JP2011090223A - Crossing optical waveguide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a crossing optical waveguide which has a simple configuration and a broad bandwidth and in which a loss due to a leakage at a crossing part is small. <P>SOLUTION: The crossing waveguide in which a plurality of optical waveguides cross in one and the same plane includes the plurality optical waveguides and a crossing part at which the plurality of optical waveguides cross in one and the same plane. The optical waveguide converges light after expanding the mode of propagating light and condenses light so that the center of the crossing part becomes a light-condensing position, and the respective mode distributions of light of the two optical waveguides disposed while interposing the crossing part in-between become symmetrical or asymmetrical about the light-condensing position. The width of the mode distribution of light propagating in the waveguides is broadened as approaching the crossing part, thus the straight advance property of light is enhanced. As the straight advance property of light is enhanced, the broadening of light at the crossing part is suppressed and the light arrives at the opposite side optical waveguide. By suppressing the broadening of the width of the mode distribution of light at the crossing part, the leakage of light from the optical waveguides crossing at the crossing part is suppressed, thus the loss of the propagating light is reduced. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical waveguide, and more particularly to a crossed optical waveguide having good crosstalk characteristics.

  Silicon photonics is a technology for forming optical devices and optical circuits that use silicon technology to form silicon thin films. Optical interconnections and optical circuits are introduced into LSIs to form optical interconnections that speed up LSIs. However, it is expected to be applied to inexpensive production of optical communication devices and sensor devices by diverting the LSI silicon process.

  Basic elements that constitute optical wiring and optical circuits used in silicon photonics include bending, branching, and intersection. Among these elements, device design that satisfies requirements such as low loss, compactness, wide bandwidth, and ease of manufacture has been established for bending and branching. On the other hand, the intersection is an element particularly necessary for making the optical wiring and the optical circuit compact, but a structure that satisfies all of these requirements has not been proposed.

  FIG. 8 is a diagram for explaining the outline of a conventionally proposed crossed optical waveguide. An intersecting optical waveguide 11A shown in FIG. 8A is configured by intersecting optical waveguides 12A1 to 12A4 at an intersecting portion 13A. In this configuration example, for example, light incident from the optical waveguide 12A4 is propagated to the optical waveguide 12A2 with the intersection 13A regarded as a gap. In this structure, the coupling efficiency η between the optical waveguide 12A4 and the optical waveguide 12A2 is expressed by the wavelength λ, the spot size w of light propagating through the optical waveguide, and the gap width D at the intersection. The larger the spot size w, the lower the loss. Become.

  In the crossed optical waveguide 11B shown in FIG. 8B, the spot size of the crossing portion is increased by making the width and thickness of the crossing portion 13B smaller than the value of the optical waveguide other than the crossing portion. The coupling loss is reduced (Patent Document 1).

  The inventor of the present application has proposed a crossed optical waveguide in which a crossing portion is constituted by a tapered optical waveguide (Non-Patent Document 1). In the configuration example of the crossed optical waveguide 11C shown in FIG. 8C, one of the optical waveguides 12C2 and 12C4 has an elliptical or parabolic tapered shape, and the other optical waveguide 12C1 has this tapered portion as the intersecting portion 13C. , Crossed with 12C3. Further, in the configuration example of the intersecting optical waveguide 11D shown in FIG. 8D, the intersecting optical waveguides 12D1 to 12D4 each have an elliptical shape or a parabolic tapered shape, and the tapered portions intersect with each other as an intersecting portion 13D. ing.

  In addition, a configuration (Non-Patent Document 2) in which tapered intersections are formed in a multilayer structure and a structure (Non-Patent Document 3) in which a rectangular mode converter is inserted have been proposed.

  In addition, a method of maintaining the balance of propagating light by a configuration in which intersecting portions are continuously provided (Non-Patent Document 4) and a configuration in which the intersecting portions are formed in a three-dimensional structure (Non-Patent Document 5) are proposed.

Japanese Patent Laid-Open No. 5-60929 (FIGS. 5 and 1)

Low Loss Intersection of Si Photonic Wire Waveguides Japanese Journal of Applied Physics vol.43.No.2.2004, pp.646-647 Tatsuhiko FUKAZAWA, Tomohisa HIRANO, Fumiaki OHNO and Toshihiko BABA Low-Loss, low-cross-talk crossings for silicon-on-insulator nanophotonic waveguides October 1,2007 / Vol.32, No.19 / OPTICS LETTRES, pp.2801-2803o.Wim Bogaerts, Pieter Dumon, Dries Van Thourhount, and Roel Baets Silicon cross-connect filters using microring resonator coupled multimode-interference-based waveguide crossings 9 June 2008 / Vol.16, No.12 / OPTICS EXPRESS pp.8649-8657 Fang Xu and Andrew W. Poon Low-Loss Bloch Waves in Open Structures and Highly Compact, Efficient Si Waveguide-Crossing Arrays Tech. Dig. LEOS Annual Meet. (2007) Milos A. Popovic, Erich P. Ippen and Franz X. Kartner Crosstalk-free design for the intersection of two dielectric waveguides 27 April 2009 / Vol.17, No.9 / OPTICS EXPRESS pp.7717-7724 Jingjing Li, David A. Fattal and Raymond G. Beausoleit

  In the C band (1.53 to 1.565 μm), which is a wavelength band used in optical communication, the loss is preferably 0.1 dB or less, the size is preferably about 15 μm square, and the number of patterning processes is small. desirable.

  The proposed configuration is unlikely to adequately meet such requirements. For example, the configuration in which the intersecting portions are continuously provided (Non-Patent Document 4) is not sufficient in terms of loss and has a problem that the bandwidth is narrow. difficult.

  Further, the configuration in which the optical waveguide is tapered (Non-Patent Document 1) cannot be said to be sufficient in terms of loss.

  Moreover, although the structure which makes a taper-shaped cross | intersection part multilayer structure (nonpatent literature 2) is improved in the point of loss, since the pattern process of two steps is required, there exists a problem that a manufacturing process becomes complicated. In addition, the structure in which the rectangular mode converter is inserted (Non-Patent Document 3) has a problem that the loss is large in an actual three-dimensional device. The configuration in which the intersecting portion is formed in a three-dimensional structure (Non-Patent Document 5) has a problem that it is difficult to manufacture.

  Accordingly, an object of the present invention is to solve the above-described conventional problems, and to provide a crossed optical waveguide having a simple configuration, a wide band, and a small loss due to leakage at a crossing portion.

  The present invention is an intersecting optical waveguide in which a plurality of optical waveguides intersect in the same plane, and includes a plurality of optical waveguides and an intersecting portion in which the plurality of optical waveguides intersect in the same plane.

  The optical waveguide of the present invention is narrowed after expanding the width of the mode distribution of propagating light, condensed so that the center of the intersecting portion becomes the condensing position, and two optical waveguides arranged with the intersecting portion interposed therebetween Each mode distribution of the light is distributed around this condensing position. In this mode distribution of light, the distribution centered on the condensing position can be symmetric or asymmetric.

  According to the crossed optical waveguide of the present invention, the width of the mode distribution of light propagating through the waveguide is increased as the crossing portion is approached, thereby improving the straightness of light. By increasing the straightness of light, the light is prevented from spreading at the intersection and reaches the opposite optical waveguide. By suppressing the spread of light at the intersection, it is possible to suppress the leakage of the light of the optical waveguide that intersects at the intersection, and to reduce the loss of propagating light.

  When the width of the mode distribution of light propagating in the waveguide is simply widened as it approaches the intersection, the light goes straight, but it enters while the mode distribution is widened at the intersection. The leaked portion leaks into the optical waveguide where the light that has entered intersects. This leakage becomes a factor of propagation loss.

  According to the present invention, in a configuration including a plurality of optical waveguides and intersections where the plurality of optical waveguides intersect in the same plane, the optical waveguide is reduced by narrowing after narrowing the width of the mode distribution of propagating light. The center of the intersection is condensed as the condensing position, and a symmetric or asymmetric mode distribution is formed between the introduction-side waveguide and the extraction-side waveguide with the condensing position as the center. By adopting this configuration, once the light whose mode distribution width has been widened is narrowed, a wavefront that is recessed inward toward the central axis of the optical waveguide is formed, and in the direction of the central axis of the optical waveguide while traveling straight in the intersection Proceed to At this time, the aperture amount of the light mode distribution width is adjusted so that the light condensing position becomes the center of the intersection. By matching the condensing position to the center of the intersection, the intersection optical waveguide and the distribution of light propagating through the intersection optical waveguide have a symmetric or asymmetric relationship about the intersection. By setting the condensing position of the light distribution as the center of the intersection, the light introduced into the intersection passes through the intersection and is guided to the other optical waveguide without leaking to the intersecting optical waveguide, and at the intersection It is possible to eliminate the loss of light at the intersections.

