JP2000180905A - Optical switch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical switch in which the number of optical switch elements can be decreased, insertion loss and crosstalk are less, and switching among ports having appropriate interval can be realized by driving voltage and good balanced size. SOLUTION: An incident end plane 7 is provided with channel optical waveguides 11 and 12, light beams made incident in parallel are diverged by a slab type optical waveguide part 3, after they are made parallel light beams by a first thin film lens 9, they are converged to an outgoing end plane 8 by a second thin film lens 10, and made incident on each optical fiber through channel optical waveguides 13 and 14. Light beams are deflected by applying voltage between one of first prism type upper part electrodes 5 and a substrate 1 being a lower part electrode, further, they are deflected in the inverse direction to previous deflection by applying voltage between one of second prism type upper part electrodes 6 and the substrate 1 being a lower part electrode, they are converged by the second thin film lens 10, and an optical path is switched.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type optical switch having an optical path switching function, such as an optical fiber, which can reduce the number of optical switch elements required to constitute a matrix optical switch, and can reduce insertion loss and crosstalk. The present invention relates to an optical switch or a matrix optical switch including an oxide ferroelectric thin film having high temperature stability, capable of realizing switching between ports at appropriate intervals with a size balanced with a driving voltage, and having high temperature stability.

[0002]

2. Description of the Related Art An optical communication network is based on optical communication between points individually connecting nodes, and from Add-D between points.
Optical communication that performs rop multiplexing, and furthermore, optical communication that connects a plurality of nodes as optical signals without converting them into electrical signals are being developed. For this reason, it is important to develop various optical components such as optical branching couplers, optical multiplexers / demultiplexers, and optical switches. Among them, matrix optical switches switch between multiple optical fibers according to demand. Or one of the most important components used for switching for securing a detour in the event of a network failure.

[0003] The form of the matrix optical switch can be classified into a bulk type and an optical waveguide type. The bulk type switches the optical path by mechanically moving prisms, mirrors, fibers, etc., and has the advantage of low wavelength dependence and relatively low loss.However, the switching speed is slow, miniaturization is difficult, and matrix formation is difficult. However, there is a problem that the assembly adjustment process is complicated, is not suitable for mass production, and is expensive. Optical waveguide devices are being studied very much because they are extremely superior in terms of switching speed, miniaturization and integration, mass productivity, and the like.

Optical waveguide type matrix optical switches can be roughly classified into two types in form. The first one switches a channel optical waveguide connecting an input port and an output port by combining a plurality of optical switches or optical gates based on a certain principle. In the second type, an optical deflector is provided between an input port and an output port to deflect light from the input port toward the output port.

[0005] Of these, the first method is most often studied from the viewpoint of flexibility in design and low light loss. In general, a channel optical waveguide is formed in LiNbO ₃ , a compound semiconductor, quartz, or a polymer, and an optical switch for electrically controlling a traveling direction of light at an intersection of each path, or an optical switch for electrically traveling light. An optical gate that opens and closes to control is provided.

In the case of LiNbO ₃ , which is the most typical material and one of the oxide ferroelectrics, when a voltage is applied to the electrode of the optical switch, the refractive index changes due to the electro-optic effect, so that the light transmission is changed. The state changes, 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.

As a principle of such an optical switch, there are 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 dividing input light into two by a directional coupler. Mach-Zehnder type method of switching the output end by separating and giving a phase difference with the refractive index caused by the electric field between the light passing through each path and controlling the interference state at the exit side directional coupler, X-crossing A method of switching a light path by controlling interference between optical modes in a unit, a method of controlling a lateral field distribution of an optical mode in a Y-branch or a non-village X-branch by using a refractive index generated by an electric field to control light. And a method of switching the light path by total reflection or Bragg reflection by controlling the refractive index by providing an electrode at the X intersection.

[0008]

However, a matrix optical switch using a plurality of optical switches (or optical gates) usually has the number of input ports x the number of output ports (N x
N) An optical switch having a crossbar configuration, for example, in the case of 8 × 8, 64 optical switches and a branch type channel connecting them are required, and there is a problem that the configuration is complicated.
Therefore, a method of devising a connection path between an input port and an output port to reduce the number of optical switches is disclosed in Japanese Patent Laid-Open No. 5-8036.
No. 1 and other publications. However, even with such a configuration, when the number of optical switches is 8 × 8, 40 optical switches and a branch type channel connecting them are required, and it is difficult to make a great improvement.

On the other hand, an optical switch using a second optical waveguide type optical deflection element includes an optical waveguide made of LiNbO ₃ or the like, a thin film lens for converting a light beam incident on the optical waveguide into parallel light, And a comb-shaped electrode for exciting a surface acoustic wave for diffracting the light beam by the acousto-optic effect. Kar-Roy and
C. S. Tsai, IEEE Photonics T
ech. Lett. , Vol. 4 (1992) 731.
And so on. An optical switch utilizing the acousto-optic effect is capable of independently deflecting each light beam even if N light beams are arranged so as to overlap each other at the deflecting portion in order to constitute an N × N matrix optical switch. It is only necessary to provide N comb-shaped electrodes, and there is an advantage that a branched channel is not required. However, it is difficult to obtain 100% diffraction efficiency or deflection efficiency, so that insertion loss and crosstalk increase. Also, since the diffraction angle or deflection angle is small, the distance between ports is made considerably smaller than the optical fiber diameter. There were indispensable problems.

As another light deflection element, a prism type light deflection element using an oxide ferroelectric material having an electro-optic effect is known. As such an element, there is a bulk element using a ceramic or a single crystal. However, a practical deflection angle cannot be obtained due to a large size and a considerably high driving voltage. On the other hand, a prism-type domain-inverted light deflection element in which prisms are arranged in a cascade using a LiNbO ₃ single crystal wafer, which is an oxide ferroelectric material, on which a Ti diffusion type optical waveguide or a proton exchange type optical waveguide is manufactured, or a prism type If the electrode light deflection element is Q. Che
n, et al. , J. et al. Lightwave Tec
h. vol. 12 (1994) 1401. And so on. However, since the electrode spacing of about 0.5 mm, which is the thickness of the LiNbO ₃ single crystal wafer, is still required, the driving voltage is still high. As a result, it was not possible to obtain a deflection angle necessary for forming a matrix optical switch.

When a compound semiconductor or a quantum well is used, a low driving voltage can be expected because a voltage can be applied from above and below the optical waveguide core. However, Koizumi et al.
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 is another problem that light absorption occurs at the same time as switching by application of an electric field, thereby deteriorating switching characteristics.

In addition, there is an optical waveguide type optical deflection element using an organic nonlinear optical material. Generally, in order to use an organic nonlinear optical material as an optical waveguide, an organic nonlinear molecule is doped in a polymer or added to a side chain or a main chain, and the polymer is used as an electric field oriented polymer which is polled by applying an electric field. For example, a prism type optical deflecting element in which an optical waveguide made of an electric field oriented polymer or the like is sandwiched between upper and lower electrodes and driven at a low voltage, and a matrix optical switch using the same are disclosed in Japanese Patent Laid-Open No. 4-181231.
No. in the official gazette. The matrix optical switch is provided with N thin film lenses for converting the N light beams incident on the optical waveguide into parallel light, and N prism electrodes for deflecting the parallel light beam, Further, there are provided N prism electrodes for deflecting the deflected light beam again, and N thin film lenses for condensing the light beam at the end of the optical waveguide.

On the other hand, it is known that an electric field oriented polymer can form a laminated structure which is difficult to realize with an inorganic material. A structure in which an optical waveguide is sandwiched between upper and lower electrodes is disclosed in Japanese Patent Application Laid-Open No. Hei 4-181231. Prior to the publication, J.I. I. T
Hackara et al, Appl. Phys. L
ett. 52 (1988) 1031. And so on. However, electric field oriented polymers have problems such as temperature stability as compared with oxide ferroelectric materials, and the development of devices that can be used practically has not progressed.
plus E, 186 (1995) 98. And so on. Also, Asahara, Optronics, 11 (1
995) 147. As described in Japanese Patent Application Laid-Open No. HEI 4-181231, the polymer has a small selection range such as a refractive index.
When a matrix optical switch such as that disclosed in Japanese Patent Application Laid-Open No. H10-209,873 is constructed, there is a problem that the size may be considerably increased.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems by reducing the number of optical switch elements required to constitute a matrix optical switch, reducing insertion loss and crosstalk, and ensuring an appropriate spacing. It is an object of the present invention to provide an optical switch or a matrix optical switch having an oxide ferroelectric thin film with high temperature stability, which can realize switching between the ports with a size balanced with the driving voltage.

[0015]

The object of the present invention is to provide a single-crystal substrate serving as a conductive or semiconductive lower electrode, an epitaxial or single-oriented oxide buffer layer formed on the surface of the single-crystal substrate, An optical waveguide of an oxide ferroelectric thin film provided on the buffer layer and having an epitaxial or unidirectional electro-optic effect having a larger refractive index than the buffer layer, and provided on the light incident end face side of the single crystal substrate. And
A first thin film lens that converts N (1 ≦ N) incident lights into parallel light, N first prism-type upper electrodes that respectively deflect N parallel lights, and N deflected lights N second prism-type upper electrodes for further deflecting the parallel light, respectively, and the parallel light provided on the light-emitting end face side of the single crystal substrate and deflected by the N second prism-type upper electrodes are condensed. A second thin-film lens that emits M (1 ≦ M) outgoing light from the light-emitting end face, and converts the light incident from each light through the incident end face into parallel light by the first thin-film lens. After that, each light is deflected by applying a voltage between the first prism type upper electrode and the single crystal substrate serving as the lower electrode, and then the second prism type upper electrode and the single crystal serving as the lower electrode are applied. Each light is deflected by applying a voltage between the substrate and the crystal substrate. By converging to the exit end face by second thin film lens is accomplished by the optical switch, characterized by switching the optical path as the desired output light by deflecting the desired incident light.

The present inventors provide an epitaxial or unidirectional buffer layer having a high dielectric constant on a conductive or semiconductive single crystal substrate serving as a lower electrode, and have a higher refractive index than the buffer layer. Provide an oxide thin film optical waveguide having an epitaxial or mono-oriented electro-optic effect with a, a high dielectric constant cladding layer having a smaller refractive index than the optical waveguide as necessary, furthermore, First, a multilayer structure in which an upper electrode was provided was invented (Jan. 1997
Japanese Patent Application No. 9-303436, filed on Jan. 18, which allows an oxide ferroelectric material to have a structure in which an optical waveguide is sandwiched between upper and lower electrodes, and the above-described prism without impairing low light propagation loss characteristics. The problem of the driving voltage of the optical deflector was solved.

The present inventors have arranged a prism type electrode as an upper electrode in this structure, studied the deflection characteristics in detail, and further studied the optical waveguide optical system of the matrix optical switch. The ability to obtain the required deflection angle to construct the switch, the absence of undeflected components in the deflected state, and the extremely small amount of scattered light have the potential to solve the problems of insertion loss and crosstalk. Was found.

The present inventors have previously invented a thin film lens using a plurality of epitaxial or unidirectionally oriented ferroelectric thin films (see Japanese Patent Application No.
No. 320332), it has become possible to provide a thin film lens having a low coupling loss and a small focal length in an optical waveguide element. The present inventors have studied the material configuration of the matrix optical switch and the laminated structure, and as a result, have found that this thin film lens can be introduced into the matrix optical switch.
The prospect of realizing a deflection type matrix optical switch with a compact size was obtained.

Further, as a result of diligent studies on various configurations of the N × N matrix optical switch using the above-mentioned laminated structure and thin-film lens, it was found that both ends of the single crystal substrate had an end face for incidence from the N incidence optical fibers to the optical waveguide and an end face. An output end face from the optical waveguide to the N output optical fibers is provided, and N first thin-film lenses are provided on the optical waveguide between the input end face and the N first upper electrodes, and the N first thin-film lenses are disposed on the optical waveguide. N second thin film lenses are provided in the optical waveguide between the second upper electrode and the emission end face;
After each of the light beams incident from each optical fiber through the incident end face is made into a parallel light by the first thin film lens, the first prism type upper electrode and the lower electrode provided at positions where the respective laser beams do not overlap each other are formed. Each laser beam is independently deflected by applying a voltage between the single crystal substrate and
Further, by applying a voltage between the second prism type upper electrode and the single crystal substrate serving as the lower electrode, each laser beam is independently deflected, and is condensed by the second thin film lens on the emission end face. It has been found that the optical path can be switched to desired N optical fibers. With such a configuration, the number of optical switch elements required to configure an N × N matrix optical switch can be reduced to 2N, and at the same time, a relatively compact switch size can be realized, and insertion loss and crosstalk can be reduced. It is possible to obtain a matrix optical switch capable of realizing switching between small and appropriately spaced ports with a relatively low driving voltage.
Providing a channel waveguide between the incident end face and the first thin-film lens and between the output end face and the second thin-film lens can also reduce crosstalk and reduce the divergence angle to the slab waveguide. It has been found that it is effective for uniformity and for relaxing the processing accuracy requirement of the end face.

The substrate which can be used as the substrate serving as the lower electrode is a conductive or semiconductive single crystal substrate, or a substrate provided with an epitaxial or unidirectional conductive or semiconductive thin film on the surface. is there. The conductive or semiconductive material is SrT doped with Nb, La, or the like.
iO ₃ , Al-doped ZnO, In ₂ O ₃ , RuO ₂ , B
aPbO ₃ , SrRuO ₃ , YBa ₂ Cu ₃ O _7-x ,
SrVO ₃ , LaNiO ₃ , La _0.5 Sr _0.5 Co
O ₃ , ZnGa ₂ O ₄ , CdGa ₂ O ₄ , CdGa ₂ O
₄ , oxides such as Mg ₂ TiO ₄ and MgTi ₂ O ₄ , S
Single 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- such as InSb, GaAsSb, InAsSb, etc.
V-based compound semiconductor, ZnS, ZnSe, ZnTe, C
II-VI based compound semiconductors such as aSe, Cdte, HgSe, HgTe, CdS, Pd, Pt, Al, A
Although metals such as u and Ag can be used, the use of an oxide is often advantageous for the film quality of the oxide thin film optical waveguide disposed on the top.

The conductive or semiconductive single-crystal substrate or the conductive or semiconductive epitaxial or oriented thin film is formed by the crystal structure of the ferroelectric thin film and the deflection speed, switching speed or modulation. It is desirable to select according to the carrier mobility required by the speed. Further, the relative dielectric constant of the ferroelectric material is several tens to several thousands, but 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 10 ^4. Ω · cm or less, desirably 10 ² Ω · cm or less is effective in terms of RC time constant and voltage drop.

Materials that can be used as a substrate when an epitaxial or unidirectional conductive or semiconductive thin film is provided on the surface are SrTiO ₃ , BaTiO _3
3 , BaZrO ₃ , LaAlO ₃ , ZrO ₂ , Y ₂ O _{3
8% -ZrO 2, MgO, MgAl} 2 O 4, LiNbO
₃ , oxides such as LiTaO ₃ , Al ₂ O ₃ and ZnO;
Single semiconductor such as Si, Ge, diamond, etc., AlA
s, AlSb, AlP, GaAs, GaSb, InP,
InAs, InSb, AlGaP, AlLnP, AlG
aAs, AlInAs, AlAsSb, GaInAs,
II such as GaInSb, GaAsSb, InAsSb
IV compound semiconductor, ZnS, ZnSe, ZnT
e, CaSe, Cdte, HgSe, HgTe, CdS
Although it is possible to use a II-VI compound semiconductor such as, for example, the use of an oxide is often advantageous to the film quality of the oxide thin film optical waveguide disposed on the top.

The buffer layer is smaller than the thin film optical waveguide material.
And the relative dielectric constant of the buffer layer
The relative permittivity ratio of the waveguide is 0.002 or more, preferably
When the ratio between the relative dielectric constant of the optical layer and the relative dielectric constant of the optical waveguide is 0.
006 or more, and the relative permittivity of the buffer layer is 8 or more
Is selected. The buffer layer material is conductive
Can maintain epitaxy relationship between substrate material and optical waveguide material
It is necessary to Can maintain this epitaxy relationship
The condition is that the buffer layer material is
Similar to the crystal structure of waveguide materials, with a difference in lattice constant of 10% or less
But it is not always necessary to follow this relationship.
At least it is only necessary to maintain the epitaxy relationship. Specifically
Is ABO₃Square perovskite oxide
SrTi as a crystal, orthorhombic or pseudo-cubic
O₃, BaTiO₃, (Sr_1-xBa_x) TiO
₃(0 <x <1.0), PbTiO₃, Pb_1-xLa
_x(Zr_yTi _1-y)_{1-x / 4}O₃(0 <x <0.
3, 0 <y <1.0, PZT, P
LT, PLZT), Pb (Mg_1/3Nb_2/3)
O₃, KNbO₃LiNb as a hexagonal system
O₃, LiTaO₃Ferroelectric, tongue, etc.
Sr in stainless bronze type oxide_xBa_1-xNb₂O
₆, Pb_xBa_1-xNb₂O₆Etc.
And Bi₄Ti₃O₁₂, Pb₂KNb₅O_Fifteen, K₃
Li₂Nb₅O_Fifteen, ZnO and the above substituted derivatives
Is chosen. The thickness of the buffer layer and the thickness of the optical waveguide
The ratio is at least 0.1, preferably at least 0.5, and
It is effective that the thickness of the buffer layer is 10 nm or more.
You.

As the material of the thin-film optical waveguide, the buffer layer
Is also selected from oxides having a large refractive index, specifically
Is ABO₃For the perovskite type, tetragonal and orthorhombic
Or pseudo-cubic system such as BaTiO₃, PbTiO
₃, Pb_1-xLa_x(Zr_yTi_1-y)
_{1-x / 4}O₃(PZT, PL depending on the values of x and y
T, PLZT), Pb (Mg_1/3Nb_2/3) O₃,
KNbO₃For example, as a hexagonal system, for example, LiNbO₃,
LiTaO₃Such as ferroelectrics, tungsten
Sr for bronze type_xBa_1-xNb₂O₆, Pb_xB
a_1-xNb₂O₆Etc. In addition, Bi₄Ti
₃O₁₂, Pb₂KNb₅O_Fifteen, K₃Li₂Nb ₅O
_FifteenAnd further substituted derivatives described above. Thin film
The thickness of the optical waveguide is usually set between 0.1 μm and 10 μm.
However, this can be selected appropriately according to the purpose.
it can.

When a cladding layer is provided, a buffer layer
Similar ones can be used. That is, the thin-film light guide
It has a smaller refractive index than the waveguide material and the cladding layer
The ratio between the relative permittivity and the relative permittivity of the optical waveguide is 0.002 or less.
Above, preferably the relative permittivity of the cladding layer and the optical waveguide
The relative dielectric constant ratio is 0.006 or more, and the cladding layer
A material having a relative dielectric constant of 8 or more is selected. Cladding layer
Material maintains epitaxy relationship with optical waveguide
It is not always necessary to be able to do it, and a polycrystalline thin film may be used.
However, if it is necessary to obtain a uniform interface,
It is necessary to be able to maintain the epitaxy relationship. This
Conditions that can maintain the epitaxy relationship of
The layer material is similar to the crystal structure of the thin film optical waveguide material,
It is desirable that the difference between the numbers is 10% or less, but not necessarily.
If you can maintain the epitaxy relationship without following this relationship
good. Specifically, ABO₃-Type perovskite oxidation
For example, as a tetragonal, orthorhombic or pseudo-cubic system,
SrTiO₃, BaTiO ₃, (Sr_1-xBa_x) T
iO₃(0 <x <1.0), PbTiO₃, Pb_{1 -X}
La_x(Zr_yTi_1-y)_{1-x / 4}O₃(0 <x <
0.3, 0 <y <1.0, PZ by the values of x and y
T, PLT, PLZT), Pb (Mg_1/3N
b_2/3) O₃, KNbO₃Such as hexagonal system
If LiNbO₃, LiTaO₃Such as ferroelectric
, Sr in tungsten bronze type oxide_xBa
_1-xNb₂O₆, Pb_xBa_1-xNb₂O₆Such,
In addition, Bi ₄Ti₃O₁₂, Pb₂KNb₅
O_Fifteen, K₃Li₂Nb₅O_Fifteen, ZnO and more
Selected from substituted derivatives. The thickness of the cladding layer and the light guide
The thickness ratio of the waveguide is 0.1 or more, preferably 0.5 or more.
And the thickness of the cladding layer is 10 nm or more
Is valid.

The prism type upper electrode is made of Al, Ti, Cr,
Ni, Cu, Pd, Ag, In, Sn, Ta, W, I
Various metal electrodes and alloys such as r, Pt, and Au, and Al doping
ZnO, In₂O₃, ITO, RuO₂, BaPb
O₃, SrRuO₃, YBa₂Cu ₃O_7-x, SrV
O₃, LaNiO₃, La_0.5Sr_0.5CoO₃,
ZnGa₂O₄, CdGa₂O₄, CdGa₂O₄, M
g₂TiO₄, MgTi₂O ₄Use oxides such as
And it is possible. Fine processing when using a cladding layer
It is desirable to use a metal electrode that is easy to
When not using an oxide electrode, preferably a transparent oxide
It is effective to use electrodes. Also, with the operation time
Use oxide if fatigue or DC drift occurs.
Is effective. Prism type upper electrode width and length
The shape of the
The width of the laser beam that determines the number of
To create a matrix with a predetermined size on a substrate
It is set according to the required deflection angle. Prism type upper part
The number of poles is set according to the connection between the input and output ports
However, in many cases, many-to-many, completely non-blocking connections
A 2N prism electrode that is twice the number of ports
You.

The thin film lens can be selected from a mode index system, a Fresnel system, and a grating system that can use a planar process, but the mode index system is preferable from the viewpoint of light collection efficiency. In the mode index method, depending on the lens shape viewed from the top of the thin-film optical waveguide, if the effective refractive index of the lens is larger than that of the thin-film optical waveguide, the effective refractive index of the circular or pupil-shaped convex lens, and the effective refractive index of the lens is determined by When the size is smaller than the wave path portion, a concave lens is selected. In general, a circular or pupil-shaped convex lens is often required as an optical waveguide element.

The width of the input / output port is 1 μm to 10 μm, preferably 3 μm to 7 μm, and the length is from the viewpoint of reducing crosstalk, making the divergence angle to the slab type waveguide portion uniform, and relaxing the end face forming position accuracy. Is from 100 μm to 100
It is desirable to form a channel of about 00 μm.
Also, if a tapered channel waveguide is provided on the thin film lens side of the channel waveguide between the exit end face and the thin film lens, the light beam can be guided to the channel waveguide even if the deflection angle fluctuates. Can be suppressed from becoming worse.

As the channel optical waveguide, any of a buried type, a ridge type, and a loaded type can be used. In the present invention, an epitaxial or unidirectional buffer layer is provided, and the buffer layer is larger than the buffer layer. Provision of a channel optical waveguide structure in which a thin-film optical waveguide has a projection, and a projection in a thin-film optical waveguide due to the lamination of thin films provided with an oxide thin-film optical waveguide having a refractive index and an epitaxial or mono-oriented electro-optic effect. It is more preferable that a channel optical waveguide structure in which a cladding layer is provided after the formation or a channel optical waveguide structure in which a thin film optical waveguide is provided after forming a recess in the buffer layer can be easily manufactured. Since the width and height or depth of the channel are also formed by laminating the thin films, it is easy to select an optimum value depending on the parameters of the optical switch, the material of the waveguide, and the manufacturing process.

The clad layer, the thin film optical waveguide, and the buffer layer are formed by electron beam evaporation, flash evaporation, ion plating, Rf-magnetron sputtering,
Ion beam sputtering, laser ablation, MBE, CVD, plasma CVD, MOCVD
Vapor phase epitaxial growth method selected from the above, solid phase epitaxial growth by heating after forming an amorphous thin film by the vapor phase growth, or solidification by heating of an amorphous thin film formed by a wet process such as a sol-gel method or a MOD method. It is produced by a phase epitaxial growth method. The upper electrode is formed by electron beam evaporation, flash evaporation, ion plating, Rf-magnetron sputtering, ion beam sputtering, laser ablation,
It is manufactured by a vapor phase growth method selected from BE, CVD, plasma CVD, MOCVD and the like, and a wet process such as a sol-gel method and a MOD method.

Patterning of the upper electrode, the thin film lens, and the channel optical waveguide is performed by wet etching,
It can be performed by a method selected from dry etching and lift-off. In the present invention, a buffer layer having an epitaxial or unidirectional orientation is provided, and an oxide thin film optical waveguide having an epitaxial or unidirectional electro-optical effect having a higher refractive index than the buffer layer is provided thereon. Therefore, in patterning the channel optical waveguide, it is easy to perform an etch stop utilizing the composition and crystallinity of each layer, and it is desirable to use wet etching and dry etching.However, in the solid phase epitaxial growth method, an amorphous thin film is wet-etched. The method of etching and subsequent solid phase epitaxial growth by heating is easiest and desirable. The end face processing for input / output can be performed by a method selected from polishing, grinding, cleavage, and etching.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical switch according to a first embodiment of the present invention will be described with reference to FIGS. When light is introduced into the optical waveguide provided on the substrate, a part of the total light intensity leaks out to the substrate, and when the transparency of the substrate is low, the component that seeps into the substrate is absorbed, and the light propagates along with the light. Loss. Generally, the transparency of a conductive substrate is low. However, FIG.
As described above, if the thickness of the exuded region is replaced by the buffer layer 2 having no absorption, the absorption by the conductive substrate 1 is eliminated, and the propagation loss can be reduced. In order for the buffer layer to function as an isolation layer between the thin-film optical waveguide and the conductive substrate, the refractive index of the buffer layer material needs to be smaller than the refractive index of the thin-film optical waveguide material. In addition, in order to reduce light propagation loss due to scattering due to the optical waveguide surface or grain boundaries in the optical waveguide to a practical level,
It is essential that the buffer layer material can maintain the epitaxy relationship between the conductive substrate material and the optical waveguide material. Also,
The optical waveguide material desirably has a high electro-optic coefficient, and the conductive substrate material desirably has a low resistivity. The thickness ratio between the buffer layer and the optical waveguide is such that the propagation loss is 1 dB.
/ Cm or less is required to be at least 0.1 or more. Further, when the operation in the single mode of TE ₀ is premised, it is appropriate to set it to 0.5 or more.

Next, when an upper metal electrode is provided on the thin-film optical waveguide, if the frequency of light in the thin-film optical waveguide exceeds the plasma frequency of the metal electrode, the light penetrates into the metal electrode with light propagation. The added components are strongly absorbed by carriers in the metal, resulting in propagation loss. However, as shown in FIG. 1, if the area where this seeping occurs is replaced by the cladding layer 4 having low absorption, the absorption by the upper metal electrode 5 is eliminated and the propagation loss can be reduced. In order for the clad layer to function as an isolation layer between the thin film optical waveguide and the metal electrode, it is generally necessary that the refractive index of the material of the clad layer is smaller than the refractive index of the material of the thin film optical waveguide.

On the other hand, a barrier is provided between the conductive substrate and the thin-film optical waveguide.
When the buffer layer exists, the voltage applied between the upper and lower electrodes
Distributes according to the capacitance of the film waveguide and buffer layer
As a result, the effective voltage that can be applied to the thin-film optical waveguide decreases.
However, a buffer layer with a certain thickness and a high dielectric constant is used.
The high effective voltage applied to the thin-film optical waveguide.
It becomes possible. FIG. 2 is an equivalent circuit showing a thin film light guide.
Capacity C of Waveguide 3_wAnd the capacitance C of the buffer layer 2_bConsisting of
It is represented by a column circuit. All applied voltage is V₀, Thin film optical waveguide
Let the relative permittivity be ε_wAnd the film thickness is d_w, The relative permittivity of the buffer layer
ε_bAnd the film thickness is d _b, Ε₀Is 8.854 × with a dielectric constant of vacuum.
10^-14(F / cm), where S is the electrode area, a thin film
Effective voltage V applied to the optical waveguide_wIs
You.

V _w = C _b / (C _w + C _b ) × V ₀ = ε _{b
d w / (ε w d b} + ε b d w) × V 0

In the present invention, since d _b / d _w is 0.1 or more, V _w / V ₀ is 0.02 or more, that is, ε _b / ε where the effective voltage is 2% or more of the applied voltage. The region where _w is 0.002 or more, desirably V _w / V ₀ is 0.1
A range of 0.006 or more can be used as the above value, that is, ε _b / ε _{w at} which the effective voltage becomes 10% or more of the applied voltage. The upper limit of ε _b / ε _w is determined by the combination of materials that can be used for the buffer layer and the thin-film optical waveguide, and is about 10. Since the relative permittivity of the buffer layer is close to 4000 as the relative permittivity of the optical waveguide, ε
It is desirable to have 8 or more values can be secured 0.002 as _b / _{ε w.} Under the condition that the effective voltage is 2% or less of the applied voltage, it is not effective for the purpose of providing an epitaxial optical waveguide having an electro-optical effect on the conductive substrate and greatly reducing the driving voltage. The above principle is exactly the same for the cladding layer.

As described above, an epitaxial or unidirectional buffer layer having a high dielectric constant is provided on a conductive or semiconductive single crystal substrate serving as a lower electrode, and a refractive index larger than that of the buffer layer is provided thereon. Provide an oxide thin film optical waveguide having an epitaxial or mono-oriented electro-optic effect with a, a high dielectric constant cladding layer having a smaller refractive index than the optical waveguide as necessary, furthermore, Providing an upper electrode on the top enables a structure in which an optical waveguide is sandwiched between upper and lower electrodes even with an oxide ferroelectric material, and a low drive voltage can be achieved without impairing low light propagation loss characteristics. .

Here, in FIG. 1, the upper electrode 5 has a prism shape, and the substrate 1 which is a lower electrode located at a distance d via the buffer layer 2, the thin film optical waveguide 3, and the cladding layer 4 if necessary. When a voltage V is applied during this time, a change in the refractive index occurs. Assuming that the length of the prism electrode is L and the width is W,

Θ = −Δn × L / W = １ ／ · r · n ³ ·
(V / d) ・ (L / W)

The following deflection occurs. The deflection when a prism-type electrode applies an electric field to a ferroelectric material having the Kerr effect, which is a secondary electro-optic effect, follows the following equation.

Θ = １ ／ · r · n ³ · (V / d) ² · (L / W)

When the prism type electrode is provided as the upper electrode as described above, a deflection angle of the laser beam required for forming the matrix optical switch or the optical switch can be obtained. And the problems of insertion loss and crosstalk can be solved.

At both ends of the substrate, an end face 7 for incidence from an optical fiber and an end face 8 for emission to an optical fiber are provided.
Channel optical waveguides 11 and 12 are provided on the incident end face 7 at intervals of 250 μm. Light beams incident parallel from the respective optical fibers through the channels diverge in the slab type optical waveguide section 3 and are incident on the incident end face 7. After being converted into parallel light by two first thin film lenses 9 provided at a position 4 mm from the end of the wave path, the second thin film lens 10 provided at two positions 4 mm from the end of the channel optical waveguide for emission uses the two thin film lenses 10. The light is condensed on the exit end face 8 and enters each optical fiber via the channel optical waveguides 13 and 14. On the other hand, after the light beam incident from the channel optical waveguide 11 is converted into parallel light by one of the first thin film lenses 9, each light beam is interposed between the first thin film lens 9 and the second thin film lens 10. A voltage of 21 V is applied between one of the first prism-shaped upper electrodes 5 having a base of 200 μm and a height of 4000 μm provided at two positions where the parallel laser beams do not overlap, and the substrate 1 as the lower electrode. As shown by the dashed line in FIG. 3, one of the second prism type upper electrodes 6 having a base of 200 μm and a height of 4000 μm provided two at a position 15 mm away from the first upper electrode 5 is further deflected by 17 mrad, Substrate 1 as lower electrode
By applying a voltage of 14 V between them, the light is deflected by 17 mrad in the direction opposite to the previous deflection, condensed by the second thin-film lens 10 and enters the channel optical waveguide 13 to switch the optical path. Similarly, the light beam incident from the channel optical waveguide 12 is
4, the optical path can be switched.

With such a basic structure, when configuring a matrix optical switch, the number of necessary optical switch elements can be reduced, and insertion loss and crosstalk are reduced.
An optical switch or a matrix optical switch that can realize switching between ports at appropriate intervals with a relatively low driving voltage is obtained. Further, channel waveguides provided between the incident end face and the first thin-film lens and between the output end face and the second thin-film lens can reduce crosstalk and reduce the divergence angle to the slab waveguide section. This is effective for uniformity and for relaxing the processing accuracy requirement of the end face.

To manufacture a 2 × 2 optical switch as in this embodiment, first, a PZT buffer layer having a composition of 2.396 in refractive index was formed on a lower electrode substrate of Nb-doped SrTiO ₃ (100) single crystal semiconductor. Epitaxial growth is performed with a thickness of 1500 nm, and then a PLZT thin film optical waveguide having a composition with a refractive index of 2.420 is epitaxially grown with a thickness of 2000 nm. After the growth of the buffer layer and before the growth of the thin-film optical waveguide, the thin-film lens has a composition with a refractive index of 2.519 and a thickness of 15 nm.
A mode index type lens can be manufactured by patterning a 00 nm epitaxial PZT thin film into a lens shape. The channel waveguide between the incident end face and the first thin-film lens and between the output end face and the second thin-film lens has a PLZT thin-film optical waveguide of 500 nm.
It can be manufactured by etching. Further, the input / output end face can be formed by polishing. The two prism-shaped upper electrodes are formed on the PZT thin-film optical waveguide with a thickness of 200 nm.
After forming a laminated thin film made of Al having a thickness of 200 nm and ITO having a thickness of 200 nm, the base 200 μm was formed by a lift-off method.
m and a height of 4000 μm. The shape of the prism electrode is as shown in FIG.

The crystallographic relationship between the PLZT buffer layer, the PZT thin-film optical waveguide, and the PZT thin-film lens layer is such that the PLZT (100) thin-film optical waveguide having a single orientation // PZT (10
0) Thin film lens layer // PZT (100) buffer layer //
Nb-SrTiO ₃ (100) substrate, in-plane orientation PLZT
[001] Thin film optical waveguide // PZT [001] Thin film lens layer // PZT [001] buffer layer // Nb-SrT
The structure of the iO ₃ [001] substrate is obtained, and the electro-optic coefficient of the PLZT thin film optical waveguide is about r = 120 pm / V. PZT, relative dielectric constant of PLZT buffer layer 1900
The effective voltage of the PZT thin-film optical waveguide obtained from the relative dielectric constant of the thin-film optical waveguide of 900 and the relative dielectric constant of the PLZT buffer layer of 1900 is 35%, and the voltage can be applied with high efficiency despite the interposition of the buffer layer. It is. With such a configuration, a good optical switch having a switching voltage of 14 V, a crosstalk of 20 dB or less, and an insertion loss of 10 dB or less can be obtained.

Next, an optical switch according to a second embodiment of the present invention will be described with reference to FIG. In the present embodiment, FIG.
A 4 × 4 matrix optical switch as shown in FIG.
In this embodiment, an optical switch can be manufactured in the same manner as in the first embodiment. However, a La-doped SrTiO ₃ (100) single crystal semiconductor, a buffer layer,
Epitaxial PZT thin films having different refractive indexes can be used for the optical waveguide and the thin film lens. In the 4 × 4 optical switch shown in FIG. 4, an end face 7 for incidence from the optical fiber and an end face 8 for emission to the optical fiber are provided at both ends of the substrate, and the end face 7 for incidence is omitted in the drawing. Channel optical waveguides are provided at intervals of 250 μm, and light beams incident parallel from the respective optical fibers via the channels are diverged in the slab-type optical waveguide portion, converted into parallel light by the first thin film lens 9, and The light is condensed on the emission end face 8 by the thin film lens 10 of FIG.
Although not shown in FIG. 4, the light enters each optical fiber through a channel optical waveguide.

At this time, after the light beam incident from the channel optical waveguide 11 is converted into parallel light by one of the first thin film lenses 9, the light beam is transmitted between the first thin film lens 9 and the second thin film lens 10. By applying a voltage between one of the first prismatic upper electrodes 5 provided at positions where the parallel laser beams do not overlap with each other and the substrate 1 as the lower electrode, as shown by the broken line in FIG. The deflection is performed by applying a voltage between one of the second prism type upper electrodes 6 provided at a position distant from the first upper electrode 5 and the substrate 1 as the lower electrode. The light is condensed by the second thin film lens 10 and enters the channel optical waveguide 13 to switch the optical path. Similarly, the optical path of the light beam incident from the channel optical waveguide 12 is switched to the channel optical waveguide 14.

With such a structure, arbitrary input and output optical fibers can be connected to each other, and the number of optical switch elements required to constitute a completely non-blocking 4 × 4 matrix optical switch is reduced to eight. Can be reduced,
A matrix optical switch having a small crosstalk of 20 dB or less and an insertion loss of 10 dB or less, and capable of realizing switching between ports at appropriate intervals with a low driving voltage can be obtained.

Next, an optical switch according to a third embodiment of the present invention will be described with reference to FIG. An 8 × 8 matrix optical switch as shown in FIG. 5 of the present embodiment can be manufactured in the same manner as in the first embodiment. In the 8 × 8 optical switch shown in FIG. 5, an end face 7 for incidence from the optical fiber and an end face 8 for emission to the optical fiber are provided at both ends of the substrate, and the end face 7 for incidence is omitted in FIG. Are provided with eight channel optical waveguides at intervals of 125 μm, and light beams which are incident in parallel from the respective optical fibers via the channels diverge in the slab type optical waveguide portion 3 and are 4 mm from the end of the incident channel optical waveguide. After being collimated by the first thin film lenses 9 provided at the eight positions, eight second thin film lenses 1 provided at a position 4 mm from the end of the channel optical waveguide for emission
The light is condensed on the emission end face 8 by 0, and enters each optical fiber via the channel optical waveguides 13 and 14.

On the other hand, after the light beam incident from the channel optical waveguide 11 is converted into parallel light by one of the first thin film lenses 9, the first thin film lens 9
And one of the first prism-type upper electrodes 5 having a base of 200 μm and a height of 4000 μm provided at eight positions where the laser beams which have become parallel light do not overlap with the thin film lens 10 of FIG. By applying a voltage of 24 V between the substrate 1 and the substrate 1, as shown by the broken line in FIG.
and eight sets of bases 200 μm and height 4000 provided at positions 30 mm away from the first upper electrode 5.
When a voltage of 24 V is applied between one of the second prism-type upper electrodes 6 of μm and the substrate 1 as the lower electrode, the beam is deflected up to 58 mrad in a direction opposite to the previous deflection,
The light is condensed by the second thin-film lens 10 and enters the channel optical waveguide 13 to switch the optical path. Similarly, the optical path of the light beam incident from the channel optical waveguide 12 is switched to the channel optical waveguide 14.

With such a structure, the number of optical switch elements required to constitute a completely non-blocking 8.times.8 matrix optical switch can be reduced to 16, the switching voltage is 24 V, and the total length of the matrix optical switch is 50 mm.
A matrix optical switch that is as compact as possible, has a low crosstalk of 20 dB or less and an insertion loss of 10 dB or less, and can realize switching between ports at appropriate intervals with a low driving voltage.

[0053]

As described above, according to the present invention, it is possible to reduce the number of optical switch elements required to constitute a waveguide type optical switch having an optical path switching function such as an optical fiber, and to reduce insertion loss and crosstalk. An optical switch or a matrix optical switch capable of realizing switching between small and appropriately spaced ports with a size balanced with the driving voltage can be realized by an oxide ferroelectric thin film having high temperature stability.

[Brief description of the drawings]

FIG. 1 is a principle diagram of an electric field distribution in an optical waveguide.

FIG. 2 is a diagram showing an equivalent circuit of an optical waveguide / buffer layer / substrate.

FIG. 3 is a diagram showing a schematic configuration of an optical switch according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a schematic configuration of an optical switch according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a schematic configuration of an optical switch according to a third embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 conductive substrate 2 buffer layer 3 thin film optical waveguide 4 clad layer 5, 6 prismatic upper electrode 7 incident end face 8 emission end face 9, 10 thin film lens 11, 12, 13, 14 channel optical waveguide

Claims (4)

[Claims] 1. A single crystal substrate serving as a conductive or semiconductive lower electrode, an epitaxial or single orientation oxide buffer layer formed on a surface of the single crystal substrate, and provided on the buffer layer An optical waveguide of an oxide or ferroelectric oxide thin film having an electro-optic effect having a refractive index larger than that of the buffer layer and having an electro-optical effect of a single orientation; and N ( 1 ≦
N) first thin-film lenses that convert the incident light into parallel light, N first prism-type upper electrodes that respectively deflect the N parallel light, and the N parallel light that is deflected. N second prism-type upper electrodes for further deflecting the parallel light, and the parallel light beams provided on the light-emitting end face side of the single crystal substrate and deflected by the N second prism-type upper electrodes. An optical switch, comprising: a second thin-film lens that emits light to emit M (1 ≦ M) outgoing light from the end surface for light emission. 2. An optical switch according to claim 1, wherein an oxide cladding layer having a smaller refractive index than said optical waveguide is provided between said optical waveguide and said upper electrode. switch. 3. The optical switch according to claim 1, wherein a conductive or semiconductive epitaxial or unidirectional thin film is formed on the surface of the single crystal substrate. Light switch. 4. The optical switch according to claim 1, wherein said optical switch is disposed between said incident end face and said first thin-film lens, and between said output end face and said second thin-film lens. An optical switch, wherein a channel waveguide is provided between the optical switches.