JP2011102891A - Optical functional waveguide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a miniaturized and highly functionalized optical functional waveguide using a harmless lithium niobate substrate without requiring high processing technology. <P>SOLUTION: The optical functional waveguide includes the lithium niobate substrate, a stripe-shaped different material optical waveguide formed on the lithium niobate substrate by using a material different from that of the lithium niobate substrate, one of an in-substrate optical waveguide part formed on a surface side opposed to the different material optical waveguide of the lithium niobate substrate by leakage of light transmitted in the different material optical waveguide or an in-substrate optical waveguide which is formed on a surface side opposed to the different material optical waveguide and in which Ti or a proton is introduced and first and second electrodes applying a modulated voltage between the different material optical waveguide and either one of the in-substrate optical waveguide part or the in-substrate optical waveguide. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical functional waveguide. For example, the optical waveguide can be reduced in size by combining an in-substrate optical waveguide portion formed on a lithium niobate substrate or an in-substrate optical waveguide and an optical waveguide made of a different material. In addition, the present invention relates to a configuration for achieving high functionality.

Conventionally, an optical waveguide is formed by diffusing Ti or protons in a LiNbO ₃ (lithium niobate) substrate which is an electro-optic crystal, and a voltage is applied to the optical waveguide to constitute an optical modulator or an optical switch. This optical modulator and optical switch are used in an optical communication system.

In this case, since almost 100% of the light propagating through the Ti-diffused LiNbO ₃ optical waveguide propagates through the Ti-diffused LiNbO ₃ optical waveguide, the group velocity of light is constant regardless of the element structure. Therefore, by controlling the shape and position of the electrode through which the microwave propagates, the propagation velocity of the microwave and the group velocity of the propagation light are matched.

In such a Ti-diffused LiNbO ₃ optical waveguide having a flat structure, it is difficult to concentrate and apply an electric field for inducing an electro-optic effect to the optical waveguide. Thus, it has been proposed to form a stripe-shaped ridge on the LiNbO ₃ substrate and use this ridge as an optical waveguide (see, for example, Patent Document 1).

Further, the Ti-diffused LiNbO ₃ optical waveguide has a large minimum bending radius of about 5 mm, so that it is difficult to form a multistage optical circuit. Therefore, in order to reduce the minimum bending radius of the waveguide, it has been studied to deepen a trench near the Ti-diffused LiNbO ₃ optical waveguide to enhance the optical confinement effect.

However, LiNbO ₃ is a material that is very difficult to perform vertical etching, and it is actually very difficult to produce the above-mentioned ridges and deep grooves.

Therefore, regarding the latter problem concerning the minimum bending, it has been proposed to stack arsenic sulfide (As ₂ S ₃ ) on a substrate on which a Ti-diffused LiNbO ₃ optical waveguide is formed to reduce the bending radius (for example, Non-patent document 1).

  On the other hand, in a silica-based optical waveguide, it has been proposed to provide a SiN optical waveguide on a ridge-shaped silica-based optical waveguide in order to realize a small bending waveguide (for example, see Non-Patent Document 2). .

Japanese Patent Application Laid-Open No. 11-326853

M.M. E. Solmat, et al. "Compact Bends for Achieving Higher Integration Densities for LiNbO3 Waveguides", IEEE Photon. Thetechnol. Lett. , Vol. 21, no. 9, pp. 557-559 (2009) Y. Kokubun, et al. "Vertically Coupled Waveguide Bends and Branches for Photonic Gate-Array Technology Usage Cross-Grid Architecture", Jpn. J. et al. appl. Phys. , Vol. 43, no. 12, pp. 8080-8084 (2004)

As described above, LiNbO ₃ is a material that is extremely difficult to etch vertically, and it is difficult to produce ridges and deep grooves, so as an actual device, the electric field is still concentrated on the optical waveguide. There is a problem that can not be.

The means for matching the group velocity of propagating light propagating through the Ti-diffused LiNbO ₃ optical waveguide with the propagation velocity of the applied microwave is the electrode shape and position through which the microwave propagates, and the degree of freedom in device design is small There is a problem.

  In the case of Non-Patent Document 1, arsenic sulfide is a highly toxic material, and a toxic arsenic oxide gas is generated when ignited. Therefore, there is a problem that an actual optical communication system cannot be configured with this material system.

Further, in the case of the above-mentioned Non-Patent Document 2, since SiO ₂ and SiN used as materials do not have an electro-optic effect effectively, an optical modulation element by voltage application or an optical switch by voltage application is configured. Can not do it. That is, there is a problem that such a configuration cannot be incorporated as an optical modulation element or an optical switch in the current optical communication system.

  Therefore, an object of the present invention is to reduce the size and increase the functionality of an optical functional waveguide that uses a harmless lithium niobate substrate without requiring advanced processing techniques.

