JP2009205086A - Optical waveguide element, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the dimension of a core and decrease the radius of its curvature as to an optical waveguide element. <P>SOLUTION: This waveguide element includes a first clad layer 30, a waveguide layer 40, and a second clad layer 50 in order on a substrate 20. The waveguide layer 40 includes a core 42 and side clads 44 provided at locations horizontally holding a core 42 between. The refractive indexes of the first clad layer 30 and the second clad layer 50 are lower than the refractive index of the core 42, and the refractive index of the side clad 44 is lower than the refractive indexes of the core 42, the first clad layer 30 and the second clad layer 50. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical waveguide element and a method for manufacturing the same.

Many optical waveguide structures for confining and propagating light have been proposed. As a typical example, a LiNbO ₃ substrate that is an electro-optic crystal is formed by diffusing Ti to increase the refractive index, a crystal formed by introducing protons into this crystal, or a quartz-based material or A layered compound semiconductor having a different composition is known.

  In recent years, an optical waveguide structure that uses a silicon material for the core and surrounds the periphery with quartz, which is a low-refractive-index substance, has attracted much attention because it can realize a very small radius of curvature (see, for example, Patent Document 1). ).

  However, the optical waveguide disclosed in Patent Document 1 is formed with a core width and height of about 300 nm so as to satisfy the single mode condition. For this reason, it is difficult to manufacture such as the need for state-of-the-art lithography technology, and the input position accuracy required in proportion to the size of the core is severe even when light is incident on the optical waveguide. Become.

  On the other hand, a structure has been proposed in which the optical waveguide has a ridge structure using a quartz-based material, and both sides of the core have an air layer (see, for example, Patent Document 2). According to the technique disclosed in Patent Document 2, since the refractive index difference between the core and the surrounding air is large, the size for realizing the single mode condition is increased. Even if it is larger than this structure, a large curvature, that is, a small curvature radius can be realized. Here, in the structure disclosed in Patent Document 2, it is necessary to make the refractive index of the substrate sufficiently lower than the equivalent refractive index for the propagating light in order to reduce the loss of the propagating light to the substrate.

In order to reduce the loss of light propagated to the substrate, a technique has been proposed in which several layers of a high refractive index are provided between the lower portion of the core and the substrate (for example, see Non-Patent Document 1).
US Pat. No. 5,838,870 Japanese Patent No. 3755961 D. Dai et al. , “A Minimized SiO2 Waveguide With an Antiresonant Reflecting Structure for Large-Scale Optical Integrations,” IEEE Phototechnologies Technologies. 19 No. 10 pp. 759-761, May 15 2007

  However, the structure disclosed in Non-Patent Document 1 requires a complicated process, such as an operation process for forming a multilayer film on a substrate for manufacturing. In addition, since a long dry etching process is performed to form a ridge-shaped optical waveguide, the damage to which the electronic circuit is damaged by the dry etching process is used for the purpose of creating the optical waveguide on the substrate on which the electronic circuit is formed. It is unsuitable when you think about it.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an optical waveguide element having an optical waveguide with a large core size and a small radius of curvature, and a method for manufacturing the same. is there.

  To achieve the above object, according to a first aspect of the present invention, a first cladding layer, a second cladding layer, and a waveguide layer provided between the first cladding layer and the second cladding layer. An optical waveguide device is provided.

  In this optical waveguide element, the waveguide layer includes a core and a side cladding provided at a position sandwiching the core in the horizontal direction. The refractive indexes of the first cladding layer and the second cladding layer are lower than the refractive index of the core. Further, the refractive index of the side cladding is lower than the refractive indexes of the first cladding layer and the second cladding layer.

  According to a preferred embodiment of the optical waveguide element of the present invention, the first cladding layer has a first convex portion in a portion in contact with the core, and an area of a portion of the core in contact with the first convex portion is: It is smaller than the area on the side in contact with the first convex part. The second cladding layer has a second convex portion in a portion in contact with the core, and the area of the portion in contact with the second convex portion of the core is smaller than the area in contact with the second convex portion.

