JPH11271699A - Optical waveguide device - Google Patents

Abstract

(57) Abstract: Provided is an optical waveguide element having an equal branching ratio of light in an optical waveguide having a branch. An optical waveguide device includes a LiNbO ₃ substrate.
A pair of electrodes 16a and 16b and an optical waveguide 14 that is branched in parallel at a branch portion to form two branched optical waveguides 14b and 14c are formed on the second optical waveguide. The electrode wiring pattern 18a and the branched optical waveguides 14b and 14c
Together with cross section A, B _2, respectively one place and, the lead wiring pattern 18b and minute Edamitsu waveguide 14c of the electrode having a cross section B ₁ of 1 place. The width of the lead wiring pattern 18a of the electrode near the intersection A (Y in FIG. 1)
Direction) is double the width of other parts,
The total length of the branches (in the Y direction in FIG. 1) at the intersection of the branched optical waveguides 14b and 14c is the same.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical waveguide device, and more particularly, to an optical waveguide device having an electrode and an optical waveguide having a branch formed on a LiNbO ₃ substrate.

[0002]

2. Description of the Related Art In general, an optical waveguide has a function of confining radiation in a certain area and guiding its energy flow parallel to the axis of a path. Therefore, at present, the size of the optical component is reduced by changing the optical waveguide represented by an optical fiber cable to an optical waveguide.

As the optical waveguide, for example, GaAs
-Based, InP-based semiconductor optical waveguides, dielectric (glass) optical waveguides formed by forming an oxide film on Si, using a glass substrate, and ferroelectric crystal optical waveguides composed of LiNbO ₃ or LiTaO ₃ crystals.

[0004] In particular, as an optical element such as an optical waveguide type modulator which carries information through an electrode on a light beam transmitted through the optical waveguide, L has excellent electro-optical characteristics.
Ti diffusion type LiNb in which Ti is diffused in iNbO ₃ crystal
An O ₃ optical waveguide is used.

[0005] In this case, as shown in FIG.
_When the electrodes 4a and 4b such as phase modulators are provided on the substrate 2, an optical waveguide element 8 in which an Au film is formed on the optical waveguide 6 is usually used.

An optical waveguide has basic elements such as straight lines, bending, branching, and coupling, and these are combined to form an optical circuit. Among them, the branch type is shown in FIG.
The one optical waveguide 6a shown in FIG. 7 is branched into two branched optical waveguides 6b and 6c, and the branched optical waveguides 6b and 6c shown in FIG. There is a Mach-Zehnder type (branch interference type) which becomes one optical waveguide 6a again.

In these branched optical waveguides 6, it is important to evenly split the light into the branched optical waveguides 6b and 6c. However, the resolution limit of the branch in photolithography, the optical waveguide after branching, It is not always easy to make the branching ratio equal for reasons such as defects and light absorption at the electrodes. As a result, when the electrodes 4a and 4b for the phase modulator are provided on the substrate, the extinction ratio which is the on / off intensity ratio of light obtained as the characteristic of the Mach-Zehnder optical waveguide having the phase modulator is obtained. There arises a problem that the height is different for each branch.

By the way, as shown in FIGS. 6 and 7,
Electrode 4 used as a phase modulator due to circuit design convenience
In many cases, the routing wiring patterns a and 4b are provided so as to intersect with the branched optical waveguides 6b and 6c of the optical waveguide 6, but this influences the above-described light branching ratio. It has been found from the results of investigations by the present inventors that this is one of the factors affecting the ON / OFF extinction ratio of the optical waveguide having the shape.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and is directed to an optical waveguide device in which an electrode and a branched optical waveguide are formed on a LiNbO ₃ substrate. The wiring pattern of the electrode is
It is an object of the present invention to provide an optical waveguide device capable of equally branching light into each branch when the optical waveguide is arranged so as to intersect each branch of the optical waveguide.

[0010]

In order to solve the above-mentioned problems, an optical waveguide device according to the present invention has at least one pair of electrodes and one or more branch portions on a LiNbO ₃ substrate, and is branched into two or more. An optical waveguide element in which the wiring pattern of the electrode intersects at least one branch of the optical waveguide at one location and at least one other branch. In a case where two branches are arranged so as to intersect, the total length of the branches at the intersection is substantially the same for each branch. Here, the length of the branch at the intersection means the distance in the traveling direction of the light of the branch of the optical waveguide at the location where the routing wiring pattern and the branch of the optical waveguide intersect. Also, the sum of the lengths of the branches at the intersection is almost the same,
It means that one sum is less than 1.1 times the other sum.

