JPH10325911A - Optical waveguide element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an optical waveguide element capable of nonreversible wave guide a miniaturization and cost reduction. SOLUTION: A waveguide 10 and the waveguide 30 are formed by transparent material in a used wavelength, and the waveguide 20 is formed by waveguide material with a low diffractive index, and a diffractive index discontinuous surface 40 is formed on a crossing part among these waveguides, and an angle 2θ between the axes of the waveguides 10 and 30 is set according to a critical angle that total reflection generates in the discontinuous surface 40. The light P1 made incident from the waveguide 10 is total reflected on the discontinuous surface 40 to be wave guided to the waveguide 30, and the light P2 made incident from the waveguide 20 transmits through the discontinuous surface 40 to be wave guided to the waveguide 10, and the nonreversible optical waveguide element is realized by the diffractive index discontinuous surface, and when reception light and transmission light are multiplexed to a piece of fiber, the control of polarization, the addition of an isolator element, etc., becomes unnecessary, and the miniaturization and cost reduction of an optical waveguide circuit is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an irreversible waveguide element used for optical fiber communication, optical fiber measurement, and the like.

[0002]

2. Description of the Related Art In two-way optical communication, a single optical fiber transmits light in the opposite directions of received light and transmitted light. The optical waveguide is connected, and a light detecting element is connected to the receiving waveguide, and a laser element is connected to the transmitting optical waveguide. This optical branching / multiplexing device generally uses an element in which two fibers are fusion-coupled or an element in which a Y-branch-shaped optical waveguide is provided on an optical waveguide substrate. Such an optical branching multiplexer is
It is possible to couple light from the transmitting light emitting element to the optical fiber while introducing light to the sensing element.

[0003]

By the way, in the conventional waveguide element described above, the reversible waveguide property of the element causes
The receiving light is also guided to the transmitting light emitting element, and there is a disadvantage that the light emitting element output becomes unstable. Therefore, when such a branch is used, an optical isolator combining a Faraday rotation element and two polarizing elements by a bulk magneto-optical effect between a light emitting element and an optical splitter, or a Faraday Using a rotating element as an optical waveguide, an optical isolator element having a limit on the phase of input light is inserted to prevent instability of the light emitting element. The addition of these elements for irreversibility leads to an increase in circuit complexity and size and an increase in circuit cost, and it is desired that an irreversible function can be imparted to an ordinary optical waveguide.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical waveguide device which can impart irreversibility to a waveguide device and can realize a reduction in size and cost. is there.

[0005]

In order to achieve the above object, an optical waveguide device according to the present invention comprises a first waveguide made of a first material, and a first waveguide made of the first material. The second waveguide formed so as to intersect the waveguide at a predetermined angle and the intersection of the first and second waveguides are made of a second material having a lower refractive index than the first material. A low refractive index portion.

Further, in the present invention, a discontinuous refractive index surface is formed between the intersection of the first and second waveguides and the low refractive index portion, and light incident from the first waveguide is formed. The angle between the discontinuous surface and the first waveguide is defined such that the light is totally reflected by the discontinuous surface and guided by the second waveguide.

In the present invention, the first and second materials are made of a material that is transparent at the wavelength used.

Further, according to the present invention, the first and the second
Is formed by thermally diffusing titanium on a lithium niobate substrate, or on a lithium niobate substrate, using as a mask a resist film provided with openings in accordance with the shapes of these waveguides. It is formed by a proton exchange method.

According to the present invention, a first material made of a first material is provided.
A low-refractive-index portion made of a second material having a lower refractive index than the first material is provided at an intersection of the first waveguide and the second waveguide, and a discontinuous refractive index surface is provided between the intersection and the low-refractive index. Is formed, and the angle of the light incident from the first waveguide is set so as to be totally reflected at the discontinuous surface. As a result, the first
Of the light incident from the waveguide of No. 1 is totally reflected at the discontinuous surface of the refractive index, and most of the incident light is guided to the third waveguide except for the waveguide loss. Is prevented. On the other hand, light transmitted from the low refractive index portion to the refractive index discontinuity surface is incident on the high refractive index medium from the low refractive index medium at the discontinuous surface, so that total reflection does not occur and slight reflection occurs. Most pass through the discontinuous surface except for and enter the first waveguide.