  In the implementation of the optical waveguide device described above, preferably, for the fundamental mode of light propagating through the core, the equivalent refractive index in the core is higher than the equivalent refractive index in the first cladding layer and the second cladding layer, and the core is For higher order modes of propagating light, the equivalent refractive index in the core is preferably set lower than the equivalent refractive indexes in the first cladding layer and the second cladding layer.

  In order to achieve the above-described object, according to the second aspect of the present invention, the first to (n + 1) cladding layers (n is an integer of 2 or more), and between the kth cladding layer and the (k + 1) th cladding layer. There is provided an optical waveguide device including a provided k-th waveguide layer (k is an integer of 1 to n).

  In this optical waveguide device, the kth waveguide layer is configured to include a kth core and a kth side cladding provided at a position sandwiching the kth core in the horizontal direction. The refractive indices of the kth cladding layer and the (k + 1) th cladding layer are lower than the refractive index of the kth core. The refractive index of the kth side cladding is lower than the refractive indexes of the kth cladding layer and the (k + 1) th cladding layer.

  According to a preferred embodiment of the optical waveguide device of the present invention, the kth cladding layer has a kth convex portion in a portion in contact with the kth core, and a portion of the kth core in contact with the kth convex portion. Is smaller than the area in contact with the kth convex portion. The (k + 1) -th clad layer has (k + 1) -th convex portions in contact with the k-th core, and the area of the k-th core in contact with the (k + 1) -th convex portion is the area in contact with the (k + 1) -th convex portion. Smaller than.

  In the implementation of the optical waveguide element described above, preferably, for the fundamental mode of light propagating through the k-th core, the equivalent refractive index in the k-th core is higher than the equivalent refractive index in the k-th cladding layer and the k + 1-th cladding layer, In addition, for the higher order mode of light propagating through the k-th core, the equivalent refractive index in the k-th core is preferably set lower than the equivalent refractive index in the k-th cladding layer and the k + 1-th cladding layer.

  In order to achieve the above-described object, according to the third aspect of the present invention, a method of manufacturing an optical waveguide device having the following steps is provided. First, a first cladding layer is formed on a substrate. Next, after forming a core forming layer on the first cladding layer, patterning is performed to form a waveguide layer having a side cladding at a position sandwiching the core in the horizontal direction. Next, a second cladding layer is formed on the waveguide layer. At this time, the refractive indexes of the first cladding layer and the second cladding layer are made lower than the refractive index of the core.

  In carrying out the above-described method for manufacturing an optical waveguide device, preferably, a step of forming a first protrusion on a surface of the first cladding layer on the side in contact with the core, and a step of forming a first protrusion on the surface of the second cladding layer on the side in contact with the core. A step of forming two convex portions. At this time, the area of the portion of the core in contact with the first convex portion is made smaller than the area of the side in contact with the first convex portion, and the area of the portion of the core in contact with the second convex portion is set to be the second convex portion. Smaller than the area on the side in contact with

  In order to achieve the above-described object, according to a fourth aspect of the present invention, there is provided a method for manufacturing an optical waveguide device having the following steps. First, a first cladding layer is formed on a substrate. Next, after forming a k-th core forming layer on the k-th clad layer, patterning is performed to form a k-th waveguide layer having a k-th side clad at a position sandwiching the k-th core and the k-th core. The process and the process of forming the (k + 1) -th cladding layer on the k-th waveguide layer are repeated by sequentially changing k from 1 to n. At this time, the refractive indexes of the kth cladding layer and the (k + 1) th cladding layer are made lower than the refractive index of the kth core.

