnectable star coupler of the present invention can be manufactured by a known optical waveguide (optical integrated circuit) manufacturing method such as an ion exchange method and a flame deposition method.

[0038]

According to the present invention, it is possible to realize a single-mode optical coupler without merging loss. By adopting this optical coupler in a circuit, an interconnectable star coupler with less excess loss can be realized. Can be realized. Further, by providing the reflecting means in the circuit, the optical waveguide can be bent at a substantially right angle, and the interconnected star coupler optical integrated circuit can be miniaturized. Further, star couplers having various characteristics can be formed, for example, a star coupler having substantially the same function as a circulator or a bidirectional access coupler can be formed.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of an optical coupler of the present invention.

FIG. 2 is a schematic diagram showing a propagation state of light incident from a common part in the optical coupler shown in FIG.

FIG. 3 is a schematic diagram showing a propagation state of light incident from one optical waveguide of a branch section in the optical coupler shown in FIG.

FIG. 4 is a schematic diagram showing a propagation state of light incident from the other optical waveguide of the branch section in the optical coupler shown in FIG.

5 is a schematic diagram showing an optical path in a branch path of the optical coupler of FIG. 1. FIG.

FIG. 6 is a plan view showing another embodiment of the optical coupler of the present invention.

FIG. 7 is a plan view showing still another embodiment of the optical coupler according to the present invention.

FIG. 8 is a plan view showing one embodiment of an interconnectable star coupler of the present invention.

FIG. 9 is a plan view showing another embodiment of the interconnectable star coupler of the present invention.

FIG. 10 is an enlarged plan view of the components of the interconnectable star coupler of the present invention.

FIG. 11 is a diagram showing an example of an interconnectable star coupler constructed using the 1 × 3 optical coupler of the present invention.

FIG. 12 is a plan view of a three-terminal star coupler having substantially the same function as a circulator in a modification of the present invention.

FIG. 13 is a plan view of a four-terminal star coupler having substantially the same function as a circulator in a modification of the present invention.

FIG. 14 is a plan view of a three-terminal star coupler having a function substantially the same as that of the bidirectional access coupler according to the modification of the present invention.

15 is a schematic diagram of a T (Y) -branch network configured using the bidirectional access coupler of FIG.

FIG. 16 is a plan view showing a conventional example of an interconnectable star coupler.

FIG. 17 is a plan view of an asymmetric Y-shaped branch path.

18 is a cross-sectional view taken along the line X-X ′ of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Common part, 2 ... Asymmetrical Y-shaped branch path, 2a, 2b ... Optical waveguide, 3 ... Connection part, 3a, 3b ... Optical waveguide, 4 ... 1x
2 evanescent optical couplers, 4a, 4b ... optical waveguide,
Reference numeral 5 ... Branch portion, 5a, 5b ... Optical waveguide, 6 ... Asymmetric Y-shaped branch path in which optical waveguides having different cross-sectional areas are branched substantially symmetrically, 6
a, 6b ... Optical waveguide, 7 ... Asymmetrical Y-shaped branch path in which optical waveguides having the same cross-sectional area are asymmetrically branched, 7a, 7b ... Optical waveguide, 8 ... Optical path difference adjusting section, 10 ... Substrate, 11a-11d ...
Optical coupler of the present invention, 12 ... 2 × 2 evanescent optical coupler, 13 ... 2 × 2 X-shaped branch path, 14 ... Bent portion of optical waveguide, 15 ... 1 × 3 optical coupler of the present invention, 16
... orthogonal part of optical waveguide, 17 ... 1x3 (asymmetric) optical branch, 18 ... 1x3 evanescent optical coupler, 19 ... optical fiber, 21a, 21b ... optical waveguide, 22a, 22
b ... Optical waveguide, 23 ... Evanescent optical coupler coupling part, 24 ... Mixing optical waveguide, 25 ... Reflecting means, 31
a-31d ... Asymmetrical Y-shaped branch path, 32a-32d ... Circulator (star coupler) terminals, 41a-41
b ... Optical coupler, 42 ... Symmetrical Y-shaped branch path, 43a-4
3d ... Terminal of bidirectional access coupler (star coupler), 50 ... Bidirectional access coupler (star coupler), 51 ... Station, 52 ... Bus (optical fiber), d ₁ , d
₂ ... Optical waveguide thickness, w ₁ , w ₂ ... Optical waveguide width, θ ...
Asymmetric Y-shaped branch path branch angle, δ ... Optical path difference, r ... Optical waveguide spacing of evanescent optical coupler, ω ₁ ... Branch angle of optical waveguide 6a with respect to original optical waveguide, ω ₂ ... Optical waveguide with respect to original optical waveguide 6b divergence angle

Claims (7)

[Claims] 1. An optical coupler for branching and multiplexing guided light, wherein an Y-shaped branch path and an evanescent optical coupler are connected in series. 2. The optical coupler according to claim 1, wherein the Y-shaped branch path is an asymmetric Y-shaped branch path. 3. The optical coupler according to claim 1 or 2, wherein the optical path length of the optical waveguide is selected so that a phase matching condition is satisfied at the combining portion of the Y-shaped branch path. . 4. The optical coupler according to claim 3, wherein the phase matching condition is satisfied by eliminating the optical path difference between the branched optical waveguides. 5. An interconnectable star coupler comprising an optical coupler according to any one of claims 1 to 4 as a constituent element in an optical waveguide circuit. 6. The interconnectable star coupler according to claim 5, wherein a reflecting means is provided in the optical waveguide circuit for changing the optical path of the guided light. 7. A star coupler in which N (N ≧ 3) optical couplers are connected in a polygonal shape, at least one of the optical couplers being an asymmetric Y-shaped branch path.