  The optical waveguide of the present invention has a configuration in which the width of the mode distribution of propagating light is enlarged and then reduced, and the light is condensed so that the light condensing position becomes the center of the intersection. In the optical axis direction toward the intersection, the width of the mode distribution of the propagating light is enlarged and then reduced, and the width of the mode distribution is reduced at the center of the intersection by reducing the width of the mode distribution. Focus on the center of the.

  The optical waveguide of the present invention can be single-mode or multi-mode, but a low-order mode is desirable. In the crossed optical waveguide of the present invention, the mode propagating through each optical waveguide is always maintained as one mode, and only the width of the mode distribution is enlarged / reduced.

  The optical waveguide of the present invention is configured to increase or decrease the width of the mode distribution, and increase or decrease the size of at least one of the width and thickness of the optical waveguide. By adjusting the width or thickness, or adjusting both the width and thickness, the width of the mode distribution of the propagating light is expanded or reduced.

  The crossed optical waveguide of the present invention is a crossed optical waveguide in which a plurality of optical waveguides intersect in the same plane, and includes a plurality of optical waveguides and a crossing portion in which the plurality of optical waveguides intersect in the same plane. A tapered portion is provided as a configuration for expanding and reducing the width of the mode distribution. Depending on the shape of the tapered portion, the width of the mode distribution is enlarged / reduced, and the propagating mode is always kept at one.

  The optical waveguide of the present invention is formed by a configuration including a first taper portion and a second taper portion that expand and contract the width of the mode distribution between each light entry / exit end portion and the intersection portion. Can do.

  The first tapered portion is configured such that at least one of the width and the thickness increases toward the intersecting portion, and the second tapered portion decreases at least one of the width and the thickness toward the intersecting portion. The configuration is as follows. In the configuration of the first taper portion and the second taper portion, the width of the mode distribution increases when the light proceeds in the direction in which the width and thickness increase, and conversely, the light decreases in width and thickness. When proceeding in the direction, the width of the mode distribution is reduced. Further, the first taper portion is provided on the lead-out input end portion side, and the second taper portion is provided on the crossing portion side. With the configuration of the tapered portion, the two optical waveguides sandwiching the intersecting portion form a symmetric or asymmetric mode distribution on the introduction side and the outlet side with the center of the intersecting portion as the condensing position.

The optical waveguide of the present invention can be formed by a SiO ₂ cladding and a Si core, and the tapered portion can be formed by a plurality of shapes.

  The 1st form which forms a taper part can form a core by elliptical shape. In the first embodiment, the side wall portions of the cores of the first tapered portion and the second tapered portion can be formed in an elliptical shape. In the elliptical shape, the focal point of the elliptical shape is set as the center of the intersection, and the center of the intersection is set as the condensing position. Form a distribution.

  The 2nd form which forms a taper part can form a core in a parabolic shape. In the second embodiment, the side wall portions of the cores of the first tapered portion and the second tapered portion can be formed in a parabolic shape. The parabolic shape is a mode in which the focal point of the parabolic shape is the center of the intersection, and the center of the intersection is the condensing position. Form a distribution.

  The 3rd form which forms a taper part can be formed in the linear shape which inclined the core. In the third embodiment, the side wall portions of the cores of the first tapered portion and the second tapered portion can be formed in a linear shape. The inclination of the linear shape of the second tapered portion is such that the center of the intersecting portion is a condensing position by setting the focal point of mode reduction to the center of the intersecting portion, and the center of the converging portion is the center of the converging portion. A symmetric or asymmetric mode distribution is formed in the optical waveguide.

  In the configuration including the tapered portion of the present invention, the angle on the cladding side is an acute angle of less than 90 degrees in the angle formed by the side wall portion of the core of the adjacent second tapered portion. By making the angle formed by the side wall portion of the core of the adjacent second tapered portion an acute angle, the width of the expanded mode distribution can be narrowed toward the intersecting portion side.

  According to the crossed optical waveguide of the present invention, low loss can be achieved with a sufficiently wide band. In the evaluation example by simulating propagation loss, the loss can be as low as 0.07 dB.

  Patent Document 1 discloses a configuration in which the coupling loss at the intersection is reduced by narrowing the width of the optical waveguide toward the intersection and increasing the spot size of the intersection, as in the present invention. Since the configuration does not increase the width of the mode distribution of propagating light, the linearity at the intersection is not sufficient, and leakage to the optical waveguide having a tolerance cannot be suppressed. Further, Patent Document 1 is a configuration in which the coupling loss at the intersection is reduced by simply increasing the spot size of the intersection. As in the present invention, the width of the expanded mode distribution is reduced and the intersection is reduced. Therefore, the light distribution cannot be symmetric with respect to the center of the intersection, and the effect of suppressing leakage at the intersection is not sufficient.

  Although Non-Patent Documents 1 and 3 show the configuration of an elliptical or rectangular mode converter, as in the present invention, the width of the expanded mode distribution is reduced and reduced to the center of the intersection. Since the light is not condensed, the light distribution cannot be symmetric with respect to the center of the intersection, and the effect of suppressing leakage at the intersection is not sufficient.

  As described above, according to the intersecting optical waveguide of the present invention, loss due to leakage at the intersecting portion can be reduced, and it can be formed only by adjusting the width and thickness of the optical waveguide. In addition, since it can be configured with one intersection without requiring a continuous intersection, the propagating light can be in a wide band.

It is a figure for demonstrating the 1st structural example of the crossing optical waveguide of this invention. It is a figure for demonstrating the 1st structural example of the crossing optical waveguide of this invention. It is a figure for demonstrating the 2nd structural example of the crossing optical waveguide of this invention. It is a figure for demonstrating the 3rd structural example of the crossing optical waveguide of this invention. It is a figure for demonstrating the 4th structural example of the crossing optical waveguide of this invention. It is a figure for demonstrating the 5th structural example of the crossing optical waveguide of this invention. It is a figure for demonstrating the example of a simulation of the crossing optical waveguide of this invention. It is a figure for demonstrating the outline | summary of the crossing optical waveguide proposed conventionally.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Hereinafter, a configuration example of the crossed optical waveguide of the present invention will be described with reference to FIGS. 1 to 6, and a simulation example will be described with reference to FIG.

  1 and 2 are diagrams for explaining a first configuration example of the crossed optical waveguide of the present invention. FIG. 3 is a diagram for explaining a second configuration example of the crossed optical waveguide of the present invention. 4 is a diagram for explaining a third configuration example of the crossed optical waveguide of the present invention, and FIG. 5 is a diagram for explaining a fourth configuration example of the crossed optical waveguide of the present invention. These are the figures for demonstrating the 5th structural example of the crossing optical waveguide of this invention. The example shown in FIGS. 1 to 6 shows a configuration example in which two optical waveguides are crossed.

  The first to third configuration examples of the crossed optical waveguide of the present invention are examples in which the expansion / reduction of the width of the mode distribution in the optical waveguide is adjusted by the width of the waveguide, and the fourth configuration of the crossed optical waveguide of the present invention. The example is an example in which the expansion / reduction of the width of the mode distribution in the optical waveguide is adjusted by the thickness of the waveguide, and the fifth configuration example of the crossed optical waveguide of the present invention is the expansion of the width of the mode distribution in the optical waveguide. An example in which the reduction is adjusted by the width and thickness of the waveguide is shown.

  In the first to third configuration examples, the first configuration example is an example in which the outer shape of the core that forms the optical waveguide is an elliptical shape, and the second configuration example is the core that forms the optical waveguide. The third configuration example shows an example in which the outer shape of the core forming the optical waveguide is configured as a tilted linear shape.

[First configuration example of crossed optical waveguide]
First, a first configuration example of the crossed optical waveguide of the present invention will be described with reference to FIGS.
The first configuration example is an example in which the expansion / reduction of the width of the mode distribution of the optical waveguide is adjusted by the width of the waveguide, and the outer shape of the core forming the optical waveguide is configured in an elliptical shape. This is an example of adjusting the width of the waveguide.

  1A is a plan view of the first configuration example, FIG. 1B is a cross-sectional view of the first configuration example, and shows a cross-section of one optical waveguide (the chain line in FIG. 1A). The portion indicated by).

The intersecting optical waveguide 1A of the first configuration example is configured by intersecting two optical waveguides 2 (2A1 to 2A4) at an intersecting portion 3A, and is high in a low refractive index SiO ₂ cladding portion 10 constituting a substrate. It can be formed by generating a Si core 11 having a refractive index. The process of generating the Si core 11 on the SiO ₂ cladding 10 can be performed using a photolithography technique.