  (1) In order to solve the above-described problems, the present invention provides an optical functional waveguide, which is made of a material different from the lithium niobate substrate on the surface of the lithium niobate substrate and the lithium niobate substrate. The formed striped dissimilar material optical waveguide and the in-substrate optical waveguide formed by leakage of light propagating through the dissimilar material optical waveguide on the surface side of the lithium niobate substrate facing the dissimilar material optical waveguide Any one of a portion or an optical waveguide in the substrate into which Ti or protons are formed, which is formed on the surface facing the different material optical waveguide, the optical waveguide portion in the substrate, or the optical waveguide portion in the substrate or in the substrate A first electrode and a second electrode for applying a modulation voltage to either one of the optical waveguides are provided.

  As described above, either the in-substrate optical waveguide portion formed on the lithium niobate substrate having an excellent electro-optic effect or the in-substrate optical waveguide introduced with Ti or proton formed on the surface side facing the optical waveguide of the different material. On the other hand, a small-sized and high-speed optical functional waveguide can be realized by combining a dissimilar material optical waveguide excellent in processability.

  (2) Further, in the above (1), the present invention provides one of the first electrode and the second electrode on the top surface of the dissimilar material optical waveguide, and the other of the first electrode and the second electrode. Is provided on the back surface of the lithium niobate substrate.

  Thus, by arranging the first electrode and the second electrode, it is possible to reliably apply the modulation voltage to the intra-substrate optical waveguide portion or the intra-substrate optical waveguide. In this case, since a voltage is applied in the vertical direction, that is, in the Z direction, it is desirable to use a Z-cut lithium niobate substrate as the lithium niobate substrate.

  (3) Further, in the above (1), the present invention provides the first electrode and the second electrode so as to face each other on the surface of the lithium niobate substrate with the dissimilar material optical waveguide interposed therebetween.

  As described above, by arranging the first electrode and the second electrode, impedance matching can be achieved without depending on the thickness of the lithium niobate substrate. In this case, since a voltage is applied in the lateral direction, it is desirable to use an X-cut lithium niobate substrate in which the lateral direction is the Z axis.

(4) Further, in the above (1), the present invention provides one of the first electrode and the second electrode on the top surface of the lithium niobate substrate, and the other of the first electrode and the second electrode. The dissimilar material optical waveguides are provided so as to face each other.
When an X-cut lithium niobate substrate is used, such an electrode arrangement may be adopted.

  (5) Further, in the above (3) or (4), the present invention provides a lithium niobate substrate having a pair of grooves along both side surfaces of the dissimilar material optical waveguide, and the dissimilar material optical waveguide. An electrode is provided in the groove so as to be opposed to each other.

  Thus, by providing a groove in the lithium niobate substrate and providing an electrode in the groove so as to face each other with the optical waveguide of the different material interposed therebetween, an optical waveguide portion or substrate in the substrate having a greater electro-optic effect can be obtained. Application to the inner optical waveguide can be ensured.

  (6) The present invention also relates to an optical functional waveguide, which is a lithium niobate substrate and a plurality of lithium niobate optical waveguides formed by introducing either Ti or proton into the lithium niobate substrate. And a dissimilar material optical waveguide for coupling formed of a material different from the lithium niobate substrate provided to optically couple the plurality of lithium niobate optical waveguides on the surface of the lithium niobate substrate. Have.

  In this way, by combining a plurality of lithium niobate optical waveguides with dissimilar material optical waveguides having excellent shaping workability, optical coupling in a small area becomes easy, thereby reducing the size of the optical functional waveguide. It becomes possible.

(7) Moreover, this invention makes the edge part of the side couple | bonded with the said lithium niobate optical waveguide of a different material optical waveguide in said (6) taper shape.
In this way, by making the end of the optical waveguide of the dissimilar material to be coupled with the lithium niobate optical waveguide tapered, the beam diameter at the tapered end can be enlarged, thereby increasing the optical coupling efficiency. be able to.

(8) Further, according to the present invention, in the above (7), at least one end portion of the dissimilar material optical waveguide constitutes a branched waveguide.
Thus, by using at least one end of the different-material optical waveguide as a branching waveguide, it is possible to easily realize downsizing of the duplexer or the multiplexer.

(9) Further, according to the present invention, in any one of the above (1) to (8), the dissimilar material optical waveguide is made of Si, SiON, SiN, TiO ₃ , or Ta ₂ O ₃ .
By using a material having a refractive index higher than that of lithium niobate as the dissimilar material optical waveguide, an optical functional waveguide having a smaller cross-sectional size can be formed.

(10) Further, according to the present invention, in the above (9), the different-material optical waveguide is composed of a plurality of optical waveguide elements having different compositions.
In this way, the refractive index can be changed stepwise by configuring the optical waveguide of different materials with a plurality of optical waveguide elements having different compositions. As a result, reflection loss can be reduced, and efficient optical transmission becomes possible.

