JPH10300953A - Optical multiplexer/demultiplexer device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form two-way waveguides and reflection end faces in one etching process by anisotropic etching operation by providing the axes of the two-way waveguides to be parallel with each other at least in the waveguide part on the side of the reflection end face and the reflection end faces to be parallel with each other. SOLUTION: A two-way waveguide array 26 is arranged so that the optical axes 01-05 of a back and forth waveguides 28 become parallel with each other. Reflection end faces 33 are provided to be parallel with each other. A planar waveguide part 14 guides a light beam from an input/output waveguide 24 to the two-way waveguide array 26, reflection light beams from the two-way waveguides 28 are again guide and the focused light beam is demultiplexed to the input/output waveguide 24. An input/output waveguide array 20 is provided with an input/output port 22 on the side of end face of a substrate 12 and makes a frequency multiplexed light beam incident on the input/output waveguide 24. The two-way waveguide array 26 is provided with the two-way waveguides 28 having different lengths for guiding the light beam incident from the planar waveguide part 14 and the reflection end faces 33 for reflecting the light beam.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical multiplexer / demultiplexer.

[0002]

2. Description of the Related Art A conventional optical multiplexing / demultiplexing device is disclosed in, for example, Japanese Patent Application Laid-Open No. 2-244105.

This optical multiplexer / demultiplexer includes a star coupler having a lens-shaped planar waveguide, a plurality of input / output waveguides (three-dimensional input / output waveguides) connected to one connection surface of the star coupler. , The input / output end face is connected to the other connection face of the star coupler, the input / output end face has a reflection end face (high reflectance termination processing) on the opposite side, and a plurality of reciprocating waveguides having different lengths ( Three-dimensional waveguide).

[0004]

However, in the conventional optical multiplexing / demultiplexing device, the reflection end faces of the reciprocating waveguides are provided in directions perpendicular to the optical axis of the radial reciprocating waveguides. For this reason, the directions of the reflection end faces are not parallel, but are directed in different directions. For this reason, for example, when forming the reflection end face using anisotropic etching, it is difficult to form the reflection end face under one etching condition.

In the conventional optical multiplexer / demultiplexer, when forming a reflection end face, for example, in the RIE method, it is necessary to set an ion beam so as to be orthogonal to an optical axis of a reciprocating waveguide and form one reflection end face at a time. there were. As a result, workability is poor, causing an increase in cost.

Further, in the conventional device, since the reciprocating waveguides are provided radially, the entire structure of the device could not be made compact.

Therefore, there has been a demand for an optical multiplexer / demultiplexer in which the reflection end face of the reciprocating waveguide array can be easily formed.

[0008] In addition, there has been a demand for a compact optical multiplexer / demultiplexer, which is more compact than before.

[0009]

According to the present invention, a planar waveguide, a plurality of input / output waveguides connected to one connection surface of the planar waveguide, and In an optical multiplexer / demultiplexer in which an end face is connected to the other connection face of the planar waveguide and has a reflection end face, and a plurality of reciprocating waveguides having different lengths are provided, the optical axis of the reciprocating waveguide is At least in the waveguide portion on the reflection end face side, they are provided in parallel with each other, and the reflection end faces are provided in parallel with each other.

As described above, according to the present invention, the optical axes of the reciprocating waveguides are provided parallel to each other at the waveguide portion on the reflection end face side, and the reflection end faces are provided parallel to each other.
When forming the reciprocating waveguide portion and the reflecting end face, the reciprocating waveguide and the reflecting end face can be formed by one etching process by anisotropic etching. Therefore,
Since the etching process is simplified as compared with the related art, the manufacturing cost of the device is reduced.

Further, since at least the waveguide portions on the side of the reflection end face are provided in parallel with each other, it is possible to increase the density of the reciprocating waveguide portion as compared with the prior art, and thus it is possible to reduce the size of the optical multiplexer / demultiplexer. Become.

In the present invention, preferably, the total length of the reciprocating waveguide from the input / output end face to the reflection end face is:
Preferably, the optical axes of the reciprocating waveguides are parallel to each other.

Also in this case, for the same reason as described above, the formation of the reflection end face of the reciprocating waveguide is simplified, and
The size of the substrate can be reduced.

In the present invention, preferably, the waveguide portion on the input / output end face side of the reciprocating waveguide is used as a first light guide for increasing the amount of light incident from the planar waveguide to the reciprocating waveguide. , It is good to configure. Further, it is preferable that the first light guide section is a divergent waveguide in which the planar waveguide side is widened.