  In carrying out the above-described method for manufacturing an optical waveguide element, preferably, the step of forming the kth convex portion on the surface of the kth cladding layer in contact with the kth core, and the side of the k + 1 cladding layer in contact with the kth core Forming a (k + 1) -th convex portion on the surface. At this time, the area of the portion of the k-th core in contact with the k-th convex portion is made smaller than the area on the side in contact with the k + 1-th convex portion, and the area of the portion of the k-th core in contact with the k + 1-th convex portion is The area is smaller than the area in contact with the (k + 1) th convex portion.

  According to the optical waveguide device of the present invention, since the cladding layers are provided above and below the core, when the thickness of the core is brought close to 0, the fundamental mode guided light gradually approaches the plane wave, and the optical waveguide is always provided. There is a propagation state in which guided light exists. Therefore, the cutoff condition of the basic mode is relaxed.

  Further, if the cutoff condition of the fundamental mode is relaxed, the dimension range for propagating only the fundamental mode increases.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the shape, size, and arrangement relationship of each component are merely schematically shown to the extent that the present invention can be understood. In the following, a preferred configuration example of the present invention will be described. However, the material and numerical conditions of each component are merely preferred examples. Therefore, the present invention is not limited to the following embodiments, and many changes or modifications that can achieve the effects of the present invention can be made without departing from the scope of the configuration of the present invention.

(First embodiment)
The structure of the optical waveguide device according to the first embodiment will be described with reference to FIG. FIG. 1 is a diagram for explaining the structure of an optical waveguide device, and shows a cut end surface cut along a plane perpendicular to the optical waveguide direction.

  In the optical waveguide device 10, a first cladding layer 30, a first waveguide layer (hereinafter, the first waveguide layer may be simply referred to as a waveguide layer) 40, and a second cladding layer 50 are formed on a substrate 20. In order. That is, the waveguide layer 40 is provided between the first cladding layer 30 used as the lower cladding and the second cladding layer 50 used as the upper cladding.

  For example, a silicon substrate is used as the substrate 20. Here, the substrate 20 is formed with any suitable electronic integrated circuit (not shown), a light receiving element (not shown), and the like including circuit elements such as transistors and resistance elements. For example, when the wavelength used is about 0.85 μm, a silicon material can be used as the light receiving element.

  As the material of the first cladding layer 30 and the second cladding layer 50, for example, quartz, spin-on-glass (SOG), photosensitive sol-gel material, or the like can be used. Photosensitive sol-gel materials include PJ5010 (model number) and PJ5023 (model number) manufactured by JSR. The refractive index of these materials is about 1.4 to 1.6.

  The waveguide layer 40 includes a first core (hereinafter, the first core may be simply referred to as a core) 42 and a first side clad (hereinafter, the first side) provided at a position sandwiching the core 42 in the horizontal direction. The clad may be simply referred to as a side clad.) 44.

As material of the core 42, for example, an inorganic material, a material obtained by adding germanium (Ge), titanium (Ti) in a quartz, a silicon oxide _{(Si 1-x O x)} , silicon nitride _{(Si 1-x N} x ) Or a photosensitive polymer which is an organic material can be used. The refractive index of these materials is about 1.5 to 1.7.

  Here, the refractive indexes of the first cladding layer 30 and the second cladding layer 50 are set lower than the refractive index of the core 42.

  The side cladding 44 is formed of a material having a refractive index lower than that of the core 42, the first cladding layer 30, and the second cladding layer 50. For example, the side clad 44 may be composed of an air layer. That is, the region other than the core 42 of the waveguide layer 40 can be filled with air.

  Next, the design conditions of the core 42 will be described with reference to FIGS.

FIG. 2 is a diagram showing the relationship between the normalized frequency and the equivalent refractive index of the core. In FIG. 2, the horizontal axis represents the normalized frequency 2πW (N _W ² -1.0) ^1/2 / λ, and the vertical axis represents the equivalent refractive index n _eff .

Here, W represents the width of the core 42, λ represents the wavelength of light propagating through the core, and N _W represents the refractive index of the core 42. Here, the core 42 is sufficiently thick.

