JP3725647B2 - Light switch - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical switch that is Ru applied in such fields as communications and information processing and machinery.
[0002]
[Prior art]
As a method for modulating guided light of an optical waveguide, a method using an electro-optic effect, an acousto-optic effect, a magneto-optic effect, a thermo-optic effect, or a nonlinear optical effect is known. Among these, those other than the thermo-optical effect can be used only in specific optical crystals such as lithium niobate, lithium tantalate, and magnetic garnet, which are known to have large effects. However, the refractive index of these optical crystals is 2 or more, which is considerably higher than the refractive index of 1.54 used for optical fibers. For this reason, a device manufactured using these optical crystals has a low light coupling efficiency when connected to an optical fiber, and a method capable of light modulation even with a glassy material that can be easily connected to the optical fiber is desired. It was.
[0003]
The thermo-optic effect is intended to control the guided light by utilizing the change in the refractive index of the material due to heat, and can be used not only for specific crystals but also for various waveguide materials including glass. In light modulation using the thermo-optic effect, a metal thin film heater is attached to a part of the optical waveguide via a dielectric layer having a low dielectric constant, and the refractive index is changed by applying heat to the optical waveguide. At this time, if a metal thin film is directly applied on the optical waveguide, the propagation loss is remarkably increased. Therefore, a dielectric layer having a low dielectric constant must first be applied on the optical waveguide, and a metal thin film should be placed thereon. . As the dielectric layer having a low dielectric constant, SiO ₂ glass is usually used and is applied with a thickness of several microns. This method has a problem that it takes time in seconds and poor responsiveness because it takes the mechanism of heating the metal thin film heater by applying electric power and then transferring heat to the optical waveguide to change the refractive index. is there.
[0004]
The present inventors have proposed a flexible inorganic / organic hybrid (Japanese Patent Application No. 8-253473) and an optical waveguide using an inorganic / organic hybrid (Japanese Patent Application No. 7-175882, Japanese Patent Application No. 8-68111). ing. Inorganic / organic hybrid optical waveguides have good light transmission characteristics, can be manufactured at a lower temperature than glass, can be used to manufacture new devices containing organic dyes, and are flexible, compared to organic polymers It has features such as being heat resistant and being able to adjust the refractive index to the optical fiber because the refractive index can be controlled in a wide range by a combination of inorganic and organic compositions. However, the inorganic / organic hybrid is a material that does not exhibit the electro-optic effect, the acousto-optic effect, and the magneto-optic effect, and cannot perform light modulation using these effects. Light modulation using the thermo-optic effect is possible, but this method is a modulation method with poor responsiveness as described above. For this reason, an optical modulation method having a quick response has been desired for an optical waveguide made of an inorganic / organic hybrid.
[0005]
[Problems to be solved by the invention]
The present invention relates to the fields of communication, information processing, machinery, etc. by forming an optical waveguide using a material having a low Young's modulus, such as an inorganic / organic hybrid, a transparent, thin film, and changing the refractive index at high speed by a stress application mechanism. in the application, and it is easy to connect to an optical fiber, there is provided a high-speed optical switch.
[0006]
[Means for Solving the Problems]
The problems are as follows: (1) a dielectric substrate, an optical waveguide formed on the substrate with a Young's modulus of 0.1 to 700 MPa , made of a transparent, thin filmable material and having a thickness of not less than 5 μm and a cutoff length ; An optical switch having a mechanism for applying stress to compress the waveguide;
(2) The switch according to (1), wherein the material having a Young's modulus of 0.1 to 700 MPa , transparent, and thinnable is an inorganic / organic hybrid,
(3) The optical switch according to (2), wherein the inorganic / organic hybrid comprises a metal alkoxide and a terminal silanol polydimethylsiloxane,
(4) The optical switch according to (1), (2) or (3), wherein the optical waveguide is a three-dimensional optical waveguide;
(5) The thickness of the optical waveguide is slightly larger than the cut-off length, and the mechanism for applying a stress that compresses the waveguide can make the thickness of the optical waveguide smaller than the cut-off length. This is achieved by the optical switch according to any one of (1) to (4).
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The present inventors have invented that an optical waveguide having a low Young's modulus produced on a dielectric substrate, which is transparent and can be thinned can be modulated by applying stress.
The optical switch according to the present invention requires a substrate for supporting the optical waveguide. Substrate materials are largely classified into dielectrics (insulators), semiconductors, and metals, but semiconductors and metals cannot be used because they increase the propagation loss of the optical waveguide. Examples of the dielectric substrate include optical crystals such as glass, inorganic / organic hybrid, and lithium niobate / KTiOPO ₄ .