Thus, it is possible to form a nonreciprocal optical waveguide element by forming a discontinuous surface of the refractive index at the intersection of the waveguides and utilizing the total reflection or passage of light on the discontinuous surface. For example, when combining received light and transmitted light transmitted by different optical fibers into one fiber, polarization control and the addition of an isolator element are not required, and the optical waveguide circuit can be reduced in size and reduced in size. Cost reduction can be realized.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment FIG. 1 is a structural view showing a first embodiment of an optical waveguide device according to the present invention. As shown in the figure, the optical waveguide element of the present embodiment includes a waveguide 10, a waveguide 20, and a waveguide 30. The waveguides 10 and 30 are made of the same waveguide material, and the waveguide 20 is made of a different waveguide material. Moreover, the refractive index of the waveguide material forming the waveguide 20 is set lower than that of the waveguide material forming the waveguides 10 and 30. For this reason, the waveguides 10 and 30 and the waveguide 20
A discontinuous refractive index surface 40 is formed at the intersection with.

Assuming that the normal to the discontinuous surface 40 is 50, the angle θ between the axis of the waveguide 10 and the normal 50 is set to be equal to or greater than the critical angle for total reflection caused by the discontinuity of the refractive index. The angle between the axis of the waveguide 30 and the normal 50 is also θ
Therefore, the angle between the waveguide 10 and the axis of the waveguide 30 is 2θ.

Hereinafter, the operation of the optical waveguide device of the present embodiment will be described with reference to FIG. Light P ₁ incident from the waveguide 10 when it reaches the discontinuity 40, the discontinuity 40, the refractive index changes from high to low, the total reflection occurs at the discontinuity 40, the waveguide loss except, most of the energy of light P ₁ incident is reflected. The reflected light is incident on the waveguide 30, and as shown in FIG.
₃ is transmitted by the waveguide 30. Therefore, the light P ₁ incident on the waveguide 10 is guided to the waveguide 30 and is not output to the waveguide 20.

On the other hand, the light P incident from the waveguide 20
_According to Snell's law, most of the energy of the incident light, for example, about 97%, is changed because the refractive index at the discontinuous surface 40 changes from low to high when it reaches the discontinuous surface 40. passes through the discontinuities 40, as transmitted light P _20, and reaches the waveguide 10. Also, small reflected light P ₂₁ generated by the discontinuity 40 is discharged to the outside of the waveguide as shown. When transmitting through the discontinuous surface of the refractive index,
The optical axis of the waveguide slightly changes due to refraction, and a waveguide loss occurs after passing through the discontinuous surface. However, by confining the optical waveguide, light having a practical intensity can be obtained from the waveguide 10 side.

Hereinafter, a method for manufacturing an optical waveguide device according to the present embodiment will be described with reference to FIG. The optical waveguide element of this embodiment can be formed by thermally diffusing titanium (Ti) on a lithium niobate (LN) substrate. In this case, the thickness of the titanium waveguide pattern of the waveguide 10 and the waveguide 30 is made thicker than the thickness of the titanium waveguide pattern in the portion including the discontinuous surface 40 and the waveguide 20;
By controlling the concentration of titanium after thermal diffusion, the discontinuous refractive index surface 40 of the waveguide can be formed. For example, the thickness of the titanium film is formed at 500 to 1000 °, and by controlling the thickness of the titanium film in this manner,
For example, the waveguide 10 having a refractive index of 2.230, the waveguide 30 and the waveguide 20 having a refractive index of 2.225 can be formed on a lithium niobate substrate having a refractive index of 2.222.

In the discontinuous surface 40 thus formed, the angle 2θ formed by the axes of the waveguide 10 and the waveguide 30 can be calculated according to the difference in the refractive index between the waveguide 10 and the waveguide 20. Here, the refractive indices of the waveguides 10 and 30 are n ₁ ,
Assuming that the refractive index of 0 is n ₂ , the critical angle θ _{0 at which} total reflection occurs at the discontinuous refractive index surface 40 is given by the following equation.

[0017]

Equation 1 θ ₀ = sin (n ₂ / n ₁ ) (1)

For example, in the above example, the refractive index n ₁
= 2.230, refractive index n ₂ = 2.225, discontinuous surface 40
The critical angle θ _{0 at} which total reflection occurs at
It is calculated as 6.2 °. Therefore, in FIG.
The angle between 0 and the axis of the waveguide 30 is (2θ = 172.4)
°). By setting the angle between the waveguide 10 and the axis of the waveguide 30 to 172.4 ° or more, the light incident from the waveguide 10 is totally reflected at the discontinuous surface 40,
The light is guided to the waveguide 30.