(11) Further, according to the present invention, in the above (10), a rare earth element is added to at least a part of the optical waveguide element.
In this way, a gain waveguide can be configured by adding a rare earth element such as Er or Pr to at least a part of the optical waveguide element, thereby further increasing the functionality of the Mach-Zehnder type interference element or the like. Is possible.

  According to the disclosed optical functional waveguide, a small and highly functional optical functional waveguide can be realized by using a harmless lithium niobate substrate without requiring an advanced processing technique.

1 is a configuration explanatory diagram of an optical functional waveguide according to an embodiment of the present invention. FIG. It is a conceptual perspective view of a coupling portion of the optical functional waveguide and Ti diffusion LiNbO ₃ waveguide. 1 is a configuration explanatory diagram of an optical functional waveguide according to a first embodiment of the present invention. FIG. It is a structure explanatory drawing of the optical function waveguide of Example 2 of this invention. FIG. 6 is a configuration explanatory diagram of an optical functional waveguide according to a third embodiment of the present invention. It is a conceptual sectional view of the direction perpendicular to the optical axis of the optical function waveguide of Example 4 of the present invention. It is a conceptual sectional view of the direction perpendicular to the optical axis of the optical function waveguide of Example 5 of the present invention. It is a structure explanatory drawing of the optical function waveguide of Example 6 of this invention. FIG. 10 is a configuration explanatory diagram of an optical functional waveguide according to a seventh embodiment of the present invention. It is explanatory drawing of an example of the taper waveguide part in Example 6 and Example 7 of this invention. It is explanatory drawing of the other example of the taper waveguide part in Example 6 and Example 7 of this invention. It is a structure explanatory drawing of the optical function waveguide of Example 8 of this invention. It is a notional top view of the optical function waveguide of Example 9 of the present invention.

Here, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is an explanatory diagram of a configuration of an optical functional waveguide according to an embodiment of the present invention, FIG. 1 (a) is a conceptual perspective view, and FIG. 1 (b) is a conceptual front view. As shown, via the dielectric film 2 on the LiNbO ₃ substrate 1, Si, SiON, SiN, TiO _2, or to form a different material optical waveguide 3 consisting of _Ta 2 _{O 3,} the different material waveguide 3 is covered with a dielectric film 4. The dielectric film 2 and the dielectric film 4 are provided in order to prevent migration of the electrode material, and a material different from the material constituting the dissimilar material optical waveguide 3 such as SiO ₂ is used. The dielectric films 2 and 4 are not essential.

A first electrode 5 is formed on the top surface of the different material optical waveguide 3 via a dielectric film 4, while a second electrode 6 is provided on the back surface of the LiNbO ₃ substrate 1. A microwave is applied between the two electrodes 6. In this case, the first electrode 5 and the second electrode 6 have a thickness, a width, or the like so that the group speed of the laser light propagating in the dissimilar material optical waveguide 3 and the propagation speed of the applied microwave coincide with each other. Set the shape.

Accordingly, the voltage is longitudinal, i.e., because they are applied to the Z-direction, in order to take full advantage of the electro-optical effect having the LiNbO _3, it is desirable to use a Z-cut LiNbO ₃ crystal as a LiNbO ₃ substrate 1. However, although the effect is inferior, it does not prevent the use of the X-cut LiNbO ₃ crystal.

When laser light is incident on the dissimilar material optical waveguide 3, part of the laser light leaks to the LiNbO ₃ substrate 1 side, and the surface side of the LiNbO ₃ substrate 1 facing the dissimilar material optical waveguide 3 becomes the in-substrate optical waveguide portion 7. Propagates laser light. At this time, the group velocity of the laser light propagating in the different material optical waveguide 3 can be controlled by the shape of the different material optical waveguide 3. Therefore, the degree of freedom in design when the group velocity of the laser light propagating in the different material optical waveguide 3 and the propagation velocity of the applied microwave are matched is increased. Here, the in-substrate optical waveguide portion formed by leakage of light propagating through the different material optical waveguide 3 is used, but Ti or proton is introduced on the surface side facing the different material optical waveguide 3. Then, an in-substrate optical waveguide may be formed.

  The arrangement of the first electrode 5 and the second electrode 6 is not limited to the arrangement shown in the figure, and the first electrode 5 and the second electrode 6 are opposed to each other with the optical waveguide 3 of the different material interposed therebetween. May be provided. Alternatively, the first electrode 5 may be provided on the top surface of the dissimilar material optical waveguide 3, and the two second electrodes 6 may be provided at positions facing each other with the dissimilar material optical waveguide 3 interposed therebetween to form a coplanar transmission line. .

Further, when the first electrode 5 and the second electrode 6 are provided at positions opposed to each other with the different material optical waveguide 3 interposed therebetween, or the two second electrodes 6 are opposed to each other with the different material optical waveguide 3 interposed therebetween. When provided at the position, grooves may be provided along both sides of the dissimilar material optical waveguide 3 of the LiNbO ₃ substrate 1, and electrodes may be arranged in the grooves. As a result, the electrode is positioned on the side surface of the in-substrate optical waveguide portion 7, so that the electric field can be concentrated and applied to the in-substrate optical waveguide portion 7 having the electro-optic effect.