In FIG. 2, curve I represents the equivalent refractive index of the core 42 for the fundamental mode, and curve II represents the equivalent refractive index of the core 42 for the higher order mode. The equivalent refractive index n _effC of the cladding is 1.46.

The equivalent refractive index _{n EffW} core 42 relative to the fundamental mode light is greater than the effective refractive index _{n Effc} of cladding, light in the fundamental mode can propagate the core 42. Similarly, the equivalent refractive index n _EffW core 42 of the higher order modes for light is greater than the effective refractive index n _Effc of cladding, light of higher modes can propagate the core 42.

Therefore, if the normalized frequency 2πW (N _W ² -1.0) ^1/2 / λ is set so that the fundamental mode light propagates through the core 42 and the higher-order mode light does not propagate through the core 42, A single mode condition is fulfilled in which the core only propagates fundamental mode light.

That is, in order to satisfy single mode conditions, the core 42 for the equivalent refractive index n _EffW core 42 relative to the fundamental mode light, the equal frequency and the equivalent refractive index n _Effc cladding and f1, the higher-order mode light the equivalent refractive index _{n EffW} is, the equal frequency and the equivalent refractive index _{n Effc} cladding is taken as f2, the normalized frequency ^{_{2πW (n W 2 -1.0) 1/2}} / λ, greater than f1 f2 A smaller value may be set.

FIG. 3 is a diagram illustrating the relationship between the refractive index N _W of the core 42 and the width W of the core 42. In FIG. 3, the horizontal axis represents the refractive index N _W of the core 42, and the vertical axis represents the width of the core 42 normalized by the optical wavelength λ.

  In FIG. 3, white circles (◯) indicate the minimum width W that satisfies the single mode condition. The minimum width W satisfying this single mode condition is determined in correspondence with the frequency f1 shown in FIG. In FIG. 3, white squares (□) indicate the maximum width W that satisfies the single mode condition. The maximum width W that satisfies this single mode condition is determined corresponding to the frequency f2 shown in FIG. When the width W of the core 42 is between ◯ and □ (range indicated by I in the figure), the single mode condition is satisfied. Here, it is assumed that the thickness T of the core 42 is sufficiently large.

  When the core 42 is a curved waveguide, the refractive index of the core 42 needs to be sufficiently higher than the first cladding layer 30 and the second cladding layer 50 in order to suppress the loss of light during propagation. However, as indicated by ○ and □ in FIG. 3, when the refractive index of the core 42 is increased, the width of the core 42 needs to be reduced. In this case, when the refractive index of the core 42 is 1.6, the width W of the core 42 is about 0.7λ.

  FIG. 3 further shows the width W of the core 42 when the thickness T of the core 42 is finite. Here, the thickness T of the core 42 and the width W of the core 42 are made equal. That is, the cross-sectional shape of the core 42 perpendicular to the light guiding direction in the core 42 is a square shape. In FIG. 3, black circles (●) indicate the minimum width of the core 42 that satisfies the single mode condition when the thickness T of the core 42 is finite. In FIG. 3, black squares (■) indicate the maximum width of the core 42 that satisfies the single mode condition when the thickness T of the core 42 is finite. The width of the core 42 that satisfies the single mode condition when the thickness T of the core 42 is finite is calculated by a differential method (FDM: Finite Difference Method).

  The range that satisfies the single mode condition of the width W of the core 42 is between ● and ■ (range indicated by II in the figure). This range is slightly narrower than that indicated by I when the core 42 is sufficiently thick. However, for example, when the refractive index Nw is 1.6, the single mode condition is satisfied when the width W / λ of the standardized core 42 is in the range of 0.8λ to 1.2λ. If it is 85 micrometers, the core 42 of 1 micrometer square is realizable.

  For example, when there is no second clad layer that is an upper clad, the guided light is affected by a low refractive index portion such as air, so the equivalent refractive index is lowered. For this reason, it is necessary to use a material having a higher refractive index as the material of the core 42, which makes it difficult to select the material. On the other hand, in the configuration having the upper clad of the present invention, it is possible to prevent the equivalent refractive index from being lowered.

  Further, when the lower clad, the core, and the upper clad have a vertically symmetric structure and the core thickness is brought close to 0, the fundamental mode guided light gradually approaches a plane wave. Since this plane wave has no cut-off state, the single mode condition is relaxed, and as a result, the size range satisfying the single mode condition is increased.

  Further, in the configuration without the upper clad, the center of the optical field distribution is pulled by the lower clad, so that the component propagating through the clad increases, and as a result, the loss of light propagating through the core increases. On the other hand, in the configuration having the upper clad of the present invention, the center of the optical field distribution is near the center of the core, so that the component propagating through the clad is reduced, and as a result, the loss of light propagating through the core is reduced. .

  The reason why a small radius of curvature R can be realized with the above-described configuration is that the light propagating through the core is difficult to be converted into radiated light if the refractive index difference between the core and the side cladding is sufficiently large. For example, in order to set the radius of curvature R to about 10 μm, it is sufficient to use quartz as the core and air as the side cladding. This can be inferred from the fact that the quartz-air interface can be used to bend light in a right-angle direction.

  Next, with reference to FIG. 4, the manufacturing method of the optical waveguide element of 1st Embodiment is demonstrated. FIG. 4 is a process diagram for explaining the method of manufacturing the optical waveguide device according to the first embodiment, and shows a cut end surface cut along a plane perpendicular to the optical waveguide direction, as in FIG.

  This method for manufacturing an optical waveguide device includes the following steps. First, for example, a silicon substrate is prepared as the substrate 20. Note that an electronic integrated circuit including a transistor, a resistance element, a light receiving element, or the like may be formed over the substrate 20.

Next, an SiO ₂ film using, for example, a photosensitive sol-gel material is formed on the substrate 20 as the first cladding layer 30 (FIG. 4A).

  Next, a core forming layer 41 is formed by applying a photosensitive polymer on the first cladding layer 30 (FIG. 4B).

  Next, the core forming layer 41 is patterned to form the core 42. This patterning may be performed by any suitable method depending on the material of the core forming layer 41. For example, when the core forming layer is formed of a photosensitive polymer, a photolithography method can be used. When the core forming layer does not have photosensitivity, a well-known wet etching may be performed after forming a mask pattern on the core forming layer (FIG. 4C).

  Next, the second cladding layer 50 is pasted onto the core 42 using any suitable means (FIG. 4D).

(Second Embodiment)
With reference to FIG. 5, the structure of the optical waveguide device according to the second embodiment will be described. FIG. 5 is a view for explaining the structure of the optical waveguide device of the second embodiment, and shows a cut end surface cut along a plane perpendicular to the optical waveguide direction.

  The optical waveguide device 11 according to the second embodiment is that the first cladding layer 32 includes the first protrusions 34 and the second cladding layer 52 includes the second protrusions 54. It is different from an element, and other than that is the same. Therefore, the overlapping description is omitted.

  The first protrusion 34 is formed near the surface of the first cladding layer 32 on the side in contact with the core 42. The area of the core 42 in contact with the first protrusion 34 is smaller than the area of the core 42 on the side in contact with the first protrusion 34. As a result, the side clad 46 is provided between the core 42 and the first clad layer 32 (indicated by A in the figure).

This 1st convex part 34 can be formed as follows, for example. In this case, the first cladding layer is formed of a SiO ₂ film, and the core 42 is formed of a resist. SiO ₂ is dissolved in hydrofluoric acid, but the resist is not dissolved. Therefore, the first cladding layer 32 is dissolved from the core 42 side. At this time, a part of the first clad layer where the core 42 is formed is also side-etched.

  Similarly, the second convex portion 54 is formed near the surface of the second cladding layer 52 on the side in contact with the core 42. The area of the core 42 in contact with the second protrusion 54 is smaller than the area of the core 42 on the side in contact with the second protrusion 54. As a result, the side cladding 46 is provided so as to enter between the core 42 and the second cladding layer 52.