With this arrangement, the unbalance of the branching ratio of light caused by the wiring pattern of the electrodes crossing over the branches of the optical waveguide can be eliminated, and the branching ratio can be made the same in each branch of the optical waveguide. it can. Here, as a method of making the total lengths of the branches at the intersection substantially the same, for a branch of the optical waveguide having only one intersection with the routing wiring pattern, at least at the intersection of the routing wiring pattern A method of increasing the width (the distance of the branch of the optical waveguide on the light traveling direction side) can be used.

Further, the optical waveguide device according to the present invention has a structure of Li
An optical waveguide device in which at least a pair of electrodes and an optical waveguide having at least one branch portion and branching into two or more are formed on an NbO ₃ substrate, wherein a wiring pattern of the electrodes is formed of the optical waveguide. By having a dummy routing wiring section that intersects at least one branched branch, the dummy branch wiring section has the same number of intersections that intersect each of the branched branches, and the total length of the branches at the intersection is It is characterized by being substantially the same in each branch. In this case, the number of intersections crossing each branch may be any number as long as it is two or more. Thus, the effects of the present invention described above can be obtained by a simple method without partially changing the width of the wiring pattern of the electrodes.

Further, the optical waveguide device according to the present invention has a structure of Li
An optical waveguide device comprising an NbO ₃ substrate and at least a pair of electrodes and an optical waveguide having at least one branch portion and branching into two or more, wherein a wiring pattern of the electrodes is at least the optical waveguide. One branched branch of and m
Intersects at one point and m +
When crossing at n places, the total length of the branches at the cross section satisfies the following expression.

[0014] ^{_{L m + n × 1.1 n ≦}} L m ≦ L m + n × 1.8 n m, n: a natural number in the range both from 1 to 3, m + n
> 2 L _m : total length of branches at the intersection where the leading wiring pattern intersects with one branch of the optical waveguide at m places L _{m + n} : leading wiring pattern corresponds to one branch of the optical waveguide The sum of the lengths of the branches at the intersections on the side intersecting with the branch at the (m + n) places. Thereby, the lead wiring pattern of the electrode has at least three branches of the optical waveguide intersecting at least three branches. In the waveguide element, the effects of the present invention described above can be suitably obtained. Here, the reason why the total length of the branches at the intersection of one branch having the smaller number of intersections is 1.1 times or more the other branch having the larger number of intersections is as follows. Specifically, in a branch having a larger number of intersections, a spatially unstable region of a waveguide propagation mode generated by a large number of intersections is present in a large number of points in the branch, so that the branched light The reason for this is to balance this in the branch with the smaller number of intersections, since the absorption rate of the cross section increases. On the other hand, the reason why the total length of the branches at the intersection of one branch having the smaller number of intersections is 1.8 times or less of the other branch having the larger number of intersections is as follows. If it exceeds, the branching ratio tends to deteriorate. For the same reason, when the number of intersections with one branch is up to two, a spatially unstable region of the waveguide propagation mode is generated, but it is negligible in the range of a practical branching ratio. Therefore, it is sufficient to make the lengths of the branches at the intersection of both the same. On the other hand, if the number of intersections with one branch exceeds six at the maximum, the loss of light in the optical waveguide element is undesirably large beyond the practical range.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the optical waveguide device according to the present invention will be described below with reference to FIGS.

An optical waveguide device 10 according to a first example of the present embodiment shown in FIG. 1 has an optical waveguide 14 formed by diffusing Ti on a LiNbO ₃ substrate 12. Are provided with a control electrode 16a as a phase modulator and a ground electrode 16b. The light is
Proceed in the Y direction.

The LiNbO ₃ substrate 12 of the optical waveguide device 10
Has a width (Z direction in FIG. 1) of about 3 mm and a length in the optical waveguide 14 direction (Y direction in FIG. 1) of about 30 mm. The optical waveguide 14 has one Y-shaped branch portion,
Each size is the width of the optical waveguide 14a before branching (Z in FIG. 1).
Direction) is 4 μm, and branches in parallel after the branch portion 2
The two branched optical waveguides 14b and 14c have the same cross-sectional shape, and have a width (Z direction in FIG. 1) of 4 μm. The control electrode 16a formed of an Au film is connected to the branched optical waveguide 14a.
b, 14c are provided at two places in parallel with each other, each having a width (Z direction in FIG. 1) of 50 μm, a length (Y direction in FIG. 1) of 12 mm, and also formed of an Au film. The ground electrode 16b is connected to the branched optical waveguides 14b, 14b.
c, and the width (Z direction in FIG. 1) is 240
μm, and the length (Y direction in FIG. 1) is 12 mm.

