JPS5944024A - Optical switch - Google Patents

Abstract

PURPOSE:To obtain various light guides by providing conductive layers as counter electrodes between the intersection part of a light guide and a substrate and on the surface of the intersection part, and providing a buffer layer between the light guide and conductive layer. CONSTITUTION:At least one conductive layer 361 of the counter electrode 36 of an optical switch 31 is beltlike on said intersection path 34 and said conductive layer is provided on the bisector of the intersection angle of the lengthwise light guide of the intersection part 34 of said light guide 33. Light in single mode propagating to the optical switch travels straight because a propagation medium does not vary in refractive index if no electric field is applied to the counter electrode. An adequate electric field is applied to the counter electrode to increase the refractive index of the light propagation medium by photoelectric effect, and the total reflection condition is satisfied to allow propagation to another light guide. Therefore, the light is turned on and off corresponding to the on-off operation of a power source when observed from one light guide end. Further, the beltlike conductive layer of the counter electrode on the intersection part is made two-thirds as great as the intersection part to obtain the function of the optical switch.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical switch, and in particular to an optical IC.
The present invention provides a thin-film optical switch for use in electronic devices.

Conventional configurations and their problems Just as conducting wires are used to conduct electricity in electronic circuits, and waveguides are used in underground microwave circuits, optical signal processing systems or optical ICs use Various optical waveguides are required.

Conventional optical switches used for miniaturized optical devices or optical ICs are as shown in FIG. 1 (IL) and (b), for example.
It was formed using a ridge type (&) or diffused type waveguide. In this case, in the ridge type, a thin layer 12 made of borosilicate glass is provided on the second side of a substrate 11 made of quartz glass, for example. Also expanded i11. In the mold, for example, LiN
(On the surface of the plate 13, a waveguide 14 consisting of 11 layers of T1 is provided.

This type of optical waveguide is used not only for light transmission, but also for various optical circuits.
For example, it is used to form a switch or an optical IC that integrates these switches.

Conventionally, for example, a diffusion type optical switch as shown in FIG. 2 has been formed. In this case, for example, the surfaces 221 of the LiNb03 single crystal layer 22 intersect with each other. In the optical waveguide 23 made of a Ti diffusion layer, a buffer layer 26 is provided on the intersection 24 of the epoch waveguide 23, and the buffer layer 26 has a structure having an electrode pair 26 for selecting the path of light. Ta.

When the optical switch having the above structure is operated by applying a direct current 7E field to the electric currents 1i9j and 26 as shown in FIG.
1 passes through the optical waveguide 231 between the electrode pair and increases the refractive index of the optical waveguide 231 between the electrode pair due to the electro-optic effect. Therefore, the light waves propagating through the optical waveguide are polarized at the intersection.Also, the extinction ratio is increased by increasing the DC electric field and satisfying the total internal reflection condition, which is used as an optical switch. was.

However, in the conventional optical switch having the above structure, as shown in FIG. 2(b), the substrate 22 and the optical waveguide 23 have the same dielectric constant and are a pair of electrodes, so the lines of electric force 28 are nonuniform , and since it is dispersive, the light waves are not very uniformly deflected. Furthermore, due to low voltage drive,
The distance between the electrode pairs can be narrowed, but it is quite difficult to process a pattern of several micrometers or more using normal processing equipment, and the distance between the electric lines of force is quite difficult to process. [There is a drawback that concentration on the leading wave path between the f pole pair deteriorates and it is not possible to effectively realize low voltage driving.

Furthermore, when the optical waveguide used in the optical switch having the structure 2 is configured with a diffused optical waveguide as shown in FIG. 1(a),
The boundary of the waveguide is unclear and, for example, when a plurality of switches are two-dimensionally integrated on the same surface, there is a limit to the degree of integration.

Further, when the ridge type structure is used, there is a drawback that it is difficult to form an optical switch on the surface because of the unevenness.

Purpose of the Invention The present invention is intended for small! (1: Changing the structure of an optical switch suitable for use in an optical device or optical re).