Since such a first light guide section is formed as a divergent waveguide, the first light guide section is not provided with the first light guide section.
It is possible to increase the amount of light incident from the planar waveguide to the reciprocating waveguide.

According to the present invention, preferably, each optical axis portion included in the first light guide portion of the reciprocating waveguide includes:
It is good to be arranged radially.

As described above, in the present invention, since the respective optical axes included in the first light guide portion are arranged radially, the light incident from the input / output waveguides passes through the planar waveguides respectively. Is guided smoothly to the reciprocating waveguide, and the phenomenon in which light propagates zigzag in the reciprocating waveguide can be prevented.

In the present invention, preferably, the waveguide portion on the reflection end face side of the reciprocating waveguide is used as a second light guide portion for reducing reflection loss of light guided through the reciprocating waveguide. It is good to be composed. Further, it is preferable that the second light guide section is a divergent waveguide having a wide reflection end face.

As described above, according to the present invention, since the waveguide portion on the reflection end face side of the reciprocating waveguide is configured as the second light guide, the reciprocating waveguide is provided as compared with the case where the second light guide is not provided. It is possible to reduce the loss (reflection loss) of light incident on the wave path at the reflection end face.

In the present invention, preferably, the waveguide portion on the input / output waveguide side where the input / output waveguide and the planar waveguide are connected is connected to the third light guide for controlling the angle of incident light. It is good to constitute as a part. Also, this third
It is preferable that the light guide section is a divergent waveguide in which the planar waveguide side is widened.

Further, the opening width d of the third light guide section, d> λ / (2√ ( 2Δn / n s) ( I to was, lambda is the wavelength, [Delta] n is the refractive index difference between the substrate and the waveguide , N _s is the refractive index of the substrate).

As described above, since the third light guide section is configured, the incident angle (also referred to as a diffraction angle) of the incident light from the input / output waveguide to the reciprocating waveguide can be controlled. That is, the diffraction angle θ _d is θ _d = λ / 2d (where d
Is the opening width. ), The larger the aperture width d, the smaller the diffraction angle. Thus, in the present invention, the diffraction angle can be set to be within the numerical aperture (NA) of the reciprocating waveguide. Also, the opening width d is
Because it is as d> λ / (2√ (2Δn / n s), by arbitrarily setting the opening width d, it is possible to arbitrarily control the diffraction angle theta _d when the light is incident to the reciprocating waveguide .

In the present invention, preferably, the input / output waveguide is formed in a mesa shape having a core, while the reciprocating waveguide is formed in a mesa shape having a height lower than that of the input / output waveguide.

As described above, the height of the mesa of the reciprocating waveguide is
By making the mesa lower than the mesa of the input / output waveguide, the confinement of light in the reciprocating waveguide can be weakened, and the fluctuation of the equivalent refractive index can be reduced (details will be described later).

[0025]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of an optical multiplexer / demultiplexer according to the present invention; FIG.
Nos. 1 to 8 merely show the shapes, sizes and arrangements of the components so that the present invention can be understood.

[First Embodiment] The structure of an optical multiplexing / demultiplexing apparatus according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a plan view for explaining a main structure of the optical multiplexer / demultiplexer according to the first embodiment. FIG. 2 is a perspective view for explaining the structure of the first light guide.

The optical multiplexer / demultiplexer according to the first embodiment is roughly composed of a planar waveguide section 14, an input / output waveguide array 20, and a reciprocating waveguide array 26. Here, the optical axes O ₁ , O ₂ , O ₃ , O ₄ and O ₅ of the reciprocating waveguide 28 are parallel to each other over the entire length from the input / output end face 31 of the reciprocating waveguide 28 to the reflection end face 33. A reciprocating waveguide array 26 is arranged. Also,
The reflection end faces 33 are provided in parallel with each other.

The planar waveguide 14 has a lens-like waveguide shape, and guides light from the input / output waveguide 24 to the reciprocating waveguide array 26 and guides reflected light from the reciprocating waveguide 28 again. Then, the focus light is branched to the input / output waveguide 24.

The input / output waveguide array 20 has an input / output port 22 on the end face side of the substrate 12.
In this case, the frequency multiplexed light from 2 is input to the input / output waveguide 24.

The input / output waveguide 24 is connected to the third light guide 25 continuously.
And the planar waveguide 14 are connected.

The reciprocating waveguide array 26 includes reciprocating waveguides 28 having different lengths for guiding light incident from the planar waveguide 14 and a reflection end face for reflecting the light of the reciprocating waveguide 28. 33. Further, a reflection film 34 is provided on the reflection end face 33 so as to be orthogonal to the optical axis of the reciprocating waveguide 28.

Further, on the reflection end face 33 side, the reflection end face 3
3, a rectangular groove 36 is provided. Here, the waveguide portion 38 on the reflection end face side including the reciprocating waveguide 28, the second light guide portion 32, and the reflection end face 33 is referred to.

The reciprocating waveguides 28 are preferably provided such that the reciprocating waveguides 28 are separated from each other. In this way, by separating the reciprocating waveguides 28, it is possible to avoid leakage of light or coupling of light between the reciprocating waveguides 28.

A first light guide 30 having the same optical axis as the reciprocating waveguide 28 is provided between the planar waveguide 14 and the reciprocating waveguide 28. The first light guide section 30 of this embodiment is a divergent waveguide having a wide planar waveguide side (FIG. 2). The first light guide 30 is also referred to as a tapered, trumpet, or fan-shaped waveguide. Then, the end face of the first light guide section 30 (input / output end face 3
The shape of 1) is an arc.

The first light guide section 30 is provided with the planar waveguide 14
This is for increasing the amount of light incident on the reciprocating waveguide 28 from.

A second light guide 32 is provided between the reciprocating waveguide 28 and the reflection end face 33. The second light guide section 32 of this embodiment is a divergent waveguide having a wide reflection end face. The second light guide 32 is also referred to as a tapered, trumpet-shaped, or fan-shaped waveguide. In addition, the end face of the second light guide section 32 has a linear shape.

The second light guide 32 is provided with the reciprocating waveguide 28
This is for reducing the reflection loss of light guided through.

The planar waveguide 14 and the input / output waveguide 24
A third light guide section 25 is provided between the first and second optical waveguides in accordance with the optical axis of the input / output waveguide. The third light guide section 25 of this embodiment is a divergent waveguide having a wide planar waveguide side. The third light guide 25 is also referred to as a tapered, trumpet-shaped, or fan-shaped waveguide. The end face of the third light guide 25 has the same shape as the first light guide 30.

The third light guide 25 is for controlling the angle of the incident light from the input / output waveguide 24.

Next, with reference to FIG. 3, the principle that the light emitted from the input / output waveguide is guided through the planar waveguide by using the optical multiplexer / demultiplexer of the first embodiment will be described. FIG.
FIG. 3 is a diagram for explaining how light is guided in a planar waveguide.

As described above, the third light guide portion 25 is provided between the one connection surface 16 of the planar waveguide 14 and the input / output waveguide 24. Further, between the other connecting surface 18 of the planar waveguide 14 and the reciprocating waveguide 28, the first light guide 3
0 is provided.

The width of the opening of the third light guide section 25 is set to d.
By changing the opening width d, the diffraction angle θ _d (degree) can be controlled. That is, the angle at which the power of the diffracted light 50b spreads (referred to as a diffraction angle) is θ.
_{Assuming d} , the diffraction angle θ _d is expressed by the following equation (1).

Θ _d = λ / 2d (1) where λ is the wavelength and d is the width of the opening of the third light guide.

[0044] (1) As apparent from the equation, as the opening width d is large, the diffraction angle theta _d decreases. Therefore, by setting the opening width d such that the light incident at the maximum amount with respect to the reciprocating waveguide 28 can be incident efficiently light 50b to the reciprocating waveguide 28 at an optimal diffraction angle theta _d. At this time, the diffraction angle θ _d is preferably set within the numerical aperture (NA) of the reciprocating waveguide 28.

The following equation (2) is obtained from Snell's law.

N _s <(n _s + Δn) cos θ _d or θ _d <√ (2Δ) (2) where Δ is a relative refractive index, and Δn / n _s (Δn is a distance between the substrate and the waveguide) the difference in refractive index, n _s is the refractive index of the substrate.)
Expressed by

From the above equations (1) and (2), the following equation (3) is obtained.
An expression is obtained.

D> λ / 2√ (2Δ) (3) For example, when Δ = 3% and λ = 1.55 μm, the opening width d is about 6 μm.

On the other hand, the first light guide section 30 outputs the diffracted light 50b
Is effectively provided to the reciprocating waveguide 28. Therefore, the light 50 incident on the first light guide 30
b is efficiently guided to the reciprocating waveguide 28.

Next, the structure of a reciprocating waveguide and a method of manufacturing the same will be described with reference to FIGS. In addition,
FIG. 4 is a plan view for explaining a main configuration of the reciprocating waveguide section. FIG. 5A is a diagram showing a cross section of the input / output waveguide according to the first embodiment, and FIG.
FIG. 4 is a view showing a cut end of a cross section of the reciprocating waveguide.

In the optical multiplexer / demultiplexer of the first embodiment, the input / output waveguide has a high mesa structure, and the reciprocating waveguide has a low mesa structure.

The input / output waveguide 24 includes a lower cladding layer 240, a core 242, and an upper cladding layer 244 provided on the substrate 12 (FIG. 5A).

On the other hand, the reciprocating waveguide 28 includes the substrate 12, the core 280, and the upper cladding layer 282. Other planar waveguides 14 have the same mesa structure as the conventional one, but the details are omitted here.

In the first embodiment, a mesa-shaped reciprocating waveguide 28 is provided on the substrate 12 (FIG. 5B).

When such a reciprocating waveguide 28 is formed, etching is first performed to form a mesa-shaped reciprocating waveguide array. At this time, the planar waveguide 14 and the input / output waveguide 24 may be formed simultaneously with the reciprocating waveguide.

Next, an impurity-doped layer (also referred to as a core) 280 and an upper clad layer 2 are formed on the substrate 12.
82 are sequentially formed. Thereafter, in order to form a reflection end face of the reciprocating waveguide 28, a groove 36 is formed in the cladding layer by using, for example, the RIE method.

Here, the example in which the core and the upper cladding layer are formed after the formation of the mesa-shaped reciprocating waveguide array has been described. However, after the core and the upper cladding layer are formed first, the mesa shape is formed by etching. May be formed.

Thereafter, a reflective film 34 is formed on the reflective end face 33 formed in the groove 36 by an evaporation method.

Conventionally, a reciprocating waveguide was formed without forming the second light guide. Therefore, during etching,
Irregularities such as roundness may occur in the portion of the reciprocating waveguide 28 near the reflection end face 33. When such an irregular portion occurs, light reflection loss easily occurs in this portion.

On the other hand, according to the present invention, since the divergent second light guide portion 32 is provided, the occurrence of the light intensity distribution (field distribution) at the reflection end face 33 is suppressed. Therefore, the light incident on the first light guide section 30 can be reflected by the reflection film 34 and made incident on the planar waveguide 14 again without causing reflection loss at the reflection end face 33.

Next, with reference to FIGS. 4 and 5, the manner in which light is reflected from the reciprocating waveguide will be described.

In this embodiment, the reciprocating waveguide array 2
6 has a low mesa structure, so that light can be guided by weakening the confinement of light in the reciprocating waveguide 28. Therefore, fluctuation of the equivalent refractive index in the reciprocating waveguide 28 can be suppressed.

The shift of the selected wavelength depends on the difference (Δn) in the refractive index between the substrate 12 and the reciprocating waveguide. That is, the shift Δλ of the selected wavelength is expressed by equation (4).

Δλ = 2δn × ΔL (4) where δn is the fluctuation of the equivalent refractive index, and ΔL is the difference between the lengths of the adjacent reciprocating waveguides.

For this reason, when Δn decreases, the fluctuation δn of the equivalent refractive index decreases as described above.
From equation (4), the shift Δλ of the selected wavelength is also small.

In the first embodiment, since a curved or radial waveguide is not used as the reciprocating waveguide 28, an extra length of the waveguide is not required. Thus, the size of the optical multiplexer / demultiplexer can be reduced.

[Second Embodiment] Next, an optical multiplexer / demultiplexer according to a second embodiment of the present invention will be described with reference to FIG. FIG. 6 is a plan view for explaining the main structure of the optical multiplexer / demultiplexer according to the second embodiment.

In the second embodiment, the input / output waveguide 24
Is bent radially with respect to the optical axis from the middle. As described above, in the present invention, since a part of the input / output waveguide 24 is formed as the radial input / output waveguide 24, the reciprocating waveguide 2
8 can be made uniform without depending on the input / output waveguide 24. Other components are the first
Since the components are the same as those of the embodiment, the details are omitted here.

[Third Embodiment] Next, an optical multiplexer / demultiplexer according to a third embodiment of the present invention will be described with reference to FIGS. FIG. 7 is a plan view for explaining the main structure of the optical multiplexer / demultiplexer of the third embodiment, and FIG. 8 is a schematic diagram for explaining the structure of the first light guide. .