As described above, according to this embodiment, the waveguides 10 and 30 are formed of a transparent material at the wavelength used, and the waveguide 2 is formed of a waveguide material having a low refractive index.
0, and a discontinuous refractive index surface 40 is formed at the intersection of these waveguides. The angle 2θ between the waveguide 10 and the axis of the waveguide 30 is set according to the critical angle at which total reflection occurs at the discontinuous surface 40. Light P ₁ incident from the waveguide 10
Is totally reflected by the discontinuous surface 40 and guided by the waveguide 30,
The light P ₂ incident from the waveguide 20 passes through the discontinuous surface 40 and is guided to the waveguide 10, so that an irreversible optical waveguide element can be realized by the discontinuous surface of the refractive index, and the received light and the When multiplexing the transmission light into one fiber, the control of polarization and the addition of an isolator element, which are conventionally required, become unnecessary, and the size and cost of the optical waveguide circuit can be reduced.

Second Embodiment FIG. 2 is a configuration diagram showing a second embodiment of the optical waveguide device according to the present invention. As shown in FIG. 2, the optical waveguide device of the present embodiment has substantially the same configuration as the optical waveguide device of the first embodiment shown in FIG.
And the waveguide 30. Further, similarly to the first embodiment, the waveguide material forming the waveguide 20a is:
The refractive index is set lower than those of the waveguide members forming the waveguide 10 and the waveguide 30.

However, in the optical waveguide device of the present embodiment, as shown, the waveguide 20a is formed to have a bent shape as compared with the optical waveguide device of FIG. Hereinafter, the operation and characteristics of the optical waveguide element having such a configuration will be described with reference to FIG.

In the optical waveguide device of the present embodiment, the waveguide 10 and the waveguide 30 are formed similarly to the optical waveguide device shown in FIG. Further, waveguides 10 and 30 and waveguide 2
Waveguide material constituting the 0a, if each similarly selected and the optical waveguide device shown in FIG. 1, the total reflection critical angle theta ₀ in the refractive index discontinuity 40 is as in the first embodiment.

As a result, the light incident from the waveguide 10 is guided as in the first embodiment. That is, the incident light P ₁ undergoes total reflection at the discontinuous surface 40, and the reflected light P ₃ is guided to the waveguide 30.

On the other hand, the light P incident from the waveguide 20
₂ is incident on the discontinuous surface 40 from the low-refractive index medium to the high-refractive index medium, so that most of the light passes through the discontinuous surface 40 and reaches the waveguide 10 except for the waveguide loss and minute reflection. When the light passes through the refractive index discontinuity surface 40, the optical axis of the guided light changes slightly due to refraction, and the intensity of the light transmitted through the discontinuity surface 40 is slightly attenuated by the waveguide loss. In order to reduce this loss, as described above, in the present embodiment, the waveguide 20a is bent as shown in FIG.
The influence of refraction can be reduced.

As described above, according to the present embodiment, the waveguides 10 and 30 are formed of a transparent material at the used wavelength, and the waveguide 20a is formed of a waveguide material having a lower refractive index. A discontinuous refractive index surface 40 is formed at the intersection of these waveguides. The angle 2θ between the waveguide 10 and the axis of the waveguide 30 is set according to the critical angle at which total reflection occurs at the discontinuous surface 40. The light P ₁ incident from the waveguide 10 is totally reflected by the discontinuous surface 40, guided to the waveguide 30, and the light P ₂ incident from the waveguide 20 a is transmitted through the discontinuous surface 40, 10 and further waveguide 2
By bending the optical waveguide 0a, the influence of refraction when light is transmitted from the waveguide 20a to the waveguide 10 is reduced, so that an irreversible optical waveguide element can be realized by a discontinuous surface of the refractive index. It is possible to reduce the size and cost of the device.

Third Embodiment FIG. 3 is a structural view showing a third embodiment of the optical waveguide device according to the present invention. As shown in FIG. 3, the optical waveguide device of the present embodiment has substantially the same configuration as the optical waveguide device of the first embodiment shown in FIG.
And the waveguide 30. The refractive index of the waveguide material forming the waveguide 20 is set lower than that of the waveguide material forming the waveguide 10a and the waveguide 30.
a, 30 at the intersection of the waveguide 20 and the refractive index discontinuity surface 40
Are formed.