Figure 2 is a conceptual perspective view of a coupling portion of the optical functional waveguide and Ti diffusion LiNbO ₃ waveguide shown in FIG. 1, Ti-diffused LiNbO ₃ waveguide formed by diffusing Ti into the LiNbO ₃ substrate 1 A tapered portion 9 is provided at the end portion of the optical waveguide 3 of the different material that is coupled to 8. The length of the taper part 9 shall be 30 micrometers-500 micrometers.

  The taper portion 9 may be a taper portion where the width of the striped waveguide changes, or a taper portion where the thickness changes, as shown in the figure. Further, it may be a minute division mode conversion waveguide in which the line / space ratio of the line & space pattern is gradually reduced.

Alternatively, the dissimilar material optical waveguide 3 may be curved and the two Ti-diffused LiNbO ₃ waveguides 8 may be optically coupled. In this case, since the dissimilar material optical waveguide 3 having excellent workability is used to form a ridge shape, the two Ti-diffused LiNbO ₃ waveguides 8 can be optically coupled by a curved portion having a smaller curvature radius. Thus, the optical functional waveguide can be reduced in size.

  Furthermore, the different material optical waveguide 3 may be composed of a plurality of different material optical waveguide elements having different compositions. For example, when the different material optical waveguide 3 is formed of SiON, the composition ratio of Si is increased. As a result, the refractive index can be increased. Thereby, since the change of a refractive index can be made in steps, reflection loss can be reduced.

Also, different materials waveguide 3 when composed of SiON or SiO _2, rare earth element SiON or SiO _2, for example, constitute a gain waveguide by doping Er (erbium) and Pr (praseodymium), etc. Also good.

Next, with reference to FIG. 3, the optical functional waveguide of Example 1 of this invention is demonstrated. FIGS. 3A and 3B are configuration explanatory views of the optical functional waveguide according to the first embodiment of the present invention, FIG. 3A is a conceptual perspective view, and FIG. 3B is a conceptual view in a direction perpendicular to the optical axis. It is sectional drawing. On the Z-cut LiNbO ₃ substrate 11, for example, a SiO ₂ buffer layer 12 having a thickness of, for example, 100 nm is formed by a CVD method, and then a polycrystalline Si layer having a thickness of 400 nm or less, for example, 300 nm is formed. .

Next, the polycrystalline Si layer is etched to have a width of 400 nm or less and 300 nm, for example, to form a striped Si waveguide 13 having a cross section of 300 nm × 300 nm. Next, the SiO ₂ buffer layer 14 having a thickness of, for example, 100 nm is formed again by the CVD method. Next, an Au upper electrode 15 is formed on the top of the Si waveguide 13, and an Au lower electrode 16 is formed on the back surface of the Z-cut LiNbO ₃ substrate 11.

  Here, the Au lower electrode 16 is grounded, and a high frequency signal of 10 GHz, for example, is applied to the Au upper electrode 15 to operate as a high-speed optical phase modulator. Further, since the cross-sectional size of the Si waveguide 13 is 300 nm square, which is equal to or less than 400 nm square, the laser light propagates through the Si waveguide 13 in a single mode.

Note that the thicknesses of the Au upper electrode 15 and the Au lower electrode 16 are designed so that the input impedance including the thickness of the Z-cut LiNbO ₃ substrate 11 matches, for example, a set 50Ω. The length along the optical axis of the optical phase modulator is, for example, 8 mm.

In the first embodiment, part of the laser light input to the Si waveguide 13 leaks to the Z-cut LiNbO ₃ substrate 11 side, and a part of the surface of the Z-cut LiNbO ₃ substrate 11 is part of the in-substrate optical waveguide. Propagate as 17. Therefore, the high frequency signal applied to the Au upper electrode 15 is concentrated and applied to the in-substrate optical waveguide portion 17 having the electro-optic effect.

  Further, in the optical functional waveguide of the first embodiment, the group speed of the propagating light can be changed by changing the shape of the Si waveguide 13, so that the degree of freedom in design increases and the speed matching between the propagating light and the microwave is achieved. Becomes easier.

  When this optical functional waveguide is connected to various optical functional circuits in multiple stages, the Si waveguide may be extended to form a bent waveguide. In that case, since the relative refractive index difference can be increased in the Si waveguide, a bending waveguide having a radius of curvature of 10 μm or less can be formed.

Next, with reference to FIG. 4, the optical functional waveguide of Example 2 of this invention is demonstrated. 4A and 4B are configuration explanatory views of an optical functional waveguide according to a second embodiment of the present invention. FIG. 4A is a conceptual perspective view, and FIG. 4B is a conceptual view in a direction perpendicular to the optical axis. It is sectional drawing. On the X-cut LiNbO ₃ substrate 21, a SiO ₂ buffer layer 22 having a thickness of, for example, 100 nm is formed by, for example, a CVD method, and then a polycrystalline Si layer having a thickness of 400 nm or less, for example, 300 nm is formed. .