  The second convex portion 54 can be formed in the same manner as the first convex portion 34.

  With this configuration, the component of the guided light that leaks from the core 42 to the first cladding layer 32 and the second cladding layer 52 is reduced. As a result, the light propagation loss can be further suppressed as compared with the configuration of the first embodiment. For this reason, it is suitable for realizing an optical waveguide having a small curvature radius.

  The operation of the second embodiment will be described with reference to FIG. FIG. 6 is a characteristic diagram for explaining the operation of the optical waveguide device according to the second embodiment shown in FIG. 5, and shows a simulation result by a three-dimensional vector beam propagation (BPM) method.

  FIG. 6 shows the curvature radius R (unit: μm) on the horizontal axis and the output light intensity on the vertical axis. Here, the output light intensity is a relative magnitude when the input light intensity is 1.

  In this simulation, the width W and the thickness T of the core 42 are both 1 μm. The side etch portion has a width of 0.1 μm and a height of 0.5 μm.

  The refractive index of the core is 1.6, the cladding is quartz, and the side cladding is air. It can be seen that when the radius of curvature R of the waveguide is 10 μm or more, the loss of light does not depend on the refractive index, and the loss due to the curved waveguide is suppressed. Here, the reason why the output takes a value smaller than 1 is due to the coupling loss in the input of light to the optical waveguide.

(Third embodiment)
With reference to FIG. 7, the structure of the optical waveguide device of the third embodiment will be described. FIG. 7 is a view for explaining the structure of the optical waveguide device of the third embodiment, and shows a cut end surface cut by a plane perpendicular to the optical waveguide direction.

  The optical waveguide device 12 of the third embodiment includes the clad layers 30 (30-1, 30-2,...) And the waveguide layers 40 (40-1, 40-2,...) Alternately on the substrate 20. The first to nth multilayer waveguide structures 15 (15-1, 15-2,...) Are formed.

  The first-layer waveguide structure 15-1 includes a first cladding layer 30-1, a first waveguide layer 40-1, and a second cladding layer 50-1. That is, the first waveguide layer 40-1 is provided between the first cladding layer 30-1 used as the lower cladding and the second cladding layer 50-1 used as the upper cladding.

  The first waveguide layer 40-1 includes a first core 42-1 and a first side cladding 44-1 provided at a position sandwiching the first core 42-1 in the horizontal direction.

  The first-layer waveguide structure 15-1 can be configured in the same manner as the optical waveguide device 10 of the first embodiment described with reference to FIG.

  The second-layer waveguide structure 15-2 is formed on the first-layer waveguide structure 15-1. Here, the second cladding layer 30-2 (50-1) serves as both the upper cladding of the first-layer waveguide structure 15-1 and the lower cladding of the second-layer waveguide structure 15-2. Yes.

  Similarly, the k-th waveguide structure 15-k includes a k-th waveguide layer 40-k between the k-th cladding layer 30-k and the (k + 1) th cladding layer 30- (k + 1). The Here, the (k + 1) th cladding layer 30- (k + 1) serves as both the upper cladding of the kth waveguide structure 15-k and the lower cladding of the (k + 1) th waveguide structure 15- (k + 1).

  The first to n + 1 cladding layers 30-1 to (n + 1) can be formed in the same manner as the first and second cladding layers of the first embodiment. The first to n waveguide layers 40-1 to 40-k can be formed in the same manner as the cladding layer of the first embodiment.

  In addition, you may provide a convex part in each clad layer similarly to 2nd Embodiment. In this case, the kth clad layer has a kth convex portion at a portion in contact with the kth core. The area of the portion of the kth core that contacts the kth convex portion is smaller than the area of the side that contacts the kth convex portion. Further, the (k + 1) -th cladding layer has (k + 1) -th convex portions at the portions in contact with the k-th core. The area of the portion of the kth core that contacts the (k + 1) th convex portion is smaller than the area of the portion that contacts the (k + 1) th convex portion.