As shown in FIG. 3, in the optical waveguide element of the present embodiment, the tapered waveguide 10_
1 and 10_2 are provided respectively. The optical waveguide element according to the present embodiment includes a tapered waveguide 1 in the waveguide 10a.
Except for providing 0_1 and 10_2, the configuration and operation of each part of the waveguide 20, the waveguide 30, and the discontinuous refractive index surface 40 are almost the same as those of the optical waveguide element of the first embodiment shown in FIG. Therefore, here, the operation of the optical waveguide element of the present embodiment will be described focusing on transmission of transmitted light in the waveguide 10a.

The operation of transmitting the light incident from the waveguide 10a is the same as in the first embodiment. That is, the incident light undergoes total reflection on the discontinuous refractive index surface 40, and most of the incident light is reflected except for the waveguide loss, and is guided to the waveguide 30.

On the other hand, when the light incident from the waveguide 20 reaches the discontinuous surface 40,
Since the refractive index changes from low to high, according to Snell's law,
In this case, most of the energy of the incident light is
And reaches the waveguide 10a. When the light passes through the discontinuous surface of the refractive index, the optical axis of the waveguide slightly changes due to refraction, and a waveguide loss occurs after passing through the discontinuous surface. On the other hand, in the optical waveguide device of the present embodiment, as shown in FIG. 3, the waveguide 10a has tapered waveguides 10_1 and 1_1.
0_2 are provided to alleviate the influence of refraction on the transmitted light from the waveguide 20.

As described above, according to the present embodiment, the waveguide 10a and the waveguide 30 are made of a transparent material at the used wavelength.
Is formed, and a waveguide 2 having a lower refractive index than the waveguide 2 is formed.
0, and a discontinuous refractive index surface 40 is formed at the intersection of these waveguides. The light incident from the waveguide 10a is totally reflected by the discontinuous surface 40, guided to the waveguide 30, and
The light incident from 0 passes through the discontinuous surface 40, is guided to the waveguide 10a, and is further formed with tapered waveguides 10_1 and 10_2 in the waveguide 10a, so that the waveguide 20 is changed to the waveguide 10a. Since the influence of refraction when light is transmitted is reduced, an irreversible optical waveguide element can be realized by a discontinuous surface of the refractive index, and the size and cost of the optical waveguide circuit can be reduced.

Fourth Embodiment FIG. 4 is a structural diagram showing a fourth embodiment of the optical waveguide device according to the present invention. As shown in FIG. 4, the optical waveguide element according to the present embodiment has substantially the same configuration as the optical waveguide element according to the first embodiment shown in FIG. 1, and includes a waveguide 10, a waveguide 20, and a waveguide 30. It is configured. The waveguide material constituting the waveguide 20 is set to have a lower refractive index than the waveguide materials constituting the waveguides 10 and 30, and the waveguides 10, 30
A discontinuous refractive index surface 40 is formed at the intersection between the waveguide and the waveguide 20.

In the above-described second and third embodiments of the present invention, when the incident light from the waveguide 20 passes through the discontinuous refractive index surface 40, the influence caused by the refraction of the light is alleviated. It was devised for this purpose. On the other hand, in the present embodiment, the light incident from the waveguide 10 is
Are devised in order to improve the waveguiding characteristics when the wave is guided to the waveguide 30 by total reflection in the above.

As shown in FIG. 4, in the optical waveguide device of the present embodiment, a waveguide extension 60 is provided at the intersection of the waveguide 10 and the waveguide 30. Hereinafter, the operation of the optical waveguide device of the present embodiment will be described with reference to FIG.

When the light P ₁ incident from the waveguide 10 reaches the discontinuous surface 40, the refractive index at the discontinuous surface 40 changes from high to low. except waveguide loss, most of the energy of light P ₁ incident is reflected. Reflected light is incident on the waveguide 30, as shown, is transmitted by the waveguide 30 as reflected light P _3. Therefore, the light P ₁ incident on the waveguide 10 is guided to the waveguide 30 and is not output to the waveguide 20.

As shown in FIG. 4, in the optical waveguide device of the present embodiment, at the intersection of the waveguide 10 and the waveguide 30,
The waveguide expansion part 60 is provided, whereby the waveguide characteristic of light from the waveguide 10 to the waveguide 30 is improved, and the light that is totally reflected by the refractive index discontinuity surface 40 and enters the waveguide 30 is provided. it is possible to reduce transmission loss in P _3, can be improved transmission efficiency in the optical waveguide element.