Leading wiring patterns 18a, 18b formed of Au fine wires are connected to the respective electrodes 16a, 16b, and the leading wiring pattern 18a is located at one position with each of the branched optical waveguides 14b, 14c. parts intersect in a cross section B ₂ a, whereas, lead wiring patterns 18b intersect at an intersection B ₁ and minute Edamitsu waveguide 14c. The width (Y direction in FIG. 1) of each wiring pattern 18a, 18b is 20 μm. However, at the intersection A and its vicinity, the width is doubled to 40 μm. Therefore, each branched optical waveguide 1 of the optical waveguide 14
4b and 14c, the branched optical waveguide 14b is 1
The branch optical waveguide 14c has two intersections B ₁ and B ₂ . The total length of the branched optical waveguides at the intersection is 20 μm at the intersection A of the branching optical waveguide 14b and 20 μm × 2 at the intersections B ₁ and B ₂ of the branching optical waveguide 14c. Is 40 μm, and is the same for each of the branched optical waveguides 14b and 14c.

The routing wiring patterns 18a, 18
The other end of b is connected to a control signal system and a connection terminal to the ground, which are indicated by reference numerals 20a and 20b in FIG.

Next, an optical waveguide device 10 according to a second example of the present embodiment shown in FIG. 2 will be described. The configuration of the optical waveguide device 10 according to the second example is basically the same as that of the first example, and the same components will be described with the same reference numerals.

In the optical waveguide device 10 of the second example, the substrate 1
2, an optical waveguide 14 formed by diffusion of Ti is provided, and a control electrode 16a as a phase modulator and a ground electrode 16b are provided on the optical waveguide 14. Light travels in the Y direction in FIG.

The optical waveguide device 10 according to the second example has
The width of each wiring pattern 18a, 18b (in FIG. 2,
(Y direction) is formed at the same 20 μm at all locations. In FIG. 2, a dummy wiring pattern 18 c having a width of 20 μm drawn from the installation electrode 16 b is provided at the upper left location of the ground electrode 16 b. The leading wiring pattern 18c is a branch optical waveguide 14b of the optical waveguide 14.
When forming a cross-section A ₁ intersect at one point. Accordingly, each of the branched optical waveguides 14b and 14c has two intersections A ₁ and A ₂ , and B ₁ and B ₂ , respectively. It is the same 20 μm × 2 for the branch optical waveguides 14b and 14c.

FIG. 3 shows an optical waveguide device 22 according to a third example of the present embodiment. In the third example, similarly to the first and second examples described above, an optical waveguide 26 formed by diffusion of Ti is provided on a substrate 24, and a control electrode 28a is provided on the optical waveguide 26. And a ground electrode 28b. Light travels in the Y direction in FIG.

The size of the substrate 24 of the optical waveguide element 22 is as follows.
The width (Z direction in FIG. 3) is about 5 mm, and the length in the optical waveguide 26 direction (Y direction in FIG. 1) is about 40 mm. The optical waveguide 26 is such that after one optical waveguide 26a is branched in the Y-shaped first branch portion in parallel with the two branched optical waveguides 26b and 26c, each of the branched optical waveguides 26b and 26c is further divided into the second branch portion. In addition, two more branches in parallel, and eventually 4
It has two branched optical waveguides 26d, 26e, 26f, 26g. In each size, the width (in the Z direction in FIG. 1) of the optical waveguide 26a before branching is 7 μm, the width of the two branched optical waveguides 26b and 26c is the same 6 μm, and the four branch optical waveguides 26d ２６26 g is the same 6 μm. The control electrode 28a includes a branch optical waveguide 26d and a branch optical waveguide 26.
e, and four locations are provided in parallel at the outside of each of the branched optical waveguides 26f and 26g, each having a width (Z direction in FIG. 1) of 70 μm and a length (Y direction in FIG. 1). ) Is 7 mm, and the ground electrode 28b includes the branch optical waveguide 26d, the branch optical waveguide 26e, and the branch optical waveguide 26d.
f and the branched optical waveguides 26g are provided at two places, each having a width (in the Z direction in FIG. 1) of 200 μm,
The length (Y direction in FIG. 1) is 7 mm.

Each of the electrodes 28a and 28b has a thickness of 15 μm.
Leading wiring pattern 30 of one width (Y direction in FIG. 1)
a, 30b are connected, and the routing wiring pattern 3
0a is one each with the branched optical waveguides 26d to 26g,
Intersection A_Two, Intersection B_Two, Intersection C_Two, And intersection D
_TwoIntersect at On the other hand, the routing wiring pattern 30b
Is a dummy wiring pattern with a width of 15 μm.
The ground 30c is connected via the ground electrode 28b,
Eventually, as in the case of the routing wiring pattern 30a, the branch light guide
Wave path 26d-26g and one place each, intersection A₁, Exchange
Difference B₁, Intersection C₁And intersection D₁Crosses at
You. Therefore, each branched optical waveguide 26d of the optical waveguide 26
From the side of ~ 26g, each two intersections A
₁And A_Two, B ₁And B_Two, C₁And C_Two, D₁And D_TwoHas
And the total branch length at the intersection is
And 15 μm × 2.

The optical waveguide device 32 according to the fourth embodiment of the present embodiment shown in FIG. 4 is similar to the first to third embodiments described above.
6, a control electrode 38a and a ground electrode 38b are provided on the optical waveguide 36. The light is Y in FIG.
Proceed in the direction.

The size of the substrate 34 of the optical waveguide element 32 is
The width (Z direction in FIG. 3) is about 3 mm, and the length in the optical waveguide 36 direction (Y direction in FIG. 1) is about 70 mm. In the optical waveguide 36, one optical waveguide 36a is branched in parallel at the Y-shaped first branch portion, and the two branched optical waveguides 36b and 36 are formed.
c. Each size is the optical waveguide 36a before branching.
Is 3 μm (in the Z direction in FIG. 1), and the width of the two branched optical waveguides 36b and 36c is the same, 3.5 μm.
Three sets of control electrodes 38a provided in two places in parallel with the outside of each of the branched optical waveguides 36b and 36c,
A total of six locations are provided, each having a width (in the Z direction in FIG. 1) of 50 μm and a length (in the Y direction in FIG. 1) of 15 mm. The ground electrode 38b corresponds to the control electrode 38a,
A total of three locations are provided between the branched optical waveguides 36b and 36c, each having a width (Z direction in FIG. 1) of 250 μm and a length (Y direction in FIG. 1) of 16 mm.

Leading wiring patterns 40a, 40b are connected to the electrodes 38a, 38b, respectively, and the leading wiring pattern 40a intersects each of the branched optical waveguides 36b, 36c at three intersections A ₁ -A _{3 and} B _2, B _4, B
₆ and the wiring pattern 40b
Represents three intersections B ₁ , B ₃ , with the branched optical waveguide 36c.
Intersect at B _5. Each routing wiring pattern 40a,
The width of the wiring 40b (Y direction in FIG. 1) is basically 50 μm, which is the same, but the intersection A ₁ of the routing wiring pattern 40a.
The locations from to A ₃ to connect to the communication terminal and the ground, which is three times the 150μm of 50 [mu] m. Therefore, each of the branched optical waveguides 36b, 36 of the optical waveguide 36
When viewed from the side of c, the branched optical waveguide 36b has a total length of branches at _three intersections A _{1 to} A ₃ of 150 μm ×
3, 450 μm, while the branched optical waveguide 36 c is 6 μm.
The sum of the branch lengths at the intersections B _{1 to} B ₆ is 5
0 μm × 6, which is 300 μm, and the sum of the branch lengths at the intersections A _{1 to} A ₃ of the branch optical waveguide 36 b is the sum of the branch lengths at the intersections B _{1 to} B ₆ of the branch optical waveguide 36 c. It is 1.5 times the total.

Next, the light branching ratios of the optical waveguide elements 10, 10, 32 of the first, second and fourth examples according to the present embodiment and the optical waveguide element 8 of FIG. The results of the evaluation are shown.

As shown in FIG. 5, the evaluation method is such that the optical waveguide 46a of the optical waveguide element 44 to be measured before the branch of the optical waveguide 46 is connected to a light source 50 via a polarization control system 48 by an optical fiber 52. On the other hand, the optical waveguides 46b and 46c on the branch side after branching of the optical waveguide 44 are alternately switched by a drive system and connected to the optical power meter 54 by the optical fiber 52. The branching ratio was determined by measuring the loss of the emitted light.

The branching ratio is determined according to the first and second embodiments according to the present embodiment.
In the fourth example, the ratios are 52:48 (56 μW: 52 μW), 50:50 (52 μW: 52 μW), and 48:52 (39 μW: 42 μW), respectively. 52 μW), and in the first, second, and fourth examples of the present embodiment,
The branch was almost equally branched in each branch as compared with the comparative example. Further, in the third example of the present embodiment shown in FIG. 3 evaluated separately, the branching ratio of the four branches is 25:26:25.
The number of pairs is 24, and it can be seen that in the third example, the light beams are branched almost equally.

