JPH01246529A - Waveguide type optical switch - Google Patents

Abstract

PURPOSE:To obtain the waveguide type optical switch which has no difficulty in production, has no dependency on polarized light and has excellent characteristic by setting the element lengths and inter-waveguide spacings of respective waveguides in such a manner that the coupling coeffts. between the waveguides to a TE wave and TM wave attain the values equal to each other. CONSTITUTION:The element lengths, inter-waveguide spacings, and refractive indices, etc., of the conditions for producing the waveguide are so set as to attain the cross state that the light entering form an input port 11a (12a) is outputted to an output port 12b (11b) while the voltage is not impressed to electrodes 14, 15a. An electric field is generated in a direction Y when the prescribed voltage is impressed to the electrodes 14, 15a and the refractive index is changed by a change in the electrooptic constant r22 of this time. The TE wave and TM wave sense the change in the refractive index of the reverse code at the same magnitude with respect to the waveguides 11 and 12 and, therefore, the switching action which does not depend on the polarized light is executed. The production of the waveguides is thereby facilitated and the optical switch having no dependency on the polarized light is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a waveguide optical switch that electrically controls the traveling direction of light propagating in a waveguide of an electro-optic crystal substrate.

[Conventional technology]

Waveguide type optical switches are expected to be used as constituent elements of optical exchangers, for example, but electro-optic crystal substrates such as anisotropic crystals (LiNb 03 and lithium oxate) have different refractive indexes depending on the polarization state. This characteristic is a constraint on system application. Therefore,
It has become an important issue to eliminate the dependence on the optical brightness of LiNbO3 anisotropic crystals, and various proposals regarding this have been exhausted.

Figure 2 shows an example of such a proposal, published in the collection of lecture papers from the 1986 IEICE Semiconductor and Materials Division National Conference, Volume 2.2-140 (published November 15, 1986). FIG. 1 is a block diagram schematically showing the described waveguide optical switch.

The one shown in the same figure (a) is a Z plate directional coupling type,
Two waveguides 2. are placed on the Z plate of the LiNb O3 crystal plate 1.
3 are arranged side by side, and electrodes 4.5 are formed directly above the waveguides 2 and 3, respectively. In this way, L i N b O
3 When a waveguide is formed on the Z plate of the crystal plate 1 and an electric field is applied in the Z direction, the refractive index for the TE wave and the TM wave is the electro-optic constant r and r13''ij are trigonal, respectively. r33 is about three times larger than '13. Therefore, here, we will discuss the Ti used when forming the waveguide 2.3. (Titanium) After selecting the diffusion concentration, waveguide pattern width and diffusion conditions, TE (Traverse)
Electric) wave, TM (Traverse M
The aim is to match the coupling lengths for agnetic (agnetic) waves.

In addition, the one shown in the same figure (b) is a YviZ-axis propagation directional coupling type, in which waveguides 2 and 3 are arranged in parallel on the Y plate of the LiNbO3 crystal plate 1, and each waveguide is placed directly above the waveguide 2. It forms an electrode 4.5.

In this way, by forming a waveguide on the Y plate and adopting the Z-axis transmission direction, the coupling lengths for TE waves and TM waves can be matched. Therefore, in this case, electrode 4.
The diagonal input/output ports are connected with no voltage applied to port 5 (input port 2a (3a) and output port 1-3).
b(2b)) Fabrication conditions for obtaining a cross state can be easily adjusted. Then, a bar state is obtained in which the input and output ports of the same waveguide are connected with a voltage applied to the electrodes 4.5. This is because the refractive index of the waveguide is due to the electro-optic effect r2
This occurs because the sign of the refractive index change changes depending on the direction of the applied electric field. Here, the T'E wave (polarized wave in the X direction in the figure) and the TM wave (polarized wave in the Y direction in the figure) have opposite polarities and experience refractive index changes of equal magnitude, so they do not depend on the polarization. It is possible to perform movements without any movement.

[Problem to be solved by the invention]

However, in the case of the Z-plate directional coupling type in the conventional example, it is necessary to match the coupling length for TE waves and TM waves by selecting manufacturing conditions, and this difficult manufacturing condition causes difficulties in manufacturing. There was a problem with sexuality.

On the other hand, in the case of the Y-plate Z-axis directional coupling type in the conventional example, the coupling lengths for the 1'E wave and the TM wave are the same, so the manufacturing conditions are not severe.

