JP5251037B2 - Optical waveguide device, manufacturing method thereof, and optical device - Google Patents

Description

The present invention relates to an optical waveguide element , a manufacturing method thereof , and an optical element .

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 stack of compound semiconductors with different compositions 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. If you think about it, it is unsuitable.

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

According to a preferred embodiment of the optical waveguide device of this invention is configured to include a metal film formed on a substrate and an optical waveguide consisting of the cladding layer are sequentially stacked on the metal layer and the core layer The The optical waveguide is formed in a ridge shape, and the periphery of the optical waveguide is filled with a material having a lower refractive index than the core layer and the cladding layer, and the cross section of the cladding layer and the core layer in the direction perpendicular to the optical waveguide direction is rectangular. The area of the upper surface of the cladding layer is smaller than the area of the upper surface of the core layer.

  In implementing the optical waveguide element described above, the refractive index of the core layer is preferably higher than the refractive index of the cladding layer.

  According to the preferred embodiment of the optical waveguide element described above, the width of the cladding layer in the direction perpendicular to the optical waveguide direction is smaller than the width of the core layer in the direction perpendicular to the optical waveguide direction.

According to another preferred embodiment of the optical waveguide element described above, the cladding layer is formed in a plurality of columnar shapes spaced apart from each other along the optical waveguide direction.
The optical element of the present invention includes an optical waveguide element and a multimode interference coupler or an arrayed waveguide grating connected to the optical waveguide element.
The optical waveguide element includes an optical waveguide composed of a metal film formed on a substrate, and a clad layer and a core layer sequentially stacked on the metal film. This optical waveguide is formed in a ridge shape, the area of the upper surface of the cladding layer is smaller than the area of the upper surface of the core layer, and the cross section in the direction perpendicular to the optical waveguide direction of the cladding layer and the core layer is rectangular, The width of the clad layer in the direction perpendicular to the optical waveguide direction is smaller than the width of the core layer in the direction perpendicular to the optical waveguide direction, and the refractive index of the core layer is higher than the refractive index of the clad layer. Is filled with a material having a lower refractive index than the core layer and the cladding layer.

According to good suitable embodiment of the method of manufacturing the above-mentioned optical waveguide device includes the following steps. First, a metal film is formed on a substrate. Next, a clad formation layer and a core formation layer are sequentially laminated on the metal film and then patterned to form a ridge-shaped optical waveguide composed of the clad layer and the core layer. Here, in forming the clad layer, side etching is performed to make the width of the clad layer perpendicular to the optical waveguide direction smaller than the width of the core layer perpendicular to the optical waveguide direction.

According to another preferred embodiment of the method for manufacturing an optical waveguide element described above, the following steps are provided. First, a metal film is formed on a substrate. Next, a clad formation layer and a core formation layer are sequentially laminated on the metal film and then patterned to form a ridge-shaped optical waveguide composed of the clad layer and the core layer. Here, the clad formation layer is formed alternately along the optical waveguide direction using two kinds of materials having different solubility in the etchant, and after forming the optical waveguide, one of the two kinds of materials is used using the etchant. As a result, the cladding layer is formed in a plurality of columns separated from each other along the optical waveguide direction. Thereby, the area of the upper surface of the cladding layer is made smaller than the area of the upper surface of the core layer .

  In the implementation of the optical waveguide element described above, it is preferable that the core forming layer is formed of a material having a higher refractive index than the cladding forming layer.

According to the optical waveguide device , the manufacturing method thereof , and the optical device of the present invention, a ridge-shaped optical waveguide shape is formed, and the periphery of the optical waveguide is filled with a material having a lower refractive index than the core and the clad. A smaller radius of curvature can be realized with the dimensions of.

  Furthermore, by providing a metal film between the clad and the substrate, radiation loss to the substrate can be reduced. Further, since the metal film can be formed by the same process as the process of making the multilayer wiring of the electronic circuit, the optical waveguide element can be manufactured by a simple process.

  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.

( Reference example )
With reference to FIGS. 1A and 1B, the structure of the optical waveguide device of the reference example will be described. FIGS. 1A and 1B are schematic views for explaining an optical waveguide element of a reference example . 1A is a plan view, and FIG. 1B shows a cut end surface taken along the line AA in FIG. 1A.

  The optical waveguide element 10 includes a metal film 40 formed on a substrate 20 and an optical waveguide 50 including a clad layer 60 and a core layer 70 sequentially stacked on the metal film 40.