The optical waveguide device according to the present invention is not limited to the above-described embodiment, but can adopt various configurations without departing from the gist of the present invention.

[0033]

As described above, in the optical waveguide device according to the present invention, an optical waveguide having at least one pair of electrodes and one or more branch portions is formed on a LiNbO ₃ substrate. An optical waveguide element, wherein the wiring pattern of the electrode intersects at least one branch of the optical waveguide at one location and intersects another branch of the optical waveguide at two locations. When arranged, the total length of the branches at the intersection is substantially the same for each branch.

For this reason, the unbalance of the branching ratio of the light caused by the wiring pattern of the electrode crossing over the branch of the optical waveguide is eliminated and becomes the same.
The effect that the loss of the extinction ratio can be made the same can be achieved.

In addition, the wiring pattern of the electrodes is at least one of the branched branches of the optical waveguide.
Intersects at one point and m +
When crossing at n places, the total length of the branches at the crossing portion satisfies the following expression.

[0036] ^{_{L m + n × 1.1 n ≦}} L m ≦ L m + n × 1.8 n m, n: a natural number in the range both from 1 to 3, m + n
> 2 L _m : total length of branches at the intersection where the leading wiring pattern intersects with one branch of the optical waveguide at m places L _{m + n} : leading wiring pattern corresponds to one branch of the optical waveguide The sum of the lengths of the branches at the intersections on the side intersecting with the branch at m + n places. For this reason, the wiring pattern of the electrode has at least three optical waveguides that intersect at least one branch of the optical waveguide. In the waveguide element, the effect that the effects of the present invention described above can be suitably obtained is achieved.

[Brief description of the drawings]

FIG. 1 is a plan view of an optical waveguide device according to a first example of the present embodiment.

FIG. 2 is a plan view of an optical waveguide device according to a second example of the present embodiment.

FIG. 3 is a plan view of an optical waveguide device according to a third example of the present embodiment.

FIG. 4 is a plan view of an optical waveguide device according to a fourth example of the present embodiment.

FIG. 5 is a diagram for explaining a method of measuring a loss characteristic of an optical waveguide.

FIG. 6 is a plan view of a conventional optical waveguide device provided with a Y-branch optical waveguide.

FIG. 7 is a plan view of an optical waveguide device provided with a conventional Mach-Zehnder optical waveguide.

[Explanation of symbols]

10, 22, 32, 44: Optical waveguide element 12, 24, 34: Substrate 14, 14a to 14c, 26, 26a to 26g, 36,
36a to 36c, 46, 46a to 46c: Optical waveguide 16a, 16b, 28a, 28b, 38a, 38b: Electrodes 18a to 18c, 30a to 30c, 40a, 40b: Leading wiring pattern

Claims (3)

[Claims] 1. An optical waveguide device comprising: a LiNbO ₃ substrate on which at least a pair of electrodes and an optical waveguide having at least one branch portion and branching into two or more are formed, wherein the wiring pattern of the electrodes is At least one of the branched branches of the optical waveguide is arranged to intersect at one location and intersect with the other one of the branched branches at two locations. Is substantially the same for each branch. 2. An optical waveguide device comprising: a LiNbO ₃ substrate on which at least a pair of electrodes and an optical waveguide having at least one branch portion and branching into two or more are formed, wherein the wiring pattern of the electrodes is Having a dummy routing wiring section intersecting at least one branched branch of the optical waveguide to have the same number of intersections each intersecting with each of the branched branches; An optical waveguide device, wherein the total length is substantially the same for each branch. 3. An optical waveguide device comprising: a LiNbO ₃ substrate on which at least a pair of electrodes and an optical waveguide having at least one branch portion and branching into two or more are formed. When at least one branched branch of the optical waveguide intersects at m places and intersects another branched branch at m + n places, the total length of the branches at the intersection is as follows: An optical waveguide device characterized by being within a range satisfying the expression. ^{_{L m + n × 1.1 n ≦}} L m ≦ L m + n × 1.8 n m, n: a natural number in the range both from 1 to 3, m + n
> 2 L _m : total length of branches at the intersection where the leading wiring pattern intersects with one branch of the optical waveguide at m places L _{m + n} : leading wiring pattern corresponds to one branch of the optical waveguide The total length of branches at the intersection of the side crossing the branch at m + n places