JP2002244168A - Method of designing optical switch and optical switch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of designing an optical switch including channels of small radii of curvature, without impairing radiation loss in manufacturing the optical switch having epitaxial or unidirectional channel optical waveguides composed of PLZT. SOLUTION: In designing the optical switch formed with the epitaxial or unidirectional channel optical waveguides, composed of Pb1-xLax(ZryTi1-y)1-x/4 O3(0<x<0.3, 0<y<1.0) on a single-crystal substrate, the optical switch is designed by determining the effective refractive index difference between the channel optical waveguides and the circumferences thereof, in such a manner that the radiation loss becomes <=1 dB according to the radii of curvature of the channels, when the channel optical waveguides include the channels of <=70 mm in the radii of curvature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for designing an optical switch which can be used for switching an optical path of an optical fiber or the like or an optical logic circuit and an optical switch, and more particularly, to an epitaxial switch composed of PLZT having an electro-optical effect. The present invention relates to an optical switch having a simple channel optical waveguide, a method of designing an optical switch including a channel having a small radius of curvature, and an optical switch obtained according to the design method.

[0002]

2. Description of the Related Art In an optical communication network, an ADM (Add-Drop Mull) which branches and inserts a signal according to an optical wavelength level between points from optical communication between points individually connecting nodes.
Optical communication that performs tiplexing) and optical communication that connects multiple nodes as they are without converting them into electrical signals are being developed. For this reason, it is important to develop various optical components such as an optical branching coupler, an optical multiplexer / demultiplexer, and an optical switch. Among them, a matrix optical device using a plurality of optical switches (or optical gates) is important. A switch is one of the most important components among various optical components, such as switching between a plurality of optical fibers according to demand, and switching to secure a detour when a network fails.

[0003] Optical switches can be classified into a bulk type and an optical waveguide type. The bulk-type optical switch switches the optical path by mechanically moving a prism, mirror, fiber, etc., and has the advantages of low wavelength dependency and relatively low loss, but has a slow switching speed and is difficult to miniaturize. Therefore, in addition to being unsuitable for matrix formation, there is a problem that the assembly and adjustment process is complicated and not suitable for mass production, so that the cost is high. On the other hand, the optical waveguide type optical switch has a high switching speed, is suitable for miniaturization and integration, and has excellent mass productivity. For this reason, regarding the optical waveguide type matrix optical switch,
Numerous considerations have been made.

Further, the optical waveguide type optical switch has a
It can be roughly divided into two types. In the first mode, a branch-type channel optical waveguide connecting an input port and an output port is switched by combining a plurality of optical switches or optical gates based on a certain principle. In the second embodiment, an optical deflector is provided between an input port and an output port to deflect light from the input port toward the output port. Of these, the optical waveguide type optical switch of the first embodiment has been studied most frequently because of its flexibility in design and low loss of light.

An optical waveguide type optical switch is generally made of LiN
A channel optical waveguide is formed in bO ₃ , a compound semiconductor, quartz, or a polymer, and an optical switch for electrically controlling the traveling direction of light at the intersection of each path, or for electrically opening and closing the traveling of light. This is provided with an optical gate for controlling the pressure.

The optical waveguide type optical switch using quartz or polymer has a core size of an optical fiber mode mode.
It has the advantage that the insertion loss is small due to the good optical coupling efficiency from the optical fiber due to the fact that it can be about the same as the field diameter. The response is slow because the direction of travel of light is switched by changing the distance. For example, T. Watanabe et al., J. Lightwave Tech. 16 (1
998) 1049. shows that the response can be as long as 6 ms. In addition, since a heating method using a heater is used, power consumption of several hundred mW may be required for only one electrode, and thus there is a problem that the application field is limited.

One of the optical waveguide type optical switches using a polymer is an optical waveguide type optical switch using an organic nonlinear optical material. Generally, an optical waveguide composed of an organic nonlinear optical material is prepared by doping an organic nonlinear molecule in a polymer, or by imparting a nonlinear structure to a side chain or a main chain of the polymer, and performing poling by applying an electric field. Fabricated as an electric field oriented polymer. For example, there is a possibility that an optical switch that can be driven at a low voltage may be configured by sandwiching an optical waveguide composed of this electric field oriented polymer between upper and lower electrodes in a sandwich shape.
186 (1995) 98.Electric field oriented polymers have problems such as temperature stability compared to oxide ferroelectric materials, and the development of practical devices has not been advanced. It is the current situation.

In the case of an optical waveguide type optical switch using a compound semiconductor or a quantum well, it is possible to increase the speed and to apply a voltage from above and below the optical waveguide core. Et al., Optics, 24 (1995) 324.
As described above, there is a problem that the insertion loss increases due to a small core size and poor optical coupling efficiency from an optical fiber, and various efforts have been made. In addition, there are problems such as deterioration of switching characteristics due to light absorption occurring simultaneously with switching by application of an electric field, and difficulty in constructing a large-scale matrix optical switch due to limited wafer size.

In the case of LiNbO ₃ , which is the most typical optical switch material and one of the oxide ferroelectrics, when a voltage is applied to the electrodes of the optical switch, the refractive index changes due to the electro-optic effect. The state of light changes at high speed, and the traveling direction of light changes depending on which state is set.
Thus, each optical switch can selectively output light from two input terminals to two output terminals. Therefore, if the traveling direction of light is appropriately set in each stage, light from an input port can be sent to a desired output port.

In an optical switch using LiNbO ₃ , a Ti diffusion type optical waveguide or a proton exchange type optical waveguide is manufactured on a single crystal wafer, but the core size can be made approximately equal to the mode field diameter of the optical fiber. Since the optical coupling efficiency from the fiber is good, it is known as a practical level optical switch with a small insertion loss.

However, since the voltage is applied by arranging a coplanar electrode on the surface of the optical waveguide,
As the distance between the electrodes increases, the electric field profile becomes less than ideal, for example, H. Okayama and M. Kawahara,
As shown in Electron. Lett. 29 (1993) 765., the drive voltage is as high as 40 volts in order to be polarization independent. In addition, an electrode length of 4 mm or more is required to prevent the driving voltage from being extremely increased. In addition, in order to fabricate an optical waveguide on a single crystal wafer by Ti diffusion or proton exchange, the effective refractive index of the channel optical waveguide cannot be made sufficiently higher than the effective refractive index around the channel optical waveguide. And it is not easy to control.
Therefore, the radius of curvature of the S-shaped channel optical waveguide is set to 50.
mm, and in the example of H. Okayama and others,
The size of the 8 × 8 matrix optical switch is as large as about 70 mm.

The switching principle of the optical paths of these optical switches is based on a method of controlling an optical path by applying an electric field to a directional coupler in which two optical waveguides are arranged close to each other, and a method of controlling input light by using a directional coupler. Mach-Zehnder switches between the output terminals by controlling the interference state at the directional coupler on the exit side by adding a phase difference with the refractive index created by the electric field between the light passing through each path and controlling the interference state at the exit side Type method, method of switching light path by controlling interference between optical modes at X intersection, refraction caused by electric field caused lateral distribution of optical mode at Y branch or asymmetric X intersection A method called digital type that controls the light path by controlling at a rate,
There is a method of switching the optical path by performing total reflection or Bragg reflection by controlling the refractive index by providing an electrode at the X intersection, and for example, the above-mentioned H. Okayama and M. Ka
Wahara, Electron. Lett. 29 (1993) 765.
Japanese Patent Publication No. 318986 and Japanese Patent Publication No. 6-5350.

[0013]

As described above, LiNb
Regardless of whether O ₃ , compound semiconductor, quartz, or polymer is used, the optical switch size,
It has not been possible to obtain an optical waveguide type matrix optical switch that simultaneously satisfies the problems of drive voltage (or drive current or power consumption), switching speed, insertion loss, and temperature stability.

In order to solve these problems, the present inventor has disclosed in Japanese Patent Application Laid-Open No. 2000-305117 or the like a PLZT: Pb _1-x La _x which is an oxide ferroelectric having an electro-optic effect.
_{(Zr y Ti 1-y)} 1-x / 4 O 3 (0 <x <0.3,0 <y <
1.0), an optical switch using an epitaxial or mono-oriented channel optical waveguide is proposed. This optical switch can be driven at high speed, has excellent temperature stability, has a low driving voltage, and has a small insertion loss. However, the size of a substrate for forming an epitaxial or unidirectional thin film optical waveguide is limited. For this reason, it is necessary to reduce the chip size of the matrix optical switch.