As described above, according to the present embodiment, the waveguides 10 and 30 are formed of a transparent material at the wavelength used, and the waveguide 20 is formed of a waveguide material having a lower refractive index. A discontinuous refractive index surface 40 is formed at the intersection of these waveguides. The light incident from the waveguide 10 is totally reflected by the discontinuous surface 40, is guided to the waveguide 30, and the light incident from the waveguide 20 is transmitted through the discontinuous surface 40,
The light is guided to the waveguide 10. Further, the waveguide 10 and the waveguide 30
By providing the waveguide extension 60 at the intersection with the waveguide, the waveguide characteristics when light is reflected and transmitted from the waveguide 10 to the waveguide 30 can be improved, the transmission loss can be reduced, and the refractive index can be reduced. An irreversible optical waveguide element can be realized by the discontinuous surface, and the optical waveguide circuit can be reduced in size and cost.

Fifth Embodiment FIG. 5 is a structural view showing a fifth embodiment of the optical waveguide device according to the present invention. As shown in FIG. 5, the optical waveguide device of the present embodiment has substantially the same configuration as the optical waveguide device of the first embodiment shown in FIG. It is constituted by a wave path 20 and a waveguide 30. The waveguide material forming the waveguide 20 has a lower refractive index than the waveguide materials forming the waveguide 10 and the waveguide 30, and has a refractive index discontinuity at the intersection of the waveguide 10, 30 and the waveguide 20. A surface 40 is formed.

In the optical waveguide device of this embodiment, the portion having a high refractive index is limited to the vicinity of the intersection of the waveguides, and the discontinuous surfaces other than the desired total reflection discontinuous surface 40 are substantially orthogonal to the waveguide. Form into shape. For example, a waveguide 70 is formed at the end of the waveguide 10 by a waveguide material having a low refractive index, and similarly, a waveguide 80 is formed at an end of the waveguide 30 by a waveguide material having a low refractive index. As the waveguide material constituting the waveguides 70 and 80, for example, the same waveguide material as that constituting the waveguide 20 can be used. The discontinuous surface 90 between the waveguide 70 and the waveguide 10 may be, for example, the waveguide 70 or the waveguide 10.
Are formed substantially perpendicular to the axis of
The discontinuous surface 100 between 0 and the waveguide 80 is formed, for example, so as to be substantially perpendicular to the axis of the waveguide 30 or the waveguide 80.

As described above, by forming the discontinuous surfaces 90 and 100 having a refractive index substantially perpendicular to the waveguide, the reflection and refraction at these discontinuous surfaces are reduced. Also, to prevent minute reflections on these discontinuous surfaces,
The angle between the discontinuous surface and the waveguide can be shifted from the orthogonal angle by 3 to 5 °. Thereby, the influence of minute reflected light on the discontinuous surface can be reduced without impairing the function of the present invention.

The operation of the optical waveguide device according to this embodiment will be described below with reference to FIG. Most of the light P ₁ incident from the waveguide 70 is transmitted through the discontinuous surface 90 at the discontinuous surface 90 between the waveguide 70 and the waveguide 10 except for slight reflection, and is guided to the waveguide 10. . Waveguide 10
When the light transmitted by the light reaches the discontinuous surface 40, the refractive index changes from high to low at the discontinuous surface 40, so that total reflection occurs at the discontinuous surface 40, and the incident light is removed except for the waveguide loss. most were light P ₁ energy is reflected. The reflected light is incident on the waveguide 30 and, as shown, a discontinuous surface 100 between the waveguide 30 and the waveguide 80.
Is transmitted to In the discontinuous surface 100, the refractive index changes from high to low. However, since the discontinuous surface 100 is formed so as to be substantially orthogonal to the waveguide 30 or the waveguide 80, the state of the discontinuous surface 40 Unlike the first embodiment, the total reflection does not occur, and most of the incident light, except for a slight reflection, is discontinuous.
00 passes, is transmitted by the waveguide 30 as light P _3.

On the other hand, the light P incident from the waveguide 20
_According to Snell's law, most of the energy of the incident light, for example, about 97%, is changed because the refractive index at the discontinuous surface 40 changes from low to high when it reaches the discontinuous surface 40. passes through the discontinuities 40, as transmitted light P _20, and reaches the waveguide 10. Further, the light is transmitted to the discontinuous surface 90 by the waveguide 10. In the discontinuous surface 90, the refractive index changes from high to low. However, as described above, since the discontinuous surface 90 is formed so as to be substantially orthogonal to the waveguide 10 or the waveguide 70, The light P ₂₀ transmitted by 10 does not undergo total reflection at the discontinuous surface 90, and most of the incident light passes through the discontinuous surface 90 except for slight reflection, and is transmitted by the waveguide 70.