  Of the optical waveguides 2 provided in the crossed optical waveguide 1A shown in FIG. 1A, one optical waveguide is composed of an optical waveguide 2A2 and an optical waveguide 2A4 that are arranged symmetrically across the intersecting portion 3A, and the other The optical waveguide is composed of an optical waveguide 2A1 and an optical waveguide 2A3 that are arranged symmetrically across the intersection 3A, and the optical waveguide (2A2, 2A4) and the optical waveguide (2A1, 2A3) are at the intersection 3A. Orthogonal.

  The optical waveguide 2A2 and the optical waveguide 2A4 are optically symmetric with respect to the intersection 3A, and any of them may be an introduction path or a lead-out path. The optical waveguide 2A1 and the optical waveguide 2A3 are also optically symmetric with respect to the intersecting portion 3A, and any of them may be an introduction path or a lead-out path.

  Here, for convenience, the optical waveguide 2A4 will be described as an introduction path, the optical waveguide 2A2 as an output path, the optical waveguide 2A3 as an introduction path, and the optical waveguide 2A1 as an output path.

  Hereinafter, the configuration of the optical waveguide will be described using an optical waveguide including the optical waveguide 2A2 and the optical waveguide 2A4. The optical waveguide composed of the optical waveguide 2A2 and the optical waveguide 2A4 intersects the optical waveguide composed of the optical waveguide 2A1 and the optical waveguide 2A3, and the light introduced from the optical waveguide 2A4 intersects the optical waveguide (optical It is required to proceed to the optical waveguide 2A2 through the intersecting portion 3A without leaking to the side of the optical waveguide comprising the waveguide 2A1 and the optical waveguide 2A3.

  In the first configuration example, the outer shape of the core of each of the optical waveguides 2A1 to 2A4 is configured as an ellipse, and the leakage between the intersecting optical waveguides is obtained by matching the elliptical focal position and the center position of the intersection 3A. Suppressing and reducing light propagation loss.

In the configuration shown in FIG. 1 (a), each optical waveguide 2A1~2A4 is produced by forming a core 11 of Si on the cladding portion 10 of SiO _2. The outer shape of the core 11 of each of the optical waveguides 2A1 to 2A4 in the first configuration example is an elliptical shape. Here, when the length (major axis) of the major axis of the ellipse is 2a and the length (minor axis) of the minor axis is 2b, the ellipse shape is generally expressed by a function of x ² / a ² + y ² / b ^2. , The focal point on the x-axis is represented by (± √ (a ² −b ² ), 0). Each of the optical waveguides 2A1 to 2A4 is configured by arranging four elliptical shapes around the focal position 5A at positions that are four-fold symmetric at intervals of 90 degrees.

Each of the optical waveguides 2A1 to 2A4 includes a first tapered portion 2a1 and a second tapered portion 2a2 that have different widths in the optical axis direction. The first taper portion 2a1 has an elliptical shape extending from the lead-in / in end portion 4 toward the intersection portion 3A, and the second taper portion 2a2 is elliptical from the first taper portion 2a1 toward the intersection portion 3A. Narrow the width. At this time, the distance d between the center position of each elliptical shape and the focal position 5A is represented by √ (a ² −b ² ), and this distance d is longer than half b of the short axis length (short diameter) 2b. When the relationship (d> b) is satisfied, the angle θ formed by the elliptical outer shape portion of the adjacent optical waveguide is an acute angle.

  FIG. 2 is a diagram for explaining the increase / decrease of the width of the optical waveguide and the angle formed by the adjacent optical waveguides. In FIG. 2, only the adjacent optical waveguide 2A4 and the optical waveguide 2A1 are shown, and the optical waveguide 2A2 and the optical waveguide 2A3 are omitted.

  In the optical waveguide 2A4, the width W1 of the first tapered portion 2a1 increases from the lead-in / in end portion 4 toward the intersecting portion 3A according to an elliptic function, and becomes the maximum width W2 at the boundary with the second tapered portion 2a2. From the boundary between the second tapered portion 2a2 and the first tapered portion 2a1, the width W3 is narrowed so as to converge at the focal position 5A in accordance with an elliptic function from the boundary 3A toward the intersecting portion 3A.

  Since the width of the second taper portion 2a2 is narrowed at the location where the adjacent optical waveguide 2A4 and the outer portion of the core of the optical waveguide 2A1 intersect, the angle θ formed by the outer portion becomes an acute angle.

  According to the positional relationship described above, in the optical waveguide 2A4, the light introduced from the lead-in / out end portion 4 has its light mode distribution width expanded toward the intersecting portion 3A in the first taper portion 2a1, and the second taper. In the portion 2a2, the width of the mode distribution of light decreases from the first tapered portion 2a1 toward the intersecting portion 3A. The light narrowed down by the second tapered portion 2a2 is collected at the focal position 5A of the intersecting portion 3A.

  Furthermore, the light condensed at the focal position 5A of the intersection 3A advances toward the optical waveguide 2A2 while expanding the width of the mode distribution of the light due to the symmetry of the light. In the optical waveguide 2A2, the width of the mode distribution of light increases from the intersecting portion 3A toward the first tapered portion 2a1 at the second tapered portion 2a2, and the opposite from the first tapered portion 2a1 at the first tapered portion 2a1. The width of the mode distribution of light decreases toward the lead-out entrance end 4 and is led out from the lead-out entrance end 4.

  Reference numerals 21 to 27 in FIG. 1A schematically show changes in the width of the mode distribution of light propagating through the optical waveguide. Reference numeral 21 denotes the width of the mode distribution of the light propagating through the lead-in / out end 4 on the optical waveguide 2A4 side, and reference numeral 22 denotes the width of the mode distribution of the light propagating through the first tapered portion 2a1 on the optical waveguide 2A4 side. Reference numeral 23 denotes the width of the mode distribution of light propagating through the second tapered portion 2a2 on the optical waveguide 2A4 side, reference numeral 24 denotes the width of the mode distribution of light propagating through the intersection 3A, and reference numeral 25 denotes the optical waveguide. Reference numeral 26 denotes the width of the mode distribution of light propagating through the second tapered portion a2 on the 2A2 side, reference numeral 26 denotes the width of the mode distribution of light propagating through the first tapered portion 2a1 on the optical waveguide 2A2 side, and reference numeral 27 denotes The width of the mode distribution of light propagating through the lead-in / out end 4 on the optical waveguide 2A2 side is shown.

  Therefore, the width of the mode distribution of the light propagating through the optical waveguide 2A4, the intersecting portion 3A, and the optical waveguide 2A2 is enlarged by the first tapered portion 2a1, and then reduced and narrowed by the second tapered portion 2a2, and the intersecting portion 3A. Passes through the focal position 5A formed at the center position of the lens with the mode distribution width being small. The propagating light passes through the focal position 5A, proceeds while expanding the width of the mode distribution due to the symmetry of the light, expands the width of the mode distribution by the second tapered portion 2a2 of the optical waveguide 2A2, and then propagates through the optical waveguide 2A2. The first tapered portion 2a1 reduces and narrows the mode distribution width.

  Therefore, the optical waveguide 2A4 and the optical waveguide 2A2 have a symmetric positional relationship with respect to the center of the intersection 3A in the structure and the light mode distribution, and the light introduced into the optical waveguide 2A4 passes through the intersection 3A. It passes without leaking to the intersecting optical waveguides (optical waveguide 2A1 and optical waveguide 2A3) side, and is guided to the optical waveguide 2A2 arranged oppositely.

FIG. 1B shows a configuration example of a cross section of the optical waveguide 2A4, the intersecting portion 3A, and the optical waveguide 2A2. The Si core 11 has a structure in which the upper and lower sides are sandwiched between SiO ₂ cladding portions 10a and 10b.

Numerical examples in the configuration of FIG. 1 can be the following examples.
In the numerical example of the core 11, the length a on the major axis side of the elliptical shape is 4 to 6 μm, the length b on the minor axis side is 0.5 to 1.5 μm, and the first taper portion 2a1 and the second taper portion 2a2 The distance c from the boundary to the portion where the outer portions of the cores of adjacent optical waveguides intersect is ˜3 μm (note that 0 μm is not included), and the thickness is 220 nm. Further, the thickness of the cladding portions 10a and 10b is 800 nm, and the width of the leading end portion 4 to the optical waveguide 2A is 400 nm. When light having a wavelength of 1.55 μm is used, the refractive index of the core 11 is 3.50, and the refractive index of the cladding part 10 is 1.44.

  The numerical examples described above are merely examples, and are not limited to these numerical values, and can be determined based on the configuration of the present invention.