[0008]
Examples of the optical waveguide manufactured on the dielectric substrate include a planar waveguide formed on the entire surface of the substrate and a three-dimensional waveguide processed so that light propagates through a specific path. The three-dimensional optical waveguide is manufactured by transferring a waveguide pattern by photolithography. Since the three-dimensional optical waveguide allows light to propagate along a predetermined path, the degree of freedom in device fabrication is greater than that of a planar waveguide.
The optical waveguide forming material needs to have a low Young's modulus so that the optical waveguide can be deformed with an appropriate stress and optically modulated. The reason why optical modulation is possible by deforming the optical waveguide will be described below. Since the same principle is applied to the optical waveguide whether it is a planar waveguide or a three-dimensional waveguide, the planar waveguide will be described.
[0009]
The effective refractive index of a two-dimensional optical waveguide fabricated on a dielectric substrate having a constant refractive index is determined by the thickness of the optical waveguide and the refractive index of the material forming the optical waveguide. The effective refractive index of the optical waveguide takes a value between the refractive index of the substrate and the refractive index of the material forming the optical waveguide. The effective refractive index increases as the thickness increases, and asymptotically approaches the refractive index of the optical waveguide forming material. To do. On the other hand, as the thickness decreases, the effective refractive index decreases. When the thickness reaches a certain thickness (cutoff length), the effective refractive index becomes the same value as the refractive index of the substrate. Cannot propagate.
[0010]
In an optical waveguide manufactured using a material having a low Young's modulus, the thickness of the optical waveguide layer is changed by applying a weight to the optical waveguide portion, whereby the effective refractive index can be changed. Based on this change in effective refractive index, light modulation can be performed by changing the light intensity and phase. Since elastic deformation with respect to stress shows high responsiveness, it is possible to perform modulation that is 6 digits or more faster than thermal modulation. The range of Young's modulus for performing such modulation is 0.1 MPa to 700 MPa, preferably 1 MPa to 500 MPa. As such a low Young's modulus material, isoprene-based rubber, butadiene-based rubber, silicone rubber and the like are known.
[0011]
The material forming the optical waveguide must be transparent to light in the wavelength region used as an optical switch . For example, when a YAG laser is used as the light source, it is desired to have a high transmittance of 99% or more for light with a wavelength of 1064 nm. Conventionally, various rubbers known as low Young's modulus materials are translucent to opaque because fillers are dispersed in order to maintain strength. For this reason, it is not suitable for optical waveguide materials.
[0012]
In order to propagate light as an optical waveguide, it is necessary to form a thin film. The film thickness needs to be larger than the cut-off length without applying stress. When an optical waveguide material is formed on a substrate, if the thickness is smaller than a certain thickness, light cannot be propagated, but this thickness is a cut-off length. As the film thickness increases, the waveguide mode becomes multimode, but there is no problem in principle. However, the change in the effective refractive index caused by the change in the film thickness is the maximum at the moment when the cutoff length is exceeded, and the change in the effective refractive index becomes smaller as the film thickness increases. The manner of this change is as shown in FIG. 2 and is not linear. Therefore, it is desirable to detect the change in the refractive index by forming the waveguide in a thickness up to a region where the amount of change is relatively large, and reducing the thickness by stress. If the thickness is too large, the change in the effective refractive index caused by the change in the film thickness due to stress becomes small, so that a film thickness of up to about 5 microns is generally appropriate.
[0013]
Examples of the stress applying mechanism include a mechanical method of applying a weight with a weight or compressing with a finger, an electrical method using a piezoelectric element, and the like.
The optical device for modulating by adding stress to such an optical waveguide, an optical switch and the like. The optical switch uses turning off the light by thinning the optical waveguide to a thickness below the cut-off length due to stress, and turning on the light by removing the stress and returning the optical waveguide layer to its original thickness. Can be produced .
[0014]
As an optical waveguide material having a low Young's modulus and being transparent and capable of being thinned, for example, an inorganic / organic hybrid material can be cited. The optical waveguide by the inorganic / organic hybrid according to the present invention can be synthesized from, for example, metal alkoxide and terminal silanol polydimethylsiloxane. In particular, when a terminal silanol polydimethylsiloxane having a molecular weight of 400 to 4500 is used, a transparent material having a low Young's modulus can be obtained. Various alkyl alkoxysilanes may be used in place of polydimethylsiloxane. The alkoxide constituting the inorganic / organic hybrid elastomer is not particularly limited, and examples thereof include methoxide, ethoxide, propoxide, butoxide and the like. Moreover, the alkoxide derivative which substituted a part of alkoxy group with (beta) -diketone, (beta) -ketoester, alkanolamine, alkyl alkanolamine, organic acid, etc. can also be used.