Hereinafter, a method for manufacturing the optical waveguide device according to the present embodiment will be described with reference to FIG. The optical waveguide element of this embodiment can be formed by thermally diffusing titanium on a lithium niobate substrate. For example, in order to set the refractive index of the portions forming the waveguide 10 and the waveguide 30 higher than the portions forming the other waveguides,
In addition, a titanium film thicker than other portions is formed according to the waveguide 30. And by thermally diffusing the titanium film,
Form a waveguide. As a result, for example, a refractive index of 2.22
The waveguide 10 and the waveguide 30 having a refractive index of 2.230 are formed on the lithium niobate substrate of No. 2;
A waveguide 20, a waveguide 70, and a waveguide 80 having a refractive index of 2.225 are respectively formed. Further, a discontinuous surface 90 is formed between the waveguide 70 and the waveguide 10, and a discontinuous surface 100 is formed between the waveguide 30 and the waveguide 80. Furthermore, a discontinuous surface 40 between the waveguide 20 and the waveguide 20 is formed at the intersection of the waveguide 10 and the waveguide 30.

The angle 2θ formed by the axis of the waveguide 10 and the axis of the waveguide 30 can be obtained by the equation (1) according to the difference in the refractive index between these waveguides and the waveguide 20. Here, since the refractive index difference between these waveguides is the same as that of the first embodiment shown in FIG. 1, the critical angle θ _{0 at which} total reflection occurs at the discontinuous surface 40 is different from that of the first embodiment. Similarly, for example, it is calculated as 86.2 °. Therefore, in FIG. 1, the angle between the waveguide 10 and the axis of the waveguide 30 is (2θ = 17).
2.4 °). By setting the angle between the waveguide 10 and the axis of the waveguide 30 to 172.4 ° or more, the light incident from the waveguide 10 is totally reflected at the discontinuous surface 40 and guided to the waveguide 30. You.

As described above, according to the present embodiment, the waveguides 10 and 30 are formed of a transparent material at the wavelength used, and the waveguide 20 is formed of a waveguide material having a lower refractive index. A discontinuous refractive index surface 40 is formed at the intersection of these waveguides. Further, waveguides 70 and 80 are formed at the ends of the waveguide 10 and the waveguide 30 by using a waveguide material having a low refractive index, and the discontinuous surface is formed so as to be substantially orthogonal to the waveguide axis. The angle 2θ between the waveguide 10 and the axis of the waveguide 30 is set according to the critical angle at which total reflection occurs at the discontinuous surface 40. The light P ₁ incident from the waveguide 70 passes through the discontinuous surface 90 and is transmitted to the waveguide 10. The light transmitted through the waveguide 10 is transmitted through the discontinuous surface 4.
0, is totally reflected at 0, is guided to the waveguide 30, and has
0 is transmitted to the waveguide 80. The light P ₂ incident from the waveguide 20 passes through the discontinuous surface 40 and
0, almost through the discontinuous surface 90, and
Therefore, an irreversible optical waveguide element can be realized due to the discontinuous surface of the refractive index, and the size and cost of the optical waveguide circuit can be reduced.

Sixth Embodiment FIG. 6 is a structural view showing a sixth embodiment of the optical waveguide device according to the present invention. As shown in FIG. 6A, the optical waveguide element of the present embodiment has substantially the same configuration at the intersection of the waveguides as the optical waveguide element of the fifth embodiment shown in FIG. 10 and a waveguide 30. Further, a waveguide 110 is formed on an extension of the waveguide 10. As shown in FIG.
A portion between the intersection of the waveguide 30 and the waveguide 110 is filled with a medium having the same refractive index as the substrate or a waveguide material forming the substrate, thereby forming a low refractive index portion. Here, this portion is regarded as a waveguide and is denoted by reference numeral 20b. As shown in the figure, the discontinuous refractive index surface 40a between the waveguide 10 and the intersection of the waveguide 30 and the waveguide 20b Are formed, and a discontinuous surface 120 is formed between the waveguide 20b and the waveguide 110.

That is, in the optical waveguide element of the present embodiment, the waveguides 10 and 10 are made of a waveguide material having a higher refractive index than the substrate.
The waveguide 30 and the waveguide 110 are formed, and the waveguide 20b is formed by a waveguide material having the same refractive index as the substrate or by the substrate itself. Therefore, the refractive index of the waveguide 20b is lower than that of the waveguide 10, 30 or 110. The angle between the waveguide 10 and the axis of the waveguide 30 is defined as the critical angle θ at which total reflection occurs at the discontinuous surface 40a.
By setting in response to _0, it is possible that is guided to the waveguide 30 of light P ₁ incident from the waveguide 10 by total internal reflection at the discontinuity 40a.