Next, the polycrystalline Si layer is etched to have a width of 400 nm or less and 300 nm, for example, to form a striped Si waveguide 23 having a cross section of 300 nm × 300 nm. Next, the SiO ₂ buffer layer 24 having a thickness of, for example, 100 nm is formed again by the CVD method. Next, Au electrodes 25 and 26 are formed on both sides of the Si waveguide 13.

Here, a high frequency signal of 10 GHz, for example, is applied to both the Au electrode 25 and the Au electrode 26 to operate as a high-speed optical phase modulator. Also in this case, a part of the laser light input to the Si waveguide 23 leaks to the X-cut LiNbO ₃ substrate 21 side and propagates a part of the surface of the X-cut LiNbO ₃ substrate 21 as the in-substrate optical waveguide portion 27. To do.

In the second embodiment, since the Au electrode 25 and the Au electrode 26 are arranged in parallel, the restriction on the thickness of the X-cut LiNbO ₃ substrate 21 for impedance matching is less strict than in the first embodiment. Thus, device design and fabrication are facilitated.

Next, with reference to FIG. 5, the optical functional waveguide of Example 3 of this invention is demonstrated. FIGS. 5A and 5B are configuration explanatory views of the optical functional waveguide according to the third embodiment of the present invention, FIG. 5A is a conceptual perspective view, and FIG. 5B is a conceptual view in a direction perpendicular to the optical axis. It is sectional drawing. The basic configuration is the same as that of the second embodiment, and the electrode arrangement is changed. On the X-cut LiNbO ₃ substrate 21, a SiO ₂ buffer layer 22 having a thickness of, for example, 100 nm is formed by, for example, a CVD method, and then a polycrystalline Si layer having a thickness of 400 nm or less, for example, 300 nm is formed. .

Next, the polycrystalline Si layer is etched to have a width of 400 nm or less and 300 nm, for example, to form a striped Si waveguide 23 having a cross section of 300 nm × 300 nm. Next, the SiO ₂ buffer layer 24 having a thickness of, for example, 100 nm is formed again by the CVD method.

  Next, an Au upper electrode 28 is formed on the top of the Si waveguide 23, and Au electrodes 25 and 26 are formed on both sides of the Si waveguide 23. Here, both the Au electrodes 25 and 26 are grounded, and a high frequency signal of 10 GHz, for example, is applied to the Au upper electrode 28 to operate as a high-speed optical phase modulator.

  In the third embodiment, a coplanar transmission line is formed in which an Au upper electrode 28 serving as a signal electrode is disposed between two Au electrodes 25 and 26 serving as ground electrodes. Compared to the above, the chirping of modulated light is reduced.

Next, with reference to FIG. 6, the optical functional waveguide of Example 4 of this invention is demonstrated. FIG. 6 is a conceptual cross-sectional view in a direction perpendicular to the optical axis of the optical functional waveguide according to the fourth embodiment of the present invention. The basic configuration is the same as that of the second embodiment, and a groove for arranging an electrode is formed. For example, the grooves 29 and 30 having a width of 5 μm and a depth of 0.5 μm are formed on the X-cut LiNbO ₃ substrate 21 by using, for example, an ion milling method with a spacing of, for example, 400 nm.

Next, for example, after a SiO ₂ buffer layer 22 having a thickness of, for example, 100 nm is formed by a CVD method, a polycrystalline Si layer having a thickness of 400 nm or less, for example, 300 nm is formed.

Next, the polycrystalline Si layer between the groove 29 and the groove 30 is etched to have a width of 400 nm or less and 300 nm, for example, to form a stripe-shaped Si waveguide 23 having a cross section of 300 nm × 300 nm. Next, the SiO ₂ buffer layer 24 having a thickness of, for example, 100 nm is formed again by the CVD method.

  Next, Au electrodes 25 and 26 are formed on the side surfaces of the grooves 29 and 30 on both sides of the Si waveguide 23. Here, both the Au electrodes 25 and 26 are grounded, and a high frequency signal of 10 GHz, for example, is applied to the Au upper electrode 28 to operate as a high-speed optical phase modulator.

  In the fourth embodiment, grooves 29 and 30 are provided on both sides of the Si waveguide 23, and Au electrodes 25 and 26 are formed on the side surfaces of the grooves 29 and 30, so that the electric field is larger than that in the second embodiment. Is efficiently applied to the in-substrate optical waveguide portion 27, and the modulation efficiency is increased.