[Second configuration example of crossed optical waveguide]
Next, a second configuration example of the crossed optical waveguide of the present invention will be described with reference to FIG.
The second configuration example is an example in which the expansion / reduction of the light mode distribution in the optical waveguide is adjusted by the width of the waveguide, and the outer shape of the core forming the optical waveguide is configured in a parabolic shape, and the parabolic shape This is an example of adjusting the width of the waveguide.

  FIG. 3A is a plan view of the second configuration example, and FIG. 3B is a cross-sectional view of the second configuration example (a portion indicated by a one-dot chain line in FIG. 3A). The cross section of the optical waveguide is shown.

As in the first configuration example, the cross optical waveguide 1B of the second configuration example is configured by crossing two optical waveguides 2 (2B1 to 2B4) at the intersection 3B to form a low refractive index that forms a substrate. The high refractive index Si core 11 can be formed in the SiO ₂ cladding 10.

  Of the optical waveguides 2 included in the crossed optical waveguide 1B shown in FIG. 3A, one optical waveguide is composed of an optical waveguide 2B2 and an optical waveguide 2B4 arranged at symmetrical positions with the crossing portion 3B interposed therebetween, and the other. The optical waveguide is composed of an optical waveguide 2B1 and an optical waveguide 2B3 that are arranged symmetrically across the intersection 3B, and the optical waveguide (2B2, 2B4) and the optical waveguide (2B1, 2B3) are at the intersection 3B. Orthogonal.

  The optical waveguide 2B2 and the optical waveguide 2B4 are optically symmetric with respect to the intersection 3B, and any of them may be an introduction path or a lead-out path. The optical waveguide 2B1 and the optical waveguide 2B3 are also optically symmetric with respect to the intersecting portion 3B, and any of them may be an introduction path or a lead-out path.

  Here, for convenience, the optical waveguide 2B4 will be described as an introduction path, the optical waveguide 2B2 as an extraction path, the optical waveguide 2B3 as an introduction path, and the optical waveguide 2B1 as an extraction path.

  Hereinafter, the configuration of the optical waveguide will be described using an optical waveguide including the optical waveguide 2B2 and the optical waveguide 2B4. The optical waveguide composed of the optical waveguide 2B2 and the optical waveguide 2B4 intersects the optical waveguide composed of the optical waveguide 2B1 and the optical waveguide 2B3, and the light introduced from the optical waveguide 2B4 intersects the optical waveguide (optical It is required to proceed to the optical waveguide 2B2 through the intersection 3B without leaking to the optical waveguide) side of the waveguide 2B1 and the optical waveguide 2B3.

  In the second configuration example, the outer shape of the core of each of the optical waveguides 2B1 to 2B4 is configured as a parabolic shape, and the leakage between the intersecting optical waveguides is obtained by matching the focal position of the parabolic shape and the center position of the intersecting portion 3B. Suppressing and reducing light propagation loss.

In the configuration shown in FIG. 3 (a), each optical waveguide 2B1~2B4 is produced by forming a core 11 of Si on the cladding portion 10 of SiO _2. The outer shape of the core 11 of each of the optical waveguides 2B1 to 2B4 in the second configuration example is formed in a parabolic shape. Here, in the parabolic shape, when the distance between the focal point and the quasi-line is 2a, the parabolic shape is generally expressed by a function of y ² = 4ax. Each of the optical waveguides 2B1 to 2B4 is configured by arranging four parabolic shapes centering on the focal position 5B at positions that are four-fold symmetrical at intervals of 90 degrees.

  Each of the optical waveguides 2B1 to 2B4 includes a first taper portion 2b1 and a second taper portion 2b2 that have different widths in the optical axis direction, and the first taper portion 2b1 and the second taper portion 2b2 are widened. It can be formed by combining parts.

  The first taper portion 2b1 is widened in a parabolic shape from the lead-in / in end portion 4 toward the intersection portion 3B, and the second taper portion 2b2 is formed between the first taper portion 2b1 and the second taper portion 2b2. The width is narrowed from the boundary toward the intersection 3B. At this time, when the distance d between the center position of each parabolic shape and the focal position 5B is longer than the length b of the widest portion in the parabolic shape (d> b), the parabolic shape of the adjacent optical waveguide The angle θ formed by the outer shape portion is an acute angle.

  In the optical waveguide 2B4, the width W1 of the first tapered portion 2b1 increases in accordance with a parabolic function from the lead-in / in end portion 4 toward the intersecting portion 3B, and reaches the maximum width W2 at the boundary with the second tapered portion 2b2. The width W3 of the second tapered portion 2b2 decreases according to the parabolic shape from the boundary between the second tapered portion 2b2 and the first tapered portion 2b1 toward the intersecting portion 3B, and the width of the mode distribution of the light is the focal position 5B. Narrowed to converge.

  Since the width of the second taper portion 2b2 is narrowed at the location where the adjacent optical waveguide 2B4 and the outer portion of the core of the optical waveguide 2B1 intersect, the angle θ formed by the outer portion becomes an acute angle.

  According to the positional relationship described above, in the optical waveguide 2B4, the light introduced from the lead-in / out end portion 4 has the width of the mode distribution of the light expanded toward the intersecting portion 3B in the first taper portion 2b1, and the second taper. In the portion 2b2, the width of the mode distribution of light decreases from the first tapered portion 2b1 toward the intersecting portion 3B. The light narrowed down by the second tapered portion 2b2 is collected at the focal position 5B of the intersecting portion 3B.

  Further, the light collected at the focal position 5B of the intersecting portion 3B travels toward the optical waveguide 2B2 while expanding the width of the light mode distribution due to the symmetry of the light. In the optical waveguide 2B2, the width of the mode distribution of light increases from the intersecting portion 3B toward the first tapered portion 2b1 at the second tapered portion 2b2, and opposite from the first tapered portion 2b1 at the first tapered portion 2b1. The width of the mode distribution of light decreases toward the lead-out entrance end 4 and is led out from the lead-out entrance end 4.

  Reference numerals 21 to 27 in FIG. 3A schematically show changes in the width of the mode distribution of light propagating through the optical waveguide, as in FIG. Reference numeral 21 denotes the width of the mode distribution of light propagating through the lead-in / out end 4 on the optical waveguide 2B4 side, and reference numeral 22 denotes the width of the mode distribution of light propagating through the first tapered portion 2b1 on the optical waveguide 2B4 side. Reference numeral 23 denotes the width of the mode distribution of light propagating through the second tapered portion 2b2 on the optical waveguide 2B4 side, reference numeral 24 denotes the width of the mode distribution of light propagating through the intersection 3B, and reference numeral 25 denotes the optical waveguide. Reference numeral 26 denotes the width of the mode distribution of light propagating through the second tapered portion 2b2 on the 2B2 side, reference numeral 26 denotes the width of the mode distribution of light propagating through the first tapered portion 2b1 on the optical waveguide 2B2 side, and reference numeral 27 denotes The width of the mode distribution of light propagating through the lead-in / out end 4 on the optical waveguide 2B2 side is shown.

  Accordingly, the light propagating through the optical waveguide 2B4, the intersecting portion 3B, and the optical waveguide 2B2 is narrowed by the second tapered portion 2b2 after the width of the mode distribution of the light is enlarged by the first tapered portion 2b1. The focal position 5B formed at the center position of the intersection 3B passes through in a small mode. Further, after passing through the focal position 5B, the propagating light travels while the width of the light mode distribution is widened due to the symmetry of the light, and the width of the light mode distribution is widened at the second tapered portion 2b2 of the optical waveguide 2B2. Thereafter, the width of the mode distribution of the light is reduced and narrowed at the first tapered portion 2b1 of the optical waveguide 2B2.

  Therefore, the optical waveguide 2B4 and the optical waveguide 2B2 have a symmetrical positional relationship with respect to the center of the intersection 3B in the structure and the mode distribution of light, and the light introduced into the optical waveguide 2B4 is transmitted at the intersection 3B. It passes through the intersecting optical waveguides (optical waveguide 2B1 and optical waveguide 2B3) without leaking, and is guided to the optical waveguide 2B2 arranged oppositely.

FIG. 3B shows a configuration example of a cross section of the optical waveguide 2B4, the intersecting portion 3B, and the optical waveguide 2B2. The Si core 11 has a structure in which the upper and lower sides are sandwiched between SiO ₂ cladding portions 10a and 10b.

Numerical examples in the configuration of FIG. 3 can be the following examples.
In the numerical example of the core 11, the length a of the parabola is 4 to 6 μm, the length b is 0.5 to 1.5 μm, and the core of the optical waveguide adjacent from the boundary between the first tapered portion 2b1 and the second tapered portion 2b2 The distance c to the part where the external parts intersect is ~ 3 μm (note that 0 μm is not included), and the thickness is 220 nm. Further, the thickness of the cladding portions 10a and 10b is 800 nm, and the width of the lead-in / out end portion 4 to the optical waveguide 2B is 400 nm. When light having a wavelength of 1.55 μm is used, the refractive index of the core 11 is 3.50, and the refractive index of the cladding part 10 is 1.44.

  The numerical examples described above are merely examples, and are not limited to these numerical values, and can be determined based on the configuration of the present invention.

[Third configuration example of crossed optical waveguide]
Next, a third configuration example of the crossed optical waveguide of the present invention will be described with reference to FIG.
The third configuration example is an example in which the expansion / reduction of the width of the mode distribution of the light of the optical waveguide is adjusted by the width of the waveguide, and the outer shape of the core forming the optical waveguide is a linear shape having an inclination. In this example, the width of the waveguide is adjusted by the inclination of the linear shape.

  FIG. 4A is a plan view of the third configuration example, and FIG. 4B is a cross-sectional view of the third configuration example (part indicated by a one-dot chain line in FIG. 4A). The cross section of the optical waveguide is shown.

As in the first configuration example, the cross optical waveguide 1C of the third configuration example is configured by crossing two optical waveguides 2 (2C1 to 2C4) at the crossing portion 3C to form a low refractive index that forms a substrate. The high refractive index Si core 11 can be formed in the SiO ₂ cladding 10.

  Of the optical waveguides 2 provided in the crossed optical waveguide 1C shown in FIG. 4A, one optical waveguide is composed of an optical waveguide 2C2 and an optical waveguide 2C4 arranged at symmetrical positions with the crossing portion 3C interposed therebetween, and the other. The optical waveguide is composed of an optical waveguide 2C1 and an optical waveguide 2C3 that are arranged symmetrically across the intersection 3C, and the optical waveguide (2C2, 2C4) and the optical waveguide (2C1, 2C3) are at the intersection 3C. Orthogonal.

  The optical waveguide 2C2 and the optical waveguide 2C4 are optically symmetric with respect to the intersection 3C, and any of them may be an introduction path or a lead-out path. Also, the optical waveguide 2C1 and the optical waveguide 2C3 are optically symmetric with respect to the intersection 3C, and any of them may be an introduction path or a lead-out path.

  Here, for the sake of convenience, the optical waveguide 2C4 will be described as an introduction path, the optical waveguide 2C2 as an extraction path, the optical waveguide 2C3 as an introduction path, and the optical waveguide 2C1 as an extraction path.

  Hereinafter, the configuration of the optical waveguide will be described using an optical waveguide including the optical waveguide 2C2 and the optical waveguide 2C4. The optical waveguide composed of the optical waveguide 2C2 and the optical waveguide 2C4 intersects the optical waveguide composed of the optical waveguide 2C1 and the optical waveguide 2C3, and the light introduced from the optical waveguide 2C4 intersects the optical waveguide (optical It is required to proceed to the optical waveguide 2C2 through the intersection 3C without leaking to the side of the optical waveguide comprising the waveguide 2C1 and the optical waveguide 2C3.

  In the third configuration example, the outer shape of the core of each of the optical waveguides 2C1 to 2C4 is configured as a linear shape having an inclination, and the focal position of the mode narrowed down by the linear inclination and the center position of the intersection 3C are matched. This suppresses leakage between intersecting optical waveguides and reduces light propagation loss.

In the configuration shown in FIG. 4 (a), each optical waveguide 2C1~2C4 is produced by forming a core 11 of Si on the cladding portion 10 of SiO _2. The outer shape of the core 11 of each of the optical waveguides 2C1 to 2C4 in the third configuration example is formed in a linear shape having an inclination. Here, in the linear shape having an inclination, when the distance in the optical axis direction between the position where the width of the optical waveguide is the minimum and the position where the optical waveguide is maximum is a and the maximum width is b, the inclination of the linear shape is b / It is represented by a. Each of the optical waveguides 2C1 to 2C4 is configured by arranging four linear shapes centering on the focal position 5C at positions that are four-fold symmetrical at 90 ° intervals.

  Each of the optical waveguides 2C1 to 2C4 includes a first taper portion 2c1 and a second taper portion 2c2 that have different widths in the optical axis direction, and the first taper portion 2c1 and the second taper portion 2c2 are widened. It can be formed by combining the parts.

  The first taper portion 2c1 is linearly widened from the lead-in / in end portion 4 toward the intersecting portion 3C, and the second taper portion 2c2 is formed between the first taper portion 2c1 and the second taper portion 2c2. The width is narrowed in a straight line shape from the boundary toward the intersection 3C. At this time, in each linear shape, the distance d between the boundary between the first tapered portion 2c1 and the second tapered portion 2c2 and the focal position 5C is longer than the length b of the widest portion in the linear shape ( When d> b), the angle θ formed by the linear outer shape portion of the adjacent optical waveguide is an acute angle.

  In the optical waveguide 2C4, the width W1 of the first tapered portion 2c1 increases linearly from the lead-in / in end portion 4 toward the intersecting portion 3C, and becomes the maximum width W2 at the boundary with the second tapered portion 2c2. The width W3 of the second tapered portion 2c2 decreases linearly from the boundary between the second tapered portion 2c2 and the first tapered portion 2c1 toward the intersecting portion 3C, and the width of the mode distribution of the light is the focal position 5C. Narrowed to converge.

  Since the width of the second taper portion 2c2 is narrowed at the location where the adjacent optical waveguide 2C4 and the outer portion of the core of the optical waveguide 2C1 intersect, the angle θ formed by the outer portion becomes an acute angle.

  According to the positional relationship described above, in the optical waveguide 2C4, the light introduced from the lead-in / in end 4 increases in the light mode toward the intersection 3C in the first tapered portion 2c1, and the second tapered portion 2c2 The width of the mode distribution of light decreases from the tapered portion 2c1 to the intersecting portion 3C. The light focused by the second tapered portion 2c2 is collected at the focal position 5C of the intersecting portion 3C.

  Furthermore, the light condensed at the focal position 5C of the intersection 3C travels toward the optical waveguide 2C2 while the width of the mode distribution of the light is widened due to the symmetry of the light. In the optical waveguide 2C2, the width of the mode distribution of light increases from the intersecting portion 3C toward the first tapered portion 2c1 at the second tapered portion 2c2, and the opposite from the first tapered portion 2c1 at the first tapered portion 2c1. The width of the mode distribution of light decreases toward the lead-out entrance end 4 and is led out from the lead-out entrance end 4.

  Reference numerals 21 to 27 in FIG. 4A schematically show changes in the width of the mode distribution of light propagating through the optical waveguide, as in FIG. Reference numeral 21 denotes the width of the mode distribution of light propagating through the lead-in / out end 4 on the optical waveguide 2C4 side, and reference numeral 22 denotes the width of the mode distribution of light propagating through the first tapered portion 2c1 on the optical waveguide 2C4 side. Reference numeral 23 denotes the width of the mode distribution of light propagating through the second tapered portion 2c2 on the optical waveguide 2C4 side, reference numeral 24 denotes the width of the mode distribution of light propagating through the intersection 3C, and reference numeral 25 denotes the optical waveguide. Reference numeral 26 denotes the width of the mode distribution of light propagating through the second tapered portion 2c2 on the 2C2 side, reference numeral 26 denotes the width of the mode distribution of light propagating through the first tapered portion 2c1 on the optical waveguide 2C2 side, and reference numeral 27 denotes The width of the mode distribution of light propagating through the lead-in / out end portion 4 on the optical waveguide 2C2 side is shown.

  Therefore, the width of the mode distribution of the light propagating through the optical waveguide 2C4, the intersection 3C, and the optical waveguide 2C2 is enlarged by the first taper 2c1, then reduced by the second taper 2c2, and the center of the intersection 3C is obtained. It passes through the focal position 5C formed at the position in a state where the width of the mode distribution of light is small. Further, after passing through the focal position 5C, the propagating light travels while the width of the light mode distribution is widened due to the symmetry of the light, and the width of the light mode distribution is expanded at the second tapered portion 2c2 of the optical waveguide 2C2. Thereafter, the width of the mode distribution of light is reduced at the first tapered portion 2c1 of the optical waveguide 2C2.

  Therefore, the optical waveguide 2C4 and the optical waveguide 2C2 have a symmetrical positional relationship with respect to the center of the intersection 3C in the structure and the mode distribution of light, and the light introduced into the optical waveguide 2C4 is transmitted at the intersection 3C. It passes without leaking to the intersecting optical waveguides (optical waveguide 2C1 and optical waveguide 2C3) side, and is guided to the optical waveguide 2C2 arranged oppositely.

FIG. 4B shows a configuration example of a cross section of the optical waveguide 2C4, the intersecting portion 3C, and the optical waveguide 2C2. The Si core 11 has a structure in which the upper and lower sides are sandwiched between SiO ₂ cladding portions 10a and 10b.