Hereinafter, the operation of the optical waveguide device according to the present embodiment will be described with reference to FIG. When the light P ₁ incident from the waveguide 10 reaches the discontinuous surface 40a, the refractive index changes from high to low at the discontinuous surface 40a, so that total reflection occurs and incident light is removed except for waveguide loss. most of the light P ₁ is reflected. The reflected light is incident on the waveguide 30,
As shown, it is transmitted by the waveguide 30 as reflected light P _3. Therefore, the light P ₁ that enters the waveguide 10 is guided to the waveguide 30, it is not to be output to the waveguide 20b.

On the other hand, the light P ₂ incident from the waveguide 110
Is incident on the discontinuous surface 120 between the waveguide 110 and the waveguide 20b. Note that the discontinuous surface 120 is formed so as to be substantially orthogonal to the waveguide 110 as shown. Therefore, at the discontinuous surface 120, the waveguide 110
From the side to the waveguide 20b side, the refractive index changes from high to low, but most of the incident light P ₂ passes through the discontinuous surface 120 except for slight reflection. That is, the light P ₂ which is transmitted from the waveguide 110 is opened from the waveguide 110 through the discontinuous surface 120 is transmitted to the waveguide 20b consisting of substrate medium, the spatial light. Further, the substrate medium (waveguide 20b)
And is incident on the discontinuous surface 40a. The distance from the discontinuous surface 120 to the discontinuous surface 40a can be set as short as several to several tens of μm, and the waveguide loss becomes almost negligible due to the straightness of light.

The light P ₂ incident from the waveguide 20b is incident on the discontinuous surface 40a from the low-refractive index medium to the high-refractive index medium. 40, reaches the waveguide 10, and the light P
₂₀ is transmitted by the waveguide 10. Also, small reflected light P ₂₁ generated by the discontinuity 40a is discharged to the outside of the waveguide as shown.

In the case of the present embodiment, it is preferable to form a cladding layer having the same refractive index as the substrate on the substrate surface in order to prevent reflection at the interface between the substrate and the space. FIG. 6B shows a cross section of the optical waveguide element in the case where the cladding layer is provided. In FIG. 6B, 1 is
For example, a lithium niobate single crystal substrate, 10 or 11
Numeral 0 indicates a waveguide, and numeral 2 indicates a substrate 1 and a cladding layer formed on the surface of the waveguide.

As shown in FIG. 6B, waveguides 10 and 110 or a waveguide 30 (not shown) are formed on the substrate 1 by a thermal diffusion method of titanium. Next, another lithium niobate thin plate is closely adhered to the surface of the substrate 1 and the waveguide formed on the substrate 1. Alternatively, a lithium niobate film is deposited by sputtering or laser ablation to form a film. Thus, the cladding layer 2 made of lithium niobate is formed.

As described above, according to the present embodiment, the waveguide 10, the waveguide 30, and the waveguide 110 are formed on the substrate from the waveguide material having a higher refractive index than the material constituting the substrate, and Waveguide 10 and waveguide 1 formed in
A low-refractive-index portion 20b (which can be regarded as a waveguide) made of a medium having the same refractive index as the substrate or the substrate itself is interposed between the two.
A discontinuous refractive index surface 40a is formed between the intersection of the waveguide 10 and the waveguide 30 and the low refractive index portion 20b. The angle 2θ between the waveguide 10 and the axis of the waveguide 30 is set according to the critical angle at which total reflection occurs at the discontinuous surface 40a. The light P ₁ incident from the waveguide 10 is totally reflected by the discontinuous surface 40 a, is guided to the waveguide 30, and the light P ₂ incident from the waveguide 110 is transmitted through the discontinuous surface 120 and has low refraction. Rate part 20b
And reaches the discontinuous surface 40. Without generating a total reflection at the discontinuity 40a, guided most of incident light to the waveguide 10, since it is transmitted by the waveguide 10 as light P _20,
An irreversible optical waveguide element can be realized by the discontinuous surface of the refractive index, and the size and cost of the optical waveguide circuit can be reduced.