Next, with reference to FIG. 7, the optical functional waveguide of Example 5 of this invention is demonstrated. FIG. 7 is a conceptual cross-sectional view in a direction perpendicular to the optical axis of the optical functional waveguide according to the fifth embodiment of the present invention. The basic configuration is the same as that of the third embodiment, and a groove for arranging the electrode is formed. For example, the grooves 29 and 30 having a width of 5 μm and a depth of 0.5 μm are formed on the X-cut LiNbO ₃ substrate 21 by using, for example, an ion milling method with a spacing of, for example, 400 nm.

Next, for example, after a SiO ₂ buffer layer 22 having a thickness of, for example, 100 nm is formed by a CVD method, a polycrystalline Si layer having a thickness of 400 nm or less, for example, 300 nm is formed.

Next, the polycrystalline Si layer between the groove 29 and the groove 30 is etched to have a width of 400 nm or less and 300 nm, for example, to form a stripe-shaped Si waveguide 23 having a cross section of 300 nm × 300 nm. Next, the SiO ₂ buffer layer 24 having a thickness of, for example, 100 nm is formed again by the CVD method.

  Next, an Au upper electrode 28 is formed on the top of the Si waveguide 23, and Au electrodes 25 and 26 are formed on the side surfaces of the grooves 29 and 30. Here, both the Au electrodes 25 and 26 are grounded, and a high frequency signal of 10 GHz, for example, is applied to the Au upper electrode 28 to operate as a high-speed optical phase modulator.

  In the fifth embodiment, grooves 29 and 30 are provided on both sides of the Si waveguide 23, and Au electrodes 25 and 26 are formed on the side surfaces of the grooves 29 and 30, so that the electric field is larger than that in the third embodiment. Is efficiently applied to the in-substrate optical waveguide portion 27, and the modulation efficiency is increased.

  Next, an optical functional waveguide according to Example 6 of the present invention will be described with reference to FIG. 8A and 8B are configuration explanatory views of an optical functional waveguide according to a sixth embodiment of the present invention. FIG. 8A is a conceptual perspective view of a 90 ° bent waveguide, and FIG. 8B is a 180 ° bent. It is a notional perspective view of a waveguide.

In either case, selectively diffusing Ti into X-cut LiNbO ₃ substrate 31, the width to form the Ti-diffused LiNbO ₃ waveguide ₃₂₁ to 323 ₄ of 2 m to 3 m, these Ti diffusion LiNbO ₃ waveguide 321 _to 323 ₄ each other to couple the is obtained by forming a 90 ° bend waveguide 40 or 180 ° bending waveguide 42 using the Si via an SiO ₂ buffer layer 33. Tapered waveguide portions 41 _{1 to} 41 ₄ having a length of 30 μm to 500 μm are formed at both ends of the 90 ° bent waveguide 40 or the 180 ° bent waveguide 42.

In this Example 6, the high-speed operation is possible and reliable Ti diffused LiNbO ₃ waveguide ₃₂₁ to 323 ₄ and the optical phase modulator, the ratio compact 90 ° difference in refractive index by large machining is easy Si A bent waveguide 40 or a 180 ° bent waveguide 42 is formed. Therefore, the optical phase modulator can be connected in series, parallel, or series-parallel, and folded to integrate a complicated optical modulation circuit or optical matrix switch.

Further, since the tapered waveguide portions 41 _{1 to} 41 ₄ having a length of 30 μm to 500 μm are formed at both ends of the 90 ° bent waveguide 40 or the 180 ° bent waveguide 41, the Ti diffusion LiNbO ₃ waveguide 32 _{1 is formed.} to 32 ₄ and the mode of propagating light by 90 ° bending waveguide 40 or 180 ° bending waveguide 42 can be adiabatically transform, it is possible to increase the optical coupling efficiency.

  Next, with reference to FIG. 9, the optical functional waveguide of Example 7 of this invention is demonstrated. FIG. 9 is a configuration explanatory view of an optical functional waveguide according to a seventh embodiment of the present invention, FIG. 9A is a conceptual perspective view of a Y-type branching waveguide, and FIG. 9B is multimode interference. It is a conceptual perspective view of a type | mold branch waveguide.

Also in this case, Ti is selectively diffused in the X-cut LiNbO ₃ substrate 31 to form Ti-diffused LiNbO ₃ waveguides 32 _{5 to} 32 ₁₀ having a width of 2 μm to ₃ μm, and these Ti-diffused LiNbO ₃ waveguides 32 are formed. _{5-32 10} mutually to demultiplex or multiplex couple is obtained by forming the a SiO ₂ buffer layer 33 or the Y-branch waveguide 43 or the multi-mode interference type branching waveguide 44. Further, tapered waveguide portions 41 _{5 to} 41 ₁₀ having a length of 30 μm to 500 μm are formed at both ends of the Y-type branch waveguide 43 or the branch waveguide 44.

In Example 7, high-speed operation and high reliability Ti diffused LiNbO ₃ waveguides 32 _{5 to} 32 ₁₀ are used as optical phase modulators, and the processing accuracy is high due to Si having a large relative refractive index difference and easy processing. A small Y-shaped branching waveguide 43 or a branching waveguide 44 is formed.