  Next, with reference to FIG. 8, the manufacturing method of the optical waveguide element of 3rd Embodiment is demonstrated. FIG. 8 is a process diagram for explaining the method of manufacturing the optical waveguide device according to the third embodiment, and shows a cut end surface cut along a plane perpendicular to the optical waveguide direction, similarly to FIG.

  This method for manufacturing an optical waveguide device includes the following steps. First, for example, a silicon substrate is prepared as the substrate 20. Note that an electronic integrated circuit including a transistor, a resistance element, a light receiving element, or the like may be formed over the substrate 20.

  Next, the first cladding layer 30-1 and the first core formation layer 41-1 are formed on the substrate 20. Here, a photosensitive material is used as the first core forming layer 41-1 (FIG. 8A).

  Next, the area | region in which the core 42-1 of the 1st core formation layer 41-1 is formed is exposed. After that, the second cladding layer 30-2 (50-1) is formed on the first core formation layer 41-1 (FIG. 8B).

  Next, the second core formation layer 41-2 is formed on the second cladding layer 30-2, and the region of the second core formation layer 41-2 where the core 42-2 is formed is exposed. Thereafter, the third cladding layer 30-3 (50-2) is formed on the second core formation layer 41-2.

  This process is repeated until the (n + 1) th cladding layer 30- (n + 1) is formed on the nth core formation layer 41-n (FIG. 8C).

  Thereafter, the solvent is poured between the clad layers through the openings 56 formed in each clad layer, and the photosensitive material filling the side clad portion is melted. As a result, an optical waveguide element having a multilayer waveguide structure is obtained.

  The opening 56 for pouring the solvent can be formed by any suitable and well-known conventional photolithography and etching. The opening 56 can be formed after forming the (k + 1) th clad layer and before forming the (k + 1) th core layer, that is, whenever each clad layer is formed (FIG. 8D). .

  A material that decomposes and vaporizes by ultraviolet rays or heat may be used for the side cladding, and the vaporized material may be taken out through the opening 56.

  In addition, the multilayer waveguide structure is formed by removing the material of the side cladding portion of each waveguide layer in the same manner as in the method of manufacturing the optical waveguide device according to the first embodiment described with reference to FIG. After forming, the step of forming the upper cladding may be repeated.

It is a figure for demonstrating the structure of the optical waveguide element of 1st Embodiment. It is a figure which shows the relationship between the normalized frequency and the equivalent refractive index of a core. It is a figure which shows the relationship between the refractive index _Nw of a core, and the width W of a core. It is process drawing for demonstrating the manufacturing method of the optical waveguide element of 1st Embodiment. It is a figure for demonstrating the structure of the optical waveguide element of 2nd Embodiment. It is a characteristic view for demonstrating operation | movement of the optical waveguide element of 2nd Embodiment. It is a figure for demonstrating the structure of the optical waveguide element of 3rd Embodiment. It is process drawing for demonstrating the manufacturing method of the optical waveguide element of 3rd Embodiment.

Explanation of symbols

10, 11, 12 Optical waveguide device
20 substrates
30, 32 Clad layer (lower clad)
34, 54 Convex
40 Waveguide layer 41 Core forming layer 42 Core 44, 46 Side cladding
50, 52 Clad layer (upper clad)
56 Opening

Claims (10)

A first cladding layer;
A second cladding layer;
A waveguide layer provided between the first cladding layer and the second cladding layer;
The waveguide layer includes a core and a side cladding provided at a position sandwiching the core in the horizontal direction,
The refractive index of the first cladding layer and the second cladding layer is lower than the refractive index of the core, and the refractive index of the side cladding is higher than the refractive index of the first cladding layer and the second cladding layer. An optical waveguide element characterized by being low. The first cladding layer has a first convex portion at a portion in contact with the core,
The area of the portion in contact with the first convex portion of the core is smaller than the area on the side in contact with the first convex portion,
The second cladding layer has a second convex portion in a portion in contact with the core,
2. The optical waveguide device according to claim 1, wherein an area of a portion of the core that is in contact with the second convex portion is smaller than an area of a side that is in contact with the second convex portion. For the fundamental mode of light propagating through the core, the equivalent refractive index in the core is higher than the equivalent refractive index in the first cladding layer and the second cladding layer,
3. The high-order mode of light propagating through the core has an equivalent refractive index in the core lower than that in the first cladding layer and the second cladding layer. 4. Optical waveguide element. First to (n + 1) cladding layers (n is an integer of 2 or more);
A k-th waveguide layer (k is an integer from 1 to n) provided between the k-th cladding layer and the (k + 1) -th cladding layer,
The kth waveguide layer includes a kth core and a kth side cladding provided at a position sandwiching the kth core in the horizontal direction,
The kth cladding layer and the (k + 1) th cladding layer have a refractive index lower than that of the kth core, and the kth side cladding has a refractive index of the kth cladding layer and the k + 1th cladding layer. An optical waveguide device having a refractive index lower than that of the optical waveguide device. The k-th cladding layer has a k-th convex portion at a portion in contact with the k-th core,
The area of the portion of the kth core that contacts the kth convex portion is smaller than the area of the side that contacts the kth convex portion,
The k + 1 clad layer has a k + 1 convex portion at a portion in contact with the kth core;
5. The optical waveguide device according to claim 4, wherein an area of a portion of the k-th core in contact with the k + 1 convex portion is smaller than an area in contact with the k + 1 convex portion. For the fundamental mode of light propagating through the kth core, the equivalent refractive index in the kth core is higher than the equivalent refractive index in the kth cladding layer and the k + 1th cladding layer,
5. The high-order mode of light propagating through the k-th core has an equivalent refractive index in the k-th core lower than that in the k-th cladding layer and the k + 1-th cladding layer. Or the optical waveguide element of 5. Forming a first cladding layer on the substrate;
Forming a core forming layer on the first cladding layer and then performing patterning to form a waveguide layer having a core and a side cladding at a position sandwiching the core in the horizontal direction;
Forming a second cladding layer on the waveguide layer,
A method of manufacturing an optical waveguide element, wherein refractive indexes of the first cladding layer and the second cladding layer are made lower than a refractive index of the core. Forming a first cladding layer on the substrate;
A k-th core forming layer is formed on the k-th clad layer (k is an integer of 1 to n and n is an integer of 2 or more), and then patterned, so that the k-th core and the k-th core are horizontally aligned. Forming a kth waveguide layer having a kth side cladding at a sandwiched position;
Repeating the step of forming the (k + 1) -th cladding layer on the k-th waveguide layer by sequentially changing k from 1 to n;
A method of manufacturing an optical waveguide device, wherein refractive indices of the k-th cladding layer and the k + 1-th cladding layer are made lower than a refractive index of the k-th core. Forming a first protrusion on a surface of the first cladding layer on a side in contact with the core;
Forming a second protrusion on the surface of the second cladding layer on the side in contact with the core,
The area of the portion of the core that contacts the first convex portion is smaller than the area of the side that contacts the first convex portion,
8. The method of manufacturing an optical waveguide element according to claim 7, wherein an area of a portion of the core that is in contact with the second convex portion is smaller than an area of a side that is in contact with the second convex portion. Forming a k-th convex portion on the surface of the k-th cladding layer on the side in contact with the k-th core;
Forming a k + 1 convex portion on a surface of the k + 1 clad layer on a side in contact with the kth core,
The area of the k-th core in contact with the k-th convex part is smaller than the area on the side in contact with the k + 1 convex part,
9. The method of manufacturing an optical waveguide device according to claim 8, wherein an area of a portion of the k-th core in contact with the k + 1 convex portion is smaller than an area in contact with the k + 1 convex portion.

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