(Structure of the Invention) The present invention provides an optical waveguide formed by covering the surface of a substrate with a film, providing intersecting grooves in the film, and embedding an optical propagation medium in the grooves. A conductive layer is provided between the intersection of the optical waveguide and the substrate and on the surface of the intersection, and serves as a counter electrode, and a buffer layer is provided between the optical waveguide and the conductive layer.

Description of examples Hereinafter, the present invention will be explained by examples using drawings.

FIG. 3 shows an optical switch according to an embodiment of the present invention.

That is, the optical switch 31 of this embodiment covers at least the surface 321 of the substrate 32 with the coating 331, and the coating 33
In the optical waveguide 33 formed by providing grooves 332 that intersect with each other in the grooves 1 and embedding an optical propagation medium 333 in the grooves 332, at least a gap 36 between the intersection 34 of the optical waveguide 33 and the substrate 32 and the intersection 332 are formed. A conductive layer 361 is provided on the surface 341 of the portion 34 as a counter electrode 36, and a buffer layer 37 is provided between the optical waveguide 33 and the conductive layer 361.

In this case, the light passes only through the light propagation medium 33; to this end, the refractive index of the light in the light propagation medium 33 is made larger than the refractive index of the light in the protective coating 331 and the surface layer of the substrate 32.

As shown in FIG. 3, the optical switch according to the embodiment of the present invention uses an optical waveguide whose surface is flat. In addition, the formation of the U-shaped groove in the optical waveguide section and the embedding of the optical propagation medium into the U-shaped groove can be performed using normal semiconductor processes, such as M-type prosthesis and photolithography processes, which are different from those seen in the conventional diffusion type. The in-plane spread of the leading liquid part is small, and it is possible to realize a sharp light wave path boundary as shown in the I'i', 1 field of U-shaped F+'♂)332 in Figure 3. .

For this reason, the fruit b11 of the present invention! The switch A' according to the example will be an inspiration for increasing the density of devices to 1% and increasing the use of ICs.

If you want to know more about this luxury, please feel free to use this tumor.1. Form 1+I<, maximum, IJ, 4 (7) l'71°i I+14 (
1'l'l Kah Rukotowo Ide L, (-Renia,
5, he invented a small, thin optical switch with a quotient of 100%.

That is, in the structure of the optical switch shown in FIG.
The medium is BaTiO3, PbTiO3 or PL.
It has been found that if it is composed of any of the ZT yarn C hybrid compounds, it is easy to form and it is also easy to create this ``insect light switch assembly f-''. In a switch, in addition to the basic condition that the refractive index of light in the optical propagation medium is larger than the refractive index of light in the surface protective layer and the substrate, for example, the refractive index of the light in the optical propagation medium is required for use as an optical switch. It is important that the propagation loss of the optical switch is small and that the substrate has a characteristic 111 on which an optical propagation medium can be formed.
In order to be applied to miniaturized or integrated optical devices,
It is necessary for the light propagation medium to exhibit, for example, a large electro-optic effect. Furthermore, the ability to form a surface protective layer and embed a light propagation medium in the U-shaped groove is also important in selecting these materials.

In the conventional 1★ technique, for example, LiN
There is a bulk single crystal of bO3, but in order to realize the structure shown in Figure 2, this kind of bulk single crystal must be polished thin and L
It is necessary to adhere to a substrate coated with a buffer layer having a lower optical refractive index than iNb0s, for example, a quartz glass layer. On the other hand, single-mode light is propagated through a high-level optical path, but this requires the thickness of the optical propagation medium to be on the order of μm, which is comparable to the wavelength of the light.

However, since it is actually impossible to polish and bond a single crystal to a μm order, normally, in the case of a single crystal substrate, such as a LiNbO3 optical propagation path, the refractive index of light is smaller than this, e.g. "M plate of LiTa03 single crystal" Second, L
The iNb05 thin layer is formed by liquid phase epitaxy at a high temperature of, for example, about 100°C.

However, such a manufacturing process cannot realize the bulky optical switch according to the embodiment of the present invention shown in FIG.

In Fig. 3, the optical waveguide 33 faces the optical waveguides (
36 (l:j), since a loss occurs, a low-loss dielectric 1 having a refractive index smaller than the refractive index of light of the optical propagation medium is used between the optical waveguide 33 and the light propagation medium.
'I, and engineer (dsi02. MgO+ α-artificial 2
05 (sapphire).