The numerical example in the configuration of FIG. 4 can be the following example.
In the numerical example of the core 11, the length a is 4 to 6 μm, the length b is 0.5 to 1.5 μm, and the outer portion of the core of the optical waveguide adjacent from the boundary between the first tapered portion 2c1 and the second tapered portion 2c2 The distance c to the intersecting portion is ˜3 μm (note that 0 μm is not included), and the thickness is 220 nm. Further, the thickness of the cladding portions 10a and 10b is 800 nm, and the width of the lead-in / out end portion 4 to the optical waveguide 2C is 400 nm. When light having a wavelength of 1.55 μm is used, the refractive index of the core 11 is 3.50, and the refractive index of the cladding part 10 is 1.44.

  The numerical examples described above are merely examples, and are not limited to these numerical values, and can be determined based on the configuration of the present invention.

[Fourth configuration example of crossed optical waveguide]
Next, a fourth configuration example of the crossed optical waveguide of the present invention will be described with reference to FIG.

The fourth configuration example is an example in which the mode increase / decrease of the optical waveguide is adjusted by the thickness of the waveguide.
FIG. 5A is a plan view of the fourth configuration example, and FIGS. 5B and 5C are cross-sectional views of the fourth configuration example (parts indicated by alternate long and short dash lines in FIG. 5A). Yes, the cross section of each optical waveguide is shown.

As in the first configuration example, the cross optical waveguide 1D of the fourth configuration example is configured by crossing two optical waveguides 2 (2D1 to 2D4) at the intersection 3D to form a low refractive index that constitutes the substrate. The high refractive index Si core 11 can be formed in the SiO ₂ cladding 10.

  Of the optical waveguides 2 included in the crossed optical waveguide 1D shown in FIG. 5A, one of the optical waveguides is composed of an optical waveguide 2D2 and an optical waveguide 2D4 that are arranged symmetrically across the intersection 3D, and the other The optical waveguide is composed of an optical waveguide 2D1 and an optical waveguide 2D3 that are arranged symmetrically across the intersection 3D, and the optical waveguide (2D2, 2D4) and the optical waveguide (2D1, 2D3) are at the intersection 3D. Orthogonal.

  The optical waveguide 2D2 and the optical waveguide 2D4 are optically symmetric with respect to the intersection 3D, and any of them may be an introduction path or a lead-out path. Also, the optical waveguide 2D1 and the optical waveguide 2D3 are optically symmetric with respect to the intersection 3D, and any of them may be an introduction path or a lead-out path.

  Here, for the sake of convenience, the optical waveguide 2D4 will be described as an introduction path, the optical waveguide 2D2 as an output path, the optical waveguide 2D3 as an introduction path, and the optical waveguide 2D1 as an output path.

  Hereinafter, the configuration of the optical waveguide will be described using an optical waveguide including the optical waveguide 2D2 and the optical waveguide 2D4. The optical waveguide composed of the optical waveguide 2D2 and the optical waveguide 2D4 intersects the optical waveguide composed of the optical waveguide 2D1 and the optical waveguide 2D3, and the light introduced from the optical waveguide 2D4 intersects the optical waveguide (optical The optical waveguide 2D2 is required to pass through the intersection 3D without leaking to the side of the optical waveguide 2D1 and the optical waveguide 2D3.

  In the fourth configuration example, the thickness of the core of each of the optical waveguides 2D1 to 2D4 is adjusted stepwise, and the focal position of the mode distribution of light narrowed down by adjusting the thickness and the center position of the intersection 3D are matched. By suppressing leakage between intersecting optical waveguides, light propagation loss is reduced.

In the configuration shown in FIG. 5 (a), each optical waveguide 2D1~2D4 is produced by forming a core 11 of Si on the cladding portion 10 of SiO _2. The core 11 of each of the optical waveguides 2D1 to 2D4 in the fourth configuration example expands / reduces the width of the mode distribution of the light by changing the thickness stepwise, and reduces the width of the mode distribution of the light once expanded. The aperture is squeezed and condensed at the focal position 5D.

  Each of the optical waveguides 2D1 to 2D4 can be configured by arranging four shapes centered on the focal position 5D at positions that are four-fold symmetric at intervals of 90 degrees.

  Each of the optical waveguides 2D1 to 2D4 includes a first taper portion 2d1 and a second taper portion 2d2 whose thickness increases and decreases in the direction of the optical axis, and includes the first taper portion 2d1 and the second taper portion 2d2. , And can be formed by combining the portions having a large thickness.

  The first tapered portion 2d1 gradually decreases in thickness from the lead-in / in end portion 4 toward the intersecting portion 3D, and the second tapered portion 2d2 includes the first tapered portion 2d1 and the second tapered portion 2d2. The thickness is increased stepwise from the boundary toward the intersection 3D.

  In the optical waveguide 2D4, the thickness T1 of the first taper portion 2d1 is gradually reduced from the lead-in / in end portion 4 toward the intersecting portion 3D, and becomes the minimum thickness T2 at the boundary with the second taper portion 2d2. . The width T3 of the second tapered portion 2d2 increases stepwise from the boundary between the second tapered portion 2d2 and the first tapered portion 2d1 toward the intersecting portion 3D, and the width of the mode distribution of light is at the focal position 5D. Narrowed to converge.

  According to the above configuration, in the optical waveguide 2D4, the width of the mode distribution of the light introduced from the lead-in / out end portion 4 increases toward the intersecting portion 3D in the first taper portion 2d1, and the second taper portion In 2d2, the width of the mode distribution of light decreases from the first tapered portion 2d1 toward the intersecting portion 3D. The light narrowed down by the second tapered portion 2d2 is condensed at the focal position 5D of the intersecting portion 3D.

  Furthermore, the light condensed at the focal position 5D of the intersecting portion 3D travels toward the optical waveguide 2D2 while widening the width of the light mode distribution due to the symmetry of the light. In the optical waveguide 2D2, the width of the mode distribution of light increases from the intersecting portion 3D toward the first tapered portion 2d1 at the second tapered portion 2d2, and the first tapered portion 2d1 is opposite from the first tapered portion 2d1. The width of the mode distribution of light decreases toward the lead-out entrance end 4 and is led out from the lead-out entrance end 4.

  Reference numerals 21 to 27 in FIG. 5A schematically show changes in the width of the mode distribution of light propagating through the optical waveguide, as in FIG. Reference numeral 21 denotes the width of the mode distribution of light propagating through the lead-in / out end 4 on the optical waveguide 2D4 side, and reference numeral 22 denotes the width of the mode distribution of light propagating through the first tapered portion 2d1 on the optical waveguide 2D4 side. Reference numeral 23 denotes the width of the mode distribution of light propagating through the second tapered portion 2d2 on the optical waveguide 2D4 side, reference numeral 24 denotes the width of the mode distribution of light propagating through the intersection 3D, and reference numeral 25 denotes the optical waveguide. Reference numeral 26 denotes the width of the mode distribution of light propagating through the second tapered portion 2d2 on the 2D2 side, reference numeral 26 denotes the width of the mode distribution of light propagating through the first tapered portion 2d1 on the optical waveguide 2D2 side, and reference numeral 27 denotes The width of the mode distribution of light propagating through the lead-in / out end 4 on the optical waveguide 2D2 side is shown.

  Accordingly, the width of the mode distribution of the light propagating through the optical waveguide 2D4, the intersection 3D, and the optical waveguide 2D2 is enlarged by the first taper 2d1, then reduced by the second taper 2d2, and the center of the intersection 3D It passes through the focal position 5D formed at the position with the width of the mode distribution of light reduced. Further, after passing through the focal position 5D, the propagating light travels while the width of the light mode distribution is widened due to the symmetry of the light, and the width of the light mode distribution is expanded by the second tapered portion 2d2 of the optical waveguide 2D2. Thereafter, the mode is reduced by the first tapered portion 2d1 of the optical waveguide 2D2.

The taper portion described above has a configuration in which the thickness is changed stepwise, but is not limited to a stepwise configuration and may be configured to change the thickness continuously. In the formation of the tapered portion of the optical waveguide, when the process of generating the Si core on the SiO ₂ cladding portion is performed using a photolithography technique, a configuration in which the thickness is changed step by step is preferable.

  Therefore, the optical waveguide 2D4 and the optical waveguide 2D2 have a symmetric positional relationship with respect to the structure and light distribution with the center of the intersection 3D as a boundary, and the light introduced into the optical waveguide 2D4 intersects at the intersection 3D. It passes without leaking to the optical waveguides (optical waveguide 2D1 and optical waveguide 2D3) side to be guided to the optical waveguide 2D2 arranged oppositely.

