JPS59185311A - Light control type optical switch - Google Patents

Abstract

PURPOSE:To unite light sensors into one body, to facilitate formation of optical microelements, and to enhance characteristics of lowering noises and crosstalk by forming a photovoltaic film on a sapphire substrate, and electrically combining this film with control electrodes. CONSTITUTION:The intended optical switch is provided with a sapphire (alpha- alumina) substrate 21, two light guides 32 crossing each other made of a PLZT type thin film 31 formed on the substrate 21, 2 control electrodes 13 arranged on the guides 32 so as to set the electrode gap 131 having a constant space on the line bisecting the acuter intersecting angles of the intersecting point 33 of the two guides 32, and a buffer layer 14 lower in refractive index then the thin film 31, formed between the guides 32 and the electrodes 13. The light guides 32 are provided with protruded band-shaped parts 32B made of the thin film 31 on the surface of the film 31, a photovoltaic film 34 is formed on the substrate 21, and this film 34 is electrically combined with the electrodes 13.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a light-controlled optical switch. In particular, the present invention relates to the structure of a total reflection type optically controlled optical switch for thin film optical waveguides and its constituent materials.

Conventional Structure and Problems Conventionally, an optical material that utilizes a change in refractive index due to an electro-optic effect, such as LiNbO3 single crystal, has been used as a light-controlled optical switch. In this case, for example, as shown in FIG. 1, a Limb'5 single crystal substrate 11 with a polished surface
Ti metal is completely diffused in the surface layer to form optical waveguides 12 that cross each other, and the control electrode 13 is connected to the optical waveguides crossing Wj1 via a buffer layer 14 made of quartz glass.
6, and a photovoltaic film 16 is further provided, and this film 16
A full electric field 3, . The idea was to completely reflect the propagating light at the interface with the low refractive index layer to create an optical switch. That is, for example, the light traveling from β1 to β12 is changed from 11 to 15 by applying a voltage.

However, the amount of change Δn in the refractive index due to the electro-optic effect of LiNbO3 single crystal is at most about 10-4 in an electric field of I KV/mm. In the case of an optical switch, a voltage of 60 vB or higher is required for switching operation, making it difficult to drive at a low voltage. moreover,
In the structure shown in FIG. 1, heat treatment of 1000°C or more is required for T1 diffusion, and micro optical elements such as micro lenses,
It is difficult to form prisms and the like, and a large-area photovoltaic film 16 is required. Also, with this type of board,
It is difficult to monolithically integrate microscopic optical elements made of semiconductor elements, such as Sl, and there is a drawback that they are impractical for high-density optical devices, such as optical switches for optical devices and ICs.

In order to overcome the above drawbacks, the present inventors proposed a light-controlled optical switch made of a PLZT-based film with a large electro-optic effect. The α-alumina) substrate 21'' is covered with a protective coating 22, and grooves 23 intersecting with each other are formed in this protective coating 22.
A RS (raised 5 trip) type optical waveguide 24 is formed by embedding PLZT ceramics in this groove 23, and a control electrode 13 is further provided on the optical waveguide 24 via a buffer layer 14 made of quartz glass. , a structure in which a photovoltaic film 26 is further formed.

In the configuration shown in FIG. 2, the electro-optic effect of the optical waveguide 24 made of a PLZT thin film is large, so the optical switch can be driven at a low voltage. Integration of elements on the same substrate was realized. Furthermore, integration with semiconductor elements has become easier due to the use of a sapphire substrate. Furthermore, the relatively small photovoltaic film 26 can be provided on the same substrate, and the electrical connection between the film 26 and the electrode 13 is easy, providing a highly reliable optical switch. can.

The PLZT thin film optical thin film optically controlled optical switch having the configuration shown in Fig. 2 above can be used for normal light ON-OFF operation using two output optical waveguides W! when no electric field is applied. The output light intensity ratio of 12a, that is, the branching ratio, is about 10 dB, and the output light intensity ratio, that is, the extinction ratio of the same waveguide when an electric field is applied and when no electric field is applied, is about 10 dB. In terms of branching ratio and extinction ratio, crosstalk characteristics are not always good in signal transmission, especially in analog transmission. In addition, the optical waveguide with this structure is a multimode waveguide, and conversion to higher-order modes is likely to occur (the S/N ratio deteriorates and the transmission distance cannot be extended, which is a drawback.This point has been improved. In order to achieve this, if a single mode was used, the optical propagation loss would increase with the above structure, and this could not be achieved.

OBJECTS OF THE INVENTION An object of the present invention is to provide the structure and constituent materials of an optically controlled optical switch comprising a thin film optical waveguide. In particular, an object of the present invention is to provide the structure and constituent materials of a light-controlled optical switch made of a PLZT-based thin film. That is, the present invention improves the PLZT thin film optically controlled optical switch path structure and improves the extinction ratio and branching ratio.

Structure of the Invention The present invention provides a method for forming PLZ on a sapphire (α-alumina) substrate.
At least two optical waveguides made of T-based thin films that intersect each other are formed, electrode gaps are provided at regular intervals on the crossing paths, and the electrode gaps are all located on the bisector of the acute intersection angle of the optical waveguides. A control electrode is placed on the intersection of the optical waveguides so that the control electrode is
A buffer layer having a refractive index smaller than that of the PLZT-based thin film is provided, and the optical waveguide is formed on the surface of the PLZT-based thin film in a band-shaped manner.
It is constructed by forming a convex part (ridge part) made of a thin film of LZT thread, and further, a photovoltaic film is provided on the sapphire substrate, and the photovoltaic film is electrically coupled to a control electrode.

Description of Examples 77. -1. FIG. 3 shows a planar structure of a main part of an optical switch according to the present invention and a sectional structure of a main part of an optical waveguide constituting the optical switch. In the figure, at least two intersecting optical waveguides 32 made of a PLZT thin film 31 are completely formed on a sapphire (α-alumina) substrate 21, and electrode gaps are provided at regular intervals on the intersecting paths 33 of the optical waveguides. has 131,
The control electrode 13 is arranged so that the electrode gap 131 is located on the bisector of the acute intersection angle of the optical waveguide 32 and forms the gap 131 above the intersection 33 of the optical waveguide 32. A buffer layer 14 having a refractive index smaller than that of the PLZT thin film 31 is provided between the PLZT thin film 31 and the control electrode 13, and the optical waveguide 32 is formed on a part 32A of the PLZT thin film 31 and on the surface of this 321. PLZT
The photovoltaic film 34 is provided on the sapphire substrate 21, and the electromotive film 34 and the control electrode 13 are electrically coupled to each other.

The present inventors discovered that in the structure shown in FIG. 3, unlike the diffusion type waveguide in a conventional optical switch, the optical waveguide 32 made of a PLZT thin film and having the IJ solid portion 32B also has little mode conversion and optical propagation loss. We have found that there is no problem, and based on these findings, we have completely realized the optical switch according to the present invention.

That is, as shown in FIG.
Unlike the bO3 optical waveguide, the optical waveguide 32 is made of a PLZT thin film 31 with a thickness of 061 to 2 μm, which is normally used as an optical waveguide, and the width of the optical waveguide 32 is 3 to 30 μm, and the difference in film thickness between the ridge portion 32B and the peripheral portion, that is, the step height is 11. Jibu's PLZT
Multi-mode optical waveguide II with the structure of the entire thin film system! The present inventors have found that even if 8 is formed, there is no problem in mode conversion, and the optical propagation loss is less than 20 dB/CTL (laser light wavelength of 1.06 μm), making it suitable for practical use as a device.Based on these findings, An optical switch according to the present invention has been realized. It was confirmed that the branching ratio characteristic of this switch is 14 dB or more at a crossing angle of 2 degrees or more.

In this case, if the width of the optical waveguide 32 is less than 3 μm, the optical image 9 base
If the propagation loss exceeds 20 dB/cIn or exceeds 30 μm, the element size becomes large and is not practical. Further, when the film thickness is 1/1 or more of the portion having the step height portion 32Bt, higher order mode conversion increases and the features of the present invention become difficult to manifest. Furthermore, the optical waveguide 32 with the above structure eliminates the expansion of the optical waveguide seen in the T1-diffuse type LiNbO5 optical waveguide, and the step height can be as low as 500 nm, J or less, making it easy to form a planar configuration and making it possible to use a minute microlens. We also confirmed what can be done with the built-in.

As a result of investigating the structure of the control electrode 13 in detail, the inventors of the present invention found that it has the optimum dimensions.The light wave passes through the low refractive index layer under the gap due to the indentation, and when the diameter is 10 μm or more, the electric field is reduced. Since no light is applied to the air gap, the driving voltage becomes higher. In addition, the best extinction ratio was obtained when the length of the air gap 131 was in the shape of 10, -2 over the entire intersection of the optical waveguides 32, but if it was at least % of the length of the intersection, the intersection angle was 2°. It was confirmed that 14 dB or more was obtained and that it is practically useful.

Further, the present inventors have either formed the photovoltaic film 34 directly on the sapphire substrate 21'' and electrically coupled it to the control electrode 13, or formed the photovoltaic film 34 on the sapphire substrate 31 via an adhesive layer. It has been confirmed that almost no electrostatic or induced electrical noise is applied even when the electrodes are integrated and electrically connected to the control electrode 13, for example, by bonding A [wire]. Further, since the photovoltaic film 34 does not apply noise to the control electrode 13 and is easy to handle, it is sufficient if it is integrated with the sapphire substrate 21, and the arrangement is not limited to that shown in FIG. It has been confirmed that with this configuration, when the photovoltaic film 34 is irradiated with light sound and subjected to a switching operation, output light with a low noise level and excellent crosstalk characteristics can be obtained.

As a result of further detailed investigation of the constituent materials in this type of configuration, the present inventors found that when the PLZT yarn thin film 31 is formed using an ion bombardment deposition method, for example, a magnetron sputtering method, the electro-optical effect is large. We have discovered that a single compositional region exists, and based on this discovery we have found that a more effective optical switch can be obtained. That is, the present inventors determined that the molar ratio Pb/Ti of pb and Ti in the sputtering target composition was 0.65.
(Pb7/'Ti (LiNb in the range of 0,90
It was found that it has an electro-optical effect equivalent to or better than that of an O3 single crystal. Furthermore, the pb/Ti molar ratio is 0.7
(OPb/Ti < 0.66 or Pb/Ti which we found to have more than twice the electro-optic effect compared to Limb's single crystal when Pb/Ti (0.8))
0.9 o tr) is less than a LiNbO3 single crystal and is not desirable for the purpose of the present invention. In addition, in conventional ceramic materials, this 0.66〈Pb/Ti
(In the composition range of 0.90, no electro-optic effect was expected, and there was no measurement data.) The present inventors attempted to thin the film in the region including this composition range, and as shown in Fig. It was confirmed that the entire optical switch could be constructed using a large electro-optic effect that was not expected in the material, and that an optical switch with low driving voltage could be formed.

FIG. 4 shows the measured values of the electro-optic effect when the Pb/Ti ratio is changed. In the figure, the curve 41 is P
The dependence of the electro-optical effect on the Pb/Ti molar ratio when an electric field of 2Kv7'mm is applied to an LZT-based thin film is shown. This curve 41
For comparison, curve 42 shows the characteristics of LiNb05 single crystal. From the same figure, the Pb/T1 molar ratio is 0.65
(Pb/Ti (LiNbOx in the range of 0,90
When the optical switch according to the present invention is constructed with the above composition, a larger electro-optic effect can be obtained, and the photovoltaic film 3
When the control electrode 1 is irradiated with light and a predetermined voltage is generated, the control electrode 1
The multimode light was completely switched at 20 V with the gap 131 of No. 3 being 4 μm.

Figure 6 shows the actual measured values of the output light intensity when the applied voltage of the optical switch having the configuration shown in Figure 3 is varied. Conventionally, PLZT thin films have a dielectric constant that is much higher than that of LiNbO3 crystals (ε≧1oO). For example, the dielectric constant of a PLZT thin film with a composition of 2B10/1oo is approximately 200Q, and it was thought that an electric field would not be applied to the optical waveguide because a low dielectric constant material is normally used as the buffer layer. However, as shown in FIG. 6, the switching operation is performed at 20 V, and the operating voltage is lower than the operating voltage of 60 to 60 V of the T1 diffused LiNb03 optical waveguide optical switch with the same control electrode gap spacing.
It was confirmed that it is practically effective.

Furthermore, the present inventors have discovered that the PtZT thin film 310111 plane is effective as an optical switch if it is parallel to the substrate surface. That is, it has been discovered that the PLZT thin film 31 has a large electro-optic effect regardless of the orientation within the main plane of the control electrode 13. Therefore, the optical waveguide 32 can be formed in any direction within the main plane, and Li
It has the advantage of being much easier to form than an N'bO3 single crystal substrate.

Furthermore, the present inventors have found that oxides such as mental oxide, titanium oxide, zirconium oxide, and zinc oxide, or sulfides such as arsenic sulfide and zinc sulfide are effective as the buffer layer 14. It was confirmed that these materials have good adhesion to the PLZT thin film 31 of 75 degrees (14 degrees) and can be formed without increasing light propagation loss.Tantalum oxide in particular is difficult to form crystal nuclei even on the PLZT thin film 31. It is an amorphous film with excellent light propagation characteristics and is transparent from visible light to infrared light.It also has a relatively large refractive index of 2.1 and a dielectric constant of about 2o, so an electric field is applied to a PLZT thin film with a high dielectric constant. All confirmed to be valid.

Specific Example 1 A surface-polished sapphire (α-alumina) 0-sided substrate (0001) i was used as the substrate 21, and the sapphire 0-sided substrate 21 was coated with a thickness of 0 by high-frequency magnetron sputtering.
．． A 4 μm thick PLZT thin film 31 was deposited. In this case, the composition of the target is PLZT (2810/100),
Sputter target diameter φ100mm, substrate temperature 680mm
℃, and the sputtering power was 2o○W. Deposited PLZ
The structure of the T-based thin film is a single crystal with (111) plane, and the refractive index is 2.6 (Ha-N6 laser 0.6328 μm)
Met.

Next, the surface of this PLZT-based layer film 31 is masked with photoresist (e.g., AZ1450B) 167 so that the optical waveguide width is 20 μm and the intersection angle is 2°, and the PLZT-based thin film 31 is subjected to ion beam etching. For example, etching was performed to a depth of 66 nm using a method. By processing in this way, a waveguide 32 having a threaded portion 32B is formed, and light can be confined and propagated in the waveguide 32 having an IJ threaded portion 32Bfz. Next, a Ta205 film was deposited as a buffer layer 14 on the PLZT thin film 31 by the magnetron snog method.The deposited Ta205 film was amorphous and had a refractive index of 2.1 (He In the above configuration, for example, He-
The photovoltaic film 34 is irradiated with Ne laser light, and the output voltage is 20
It was confirmed that the switching operation was performed on the VIJ.

In addition, even if the above optical switch is installed in a metal container and light is irradiated onto the photovoltaic film through an optical fiber, the switching operation will be the same, and by improving the branching ratio and extinction ratio, it will be able to perform the same switching operation.
It was confirmed that the O3 optical waveguide optical switch had poor noise resistance and crosstalk characteristics.

Effects of the Invention As described above, in the optically controlled optical switch according to the present invention, the photodetecting elements, which could not be formed in the conventional T1 diffused optical waveguide optical switch, can be completely integrated, and micro optical elements can also be easily formed. Furthermore, although it is a multi-mode device, it has low noise and excellent crosstalk characteristics, and its industrial value is outstanding.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing the structure of a conventional optically controlled optical switch, and Fig. 2 is a perspective view showing the structure of a conventional optically controlled optical switch.
FIG. 6 is a diagram showing the change in birefringence when a voltage of V/mm is applied, and FIG. 6 is a diagram showing the switching characteristics of the optically controlled optical switch according to an embodiment of the present invention. 175 13... Control electrode, 14... Buffer layer, 21... Sapphire substrate, 31...
・PLZT thin film, 32... Optical waveguide, 32B
・・・・・・Ridge part (convex part), Fig. 1 15 Fig. 2 14 '25 Fig. 3 Fig. 4 pb71-,

Claims (1)

[Scope of Claims] (1) at least two mutually intersecting optical waveguides made of a sapphire (α-alumina) substrate and a PLZT thin film provided on the sapphire substrate; electrode gaps at regular intervals; a control electrode disposed on the intersection of the optical waveguide such that the electrode gap is located on a bisector of an acute intersection angle of the waveguide; and the optical waveguide and the control electrode. a buffer layer having a refractive index smaller than that of the PLZT thin film provided between the two, and the optical waveguide is electrically coupled to the control electrode of the PLZT thin film. Switch 0 (2) In the PLZT thin film, the moles of pb and Ti are 27
51. The optically controlled optical switch according to claim 1, wherein the ratio Pb/Ti is in the range of 0.65 Pb/Ti≦0.90.