[0015]
【Example】
Example 1 Water is added to a stirred solution of ethanol, terminal silanol polydimethylsiloxane (molecular weight 1500), Ta (OC ₂ H ₅ ) ₅ , and ethyl acetoacetate to prepare a sol. The molar ratio of terminal silanol polydimethylsiloxane, Ta (OC ₂ H ₅ ) ₅ , ethyl acetoacetate, and water is 0.1: 1: 2: 2. This sol is applied on a glass substrate having a refractive index of 1.52. When heat-treated at 300 ° C. for 20 minutes and measured with an ellipsometer, an optical waveguide layer made of an inorganic / organic hybrid having a thickness of 0.7 microns and a refractive index of 1.663 was obtained. The wavelength at which the refractive index was measured is 663 nm. A stress having a constant bottom area was placed on the optical waveguide to apply stress. The stress required to reduce the thickness by 20% was 5.8 g / mm ² . The Young's modulus was 282 MPa. FIG. 2 shows the calculation results of the thickness and effective refractive index of the optical waveguide. The cut-off length was 0.2 microns, and light did not propagate when the waveguide layer was made thinner than 0.2 microns due to stress.
[0016]
(Example 2) Water is added to a stirred solution of ethanol, dimethyldiethoxysilane, Ti (OC ₂ H ₅ ) ₄ , and acetylacetone to hydrolyze to prepare a sol. The molar ratio of dimethyldiethoxysilane, Ti (OC ₂ H ₅ ) ₄ , acetylacetone, and water is 10: 1: 2: 2. This sol is applied on a glass substrate having a refractive index of 1.52. When heat-treated at 300 ° C. for 20 minutes and measured with an ellipsometer, an optical waveguide layer made of an inorganic / organic hybrid having a thickness of 1.2 microns and a refractive index of 1.580 was obtained. Young's modulus was 2.4 Mpa. The optical waveguide layer patterned by dry etching was etched to produce a ridge-type three-dimensional optical waveguide having a width of 12 microns and a thickness of 1.2 microns. The cut-off length was 0.6 microns.
[0017]
In FIG. 1, the optical waveguide 4 is branched into a pressure application unit 5 and a no-load unit 6 on the way. The pressure application unit 5 and the no-load unit 6 are exactly the same optical waveguide having the same width and thickness. Applying pressure to one of the branches to propagate light, the other to propagate light with no load, and combining the light from the two branch waveguides cancels the refractive index change due to ambient effects such as temperature changes Therefore, only the change in effective refractive index due to pressure appears in the phase shift of the light wave, and the light intensity decreases. The stress applying unit 7 applies stress by placing a weight. A laser beam 3 mW of 633 nm is input from the incident laser light source 2. By placing a weight on the optical waveguide to which pressure is applied so as to apply a pressure of 12 g / mm ² , the emitted light intensity is 0, and by removing the pressure, the emitted light intensity of 2.4 mW can be obtained by the photodetector 3. did it. This functions as an optical switch.
[0019]
【The invention's effect】
The present invention provides an optical switch using a new optical modulation method that is easy to connect to an optical fiber and has a quick response by forming an optical waveguide made of a material having a low Young's modulus, a transparent, and thin film. Is. The present invention, so far even in high-speed inorganic-organic hybrid that could not light modulation can be manufactured because optical switch optical modulation becomes possible.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an optical switch according to an embodiment of the present invention.
FIG. 2 is a mode dispersion curve of an optical waveguide layer made of an inorganic / organic hybrid film formed on a glass substrate. Only the basic mode is shown.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Incident laser light source 3 Photodetector 4 Optical waveguide 5 Pressure application part 6 No load part 7 Stress application part

Claims (5)

A dielectric substrate, an optical waveguide formed on the substrate, having a Young's modulus of 0.1 to 700 MPa , made of a transparent, thin filmable material and having a thickness of not less than a cutoff length and not more than 5 microns, and stress for compressing the waveguide An optical switch having a mechanism for adding. 2. The optical switch according to claim 1, wherein the material having a Young's modulus of 0.1 to 700 MPa , transparent, and thin filmable is an inorganic / organic hybrid. 3. The optical switch according to claim 2, wherein the inorganic / organic hybrid comprises a metal alkoxide and a terminal silanol polydimethylsiloxane.   The optical device according to claim 1, wherein the optical waveguide is a three-dimensional optical waveguide. The thickness of the optical waveguide is slightly larger than a cut-off length, and a mechanism for applying a stress for compressing the waveguide is capable of making the thickness of the optical waveguide smaller than the cut-off length. The optical switch according to any one of 1 to 4.

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