FIG. 5B shows an example of the cross-sectional configuration of the optical waveguide 2D4, the crossing portion 3D, and the optical waveguide 2D2, and FIG. 5C shows the cross-sectional configuration of the optical waveguide 2D3, the crossing portion 3D, and the optical waveguide 2D1. An example is shown. The Si core 11 has a structure in which the upper and lower sides are sandwiched between SiO ₂ cladding portions 10a and 10b.

Numerical examples in the configuration of FIG. 5 can be the following examples.
In the numerical example of the core 11, the thickness of the derived light portion is 220 nm. Further, the thickness of the cladding portions 10a and 10b is 800 nm, and the width of the lead-in / out end portion 4 to the optical waveguide 2C is 400 nm. When light having a wavelength of 1.55 μm is used, the refractive index of the core 11 is 3.50, and the refractive index of the cladding part 10 is 1.44.

  The numerical examples described above are merely examples, and are not limited to these numerical values, and can be determined based on the configuration of the present invention.

[Fifth Configuration Example of Crossed Optical Waveguide]
Next, a fifth configuration example of the crossed optical waveguide of the present invention will be described with reference to FIG.
The fifth configuration example shows an example in which the mode increase / decrease in the waveguide is adjusted by the width of one waveguide and the thickness of the other waveguide intersecting is adjusted.

  FIG. 6A is a plan view of the fifth configuration example, and FIGS. 6B and 6C are cross-sectional views of the fifth configuration example (parts indicated by alternate long and short dash lines in FIG. 6A). Yes, the cross section of each optical waveguide is shown.

As in the first configuration example, the crossed optical waveguide 1E of the fifth configuration example is configured by crossing two optical waveguides 2 (2E1 to 2E4) at a crossing portion 3E to form a low refractive index that constitutes a substrate. The high refractive index Si core 11 can be formed in the SiO ₂ cladding 10.

  Of the optical waveguides 2 included in the crossed optical waveguide 1E shown in FIG. 6A, one optical waveguide is composed of an optical waveguide 2E2 and an optical waveguide 2E4 arranged at symmetrical positions with the crossing portion 3E interposed therebetween, and the other. The optical waveguide is composed of an optical waveguide 2E1 and an optical waveguide 2E3 that are arranged symmetrically across the intersection 3E, and the optical waveguide (2E2, 2E4) and the optical waveguide (2E1, 2E3) are at the intersection 3E. Orthogonal.

  The optical waveguide 2E2 and the optical waveguide 2E4 are optically symmetric with respect to the intersection 3E, and any of them may be an introduction path or a lead-out path. The optical waveguide 2E1 and the optical waveguide 2E3 are also optically symmetric with respect to the intersecting portion 3E, and any of them may be an introduction path or a lead-out path.

  Here, for the sake of convenience, the optical waveguide 2E4 will be described as an introduction path, the optical waveguide 2E2 as an extraction path, the optical waveguide 2E3 as an introduction path, and the optical waveguide 2E1 as an extraction path.

  Similarly to the first configuration example, the optical waveguide 2E2 and the optical waveguide 2E4, which are one of the optical waveguides, have an outer shape of the core formed in an elliptical shape, and the optical waveguide 2A4 of the first configuration example and the optical waveguide, respectively. The configuration can be the same as that of the waveguide 2A2. Further, the optical waveguide 2E3 and the optical waveguide 2E1, which are the other optical waveguides, are formed by adjusting the thickness of the core stepwise in the same manner as in the fourth configuration example, and the optical waveguide 2D3 in the fourth configuration example, respectively. The same configuration as that of the optical waveguide 2D1 can be adopted.

  The optical waveguide composed of the optical waveguide 2E2 and the optical waveguide 2E4 intersects the optical waveguide composed of the optical waveguide 2E1 and the optical waveguide 2E3. The light introduced from the optical waveguide 2E4 is required to pass through the intersecting portion 3E without leaking to the intersecting optical waveguide (the optical waveguide composed of the optical waveguide 2E1 and the optical waveguide 2E3) and proceed to the optical waveguide 2E2. Further, it is required that the light introduced from the optical waveguide 2E3 passes through the intersecting portion 3E without leaking to the intersecting optical waveguide (the optical waveguide composed of the optical waveguide 2E2 and the optical waveguide 2E4) and proceeds to the optical waveguide 2E1. It is done.

  In the fifth configuration example, the outer shapes of the cores of the waveguides 2E4 and 2E2 are configured in an elliptical shape, the focal position of the elliptical shape and the center position of the intersection 3E are aligned, and the thickness of the cores of the optical waveguides 2E3 and 2E1 By adjusting the thickness stepwise and aligning the focal position of the mode distribution of light focused by adjusting the thickness and the center position of the intersecting portion 3E, leakage between the optical waveguides intersecting each other is suppressed, and light propagation Reduce loss.

In the configuration shown in FIG. 6 (a), the optical waveguide 2E4,2E2 is generated by forming the core 11 of Si on the cladding portion 10 of SiO _2, the outer shape of the core 11 is formed in an elliptical shape. The elliptical core, which can be the same as the first configuration, is configured by arranging two elliptical shapes at symmetrical positions around the focal position 5E.

  Each of the optical waveguides 2E4 and 2E2 includes a first tapered portion 2e1 and a second tapered portion 2e2 that have different widths in the optical axis direction. The first taper portion 2e1 has an elliptical shape extending from the lead-in / in end portion 4 toward the intersection portion 3E, and the second taper portion 2e2 is elliptical from the first taper portion 2e1 toward the intersection portion 3E. Narrow the width. At this time, the angle θ formed between the second tapered portion 2e2 and the linear outer shape portion of the adjacent optical waveguides 2E3 and 2E1 is an acute angle.

  According to the positional relationship described above, in the optical waveguide 2E4, the light introduced from the lead-in / out end 4 increases in the light mode toward the intersection 3E in the first taper 2e1, and the second taper 2e2 The width of the mode distribution of light decreases from the tapered portion 2e1 to the intersecting portion 3E. The light reduced and narrowed by the second tapered portion 2e2 is condensed at the focal position 5E of the intersecting portion 3E.

  Furthermore, the light collected at the focal position 5E of the intersection 3E travels toward the optical waveguide 2E2 while the width of the mode distribution of the light is widened due to the symmetry of the light. In the optical waveguide 2E2, the width of the mode distribution of light increases from the intersecting portion 3E toward the first tapered portion 2e1 at the second tapered portion 2e2, and opposite from the first tapered portion 2e1 at the first tapered portion 2e1. The width of the mode distribution of light decreases toward the lead-out entrance end 4 and is led out from the lead-out entrance end 4.

  Therefore, the width of the mode distribution of the light propagating through the optical waveguide 2E4, the intersecting portion 3E, and the optical waveguide 2E2 is enlarged by the first tapered portion 2e1 and then reduced and narrowed by the second tapered portion 2e2. It passes through the focal position 5E formed at the center position of 3E with the width of the mode distribution of light reduced. After propagating light passes through the focal position 5E, it advances while expanding the width of the mode distribution of light from the symmetry of light, and after the width of the mode distribution of light is expanded by the second tapered portion 2e2 of the optical waveguide 2E2, The width of the mode distribution of light is reduced at the first tapered portion 2e1 of the optical waveguide 2E2.

  Therefore, the optical waveguide 2E4 and the optical waveguide 2E2 have a symmetrical positional relationship with respect to the center of the intersection 3E in the structure and the mode distribution of light, and the light introduced into the optical waveguide 2E4 passes through the intersection 3E. It passes without leaking to the intersecting optical waveguides (optical waveguide 2E1 and optical waveguide 2E3) side, and is guided to the optical waveguide 2E2 arranged oppositely.

FIG. 6B shows an example of the cross-sectional configuration of the optical waveguide 2E4, the crossing portion 3E, and the optical waveguide 2E2, and FIG. 6C shows the cross-sectional configuration of the optical waveguide 2E3, the crossing portion 3E, and the optical waveguide 2E1. An example is shown. The Si core 11 has a structure in which the upper and lower sides are sandwiched between SiO ₂ cladding portions 10a and 10b.

FIG. 6B shows a configuration example of a cross section of the optical waveguide 2E4, the intersecting portion 3E, and the optical waveguide 2E2. The Si core 11 has a structure in which the upper and lower sides are sandwiched between SiO ₂ cladding portions 10a and 10b.

Further, in the configuration shown in FIG. 6 (c), each optical waveguide 2E1,2E3 is generated by forming the core 11 of Si on the cladding portion 10 of SiO _2, the core 11 changes the thickness stepwise As a result, the width of the mode distribution of the light is increased / decreased, the width of the mode distribution of the once expanded light is reduced and narrowed down and condensed at the focal position 5E.

  Each of the optical waveguides 2E1 and 2E4 is arranged at a position that is symmetrical about the focal position 5E.

  Each of the optical waveguides 2E1 and 2E3 includes a first taper portion 2e1 and a second taper portion 2e2 whose thickness increases and decreases in the optical axis direction, and includes the first taper portion 2e1 and the second taper portion 2e2. , And can be formed by combining the portions having a large thickness.

  The first taper portion 2e1 gradually decreases in thickness from the lead-in / in end portion 4 toward the intersecting portion 3E, and the second taper portion 2e2 includes the first taper portion 2e1 and the second taper portion 2e2. The thickness is gradually increased from the boundary to the intersection 3E, and the width of the light mode distribution is narrowed so as to converge at the focal position 5E.

  With the configuration described above, in the optical waveguide 2E3, the width of the mode distribution of the light introduced from the lead-in / out end portion 4 in the first tapered portion 2e1 increases toward the intersecting portion 3E, and the second tapered portion 2e2 The width of the mode distribution of light decreases from the first tapered portion 2e1 toward the intersecting portion 3E. The light reduced and narrowed by the second tapered portion 2e2 is condensed at the focal position 5E of the intersecting portion 3E.

  Further, the light collected at the focal position 5E of the intersection 3E travels toward the optical waveguide 2E2 while widening the mode distribution of the light due to the symmetry of the light. In the optical waveguide 2E2, the width of the mode distribution of light increases from the intersecting portion 3E toward the first tapered portion 2e1 at the second tapered portion 2e2, and the first tapered portion 2e1 is opposite from the first tapered portion 2e1. The width of the mode distribution of the light is reduced toward the lead-out end 4 on the side, and the light is derived from the lead-out end 4.

  The optical waveguide 2E3 and the optical waveguide 2E1 are symmetrical in terms of structure and light distribution with the center of the intersection 3E as a boundary, and the light introduced into the optical waveguide 2E3 intersects at the intersection 3E. The light passes through the waveguides (optical waveguide 2E2 and optical waveguide 2E4) without leaking, and is guided to the optical waveguide 2E1 disposed oppositely.

  In the above-described configuration example of the crossed optical waveguide, the input / output waveguide and the crossed waveguide have a common configuration in which the condensing position is the center of the crossing. In this configuration, the waveguides disposed on both sides of the condensing positions of the input / output waveguide and the crossing waveguide may be asymmetrical in addition to the configuration in which the light mode distribution is symmetric.

  For example, in a configuration in which the outer shape of the optical waveguide is formed in an elliptical shape, when the light mode distribution is symmetric, the major and minor axes of the elliptical shape are the same size, while the light mode distribution is asymmetric. In this case, the sizes of the major axis and the minor axis of the elliptical shape are different. In any configuration, the ratio between the major axis and the minor axis of the elliptical shape is set so that the condensing position is the center of the intersection.

  Even when the outer shape of the optical waveguide is configured as a parabola shape or an inclined linear shape, the focusing position is symmetric or asymmetric with respect to the intersection center by adjusting the size of the shape. It can be set as a simple structure.

[Example of crossed optical waveguide simulation]
A simulation example of the first configuration example of the crossed optical waveguide of the present invention will be described with reference to FIG.

 FIG. 7 shows an example of a configuration in which the outer shape of the core is an elliptical shape when the refractive index of the core is 3.50, the refractive index of the cladding is 1.44, and the wavelength λ is 1.55 μm. It is.

  FIG. 7A shows a case where the major axis size shown in FIG. 1 is a = 4.556 μm, the minor axis size is b = 1.222 μm, and the second tapered portion 2a2 is c = 2.696 μm. A simulation example is shown. The transmission loss in this example is 0.18 dB.

 FIG. 7B shows the case where the major axis size shown in FIG. 1 is a = 5.667 μm, the minor axis size is b = 1.185 μm, and the second tapered portion 2a2 is c = 0.722 μm. A simulation example is shown. The transmission loss in this example is 0.07 dB.

 According to the example shown in FIGS. 7A and 7B, the introduced light is condensed and extracted after being collected at the intersection, and the distribution of the light propagating through the introduction-side and emission-side optical waveguides is as follows: It can be confirmed that it is symmetrical about the intersection.

  The present invention is not limited to the above embodiments. Various modifications can be made based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

  The crossed optical waveguide of the present invention can be applied to optical communication parts such as LSI chips, optical transceivers and high-speed internets, sensors, and the like.

1A to 1E Crossed optical waveguide 2, 2A to 2E Optical waveguide 2A1 to 2A4 Optical waveguide 2B1 to 2B4 Optical waveguide 2C1 to 2C4 Optical waveguide 2D1 to 2D4 Optical waveguide 2E1 to 2E4 Optical waveguide 2a1 Taper 2a2 Taper 2b1 Taper 2b2 2c1 taper part 2c2 taper part 2d1 taper part 2d2 taper part 2e1 taper part 2e2 taper part 3A-3E crossing part 4 lead-in / in end part 5A-5E focal point position 10, 10a, 10b clad part 11 core 11A-11D cross optical waveguide 12A1- 12A4 optical waveguide 12C1 optical waveguide 12D1-12D4 optical waveguide 13A-13D intersection

Claims (9)

In crossed optical waveguides where multiple optical waveguides intersect in the same plane,
A plurality of optical waveguides and an intersection where the plurality of optical waveguides intersect in the same plane,
The optical waveguide is narrowed after converging the mode distribution of light propagating through the optical waveguide, condensing the center of the intersecting portion as a condensing position, and two optical waveguides arranged opposite to each other across the intersecting portion. A crossed optical waveguide characterized in that a mode distribution of light is symmetric or asymmetric with respect to the light collection position.   In the optical axis direction toward the intersection, the width of the mode distribution of the propagating light is enlarged and then reduced, and the width of the mode distribution is narrowed down at the center of the intersection by reducing the width of the mode distribution. The crossed optical waveguide according to claim 1, wherein the light is condensed at the center of the portion. The optical waveguide is
The cross light according to claim 1 or 2, wherein the width of the mode distribution of propagating light is expanded and / or reduced by increasing or decreasing the size of at least one of width and thickness. Waveguide. In crossed optical waveguides where multiple optical waveguides intersect in the same plane,
A plurality of optical waveguides and an intersection where the plurality of optical waveguides intersect in the same plane,
The optical waveguide has a first taper portion and a second taper portion for expanding or reducing the width of the mode distribution of light between each light entry / exit end portion and the intersection portion,
The first tapered portion has a width that increases toward the intersection,
The second tapered portion has a width that decreases toward the intersection,
Providing the first tapered portion on the lead-in / in end portion side, providing the second tapered portion on the intersecting portion side,
The two optical waveguides sandwiching the intersecting part form a symmetric mode distribution on the introduction side and the derivation side with the center of the intersecting part as the condensing position and the condensing position as the center of symmetry. Optical waveguide. In crossed optical waveguides where multiple optical waveguides intersect in the same plane,
A plurality of optical waveguides and an intersection where the plurality of optical waveguides intersect in the same plane,
The optical waveguide has a first taper portion and a second taper portion for expanding or reducing the width of the mode distribution of light between each light entry / exit end portion and the intersection portion,
The first tapered portion has a thickness that decreases toward the intersection,
The second tapered portion increases in thickness toward the intersection,
Providing the first tapered portion on the lead-in / in end portion side, providing the second tapered portion on the intersecting portion side,
The two optical waveguides sandwiching the intersecting part form a symmetric mode distribution on the introduction side and the derivation side with the center of the intersecting part as the condensing position and the condensing position as the center of symmetry. Optical waveguide. The optical waveguide is formed by a SiO ₂ cladding and a Si core,
The side walls of the cores of the first tapered portion and the second tapered portion have an elliptical shape,
The crossed optical waveguide according to claim 4, wherein the elliptical shape has a focal point of the elliptical shape as a center of the intersecting portion. The optical waveguide is formed by a SiO ₂ cladding and a Si core,
The side wall portions of the cores of the first tapered portion and the second tapered portion have a parabolic shape,
5. The crossed optical waveguide according to claim 4, wherein the parabolic shape of the second tapered portion has a focal point of the parabolic shape as a center of the intersecting portion. The optical waveguide is formed by a SiO ₂ cladding and a Si core,
The side wall portions of the cores of the first tapered portion and the second tapered portion have a linear shape,
5. The crossed optical waveguide according to claim 4, wherein the linearly inclined slope of the second tapered portion has a mode-decreasing focus at the center of the intersecting portion. The optical waveguide is formed by a SiO ₂ cladding and a Si core,
The crossed optical waveguide according to any one of claims 4, 6, 7, and 8, wherein an angle on a clad side formed by a side wall portion of a core of an adjacent second tapered portion is an acute angle. .