In each of the embodiments described above, a method for forming a waveguide on a lithium niobate substrate by a thermal diffusion method has been described as a method for forming a waveguide, but the present invention is not limited to this. A method of forming another waveguide, for example, a resist film is formed on a lithium niobate substrate, an opening is formed in the resist film according to the shape of the waveguide, and a proton exchange method is performed using the opening as a mask. In the same manner, a waveguide can be formed on a substrate and a refractive index discontinuity surface can also be formed by a method of forming a waveguide, a dry process method using an organic material, or the like. Thus, it goes without saying that the present invention is not limited to the material and processing method of the waveguide, but can be applied to other methods.

[0054]

As described above, according to the optical waveguide device of the present invention, a non-reciprocal type optical waveguide device is realized by a refractive index discontinuous surface formed between waveguide materials having different refractive indexes. There are advantages that can be done. Furthermore, according to the optical waveguide element of the present invention, for example, when multiplexing the reception light and the transmission light into one optical fiber, the control of the conventionally required polarization and the addition of an isolator element become unnecessary, Miniaturization of optical waveguide circuits,
Cost reduction can be achieved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating a first embodiment of an optical waveguide element according to the present invention.

FIG. 2 is a configuration diagram showing a second embodiment of the optical waveguide element according to the present invention.

FIG. 3 is a configuration diagram showing a third embodiment of the optical waveguide element according to the present invention.

FIG. 4 is a configuration diagram showing a fourth embodiment of the optical waveguide element according to the present invention.

FIG. 5 is a configuration diagram showing a fifth embodiment of the optical waveguide element according to the present invention.

FIG. 6 is a configuration diagram showing a sixth embodiment of the optical waveguide element according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Cladding layer, 10, 20, 30, 10
a, 20a, 20b, 70, 80, 110 ... waveguide, 4
0, 90, 100, 120, 40a ... refractive index discontinuous surface,
60 ... waveguide _{extensions, P 1, P 2, P} 20, P 21, P 3 ...
light

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yasuhiro Kubota 25th Wadai, Tsukuba, Ibaraki Prefecture NOK Co., Ltd. (72) Inventor Shinji Ushijima 25th Wadai, Tsukuba City, Ibaraki NOK Co., Ltd.

Claims (15)

[Claims] 1. A first waveguide made of a first material, and a second waveguide made of the first material and intersecting the first waveguide at a predetermined angle. An optical waveguide element having a low-refractive-index portion made of a second material having a lower refractive index than the first material at an intersection of the first and second waveguides. 2. A discontinuous refractive index surface is formed between an intersection of the first and second waveguides and the low refractive index portion, and
The angle between the discontinuous surface and the first waveguide is defined so that the light incident from the waveguide is totally reflected by the discontinuous surface and guided by the second waveguide. The optical waveguide device according to claim 1. 3. The optical waveguide device according to claim 1, wherein the first and second materials are made of a material that is transparent to a wavelength to be used. 4. The optical waveguide device according to claim 1, further comprising a third waveguide formed of said second material at an intersection of said first and second waveguides. 5. The optical waveguide device according to claim 4, wherein said third waveguide is formed on an extension of said first waveguide. 6. The optical waveguide device according to claim 1, wherein said first waveguide has a tapered waveguide formed in a tapered shape. 7. The optical waveguide device according to claim 1, wherein an intersection of said first and second waveguides is formed wider than a width of said first or second waveguide. 8. A fourth or fourth waveguide made of a third material having a low refractive index due to a first material constituting the first or second waveguide, at an end of the first or second waveguide. The optical waveguide device according to claim 1, wherein five waveguides are formed. 9. The optical waveguide device according to claim 8, wherein said third material is the same material as said second material. 10. The fourth or fifth waveguide and the first or fifth waveguide.
9. The optical waveguide device according to claim 8, wherein the refractive index discontinuity surface between the second waveguides is formed so as to be substantially orthogonal to each of the connected waveguides. 11. The optical waveguide device according to claim 1, wherein said first and second waveguides are formed by thermally diffusing titanium on a lithium niobate substrate. 12. The first and second waveguides are formed on a lithium niobate substrate by a proton exchange method using a resist film provided with openings according to the shapes of these waveguides as a mask. The optical waveguide device according to any one of claims 1 to 10, wherein 13. The light guide according to claim 1, further comprising a sixth waveguide formed of the first material on the same straight line as the first waveguide with the low refractive index portion interposed therebetween. Wave element. 14. The optical waveguide device according to claim 13, wherein the distance between the sixth waveguide and the intersection of the first and third waveguides is set to several μm to several tens μm. 15. A cladding layer formed of a material having a refractive index substantially equal to a material constituting the substrate, on a surface of the substrate on which the first, second and sixth waveguides are formed. The optical waveguide device according to claim 13, further comprising: