JPH08334638A - Optical wavelength multiplexer/demultiplexer - Google Patents

Abstract

PURPOSE: To provide an optical wavelength multiplexer/demultiplexer which is highly isolated. CONSTITUTION: The optical wavelength multiplexer/demultiplexer has a substrate 10, at least one piece of channel waveguides 11 for input formed on this substrate 10, input side slab waveguide 12 having plate structure connected to the channel waveguides 11 for input, array waveguide diffraction gratings 14 which is connected to the input side slab waveguide 12 and consist of plural channel waveguides 13a to 13j having the waveguide lengths of Li (i=1, 2, 3,...), an output side slab waveguide 15 connected to these array waveguide diffraction gratings 14 and plural pieces of channel waveguides 16 for output connected to the output side slab waveguide 15. High-refractive index materials having the refractive index larger than the refractive index of the clad of the channel waveguides 16 for output are arranged near the respective channel waveguides 16 for output.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In the field of optical communication, a method (wavelength division multiplexing method) for expanding information capacity by mounting a plurality of different signals on light beams having different wavelengths and transmitting them by one optical fiber has been studied. There is. In this method, an optical wavelength multiplexer / demultiplexer that multiplexes or demultiplexes lights of different wavelengths plays an important role. Above all, an optical wavelength multiplexer / demultiplexer using an array diffraction grating is promising because it can increase the number of multiplexed communication capacities at narrow wavelength intervals.

FIG. 11 is a plan view of a conventional optical wavelength multiplexer / demultiplexer.

In FIG. 1, a substrate 1 and at least one input channel waveguide 2 formed on the substrate 1 are shown.
An input-side slab waveguide 3 connected to the input-side channel waveguide 2; an array waveguide diffraction grating 5 including a plurality of channel waveguides 4 connected to the input-side slab waveguide 3; An output wavelength slab waveguide 6 connected to the waveguide diffraction grating 5 and a plurality of output channel waveguides 7 connected to the output side slab waveguide 6 constitute an optical wavelength multiplexer / demultiplexer 8. There is.

The wavelength multiplexed light Lm input to the input channel waveguide 2 spreads in the input side slab waveguide 3 and is guided to the arrayed waveguide diffraction grating 5. After that, a desired phase difference is received by the arrayed waveguide diffraction grating 5 and propagates to the output side slab waveguide 6. At this time, light is condensed according to the phase difference received by the arrayed waveguide diffraction grating 5. . That is, the light can be extracted from the output channel waveguide 7 that varies depending on the wavelength.

[0006]

However, in the conventional optical wavelength multiplexer / demultiplexer 8, the light that has been demultiplexed once and propagated through the output channel waveguide 7 is adjacent to another output channel with a radiation mode. There is a problem that the light is recombined with the light in the waveguide 7 and sufficient isolation cannot be obtained.

Therefore, an object of the present invention is to solve the above problems and provide an optical wavelength multiplexer / demultiplexer with high isolation.

[0008]

In order to achieve the above object, the present invention provides a substrate, at least one input channel waveguide formed on the substrate, and a connection to the input channel waveguide. An input side slab waveguide having a flat plate structure and a waveguide length Li connected to the input side slab waveguide
(I = 1, 2, 3, ...) Arrayed waveguide diffraction grating consisting of a plurality of channel waveguides, an output side slab waveguide connected to the arrayed waveguide diffraction grating, and an output side slab waveguide In an optical wavelength multiplexer / demultiplexer including a plurality of output channel waveguides connected to each other, a high-refractive index material made of a material having a refractive index higher than that of the cladding is provided in the vicinity of the output channel waveguide. It is arranged.

It is more preferable that the high refractive index material is made of a material having a refractive index higher than that of the core of the output channel waveguide.

In addition to the above structure, the present invention is one in which a high refractive index material is formed in a core shape and is arranged between output channel waveguides.

In addition to the above structure, the present invention is one in which the high refractive index material is formed in a plate shape and is arranged in the vicinity of the output channel waveguide.

In addition to the above structure, the present invention provides a high refractive index material,
It is arranged near the output slab waveguide.

In addition to the above structure, as a high refractive index material used for the optical wavelength multiplexer / demultiplexer of the present invention, TiO ₂ and Ti-doped S
Any of iO ₂ , P ₂ O ₅ , Al ₂ O ₃ , SiN or Si is used.