  For example, a silicon substrate is used as the substrate 20. Here, on the substrate 20, as the electronic integrated circuit 30, any suitable known well-known integrated circuit including circuit elements such as transistors and resistor elements may be formed.

  The material of the metal film 40 is preferably a material that absorbs less light. For example, gold (Au), silver (Ag), copper (Cu), aluminum (Al), etc. are used.

  The optical waveguide 50 is formed in a ridge shape, and the refractive index of the core layer 70 is higher than the refractive index of the cladding layer 60. The periphery of the optical waveguide 50 is filled with a material having a lower refractive index than the core layer 70 and the cladding layer 60.

As a material of the core layer 70, for example, an inorganic material obtained by adding germanium (Ge), titanium (Ti) or the like to quartz, silicon oxide (Si _1-x O _x ), silicon nitride (Si _1-x). N _x ) or a photosensitive polymer that is an organic material can be used. The refractive index of these materials is about 1.5 to 1.7.

  Further, as the material of the cladding layer 60, quartz, spin on glass (SOG), photosensitive sol-gel material, or the like can be used. As photosensitive sol-gel materials, there are PJ5010 (model number) and PJ5023 (model number) manufactured by JSR. The refractive index of these materials is about 1.4 to 1.6.

  The periphery of the optical waveguide 50 is filled with, for example, air as a material having a refractive index lower than that of the cladding layer 60 and the core layer 70. The refractive index around the optical waveguide 50 at this time is 1.

Next, a method for manufacturing the optical waveguide element of the reference example will be described. The manufacturing method of the optical waveguide device of the reference example includes the following steps. First, a metal film 40 is formed on a silicon substrate, for example, as the substrate 20. Note that the substrate 20 may include any suitable known well-known integrated circuit in which circuit elements such as transistors and resistor elements and wirings are formed on a semiconductor substrate as the electronic integrated circuit 30.

  The metal film 40 is formed, for example, by forming a film of the above metal material on the entire upper surface of the substrate 20 by sputtering, and then leaving the necessary metal material film by photolithography and dry etching.

  Next, a clad formation layer and a core formation layer are sequentially laminated on the metal film 40 and then patterned to form a ridge-shaped optical waveguide 50 including the clad layer 60 and the core layer 70.

  In the step of forming the optical waveguide, first, for example, an SOG film is formed as a clad formation layer by spin coating and baking. Next, for example, a photosensitive polymer is applied as a core forming layer on the clad forming layer, and then patterned by photolithography to form the core layer 70. Next, the clad forming layer is patterned by wet etching to form the clad layer 60.

  In addition, when the clad formation layer has photosensitivity such as a photosensitive sol-gel material, the clad layer 60 may be formed by photolithography. Further, when the material of the core forming layer is not photosensitive, a mask covering the region for forming the optical waveguide is formed on the core forming layer, and the core layer 70 is formed by wet etching. good.

  Thus, the patterning for forming the optical waveguide may be performed by any suitable method depending on the material of the core forming layer and the clad forming layer.

  Note that the photolithography and dry etching for forming the metal film 40 may be performed before the clad formation layer and the core formation layer are stacked, or at the same time as or after the formation of the core layer and the clad layer by patterning. You can go.

The operation of the optical waveguide device of the reference example will be described with reference to FIGS. 2, 3 and 4 are characteristic diagrams for explaining the operation of the optical waveguide device of the reference example , and show simulation results by a three-dimensional beam propagation (BPM) method.

  2A and 2B show the output light intensity with respect to the thickness S of the cladding layer 60 in the straight waveguide. 2A and 2B, the horizontal axis indicates the thickness S (unit: μm) of the cladding layer 60, and the vertical axis indicates the output light intensity. The output light intensity on the vertical axis is a relative magnitude when the input light intensity is 1.

  As simulation conditions, the substrate 20 is a silicon substrate, the width W of the optical waveguide 50 and the thickness H of the core layer 70 are both 1 μm, the thickness T of the metal film 40 is 0.1 μm, and the length L of the optical waveguide 50 is The calculation was performed for a case where light having a wavelength of 1.55 μm propagated as 1000 μm. The refractive index of the core layer 70 is 1.56, the refractive index of the cladding layer 60 is 1.46, and the refractive index around the optical waveguide 50 is 1.0.

  Here, TE waves are used as the polarization of propagating light. This is because the TM wave is largely absorbed by the metal film.

  In FIG. 2A, the material of the metal film is gold (Au), and in FIG. 2B, the material of the metal film is copper (Cu). In any case, when the thickness S of the cladding layer 60 is 2 μm or more, there is almost no dependency on the thickness S of the cladding layer 60, that is, no propagation loss. The reason why the output light intensity is about 0.9, which is smaller than 1, is due to the coupling loss in the light input to the optical waveguide 50.

  Comparing FIG. 2A and FIG. 2B, when the thickness S of the cladding layer 60 is small, when the material of the metal film 40 is Au, the output light intensity is higher than that of Cu. For example, when the thickness S of the cladding layer 60 is 0.5 μm, the output light intensity is approximately 0.65 when the material of the metal film 40 is Au, whereas the output light intensity is approximately 0.65 when the material of the metal film 40 is Cu. Is about 0.5. This is because Cu absorbs light more than Au.

  3A and 3B show the output light intensity with respect to the radius of curvature in the curved waveguide. 3A and 3B, the abscissa indicates the curvature radius R (unit: μm), and the ordinate indicates the output light intensity. The output light intensity on the vertical axis is a relative magnitude when the input light intensity is 1.

  The conditions of the simulation here are the same as the cases of FIGS. 2A and 2B except for the conditions regarding the shape of the optical waveguide, and the other points are the same. Here, the optical waveguide is a curved waveguide having a length L of 100 μm. When the radius of curvature R is small, the circumference of the radius R is propagated a plurality of times. On the other hand, when the radius of curvature R is large, a part of the circumference of the radius R is propagated.

  In FIG. 3A, the material of the metal film 40 is gold (Au), and in FIG. 3B, the material of the metal film 40 is copper (Cu). 3A and 3B show curves I, II, and III, respectively, when the thickness S of the cladding layer 60 is 0.5 μm, 1.0 μm, and 1.5 μm.

  Regardless of whether the material of the metal film 40 is Au or Cu, and the thickness S of the cladding layer 60 is 0.5 μm, 1.0 μm, or 1.5 μm, the radius of curvature R is 6 μm. In the above region, there is almost no dependency on the radius of curvature R, that is, no radiation loss outside the optical waveguide 50. The reason why the output light intensity is about 0.9, which is smaller than 1, is due to the coupling loss in the light input to the optical waveguide 50. The variation in the intensity of the output light due to the difference in the thickness S of the cladding layer 60 is due to the difference in coupling loss.

  4A and 4B are diagrams showing simulation results when a quartz substrate is used as the substrate.

  FIG. 4A shows the output light intensity with respect to the thickness S of the cladding layer 60 in the straight waveguide. 4A, the horizontal axis indicates the thickness S (unit: μm) of the cladding layer 60, and the vertical axis indicates the output light intensity. The output light intensity on the vertical axis is a relative magnitude when the input light intensity is 1.

  The simulation conditions are the same as in the case of FIG. 2A except that the substrate 20 is a quartz substrate.

  As shown in FIG. 4A, in the region where the thickness S of the cladding layer 60 is 2 μm or more, there is almost no dependence on the thickness S of the cladding layer 60, that is, no propagation loss. This is the same as the result of FIG. The reason why the output light intensity is about 0.9, which is smaller than 1, is due to the coupling loss in the light input to the optical waveguide 50.

  FIG. 4B shows the output light intensity with respect to the radius of curvature R in the curved waveguide. In FIG. 4B, the abscissa indicates the radius of curvature R (unit: μm), and the ordinate indicates the output light intensity. The output light intensity on the vertical axis is a relative magnitude when the input light intensity is 1. FIG. 4B shows curves I, II, and III when the thickness S of the cladding layer 60 is 0.5 μm, 1.0 μm, and 1.5 μm, respectively.

  The simulation conditions are the same as in the case of FIG. 3A except that the substrate 20 is a quartz substrate.

  As shown in FIG. 4B, when the radius of curvature R is 6 μm or more, there is almost no dependency on the radius of curvature R, that is, no radiation loss outside the optical waveguide. This is the same as the result of FIG. The reason why the output light intensity is about 0.9, which is smaller than 1, is due to coupling loss in the input of light to the optical waveguide. The variation in the intensity of the output light due to the difference in the thickness S of the cladding layer 60 is due to the difference in coupling loss.

According to the optical waveguide element of the reference example and the manufacturing method thereof, the ridge-shaped optical waveguide shape is formed, and the periphery of the optical waveguide is filled with a material having a refractive index lower than that of the core layer and the cladding layer. A smaller radius of curvature of 10 μm or less can be realized with a core width larger than 300 nm, which is about 1 μm, and a width and height of the layer. Further, the thickness of the cladding layer may be about 2 μm, and the formation process of the multilayer wiring relating to the electronic circuit formed on the substrate can be easily applied to the formation of the cladding layer.

  Furthermore, by providing a metal film between the cladding layer and the substrate, radiation loss to the substrate can be reduced.

  Further, if a ridge-shaped optical waveguide is manufactured by a photolithography process, a long-time dry etching process is not required, so that damage to the electronic circuit formed on the substrate can be reduced.

(Other configuration examples)
With reference to FIG. 5, another configuration example of the optical waveguide device of the reference example will be described. FIG. 5 is a schematic diagram for explaining another configuration example of the optical waveguide element of the reference example .

  FIG. 5A shows a cut end surface of a main part of another configuration example. This configuration example is different from the configuration described with reference to FIG. 1 in that the metal film 42 exists only in a region sandwiched between the optical waveguide 50 and the substrate 20, and the other points are the same. is there.

With reference to FIGS. 5B and 5C, the operation of another configuration example will be described. FIGS. 5B and 5C are characteristic diagrams for explaining the operation of the optical waveguide device 12 of another configuration example of the reference example , and show simulation results by the three-dimensional BPM method.

  FIG. 5B shows the output light intensity with respect to the thickness S of the cladding layer 60 in the straight waveguide. In FIG. 5B, the horizontal axis indicates the thickness S (unit: μm) of the clad layer 60, and the vertical axis indicates the output light intensity. The output light intensity on the vertical axis is a relative magnitude when the input light intensity is 1.

  As simulation conditions, the substrate 20 is a silicon substrate, the width W of the optical waveguide 50 and the thickness H of the core layer 70 are both 1 μm, the thickness T of the metal film 42 is 0.1 μm, and the length L of the optical waveguide 50 is as follows. The calculation was performed for a case where light having a wavelength of 1.55 μm propagated as 1000 μm. The refractive index of the core layer 70 is 1.56, the refractive index of the cladding layer 60 is 1.46, and the refractive index around the optical waveguide 50 is 1.0. The material of the metal film is copper (Cu).

  As shown in FIG. 5B, in the region where the thickness S of the cladding layer 60 is 2 μm or more, there is almost no dependency on the thickness S of the cladding layer 60, that is, no propagation loss. The reason why the output light intensity is about 0.9, which is smaller than 1, is due to the coupling loss in the light input to the optical waveguide 50.

  FIG. 5C shows the output light intensity with respect to the curvature radius R in the curved waveguide. FIG. 5C shows the curvature radius R (unit: μm) on the horizontal axis and the output light intensity on the vertical axis. The output light intensity on the vertical axis is a relative magnitude when the input light intensity is 1. Further, the thickness S of the cladding layer is 1.5 μm.

  As shown in FIG. 5C, when the radius of curvature R is 6 μm or more, there is almost no dependence on the radius of curvature R, that is, no radiation loss outside the optical waveguide. The reason why the output light intensity is about 0.9, which is smaller than 1, is due to the coupling loss in the light input to the optical waveguide 50.

  Thus, even when the metal film is present only between the optical waveguide and the substrate, the same effect can be obtained even when the area of the metal film is wider than the area of the optical waveguide.

(First Embodiment)
With reference to FIG. 6, the structure of the optical waveguide device according to the first embodiment will be described. FIG. 6 is a schematic diagram for explaining the optical waveguide element 14 of the first embodiment, and shows a cut end surface of a main part.

The optical waveguide element 14 of the first embodiment is different from the optical waveguide of the reference example in the cross-sectional shape of the optical waveguide 54, and the other configuration is the same as that of the reference example, and thus redundant description is omitted.

In the optical waveguide device 14 of the first embodiment, the cross section of the cladding layer 64 and the core layer 70 in the direction perpendicular to the optical waveguide direction is rectangular, and the area of the upper surface of the cladding layer 64 is the area of the upper surface of the core layer 70. Smaller than. Here, a case where the width of the cladding layer 64 in the direction perpendicular to the optical waveguide direction is smaller than the width of the core layer 70 in the direction perpendicular to the optical waveguide direction will be described. The material of the clad layer 64 and the core layer 70 can be the same as those in the reference example .

Here, according to the structure of the optical waveguide element 14 of the first embodiment, the width of the clad layer 64 is smaller than the width of the core layer 70, and the lower side of the core layer 70 (the part indicated by the arrow A in FIG. 6). ) Enters a substance (for example, air) having a lower refractive index than the core layer 70 and the cladding layer 64. For this reason, even if the clad layer 64 and the core layer 70 are formed of the same material, it becomes possible to confine the propagation light in the optical waveguide 54.

The clad layer 64 may be formed of a material having a refractive index lower than that of the core layer 70. It is preferable to make the refractive index of the cladding layer 64 smaller than the refractive index of the core layer 70 because the proportion of the propagating light absorbed by the metal film 40 decreases. Further, the multimode interference: In (MMI Multi-Mode Interference) coupler and the planar waveguide of the arrayed waveguide lattice (AWG), for cladding having a low refractive index at the bottom of the core is required, the optical of the first embodiment In order to smoothly connect the waveguide element and these MMI couplers and AWGs, it is preferable that the material of the cladding layer 64 be of a low refractive index.

Next, a method for manufacturing the optical waveguide device of the first embodiment will be described. Since the process until the metal film 40 is formed is the same as that in the reference example , the duplicate description is omitted.

  A clad formation layer and a core formation layer are sequentially laminated on the metal film 40 and then patterned to form a ridge-shaped optical waveguide 54 including the clad layer 64 and the core layer 70. Here, when the cladding layer 64 is formed, side etching is performed to make the width Wcl of the cladding layer 64 perpendicular to the optical waveguide direction smaller than the width W of the core layer 70 perpendicular to the optical waveguide direction. To do.

  In the step of forming the optical waveguide 54, first, for example, an SOG film is formed as a clad formation layer by spin coating and baking. Next, as a core forming layer, for example, a photosensitive polymer is applied on the clad forming layer, and then patterned by photolithography to form the core layer 70. Next, the clad forming layer is patterned by wet etching to form the clad layer 64.

Here, for example, SiO ₂ is dissolved in hydrofluoric acid, but the resist is not dissolved in hydrofluoric acid. Therefore, it is preferable to form the clad formation layer with SiO ₂ and the core formation layer with resist.

  Further, both the clad forming layer and the core forming layer are formed of a negative resist, and the vicinity of the surface is exposed by irradiation with ultraviolet rays, and the region on the metal film 40 side of the resist not exposed at the time of development is partially Thus, the cross-sectional shape shown in FIG. 6 can be obtained.

With reference to FIG. 7, the operation of the optical waveguide device of the first embodiment will be described. FIG. 7 is a characteristic diagram for explaining the operation of the optical waveguide device of the first embodiment, and shows a simulation result by the three-dimensional BPM method.

  FIG. 7A shows the output light intensity with respect to the thickness S of the cladding layer 64 in the linear waveguide. In FIG. 7A, the horizontal axis indicates the thickness S (unit: μm) of the cladding layer 64, and the vertical axis indicates the output light intensity.

  FIG. 7B shows the output light intensity with respect to the radius of curvature in the curved waveguide. FIG. 7B shows the radius of curvature R (unit: μm) on the horizontal axis and the output light intensity on the vertical axis.

  The output light intensity on the vertical axis in FIGS. 7A and 7B is a relative magnitude when the input light intensity is 1.

  As simulation conditions, the substrate 20 is a silicon substrate, the width W of the core layer 70 and the thickness H of the core layer 70 are both 1 μm, the thickness T of the metal film is 0.1 μm, and the width Wcl of the cladding layer 64 is The calculation was made for the case where light having a wavelength of 1.55 μm propagates, assuming 0.4 μm. The refractive index of the core layer 70 and the cladding layer 64 is 1.56, the refractive index around the optical waveguide 54 is 1.0, and the material of the metal film 40 is copper (Cu).

  FIG. 7A is a simulation result in the case of a straight waveguide, and the length L of the optical waveguide is 1000 μm. When the thickness S of the cladding layer 64 is 1 μm or more, there is almost no dependency on the thickness S of the cladding layer 64, that is, there is almost no propagation loss. The reason why the output light intensity is about 0.9, which is smaller than 1, is due to coupling loss in the input of light to the optical waveguide 54.

As described above, according to the optical waveguide device and the manufacturing method thereof according to the first embodiment, in addition to the effect of the reference example , the thickness S of the cladding layer 64 can be made smaller than that of the optical waveguide device of the reference example. Since the thickness S of the layer 64 is reduced, the production is facilitated.

FIG. 7B is a simulation result in the case of a curved waveguide, and the length L of the optical waveguide 54 is set to 100 μm. Similar to the reference example , when the radius of curvature is 6 μm or more, there is almost no dependency on the radius of curvature R, that is, no radiation loss outside the optical waveguide. The reason why the output light intensity is about 0.8, which is smaller than 1, is due to coupling loss in the input of light to the optical waveguide 54. The variation in the intensity of the output light due to the difference in the thickness S of the cladding layer 64 is due to the difference in coupling loss.