That is, when the branching waveguide is formed by the conventional Ti-diffused LiNbO ₃ waveguide, it is difficult to produce the branching at a ratio of 1: 1 accurately because of the diffusion process. However, in the seventh embodiment, since the branch path itself is formed by a Si waveguide having excellent processing accuracy, it is easy to set the branch ratio to 1: 1 accurately.

In particular, if the Si waveguide is etched by laser trimming or the like, branching with higher accuracy becomes possible. For example, a Mach-Zehnder optical modulator having a very high extinction ratio can be realized.

Also in this case, since the tapered waveguide portions 41 _{5 to} 41 ₁₀ having a length of 30 μm to 500 μm are formed at both ends of the Y-type branching waveguide 43 or the branching waveguide 44, the Ti diffusion LiNbO ₃ waveguide 32 _{5 to} 32 ₁₀ and the mode of light propagating through the Y-type branching waveguide 43 or the branching waveguide 44 can be adiabatically converted, and the optical coupling efficiency can be increased.

  FIG. 10 is an explanatory diagram of an example of a tapered waveguide portion in Example 6 and Example 7, FIG. 10 (a) is a conceptual perspective view, and FIG. 10 (b) is a conceptual plan view. FIG. 10C is a conceptual side sectional view. In this case, the taper waveguide portion is a lateral taper waveguide portion 51 having a length of, for example, 30 μm to 500 μm and a width changed to a taper shape. Here, one end side of the 90 ° bending waveguide 40, the 180 ° bending waveguide 42 in FIG. 8 or the Y-type branching waveguide 43 and the Mach-Zehnder type branching waveguide 44 in FIG. ing.

  FIG. 11 is an explanatory diagram of another example of the tapered waveguide portion in the sixth and seventh embodiments. FIG. 11 (a) is a conceptual perspective view, and FIG. 11 (b) is a conceptual plan view. FIG. 11 (c) is a conceptual side sectional view. In this case, the length of the tapered waveguide portion is, for example, 30 μm to 500 μm, and the thickness thereof is a longitudinal taper waveguide portion 52 having a tapered shape. Also here, one end side of the 90 ° bending waveguide 40, 180 ° bending waveguide 42 in FIG. 8 or the Y-type branching waveguide 43 and Mach-Zehnder type branching waveguide 44 in FIG. 9 is shown as an Si waveguide 50. ing.

  Next, with reference to FIG. 12, an optical functional waveguide according to an eighth embodiment of the present invention will be described. The tapered waveguide portion in the optical functional waveguide according to the sixth embodiment or the seventh embodiment described above is divided into a minute division type mode. This is replaced with a conversion waveguide. 12A and 12B are configuration explanatory views of an optical functional waveguide according to an eighth embodiment of the present invention. FIG. 12A is a conceptual perspective view, FIG. 12B is a conceptual plan view, and FIG. (C) is a conceptual sectional side view.

As shown in FIGS. 12A to 12C, a minute division type mode conversion waveguide 53 having a length of, for example, 30 μm to 500 μm is provided at the coupling portion between the Si optical waveguide 50 and the Ti-diffused LiNbO ₃ waveguide 32. . In this case, the minute division type mode conversion waveguide 53 gradually changes the line / space line / space ratio from 400/100 to 100/400 with a period of 500 nm, for example. Also here, one end side of the 90 ° bent waveguide 40, the 180 ° bent waveguide 42 in FIG. 8 or the Y-type branch waveguide 43 and the Mach-Zehnder type branch waveguide 44 in FIG. 9 is shown as an Si waveguide 50. ing.

Since this microdivision mode conversion waveguide 53 has a higher degree of design freedom than a tapered waveguide, efficient mode conversion is possible. As a result, the Ti diffusion LiNbO ₃ waveguide 32 and each Si waveguide The optical coupling efficiency can be increased.

Next, with reference to FIG. 13, the optical functional waveguide of Example 9 of this invention is demonstrated. FIG. 13 is a conceptual plan view of an optical functional waveguide according to a ninth embodiment of the present invention. Here, the optical functional waveguide will be described as a Mach-Zehnder optical intensity modulator. On the X-cut LiNbO ₃ substrate 61, the Er-doped SiON waveguides 63 and 64, the SiON branching waveguides 65 and 66, the Si-rich SiON waveguides 67 to 70, and the Si waveguide 71 through the SiO ₂ buffer layer 62. , 72 are integrated. Although not shown, the Si waveguides 71 and 72 constitute an optical phase modulator having the structure shown in FIG. As described above, the SiON branch waveguides 65 and 66 are configured to obtain a highly accurate branch ratio by laser trimming.

  The Er-doped SiON waveguides 63 and 64 become gain waveguides when 1.48 μm excitation light is incident, and it is possible to compensate for propagation loss. Further, since the Si-rich SiON waveguides 67 to 70 having a higher relative refractive index than SiON are provided between the SiON branch waveguides 65 and 66 and the Si waveguides 71 and 72, the refractive index changes stepwise. Yes. As a result, the connection loss can be reduced as compared with the case where the SiON branch waveguides 65 and 66 and the Si waveguides 71 and 72 are directly connected. Here, a microwave signal is applied to the Si waveguides 71 and 72 as in the fourth embodiment, thereby functioning as a Mach-Zehnder light intensity modulator.

  Since the relative refractive index of SiON is lower than that of Si, the cross-sectional sizes of the SiON branch waveguides 65 and 66 and the Si-rich SiON waveguides 67 to 70 when propagating single mode laser light are the same as those of the Si waveguides 71 and 72. It becomes larger than the cross-sectional size. Therefore, at the connection portion between the Si-rich SiON waveguides 67 to 70 and the Si waveguides 71 and 72, the cross-sectional size of the Si-rich SiON waveguides 67 to 70 is tapered so as to match the cross-sectional size of the Si waveguides 71 and 72. Anyway.

1 LiNbO ₃ substrate 2 dielectric film 3 different material optical waveguide 5 the first electrode 6 and the second electrode 7 substrate optical waveguide portion 8 Ti diffused LiNbO ₃ waveguide 9 tapered portion 11 Z-cut LiNbO ₃ substrate 12,22,33 , 62 SiO ₂ buffer layer 13, 23 Si waveguide 14, 24 SiO ₂ buffer layer 15, 28 Au upper electrode 16 Au lower electrode 17, 27 In-substrate optical waveguide portion 21, 31, 61 X-cut LiNbO ₃ substrate 25, 26 Au electrodes 29, 30 Grooves 32, 32 _{1 to} 32 ₁₀ Ti diffusion LiNbO ₃ waveguide 40 90 ° bent waveguide 41 _{1 to} 41 ₁₀ taper waveguide portion 42 180 ° bent waveguide 43 Y-type branch waveguide 44 Multimode interference Type branching waveguide 50 Si waveguide 51 Lateral taper waveguide part 52 Vertical taper waveguide part 53 Microdivision mode conversion waveguide 6 , 64 Er doped SiON waveguides 65 and 66 SiON branching waveguides 67 to 70 Si-rich SiON waveguides 71 and 72 Si waveguides

Claims (11)

A lithium niobate substrate;
Striped dissimilar material optical waveguide formed on the surface of the lithium niobate substrate with a material different from the lithium niobate substrate;
An in-substrate optical waveguide portion formed by leakage of light propagating through the different material optical waveguide on the surface side of the lithium niobate substrate facing the striped different material optical waveguide, or the different material optical waveguide Any one of the in-substrate optical waveguides introduced with Ti or protons formed on the surface side facing
An optical functional waveguide comprising: the dissimilar material optical waveguide; and a first electrode and a second electrode for applying a modulation voltage to either the intra-substrate optical waveguide portion or the intra-substrate optical waveguide.   One of the first electrode and the second electrode is provided on the top surface of the dissimilar material optical waveguide, and the other of the first electrode and the second electrode is provided on the back surface of the lithium niobate substrate. The optical functional waveguide according to claim 1.   2. The optical functional waveguide according to claim 1, wherein the first electrode and the second electrode are provided on the surface of the lithium niobate substrate so as to face each other with the optical waveguide of the different material interposed therebetween.   One of the first electrode and the second electrode is provided on the top surface of the lithium niobate substrate, and the other of the first electrode and the second electrode faces each other with the dissimilar material optical waveguide interposed therebetween. The optical functional waveguide according to claim 1, wherein the optical functional waveguide is provided.   A pair of grooves are formed in the lithium niobate substrate along both side surfaces of the dissimilar material optical waveguide, and electrodes provided so as to face each other with the dissimilar material optical waveguide interposed therebetween are provided in the groove. The optical functional waveguide of Claim 3 or Claim 4. A lithium niobate substrate;
A plurality of lithium niobate optical waveguides formed by introducing either Ti or protons into the lithium niobate substrate;
Light having a different material optical waveguide for coupling formed of a material different from the lithium niobate substrate provided to optically couple the plurality of lithium niobate optical waveguides on the surface of the lithium niobate substrate Functional waveguide.   The optical functional waveguide according to claim 6, wherein an end portion of the dissimilar material optical waveguide on the side coupled with the lithium niobate optical waveguide is tapered.   The optical functional waveguide according to claim 6 or 7, wherein at least one end of the different-material optical waveguide constitutes a branching waveguide. 9. The optical functional waveguide according to claim 1, wherein the different-material optical waveguide is made of any one of Si, SiON, SiN, TiO ₂ , and Ta ₂ O ₃ .   The optical functional waveguide according to claim 9, wherein the different-material optical waveguide includes a plurality of optical waveguide elements having different compositions.   The optical functional waveguide according to claim 10, wherein a rare earth element is added to at least a part of the optical waveguide element.

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