In the third embodiment, the optical axis _Od included in the first light guide 30a of the reciprocating waveguide 28 is arranged radially (FIG. 7). At this time, the first light guide 30a
It is preferable to bend the first light guide portion 30a so that the optical axis O _{d of} the first light guide and the direction θ _d of the diffracted light 50b substantially match (FIG. 8). The direction (angle) of the optical axis of the first light guide 30a.
Is the Beam Propagation Method
Using the simulation of (BPM), Δ (Δn / n
_(s × 100).

The first light guide section 30 is formed by such a method.
By providing a, the diffracted light 50b is smoothly guided to the reciprocating waveguide 28, and the light can be prevented from zigzag propagating in the reciprocating waveguide 28.

Further, in the third embodiment, a stepped etching region 40 is provided on the reflection end face 33 side instead of the square groove of the first embodiment. The etching region 40 is provided up to the end face 42 of the substrate 12.

As described above, in the third embodiment, since the etching region 40 is provided up to the end face 42 of the substrate 12, when the reflection film is formed on the reflection end face by using the vapor deposition method,
Since there is nothing to shield on the end surface 42 side of the substrate 12, the formation of the reflection film 34 becomes easy.

Further, when the intensity of the incident light is adjusted by monitoring the light leaked from the reflection film 34, there is no shielding on the reflection end face side, so that the light can be easily monitored.

The results obtained by performing BPM simulation on the optical multiplexer / demultiplexer of the third embodiment and obtaining the reflection loss will be described below.

Here, the width d of the opening of the third light guide 25 is set.
Was performed 5 [mu] m, 500 [mu] m length L _s of the planar waveguide, 2 [mu] m waveguide width B, and simulation taking 3% and λ the Δ a 1.55μm to factor.

According to the result of the simulation by the BPM method, the reflection loss was improved by about 20% compared to the fundamental mode.

In the above-described embodiment, the planar waveguide, the input / output waveguide, and the reciprocating waveguide have a mesa structure having a convex shape on the substrate as a completed state of the optical multiplexer / demultiplexer. But,
The waveguide is not limited to the mesa structure at all, but may be a ridge, a rib, or an embedded structure in which the waveguide is embedded in a substrate.

[0079]

As is clear from the above description, according to the optical multiplexer / demultiplexer of the present invention, the optical axes of the reciprocating waveguides are provided parallel to each other at least in the waveguide portion on the reflection end face side, and The end faces are provided parallel to each other.

As described above, in the present invention, since the reflection end faces are provided in parallel with each other, when the reflection end faces are formed by anisotropic etching, a plurality of reflection end faces are simultaneously formed by setting one ion beam. be able to. For this reason, the fabrication of the reflective end face is easier than in the past,
Therefore, work efficiency is greatly improved.

Further, in the present invention, the waveguide portion on the input / output end face side of the reciprocating waveguide is configured as a first light guide for increasing the amount of light incident from the planar waveguide to the reciprocating waveguide. It is.

Therefore, light in the planar waveguide can be guided to the reciprocating waveguide while suppressing radiation loss. Therefore, the amount of light incident on the reciprocating waveguide increases.

In the present invention, the respective optical axis portions included in the first light guide of the reciprocating waveguide are radially arranged.

For this reason, the light incident from the input / output waveguide is smoothly guided to the respective reciprocating waveguides via the planar waveguide, so that the light propagates zigzag in the reciprocating waveguide. The phenomenon can be prevented.

Further, in the present invention, the waveguide portion on the reflection end face side of the reciprocating waveguide is configured as a second light guide for reducing the reflection loss of light guided through the reciprocating waveguide.

Therefore, the reflection loss (loss) can be reduced and the light in the reciprocating waveguide can be reflected as compared with the case where the second light guide portion is not provided.

Further, according to the present invention, the waveguide portion on the input / output waveguide side where the input / output waveguide and the planar waveguide are connected is used as a third light guide for controlling the angle of incident light. It is composed.

As described above, by providing the third light guide section,
Since the diffraction angle of the incident light can be controlled by changing the opening width of the light guide, the incident light can be efficiently incident on each of the reciprocating waveguides.

In the present invention, the input / output waveguide is formed in a mesa shape having a core, and the reciprocating waveguide is formed in a mesa shape having a height lower than that of the input / output waveguide. For this reason, since the light can be guided while weakening the confinement of the light in the reciprocating waveguide, the fluctuation of the equivalent refractive index of the reciprocating waveguide can be reduced.

[Brief description of the drawings]

FIG. 1 is a plan view for explaining a main structure of an optical multiplexer / demultiplexer according to a first embodiment of the present invention.

FIG. 2 is a perspective view for explaining a structure of a first light guide unit.

FIG. 3 is a diagram provided to explain the principle of light diffraction in a planar waveguide.

FIG. 4 is a diagram for explaining a configuration of a reciprocating waveguide unit.

FIG. 5A is a diagram provided for explaining a structure of an input / output waveguide of the optical multiplexer / demultiplexer according to the first embodiment;
(B) is a figure offered for explaining the structure of the reciprocating waveguide;

FIG. 6 is a plan view for explaining a main structure of an optical multiplexer / demultiplexer according to a second embodiment of the present invention.

FIG. 7 is a plan view for explaining a main structure of an optical multiplexer / demultiplexer according to a third embodiment of the present invention.

FIG. 8 is a diagram schematically illustrating a structure of a first light guide unit of the optical multiplexer / demultiplexer according to the third embodiment.

[Explanation of symbols]

 10: Optical multiplexing / demultiplexing device 12: Substrate 14: Planar waveguide 16: One connecting surface of planar waveguide 18: The other connecting surface of planar waveguide 20: Input / output waveguide array 22: Input / output port 24: Input / output Waveguide 25: Third light guide 26: Reciprocal waveguide array 28: Reciprocal waveguide 30, 30a: First light guide 31: Input / output end face 32: Second light guide 33: Reflection end face 34: Reflective film 36 : Groove 38: Waveguide portion on reflection end face side 40: Stepped etching area 42: End face of substrate

Claims (11)

[Claims] 1. A planar waveguide, a plurality of input / output waveguides connected to one connecting surface of the planar waveguide, and an input / output end face connected to the other connecting surface of the planar waveguide on a substrate. In the optical multiplexer / demultiplexer provided with a reflection end face and a plurality of reciprocating waveguides having different lengths, the optical axis of the reciprocation waveguide, at least in the waveguide portion on the reflection end face side, An optical multiplexing / demultiplexing device comprising: a plurality of reflection end faces provided in parallel with each other; 2. The optical multiplexer / demultiplexer according to claim 1, wherein the optical axes of the reciprocating waveguides are parallel to each other over the entire length from the input / output end face to the reflection end face of the reciprocating waveguide. Optical multiplexer / demultiplexer. 3. The optical multiplexing / demultiplexing device according to claim 1, wherein the input / output end face side of the reciprocating waveguide is increased in the amount of light incident on the reciprocating waveguide from the planar waveguide. An optical multiplexing / demultiplexing device, which is configured as a first light guide section for causing the optical multiplexing / demultiplexing device. 4. The optical multiplexer / demultiplexer according to claim 3, wherein the first light guide is a divergent waveguide. 5. The optical multiplexer / demultiplexer according to claim 3, wherein respective optical axis portions included in the first light guide portion of the reciprocating waveguide are radially arranged. Demultiplexer. 6. The optical multiplexer / demultiplexer according to claim 1, wherein a waveguide portion on the reflection end face side of the reciprocating waveguide is provided with a second portion for reducing reflection loss of light guided through the reciprocating waveguide. An optical multiplexer / demultiplexer configured as a light guide. 7. The optical multiplexer / demultiplexer according to claim 6, wherein the second light guide is a divergent waveguide. 8. The optical multiplexing / demultiplexing device according to claim 1, wherein the input / output waveguide and the planar waveguide are connected to each other at a portion of the waveguide on the input / output waveguide side, the angle of the incident light being changed. An optical multiplexer / demultiplexer, which is configured as a third light guide section for controlling. 9. The optical multiplexer / demultiplexer according to claim 8, wherein the third light guide is a divergent waveguide. 10. The optical multiplexer / demultiplexer according to claim 9, wherein d is an opening width at the divergent waveguide portion, and d> λ / (2√ (2Δn / n). _s) (I to was, lambda is the wavelength, [Delta] n is the refractive index difference between the substrate and the waveguide, n _s is the refractive index of the substrate) and the optical multiplexing and demultiplexing device, characterized by. 11. The optical multiplexer / demultiplexer according to claim 1, wherein the input / output waveguide has a mesa shape having a core, and the reciprocating waveguide has a mesa shape having a height lower than that of the input / output waveguide. An optical multiplexing / demultiplexing device.