However, when a waveguide is formed by Ti diffusion on a Y plate, there is a problem that side diffusion occurs in which Ti diffuses not only in the thickness direction of the crystal but also along the crystal surface. In order to eliminate the influence of this side diffusion, it is necessary to diffuse Ti over the entire surface of the Y plate and then reduce the refractive index by ion exchange to form a waveguide. There was a problem that the process became complicated.

In addition, Li with the same coupling length for TE waves and TM waves
It is also possible to form waveguides on the X-plate of the NbO3 crystal plate, but in this case it is necessary to provide electrodes between the waveguides. However, the waveguide spacing is as narrow as about 5 to 8 μm, making it extremely difficult and impractical to form electrodes there.

Therefore, the present invention has been made to solve the problems of the prior art as described above, and its purpose is to:
The object of the present invention is to provide a waveguide type optical switch which is free from manufacturing difficulties and has excellent characteristics without polarization dependence.

[Means to solve the problem]

In order to achieve the above object, a waveguide type optical switch according to the present invention includes an electro-optic crystal substrate, and three waveguides arranged in parallel at predetermined intervals on the X-plate of the electro-optic crystal substrate. , a first electrode provided at a position directly above the central waveguide among the three waveguides, and a first electrode provided outwardly at a position immediately above the waveguides on both sides of the three waveguides, and second and third electrodes extending along the waveguide on both sides,
The present invention is characterized in that the element length of each of the waveguides and the interval between the waveguides are set so that the coupling coefficients between the waveguides for E waves and TM waves are approximately equal to each other.

[for y]

In the present invention having the above configuration, three waveguides of a predetermined element length are arranged side by side at a predetermined interval on an electro-optic semi-crystalline substrate, the waveguides on both sides are used for input/output, and the waveguide in the middle is used for input/output. It is responsible for the bridging function between the input and output waveguides. Thereby, the distance between both the input and output waveguides can be ensured, and the width of the first electrode provided between both the waveguides can be increased. Therefore,
The formation of the first electrode becomes easy, and the use of an X plate, which was difficult due to the narrow waveguide spacing, becomes possible.

In addition, by arranging three waveguides in parallel, crosstalk can be eliminated in two stages, similar to when two sets of waveguides that share a central waveguide are connected in series, and the coupling length can be reduced. It is possible to have a large tolerance for errors.

Furthermore, when a waveguide is formed on the X plate of the electro-optic crystal substrate, the coupling lengths for TM waves and TE waves are the same, so polarization dependence can be easily removed.

〔Example〕

The present invention will be explained below based on illustrated embodiments.

FIG. 1 is a configuration diagram showing a first embodiment of a waveguide type optical switch according to the present invention.

In the figure, 10 is Li as an electro-optic crystal substrate.
Nb 03 X plate, 11.12 and 13 are Li Nb
This is a waveguide formed by diffusing Ti on the 03-X plate 10. Of these, 11 and 12 are input/output waveguides (input/output waveguide), and 13 is a waveguide (intermediate waveguide) that serves as a bridge between the waveguides F#111 and 12.
a and llb are the input port and output port of the waveguide 11, respectively, and 12a and 12b are the waveguide 12, respectively.
are the input and output ports of

Further, 14 is a first electrode formed on the LiNb 03-X plate 10 at a position directly above the intermediate waveguide 13, and 15a
and 15b are second and third electrodes formed on the LiNb 03-X plate 10 at positions directly above the input/output waveguides 11 and 12. Note that the electrode 14 is connected to a drive power source 16, the electrode 15a is connected to a drive power source 17, and the electrode 15b is grounded.

In this embodiment, the waveguides 12 and 12 are arranged in parallel, and the waveguide 13 is arranged in parallel between the waveguides 11 and 12. And LiNb03-X board 10
At the top, an electrode 14 is placed directly above the intermediate waveguide 13, an electrode 15a is placed outside the waveguide 11, and an electrode 1 is placed outside the waveguide 12.
5b is formed such that the respective electrodes 15a, 15b and 14 extend in the same direction as the waveguides 11, 12 and 13.

In addition, the waveguide fabrication conditions are such that when no voltage is applied to the electrodes 14.15a, the element is in a cross state in which light entering from the input port 11a (12a) is output to the output port 12b (11b). Set the waveguide length, waveguide spacing, refractive index, etc.

When a predetermined voltage is applied to the electrodes 14.15a, an electric field is generated in the Y direction, and the refractive index changes due to the change in the electro-optic constant r2□ at this time. When voltage is applied only to the electrode 14 from the power supply 16, the TE wave and TM wave are transmitted through the waveguide 11.
Since a refractive index change of the same magnitude and opposite sign is felt for and 12, a switching operation that does not depend on polarization can be performed.

That is, when a voltage is applied to the electrode 14, the light input to the input port 11a (12a) is transferred to the output port 11b.
(12b) becomes a bar state.

Note that the voltage vb applied to the electrode 15a by the power source 17 is for controlling and adjusting the asymmetry of the change in refractive index to perform optimal operation.

Furthermore, in this example, by using three waveguides, it is possible to reduce the change in the Talostalk value with respect to the element length/coupling length, so in order to eliminate polarization dependence for TM waves and TE waves, The tolerance of the manufacturing conditions for matching the bond length is loose and easy to achieve.

FIG. 3 is a configuration diagram showing a second embodiment of the present invention, and FIG. 4 is a characteristic curve diagram showing crosstalk characteristics of the second embodiment.

In the figure, the same parts as in the first embodiment are given the same reference numerals, and the second embodiment differs from the first embodiment in the shape of the waveguide and the shape of the electrodes along it. .

That is, in the second embodiment, the waveguides 21 and 22 are formed in a curved shape so as to approach each other near the center thereof.

Further, the planar shape of the electrode 24, the electrode 25a, and the electrode 25b has curved sides along the waveguide. Here, the coupling coefficients K of both the waveguide FRIs 21 and 13 and the waveguides 22 and 13 are manufactured so as to have the following relationship with respect to the propagation distance ζ.

I(= Ko e x P (−(ζ −L/
2)/100) Here, Ko is the coupling coefficient when ζ=O, and L is the element length of the waveguide. Also, L
K so that a cross state is obtained when the propagation constant difference Δβ between the waveguides is 0 for Δβ = 100. -0,12.

In this case, as shown in FIG. 4, the propagation constant difference Δβ increases and the crosstalk rapidly decreases, resulting in a bar state.

FIG. 5 is a configuration diagram showing a modification of the first embodiment, and FIG. 6 is an explanatory diagram showing the distribution of the electric field strength Ez in the Z direction in FIG. Since this example has a structure similar to that of the first embodiment, the same components are given the same reference numerals and explained as follows:
In this modification, the width W of the second and third electrodes 15a and 15b
is formed to be equal to the width of the first electrode 14. By forming it in this way, the electric field strength distribution can be made symmetrical about the zero point as shown in Fig. 6, and as a result, the tolerance when the electrode mounting position deviates from the designed position can be increased.
It can have good switching characteristics. Note that this modification can also be applied to the second embodiment.

〔Effect of the invention〕

As explained above, in the present invention, by arranging three waveguides in parallel on the X plate of the electro-optic crystal substrate,
Since the interval between the input and output waveguides can be widened, electrodes can be easily manufactured.

Further, by arranging three waveguides in parallel, a large tolerance can be given to coupling length errors, which facilitates the production of the waveguides.

Furthermore, when a waveguide is formed on the X-plate of the electro-optic crystal substrate, the TE wave and the TM wave experience the same refractive index, which has the effect of providing an optical switch without polarization dependence. .

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of a waveguide optical switch according to the present invention, FIGS. 2(a) and (b) are block diagrams of a conventional waveguide optical switch, and FIG. 3 is a block diagram of a conventional waveguide optical switch. FIG. 4 is a characteristic curve diagram showing the characteristics of the second embodiment, FIG. 5 is a configuration diagram showing a modification of the first embodiment, and FIG. 6 is a diagram showing a modification of the first embodiment. FIG. 2 is an explanatory diagram showing the electric field strength distribution of FIG. 10...Nb O3-x plate (electro-optic crystal substrate)
11.12.13... Waveguide, 14... First electrode, 15a... Second electrode, 15b... Third electrode. 0 patent applicants Patent attorney, agent for Oki Electric Industry Co., Ltd. 1) Actual number 629 (a lot, λiλsa7in) Figure 3, Figure 4U!jJ

Claims (1)

[Claims] An electro-optic crystal substrate, three waveguides arranged in parallel at predetermined intervals on the X-plate of the electro-optic crystal substrate, and a central waveguide among the three waveguides. A first electrode provided directly above the waveguides, and second and third electrodes provided directly above the waveguides on both sides of the three waveguides and extending along the waveguides on both sides. electrodes, and the element length of each of the waveguides and the spacing between the waveguides are set so that coupling coefficients between the waveguides for TE waves and TM waves are approximately equal to each other. Wave type optical switch.