JP2001056414A - Optical waveguide device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high dispersion of birefringence in a wide wavelength range by forming a plurality of cores each having a higher refractive index than that of a clad on a dielectric substrate to be used as the clad so as to obtain the distribution of the refractive index showing a plurality of maxima. SOLUTION: When a Ti diffusion method is used, for example, a patterned Ti metal film is deposited on a LiNbO3 substrate 111 and diffused into the substrate by heat treatment to form a plurality of cores 112 having a high refractive index near the surface. During the heat treatment, external diffusion of Li2O is caused to decrease the trapping effect for light. To prevent that, the treatment is performed in Li2O or LiNbO3 powder. For example, in a proton exchange method, LiNbO3 is dipped in a fused liquid of benzoic acid (C6 H5COOH) at about 210 to 250 deg.C for several ten minutes to exchange Li+ and H+ so that a region having a high refractive index can be obtained. Thus, the distribution of the refractive index shows two peaks n1 corresponding to the two cores 112 formed by the Ti diffusion method on the LiNbO3 substrate 111.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used, for example, for an optically controlled phased array antenna that transmits a plurality of radio signals in a predetermined directivity direction by processing a plurality of radio signals in an optical space. An improved optical waveguide device having improved high birefringence dispersion.

[0002]

2. Description of the Related Art An optically controlled phased array antenna device which independently processes a plurality of radio signals to transmit radio waves in a predetermined directional direction is disclosed in, for example, Japanese Patent Application Laid-Open No. Hei 9-139620. Application (hereinafter referred to as a first conventional example) and Japanese Patent Application Laid-Open No. 10-233.
615 Patent Application (hereinafter, referred to as a second conventional example)
Are disclosed. In the first conventional example, a multi-beam antenna is realized using a beam forming circuit using an optical signal processing technique. However, the directivity of each beam is fixed and cannot be changed. there were. To solve this problem, we have:
In the second conventional example, a variable directivity multi-beam antenna capable of changing the directivity by a beam forming circuit using an optical signal processing technique is realized.

However, in the second conventional example,
Since the directivity of each beam is changed by mechanically moving the end of the optical fiber cable by its supporting and moving mechanism, it is difficult to move the end with high precision, and therefore, It could not be controlled with precision. Further, since it is necessary to provide a mechanical mechanism such as the above-mentioned support moving mechanism, the optical circuit of the second conventional example cannot be optically integrated.

In order to solve the above-mentioned problem of the second conventional example, the applicant of the present invention has disclosed in Japanese Patent Application No. Hei 10-249519 that the directivity of each beam is higher than that of the conventional example. A light-controlled phased array antenna device (hereinafter, referred to as a third conventional example) that can be controlled with high accuracy and that can be optically integrated has been proposed.

[0005]

In the third conventional example, a birefringent optical waveguide device 80 having a higher birefringence dispersion (see FIG. 23) is required. When the birefringent optical waveguide device 80 is used, the refractive index changes according to the wavelength of the transmitted optical signal, so that the phase of the transmitted optical signal can also be changed according to the wavelength of the optical signal, The direction of the beam after photoelectric conversion can be changed. However, the prior art has a problem that the birefringence dispersion is relatively low and the amount of change in the beam direction is small.

An object of the present invention is to solve the above-mentioned problems and to provide an optical waveguide device having a high birefringence dispersion improved as compared with the prior art.

[0007]

In the optical waveguide device according to the first aspect of the present invention, a predetermined material is diffused on a dielectric substrate serving as a clad by a thermal diffusion method or a predetermined material is used by a proton exchange method. In this case, a plurality of cores each having a refractive index higher than that of the cladding are formed, and the refractive index has a plurality of maximum values in the refractive index distribution characteristics.

Further, in the optical waveguide device according to the second aspect of the present invention, the core has a predetermined thickness and the refractive index of the core is higher than that of the cladding on the dielectric substrate or the semiconductor substrate serving as the cladding. After forming a plurality of layers serving as a large core and a channel, a dielectric material or a semiconductor material serving as a clad is formed so as to surround the plurality of layers,
It is characterized by having at least one local maximum refractive index in the refractive index distribution characteristics.

In the optical waveguide device according to the second invention,
Preferably, the plurality of layers include at least three layers, and the core layer is sandwiched between two channels. Further, in the optical waveguide device according to the second invention, preferably, the refractive index of the material of the channel layer is smaller than the refractive index of the material of the clad. Furthermore, in the optical waveguide device according to the second invention,
Preferably, the refractive index of the material for the core layer is at least 1.08 times the refractive index of the material for the channel.
Still further, in the optical waveguide device according to the second invention,
Preferably, it has a plurality of local maximum refractive indexes in the refractive index distribution characteristics. Here, more preferably, two of the plurality of maximum value refractive indexes are different from each other.

[0010] In the optical waveguide device according to the third aspect of the present invention, preferably, the optical waveguide device has a polygonal cross-sectional shape in which a protruding portion is added in a rectangular shape on a dielectric substrate or a semiconductor substrate to be a clad, and the cladding has After forming a plurality of layers serving as a core having a large refractive index, a dielectric material or a semiconductor material serving as a clad is formed so as to surround the plurality of layers.

[0011] In an optical waveguide device according to a third invention,
Preferably, the outer shape of the cross-sectional shape of the core changes in a step-like shape.

In the optical waveguide device according to a fourth aspect of the present invention, a core having a rectangular shape having a length and a width and having a refractive index larger than that of the clad is formed on a dielectric substrate or a semiconductor substrate serving as a clad. After forming the layer, in the optical waveguide device formed by forming a dielectric material or a semiconductor material to be a clad so as to surround the layer, the length and the width of the core are set to an aspect ratio that is a ratio of the length and the width of the core. The length and width of the core are set so that the birefringence dispersion substantially has a maximum value with respect to the ratio.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

<Basic Principle of Embodiment> In an embodiment according to the present invention, the present inventors propose an optical waveguide device having a high birefringence dispersion which is improved as compared with the prior art. Higher birefringence does not necessarily result in higher birefringence dispersion. In the present embodiment, three embodiments of the optical waveguide device having higher birefringence dispersion will be disclosed. Here, as described in detail later, the SiO ₂ / Si optical waveguide 115 having the three-layer structure according to the second embodiment has a lower birefringence than that of the conventional LiNbO ₃ optical waveguide. And have higher birefringence dispersion than others.

First, the birefringence B and the birefringence dispersion dB / dλ in the single mode optical waveguide will be described.
In a single-mode optical waveguide, the birefringence due to the mode is based on different effective indices of refraction between the x-axis and y-axis polarizations orthogonal to each other, and the birefringence B and the birefringence dispersion d
B / dλ is defined as follows.

[0016]

## EQU1 ## B = β / k ₀ = n _x −n _y

[Number 2] _{dB / dλ = d (n x} -n y) / dλ

Here, β is the propagation constant of the optical waveguide, k
₀ is the wave number of free space, lambda is optical wavelength, the n _x and n _y is the effective refractive index of the TE fundamental mode and the TM fundamental mode, respectively. The birefringence B and the birefringence dispersion dB / dλ in Equations 1 and 2 above indicate that the higher birefringence dispersion dB / dλ depends on the dispersion of the different effective refractive indices between the TE and TM fundamental modes. The higher birefringence B depends on the difference in the effective refractive index between the TE and TM fundamental modes at one wavelength. Therefore, the characteristics of the birefringence B and the birefringence dispersion dB / dλ are different.

Difference in refractive index between cladding and core of optical waveguide

## EQU3 ## It can be seen that the higher the Δn = n _co −n _cl , the higher the birefringence B.

Therefore, in order to compare the birefringences B in the optical waveguides having different shapes, the limiting condition Δn ≦ 0.1 was assumed for the difference in the refractive index in each embodiment. In an experimental simulation of an optical waveguide (first embodiment) described in detail below, B
Alternate direction implicit method (ADI; Alteratin) of PM-CAD
g direction implicit method) (for example, see Prior Art Document 2 “Optiwave Corporation Co.,” BPM
-CAD waveguide optics modeling software system ”,
Version 3.0 ". ).

As a basic preliminary study, an optical waveguide having a simple step index type rectangular structure (size a × b) core shown in the upper right of FIG. 4 will be analyzed. This optical waveguide can be manufactured, for example, by the method of the second or third embodiment described later in detail or a modification example thereof. FIG. 4 shows an optical waveguide 1 having a rectangular core.
Birefringence B and birefringence dispersion dB / d for 55 μm light
9 shows the dependence on λ and the aspect ratio a / b in various size ranges. Here, the optical waveguide is limited to single mode propagation.

As is apparent from FIG. 4, the smaller the shape of the optical waveguide having the rectangular core, the higher the birefringence B. This is completely different from the characteristic of the birefringence dispersion dB / dλ. It can be seen that the birefringence dispersion dB / dλ has a non-monotonic dependence on the aspect ratio a / b, and that the shape of the optical waveguide greatly affects the birefringence dispersion dB / dλ. For the same aspect ratio a / b of an optical waveguide having a rectangular core, the birefringence B is higher for an optical waveguide having a larger size a. However, the birefringence dispersion dB / dλ decreases as the size increases. This means that the value of birefringence B needs to be reduced in order to obtain a higher birefringence dispersion dB / dλ.

That is, as is apparent from FIG. 4, the birefringence dispersion dB / dλ has a maximum value which is the optimum maximum value for the aspect ratio a / b. Therefore, as shown in FIG.
In an optical waveguide formed by being surrounded by 0, the length b and the width a of the core are substantially equal to the aspect ratio a / b which is the ratio of the length b to the width a of the core. It is preferable to set the length and width of the core so that the maximum value is obtained.

Note that FIG.
According to the experimental simulation based on the above, in the optical waveguide having the maximum birefringence dispersion dB / dλ, the birefringence dispersion dB / dλ = 2.6 × 10 ⁻³ μm ⁻¹ and the birefringence B = 2.3.
× 10 ^-3 , width a = 0.6 μm and length b = 2 μm.

<First and Second Embodiments> Next, a graded index type Ti: LiNbO ₃ optical waveguide 110 formed from a LiNbO ₃ substrate 111 shown in FIG.
(First embodiment) and glass (SiO ₂ ) shown in FIG.
Index type SiO ₂ / Si generated from
The structure and the manufacturing method of the optical waveguide (second embodiment) will be described.

The T according to the first embodiment shown in FIG.
The i: LiNbO ₃ optical waveguide 110 is manufactured as follows. For example, when the Ti diffusion method is used, FIG.
1A, a patterned Ti metal film is deposited on a LiNbO ₃ substrate 111 and diffused inside by heat treatment to form a plurality of cores 112 having high refractive index portions near the surface. is there. About 1 heat treatment
The process is performed at 000 ° C. for several hours. At that time, external diffusion of Li ₂ O occurs, and the light confinement effect is weakened. In order to prevent this, treatment is performed in a powder of Li ₂ O or LiNbO ₃ . For example, in the proton exchange method, LiN
The bO ₃ is added to the benzoic acid (C ₆ H ₅ COOH)
A high refractive index portion can be obtained by immersing for several tens of minutes at ~ 250 ° C and exchanging between Li ⁺ and H ⁺ . Furthermore, LiT
aO _{3 is} also an electro-optic crystal having almost the same characteristics as LiNbO _3, and an optical waveguide can be manufactured by thermal diffusion of Nb, Ti, and Cu. However, the Curie temperature is 89
Since it is 0 ° C., which is lower than the heat treatment temperature, poling is necessary. _{PLZT (Pb 1-x La x} ) (Zr y Ti 1-y) 1-x /
₄ O ₃ ) is also a material exhibiting a large electro-optical effect, and a single crystal film can be grown on a sapphire substrate by, for example, a sputtering method. The refractive index distribution in LiNbO ₃ becomes Gaussian in the depth direction by the Ti diffusion method and step-like in the proton exchange method, but becomes Gaussian by heat treatment. These LiNbO ₃ -based optical waveguides usually operate in a single mode. Further, Table 1 shows an example of the materials of the core and the clad which can be used in the first embodiment, and an example of the manufacturing method.

[0026]

[Table 1] Graded index optical waveguide (first embodiment) ――――――――――――――――――――――――――――――― ― Core clad manufacturing method ―――――――――――――――――――――――――――――――― Ti: LiNbO ₃ LiNbO ₃ thermal diffusion method Nb: LiTaO ₃ LiTaO ₃ thermal diffusion method Cu: LiTaO ₃ LiTaO ₃ thermal diffusion method ――――――――――――――――――――――――――――――――

Next, according to the second embodiment, the SiO ₂ /
A method for manufacturing the Si optical waveguide 115 (FIG. 2) will be described. Here, for example, a flame deposition method or a reactive ion etching method is used. 2, the Si substrate 121
A channel 131, a core 132, and a porous glass film are deposited by oxy-hydrogen flame using a flame deposition method, and are heated and made transparent to repeatedly form a uniform film having a refractive index distribution in a thickness direction. And a channel 133 are formed. Next, etching is performed using reactive ion etching with a-Si as a mask to form an optical waveguide pattern. Further, the Si deposition layer 12 serving as a clad
2 is deposited by using a flame deposition method, and is then heated and made transparent again to obtain an optical waveguide. In addition, for example, in the CVD method, a porous film or a transparent film is obtained on a substrate by thermal oxidation of a source gas. In the RF sputtering method, an optical waveguide film having a controlled refractive index can be obtained by selecting a target composition.

Also, a Si substrate 121 made of quartz glass
A dielectric substrate such as a glass-based substrate such as borosilicate glass or soda-lime glass may be used instead of the quartz-based substrate. In this case, an optical waveguide can be formed by forming a high refractive index portion using a known ion exchange method or sputtering method. Further, Table 2 shows an example of the materials of the core, the cladding, and the channel that can be used in the second embodiment, and an example of the manufacturing method.

[0029]

[Table 2] Step-index type optical waveguide (second embodiment) ―――――――――――――――――――――――――――――――― Core Clad channel Manufacturing method ―――――――――――――――――――――――――――――――――――― Koningk 7059 High-color glass Fused quartz (SiO ₂ ) RF Suha ° Ttarinku Bu method Koninku Bu 7059 Pas Irekkusuka Bu Las fused silica (SiO ₂₎ RF Suha ° Ttarinku Bu method Koninku Bu 7059 sorter Bu Ka Bu Las fused silica (SiO ₂₎ RF Suha ° Ttarinku Bu method Koninku Bu 7059 sorter Bu Ka Bu Las Ha Bu Ikoruka Bu Las RF Suha ° Ttarinku Bu method Koninku Bu 7059 sorter Bu Ka Bu Las Pas Irekkusuka Bu Las RF Suha ° Ttarinku Bu method sorter Bu Ka Bu Las Ha Bu Ikoruka Bu Las Fused quartz (SiO ₂ ) RF shutter link method saw Takaras Hirex glass Fused quartz (SiO ₂ ) RF shutter link method GeO ₂ tow sorter glass Fused quartz (SiO ₂ ) F-top fused quartz CVD method Polyurethane sorter glass PMMA Shen coat method Law ――――――――――――――――――――――――――――――――――

Next, a method for obtaining a higher birefringence dispersion dB / dλ in the first and second embodiments will be described. Ti: LiNbO ₃ optical waveguide, due to its uniaxial refractive index n _e and n _o, can exhibit a very high birefringence B = 0.065 at a wavelength of 1.55 .mu.m. However, the birefringence dispersion dB / dλ is only about 2.5 × 10 ⁻³ μm ⁻¹ at a wavelength of 1.55 μm. In contrast, the step index type SiO ₂ /
The Si optical waveguide is easy to process and connect to the optical fiber. However, the birefringence B and the birefringence dispersion dB / dλ are usually not as high in the prior art as shown in FIG. Therefore, in order to obtain a higher birefringence dispersion dB / dλ, it is necessary to invent a new optical waveguide structure.

In the first embodiment according to the present invention,
As shown in FIGS. 1A and 1B, a graded index type having two peak refractive indices n ₁ corresponding to two cores 112 formed on a LiNbO ₃ substrate 111 by a Ti diffusion method. A Ti: LiNbO ₃ optical waveguide 110 is shown. On the other hand, in the second embodiment, as shown in FIG. 2A, the core 132 is made of SiO ₂ , the core 132 is sandwiched between the channels 131 and 132, and these consist of the Si substrate 121 and the Si deposition layer 122. A step index type SiO ₂ / Si optical waveguide 115 surrounded by a clad 120 is shown. In the example of FIG. 2, the refractive index is, as shown in FIG.
(Refractive index n _{1 of} core 132)> (refractive index n _{0 of} clad 120)> (refractive index n _{2 of} channels 131 and 133).

FIG. 5 is a graph showing the wavelength characteristics of the birefringence dispersion in the optical waveguides of the conventional example and the first and second embodiments. As is clear from FIG.
At 5 μm, graded index type Ti: L
In the structure of the iNbO ₃ optical waveguide, the birefringence dispersion dB / dλ =
5.0 × 10 ⁻³ μm ⁻¹ is obtained. Also, an AlGaAs according to a second modification of the second embodiment described in detail later.
In the structure of the / GaAs optical waveguide, a relatively high birefringence dispersion dB / dλ = 3.8 × 10 ⁻³ μm ⁻¹ is obtained.

FIG. 6 is a diagram showing the structure, refractive index distribution characteristics, and birefringence dispersion of an optical waveguide according to the conventional example and the first embodiment. In FIG. 6, the range of light wavelength λ = 1.5 μm
To 1.6 μm, center light wavelength λ ₀ = 1.55 μm, thickness h of the core strip before diffusion = 0.075 μm, diffusion constant of Ti in the x direction = 4 μm, diffusion constant D of Ti in the y direction
y = 3.5 μm, and the center refractive index position y = 0 μm. Also, d is the interval between peaks, and w is the starting width (default value) of the optical waveguide.

As is clear from FIG. 6, in the refractive index distribution characteristic indicating the refractive index with respect to the length in the horizontal direction, in the Ti: LiNbO ₃ optical waveguide 110 having the refractive index of two or three peaks, one peak is obtained. Has a higher birefringence dispersion dB / dλ than the conventional example having a refractive index of In the above embodiments, the optical waveguide having a refractive index of two or three peaks (maximum value or maximum value) is described. However, the present invention is not limited to this, and four or more peaks (maximum values) are used. Value or the maximum value), the birefringence dispersion dB / dλ is higher than that of the conventional example.
Can be obtained.

FIG. 7 is a longitudinal sectional view showing the structure of the SiO ₂ layer according to the _second embodiment. In various examples shown in FIGS.
133, a total of N layers of SiO ₂ layers 135-1
To 135-N. Here, each SiO ₂ layer 1
The refractive index distribution characteristics of 35-1 to 135-N are, for example,
As shown in FIG. 8, the shape may be a rectangular pulse shape 141, an upper portion may have a rounded shape 142, or a lower portion may have an expanded shape 143. That is, it is sufficient if the shape is substantially a rectangular pulse.
In order to obtain a higher birefringence dispersion dB / dλ,
In the second embodiment, the core 13 is a SiO ₂ layer.
It is preferable that the thicknesses of the plurality of layers serving as the channel 2 and the channels 131 and 133 are maintained at substantially the same thickness in each layer.

FIGS. 9 to 17 are views showing the structures, refractive index distribution characteristics and birefringence dispersion of various examples of the optical waveguide according to the second embodiment. Here, the light wavelength λ =
It is assumed that a plurality of N layers having a thickness of 1.5 to 1.6 μm, a width b (μm) and a thickness a _{1 to} a _N (μm) are used. Also,
The parameters of each refractive index are as follows. n ₀ = n _cl = 1.45, Δn ₊ = n _co −n ₀ ≦ 0.1, Δ
n ₋ = n _ch −n ₀ ≧ −0.02, n ₋ = 1.43, n ₁ =
1.46, n ₂ = 1.48, n ₃ = 1.5, n ₄ = 1.5
2, n ₅ = 1.55. Here, n _cl is the refractive index of the cladding 120, n _ch is the refractive index of the channels 131 and 133, and n _co is the core 1
A refractive index of 32.

As apparent from the various embodiments shown in FIGS. 9 to 17, the following conditions are preferable in order to obtain a higher birefringence dispersion dB / dλ. (1) The plurality of layers includes at least three layers, and the core 13
The layer to be 2 is sandwiched between two channels 131 and 133. (2) The refractive index of the material of the layer to be the channels 131 and 133 is smaller than the refractive index n _{0 of the} material of the clad 132. (3) The refractive index of the material of the layer to be the core 132 preferably changes steeply with respect to the length in the horizontal direction as compared with the refractive index of the material to be the channels 131 and 133, and more preferably, It is 1.08 times (= n ₅ / n ₋ ) or more (for example, FIG. 9A, FIG. 10, FIG. 11, FIG. 12, FIG. 13, etc.). (4) It has a plurality of maximum value refractive indexes in the refractive index distribution characteristics. Here, more preferably, two of the plurality of maximum value refractive indexes are different from each other. That is, it has a maximum refractive index n5 and a second highest refractive index n4 (for example,
11 (b), 13 (c), 13 (d), 14
(B), FIG. 16 (b), FIG. 17 (c), etc.).

<First Modification of Second Embodiment> FIG.
FIG. 9 is a diagram showing structures, refractive index distribution characteristics, and birefringence dispersion of various examples of a PMMA optical waveguide according to a first modification of the second embodiment. In this first modification, the cladding 1
20 is made of PMMA (polymethyl methacrylate) instead of Si, and the core 132 and channels 131 and 133 are used.
In JP, a high refractive index portion is obtained by adding F (fluorine) to PMMA instead of SiO ₂ . Here, the core 132 and the channels 131,
133 can be formed.

The optical waveguide of the first modified example is called a so-called polymer optical waveguide, and has a refractive index by a known selective photopolymerization method or photolonking method, or by dissolving a dye in a polymer by irradiating light. It can be created using a method that makes a difference. Here, by changing the fluorine content of PMMA, the refractive index can generally be changed from 1.36 to 1.48.

Although PMMA is used in the above first modification, the present invention is not limited to this, and a dielectric such as a resin such as polyimide may be used.

<Second Modification of Second Embodiment> FIG.
Is AlGaAs / Ga of the second modification of the second embodiment.
It is a figure which shows the structure of various Examples regarding an As optical waveguide, a refractive index distribution characteristic, and birefringence dispersion. In the second modification, GaAs is used as the cladding 120 instead of Si, and the core 132 and the channels 131 and 133 are made of SiO _2.
Instead of Al _x Ga _{1 -x} As. Here, FIG.
By changing x as shown by 0, the refractive index can be changed to obtain a high refractive index portion, and the core 13
2 and channels 131 and 133 can have a difference in refractive index. As is clear from FIG. 20, Al _x Ga _{1 -x} A
Changing x in s from 0 to 1 changes the index of refraction from about 3.37 to about 2.88.

In the above-described modified example, a semiconductor such as GaAs is used, but InGaAs, InP, GaN, Si
A semiconductor such as Ge may be used.

<Third Embodiment> FIG. 3 is a longitudinal sectional view showing the structure of a SiO ₂ / Si optical waveguide 116 according to a third embodiment of the present invention. The third embodiment has a polygonal cross-sectional shape in which a protruding portion is added to a rectangular shape on a Si substrate 121 serving as a clad 120, and the clad 1
After forming a plurality of SiO ₂ layers 136-1 and 136-2 to be the cores 130 having a refractive index larger than 20, a Si deposition serving as a clad is formed to surround the plurality of SiO ₂ layers 136-1 and 136-2. The feature is that the layer 122 is formed. Here, the plurality of SiO ₂ layers 136-1,
136-2 have, for example, the same refractive index.

FIG. 21 is a diagram showing the structure, refractive index distribution characteristics and birefringence dispersion of various examples of the optical waveguide according to the conventional example and the third embodiment. Here, the light wavelength λ = 1.5
To a 1.6 [mu] m, [Delta] n ₊ = (refractive index n _co of the core 130) - (the refractive index n _cl of the cladding 120) = 0.1, a refractive index n _cl = 1.45 cladding 120. As is clear from FIG. 21, the core 130 of the optical waveguide according to the third embodiment has a polygonal cross-sectional shape obtained by adding at least one protrusion to a rectangular shape, and more preferably,
It has a shape in which a plurality of protrusions are added to a rectangular shape, and more preferably, the outer shape changes in a step-like shape.

FIG. 22 is a view showing various modified examples of the shape of the refractive index distribution characteristic of the dispersion shifted optical fiber cable according to the present invention. The shape of the refractive index distribution characteristic of the optical waveguide according to the present invention is not limited to the shape described above, and as shown in FIG. 22, a triangular shape, a trapezoidal shape, a depressed shape,
It may have a segment core shape or a step shape.

As described above, according to the optical waveguide of the embodiment of the present invention, it is possible to obtain a high improved birefringence dispersion over the conventional example over a wide wavelength range. Hereinafter, application examples using the optical waveguide according to the first to third embodiments will be described.

<Application Example> FIG. 23 is a block diagram showing a configuration of a light-controlled phased array antenna apparatus of an application example using the optical waveguide device according to the present invention. This optically controlled phased array antenna device includes a known wavelength variable light source device 10a, 10b, 10c and a Ramipole polarizer 45.
By using the birefringent optical waveguide device 80 on which the optical signal is formed to change the wavelength of the optical signal output from the wavelength tunable light source devices 10a, 10b, and 10c, the light is radiated from the array antenna 70 arranged in a linear array. It is characterized in that the directivity direction of each beam is changed.

In FIG. 23, the wavelength variable light source device 10
The output terminals of a, 10b, and 10c correspond to the output terminals of the optical isolator 12 in FIG. Here, each of the variable wavelength light source devices 10a, 10b, and 10c is a known wavelength capable of changing the wavelength of emitted light while maintaining a constant frequency difference between the wavelength of the vertical polarization component and the wavelength of the horizontal polarization component. It is a variable light source device.

In FIG. 23, the wavelength variable light source device 10
The wavelengths of the optical signals output from the a, b, and c are controlled by the beam controller 30 by the wavelength tunable light source device 10.
Diffraction grating plate 6 in a, 10b, 10c (see FIG. 20)
By changing the rotation angle of the array antenna 70, the directional direction radiated from the array antenna 70 is changed as described later in detail. Here, the optical signals output from the wavelength tunable light source devices 10a, 10b, and 10c include a vertical polarization component and a horizontal polarization component that are orthogonal to each other, and the difference frequency therebetween is different for each of the devices 10a, 10b, and 10c. Differently, device 10a has a difference frequency Δf1,
0b has the difference frequency Δf2 and the device 10c has the difference frequency Δf2.
When f3, the beam B1 of the radio signal radiated from the array antenna 70 has a radio frequency of the difference frequency Δf1, the beam B2 of the radio signal has a radio frequency of the difference frequency Δf2, Beam B3 has a difference frequency Δf
3 radio frequencies.

The optical signal output from the wavelength tunable light source device 10a includes a vertical polarization component and a horizontal polarization component orthogonal to each other, and is deflected and separated by the deflecting beam splitter 32a. The optical signal of the other horizontal polarization component is input to the deflection beam splitter 33a via an external optical modulator (hereinafter, referred to as EOM) 31a for intensity-modulating the optical signal according to the input first digital data signal. Is the deflection beam splitter 3
3a. The deflection beam splitter 33a deflects and combines the two input optical signals and outputs the resultant signal to the optical waveguide 41a in the birefringent optical waveguide device 80. Here, the optical signal of the horizontal deflection component is used as a reference optical signal in the second conventional example, and the photodiodes 51-1 to 51-N
Are used as local oscillation signals in the square detection. Therefore, the deflection beam splitters 32a, 33a and E
The OM 31a constitutes an optical modulation device 60a that optically modulates only the optical signal of the vertical polarization component.

The optical signal output from the wavelength tunable light source device 10b includes a vertical polarization component and a horizontal polarization component orthogonal to each other, and includes the deflection beam splitters 32b and 33b and the EOM 31b, like the optical modulation device 60a. The light is output to the optical waveguide 41b in the birefringent optical waveguide device 80 via the optical modulator 60b. Here, EOM3
1b intensity-modulates the input optical signal of the horizontally polarized component according to the second digital data signal and outputs the modulated signal.

Further, the optical signal output from the wavelength tunable light source device 10c includes a vertical polarization component and a horizontal polarization component which are orthogonal to each other, and is similar to the optical modulation devices 60a and 60b.
Deflection beam splitters 32c, 33c and EOM 31c
The light is output to the optical waveguide 41c in the birefringent optical waveguide device 80 via the optical modulator 60c composed of Here, the EOM 31c modulates the intensity of the input optical signal of the horizontal polarization component according to the third digital data signal, and outputs the resultant signal.

The variable wavelength light source device 10a and the optical waveguide 41a of the birefringent optical waveguide device 80, the variable wavelength light source device 10b and the optical waveguide 41b of the birefringent optical waveguide device 80, and The wavelength tunable light source device 10c and the optical waveguide 41c of the birefringent optical waveguide device 80 are preferably connected by an optical fiber cable, and may be connected by an optical waveguide instead. Good.

In the birefringent optical waveguide device 80, the optical waveguides 41 a, 41 b, and 41 c are made of LiNbO 4 so as to be guided from the edge of the device 80 to one edge of the two-dimensional optical waveguide 42 by Ti diffusion. ₃ is formed on the birefringent optical waveguide substrate 40. The two-dimensional optical waveguide 42 formed by Ti diffusion is formed in the birefringent optical waveguide substrate 40 by a known Ti diffusion method.
With respect to the three optical signals emitted from the edge portions of a, 41b, and 41c, light is emitted only in the vertical direction (corresponding to the polarization change direction of the vertical polarization component) that is the thickness direction of the substrate 40. Is a rectangular planar optical waveguide for confining the optical waveguide. T
A plurality N of optical waveguides 44-1 to 44-N are connected to one edge of the two-dimensional optical waveguide 42 by i-diffusion, which is opposite to the other edge.

The optical signal emitted from the optical waveguide 41a spreads in the horizontal direction within the plane of the two-dimensional optical waveguide 42 and enters the incident portions of all the optical waveguides 44-1 to 44-N.
Similarly, the optical signal emitted from the optical waveguide 41b spreads in the horizontal direction within the plane of the two-dimensional optical waveguide 42 and enters the incident portions of all the optical waveguides 44-1 to 44-N. Further, similarly, the optical signal emitted from the optical waveguide 41c spreads in the horizontal direction within the plane of the two-dimensional optical waveguide 42 and enters the incident portions of all the optical waveguides 44-1 to 44-N. Accordingly, the two-dimensional optical waveguide 42 converts each optical signal output from each of the three optical waveguides 41a, 41b, 41c into N optical waveguides 4 in the form of an optical star coupler.
4-1 to 44-N and output.

The optical waveguides 44-1 through 44-N are three-dimensional optical waveguides 43 formed by a known Ti diffusion method and formed by Ti diffusion.
Regarding a plurality of N optical signals incident on 4-1 to 44-N, the vertical direction (corresponding to the polarization change direction of the vertical polarization component), which is the thickness direction of the substrate 40, and the thickness direction. This is an optical waveguide for confining light in the left-right direction (horizontal direction; corresponding to the polarization change direction of the horizontal polarization component), which is a vertical direction, and transmitting an optical signal in a single mode. Here, the optical waveguides 44-1 to 44-N have respective optical path lengths in ascending order, for example, so that the optical path differences are different from each other by, for example, 1 mm.
Antenna elements 53-1 to 53- of array antenna 70
N is changed according to the installation position. Each optical waveguide 44-1 to 44- of the three-dimensional optical waveguide 43 by Ti diffusion
At the other end of the N, a Ramipole-type polarizer 45 is formed by directly and collectively coating so as to form an InGaAs layer on the InP layer. This is an optical element that deflects and extracts only a deflection component inclined by about 45 degrees from the vertical polarization component and the horizontal polarization component of the optical signal emitted from -1 to 44-N and outputs the result. In this case, the Ramipole type polarizer 4
Reference numeral 5 depolarizes and extracts the polarization components of both the vertical polarization component and the horizontal polarization component of the optical signal while slightly attenuating them, and outputs the polarization components to the photodiodes 51-1 to 51-N. The Ramipole-type polarizer 45 may be coated as described above, or may be formed by individually coating the optical waveguides 44-1 to 44-N.

Therefore, the two-dimensional optical waveguide 42 is an optical device that combines and combines three incident optical signals, and then distributes and demultiplexes the optical signals to a plurality of N optical waveguides 44-1 to 44-N. Next, both the vertical polarization component and the horizontal polarization component in each of the optical waveguides 44-1 to 44-N are polarization-extracted by the Ramipole polarizer 45 and output.

The optical signals output from the optical waveguides 44-1 to 44-N are respectively incident on the photodiodes 51-1 to 51-N via the Ramipole type polarizer 45, and are subjected to the square detection method. After being mixed and photoelectrically converted into microwave signals having a difference frequency Δf1, Δf2, Δf3 between two polarization components, the converted microwave signals are subjected to power conversion by the radio frequency power amplifiers 52-1 to 52-N. After being amplified, each antenna element 53-1 of the array antenna 70 is amplified.
To 53-N toward free space. Here, in the array antenna 70, each antenna element 53
-1 to 53-N are arranged in a linear array on a straight line at predetermined intervals of, for example, half a wavelength.

FIG. 24 is a graph showing the wavelength dependence of the refractive index of each optical waveguide of the birefringent optical waveguide device 80 of FIG. 21 (simulation result). By thermally diffusing Ti in the birefringent optical waveguide substrate 40 made of LiNbO ₃ like the optical waveguides 42 and 43, the refractive index can be changed from the original refractive index by about 1%, for example, and 24, the refractive index of the ordinary light and the extraordinary light changes with respect to the light wavelength, and the change of the refractive index differs depending on the direction of deflection. That is,
Since the refractive index changes according to the wavelength of the transmitted light, the phase of the transmitted light can also be changed according to the wavelength of the light.

FIG. 25 shows a tunable light source device 10a, 10b, 10c in the array antenna control device of FIG.
5 is a graph showing a phase difference (simulation result) between adjacent antenna elements when the wavelength is changed by the above. The condition of the simulation result is that the difference frequency between the vertical polarization component and the horizontal polarization component, that is, the microwave frequency of the radio signal radiated from the array antenna 70 is 60 GHz, and each optical waveguide of the three-dimensional optical waveguide 43 Wave paths 44-1 to 44
This is the case where the optical path difference between adjacent optical waveguides at −N is set to 1 mm. As is apparent from FIG. 25, the phase difference between each adjacent antenna element in the array antenna 70 is substantially linearly changed by changing the wavelength of the optical signal output from the wavelength variable light source device 10a, 10b, 10c. It can be seen that it can be changed to Therefore,
By changing the wavelength of the optical signal, the beams B1, B
2 and B3 can be changed.

As described above, according to the present embodiment,
It has the following unique effects. (1) The directional direction of each beam radiated by a multi-beam antenna composed of a plurality of N beams is changed by the wavelength tunable light source device
It can be controlled independently by changing the emission wavelengths of Oa, 10b, and 10c, and can be controlled with high precision because no mechanical mechanism is used as compared with the second conventional example. (2) Compared to the case where a conventional microwave circuit is used,
It can be formed with a simple configuration, and can handle and transmit a wideband signal. (3) At least the birefringent optical waveguide device 80 can be optically integrated as an optical waveguide, is highly practical, can be reduced in size and weight, and can significantly reduce the manufacturing cost. Further, the optical modulators 60a, 60b, and 60c can also be optically integrated, and can be further reduced in size and weight, thereby reducing manufacturing costs.

In the above embodiments, the three-dimensional and two-dimensional optical waveguides 42 and 43, which are distributed index optical waveguides, are formed by the Ti diffusion method. However, the present invention is not limited to this, and the LiTaO ₃ When a dielectric substrate such as an optical crystal substrate is used, a core can be formed by thermally diffusing Nb, Ti or Cu. Further, by a known proton exchange method, a part of lithium ions (Li ⁺ ) of the LiNbO ₃ crystal substrate is exchanged with protons (H ⁺ ) to form a proton exchange optical waveguide which is a distributed index optical waveguide. Is also good. In this case, the LiNbO ₃ crystal substrate is immersed in a benzoic acid (C ₆ H ₅ COOH) melt at about 210 to 250 ° C. for several tens of minutes to remove a part of the lithium ions (Li ⁺ ) of the LiNbO ₃ crystal substrate. By exchanging with protons (H ⁺ ), a high refractive index portion can be obtained.

In the above embodiment, the array antenna 70 formed of a linear array is used, but the present invention is not limited to this, and a two-dimensional array antenna may be used. In the case of this modification, each beam can be changed three-dimensionally in a space extending in a direction perpendicular to the plane of the array antenna, instead of being changed in a plane as in the embodiment. .

In the above embodiment, the difference frequencies Δf1, Δf of the wavelength-variable light source devices 10a, 10b, 10c
2 and Δf3 are set to be different from each other, but the present invention is not limited to this and may be set to the same value. in this case,
From the array antenna 70, for example, beams B1, B2, and B3 having the same radio frequency and different directions can be emitted.

<Effects when Optical Waveguide is Applied> Lastly, effects when the optical waveguides of the first to third embodiments are applied as a three-dimensional optical waveguide 43 to a light-controlled phased array antenna device of an application example will be described. I do. The optically controlled phased array antenna device of the application example mainly includes (1) a plurality of M
Wavelength tunable light source devices 10a, 10b, 10c;
(2) a birefringent optical waveguide device 80 integrated on one birefringent optical waveguide substrate 40; and (3) an array antenna composed of a plurality of N antenna elements 53-1 to 53-N.
0. Its function is to simultaneously radiate a plurality of M beams from the array antenna 70 and change the wavelength of the variable wavelength light source devices 10a, 10b, 10c so that the directivity of each beam can be deflected independently of other beams. It is. The high-birefringence dispersive optical waveguide according to the present invention is a light-controlled phased array antenna apparatus according to an application example, wherein “a plurality of N optical waveguides are formed on the birefringent optical waveguide substrate with a predetermined optical path length difference from each other. The following advantages are provided by using the “N number of second optical waveguides” that transmit the optical signal of “N”. (1) When the wavelength change width of the variable wavelength light source device is the same, the deflection range of the antenna radiation beam corresponding to the light source can be widened. (2) When the deflection range of the antenna radiation beam is the same, the wavelength change width of the corresponding tunable optical microwave light source can be reduced. (3) In the case of (2), the number M of beams radiated simultaneously from the antenna can be increased. This is because the wavelength change range of the light source corresponding to each beam needs to be set to a different wavelength range in order to avoid emission of unnecessary radio waves. On the other hand, at present, the wavelength range in which a tunable light source can be realized is, for example, 1450 nm.
To 1590 nm (for example, in the case of an 8168F light source manufactured by Hewlett-Packard Company). Therefore, the achievable number of beams M is (the entire achievable wavelength range of the wavelength variable light source) / (the wavelength change width of each light source). If the wavelength change width of the denominator is small according to the present invention, the number of beams M can be greatly increased.

[0066]

As described in detail above, according to the optical waveguide device of the present invention, it is possible to obtain improved birefringence dispersion higher than that of the conventional example over a wide wavelength range. Further, by applying the optical waveguide device according to the present invention to the third conventional optically controlled phased array antenna device, the following specific effects can be obtained. (1) When the wavelength change width of the variable wavelength light source device is the same, the deflection range of the antenna radiation beam corresponding to the light source can be widened. (2) When the deflection range of the antenna radiation beam is the same, the wavelength change width of the corresponding tunable optical microwave light source can be reduced. (3) In the case of (2), the number M of beams radiated simultaneously from the antenna can be increased. This is because the wavelength change range of the light source corresponding to each beam needs to be set to a different wavelength range in order to avoid emission of unnecessary radio waves. On the other hand, at present, the wavelength range in which a wavelength tunable light source can be realized is, for example,
To 1590 nm (for example, in the case of an 8168F light source manufactured by Hewlett-Packard Company). Therefore, the achievable number of beams M is (the entire achievable wavelength range of the wavelength variable light source) / (the wavelength change width of each light source). If the wavelength change width of the denominator is small according to the present invention, the number of beams M can be greatly increased.

[Brief description of the drawings]

FIG. 1A is a longitudinal sectional view showing a structure of a Ti: LiNbO ₃ optical waveguide 110 according to a first embodiment of the present invention, and FIG. 1B is a horizontal length of the optical waveguide 110. 6 is a graph showing a refractive index distribution characteristic with respect to.

FIG. 2A is a longitudinal sectional view showing a structure of an SiO ₂ / Si optical waveguide 115 according to a _second embodiment of the present invention, and FIG. 2B is a longitudinal view of the optical waveguide 115 in a thickness direction. 6 is a graph showing a refractive index distribution characteristic with respect to the height.

FIG. 3 shows a SiO _{2 according} to a third embodiment of the present invention.
5 is a longitudinal sectional view showing the structure of the / Si optical waveguide 116. FIG.

FIG. 4 is a graph showing characteristics of birefringence and birefringence dispersion with respect to an aspect ratio in an optical waveguide having a rectangular core.

FIG. 5 is a graph showing wavelength characteristics of birefringence dispersion in the optical waveguides of the conventional example and the first and second embodiments.

FIG. 6 is a diagram showing a structure, refractive index distribution characteristics, and birefringence dispersion of an optical waveguide according to a conventional example and the first embodiment.

FIG. 7 is a longitudinal sectional view illustrating a configuration of an SiO ₂ layer according to a _second embodiment.

FIG. 8 is a diagram showing a refractive index distribution characteristic in the optical waveguide of the second embodiment of FIG. 7;

FIGS. 9 (a), (b), (c) and (d) are diagrams showing the structures, refractive index distribution characteristics and birefringence dispersion of various examples of the optical waveguide according to the second embodiment, respectively. is there.

FIGS. 10 (a), (b), (c) and (d) are diagrams respectively showing the structures, refractive index distribution characteristics and birefringence dispersion of various examples of the optical waveguide according to the second embodiment. is there.

FIGS. 11 (a), (b), (c) and (d) are diagrams respectively showing the structures, refractive index distribution characteristics and birefringence dispersion of various examples of the optical waveguide according to the second embodiment. is there.

FIGS. 12 (a), (b), (c) and (d) are diagrams respectively showing the structures, refractive index distribution characteristics and birefringence dispersion of various examples of the optical waveguide according to the second embodiment. is there.

FIGS. 13 (a), (b), (c) and (d) are diagrams respectively showing the structures, refractive index distribution characteristics and birefringence dispersion of various examples of the optical waveguide according to the second embodiment. is there.

FIGS. 14 (a), (b), (c) and (d) are diagrams respectively showing the structures, refractive index distribution characteristics and birefringence dispersion of various examples of the optical waveguide according to the second embodiment. is there.

FIGS. 15 (a), (b), (c) and (d) are diagrams showing the structures, refractive index distribution characteristics and birefringence dispersion of various examples of the optical waveguide according to the second embodiment, respectively. is there.

FIGS. 16 (a), (b), (c) and (d) are diagrams respectively showing the structures, refractive index distribution characteristics and birefringence dispersion of various examples of the optical waveguide according to the second embodiment. is there.

FIGS. 17 (a), (b) and (c) each show a second example.
It is a figure which shows the structure, the refractive index distribution characteristic, and the birefringence dispersion of various Examples regarding the optical waveguide of embodiment.

FIGS. 18 (a), (b) and (c) each show a second example.
FIG. 14 is a diagram showing structures, refractive index distribution characteristics, and birefringence dispersion of various examples according to a PMMA optical waveguide of a first modification of the embodiment.

FIGS. 19 (a), (b) and (c) each show a second example.
FIG. 14 is a diagram showing structures, refractive index distribution characteristics, and birefringence dispersion of various examples according to the AlGaAs / GaAs optical waveguide of the second modification of the embodiment.

FIG. 20 shows an AlGa according to a second modification of the second embodiment.
Al _x Ga _1-x A used in As / GaAs optical waveguide
It is a graph which shows the change of the refractive index with respect to x of s.

FIG. 21 is a diagram showing structures, refractive index distribution characteristics, and birefringence dispersion of various examples of the optical waveguide according to the conventional example and the third embodiment.

FIG. 22 is a view showing various modifications of the shape of the refractive index distribution characteristic of the dispersion-shifted optical fiber cable according to the present invention.

FIG. 23 is a block diagram showing a configuration of a light-controlled phased array antenna device of an application example using the optical waveguide device according to the present invention.

24 is a graph showing the wavelength dependence of the refractive index of each optical waveguide of the birefringent optical waveguide device 80 of FIG.

FIG. 25 shows a wavelength-variable light source device 10a, 10b, 10 in the optically controlled phased array antenna device of FIG.
9 is a graph showing a phase difference between adjacent antenna elements when the wavelength is changed by c.

[Explanation of symbols]

10a, 10b, 10c: variable wavelength light source device, 30: beam controller, 31a, 31b, 31c: external optical modulator (EOM), 32a, 32b, 32c, 33a, 33b, 33c: deflection beam splitter, 40: birefringence 41a, 41b, 41c: optical waveguide, 42: two-dimensional optical waveguide by Ti diffusion, 43: three-dimensional optical waveguide by Ti diffusion, 44-1 to 44-N: optical waveguide, 45: rasipole type polarized light 51-1 to 51-N: photodiodes, 52-1 to 52-N: radio frequency power amplifiers, 53-1 to 53-N: antenna elements, 60a, 60b, 60c: optical modulators, 70: array Antenna, 80: birefringent optical waveguide device, 100: external cavity semiconductor laser device, B1, B2, B3: beam, 110: i: LiNbO ₃ waveguide, 111 ... LiNbO ₃ substrate, 112 ... Ti core by diffusion, 115 ... SiO ₂ / Si optical waveguides, 116 ... SiO ₂ / Si optical waveguides, 120 ... cladding, 121 ... Si substrate, 122 ... Si deposited layer, 130 ... core, 131 ... channel, 132 ... core, 133 ... channel 135-1 to 135-N ... SiO ₂ layer, 136-1,136-2 ... SiO ₂ layer, 141 to 143 ... refractive index distribution Characteristic.

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[Procedure amendment]

[Submission date] March 23, 2000 (200.3.2.
3)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Keizo Inagaki 5 Sanraya, Inaya, Seika-cho, Soraku-cho, Kyoto Pref. Inside ATI R & D Center for Environmentally Adaptable Communications (72) Inventor Yoshihiko Mizuguchi Kyoto Soraku No. 5, Sanraya, Inaya, Seika-cho, Gunma F-term (reference) 2A047 KA04 PA12 PA13 PA21 PA24 QA02 QA03 QA04 TA00 5J021 AA05 AA07 AA09 BA03 DB07 FA00 FA02 FA26 HA02

Claims (10)

[Claims] 1. A method in which a predetermined material is diffused on a dielectric substrate serving as a clad by a thermal diffusion method or exchanged by using a predetermined material by a proton exchange method, thereby each having a refractive index larger than that of the clad. An optical waveguide device comprising: a plurality of cores; and a plurality of maximum refractive indexes in a refractive index distribution characteristic. 2. A core and a plurality of layers each having a predetermined thickness and a refractive index of a core larger than the refractive index of the clad are formed on a dielectric substrate or a semiconductor substrate serving as a clad. Thereafter, a dielectric material or a semiconductor material serving as a clad is formed so as to surround the plurality of layers, and the optical waveguide device has at least one maximum refractive index in a refractive index distribution characteristic. 3. The optical waveguide device according to claim 2, wherein the plurality of layers include at least three layers, and the core layer is sandwiched between two channels. 4. The optical waveguide device according to claim 2, wherein a refractive index of a material of the layer serving as the channel is smaller than a refractive index of a material of the cladding. . 5. The optical waveguide device according to claim 2, wherein the refractive index of the material of the core layer is at least 1.08 times the refractive index of the material of the channel. An optical waveguide device, comprising: 6. The optical waveguide device according to claim 2, wherein the optical waveguide device has a plurality of local maximum refractive indexes in a refractive index distribution characteristic. 7. The optical waveguide device according to claim 6, wherein two of the plurality of maximum value refractive indexes are different from each other. 8. A plurality of layers each having a polygonal cross-sectional shape obtained by adding a protrusion to a rectangular shape and having a refractive index larger than that of the clad are formed on a dielectric substrate or a semiconductor substrate serving as a clad. An optical waveguide device, comprising: forming a dielectric material or a semiconductor material to be a clad so as to surround the plurality of layers. 9. The optical waveguide device according to claim 8, wherein the cross-sectional shape of the core has a stepped outer shape. 10. A layer having a rectangular shape having a length and a width and having a refractive index larger than that of the clad is formed on a dielectric substrate or a semiconductor substrate serving as a clad and surrounding the layer. In an optical waveguide device formed by forming a dielectric material or a semiconductor material as a cladding as described above, the length and width of the core are substantially equal to the aspect ratio, which is the ratio of the length and width of the core, and the birefringence dispersion is substantially. An optical waveguide device characterized in that the length and width of the core are set to have maximum values.