In addition to the above structure, the gap between the output channel waveguide of the present invention and the high refractive index material is approximately 3 μm to 20 μm.
m.

[0015]

According to the above structure, since the high-refractive index material made of a material having a refractive index higher than that of the cladding is arranged near the output channel waveguide, the light propagating through the output channel waveguide is prevented. Even if an attempt is made to propagate the radiation mode to another adjacent output channel waveguide, it will be absorbed by the high-refractive index material before that, so that the recombination of the radiation mode of the light with the other channel waveguide will occur. To be prevented.

[0016]

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a plan view showing an embodiment of the optical wavelength multiplexer / demultiplexer according to the present invention, and FIG. 2 is a partially enlarged view of a circle C thereof. 3 is a sectional view taken along the line AA of FIG.

As shown in the figure, one input channel waveguide (hereinafter referred to as "input waveguide") 11 composed of a core and a clad is formed on a substrate 10 (Si or quartz). An input side slab waveguide 12 having a flat plate structure is connected to the input waveguide 11. The input side slab waveguide 12 has a waveguide length of Li (i = 1, 2, 3,
...) is connected to an array waveguide diffraction grating 14 composed of a plurality of (10 in the figure, but not limited to) channel waveguides 13a to 13j, and the array waveguide diffraction grating 14 has an output side. The slab waveguide 15 is connected. The output side slab waveguide 15 is connected with a plurality of (five in the drawing, but not limited to) output channel waveguides (hereinafter referred to as “output waveguides”) 16.

The waveguide length Li of the arrayed waveguide diffraction grating 14
(Li = 1, 2, 3, ...) Each channel waveguide 13a-
13j has a waveguide length difference ΔL satisfying Formula 1, and

[0020]

## EQU1 ## ΔL = λ · m / n _eff (where λ: wavelength used, n _eff : effective refractive index, m: positive integer) are arranged in order of length.

As shown in FIG. 2, between the output waveguides 16 of the optical wavelength multiplexer / demultiplexer 20 of the present embodiment, a core made of a material having a refractive index higher than that of the core of the output waveguide 16 is provided. The high refractive index material 17 is arranged. (The high-refractive index material 17 is not shown in FIG. 1.) A buffer layer 18 is formed between the substrate 10 and the core (output waveguide) 16 and the high-refractive index material 17, and the core 16 and the high-refractive index material are provided. The material 17 is covered with a clad 19.

Next, the operation of the embodiment will be described.

Generally, light is propagated in the form of modes.

FIG. 4 is a diagram showing a conceptual diagram of the fundamental mode of light, and the arrow P indicates the propagation direction of light. However, the light actually propagating through the arrayed-waveguide diffraction grating type optical wavelength multiplexer / demultiplexer includes a radiation mode leaking from the tapered portion of the output waveguide in addition to the fundamental mode.

FIG. 5 shows the state of light propagating through the conventional optical wavelength multiplexer / demultiplexer 8 shown in FIG. The radiation mode generated in the tapered portion of the output side waveguide 7a propagates in the clad on the substrate 1, and the other adjacent output side waveguides 7b and 7c.
Will be combined with. That is, the light once split (demultiplexed) for each wavelength is recombined with another waveguide due to the generation of the radiation mode, which causes the isolation to be lowered.

Therefore, in this embodiment, as shown in FIG. 6, the output waveguide 1 is provided between the plurality of output waveguides 16a, 16b, 16c.
The high refractive index material 17 made of a material having a refractive index substantially the same as or higher than the refractive index of the cores 6a, 16b and 16c is arranged. The radiation mode generated in the tapered portion of the output waveguide 16a is generated by the other adjacent output waveguides 16b and 16c.
Since the high-refractive index material 17 is coupled to the output waveguides 16b and 16c before reaching, the re-coupling to the other output waveguides 16b and 16c is eliminated. Thereby, high isolation can be secured. That is, it is possible to realize an optical wavelength multiplexer / demultiplexer capable of suppressing the recombining of the split light.

In the optical wavelength multiplexer / demultiplexer of this embodiment, the high refractive index material 17 is provided between the output channel waveguides 16 and
The radiation mode is effectively absorbed by the high refractive index material 17 by disposing the radiation mode near the output side slab waveguide 15.

Next, the optical wavelength multiplexer / demultiplexer will be described using numerical values, but the present invention is not limited to this.

The material of the core 16 is TiO ₂ --SiO _2.
2 (refractive index 1.4689), and the material of the clad 19 and the buffer layer 18 is B ₂ O ₃ —P ₂ O ₅ —Si.
(Refractive index 1.458) and arrayed waveguide diffraction grating 1
The core dimensions of the channel waveguides 13a to 13j constituting 4 are 6 μm × 6 μm. The material of the high refractive index material 17 arranged between the output waveguides 16 is TiO ₂ —SiO ₂ (refractive index 1.472) in which the Ti doping amount is larger than that of the core 16.
7) was used. The substrate 10 was made of SiO ₂ .

FIG. 7 is a diagram showing the wavelength dependence of insertion loss when light from a white light source is input to the optical wavelength multiplexer / demultiplexer. In the figure, the horizontal axis represents wavelength and the vertical axis represents insertion loss. A curve L ₁ shows the characteristics of the optical wavelength multiplexer / demultiplexer of this embodiment, and a curve L ₂ shows the characteristics of the conventional optical wavelength multiplexer / demultiplexer. The figure shows the measurement results for the 1.555 μm port. Compared to the characteristics (L ₂ ) of the conventional optical wavelength multiplexer / demultiplexer, an optical wavelength multiplexer / demultiplexer in which a high refractive index material is placed between the output waveguides is used. The insertion loss is about 10 according to the characteristics (L ₁ ).
It can be seen that the size is increased by dB and the isolation is high.

In the above, by disposing the high refractive index material 17 made of a material having a refractive index higher than that of the core of the output waveguide 16 between the output waveguides 16 of the optical wavelength multiplexer / demultiplexer 20, The optical wavelength multiplexer / demultiplexer 20 with high isolation can be realized. Although TiO ₂ —SiO ₂ was used as the material of the high refractive index material 17 in this embodiment,
Not limited to this, TiO ₂ , P ₂ O ₅ ,
It may be Al ₂ O ₃ , SiN or Si.

Next, the optimum conditions will be described.

FIG. 8 shows the change in isolation when the gap between the core and the high refractive index material is used as a parameter. TiO ₂ —SiO ₂ was used as the high refractive index material. In the figure, the horizontal axis indicates the gap between the core and the high refractive index material, and the vertical axis indicates the isolation.

In the conventional optical wavelength multiplexer / demultiplexer (FIG. 11), the isolation was about 20 dB, but when the gap G between the high refractive index material and the core was 20 μm or less, the isolation was higher than that of the conventional one. You can see that If the gap G is smaller than 3 μm, the loss of the signal light increases, so the optimum value of the gap G is 3 to 20.
It is preferably μm.

FIG. 9 is a plan view of another embodiment of the optical wavelength multiplexer / demultiplexer of the present invention, and FIG. 10 is a sectional view taken along line BB thereof. The same reference numerals are used for the same members as those in the embodiment shown in FIG.

The difference from the embodiment shown in FIG. 1 is that instead of the high-refractive index material 17 shown in FIG. 1, a high-refractive index material 30 formed in a substantially square plate shape is used. The point is that the material 30 is arranged so as to cover each output waveguide 16.

As shown in the drawing, a high-refractive index material 30 formed in a substantially square shape is arranged on the output waveguide 16 and near the output side slab waveguide 15. When the wavelength-multiplexed signal Lm is input to the input waveguide 11 of the optical wavelength multiplexer / demultiplexer 31 as described above, light spreads in the input side slab waveguide 12 and array waveguide diffraction occurs, as in the embodiment shown in FIG. Lattice 14
Is guided to. After that, the array waveguide diffraction grating 14 receives the phase difference and propagates to the output side slab waveguide 15. At this time, the light is condensed according to the phase difference received by the arrayed-waveguide diffraction grating 14, and is input to the output waveguide 16 which is different for each wavelength. Since the radiation mode of the light propagating through the output waveguide 16 is absorbed by the high refractive index material 30, it is possible to ensure high isolation without recombination.

[0038]

In summary, according to the present invention, the following excellent effects are exhibited.

Since a high refractive index material made of a material having a refractive index higher than that of the cladding of the output channel waveguide is arranged near each output channel waveguide of the optical wavelength multiplexer / demultiplexer, high isolating It is possible to realize a distributed optical wavelength multiplexer / demultiplexer.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of an optical wavelength multiplexer / demultiplexer according to the present invention.

FIG. 2 is a partially enlarged view of a circle C shown in FIG.

3 is a cross-sectional view taken along the line AA of FIG.

FIG. 4 is a diagram showing a conceptual diagram of a basic mode of light.

5 is a diagram showing a state of light propagating through the conventional optical wavelength multiplexer / demultiplexer shown in FIG.

FIG. 6 is a diagram showing a state of light propagating through the optical wavelength multiplexer / demultiplexer according to the embodiment shown in FIG.

FIG. 7 is a diagram showing wavelength dependence of insertion loss when light from a white light source is input to the optical wavelength multiplexer / demultiplexer.

FIG. 8 is a diagram showing a change in isolation when the gap between the core and the high refractive index material is used as a parameter.

FIG. 9 is a plan view of another embodiment of the optical wavelength multiplexer / demultiplexer of the present invention.

10 is a sectional view taken along line BB of the optical wavelength multiplexer / demultiplexer shown in FIG.

FIG. 11 is a plan view of a conventional optical wavelength multiplexer / demultiplexer.

[Explanation of symbols]

 10 substrate 11 input channel waveguide (input waveguide) 12 input side slab waveguide 13a to 13j channel waveguide 14 array waveguide diffraction grating 15 output side slab waveguide 16 output channel waveguide (output waveguide, core) 17 High refractive index material

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[Procedure amendment]

[Submission date] June 29, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0029

[Correction method] Change

[Correction content]

The material of the core 16 is TiO ₂ --SiO _2.
2 (refractive index 1.4689), and the material of the clad 19 and the buffer layer 18 is B ₂ O ₃ —P ₂ O ₅ —Si.
O ₂ (refractive index 1.458) was used, and the core dimensions of the channel waveguides 13 a to 13 j forming the arrayed waveguide diffraction grating 14 were set to 6 μm × 6 μm. The material of the high refractive index material 17 arranged between the output waveguides 16 is Ti from the core 16.
TiO ₂ —SiO ₂ with a large doping amount (refractive index 1.4
727) was used. The substrate 10 was made of SiO ₂ .

Claims (7)

[Claims] 1. A substrate, at least one input channel waveguide formed on the substrate, an input side slab waveguide connected to the input channel waveguide and having a flat plate structure, and the input side slab. Connected to the waveguide and the waveguide length is L
An array waveguide diffraction grating composed of a plurality of channel waveguides of i (i = 1, 2, 3, ...), an output side slab waveguide connected to the array waveguide diffraction grating, and an output side slab waveguide In the optical wavelength multiplexer / demultiplexer having a plurality of output channel waveguides connected to each other, a refractive index larger than the refractive index of the cladding of the output channel waveguide is provided in the vicinity of each of the output channel waveguides. An optical wavelength multiplexer / demultiplexer characterized in that a high refractive index material made of the material is disposed. 2. The optical wavelength multiplexer / demultiplexer according to claim 1, wherein the high refractive index material is made of a material having a refractive index higher than that of the core of the output channel waveguide. 3. The optical wavelength multiplexer / demultiplexer according to claim 1, wherein the high refractive index material is formed in a core shape and is arranged between the output channel waveguides. 4. The optical wavelength multiplexer / demultiplexer according to claim 1, wherein the high refractive index material is formed in a plate shape and is arranged so as to cover each of the output channel waveguides. 5. The optical wavelength multiplexer / demultiplexer according to claim 1, wherein the high refractive index material is arranged in the vicinity of the output side slab waveguide. 6. The method according to claim 1, wherein any one of TiO ₂ , Ti-doped SiO ₂ , P ₂ O ₅ , Al ₂ O ₃ , SiN and Si is used as the high refractive index material. Optical wavelength multiplexer / demultiplexer. 7. The optical wavelength multiplexer / demultiplexer according to claim 1, wherein a gap between the output channel waveguide and the high refractive index material is approximately 3 μm to 20 μm.