However, when the radius of curvature of the channel optical waveguide is reduced in order to manufacture a large-scale matrix optical switch, there is a problem that the radiation loss increases.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for manufacturing an optical switch having an epitaxial or unidirectional channel optical waveguide composed of PLZT. An object of the present invention is to provide a method of designing an optical switch for designing a compact optical switch including a channel having a small radius of curvature without impairing the optical switch. Another object of the present invention is to provide a PLZT
An optical switch provided with an epitaxial or unidirectional channel optical waveguide constituted by the above, is to provide a compact optical switch including a channel with small radiation loss and a small radius of curvature.

[0017]

In addition, the invention according to claim 1 provides a method for forming Pb on a single crystal substrate.
_1-xLa_x(Zr_yTi_1-y)_{1-x / 4}O_Three(0 <x <0.3,
0 <y <1.0)
Optical switch with unidirectional channel optical waveguide
A method for designing an optical switch, comprising:
Channel optical waveguide has a channel with a radius of curvature of 70 mm or less.
If included, the radiation loss depends on the radius of curvature of the channel.
The channel optical waveguide and its
Find the effective refractive index difference from the surroundings, based on the effective refractive index difference
And designing an optical switch.

[0018] According to a second aspect of the invention, on a single crystal _{substrate, Pb 1-x La x (} Zr y Ti 1-y) 1- x / 4 O 3 (0 <x <
0.3, 0 <y <1.0), wherein the channel optical waveguide comprises a channel having a radius of curvature of 70 mm or less; The effective refractive index difference between the channel optical waveguide and its surroundings is determined according to the radius of curvature of the channel so that the radiation loss is 1 dB or less. In this optical switch, the effective refractive index difference is preferably set to 0.1% or more.

An optical switch provided with a channel optical waveguide having a general electro-optical effect, such as LiNbO ₃ , emits light when the radius of curvature of the channel is 70 mm or less due to the fluctuation of the effective refractive index difference between the channel optical waveguide and its surroundings. Losses vary greatly.

On the other hand, in an optical switch having an epitaxial or mono-oriented channel optical waveguide composed of PLZT, a buffer layer and an optical waveguide layer are formed by epitaxially growing a PLZT thin film on a substrate, and
Since the channel optical waveguide is formed by photolithography and etching, channel optical waveguides of various shapes can be accurately formed, and the effective refractive index difference can be accurately controlled according to the radius of curvature of the channel. It has the feature of.

In the method for designing an optical switch according to the present invention, based on the above characteristics, the effective refractive index difference is determined according to the radius of curvature of the channel so that the radiation loss is 0.1 dB or less. Since the optical switch is designed to be obtained, it is possible to reliably obtain an optical switch having a negligible radiation loss. This makes it possible to obtain a compact optical switch including a channel having a small radiation loss and a small radius of curvature, and thus to constitute a large-scale matrix optical switch.

In the present invention, the term “unidirectional” is used.
Is at least crystallized by θ-2θ X-ray diffraction pattern.
The orientation is unidirectionally oriented in one direction, that is, random orientation
Plane is identified as less than 1% of the diffraction intensity of the single orientation plane
Means something. Also, Pb _1-xLa_x(Zr_yT
i_1-y)_{1-x / 4}O_Three(0 <x <0.3, 0 <y <1.0)
Is PZT, PLT, or PLZ depending on the values of x and y.
Called T.

[0023]

Embodiments of the present invention will be described below in detail with reference to the drawings. (First Embodiment) FIG. 1 is a plan view of a Y-branch 1 × 2 optical switch according to a first embodiment, and FIG.
It is sectional drawing in the Y branch part. As shown in FIG. 1, the optical switch has an input end face 14 and an output end face 15, and the input end face 14 is provided with one input port 16, and the output end face 15 is provided with two output ports 17 and 18.
Is provided. The input port 16 and the output ports 17 and 18 are joined at the Y-branch 9 by an S-shaped channel optical waveguide 10 and a linear channel optical waveguide 11.

Further, as shown in FIG. 2, in this optical switch, Nb-doped SrTiO ₃ (10
0) A wavelength of 1.55 μm is formed on a substrate 3 made of a single crystal semiconductor.
m (hereinafter referred to as the refractive index, wavelength 1.5
(Meaning the refractive index at 5 μm) is 2.395
An epitaxial or unidirectional buffer layer 4 made of ZT is laminated. A groove 20 is provided on the surface of the buffer layer 4.
Epitaxial or unidirectional optical waveguide layer 6 made of PZT having a composition with a refractive index of 2.450 on buffer layer 4
Are stacked, and the above-described channel optical waveguides 10 and 11 are stacked.
Are formed.

On the optical waveguide layer 6, upper electrodes 12 and 13 made of an Au thin film and an ITO thin film for applying a voltage to the Y branch portion 9 are provided. Upper electrodes 12, 13
Is connected to a power supply S via a drive circuit D connected to a control circuit C, and the substrate 3 serving as a lower electrode and the power supply S are grounded. In the following embodiments, the illustration of the drive circuit M, the control circuit C, and the power supply S is omitted.

In the present embodiment, the opening angle of the Y branch portion 9 is 0.2 degrees, the radius of curvature of the S-shaped channel optical waveguide 10 is 14 mm, and the interval between the linear channel optical waveguides 11 is 1.
25 μm. The depth of each channel is 0.40
μm, and the width of each channel is 5.0 μm.

Next, an effective refractive index difference Δn between the channel optical waveguide and its periphery, which can reduce the radiation loss to a negligible level, in the optical switch made of the above-mentioned material is determined. FIG. 3 shows the relationship between the effective refractive index difference Δn and the radius of curvature of the S-shaped channel optical waveguide (shown by a solid line) when the radiation loss is 1 dB, and the radiation loss is 10 dB in the above optical switch. The relationship between the effective refractive index difference Δn and the radius of curvature of the S-shaped channel optical waveguide (shown by a dotted line) is shown.

As can be seen from the figure, when the radius of curvature of the S-shaped channel optical waveguide is 70 mm or less, the effective refractive index difference Δ
The radiation loss changes greatly due to the change in n, and the radiation loss can be reduced to a negligible level by slightly increasing the effective refractive index difference Δn. For example, if the radius of curvature of the S-shaped channel optical waveguide is 70 mm, the radiation loss is 1.0 dB when the effective refractive index difference is 0.10%, but the radiation loss is 0.1 dB when the effective refractive index difference is 0.12%. And to a negligible level.

In the optical switch of the present embodiment, since the radius of curvature of the S-shaped channel optical waveguide is 14 mm, the effective refractive index difference between the channel optical waveguide and its surroundings is 0.2.
%, The radiation loss can be reduced to 0.1 dB or less.

Here, a method of calculating the effective refractive index difference Δn between the channel optical waveguide and its surrounding will be described. First, using the refractive index of the buffer layer, the refractive index of the upper layer of the optical waveguide layer (the air layer in the present embodiment), and the thickness and refractive index of the slab optical waveguide surrounding the channel optical waveguide, The effective refractive index of the part is calculated from the mode dispersion equation.
Next, using the refractive index of the buffer layer, the refractive index of the upper layer of the optical waveguide layer, the thickness and the refractive index of the channel optical waveguide, the effective refractive index of the channel optical waveguide is calculated from the mode dispersion equation. Then, the difference between the two effective refractive indices is divided by the effective refractive index of the slab optical waveguide to calculate the effective refractive index difference Δn. The effective refractive index difference Δn may be calculated from the effective refractive indexes of the slab portion and the channel optical waveguide measured by the prism coupling method.

Accordingly, if the effective refractive index difference between the channel optical waveguide and its surroundings can be determined so that the radiation loss can be reduced to a negligible level, the refractive index of the buffer layer, the refractive index of the upper layer of the optical waveguide layer, The thickness and the refractive index of the slab portion surrounding the channel optical waveguide, and any of the thickness and the refractive index of the channel optical waveguide are appropriately changed,
The effective refractive index difference can be set to that value.

As described above, in this embodiment, the PLZT
In an optical switch with an epitaxial or unidirectional channel optical waveguide composed of
Since a buffer layer and an optical waveguide layer are formed by epitaxial growth of a ZT thin film, and a channel optical waveguide is formed by photolithography and etching, channel optical waveguides of various shapes can be accurately formed, and the curvature radius of the channel can be reduced. Accordingly, based on the characteristic that the effective refractive index difference can be accurately controlled, the effective refractive index difference Δn is adjusted according to the radius of curvature of the S-shaped channel optical waveguide so that the radiation loss becomes 0.1 dB or less. ,
Since the optical switch is designed so as to obtain this effective refractive index difference, it is possible to obtain an optical switch whose radiation loss is negligible.

Further, the obtained optical switch has an epitaxial or unidirectional channel optical waveguide made of PLZT having a high efficiency electro-optical effect, and therefore, the driving voltage is lower than that of the conventional optical switch. Low, fast switching speed, excellent temperature stability, and low insertion loss.

Next, an example of the optical switch according to this embodiment will be described.

First, anhydrous lead acetate Pb (CH ₃ COO) ₂ ,
Zirconium isopropoxide _{Zr (O-i-C 3} H 7)
₄ and titanium isopropoxide Ti (O-i-C
_{Using 3} H ₇ ) ₄ as a starting material, a predetermined amount is dissolved in 2-methoxyethanol according to the composition of the buffer layer, and distillation and reflux are performed. Finally, a precursor for a buffer layer having a Pb concentration of 0.6 M is obtained. A solution was obtained.

This buffer layer precursor solution is washed, etched and dried in advance with Nb-doped SrTiO.
₃ (100) was spin coated onto a single crystal substrate, O ₂
The temperature was raised in the atmosphere and kept at 350 ° C.
After holding at ℃, it was cooled. By repeating this, solid-phase epitaxial growth was performed, and a PZT epitaxial thin film having a composition with a refractive index of 2.395 was formed with a thickness of 2.6 μm.

Next, the above-mentioned buffer layer precursor solution was spin-coated on the PZT epitaxial thin film, heated in an O ₂ atmosphere and kept at 350 ° C.
Cool. By repeating this, a PZT amorphous thin film was formed with a thickness of 0.4 μm. Next, the photoresist is spin-coated, exposed after pre-baking,
By performing development, a resist pattern having an opening corresponding to the channel optical waveguide was formed. After the post-baking, a part of the PZT amorphous thin film was removed by wet etching using an aqueous HCl solution.

As described above, the PZT amorphous thin film is processed, and the Y branch portion having an opening angle of 0.2 degrees, the S-shaped channel optical waveguide having a curvature radius of 14 mm, and the interval 125
A concave groove (trench) having a depth of 0.4 μm and a width of 5.0 μm corresponding to each of the linear channel optical waveguides of μm was formed. Next, after removing the resist with a remover, the processed PZT amorphous thin film is subjected to solid phase epitaxial growth to be integrated with the previously formed PZT epitaxial thin film, and a PZT epitaxial buffer having a concave groove formed on the surface. A layer was formed.

Further, the surface of the PZT epitaxial buffer layer was spin-coated with a precursor solution for the optical waveguide layer prepared in the same manner as the precursor solution for the buffer layer.
₂ Raise the temperature in the atmosphere and hold at 350 ° C.
After holding at 0 ° C., it was cooled. By repeating this, solid phase epitaxial growth is performed and the refractive index becomes 2.450.
PZT epitaxial optical waveguide layer having a composition of 2.2 μm
It formed with the film thickness of.

By the above process, a channel optical waveguide having an effective refractive index difference of 0.2% from the surroundings was formed.

On the PZT epitaxial optical waveguide layer at the Y branch portion, a 200 nm-thick A
1 and a 200 nm-thick laminated thin film made of ITO, and then a lift-off method is used to form an upper electrode having a width of 5.0 μm and a length of 3.0 mm. An optical switch was manufactured. The incident end face and the outgoing end face were formed by polishing.

The crystallographic relationship of the stacked layers is as follows: a single-oriented PZT (100) optical waveguide layer // PZT (100) buffer layer // Nb-SrTiO ₃ (100) substrate;
In-plane orientation PZT [001] optical waveguide layer // PZT [00
1] Buffer layer // Nb-SrTiO ₃ [001] substrate.

The electro-optic coefficient r = 50 of the PZT optical waveguide layer
pm / V was obtained. Relative dielectric constant of PZT buffer layer 60
The effective voltage of the PZT optical waveguide layer obtained from 0 and the relative dielectric constant 900 of the PZT optical waveguide layer is 47%, and it is possible to apply a voltage with high efficiency despite the interposition of the buffer layer. .

When a single mode optical fiber is disposed on the input end face and the output end face of this optical switch, and a laser beam having a wavelength of 1.55 μm is introduced from the disposed optical fiber to the input port of the input end face, 3 dB ( (50%) and split into two channels with equal intensity to the output port of the output end face and the two optical fibers.
On the other hand, the lower Nb-doped SrTiO ₃ substrate electrode
When a voltage of 5 V is applied to one of the two upper electrodes, the refractive index of the optical waveguide on the side to which the voltage is applied decreases, so that the laser light introduced from the incident end face is At the Y branch, a channel to which no voltage was applied and the refractive index did not decrease was selected, and the optical fiber path was switched by the digital switch.

Further, the 1 × 2 optical switch of this embodiment has a radiation loss of 0.1 dB or less, despite the fact that the total length is reduced to about 10 mm including an S-shaped channel optical waveguide having a curvature radius of 14 mm. In comparison with the case where a 1 × 2 optical switch is formed by the conventional method, the driving voltage is
The switching frequency was 50 MHz or more, the crosstalk was 20 dB or less, the insertion loss was 3 dB or less, and the polarization was independent and the characteristics were good.

(Second Embodiment) FIG. 4 is a plan view of a 1 × 8 optical switch according to a second embodiment, and FIG.
Is an enlarged view of the branch portion. As shown in FIG. 4, the 1 × 8 optical switch is a single mode digital 1 × 8 optical switch in which the 1 × 2 optical switches according to the first embodiment are combined in three stages. The laminated structure and the laminated material are the same as those of the optical switch according to the first embodiment. Further, since the radius of curvature of the S-shaped channel optical waveguide is also 14 mm, which is the same as that of the optical switch of the first embodiment, the effective refractive index difference between the channel optical waveguide and its surroundings should be 0.2% or more. The radiation loss is 0.1d
B or less.

As described above, in the present embodiment, as in the first embodiment, based on the above-described characteristics of the optical switch having the epitaxial or unidirectional channel optical waveguide formed of PLZT, The effective refractive index difference Δn is determined according to the radius of curvature of the S-shaped channel optical waveguide so that the loss is 0.1 dB or less, and the optical switch is designed so as to obtain the effective refractive index difference. Can obtain an optical switch of a negligible level.

Further, the obtained optical switch has an epitaxial or unidirectional channel optical waveguide composed of PLZT having a high efficiency electro-optic effect, so that the driving voltage is lower than that of the conventional optical switch. Low, fast switching speed, excellent temperature stability, and low insertion loss.

Next, an example of the optical switch according to the second embodiment will be described.

[0050] The precursor solution for the buffer layer is adjusted according to the composition of the buffer layer, cleaning, etching, drying by spin coating to a previously went Nb-doped SrTiO ₃ (100) single crystal substrate, in an O ₂ atmosphere Increase the temperature to 350
After it was kept at 750 ° C., it was cooled. By repeating this, solid-phase epitaxial growth was performed, and a PZT epitaxial thin film having a composition with a refractive index of 2.395 was formed with a thickness of 2.6 μm.

Next, the precursor solution for the buffer layer was spin-coated on the PZT epitaxial thin film, heated in an O ₂ atmosphere and kept at 350 ° C.
Cool. By repeating this, a PZT amorphous thin film was formed with a thickness of 0.4 μm. Next, the photoresist is spin-coated, exposed after pre-baking,
By performing development, a resist pattern having an opening corresponding to the channel optical waveguide was formed. After the post-baking, a part of the PZT amorphous thin film was removed by wet etching using an aqueous HCl solution.

As described above, the PZT amorphous thin film is processed, and a Y branch portion having an opening angle of 0.2 degree, an S-shaped channel optical waveguide having a curvature radius of 14 mm, and a spacing of 250 mm are formed.
A concave groove having a depth of 0.4 μm and a width of 5.0 μm was formed corresponding to each of the linear channel optical waveguides of μm. Next, after removing the resist with a remover, the processed PZT amorphous thin film is subjected to solid phase epitaxial growth to be integrated with the previously formed PZT epitaxial thin film, and a PZT epitaxial buffer having a concave groove formed on the surface. A layer was formed.

Further, the surface of the PZT epitaxial buffer layer was spin-coated with the precursor solution for the optical waveguide layer prepared in the same manner as the precursor solution for the buffer layer.
₂ Raise the temperature in the atmosphere and hold at 350 ° C.
After holding at 0 ° C., it was cooled. By repeating this, solid phase epitaxial growth is performed and the refractive index becomes 2.450.
PZT epitaxial optical waveguide layer having a composition of 2.2 μm
It formed with the film thickness of.

Through the above process, a channel optical waveguide having an effective refractive index difference of 0.2% from the surroundings was formed.

On the PZT epitaxial optical waveguide layer at the Y branch portion, a 200 nm-thick A
After forming a laminated thin film made of l and ITO having a thickness of 200 nm, an upper electrode having a width of 5.0 μm and a length of 3.0 mm is formed for each 1 × 2 optical switch by a lift-off method. Single with three 1 × 2 optical switches
A digital 1 × 8 optical switch of mode was fabricated.

One single mode optical fiber is arranged on the input end face of this optical switch, and 250 μm is set on the output end face.
Eight single mode optical fibers were arranged at m intervals. 1.55μ wavelength from the optical fiber placed on the incident end face
When m laser light is introduced into the input port of the 1 × 8 optical switch according to the present embodiment, each Y branch is branched into two channels at an intensity of 3 dB (50%), and eight of the output ports on the output end face are provided. With equal intensity.

On the other hand, for each 1 × 2 optical switch provided in three stages, the lower Nb-doped SrTiO ₃ substrate electrode and one of the two upper electrodes provided in each 1 × 2 optical switch were used. When a voltage of 5 V is applied during this time, the refractive index of the optical waveguide on the side to which the voltage is applied decreases, so that the laser light introduced from the incident end face is applied with a voltage by each 1 × 2 optical switch. A channel which is not selected, that is, has no refractive index reduction, is selected, and the optical fiber path is switched in the digital type switch.

Further, the 1 × 8 optical switch of this embodiment has a radiation loss of 0.1 dB or less, despite its miniaturization of about 24 mm in length including an S-shaped channel optical waveguide having a radius of curvature of 14 mm. In comparison with the case where a 1 × 8 optical switch is configured by the conventional method, the driving voltage is
The switching frequency was 50 MHz or more, the crosstalk was 20 dB or less, the insertion loss was 4 dB or less, and the polarization was independent and the characteristics were good.

(Third Embodiment) As shown in FIG. 6, the optical switch according to the third embodiment is a Y-branch type optical switch having the same principle as the optical switch according to the first embodiment. This is a digital type completely non-blocking type 8 × 8 optical switch in which 112 × 2 optical switches are arranged in a tree shape. The laminated structure and laminated material of this optical switch are the same as those of the optical switch of the first embodiment, but the depth of each channel is 0.50 μm.
The radius of curvature of the m, S-shaped channel optical waveguide is 9 mm.

Similarly to the first embodiment, based on the relationship shown in FIG. 3, the effective refractive index difference Δn between the channel optical waveguide capable of reducing the radiation loss to a negligible level and the periphery thereof is obtained. Can be. In the optical switch according to the present embodiment, since the radius of curvature of the S-shaped channel optical waveguide is 9 mm, the radiation loss is reduced by setting the effective refractive index difference between the channel optical waveguide and its periphery to 0.26% or more. It can be 0.1 dB or less.

As described above, in the present embodiment, as in the first embodiment, based on the above-described features of the optical switch having the epitaxial or unidirectional channel optical waveguide constituted by PLZT, The effective refractive index difference Δn is determined according to the radius of curvature of the S-shaped channel optical waveguide so that the loss is 0.1 dB or less, and the optical switch is designed so as to obtain the effective refractive index difference. Can obtain an optical switch of a negligible level.

Further, the obtained optical switch has an epitaxial or unidirectional channel optical waveguide composed of PLZT having a high efficiency electro-optical effect, so that the driving voltage is lower than that of the conventional optical switch. Low, fast switching speed, excellent temperature stability, and low insertion loss.

Next, an example of the optical switch according to the third embodiment will be described.

The buffer layer precursor solution adjusted in accordance with the composition of the buffer layer is spin-coated on an Nb-doped SrTiO ₃ (100) single crystal substrate which has been washed, etched and dried in advance, and is subjected to an O ₂ atmosphere. Increase the temperature to 350
After it was kept at 750 ° C., it was cooled. By repeating this, solid-phase epitaxial growth was performed, and a PZT epitaxial thin film having a composition with a refractive index of 2.395 was formed with a thickness of 2.6 μm.

Next, the buffer layer precursor solution was spin-coated on the PZT epitaxial thin film, and the temperature was raised in an O ₂ atmosphere and maintained at 350 ° C.
Cool. By repeating this, a PZT amorphous thin film was formed with a thickness of 0.5 μm. Next, the photoresist is spin-coated, exposed after pre-baking,
By performing development, a resist pattern having an opening corresponding to the channel optical waveguide was formed. After the post-baking, a part of the PZT amorphous thin film was removed by wet etching using an aqueous HCl solution.

As described above, the PZT amorphous thin film is processed to correspond to each of the Y-branch portion having an opening angle of 0.2 °, the S-shaped channel optical waveguide having a radius of curvature of 9 mm, and the linear channel optical waveguide. And a concave groove having a depth of 0.5 μm and a width of 5.0 μm. Next, after the resist is removed by a remover, the processed PZT amorphous thin film is subjected to solid phase epitaxial growth to be integrated with the previously formed PZT epitaxial thin film, and a PZT epitaxial buffer having a concave groove formed on the surface. A layer was formed.

Further, the surface of the PZT epitaxial buffer layer was spin-coated with the optical waveguide layer precursor solution prepared in the same manner as the buffer layer precursor solution, and
₂ Raise the temperature in the atmosphere and hold at 350 ° C.
After holding at 0 ° C., it was cooled. By repeating this, solid phase epitaxial growth is performed and the refractive index becomes 2.450.
PZT epitaxial optical waveguide layer having a composition of 2.2 μm
It formed with the film thickness of.

Through the above process, a channel optical waveguide having an effective refractive index difference of 0.3% from the surroundings was formed.

On the PZT epitaxial optical waveguide layer at the Y branch portion, a 200 nm-thick A
After forming a laminated thin film made of l and 200 nm thick ITO, an upper electrode having a width of 5.0 μm and a length of 2.5 mm is formed for each 1 × 2 optical switch by a lift-off method. Single with six 1 × 2 optical switches
A mode digital 8 × 8 optical switch was fabricated.

Eight single mode optical fibers were arranged on the incident end face of this optical switch, and eight single mode optical fibers were also arranged on the emission end face. When a laser beam having a wavelength of 1.55 μm is introduced from the optical fiber disposed on the incident end face to the incident port of the 8 × 8 optical switch according to the present embodiment, each Y-branch unit has two channels with an intensity of 3 dB (50%). The light is branched and distributed with equal intensity to the eight optical fibers at the exit port on the exit end face.

On the other hand, for each 1 × 2 optical switch provided in six stages, the lower Nb-doped SrTiO ₃ substrate electrode and one of the two upper electrodes provided in each 1 × 2 optical switch were When a voltage of 5 V is applied during this time, the refractive index of the optical waveguide on the side to which the voltage is applied decreases, so that the laser light introduced from the incident end face is applied with a voltage by each 1 × 2 optical switch. A channel which is not selected, that is, has no refractive index reduction, is selected, and the optical fiber path is switched in the digital type switch.

The 8 × 8 optical switch according to the present embodiment has a radiation loss of 0.1 dB or less, despite its miniaturization of about 38 mm in length including an S-shaped channel optical waveguide having a curvature radius of 9 mm. In comparison with the case where an 8 × 8 optical switch is configured by a conventional method, the driving voltage is 5 V, which is 1
The switching frequency was 50 MHz or more, the crosstalk was 40 dB or less, the insertion loss was 5 dB or less, and the polarization was independent and the characteristics were good.

(Fourth Embodiment) An optical switch according to a fourth embodiment is a tree-shaped 1 × 2 Y-branch optical switch having the same principle as the optical switch according to the first embodiment. An array of digital, completely non-occluding 4 × 4 optical switches.

The laminated structure of this optical switch is the same as that of the optical switch of the first embodiment, except that the depth of each channel is 0.15 μm and the radius of curvature of the S-shaped channel optical waveguide is 70 mm. I have. Also, this optical switch
An epitaxial or unidirectional buffer layer made of PLZT having a composition with a refractive index of 2.250, and a buffer layer with a refractive index of 2.
And an optical waveguide layer composed of PLZT having a composition of 450 and having an arbitral or unidirectional orientation.

Next, in the optical switch made of the above material, the effective refractive index difference Δ when the radiation loss is 1 dB
The relationship between the radii of curvature of the n- and S-shaped channel optical waveguides is examined, and the effective refractive index between the channel optical waveguide and the periphery thereof can be reduced to a negligible level in the optical switch made of the above-mentioned material. When the difference Δn is obtained, in the optical switch according to the present embodiment, the radius of curvature of the S-shaped channel optical waveguide is 70 mm, and the effective refractive index difference between the channel optical waveguide and its periphery is set to 0.1% or more. It was found that the radiation loss can be reduced to 0.1 dB or less.

As described above, in the present embodiment, as in the first embodiment, based on the above-described characteristics of the optical switch having the epitaxial or unidirectional channel optical waveguide constituted by PLZT, The effective refractive index difference Δn is determined according to the radius of curvature of the S-shaped channel optical waveguide so that the loss is 0.1 dB or less, and the optical switch is designed so as to obtain the effective refractive index difference. Can obtain an optical switch of a negligible level.

Further, since the obtained optical switch has an epitaxial or unidirectional channel optical waveguide composed of PLZT having a high efficiency electro-optical effect, the driving voltage is lower than that of the conventional optical switch. Low, fast switching speed, excellent temperature stability, and low insertion loss.

Next, an example of the optical switch according to the present embodiment will be described.

The buffer layer precursor solution adjusted according to the composition of the buffer layer is spin-coated on an Nb-doped SrTiO ₃ (100) single crystal substrate which has been washed, etched and dried in advance, and is then dried in an O ₂ atmosphere. Increase the temperature to 350
After it was kept at 750 ° C., it was cooled. By repeating this, solid phase epitaxial growth was performed, and a PLZT epitaxial thin film having a composition with a refractive index of 2.250 was formed with a thickness of 2.0 μm.

Next, the buffer layer precursor solution was added to P
Spin coating on LZT epitaxial thin film,
The temperature was raised in an O ₂ atmosphere, maintained at 350 ° C., and then cooled. By repeating this, a PZT amorphous thin film was formed with a thickness of 0.15 μm. Next, a photoresist was spin-coated, prebaked, exposed, and developed to form a resist pattern having openings corresponding to the channel optical waveguides. After the post-baking, a part of the PZT amorphous thin film was removed by wet etching using an aqueous HCl solution.

As described above, the PZT amorphous thin film is processed to correspond to each of the Y-branch portion having an opening angle of 0.2 °, the S-shaped channel optical waveguide having a radius of curvature of 70 mm, and the linear channel optical waveguide. , Depth 0.15 μm,
A concave groove having a width of 5.0 μm was formed. Next, after the resist is removed by a remover, the processed PZT amorphous thin film is subjected to solid-phase epitaxial growth to be integrated with the previously formed PZT epitaxial thin film, and a PZT epitaxial thin film having a concave groove formed on the surface.
A buffer layer was formed.

Further, a PZT optical waveguide layer precursor solution prepared in the same manner as the PZT buffer layer precursor solution was spin-coated on the surface of the PZT epitaxial buffer layer, and the temperature was raised to 350 ° C. in an O ₂ atmosphere. After it was kept at 750 ° C., it was cooled. By repeating this, solid-phase epitaxial growth was performed to form a PLZT epitaxial optical waveguide layer having a composition with a refractive index of 2.450 with a film thickness of 2.2 μm.

By the above process, a channel optical waveguide having an effective refractive index difference of 0.1% from the surroundings was formed.

On the PZT epitaxial optical waveguide layer at the Y branch portion, a 200 nm-thick A was formed by sputtering.
1 and a 200 nm-thick laminated thin film made of ITO, and then 5 μm in width and 6.0 in length by a lift-off method.
An upper electrode having a shape of mm was formed for each 1 × 2 optical switch, thereby producing a single mode digital 4 × 4 optical switch having four 1 × 2 optical switches.

Four single mode optical fibers were arranged on the incident end face of this optical switch, and four single mode optical fibers were also arranged on the exit end face. When a laser beam having a wavelength of 1.55 μm is introduced from the optical fiber disposed on the incident end face to the incident port on the incident end face, 3 dB (5
(0%) and split into two channels with equal intensity to the output port of the output end face and the two optical fibers. On the other hand, between the lower Nb-doped SrTiO ₃ substrate electrode and one of the two upper electrodes, 5
When a voltage of V is applied, the refractive index of the optical waveguide on the side to which the voltage is applied decreases, so that the laser light introduced from the incident end face does not receive a voltage at the Y-branch and the refractive index Was selected, and the optical fiber path was switched in the digital switch.

The 4 × 4 optical switch according to the present embodiment has a total length of about 44 mm including an S-shaped channel optical waveguide having a curvature radius of 70 mm. The loss is less than 0.1 dB, the driving voltage is 5 V, which is about one tenth of the conventional one, the switching frequency is 20 MHz or more, and the crosstalk is 40 d compared to the case where a 4 × 4 optical switch is formed by the conventional method.
B, the insertion loss was 5 dB or less, and the polarization was independent and the characteristics were good.

Although the optical switch design method of the present invention and the specific embodiments of the optical switch manufactured based on the design method have been described above, the present invention is not limited to these embodiments. As described, it may be manufactured using another material, or may be manufactured using another thin film forming method. Further, the structure thereof may be appropriately changed without impairing the effects of the present invention.

The substrate that can be used as the lower electrode in the present invention is a conductive or semiconductive single crystal substrate,
Alternatively, it is a substrate provided with an epitaxial or unidirectional conductive or semiconductive thin film on the surface.

As the conductive or semiconductive substrate material, SrTiO ₃ doped with Nb or La, ZnO doped with Al, In ₂ O ₃ , RuO ₂ , BaPbO ₃ ,
SrRuO ₃ , YBa ₂ Cu ₃ O _7-x , SrVO ₃ , LaN
iO ₃ , La _0.5 Sr _0.5 CoO ₃ , ZnGa ₂ O ₄ , CdG
_{a 2 O 4, CdGa 2 O} 4, Mg 2 TiO 4, oxides such as _{MgTi 2 O 4, Si, Ge} , elemental semiconductors such as diamond, AlAs, AlSb, AlP, GaAs , GaS
b, InP, InAs, InSb, AlGaP, All
nP, AlGaAs, AlInAs, AlAsSb, G
aInAs, GaInSb, GaAsSb, InAsS
III-V compound semiconductors such as b, ZnS, ZnS
e, ZnTe, CaSe, Cdte, HgSe, HgT
Group II-VI compound semiconductors such as e, CdS, Pd, P
Metals such as t, Al, Au, and Ag can be used. Among them, it is preferable to use an oxide as the substrate material because it is advantageous for the film quality of the optical waveguide layer made of an oxide ferroelectric disposed on the top.

The conductive or semiconductive single-crystal substrate or the conductive or semiconductive epitaxial or single-oriented thin film has a crystal structure of an oxide ferroelectric constituting an optical waveguide layer, and Preferably, it is chosen according to the carrier mobility required by the deflection speed, switching speed or modulation speed.

The relative dielectric constant of the ferroelectric material is several tens to several thousands. However, in order for an optical waveguide element made of such a ferroelectric material to exhibit a response of 1 kHz or more, the resistivity of the substrate is required. Is preferably 10 ⁴ Ω · cm or less, and from the viewpoint of RC time constant and voltage drop, 10 ² Ω · c
m is more preferable.

When an epitaxial or unidirectionally conductive or semiconductive thin film is provided on the substrate surface, materials that can be used as the substrate include SrTiO ₃ ,
BaTiO ₃ , BaZrO ₃ , LaAlO ₃ , ZrO ₂ , Y
₂ O ₃ 8% —ZrO ₂ , MgO, MgAl ₂ O ₄ , LiNb
Oxides such as O ₃ , LiTaO ₃ , Al ₂ O ₃ , ZnO, S
Simple semiconductors such as i, Ge, and diamond, AlAs,
AlSb, AlP, GaAs, GaSb, InP, In
As, InSb, AlGaP, AlLnP, AlGaAs
s, AlInAs, AlAsSb, GaInAs, Ga
III-V such as InSb, GaAsSb, InAsSb, etc.
Group compound semiconductor, ZnS, ZnSe, ZnTe, C
aSe, Cdte, HgSe, HgTe, CdS, etc.
A II-VI group compound semiconductor or the like can be used.
Even if a conductive or semiconductive thin film is provided on the surface,
It is preferable to use an oxide as the substrate material because it is advantageous for the film quality of the optical waveguide layer made of an oxide ferroelectric disposed on the top.

When a buffer layer exists between the conductive substrate and the optical waveguide layer, the voltage applied between the upper and lower electrodes is distributed according to the respective capacities of the optical waveguide layer and the buffer layer, and the effective voltage that can be applied to the optical waveguide layer is descend. However, a high effective voltage can be applied to the optical waveguide layer by using a buffer layer having a constant thickness and a high dielectric constant. Therefore, the buffer layer has a refractive index smaller than that of the optical waveguide layer material, and the ratio of the relative dielectric constant of the buffer layer to the relative dielectric constant of the optical waveguide layer is 0.002 or more, preferably 0.006 or more. It is preferable to select an oxide in which the relative dielectric constant of the buffer layer itself is 8 or more.

Further, the material of the buffer layer is made of an epitaxy between the conductive substrate material and the optical waveguide material in order to reduce the light propagation loss caused by the scattering due to the surface of the optical waveguide or the grain boundaries in the optical waveguide to a practical level. It is necessary to be able to hold Conditions that can maintain this epitaxy relationship include:
It is desirable that the buffer layer material is similar to the crystal structure of the conductive substrate material and the optical waveguide layer material and the difference in lattice constant is 10% or less. However, if the epitaxy relationship can be maintained, this relationship does not necessarily have to be followed.

The buffer layer material used in the present invention includes:
Specifically, in an ABO ₃ type perovskite oxide, a tetragonal system, an orthorhombic system or a pseudo-cubic system, for example,
SrTiO ₃ , BaTiO ₃ , (Sr _1-x Ba _x ) TiO ₃
(0 <x <1.0), PbTiO ₃ , Pb _1-x La _x (Z
_{r y Ti 1-y) 1} -x / 4 O 3 (0 <x <0.3,0 <y <1.
0, PZT by the values of x and y, PLT, referred to as _{PLZT), Pb (Mg 1/} 3 Nb 2/3) O 3, KNbO 3 , etc., representative example, such as LiNbO _3, LiTaO ₃ as a hexagonal Sr _x Ba _{1 -x} Nb ₂ O ₆ , Pb _x Ba _{1 -x} Nb ₂ O _{6 and the} like in addition to ferroelectrics and tungsten bronze type oxides, and Bi ₄ Ti ₃ O ₁₂ and Pb ₂ KNb
₅ O ₁₅ , K ₃ Li ₂ Nb ₅ O ₁₅ , ZnO, and substituted derivatives of the above compounds.

The optical waveguide layer has a high electro-optic coefficient.
And an oxide having a larger refractive index than the buffer layer material
A ferroelectric material is selected. Optical waveguide layer used in the present invention
As the material, specifically, ABO_ThreeVintage perovskite
In the type, as tetragonal, orthorhombic or pseudo-cubic, for example, B
aTiO_Three, PbTiO_Three, Pb_1-xLa_x(Zr_yT
i_1-y)_{1-x / 4}O_Three(PZT, PL depending on the values of x and y
T, PLZT), Pb (Mg_1/3Nb_2/3) O_Three, KNb
O_ThreeFor example, as a hexagonal system, for example, LiNbO_Three, LiTa
O _ThreeFerroelectric, tungsten bronze
In the type Sr_xBa_1-xNb_TwoO ₆, Pb_xBa_1-xNb_TwoO₆What
In addition to this, Bi_FourTi_ThreeO₁₂, Pb_TwoKNb _FiveO
₁₅, K_ThreeLi_TwoNb_FiveO₁₅And further substituted derivatives and the like
Selected from

The ratio of the thickness of the buffer layer to the thickness of the optical waveguide layer is preferably at least 0.1 in order to reduce the propagation loss to 1 dB / cm or less.
_When the operation in the single mode of ₀ is assumed,
More preferably, it is 5 or more. At the same time, the thickness of the buffer layer is preferably 10 nm or more. The thickness of the optical waveguide layer is usually set between 0.1 μm and 10 μm, but this can be appropriately selected depending on the purpose.

A cladding layer for reducing propagation loss due to light absorption of the upper electrode can be provided on the surface of the optical waveguide layer. For example, as shown in FIG. 7, on a single crystal substrate 3 serving as a lower electrode, a PZT
An epitaxial or mono-oriented buffer layer 4 of PZT, an epitaxial or mono-oriented optical waveguide layer 6 of PZT, and an epitaxial or uni-oriented cladding layer 7 of PZT are laminated in this order. On the surface of the cladding layer 7, upper electrodes 12 and 13 for applying a voltage to the Y branch portion 9 may be provided.

When a clad layer is provided, the same material as the buffer layer can be used for the clad layer material. That is, the material has a smaller refractive index than the material of the optical waveguide layer, and the ratio of the relative dielectric constant of the cladding layer to the relative dielectric constant of the optical waveguide is 0.002 or more. A material having a relative dielectric constant ratio of 0.006 or more and a relative dielectric constant of the cladding layer of 8 or more is selected.

The material of the cladding layer is not necessarily required to be able to maintain the epitaxy relationship with the optical waveguide layer, and may be a polycrystalline thin film. However, when maintaining the epitaxy relationship with the optical waveguide material, a uniform interface is required. Is preferable. As a condition for maintaining the epitaxy relationship, it is desirable that the cladding layer material is similar to the crystal structure of the optical waveguide layer material and the difference in lattice constant is 10% or less. It is not necessary.

The clad layer material used in the present invention includes:
Specifically, ABO_ThreePerovskite oxide
Is represented as tetragonal, orthorhombic or pseudo-cubic, for example Sr
TiO _Three, BaTiO_Three, (Sr_1-xBa_x) TiO_Three, P
bTiO_Three, Pb_1-xLa_x(Zr _yTi_1-y)_{1-x / 4}O_Three,
Pb (Mg_1/3Nb_2/3) O_Three, KNbO_ThreeSuch as hexagonal
For example, LiNbO_Three, LiTaO_ThreeRepresented by
Ferroelectric, tungsten bronze type oxide_x
Ba_1-xNb_TwoO₆, Pb_xBa_1-xNb_TwoO₆Etc.
Besides, Bi_FourTi_ThreeO₁₂, Pb_TwoKNb_FiveO₁₅, K_ThreeL
i_TwoNb_FiveO₁₅, ZnO and substituted derivatives of the above compounds
Selected from

The ratio between the thickness of the cladding layer and the thickness of the optical waveguide layer is preferably at least 0.1, more preferably 0.5 or more, as in the buffer layer. At the same time, the thickness of the cladding layer is preferably 10 nm or more.

A lower electrode substrate, a buffer layer, an optical waveguide layer,
Various combinations of materials for the cladding layer satisfying the above conditions are possible. Among them, the doped SrTiO ₃ single crystal semiconductor substrate or the doped SrTiO ₃
It is preferable to use a substrate provided with a TiO ₃ semiconductor thin film as a lower electrode. This substrate material has a similar perovskite structure and a small difference in lattice constant, so that good epitaxial growth is possible. The material has a higher refractive index than the refractive index of the material (2.399), has a high electro-optic coefficient, and has a composition ratio (ie, Pb, La,
Since it is possible to greatly change the refractive index only by changing the ratio of Zr and Ti, the material of each of the buffer layer, the optical waveguide layer, and the cladding layer is Pb _1-x La _x (Z
it is most effective to use a _{r y Ti 1-y) 1} -x / 4 O 3.

For the upper electrode, Al, Ti, Cr, Ni,
Cu, Pd, Ag, In, Sn, Ta, W, Ir, P
Various metals and alloys such as t and Au, Al-doped ZnO, I
n_TwoO_Three, ITO, RuO_Two, BaPbO_Three, SrRu
O_Three, YBa_TwoCu_ThreeO_7-x, SrVO _Three, LaNiO_Three, L
a_0.5Sr_0.5CoO_Three, ZnGa_TwoO_Four, CdGa_TwoO_Four,
CdGa_TwoO_Four, Mg_TwoTiO_Four, MgTi_TwoO_FourSuch as oxidation
Things can be used. When using a cladding layer
It is desirable to use metal electrodes that are easy to process finely
When no cladding layer is used, an oxide electrode is preferable.
Alternatively, it is effective to use a transparent oxide electrode. Also,
When fatigue or DC drift occurs with the operation time
It is effective to use an oxide.

Optical switches having channel optical waveguides are classified into Mach-Zehnder interference switches, directional coupling switches, total reflection switches, Bragg reflection switches, and digital switches according to the switching principle of the optical path. The optical switch design method of the present invention can be applied to all these types of optical switches.

For example, the present invention can be applied to a single mode Mach-Zehnder interference type 2 × 2 optical switch (FIG. 9) and a single mode directional coupler type 2 × 2 optical switch (FIG. 10). . In these optical switches, a buffer layer 4 is laminated on a single crystal substrate serving as a lower electrode,
A groove 20 is provided on the surface of the buffer layer 4. The optical waveguide layer 6 is laminated on the buffer layer 4 so as to fill the groove 20, so that a channel optical waveguide (shown by a dotted line) is formed. On the optical waveguide layer 6, upper electrodes 12, 13 for applying a voltage to the channel optical waveguide are provided. Further, the present invention can be applied to a total reflection type switch (FIG. 11). This optical switch includes a channel optical waveguide including an X-crossing type channel 19, and an upper electrode 8 for applying a voltage to the channel optical waveguide is provided on the X-crossing type channel.

[0107] Among various optical switches, a digital type switch maintains its state even when a higher voltage is applied after the optical path is switched at a constant voltage, and a plurality of operating points are not generated. It is most desirable in terms of excellent operating voltage tolerance, being able to be independent of polarization, and having small wavelength dependence.

The optical switch according to the present invention is, for example, shown in FIG.
As shown in (1), it can be configured as an optical switch having a channel optical waveguide formed in a convex shape above the optical waveguide layer. In this optical switch, an epitaxial or unidirectional buffer layer 4 made of PZT is laminated on a single crystal substrate 3 serving as a lower electrode. On the buffer layer 4, an optical waveguide layer 6 made of PZT is laminated, and a channel optical waveguide is formed by providing a convex portion 21 on the surface of the optical waveguide layer 6. . An upper electrode 8 for applying a voltage to the Y-branch 9 is provided on the protrusion 21 provided on the surface of the optical waveguide layer 6.

The channel optical waveguide has a branch type, a cross type,
It may be any of a directional coupling type, a Mach-Zehnder interference type, an S-shaped type, a linear type, and an X-cross type. Further, a channel optical waveguide combining a plurality of types may be used. Also,
The channel optical waveguide may have any structure of a buried type, a ridge type, and a rib type. In the present invention, the buffer layer and the optical waveguide layer are formed by laminating a thin film on a substrate. Then, a channel optical waveguide structure in which a convex portion was provided in the optical waveguide layer, a channel optical waveguide structure in which a cladding layer was provided after providing the convex portion in the optical waveguide layer, or an optical waveguide layer was provided after providing a concave portion in the buffer layer. A channel optical waveguide structure is preferred.

In the present invention, since the buffer layer and the optical waveguide layer are formed by laminating a thin film on the substrate, the width, height and depth of the channel optical waveguide can be easily optimized. It is preferable to provide an offset between the S-shaped channel optical waveguides having different bending directions or between the S-shaped channel optical waveguide and the linear channel optical waveguide as necessary. By providing the offset, the light propagation loss can be reduced.

The method for forming the buffer layer, the optical waveguide layer, and the cladding layer includes electron beam evaporation, flash evaporation, ion plating, Rf-magnetron sputtering, ion beam sputtering, laser ablation, and MBE (MBE). Molecular beam epitaxy),
CVD (Chemical Vapor Deposition), Plasma CVD, MOCV
D (organic metal-organic chemical vapor deposition) or the like, a solid-phase epitaxial growth method in which an amorphous thin film is formed by the above-mentioned vapor-phase growth and then heated and crystallized, or a sol-gel method , MOD (Metal Organic)
A thin film forming method such as a solid phase epitaxial growth method by heating and crystallization of an amorphous thin film manufactured by a wet process such as a deposition method can be used.

Among these, it is desirable to form each layer by solid phase epitaxial growth from the viewpoint of waveguide quality and waveguide patterning. In particular, the sol-gel method and M
By applying a solution of an organometallic compound such as a metal alkoxide or an organometallic salt to a substrate by a wet process such as an OD method and heating the amorphous thin film, and then heating and crystallizing the amorphous thin film. Solid-phase epitaxial growth has lower equipment costs and better uniformity on the substrate surface than various vapor-phase growth methods, and is important in forming a buffer layer, an optical waveguide layer, and a cladding layer. It is possible to control the rate easily and with good reproducibility simply by changing the composition of the organometallic compound precursor, and it is possible to grow the buffer layer, optical waveguide layer, and cladding layer with low light propagation loss, and to form an amorphous thin film. Is most suitable for patterning as well.

The organometallic compound used in the wet process is a reaction product of various metals with an organic compound, preferably an organic compound having a boiling point of 80 ° C. or more at normal pressure. , Metal alkoxides, and metal salts, but are not limited thereto. As the organic ligand of the metal alkoxide compound, R ¹ O—
Or R ² OR ³ O— (wherein R ¹ and R ² represent an aliphatic hydrocarbon group, and R ³ represents a divalent aliphatic hydrocarbon group which may have an ether bond) . Such metal alkoxide compound, was placed a metal, in an organic solvent represented by R ¹ OH or R ² OR ³ OH, can be synthesized by performing distillation or reflux, of R ¹ and R ² As the aliphatic hydrocarbon group, an alkyl group having 1 to 4 carbon atoms is preferable, and R ³ is an alkylene group having 2 to 4 carbon atoms, all carbon atoms having an alkylene group having 2 to 4 carbon atoms bonded by an ether bond. Divalent groups of the formulas 4 to 8 are preferred.

In a wet process, these organometallic compounds are reacted with a solvent in a predetermined composition (or dissolved in a solvent), and then applied to a substrate. Although the organometallic compound can be applied after being hydrolyzed, it is desirable not to hydrolyze it in order to obtain an epitaxial ferroelectric thin film. further,
The reaction with the solvent or the dissolution in the solvent is preferably performed in a dry nitrogen or argon atmosphere from the viewpoint of the quality of the obtained thin film.

The solvent is preferably selected from alcohols, diketones, ketone acids, alkyl esters, oxyacids, oxyketones, acetic acid and the like having a boiling point at normal pressure of 80 ° C. or higher. As the solvent having a boiling point of 80 ° C. or higher, specifically, a solvent which facilitates an alcohol exchange reaction of a metal alkoxide is preferable.
₃ ) ₂ CHOH (boiling point 82.3 ° C), CH ₃ (C ₂ H ₅ ) C
HOH (boiling point 99.5 ° C.), (CH ₃ ) ₂ CHCH ₂ OH
(Boiling point 108 ° C.), C ₄ H ₉ OH (boiling point 117.7 ° C.),
(CH ₃ ) ₂ CHC ₂ H ₄ OH (boiling point 130.5 ° C.), CH
₃ OCH ₂ CH ₂ OH (boiling point 124.5 ° C.), C ₂ H ₅ OC
H ₂ CH ₂ OH (boiling point 135 ° C.), C ₄ H ₉ OCH ₂ CH ₂ O
Alcohols such as H (boiling point 171 ° C.) are most preferred, but not limited thereto, and C ₂ H ₅ OH (boiling point 78.3 ° C.) can be used.

Examples of the method for applying the solution of the organometallic compound on the single crystal substrate include a spin coating method, a dipping method, a spray method, a screen printing method, and an ink jet method. These coating steps are preferable in terms of the quality of a thin film obtained in a dry nitrogen or argon atmosphere.

After the application, if necessary, a pretreatment is carried out in an atmosphere containing oxygen, preferably in oxygen, at 0.1 to 10%.
The substrate is heated at a heating rate of 00 ° C./sec, preferably 1 to 100 ° C./sec, and is applied at a temperature in a range of 100 ° C. to 500 ° C., preferably 200 ° C. to 400 ° C. where crystallization does not occur. An amorphous thin film is formed by thermally decomposing the layer. Further, in an atmosphere containing oxygen, desirably in oxygen, high-speed heating is performed at a heating rate of 1 to 500 ° C./sec, preferably 10 to 100 ° C./sec.
The ferroelectric thin film is solid-phase epitaxially grown from the substrate surface by heating at a temperature in the range of from 1200 to 1200 ° C., preferably from 600 to 900 ° C.

In this epitaxial crystallization, heating is performed at the above temperature for 1 second to 24 hours, preferably 10 seconds to 12 hours. As these oxygen atmospheres, it is desirable to use an oxygen atmosphere dried for at least a certain time from the viewpoint of the quality of the obtained thin film, but it is also possible to humidify as necessary. In these epitaxial crystallization steps, the thickness of one layer at a time is 10 nm or more.
It is preferable to carry out solid phase epitaxial growth of a ferroelectric thin film having a thickness of 1000 nm, preferably 10 nm to 200 nm. When the thickness is large, it is preferable to carry out solid phase epitaxial growth in several steps. After each epitaxial growth, cooling is preferably performed at a cooling rate of 0.01 to 100 ° C./sec.

The upper electrode is formed by electron beam evaporation, flash evaporation, ion plating, Rf-magnetron
Sputtering, ion beam sputtering, laser ablation, MBE, CVD, plasma C
It is manufactured by a vapor phase growth method selected from VD, MOCVD, or the like, or a wet process such as a sol-gel method or a MOD method. The shape of the upper electrode is appropriately selected according to the form of the optical switch, and the patterning of the upper electrode can be performed by a method selected from wet etching, dry etching, and lift-off.

The patterning between the channel optical waveguides can be performed by a method selected from wet etching, dry etching, and lift-off. When the amorphous thin film on the surface of the epitaxial thin film is etched using the solid-phase epitaxial growth method, it is easy to perform an etch stop utilizing the difference in the composition and crystallinity of each layer, and a photoresist or an electron beam is applied to the surface of the amorphous thin film. After applying the resist, by exposing and etching, only the amorphous thin film on the surface of the epitaxial thin film can be patterned.

Etching is performed using HCl, HNO ₃ , HF,
Wet etching using an aqueous solution of H ₂ SO ₄ , H ₃ PO ₄ , C ₂ H ₂ O ₂ , NH ₄ F or a mixed aqueous solution thereof, CCl
₄ , CCl ₂ F ₂ , CHClFCF ₃ etc., and their O ₂
Dry etching such as reactive ion etching or ion beam etching using a gas mixture of the above can be used, but etching can be easily performed at a high etching rate by wet etching.

That is, since a technique called solid phase epitaxial growth, in which an amorphous thin film is formed on the surface of an epitaxial thin film, is employed, when combined with wet etching, etching can be easily performed at a high etching rate and at the same time. , Etching in the depth direction of the channel stops at the surface of the epitaxial layer,
The etching in the channel width direction is preferable because the amorphous layer under the mask is under-etched or side-etched, so that the depth and the width can be separately controlled.

Specifically, it is preferable to form an optical waveguide layer by the following methods (1) to (4).

After an epitaxial buffer layer is solid-phase epitaxially grown on a lower electrode substrate of a single crystal semiconductor, an amorphous thin film serving as an epitaxial buffer layer is formed, and a channel-shaped concave portion is formed in the amorphous thin film by wet etching. A method in which solid phase epitaxial growth is performed by heating, and further, a solid phase epitaxial growth of an optical waveguide layer is performed thereon; A method in which a channel-shaped recess is formed in an amorphous thin film by wet etching, an amorphous thin film serving as an optical waveguide layer is formed thereon, and solid phase epitaxial growth is performed by heating. After the solid buffer layer is grown by solid phase epitaxial growth, the epitaxial optical waveguide layer is grown by solid phase epitaxial growth to form an amorphous thin film to be an epitaxial optical waveguide layer, and after forming a channel-shaped convex portion on the amorphous thin film by wet etching. , A method of performing solid phase epitaxial growth by heating, and a method of forming an optical waveguide layer described above,
An acute angle at the intersection of the channel optical waveguides at the branching or asymmetric X intersection can be processed into an ideal shape with good controllability, and is particularly suitable for manufacturing a digital optical switch. In the method of forming an optical waveguide layer, since the amorphous buffer layer having the channel-shaped concave portion and the amorphous optical waveguide layer are simultaneously subjected to solid phase epitaxial growth, the concave portion of the buffer layer is exposed to oxygen or the like at a high temperature. This is particularly preferable because a smooth surface can be obtained in a short time.

The end face processing for input / output is performed by polishing,
It can be performed by a method selected from grinding, cleavage, and etching.

As described above, in the conventional optical switch having the channel optical waveguide having the electro-optical effect, when the radius of curvature of the channel is 70 mm or less, the radiation loss due to the fluctuation of the effective refractive index difference between the channel optical waveguide and its surroundings. Changes significantly. On the other hand, in an optical switch having an epitaxial or mono-oriented channel optical waveguide composed of PLZT, a buffer layer and an optical waveguide layer are formed by epitaxially growing a PLZT thin film on a substrate,
Since the channel optical waveguide is formed by photolithography and etching, channel optical waveguides of various shapes can be accurately formed, and the effective refractive index difference can be accurately controlled according to the radius of curvature of the channel. It has the feature of.

In the method for designing an optical switch according to the present invention, based on the above characteristics, the effective refractive index difference is determined according to the radius of curvature of the channel so that the radiation loss is 0.1 dB or less. Since the optical switch is designed to be obtained, it is possible to reliably obtain an optical switch having a negligible radiation loss. This makes it possible to obtain a compact optical switch including a channel having a small radiation loss and a small radius of curvature, and thus to constitute a large-scale matrix optical switch.

Further, the optical switch of the present invention has an epitaxial or unidirectional channel optical waveguide made of PLZT having a high efficiency electro-optic effect, so that the driving voltage is lower than that of the conventional optical switch. Low, capable of high-speed switching, excellent in temperature stability, and low in crosstalk and insertion loss.

[0129]

According to the method for designing an optical switch of the present invention, when manufacturing an optical switch having an epitaxial or unidirectional channel optical waveguide composed of PLZT, the curvature can be reduced without impairing radiation loss. A compact optical switch including a small-radius channel can be designed.

Further, according to the present invention, there is provided an optical switch having an epitaxial or unidirectional channel optical waveguide composed of PLZT, which has a small radiation loss,
A compact optical switch including a channel with a small radius of curvature is provided.

[Brief description of the drawings]

FIG. 1 shows a Y-branch type 1 according to a first embodiment of the present invention.
It is a top view of a * 2 optical switch.

FIG. 2 shows a Y-branch type 1 according to the first embodiment of the present invention.
It is sectional drawing of a * 2 optical switch.

FIG. 3 is a diagram showing the relationship between the effective refractive index difference and the radius of curvature of the S-shaped channel optical waveguide in the optical switch according to the first embodiment of the present invention.

FIG. 4 is a plan view of a 1 × 8 optical switch according to a second embodiment of the present invention.

FIG. 5 is an enlarged view of a branch section of a 1 × 8 optical switch according to a second embodiment of the present invention.

FIG. 6 is a plan view of an 8 × 8 optical switch according to a third embodiment of the present invention.

FIG. 7 is a cross-sectional view of an optical switch including a cladding layer.

FIG. 8 is a cross-sectional view of an optical switch including a convex channel optical waveguide.

FIG. 9 is a plan view of the Mach-Zeng interference switch.

FIG. 10 is a plan view of a directional coupler switch.

FIG. 11 is a plan view of a total reflection switch.

[Explanation of symbols]

 Reference Signs List 3 substrate 4 buffer layer 6 optical waveguide layer 7 cladding layer 8, 12, 13 upper electrode 9 Y branch 10 S-shaped channel optical waveguide 11 linear channel optical waveguide 14 entrance end face 15 exit end face 16 entrance port 17, 18 exit port 19 X intersection 20 Groove 21 Convex

Claims (3)

[Claims] To 1. A single crystal _{substrate, Pb 1-x La x (} Zr y T
i _1-y ) _{1-x / 4} O ₃ (0 <x <0.3, 0 <y <1.0)
An optical switch design method for designing an optical switch in which an epitaxial or mono-oriented channel optical waveguide is formed, wherein the channel optical waveguide includes a channel having a radius of curvature of 70 mm or less. An optical switch design method for determining an effective refractive index difference between a channel optical waveguide and its surroundings so that radiation loss is 1 dB or less according to a radius of curvature of a channel, and designing an optical switch based on the effective refractive index difference . To 2. A single crystal _{substrate, Pb 1-x La x (} Zr y T
i _1-y ) _{1-x / 4} O ₃ (0 <x <0.3, 0 <y <1.0)
An optical switch having an epitaxial or mono-oriented channel optical waveguide formed by: wherein the channel optical waveguide includes a channel having a radius of curvature of 70 mm or less, and wherein the channel optical waveguide is formed according to the radius of curvature of the channel. An optical switch in which the effective refractive index difference between the optical switch and its surroundings is determined so that the radiation loss is 1 dB or less. 3. The optical switch according to claim 3, wherein said effective refractive index difference is 0.1% or more.