(Comparative example)
A comparative example will be described with reference to FIG. FIG. 8 is a schematic diagram for explaining a comparative example of the optical waveguide device.

FIG. 8A shows a cut end surface of a main part of the comparative example. In the optical waveguide device 110 of the comparative example, the point that the optical waveguide 150 is formed on the substrate 120 without the metal film and the refractive index of the cladding layer 160 is 1.46 are shown in FIG. The configuration is different from that of the first embodiment described with reference to the first embodiment, and the other points are the same.

  With reference to FIGS. 8B and 8C, the operation of the comparative example will be described. FIGS. 8B and 8C are characteristic diagrams for explaining the operation of the optical waveguide device of the comparative example, and show simulation results by the three-dimensional BPM method.

  FIG. 8B shows the output light intensity with respect to the thickness S of the clad layer 160 in the linear waveguide. In FIG. 8B, the horizontal axis indicates the thickness S (unit: μm) of the cladding layer 160, and the vertical axis indicates the output light intensity. FIG. 8C shows the output light intensity with respect to the radius of curvature in the curved waveguide. FIG. 8C shows the curvature radius R (unit: μm) on the horizontal axis and the output light intensity on the vertical axis.

  The output light intensity on the vertical axis in FIGS. 8B and 8C is a relative magnitude when the input light intensity is 1.

  In this comparative example, the refractive index of the core layer 170 is 1.56, whereas the refractive index of the cladding layer 160 is 1.46, and the refractive index of the cladding layer 160 is higher than the refractive index of the core layer 170. Is also getting smaller. That is, this comparative example shows the result of calculation under conditions more advantageous than the simulation conditions shown in FIG.

  In FIG. 8B, curves I, II, and III are shown for the case where the magnitude of the cut in the width direction of the clad layer is 0 μm, 0.15 μm, and 0.3 μm, respectively.

  As shown in FIG. 8B, when there are notches of 0.3 μm on both sides in the width direction of the clad layer 160 and the width Wcl of the clad layer 160 is 0.4 μm (curve III), the clad There is almost no propagation loss in the region where the thickness S of the layer 160 is 2 μm or more. Note that in FIG. 7A, the clad layer has a refractive index of 1 μm or more and a propagation loss in spite of a simulation under a condition more disadvantageous than the comparative example shown in FIG. 8B. It can be seen that the presence of the metal film is effective.

Further, when the notch size Oh of the cladding layer is 0 μm (curve I), that is, when the width W of the core layer 170 and the width Wcl of the cladding layer 160 are the same, the thickness S of the cladding layer 160 is 1.7 μm. However, the output light intensity is 0.2 or less. Since the output light intensity increases as the cuts on both sides of the cladding layer 160 are increased, it is advantageous to form the width Wcl of the cladding layer 160 narrower than the width W of the core layer 170 as in the first embodiment. You can see that

According to FIG. 8C, even when the metal film is not provided, if the thickness S of the cladding layer is 1.7 μm, the output light intensity is substantially constant at a curvature radius of 6 μm or more. The result similar to 1st Embodiment demonstrated with reference to FIG. 7 is shown.

( Second Embodiment)
With reference to FIGS. 9A, 9B, and 9C, the structure of the optical waveguide device of the second embodiment will be described. FIGS. 9A, 9B, and 9C are schematic views for explaining the optical waveguide device of the second embodiment. 9A is a plan view, FIG. 9B shows a cut end surface taken along the line AA in FIG. 9A, and FIG. 9C is a diagram of FIG. The cut | disconnected end surface taken along the BB line of 9 (A) is shown.

  Although the optical waveguide is illustrated as a straight waveguide here, it may be a curved waveguide.

The optical waveguide element 16 of the second embodiment is different from the optical waveguide element of the reference example in the cross-sectional shape along the waveguide direction of the optical waveguide 56 (direction along line BB in FIG. 9A). The other configuration is the same as that of the reference example, and thus a duplicate description is omitted.

In the optical waveguide device 16 of the second embodiment, the cross section of the cladding layer 66 and the core layer 76 in the direction perpendicular to the optical waveguide direction is rectangular, and the area of the upper surface of the cladding layer 66 is the area of the upper surface of the core layer 76. Smaller than.

  Here, the case where the clad layer 66 is formed in a plurality of columns separated from each other along the optical waveguide direction will be described.

  Since the width of the clad layer 66 is formed in a columnar shape spaced apart from each other, it is more refracted than the core layer 76 and the clad layer 66 between the columnar portions below the core layer 76 (portion indicated by arrow C in the figure). A low rate material (eg air) enters. For this reason, even if the clad layer 66 and the core layer 76 are formed of the same material, it is possible to confine the propagation light in the optical waveguide 56.

  The clad layer 66 may be made of a material having a refractive index lower than that of the core layer 76. It is preferable to make the refractive index of the clad layer 66 smaller than the refractive index of the core layer 76 because the proportion of propagating light absorbed by the metal film 46 decreases.

Next, a method for manufacturing the optical waveguide device 16 of the second embodiment will be described. Since the steps until the metal film 46 is formed are the same as those in the reference example , the duplicate description is omitted.

  A clad formation layer is formed on the metal film 46. Here, the clad forming layer is formed by alternately forming two kinds of materials having different solubility in the etchant, for example, SU-8 (manufactured by Microchem) and a spin-on-glass film along the optical waveguide direction.

  For example, after a core formation layer is formed on the clad formation layer by SU-8, an optical waveguide is formed by photolithography. Thereafter, the spin-on-glass film is removed using an etchant, whereby the clad layer is formed in a plurality of columns separated from each other along the optical waveguide direction.

The operation of the optical waveguide device according to the second embodiment will be described with reference to FIG. FIG. 10 is a characteristic diagram for explaining the operation of the optical waveguide device of the second embodiment, and shows a simulation result by the three-dimensional BPM method.

  FIG. 10A shows the output light intensity with respect to the thickness S of the cladding layer 66 in the linear waveguide. In FIG. 10A, the horizontal axis indicates the thickness S (unit: μm) of the clad layer 66, and the vertical axis indicates the output light intensity. FIG. 10B shows the output light intensity with respect to the radius of curvature in the curved waveguide. FIG. 10B shows the radius of curvature R (unit: μm) on the horizontal axis and the output light intensity on the vertical axis.

  The output light intensity on the vertical axis in FIGS. 10A and 10B is a relative magnitude when the input light intensity is 1.

  As simulation conditions, the substrate 20 is a silicon substrate, the width W of the optical waveguide 56 and the thickness H of the core layer 76 are both 1 μm, the thickness T of the metal film is 0.1 μm, and light having a wavelength of 1.55 μm propagates. Calculated for the case. The refractive index of the core layer 76 and the cladding layer 66 is 1.56, and the refractive index around the optical waveguide is 1.0.

  Here, the columnar portion of the cladding layer 66 is formed as follows. Each columnar portion has a width in the direction perpendicular to the optical waveguide direction of 1 μm, the same as the width W of the core layer, and a length Ls in the optical waveguide direction of 1 μm. There are 40 columnar parts.

  10A and 10B, the material of the metal film 46 is copper (Cu).

FIG. 10A shows a simulation result in the case of a straight waveguide, in which the length L of the optical waveguide is 1000 μm. In the region where the thickness of the clad layer 66 is 0.5 μm or more, there is almost no dependence on the thickness S of the clad layer 66, that is, no propagation loss. The reason why the output light intensity is about 0.7, which is smaller than 1, is due to the coupling loss in the input of light to the optical waveguide. As described above, according to the optical waveguide device 16 of the second embodiment, the thickness S of the clad layer 66 can be made smaller than that of the optical waveguide device of the reference example or the first embodiment, and the production becomes easier. .

FIG. 10B is a simulation result in the case of a curved waveguide, and the length L of the optical waveguide is 100 μm. Like the first embodiment, the radius of curvature R is 6μm or more dependence on the radius of curvature R, i.e., the radiation loss to the optical waveguide outside is not Donna photons. The reason why the output light intensity is about 0.8, which is smaller than 1, is due to the coupling loss at the input of light to the optical waveguide 56. The variation in the intensity of the output light due to the difference in the thickness S of the cladding layer 66 is due to the difference in coupling loss.

According to the optical waveguide device and a manufacturing method thereof in the second embodiment, in addition to the effect of the reference example it can be further smaller than the optical waveguide device of the reference example the thickness S of the cladding layer 66.

It is the schematic of the optical waveguide element of a reference example . FIG. 6 is a characteristic diagram (part 1) for explaining the operation of the optical waveguide device of the reference example . FIG. 10 is a characteristic diagram (part 2) for explaining the operation of the optical waveguide device of the reference example . FIG. 10 is a characteristic diagram (part 3) for explaining the operation of the optical waveguide device of the reference example . It is the schematic which shows the other structural example of the optical waveguide element of a reference example . It is the schematic of the optical waveguide element of 1st Embodiment. It is a characteristic view for demonstrating operation | movement of the optical waveguide element of 1st Embodiment. It is the schematic which shows a comparative example. It is the schematic of the optical waveguide element of 2nd Embodiment. It is a characteristic view which shows the operation | movement of the optical waveguide element of 2nd Embodiment.

Explanation of symbols

10, 12, 14, 16, 110 Optical waveguide device 20, 120 Substrate 30 Electronic integrated circuit 40, 42, 46 Metal film 50, 54, 56, 150 Optical waveguide 60, 64, 66, 160 Clad layer 70, 76, 170 Core layer

Claims (13)

A metal film formed on the substrate;
An optical waveguide comprising a clad layer and a core layer sequentially laminated on the metal film;
The optical waveguide is formed in a ridge shape,
The periphery of the optical waveguide is filled with a material having a lower refractive index than the core layer and the cladding layer,
An optical waveguide device characterized in that a cross section in a direction perpendicular to the optical waveguide direction of the cladding layer and the core layer is rectangular, and the area of the upper surface of the cladding layer is smaller than the area of the upper surface of the core layer . The optical waveguide device of claim 1, the refractive index of the core layer, being higher than the refractive index of the cladding layer.   The refractive index of the core layer is set to a value in the range of 1.5 to 1.7, and the refractive index of the cladding layer is set to a value in the range of 1.4 to 1.6. 2. An optical waveguide device according to 1.   The refractive index of the core layer is equal to the refractive index of the cladding layer
The optical waveguide device according to claim 1. Wherein the optical waveguide direction perpendicular to the direction of the width of the cladding layer, according to any one of claims 1 to 4, characterized in that the smaller than a right angle to the direction of width to the optical waveguide direction of the core layer Optical waveguide element. The clad layer, the optical waveguide along the direction apart from each other, an optical waveguide device according to any one of claims 1-4, characterized in that it is formed in a plurality of columnar.   The optical waveguide element according to any one of claims 1 to 6, wherein the material of the metal film is a metal selected from the group consisting of Au, Ag, Cu, and Al.   8. The optical waveguide device according to claim 1, wherein the light guided through the optical waveguide is TE polarized light.   The optical waveguide device according to claim 1, wherein the substrate includes an electronic integrated circuit.   An optical waveguide comprising a metal film formed on a substrate, and a clad layer and a core layer sequentially stacked on the metal film;
  The optical waveguide is formed in a ridge shape, the area of the upper surface of the cladding layer is smaller than the area of the upper surface of the core layer, and the cross section of the cladding layer and the core layer in a direction perpendicular to the optical waveguide direction is rectangular. And the width of the cladding layer in the direction perpendicular to the optical waveguide direction is smaller than the width of the core layer in the direction perpendicular to the optical waveguide direction,
  An optical waveguide element in which the refractive index of the core layer is higher than the refractive index of the cladding layer, and the periphery of the optical waveguide is filled with a material having a lower refractive index than the core layer and the cladding layer;
  An optical device comprising a multimode interference coupler or an arrayed waveguide grating connected to the optical waveguide device. Forming a metal film on the substrate;
A step of sequentially laminating a clad formation layer and a core formation layer on the metal film and then performing patterning to form a ridge-shaped optical waveguide composed of the clad layer and the core layer,
In forming the cladding layer,
Manufacturing of an optical waveguide device characterized in that, by performing side etching, the width of the cladding layer in the direction perpendicular to the optical waveguide direction is made smaller than the width of the core layer in the direction perpendicular to the optical waveguide direction. Method. Forming a metal film on the substrate;
A step of sequentially laminating a clad formation layer and a core formation layer on the metal film and then performing patterning to form a ridge-shaped optical waveguide composed of the clad layer and the core layer,
The clad formation layer is formed alternately along the optical waveguide direction by using two kinds of materials having different solubility in the etchant,
After forming the optical waveguide, one of the two materials, by removing using the etchant, the cladding layer, along the optical waveguide direction, forming a plurality of columnar spaced from each other The method for manufacturing an optical waveguide element, wherein the area of the upper surface of the cladding layer is made smaller than the area of the upper surface of the core layer . Method for manufacturing an optical waveguide device according to claim 11 or 12 wherein the core-forming layer, and forming with the higher refractive index than the cladding layer material.

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