It has been confirmed that loss can be reduced by inserting a buffer layer 37 made of at least one of spinel, SrTiO3, and GaP.

The counter electrode 26 shown in FIG. 3 is made of Au, λg, Pt, C.
It is effective to constitute at least one type of uAl gold layer. In this case, the same effect can be obtained even if a transparent conductive film is used, for example.

As a result of exploring the configuration of the optical switch of the present invention and the possibility of its realization by changing the constituent materials, we found that, for example, a PbTi0s thin film is suitable as the optical propagation medium, a quartz glass substrate is suitable for the JI (plate), and a surface protective layer is suitable. It was confirmed that quartz glass is suitable for the buffer layer, and sapphire (ct-mu1zOi) is suitable for the buffer layer.In other words, this kind of constituent material can be used at relatively low temperatures by introducing thin film forming techniques such as sputtering and vacuum evaporation. It was confirmed that an optical switch having the structure according to the invention can be realized and is effective in realizing optical integrated devices such as optical ICs.

Next, the formation procedure and constituent material elements of the optical switch according to the present invention will be explained in more detail.

First, for example, quartz glass is used as a substrate, and on this, for example, A
A U film is vacuum-deposited to a thickness of about 0.2 μm, and a sapphire (α-mu 120s) film is further deposited thereon to a thickness of about 0.2 μm, for example, by high-frequency nuputtering. In this case, the temperature of the substrate during vapor deposition is about 200 to 300°C. Then, for example, a quartz glass film is placed on the sapphire film to a thickness of 0.
A thickness of about 5 μm is deposited by, for example, high-frequency sputtering, and a U-shaped groove is formed by, for example, photolithography, which is used in a normal semiconductor manufacturing process.

Next, high frequency sputtering is applied again to the U-shaped groove of P.
A bTi0s thin film is deposited to a thickness of quartz glass.

In this case, the substrate temperature is about 600'C and the chemical composition is P.
Assuming that there is no deviation from the chemical equivalence ratio of bTiO3, (
110) A transparent orientation 11ζ of PbTi05 is formed.

At the intersections of the optical waveguides thus formed, a buffer layer is formed by depositing, for example, stone-dried galanus to a thickness of about 0.2 μm, for example, by high-frequency sputtering. Furthermore, for example, a film of 0.2 μm is vacuum-deposited, and a counter electrode is further formed by conventional photolithography.

Furthermore, the present inventors have discovered that there is an optimal configuration for the counter electrode in the optical switch according to the present invention, and based on this, a high-performance optical switch has been realized. That is, the counter electrode 36 in the optical switch 31 having the configuration shown in FIG. It has been found that it is preferable to provide the above-mentioned band-shaped conductive layer on the bisector of the intersection angle. Furthermore, the width of the strip-shaped conductive layer 3610 is smaller than the width of the optical waveguide 33;
Moreover, it has been found that the longitudinal dimension of the strip-shaped conductive layer 361 on the intersection 34 of the waveguide should be equal to or greater than the length of the intersection 34 in the longitudinal direction.

Therefore, when single-mode light propagates to the optical switch, there is no change in the refractive index of the propagation medium unless an electric field is applied to the opposing electrode, and the propagating light travels straight. On the other hand, when an appropriate electric field is applied to the opposing electrode, the refractive index of the optical propagation medium increases due to the photoelectric effect, the total refraction condition is satisfied, and the propagating light undergoes total refraction and propagates to another optical waveguide. Therefore, when observed from one end of the optical waveguide, the power is turned on and off (0N-OFF).
) the light will be turned on and off in response to the As mentioned above, in order to operate as an optical switch, the width of the band-shaped conductive layer of the counter electrode must be narrower than the width of the optical waveguide. No reflection occurs and the light waves travel straight through the waveguide. However, if the longitudinal dimension of the strip-shaped conductive layer of the opposing electrodes above the intersection is less than 24 times the longitudinal dimension of the intersection, the total reflection condition cannot be satisfied at the intersection between the opposing electrodes by applying a DC electric field. However, some of the light waves travel straight through the waveguide, making it impossible to obtain a large extinction ratio. Therefore, by making the size of the band-shaped conductive layer of the opposite 1L pole on the intersection part larger than or equal to the size of the intersection part, it can function as an optical switch.

