JPH0419713A - Waveguide type optical switch - Google Patents

Abstract

PURPOSE:To reduce an operating voltage required for output control over light by making the refractive index difference between waveguides larger at a center part (area I) in an area nearby the waveguides than in an area (II) except the area I, and providing control electrodes in both the areas I and II. CONSTITUTION:The waveguide type optical switch 10 which is a directional coupler type equipped with 1st and 2nd waveguides 12 and 14 put close so as to cause mutual light operation in an area III nearby the waveguides and the control electrodes 16 and 18 provided for the waveguides is so constituted that the refractive index between the waveguides is made larger at the center part I in the area nearby the waveguides than in the area II except the area I. The control electrodes 16 and 18 are provided on both the 1st area I and the area II except the center part. Consequently, light which is guided in the 1st waveguide 12 and light which is guided in the 2nd waveguide 14 are coupled relatively weakly in the area I and relatively strongly in the area II to reduce the operating voltage required for the output control over the light.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to a waveguide type optical switch, particularly in the direction T! : Connected to a coupler type optical switch.

(Prior art) Conventionally, as a waveguide type optical switch, for example, a directional coupler type as disclosed in Optical Integrated Circuits co-authored by Hiroshi Nishihara, Masamitsu Haruna, and Toshiaki Kusuhara, Ohmsha, 1985, p. 304-308. Is there something like that? This optical switch arranges two optical waveguides close to each other and controls the waveguides.
It has a structure in which a pole is provided, and when the operating voltage VO applied to the control electrode is a half-wavelength voltage V1, it outputs light in a bar state, and the operating voltage V. When I V o =O, light is output in a cross state.

(Problem to be Solved by the Invention) However, the above-mentioned conventional switch has a half-wavelength voltage v1
is large, so the maximum operating voltage V required for controlling the light output
. There was a problem that the value of .

Although the operating principle is different, if we compare it with a Matsuhatsu Ender type (branching interference type) optical modulator assuming the same element length,
In the case of the Matsuhatsu Ender type switch, Vo"■, then (propagation constant difference between the two waveguides) When the propagation constant of This is approximately twice the operating voltage VO=V.

SUMMARY OF THE INVENTION An object of the present invention is to provide a waveguide type optical switch in which the coupling of light between waveguides in the center of a region adjacent to the waveguides is reduced in order to solve the above-mentioned conventional problems.

(Means for Solving the Problems) In order to achieve this object, the waveguide type optical switch of the present invention includes first and second guides placed close to each other so as to cause light interaction in a region near the waveguide. In a directional coupler-type waveguide optical switch comprising a waveguide and a control electrode provided for the waveguide, the difference in refractive index between the waveguides at the center of the region adjacent to the waveguide is It is characterized in that the refractive index difference between the waveguides is greater than the difference in refractive index between the waveguides in the region excluding the central portion of the region, and the control electrode is provided both in the central portion of the region near the waveguide and in the region excluding the central portion.

(Function) According to the waveguide type optical switch having such a configuration, the refractive index difference between the waveguides in the central part of the waveguide-proximal region (hereinafter referred to as "region") can be reduced to a region other than the central part of the waveguide-proximal region. (below,
The difference in refractive index between the waveguides in region II) is made larger than that in region II).

By forming a refractive index difference in the regions H and H in this way, the operating voltage V. − It is possible to generate a propagation constant difference Δβ between the first and second waveguides in the state of 〇, and to make the propagation constant difference Δβ larger than the coupling coefficient between the first and second waveguides. . As a result, the light guided through the first waveguide and the light guided through the second waveguide are relatively weakly coupled in the region H and relatively strongly coupled in the region H. Therefore, the operating voltage V required for controlling the light output. ``V+ (V+ is a half-wavelength voltage) can be reduced.In addition, in the area processing and (1), the light guided through the first and second waveguides is coupled so as to cause optical interaction.

Further, according to the waveguide optical switch of the present invention, control electrodes are provided in both region (1) and region (2).

As the length of the region occupied by the control electrode along the waveguide in region H increases, the operating voltage V increases. = v1 reduction amount can be increased. Operating voltage V. In order to reduce this, it is most preferable to provide the control electrode from the beginning to the end of the region near the waveguide.

(Examples) Examples of the present invention will be described below with reference to the drawings. It should be noted that the drawings are only schematic representations to the extent that the invention can be understood, and therefore the invention is not limited to the illustrated examples.

FIG. 1 is a plan view schematically showing the configuration of a first embodiment of the present invention.

As shown in the same figure, the waveguide type optical switch 1 of this embodiment
0 is a directional coupler type optical switch, which includes first and second waveguides 12 and 14 that are placed close to each other so as to cause light interaction in the waveguide adjacent region (2), and a light switch for controlling the light output. Control electrode 16, provided for waveguide 12.14]
8. In FIG. 1, these electrodes 16 and 18 are shown with hatching.

Then, the waveguide 1 in the center part ■ of the waveguide adjacent region ■
The refractive index difference α(I) between the waveguides 12 and 14 is made larger than the refractive index difference α(n) between the waveguides 12 and 14 in the area (2) excluding the central part of the waveguide adjacent area m, and the control electrode 16 .18 is provided in both area engineering and area n.

This will be explained in more detail with reference to FIGS. 1 and 2. FIG. 2 is a plan view for explaining the waveguide of the first embodiment.
6.18 is a diagram omitted.

In this embodiment, a substrate 20 having an electro-optic effect, for example a LiNbO3 substrate, is prepared, and a waveguide 12 is formed on this substrate 2o.
．． 14v! establish. As shown in Figure 2, the adjacent area ■
In , the center position M of region ■ in the waveguide extending direction H
The shape of the waveguide 12.14, particularly the planar shape and/or three-dimensional shape, is made to be approximately line symmetrical with respect to the line of symmetry S passing through the line, and in the adjacent region m, the waveguide 12.14 is linearly shaped. are placed parallel to each other.

Then, the refractive index difference α(I
) and α(H) are controlled by the waveguide width. Here, as shown in FIG. 2, the waveguide width of the waveguide 12 in region I is d (I), and the waveguide width of the waveguide 14 is D (I
), and the waveguide width of the waveguide]2 in the region (■) on the left side of FIG. 2 is d(Ill), and the waveguide width of the waveguide 14 is tD
(Ill), if the waveguide width of the waveguide 12 in the region (■) on the right side of Figure 2 is expressed as d (Ur) and the waveguide width tD (II r) of the waveguide 14, the following equation (1) ~ (2)
If the width of each waveguide is set to satisfy α(1)〉
α(II).

d(1) −DCIN > 1d(III) −D(Il
l)l...(1)d(I) -〇(I)l>1d
(Ilr)-D(Ilrl...(2) In this example, in order to make the refractive index difference α(n) between the waveguides in region H almost zero, d(IIr)-D(IIr)=d (I
II) -D(III)=○.

By setting α(,II)ξ○ in this way, the operating voltage V. When =0, the light can be transferred from the waveguide 12 to 14 or from 14 to 12 in region H to obtain a cross state.

In this embodiment, as shown in FIG. 1, control electrodes 16, 18 are provided extending from the starting end X to the ending end Y of the adjacent region (2). Note that the symbols 12a and 12b in the figure are the optical input end and output end of the waveguide 12, and 14a and 14b.
denotes the light input end and output end of the waveguide 14.

Next, when the waveguide type optical switch 10 of this embodiment is closed and light is incident on the waveguide 12 at the starting end position If we consider the optical output power P using a coupling equation, the output power P in this case can be expressed by equation (3) shown on the next page.

(3) In the formula, pc represents the bond length Ac = (T[/2)
/K (K is the coupling coefficient), ΔB is the propagation constant difference that occurs in the waveguide 12.1411ffi according to the magnitude of the voltage VD by applying a voltage (VO≠0) to the control electrode, and Δ83 is the difference in the propagation constant that occurs in the waveguide 12.1411ffi when a voltage (VO≠0) is applied to the control electrode. voltage (V.

The value of ΔB, which represents the propagation constant difference caused by the refractive index difference of the waveguide M in the region when no voltage is applied, is the operating voltage V. changes in proportion to. In addition, Δβ and Δ
β, are mutually independent variables.

According to the analysis using equation (3), β/L1j! , Δβ, ·L/■=o′\, that is, the operating voltage V. =○ indicates the waveguide type optical switch 10 of this embodiment.
To operate in a crossed state, use the following equations (4) and (5).
L/1 c and Δβ8・L/n% to satisfy
I found out that I need to set it.

Figure 3 shows an example of the analysis results. Figure 3 shows 8 cover P.
is taken on the vertical axis and Δβ, ·L/vl-on the horizontal axis, A/L=
1/3, L/I2. ,=1.5 and Δβ,・L/T[=
ΔB when set to 5.8.

It shows the change in output power P with respect to the change in L/7+.

According to the analysis using equation (3), (when 1/L-173, the operating voltage v0 = 0, the waveguide optical switch) is operated in a crossed state, and the light incident from the input end 12a is output. In order to output from the end 14b, L/I2c: =1
．． 5 and △β3 ・L/T'[=5.8,
On the other hand, like this! /L=1/3, L#c=1. s and Δβ, ·L/T[=5.8, as can be understood from diagram M3, the operating voltage V. Adjust that to 80,・L/
When T[=1.3 (the value indicated by the arrow in the figure), the output power P becomes (nearly zero). Therefore, the waveguide optical switch 10 is operated in the bar state and the input terminal 12a is It is possible to output the light incident from the output end 12b.

In the conventional directional coupler type, Δβ,・L/yr=
1.7 (value indicated by arrow B in the figure). Since it operates in the bar state when adjusting the operating voltage V required for controlling the light output. -V+ (V+ is a half-wave voltage) is lower in this embodiment. According to this example, ΔB,・L/T [necessary to obtain the bar state] is 20%
This can be lowered than in the past.

Below are other examples of analysis results■～■7i! List.

■Operating voltage V when A/L=0.5. To create a cross state at =O, L/β. =2 and Δβ, L/TT=3.4. When this is done, the operating voltage V. Adjust △β,
・If L/TI=1.4, a bar state can be obtained.

Orashi/β. =2 and Δβ, ./TI=7.8. When this is done, the operating voltage V. Adjust Δ
By setting β,·L/T[=1.25, a bar state can be obtained.

■ Operating voltage V when ρ/L=0.7. - To create a cross state with 〇, L, #c = 3.5 and 8β, L/n = 4.4. When this is done, the operating voltage V. Adjust Δ
By setting β,·L/T[=1.4, a bar state can be obtained.

In the above analysis, A/L, L/β0 and ΔB are set so as to obtain a cross state when the operating voltage V0=○.

/T[, but the operating voltage v0≠OT
- ρ/L, L/β so as to obtain a reloss condition.

and Δ3. - It is also possible to design L/TT.

Furthermore, by analyzing the eigenmodes, the conditions for obtaining a bar state in the waveguide optical switch 10 of this embodiment can be found. This condition can be expressed as the following equation (6). is larger than the refractive index difference α(I'l) in region H, so if Δβ,〉〉K, then under the condition that formula (4) is satisfied, from formula (6), the following is shown in the next page. (7)
We can obtain the formula.

In equation (7), if A−+L, then △β, ・shi/■ → 1
Therefore, as the length β of the region ■ approaches the length of the adjacent region ■, the operating voltage increases. =■, can be decreased as it ages.

FIG. 4 is a plan view schematically showing the structure of a modified example of the bacteria embodiment. It should be noted that constituent components corresponding to those of the above-mentioned embodiment are designated by the same reference numerals.

In this modification, the control electrode provided for the waveguide 14]8
is composed of three electrode members 18a to 18c, and the electrode member 18a is placed in the area H on the left side in FIG.
b for area engineering, and electrode member 18c! The configuration is the same as that of the first embodiment except that it is provided in the region H on the right side in FIG. In design, for example, the operating voltage V. =
= n/L, L so that a cross state can be obtained with ○
Even if a waveguide optical switch 10 is completed in which a cross state cannot be obtained at the operating voltage VO = 0 due to manufacturing errors despite designing /Rc, Δβ, ·L/π,
Electrode members 18a to 18 provided separately for each area (■) and (■)
By arbitrarily adjusting the voltage applied to c,
It is possible to obtain a cross state. Therefore, the creation accuracy can be relaxed.

FIG. 5 is a plan view schematically showing the configuration of a second embodiment of the present invention. It should be noted that constituent components corresponding to those of the first embodiment described above are denoted by the same reference numerals.

In the second embodiment, the refractive index difference between the waveguides is controlled by adding a refractive index controlling substance to the waveguides.

At the same time, the waveguide widths of the waveguides 12 and 14, especially the waveguide widths in the area and H, are made the same. Other than this, the configuration is the same as that of the above-described first embodiment. In FIG. 5, the region 22 to which the refractive index controlling substance is added is surrounded by a dashed line and marked with a dot.

FIG. 6 is a diagram for explaining the waveguide and the region to which the refractive index controlling substance is added in the second embodiment.

As shown in FIGS. 5 and 6, in the second embodiment, the region 22 doped with the refractive index controlling substance is set to include the waveguide 12 and the substrate 20 in region (2) when viewed in plan. A refractive index controlling substance is added to the doped region 22 . Addition area 2
The depth of waveguide 2 should be greater than or equal to the depth of waveguide 2. No refractive index controlling substance is added to the waveguide 14. By adding in this manner, the refractive index difference α(I) between the waveguides in the area can be made larger than the refractive index difference α(11) between the waveguides in the area n.

Substrate 20': L I N b 03 substrate or LiT
In the case of an aO3 substrate, the refractive index controlling substance is, for example, T.
i or proton may be used.

In the illustrated example, when the doped region 22 is viewed in plan, it is set to include the waveguide] 2 of the region H and the substrate 20, but
When viewed from above, the refractive index of the doped region 22 may be set to include only the waveguide 12 and the substrate 20 of the region (2). The refractive index of the waveguide 12 may be larger or smaller than that of the waveguide 12, or the refractive indices of these 22 and ]2 may be made equal. When only the waveguide 12 in region (1) is included, the refractive index of the doped region 22 is made larger or smaller than the refractive index of the waveguide 12.

Further, in the illustrated example, the refractive index control substance was not added to the waveguide 14, but the refractive index control substance was added to both the waveguides 12 and 14 to increase the refractive index difference α(I) in the region I. may be made larger than the refractive index difference α(II) in region (2).

This invention is not limited to the above-described embodiments, and therefore, the shape, arrangement value 1, dimensions, forming method, forming material, numerical conditions, and others of each component may be changed as desired. can.

For example, in the above-described embodiment, the planar shape of the waveguide in the proximate region (2) is a linear shape, but the planar shape of the waveguide in the proximal region (2) may be curved. In the case of a curved shape, it is preferable that the first and second waveguides that are close to each other have an arcuate shape such that they move away from each other in the region H and approach each other in the region H.

Also, if formulas (1) and (2) are satisfied, d(IIr) −D(IIr)= d(III) −
It is not necessary to set D(III)=O.

(Effects of the Invention) As is clear from the above description, according to the waveguide optical switch of the present invention, the difference in refractive index between the waveguides in the central part (region area) of the area adjacent to the waveguide can be reduced by changing the refractive index difference between the waveguides. Since it is made larger than the refractive index difference between the waveguides in the region excluding the central part of the adjacent region (region ■), the propagation constant difference Δβ, 1, and the propagation constant difference Δβ can be made larger than the coupling coefficient between the first and second waveguides. As a result, the light guided through the first waveguide and the light guided through the second waveguide are relatively weakly coupled in the region and relatively strongly coupled in the region Therefore, the operating voltage V required for controlling the light output. =V+ (V+ is a half-wave voltage) can be reduced.

Roughly speaking, according to the waveguide type optical switch of the present invention, control electrodes are provided in both the area 1 and the area (2).

As the width or length of the area occupied by the control electrode along the waveguide in region (■) increases, the maximum operating voltage V0 increases.
The amount of reduction can be increased.

[Brief explanation of drawings]

FIG. 1 is a plan view schematically showing the configuration of a first embodiment of the present invention, FIG. 2 is a plan view illustrating a waveguide according to an advanced embodiment of the present invention, and FIG. FIG. 4 is a plan view schematically showing the configuration of a modified example of the embodiment of the present invention, and FIG. 5 is a diagram showing an example of the configuration of the second embodiment of the present invention. FIG. 6 is a plan view schematically showing a waveguide and a region to which a refractive index controlling substance is added according to a second embodiment of the present invention. 10... Waveguide type optical switch 12.14... Waveguide 16.18... Control electrode 2
2...Refractive index controlling substance doped region■...Central part of the region near the waveguide■...A region other than the center part of the region near the waveguide■...Region near the waveguide. 10 Waveguide type optical switch 2.14 Waveguide 2a, 14a Input end 2b, 14b Output end 16.18 Control electrode 20 Substrate Plan view of the first embodiment Figure 1 ■ Description of the waveguide of the third embodiment Figure ΔB, L/TT An example of the analysis result of the 1st Tora Example. 3. 8a + 8b 8c. Modification of the 1st Tora Example. 4. A plan view of the 2nd Example.

Claims (5)

[Claims] (1) A directional coupler type guide comprising first and second waveguides placed close to each other so as to cause light interaction in a region near the waveguide, and a control electrode provided for the waveguide. In the wave-type optical switch, the refractive index difference between the waveguides in the central part of the waveguide-proximal region is made larger than the refractive index difference between the waveguides in the region other than the central part of the waveguide-proximate region, and the control electrode is provided in both a central portion of the waveguide proximate region and a region excluding the central portion. (2) The waveguide optical switch according to claim 1, wherein the refractive index difference between the waveguides is controlled by the waveguide width. (3) The waveguide optical switch according to claim 1, wherein the refractive index difference between the waveguides is controlled by adding a refractive index controlling substance to the waveguides. (4) The waveguide type light according to any one of claims 1 to 3, wherein the refractive index difference between the waveguides in a region other than a central portion of the waveguide-proximate region is approximately zero. switch. (5) The waveguide optical switch according to any one of claims 1 to 4, wherein the control electrode is provided from a starting end to a terminal end of the waveguide adjacent region.