The present inventors also discovered that there is an optimal shape for the optical waveguide constituting the optical switch according to the present invention, and based on this finding, invented a high-performance optical switch.

That is, it has been found that in the optical switch having the configuration shown in FIG. 2, it is preferable that the crossing angle of the optical waveguides that intersect with each other is 40 or less. Even in PLZT, which has the largest electro-optic effect, the change in refractive index Δn due to the application of an electric field of 20 KV/cm, which causes discharge breakdown, is about 10-2, which is satisfied only when the intersection angle is about 20 or less. When the intersection angle is between 20 and 40, the reflection coefficient is large, so it can operate as an optical switch.

However, if it exceeds 40, a sufficient reflection coefficient cannot be obtained.

In addition, the present inventors have determined that there is an optimal dimension for the member of the leading waveguide constituting the optical switch according to the embodiment of the present invention, and based on this, they have invented a high-performance compact thin film switch. That is, it has been found that the width of the leading waveguide 230 is preferably from 0.5 μm to 400 μm. That is,
If the width of the leading waveguide exceeds 400 μm, even if the longitudinal dimension of the optical waveguide intersection has an intersection angle of 46*
' Since it is more than Mll-F, it is not suitable for miniaturizing optical switches.

The width of the optical waveguide is 0. Below s tt m, propagation loss due to the machining of the side surfaces of the optical waveguide cannot be ignored.

Specifically, the optical switch having the above configuration has optical waveguides that intersect at a crossing angle of 2°, and the width of this optical waveguide is 40°.
/Z m, the width of the strip-shaped conductive layer is 471 m, and the thickness of the optical waveguide is 1 μm. When an appropriate electric field is applied to this optical switch, the electric field lines 38 are uniform and concentrated between the opposing types 1@26, as shown in FIG. 3(b), so that the electric field can be effectively reduced. You can do it by using it. Moreover, since the facing type 11fjj spacing is simply dependent on the thickness of the waveguide, it has the advantage that the electrode spacing can be made closer compared to the conventional optical waveguide, and a more uniform electric field can be obtained. Therefore, the optical switch formed as described above has a wavelength of 0.632 B.
In the case of urIL light waves, 20 dB with an applied voltage of 20 V
It was confirmed that an extinction ratio of When a conventional optical switch is manufactured using a conventional T1 diffused guided waveguide, the extinction ratio is 20 dB at an applied voltage of 40 V due to the spread of electric lines of force, and in the above example, extremely low voltage driving is achieved. It can be confirmed that this has been done.

In the explanation below, PbTiOs was mentioned as an optical propagation medium, but in addition to PbTiOs, BaTiO3 and PL
ZT series thin 111 [Example work] PLZT (9/65/3.5)
, PLT, and PZT can be formed by the same manufacturing process as PbTiOs and have a large electro-optic effect, and are effective as constituent materials for the switch according to the present invention.

Furthermore, as a similar constituent material, B G is used as a light propagation medium.
O(Bi12Goo,,o), BTO(Bi12
TiO,,o) certain Id, BSO(Bi12SiO
20) f+'iNwo use il? It was confirmed that it was Neetka iTi. Furthermore, LiT is used as a light propagation medium material.
It was confirmed that a0s or LiNb05 thin film can be used.

In the above explanation, quartz glass was used as the surface coating, but the surface coating only needs to have a smaller refractive index than the light propagation medium, and the U-shaped groove can be easily formed, for example, by photoetching. , but is not limited to quartz glass. For example, in addition to borosilicate glass, soda glass, silicon nitride, etc. can also be used.

In the above explanation, sapphire (α-
As mentioned above, silica glass can be used as a buffer layer because its refractive index for light is smaller than that of the light propagation medium.
Further, it is only necessary that a thin film made of a propagation medium can be easily formed on the surface thereof, and the material is not limited to sapphire or quartz glass. For example, in addition to borosilicate glass and soda glass, silicon nitride':9 can also be used for practical purposes.

The substrate or light propagation 1j shown in the above example of just 14ζ
11. Body +: 4 years old Even in children other than 1 year old, by changing the chemical composition and its crystal power (, l, etc.), it is possible to form the tf7i light switch of the present invention.

For example, Ill-V group r-hybrid compounds can also be used as long as the basic conditions ('1) of the structure of the present invention are satisfied. For example, the optical propagation medium is GaP or GaAs. In this case, it can be used as a leading waveguide for infrared light. It is also effective. In addition, compounds of the ■-\[ group are also suitable for small use. For example, it is preferable to use Zn5e single crystal for the substrate and ZnTe for the optical propagation medium.

Also, these ■-■ group compounds, such as ZnO.

ZnS, Odd, Zn5e, ZnTe, or a compound thereof may be used as the light propagation medium. When ZnO is used as a light propagation medium (for example, a ZnO layer is deposited on borosilicate glass), a ZnO film is sputter-deposited after sputter-depositing silica glass, and then a ZnO film is sputter-deposited. When the substrate temperature is 100℃ or less, the optical
It was confirmed that an oriented film was formed and is useful for forming this type of optical waveguide.

The present inventors used a solar cell as an electric field supply source in an optical switch configured according to the present invention.

Figures 4(a) and 4(b) show the W7B configuration of this optical switch. The optical switch with this configuration is the opposite type wX36''1
It has a structure in which an insulating layer 41 is provided on the insulating layer 41, a solar cell 42 is further laminated on the insulating layer 41'', and the solar cell 42 and the facing type FM 3e are electrically coupled using a conductive layer 43.

Using an optical switch with this structure, it is possible to drive the optical switch by turning on or off light to the solar cell.Moreover, since the optical switch with the structure of the present invention is used, the extinction ratio is large, and moreover, the opposite Since solar cells are stacked on the ti-h, there is no need for an external power source, and there are advantages in that unnecessary electric fields are not applied to other parts. Since this switch does not require complicated electrical wiring, it is extremely suitable for integration, and it is possible to form an optical IC that is controlled only by light.

Furthermore, the present invention has developed a third optical wave path as a four-wave path for an optical switch.
The configuration shown in the figure was used, and FIG.

FIG. 6: It has been found that the effects of the present invention can be obtained even when using an optical waveguide having the configuration shown in FIG.

Here, the optical waveguide 61 shown in FIG. 6 has basically the same structure as the ridge type shown in FIG. 66 and the optical propagation medium do not come into contact with each other,
The structure is such that the refractive index of the buffer layer is smaller than the refractive index of the optical propagation medium.

In FIG. 6, a counter electrode 64 is provided between a substrate 62 and a light propagation medium 63, and a buffer layer 65 having a smaller refractive index for light than the light propagation medium separating the counter electrode 64 and the light propagation medium 63 is provided. An optical waveguide 61 is shown in which a loading layer 66 having a smaller optical refractive index than the wide M medium is provided on the surface 631 of the propagation medium 63, and only the optical propagation medium 632 under the loading layer 66 propagates light waves. By sequentially providing counter electrodes facing the buffer layer on the optical waveguides 51 and 62, the optical switch has the same effect as the optical switch 31 having the structure shown in FIG.

Effects of the Invention As is clear from the above explanation, the optical switch according to the present invention can eliminate the non-uniformity and dispersion of the electric field that was observed in the conventional electrode pair type, and
Fθ (The spacing can be reduced to the thickness of the optical propagation medium, making it easy to drive an optical switch with low voltage. For example, by using an optical waveguide made of a material with a large Pockels constant such as a PLZT compound, Since the refractive index difference △n can be easily obtained at low tl, an extinction ratio of 20 dB or more can be obtained.In addition, the processing accuracy of the optical switch can be achieved using the current semiconductor (4) process. Therefore, the optical switch according to the present invention is effective for miniaturization and integration of optical devices, and for integrated functional devices such as optical ICs.

[Brief explanation of drawings]

FIGS. 1A and 1B are diagrams showing an example of the structure of a thin film optical waveguide, and FIGS. 2A and 2B are a perspective view and a sectional view of the main parts, respectively, showing the structure of a conventional switch. Figure 3(a). φ) is a perspective view and a cross-sectional view of essential parts, and the fourth
Figures (a) and (b) are a perspective view and a cross-sectional view of the main parts, respectively, showing the structure of an optical switch according to an embodiment of the present invention, and Fig. 6 shows an embodiment of the structure of a leading waveguide used in the optical switch. The figure shown in FIG. 32..., V plate, 33... optical waveguide, 34... intersection, 36... between intersection and substrate, 36... ...Opposing 'ij3: l'l'
lt, 37... Buffer 1 so, 321...
・li ("Plate surface, 331...11 (protective coating), 332...Groove (0 characters 7, 1.7), 3
33... Light propagation medium, 341... Kono(''
part surface, 361... band-like] n-electrode layer (counter electrode)
, 38...City; Keino J Line. Names of the 111 people in charge: Ben Jjlj+ Toshi Nakao, male
1 person Figure 1 2 2 Figure 24 26f (α) 231 2B 354 IA 4 Figure

Claims (1)

[Scope of Claims] (1) In a guide waveguide formed by covering the surface of a substrate with a film, providing mutually intersecting grooves in the coating, and burying an optical propagation medium in the grooves, at least the guide waveguide A conductive layer is provided between the intersection of the optical waveguide and the substrate and the surface of the intersection is used as a counter electrode, and a buffer layer is provided between the optical waveguide and the conductive layer. switch. (2) The optical switch according to claim 1, wherein the optical refractive index of the optical propagation medium is greater than the optical refractive index of the coating and the buffer layer. (3) The optical propagation medium is BaTiO3, PbTiOs,
The optical switch according to claim 1, characterized in that the optical switch is made of at least one kind of PLZT-based compound. (4) Optical propagation medium is BGO (Bi12GaO20),
BT 0 (Bi12Ti02o) or Bo
2. The optical switch according to claim 1, characterized in that the optical switch is constituted by o (Bi 12sio2o ). (6) Optical propagation medium is LiTa0s or LiNb0
5. The optical switch according to claim 1, characterized in that the optical switch comprises: (6) The optical switch according to claim 1, wherein the optical propagation medium is made of GaP, GaAs, or a compound thereof. (7) Optical propagation medium is ZnO, ZnS, CdS, Zn
5e, ZnTe, or one of these compounds. 4) The optical switch according to claim 1, wherein the buffer layer is made of a material having a refractive index smaller than at least a refractive index of light of the light transport medium. (9) Opposite electrodes: MuU, Mug, Pt, Cu, AI
The optical switch according to claim 1, characterized in that the optical switch is made of at least one of the following. (10) The optical switch according to claim 1, wherein the counter electrode is made of a transparent conductive film. (11) Transparent conductive film made of SnO2, In2O3, ITO (
11. The switch according to claim 10, characterized in that the switch is made of at least one type of InzOs-5nO2. (12) At least one of the conductive electrodes 1;'J is strip-shaped on the intersection, and the bisector of the intersection angle of the light 19 wavepath in the longitudinal direction of the intersection of the leading wavepath] is strip-shaped in the second direction. An optical switch according to claim 1, characterized in that it is provided with a conductive layer. (13) The width of the strip-shaped conductive layer is smaller than the width of the leading waveguide, and the strip-shaped conductive layer 1.1゛.
1 is the length of the intersection in the longitudinal direction? Claim 1 characterized in that there are 1 or more
The optical switch described in item 2. (14) The optical switch according to claim 1, characterized in that q indicates that the intersection angle of the intersection of the leading waveguides is 4o or less. (15) The width of the leading wavepath is from 0.6 to 1 o o ttm
An optical switch according to claim 1, characterized in that: (16) An insulating layer is provided on the conductive layer provided at least on the surface of the intersection of the optical waveguide, a solar cell is laminated on this insulating layer, and the solar cell and the counter electrode are electrically coupled. An optical switch according to claim 1, characterized in that: