Optical concentration measuring device and optical waveguide

Abstract

To provide an optical concentration measuring device and an optical waveguide that can form a diffraction grating part and a light propagation part as a core layer, with high performance.SOLUTION: The optical concentration measuring device of the present invention is an optical concentration measuring device for measuring the concentration of a measurement target gas or of a measurement target liquid, which includes: a light source which can make a light enter a core layer; a detector which can receive a light having propagated in the core layer; and an optical waveguide. The optical waveguide includes: a substrate; and a core layer having a light propagation part in which light can propagate in an extension direction and a diffraction grating part. The diffraction grating part has a diffraction grating region and an extension region connected to the diffraction grating region, and the diffraction grating part includes a different material from the material of the light propagation part. For the light propagating in the core layer, there is an optical connection between a first optical connection region of the extension region and a second optical connection region of the light propagation part.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an optical concentration measuring device and an optical waveguide. [Background technology]

[0002] Light propagating through a structure, such as a thin film made of a crystal, undergoes repeated total reflection at the interface with the outside of the structure if the refractive index of the material forming the structure is greater than that of the material outside the structure. When the light propagating through the structure is totally reflected at this interface, it seeps out to the outside, which has a lower refractive index. This seepage is called an evanescent wave (see Figure 15). The evanescent wave EW can be absorbed by a material 52 adjacent to the structure 51 as the light L propagates. This makes it possible to detect and identify the material 52 in contact with the structure 51 from changes in the intensity of the light L propagating through the structure 51. An analytical method utilizing the principle of the evanescent wave EW described above is called attenuated total reflection spectroscopy (ATR), and is used for analyzing the chemical composition of the material 52. Infrared light is typically used as the propagating light. Since substances have the property of selectively absorbing infrared rays of specific wavelengths, analysis and sensing of substances can be performed by transmitting infrared rays that match the absorption spectrum of the substance to be measured.

[0003] Patent Document 1 proposes an optical waveguide sensor that applies the ATR method to a sensor. This optical waveguide sensor has a core layer formed on a substrate, through which light passes, and detects substances in contact with the core layer by utilizing evanescent waves. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-300212 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, a sensor using the ATR method has a portion where light from a light source is introduced into the core layer of the optical waveguide and a portion where it is extracted from the core layer of the optical waveguide toward a photodetector. Therefore, a diffraction grating is provided as part of the core layer at each of the portions where light from the light source is introduced into the core layer of the optical waveguide and the portion where it is extracted from the core layer of the optical waveguide toward a photodetector to bend the optical axis of the light. Furthermore, such a diffraction grating needs to have a structure that matches the size and shape of the light source and the photodetector in order to efficiently input light into the optical waveguide or output light from the optical waveguide.

[0006] On the other hand, as mentioned above, in this sensor, the light introduced into the core layer needs to seep out of the light propagation section as an evanescent wave and be absorbed by the external substance to be measured, so it is necessary to increase the propagation distance of light in the light propagation section (propagation path).

[0007] Therefore, in such sensors, a diffraction grating portion and a light propagation portion are provided as a core layer, but the diffraction grating portion and the light propagation portion each have different required functions, and therefore different shapes, sizes, and materials. Therefore, in such sensors, when manufacturing the diffraction grating portion and the light propagation portion within a single core layer, it has been difficult to form both the diffraction grating portion and the light propagation portion with high performance.

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an optical concentration measuring device and an optical waveguide that are capable of forming both a diffraction grating portion and a light propagation portion as a core layer with high performance. [Means for solving the problem]

[0009] In order to achieve the above object, an optical concentration measuring device according to one aspect of the present invention comprises: a light source capable of irradiating light onto the core layer; a detector capable of receiving light that has propagated through the core layer; An optical concentration measuring device for measuring the concentration of a gas or liquid to be measured, comprising: The optical waveguide is A substrate; the core layer having a light propagation portion through which light can propagate in the extending direction and a diffraction grating portion; Equipped with the diffraction grating portion has a diffraction grating region and an extension region connected to the diffraction grating region, at least a part of the diffraction grating portion is made of a material different from that of the light propagation portion, The first optical coupling region of the extension region and the second optical coupling region of the light propagation portion are optically coupled to the light propagating through the core layer.

[0010] In order to achieve the above object, an optical waveguide according to another aspect of the present invention comprises: An optical waveguide used in an optical concentration measuring device for measuring the concentration of a gas or liquid to be measured, A substrate; a core layer having a light propagation portion through which light can propagate in the extending direction and a diffraction grating portion; Equipped with the diffraction grating portion has a diffraction grating region and an extension region connected to the diffraction grating region, at least a part of the diffraction grating portion is made of a material different from that of the light propagation portion, The first optical coupling region of the extension region and the second optical coupling region of the light propagation portion are optically coupled to the light propagating through the core layer. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an optical concentration measuring device and an optical waveguide in which both the diffraction grating portion and the light propagation portion as the core layer can be formed with high performance. [Brief explanation of the drawings]

[0012] [Figure 1]1 is a diagram showing a schematic configuration of an optical concentration measurement device and an optical waveguide according to a first embodiment of the present invention. [Figure 2] 2 is a schematic plan view of the optical waveguide of FIG. 1 as viewed from the light source or photodetector side. [Figure 3] 2A and 2B are schematic diagrams showing a first diffraction grating portion and a part of a propagation path of the optical waveguide of FIG. 1, where (a) is a plan view and (b) is a cross-sectional view showing a cross section cut along line AA. [Figure 4] FIG. 4 is a cross-sectional view showing a modified example of the optical waveguide used in the optical concentration measurement device according to the first embodiment of the present invention. [Figure 5] 3 is a cross-sectional view showing a part of a main part of an optical waveguide for explaining a method of manufacturing an optical waveguide used in the optical concentration measurement device according to the first embodiment of the present invention. FIG. [Figure 6] 3 is a cross-sectional view showing a part of a main part of an optical waveguide for explaining a method of manufacturing an optical waveguide used in the optical concentration measurement device according to the first embodiment of the present invention. FIG. [Figure 7] 3 is a cross-sectional view showing a part of a main part of an optical waveguide for explaining a method of manufacturing an optical waveguide used in the optical concentration measurement device according to the first embodiment of the present invention. FIG. [Figure 8] 3 is a cross-sectional view showing a part of a main part of an optical waveguide for explaining a method of manufacturing an optical waveguide used in the optical concentration measurement device according to the first embodiment of the present invention. FIG. [Figure 9] 3 is a cross-sectional view showing a part of a main part of an optical waveguide for explaining a method of manufacturing an optical waveguide used in the optical concentration measurement device according to the first embodiment of the present invention. FIG. [Figure 10] 3 is a cross-sectional view showing a part of a main part of an optical waveguide for explaining a method of manufacturing an optical waveguide used in the optical concentration measurement device according to the first embodiment of the present invention. FIG. [Figure 11] 3 is a cross-sectional view showing a part of a main part of an optical waveguide for explaining a method of manufacturing an optical waveguide used in the optical concentration measurement device according to the first embodiment of the present invention. FIG. [Figure 12] 3 is a cross-sectional view showing a part of a main part of an optical waveguide for explaining a method of manufacturing an optical waveguide used in the optical concentration measurement device according to the first embodiment of the present invention. FIG. [Figure 13] 10 is a schematic plan view of an optical waveguide used in an optical concentration measurement device according to a second embodiment of the present invention, as viewed from the light source or photodetector side. FIG. [Figure 14] 14A and 14B are schematic diagrams showing a first diffraction grating portion and a part of a propagation path of the optical waveguide of FIG. 13, where (a) is a plan view and (b) is a cross-sectional view showing a cross section cut along line BB. [Figure 15] 1A and 1B are diagrams for explaining evanescent waves of light propagating through an optical waveguide; DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described below through embodiments of the invention, but the following embodiments do not limit the scope of the invention according to the claims. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention.

[0014] <Optical concentration measuring device> An optical concentration measuring device according to an embodiment of the present invention includes an optical waveguide according to an embodiment of the present invention described below, a light source capable of irradiating light into a core layer, and a detector capable of receiving light propagated through the core layer.

[0015] Hereinafter, each of the components constituting the optical concentration measuring device will be described with specific examples.

[0016] <Optical waveguide> An optical waveguide according to an embodiment of the present invention is an optical waveguide used in an optical concentration measuring device for measuring the concentration of a gas or liquid to be measured. The optical waveguide includes a substrate, a light propagation portion through which light propagates in an extension direction, and a core layer having a diffraction grating portion. In the optical waveguide, the diffraction grating portion has a diffraction grating region and an extension region connected to the diffraction grating region, and at least a portion of the diffraction grating portion is made of a material different from that of the light propagation portion. Light propagating through the core layer is optically coupled to a first optical coupling region of the extension region and a second optical coupling region of the light propagation portion.

[0017] In the optical concentration measuring device and optical waveguide according to this embodiment, at least a portion of the diffraction grating portion is made of a different material from the light propagation portion, so the diffraction grating portion and the light propagation portion as core layers can be easily formed separately with sizes, shapes, and materials suited to their respective functions. Furthermore, the first optical coupling region of the extension region and the second optical coupling region of the light propagation portion optically couple light propagating through the core layer, allowing light from a light source captured by the diffraction grating portion to be guided from the diffraction grating portion to the light propagation portion, or light propagating through the light propagation portion to be introduced from the light propagation portion to the diffraction grating portion. In the first optical coupling region and the second optical coupling region, light propagating through the core layer is optically coupled from the first optical coupling region to the second optical coupling region, or from the second optical coupling region to the first optical coupling region.

[0018] Here, in this embodiment, the extension direction is a direction that exists so as to extend along at least one direction. For example, in a three-dimensional structure, the path that travels from one end to another end (or from one arbitrary point to another arbitrary point) in the shortest distance while touching the three-dimensional structure is the extension direction. Alternatively, the direction that travels from one end to another end (or from one arbitrary point to another arbitrary point) so as to minimize the amount of change in cross-sectional area is also the extension direction. The extension direction includes not only linear directions but also curved directions.

[0019] In this embodiment, the extension region is capable of propagating light, and specifically, one end of the extension region is connected to the diffraction grating region, and the other end terminates without being connected to any other core layer, and has a portion extending in the extension direction of the second optical coupling region of the light propagation portion. The connection between the extension region and the diffraction grating region refers to a state in which the extension region and the diffraction grating region are continuous and made of the same material as at least one of the layers that form the diffraction grating region, and the extension region is formed inside of it from the same material as the connection point.

[0020] In the present invention, "different materials" refers not only to materials containing different elements, but also to materials containing the same elements but with different crystalline states, because optically, even if the constituent elements of the materials are the same, the propagation phenomenon of light will be different if the crystalline states are different.

[0021] In this embodiment, the expression "the first optical coupling region of the extension region and the second optical coupling region of the optical propagation unit are optically coupled to each other with respect to light propagating through the core layer" refers to the transition of light from one end to the other using evanescent waves when light propagated through the extension region or the optical propagation unit flows from the first optical coupling region to the second optical coupling region, or from the second optical coupler to the first optical coupling region, or the transition of light from one end to the other by directly contacting the first optical coupling region and the second optical coupling region. Alternatively, the expression refers to the case where the first optical coupling region is located at the other end of the extension region, the second optical coupling region is located at the end of the optical propagation unit, and the second optical coupling region is disposed adjacent to the end of the first optical coupling region (the other end of the extension region) on the extension line of the first optical coupling region, thereby allowing light to flow from one end to the other.

[0022] In this embodiment, the first optical coupling region of the extension region and the second optical coupling region of the optical propagation portion are not limited to a specific coupling form as long as they are optically coupled. However, it is preferable that the propagation direction of light propagating through the core layer does not substantially change before and after the transition from the first optical coupling region to the second optical coupling region and / or before and after the transition from the second optical coupling region to the first optical coupling region. That is, it is preferable that the first optical coupling region and the second optical coupling region function as directional couplers for light propagating through the core layer. By functioning as a directional coupler, ideally, the two can be optically coupled with 100% efficiency. Note that the first optical coupling region and the second optical coupling region functioning as directional couplers refers to an optically coupled state in which the propagation direction of light does not substantially change before and after the transition from one to the other using evanescent waves.

[0023] In this embodiment, the positional relationship between the extension region of the diffraction grating section and the light propagation section can be any as long as the first optical coupling region of the extension region and the second optical coupling region of the light propagation section can be optically coupled. For example, the extension region and the light propagation section can be positioned so that they are adjacent to each other in a direction perpendicular to the extension direction of the light propagation section (second optical coupling region) in the optical waveguide. Alternatively, at least a portion of the extension region and at least a portion of the light propagation section can be positioned so that they are included in a plane perpendicular to the extension direction of at least a portion of the light propagation section. Alternatively, the extension region and the light propagation section can be positioned so that the ends of the extension region and the light propagation section are adjacent to each other (the first optical coupling region and the second optical coupling region are adjacent to each other) and the end of the extension region (first optical coupling region) is located on the extension line of the light propagation section. Furthermore, when the extension region and the light propagation section are positioned adjacent to each other in a direction perpendicular to the extension direction of the light propagation section, they can be positioned at the same position in the thickness direction within the optical waveguide, or at different positions in the thickness direction.

[0024] Among these, in this embodiment, it is preferable that the extension region and the light propagating portion are adjacent to each other in a direction perpendicular to the extending direction of the light propagating portion and are located at different positions in the thickness direction.

[0025] In this embodiment, the extension region and the light propagation section are adjacent to each other in a direction perpendicular to the extension direction of the light propagation section, and are located at different positions in the thickness direction. This makes it easy to position the diffraction grating section and the light propagation section, which have different functions, in different layers using different materials. This allows for more efficient processing to be performed according to the respective functions of the diffraction grating section and the light propagation section, and allows the diffraction grating section and the light propagation section to intersect in a three-dimensional manner, thereby enabling efficient use of the area.

[0026] Furthermore, in this embodiment, even if the extension region and the light propagation section are adjacent to each other in a direction perpendicular to the extension direction of the extension region and are at the same position in the thickness direction, or even if the ends of the extension region and the light propagation section are adjacent to each other and the end of the light propagation section is located on the extension line of the extension region, the diffraction grating section and the light propagation section, which have different functions, can be located in different layers made of different materials, and therefore processing can be performed to match the respective functions of the diffraction grating section and the light propagation section.

[0027] Here, in this embodiment, when the extension region and the light propagation portion are positioned adjacent to each other in a direction perpendicular to the extension direction of the light propagation portion (including when the first light coupling region and the second light coupling region function as directional couplers), it is preferable that the distance between the first light coupling region and the second light coupling region is equal to or less than the following formula (1).

number

[0028] The distance between the first optical coupling region and the second optical coupling region refers to the shortest distance from each position on the outer surface of the first optical coupling region facing the second optical coupling region to the outer surface of the second optical coupling region. The lower limit of the distance between the first optical coupling region and the second optical coupling region is not particularly limited, and the first optical coupling region and the second optical coupling region may be in contact with each other. When the first optical coupling region and the second optical coupling region are in direct contact with each other, n mid is not defined, but is included in the distance defined by the above formula (1) and below because the distance between the first optical coupling region and the second optical coupling region is 0 μm.

[0029] Furthermore, the distance between the first optical coupling region and the second optical coupling region is preferably 0.7 μm or less. For example, in an optical concentration measuring device for detecting CO2, a typical gas floating in the environment, infrared light with a vacuum wavelength of approximately 4.3 μm is generally used as the light propagating through the core layer. In this case, the most common combination of materials for constructing the optical waveguide is a core layer made of silicon, and the portion sandwiched between the first optical coupling region and the second optical coupling region is made of a silicon oxide film. In this example, n coup is about 3.4, n mid is approximately 1.4, and the value of the above formula (1) is approximately 0.66 μm. That is, it is 0.7 μm or less. However, in order to more efficiently optically couple the first optical coupling region and the second optical coupling region, the distance between the first optical coupling region and the second optical coupling region may be 0.4 μm or less, more preferably 0.2 μm or less, and even more preferably 0.1 μm or less. Furthermore, a silicon nitride film or the like can be used as the material constituting the portion sandwiched between the first optical coupling region and the second optical coupling region. For example, when a silicon nitride film is used, n mid is approximately 2.0.

[0030] In this embodiment, the refractive index of the first optical coupling region and the second optical coupling region can be set arbitrarily, but the equivalent refractive index of the first optical coupling region for light propagating through the core layer is preferably 0.7 to 1.3 times, more preferably 0.8 to 1.2 times, and even more preferably 0.9 to 1.1 times that of the second optical coupling region. The equivalent refractive index of the first optical coupling region for light propagating through the core layer is 0.7 to 1.3 times that of the second optical coupling region, and the more similar the equivalent refractive indexes of the two are, the more improved the optical coupling efficiency.

[0031] In this embodiment, the refractive index of the material forming the first optical coupling region is preferably 0.9 to 1.1 times, and more preferably 0.95 to 1.05 times, that of the material forming the second optical coupling region. The more similar the refractive indexes of the material forming the first optical coupling region and the material forming the second optical coupling region are, the easier it is to match the equivalent refractive indexes of the first and second optical coupling regions with respect to light propagating through the core layer, thereby improving optical coupling efficiency.

[0032] In this embodiment, the film thickness of the first optical coupling region is preferably 0.7 to 1.3 times the film thickness of the second optical coupling region, more preferably 0.8 to 1.2 times, and even more preferably 0.9 to 1.1 times. When the film thickness of the first optical coupling region is 0.7 to 1.3 times the film thickness of the second optical coupling region, and the film thicknesses of the first optical coupling region and the second optical coupling region are more equal, it becomes easier to match the equivalent refractive index of the first optical coupling region and the second optical coupling region with respect to light propagating through the core layer, and optical coupling efficiency improves.

[0033] In this embodiment, when the film thickness of the first optical coupling region or the film thickness of the second optical coupling region varies within the first optical coupling region or the second optical coupling region, the film thickness of the first optical coupling region and the film thickness of the second optical coupling region refer to the respective film thicknesses at the portions where the distance between the first optical coupling region and the second optical coupling region is shortest.

[0034] In this embodiment, the width of the first optical coupling region is preferably 0.7 to 1.3 times the width of the second optical coupling region, more preferably 0.8 to 1.2 times, and even more preferably 0.9 to 1.1 times. When the width of the first optical coupling region is 0.7 to 1.3 times the width of the second optical coupling region, and the widths of the first optical coupling region and the second optical coupling region are more equal, it becomes easier to match the equivalent refractive indexes of the first optical coupling region and the second optical coupling region with respect to light propagating through the core layer, thereby improving optical coupling efficiency.

[0035] In this embodiment, the width of the first optical coupling region and the width of the second optical coupling region portion refer to the respective widths at the portions where the distance between the first optical coupling region and the second optical coupling region is shortest, when the width of the first optical coupling region or the width of the second optical coupling region varies within the first optical coupling region or the second optical coupling region.

[0036] In this embodiment, the extension region is preferably made of at least one of the materials constituting the diffraction grating region and is continuously connected to the diffraction grating region, which makes it possible to avoid unintended light loss within the diffraction grating portion.

[0037] Furthermore, in this embodiment, it is preferable that at least a portion of the optical propagation portion is spaced from the extension region by a distance greater than the distance between the first optical coupling region and the second optical coupling region, and more preferably by a distance greater than the following formula (2) or greater than 0.7 μm.

number

[0038] If the light propagation portion is close to the extension region in a region other than the second optical coupling region, unintended optical coupling occurs between the extension region and the light propagation portion. This unintended optical coupling causes light to transition from the extension region to the light propagation portion or from the light propagation portion to the extension region, resulting in light loss. Therefore, by positioning at least a portion of the light propagation portion at a distance from the extension region greater than the distance between the first optical coupling region and the second optical coupling region, unintended optical coupling between the light propagation portion and the extension region is less likely to occur. Furthermore, by positioning at least a portion of the light propagation portion at a distance from the extension region greater than Equation (2) or greater than 0.7 μm, unintended optical coupling between the light propagation portion and the extension region is even less likely to occur. The reason why the distance at which optical coupling is difficult is defined by Equation (2) is the same as Equation (1), which defines the distance between the first optical coupling region and the second optical coupling region, and therefore a detailed description thereof will be omitted. The distance between at least a portion of the light propagating portion and the extension region is the shortest distance between the outer surface of at least a portion of the light propagating portion and the outer surface of the extension region.

[0039] In this embodiment, at least one of the light propagating portion and the extension region may have a terminal portion, and the distance between the terminal portion of the light propagating portion and the diffraction grating portion and / or the distance between the terminal portion of the extension region and the light propagating portion is preferably greater than the value of formula (2) or greater than 0.7 μm. gap is to be interpreted as the refractive index of the material present in the portion sandwiched between the terminal portion of the light propagation portion and the diffraction grating portion, or the material present in the portion sandwiched between the terminal portion of the extension region and the light propagation portion. Note that if there are multiple materials present in the portion sandwiched between the terminal portion of the light propagation portion and the diffraction grating portion, or the portion sandwiched between the terminal portion of the extension region and the light propagation portion, the refractive index shall be the largest of the refractive indexes of the multiple materials.

[0040] If the end of the light propagation section is located near the diffraction grating section, the equivalent refractive index of the diffraction grating section changes suddenly as light propagating through the diffraction grating section passes near the end of the light propagation section, causing reflection, scattering, and other disturbances to the light propagating through the diffraction grating section. Similarly, if the end of the extension section is located near the light propagation section, the equivalent refractive index of the light propagation section changes suddenly as light propagating through the light propagation section passes near the end of the extension section, causing reflection, scattering, and other disturbances to the propagating light. Because these disturbances result in unintended loss of propagating light, it is preferable to position the end of the light propagation section and the diffraction grating section, and / or the end of the extension section and the light propagation section, at a certain distance. The distance defined by Equation (2) or 0.7 μm is the distance at which evanescent waves of light propagating through one of the core layers of the light propagation section and the diffraction grating section are unlikely to optically couple to the other core layer. The distance between the end portion of the light propagation portion and the diffraction grating portion is the shortest distance between the outer surface of the end portion of the light propagation portion and the outer surface of the diffraction grating portion, and the distance between the end portion of the extension region and the light propagation portion is the shortest distance between the outer surface of the end portion of the extension region and the outer surface of the light propagation portion.

[0041] In this embodiment, a first distance change region may be provided in which the distance between the diffraction grating portion and the light propagation portion decreases in a direction from the diffraction grating portion toward the first optical coupling region in a region where the diffraction grating portion and the light propagation portion overlap in a plan view. Furthermore, the first distance change region may have a portion in which the distance to the light propagation portion gradually changes from a distance greater than formula (2) or a distance greater than 0.7 μm to a distance equal to or less than formula (1) or a distance equal to or less than 0.7 μm. However, n gap is to be interpreted as the refractive index of the material present in the portion sandwiched between the light propagation portion and at least a portion of the diffraction grating portion. Note that if there are multiple materials present in the portion sandwiched between the light propagation portion and at least a portion of the diffraction grating portion, the refractive index is to be the largest of the refractive indices of the multiple materials. In addition, it is preferable that the maximum angle of the first distance change region with respect to the light propagation portion is 45° or less.

[0042] In a region where the diffraction grating unit and the light propagation unit overlap in a planar view, a first distance change region is provided in which the distance between the diffraction grating unit and the light propagation unit decreases in a direction from the diffraction grating region toward the first optical coupling region, thereby providing a structure in which at least a portion of the diffraction grating unit and the light propagation unit gradually approach each other. Therefore, the equivalent refractive index of at least a portion of the diffraction grating unit and the light propagation unit does not suddenly change with respect to the propagating light, and the diffraction grating unit and the light propagation unit can be efficiently optically coupled in the first optical coupling region and the second optical coupling region. Furthermore, in the first distance change region, the distance between at least a portion of the diffraction grating unit and the light propagation unit gradually changes from a distance greater than Equation (2) or greater than 0.7 μm, at which they are not optically coupled, to a distance less than Equation (1) or less than 0.7 μm, at which they are optically coupled. This allows for efficient optical coupling in the first optical coupling region and the second optical coupling region while avoiding unintended optical coupling in regions other than the first optical coupling region and the second optical coupling region. The distance between at least a part of the diffraction grating section and the light propagation section in the first distance change region refers to the shortest distance from each position on the outer surface of the diffraction grating section to the outer surface of the light propagation section in the first distance change region.

[0043] Furthermore, by having the maximum angle of the first distance change region relative to the light propagation portion be 45° or less, it is possible to reduce light loss in the first distance change region, and it is more preferable that it be 30° or less. Furthermore, if the angle is too gentle, the first distance change region will be too large (or long) to ensure an appropriate distance between at least a part of the diffraction grating portion and the light propagation portion, so the maximum angle of the first distance change region relative to the light propagation portion is preferably 10° or more, and more preferably 15° or more.

[0044] Next, each of the constituent elements of the optical waveguide will be described with specific examples.

[0045] <<Core Layer>> In this embodiment, the core layer has a light propagation portion through which light propagates in the extending direction, and a diffraction grating portion.

[0046] The core layer is capable of propagating light in the extending direction.

[0047] The material of the core layer is not particularly limited. Examples of the core layer include single crystal silicon, polycrystalline silicon, amorphous silicon, silicon nitride, silicon germanium, germanium, gallium arsenide, indium phosphide, indium antimony, indium gallium arsenide, indium gallium phosphide, indium fluoride, diamond, sapphire, lithium niobate, and chalcogenide glass. The core layer may be a multilayer film instead of a single layer film.

[0048] In this embodiment, as described above, at least a portion of the diffraction grating portion is made of a material different from that of the light propagation portion. In particular, it is preferable that the material forming the light propagation portion is a single crystal material, and that the material forming the diffraction grating portion contains a polycrystalline or amorphous material. Most preferably, the material forming the light propagation portion is single crystal silicon, and the material forming the diffraction grating portion contains polycrystalline silicon or amorphous silicon.

[0049] By using different materials to form the core layers in the diffraction grating section and the light propagation section, it becomes possible to form the core layers optimally according to the functions required of each core layer in terms of shape, size, refractive index, surface roughness, etc. Furthermore, by using different materials to form the core layers in the diffraction grating section and the light propagation section, it is possible to process each core layer independently, and it is possible to process one without being restricted by the other's condition, thereby improving the degree of freedom in processing.

[0050] More specifically, for example, in the light propagation portion, which is the portion that detects the substance to be measured, it is preferable to form the film thickness of the core layer sufficiently smaller than the wavelength of the light propagating through the core layer (the wavelength within the core layer) in order to allow a large amount of evanescent waves to seep out from the core layer. Furthermore, in order to improve the detection sensitivity of the substance to be measured, it is necessary to increase the propagation distance of light in the light propagation portion. For light propagation portions intended to propagate light over long distances, a single-crystal material with low surface roughness for the core layer is preferred in order to minimize propagation loss. Single-crystal silicon is the most common and easily processable single-crystal material for the core layer. Forming a light propagation portion containing single-crystal silicon allows the light propagation portion to be formed most cost-effectively and optimally.

[0051] On the other hand, in the diffraction grating section, which introduces light from the light source into the core layer, the core layer preferably has a film thickness comparable to the wavelength of the light propagating through the core layer (the wavelength within the core layer) to increase the light introduction efficiency. If the film thickness of the diffraction grating section is too thin, it becomes extremely difficult to introduce light into the core layer. Furthermore, it is preferable that the surface of the diffraction grating region of the diffraction grating section has fine, random asperities (roughness). This is because the optical concentration measuring device of this embodiment detects the substance to be measured by propagating light that matches the absorption spectrum of the substance to be measured, and the wavelength band of the propagated light is preferably comparable to the absorption spectrum of the substance to be measured. For example, if the diffraction grating region is formed as a strictly regular periodic pattern, the diffraction grating region will select a more uniform wavelength, approaching a line spectrum. In other words, the more strictly regular the diffraction grating region, the narrower the selected wavelength band. On the other hand, the absorption wavelength range of a substance has a certain width and is not strictly a single wavelength. For example, the typical absorption wavelength of CO2, a gas suspended in the environment, ranges from approximately 4.20 to 4.35 μm, which is a relatively wide distribution. In other words, excessive selection of light to a strict single wavelength would result in discarding the wavelength range effective for concentration measurement, which is undesirable for an optical concentration measurement device. In particular, the optical concentration measurement device of this embodiment allows the use of an incoherent light source such as an LED as the light source, as described below. From the perspective of effectively utilizing light having a certain wavelength range (wavelength band) from the incoherent light source, it is preferable that the wavelength band selected by the diffraction grating region also has a certain width. That is, in this embodiment, the surface of the diffraction grating region of the diffraction grating section is formed with random fine irregularities (roughness), thereby enabling more efficient coupling between the light emitting element and the optical waveguide as an optical waveguide. Using a polycrystalline or amorphous material as the material for the core layer forming the diffraction grating section allows for appropriate roughness to be generated on the surface of the core layer.The most common and easily processable polycrystalline or amorphous core layer materials are polycrystalline silicon or amorphous silicon, and forming a diffraction grating portion containing single crystal silicon or amorphous silicon allows the diffraction grating portion to be formed most cost-effectively. Note that the random fine irregularities (roughness) formed on the surface of the diffraction grating region are different from the periodic irregularities that form the diffraction grating region described below.

[0052] Furthermore, in this embodiment, a cross section perpendicular to the extension direction at any position along the extension direction of the core layer may have a shape in which the distance from the center of the core layer to the outer surface of the cross section varies, such as a rectangle, or may have a shape in which the distance from the center of the core layer to the surface of the cross section does not vary, such as a circle.

[0053] In this embodiment, at least a portion of the core layer may be exposed or covered with a thin film. This allows the exposed or covered portion of the core layer to come into direct contact with the gas or liquid under measurement, or to come into contact with the gas or liquid under measurement via the thin film, allowing the evanescent wave to interact with the gas or liquid under measurement, thereby enabling the concentration of the gas or liquid under measurement to be measured. In this embodiment, the thin film is preferably thinner than ¼ of the vacuum wavelength of the light propagating through the core layer.

[0054] In addition, in this embodiment, the light propagating through the core layer may be infrared light as an analog signal. Here, infrared light as an analog signal means that the signal does not determine the change in light energy as a binary value of 0 (low level) or 1 (high level), but rather handles the amount of change in light energy. This allows the optical waveguide according to this embodiment to be applied to sensors and analytical devices. In this case, the vacuum wavelength of the infrared light may be 2 μm or more and less than 12 μm. This wavelength band is absorbed by gases typically suspended in the environment (CO2, CO, NO, NO, SO, SO, CH4, HO, CHO, etc.). This allows the optical waveguide according to each embodiment to be used as a gas sensor.

[0055] The core layer may also include a portion that extends in a curved shape, which allows the aspect ratio of the outline of the core layer to approach 1 when the entire core layer is viewed in a plane, thereby enabling the optical waveguide and the optical concentration measuring device to be made smaller.

[0056] Furthermore, as described above, the diffraction grating portion of the optical waveguide can include a first diffraction grating portion that receives light from the light source and guides the light to the light propagation portion, and a second diffraction grating portion that introduces light from the light propagation portion and outputs the light to the detector.

[0057] In this embodiment, as described above, the diffraction grating unit has a diffraction grating region and an extension region, at least a portion of the diffraction grating unit is made of a material different from that of the light propagation unit, and the first optical coupling region of the extension region and the second optical coupling region of the light propagation unit are optically coupled to light propagating through the core layer. However, in this embodiment, as long as one of the first diffraction grating unit and the second diffraction grating unit has a diffraction grating region connected to the extension region having the first optical coupling region and the extension region is optically coupled to the light propagation unit as described above, the other may not have a diffraction grating region connected to the extension region having the first optical coupling region. Furthermore, if there are multiple diffraction grating regions in the first diffraction grating unit or multiple diffraction grating regions in the second diffraction grating unit, it is also possible to have at least one of the diffraction grating regions connected to the extension region having the first optical coupling region and the remaining diffraction grating regions not connected to the extension region having the first optical coupling region.

[0058] <<<Optical propagation section>>> In this embodiment, the light propagation unit has a propagation path through which light can propagate in the extension direction. The cross section of the propagation path perpendicular to the extension direction at any position along the extension direction of the propagation path may have a shape in which the distance from the center of the core layer to the outer surface of the cross section varies, such as a rectangle, or may have a shape in which the distance from the center of the core layer to the surface of the cross section does not vary, such as a circle.

[0059] In this embodiment, the propagation path can have a substantially uniform film thickness in the extension direction, and a substantially uniform film thickness means, for example, that the difference in film thickness is 200 nm or less. The propagation path may have portions with different widths in the extension direction. When the light propagation section has multiple propagation paths, the multiple propagation paths may have different film thicknesses or widths. The film thickness of the core layer may or may not be uniform throughout the entire region of the light propagation section.

[0060] Furthermore, although the light propagation portion may be formed of multiple layers, it is preferable that it be formed of a single layer, because if the light propagation portion is formed of multiple layers, light may transition from one layer to another or the propagation mode may be converted during the light propagation process, resulting in increased propagation loss.

[0061] <<<Diffraction grating section>>> In this embodiment, the diffraction grating section can have a first diffraction grating section that receives light from the light source and guides the light to the light propagation section, and a second diffraction grating section that introduces light from the light propagation section and outputs the light to the detector.

[0062] In this embodiment, the first diffraction grating portion may have a diffraction grating region that introduces external light into the core layer, and the second diffraction grating portion may have a diffraction grating region that extracts light to the outside of the core layer. In this embodiment, the diffraction grating region may be a portion whose surface is uneven with a specific period (which may be multiple periods), or may have a configuration in which, when the optical waveguide is viewed in cross section on a plane including the recessed and protruding portions, the recessed grooves of the uneven surface become deep and separate the core layer. In such a configuration, the protruding portions are formed in a discontinuous island shape.

[0063] The diffraction grating region can be provided so that the pattern of parallel concave and convex portions extends linearly or arcuately in a plan view, but the extension shape of the concave and convex portions can be any shape. The diffraction grating region of the diffraction grating portion is defined as a region in which concave and convex portions are formed. More specifically, the diffraction grating region of the diffraction grating portion is an inner region sandwiched between the outermost wall surfaces of at least one of the outer walls defining the convex portions and the inner walls defining the concave portions.

[0064] In this embodiment, the shape of the diffraction grating region in a plan view can be any shape, for example, a shape having a portion whose width increases from the extension region side of the diffraction grating region toward the end side opposite the extension region. Specifically, the shape can be a sector shape having a center within the extension region of the diffraction grating portion and increasing toward the end side opposite the extension region. The shape of the diffraction grating region is preferably a shape that is line-symmetrical with respect to any imaginary line extending from the connection side toward the end side.

[0065] In this embodiment, the structure of the second diffraction grating section can be the same as that of the first diffraction grating section, or the structure of the second diffraction grating section can be converted from that of the first diffraction grating section. Converting from the structure of the first diffraction grating section means that the shape, configuration, and arrangement of the diffraction grating region of the second diffraction grating section are rotated, enlarged, reduced, translated, line-symmetric, or point-symmetric with respect to the shape, configuration, and arrangement of the diffraction grating region of the first diffraction grating section. It is acceptable for the respective structures to differ within a dimension within the wavelength in vacuum of the light propagating through the core layer, preferably within 1 μm. By making the structure of the second diffraction grating section the same as that of the first diffraction grating section, or by converting the structure of the second diffraction grating section from that of the first diffraction grating section, the wavelength selectivity of the first diffraction grating section and the wavelength selectivity of the second diffraction grating section can be approximately equal, thereby avoiding optical loss that occurs when the wavelength selectivity of the first diffraction grating section and the second diffraction grating section differs.

[0066] <<Substrate>> In this embodiment, the substrate is not particularly limited as long as a core layer can be formed on the substrate, and a support layer (described later) can also be formed on the substrate. Specifically, the substrate can be a silicon substrate, a gas substrate, or the like.

[0067] <<Support layer>> In this embodiment, a support layer can be optionally provided. The support layer connects at least a portion of the substrate and at least a portion of the core layer. The support layer is not particularly limited as long as it can bond the substrate and the core layer, but is preferably made of a material with a lower refractive index than the core layer for light of any wavelength or light propagating through the core layer. As an example, the support layer can be formed from SiO2 or the like. In the present invention, the support layer is not an essential component. The core layer may be bonded to the substrate via a support layer, or the core layer may be formed directly on the substrate. Alternatively, the support layer may be partially present, or at least a portion of the core layer may be floating rather than bonded to the support layer. That is, in an optical waveguide with such a configuration, a space is formed between the substrate and the core layer except for the region where the support layer is provided. By floating a portion of the core layer, the amount of interaction between the evanescent wave and the measured substance can be increased, thereby improving sensor sensitivity.

[0068] In this embodiment, as an example of a method for forming a support layer, a buried oxide (BOX: Buried Oxide) layer (SiO layer) of an SOI (Silicon On Insulator) substrate is etched to form a structure in which the core layer (Si layer) and the substrate (Si layer) are supported by the BOX layer.

[0069] <Light source> The light source is not particularly limited as long as it can introduce light into the core layer. When infrared light is used to measure gas, an incandescent lamp, a ceramic heater, a MEMS (Micro Electro Mechanical Systems) heater, an infrared LED (Light Emitting Diode), or the like can be used as the light source. That is, it may be an incoherent light source. The light source may be arranged in any form as long as it can be optically connected to the optical waveguide. For example, the light source may be arranged adjacent to the optical waveguide in the same solid body as the optical waveguide, or it may be arranged as a separate solid body at a certain distance from the optical waveguide. Furthermore, when ultraviolet light is used to measure gas, a mercury lamp, an ultraviolet LED, or the like can be used as the light source.

[0070] The light propagating through the core layer of the optical waveguide provided in the optical concentration measuring device may be infrared light as an analog signal. Here, infrared light as an analog signal means that the signal does not determine the change in light energy as a binary value of 0 (low level) or 1 (high level), but rather handles the amount of change in light energy. This allows the optical concentration measuring device to be used as a sensor or an analytical device. In this case, the vacuum wavelength of the infrared light may be 2 μm or more and less than 12 μm. This wavelength band is absorbed by gases typically suspended in the environment (CO2, CO, NO, NO, SO, SO, CH4, HO, CHO, etc.). This allows the optical concentration measuring device according to this embodiment to be used as a gas sensor.

[0071] <Detector> The detector is not particularly limited as long as it can receive light propagated through the core layer of the optical waveguide. When infrared light is used to measure gas, the detector can be a thermal infrared sensor such as a pyroelectric sensor, a thermopile, or a bolometer, or a quantum infrared sensor such as a diode or a phototransistor. When ultraviolet light is used to measure gas, the detector can be a quantum ultraviolet sensor such as a diode or a phototransistor.

[0072] Optical concentration measuring device according to an embodiment of the present invention An optical concentration measuring device according to an embodiment of the present invention will be described with reference to FIG.

[0073] The optical concentration measuring device 14 of this embodiment is installed and used in an external space 16 where a gas whose concentration is to be detected is present. The optical concentration measuring device 14 includes an optical waveguide 15 of an embodiment described below, a light source 17 capable of irradiating light into the core layer 12, and a photodetector 18 capable of receiving light that has propagated through the core layer 12. The optical concentration measuring device 14 also includes a first diffraction grating unit 11 that introduces light from the light source 17 and outputs the light to the light propagation unit 10, and a second diffraction grating unit 13 that introduces light from the light propagation unit 10 and outputs the light to the photodetector 18.

[0074] In the optical concentration measuring device 14 of this embodiment, the light source 17 emits infrared rays having a wavelength of 2 μm or more and less than 12 μm toward the core layer 12. By using the infrared rays, the evanescent waves EW that permeate from the core layer 12 are absorbed by the substance to be measured present in the external space 16, such as gases such as CO2, CO, NO, NO, SO, SO, CH4, HO, and CHO, and the concentration of the substance to be measured can be detected.

[0075] The optical concentration measuring device 14 of this embodiment can be obtained by manufacturing an optical waveguide 15 according to an embodiment of the present invention described below, and further, as shown in FIG. 1, installing a light source 17 so that infrared rays IR can be incident on one diffraction grating portion 11 (grating coupler) of the optical waveguide 15, and arranging a photodetector 18 so that infrared rays IR emitted from the other diffraction grating portion 13 (grating coupler) of the optical waveguide 15 can be received.

[0076] [Optical waveguide according to an embodiment of the present invention] First Embodiment An optical waveguide according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 4. FIG.

[0077] As described above, FIG. 1 is a schematic diagram showing the general configuration of the optical concentration measuring device 14 according to this embodiment, and is also a conceptual diagram of the ATR method using the optical waveguide 15 according to the first embodiment.

[0078] The optical waveguide 15 includes a substrate 19, a core layer 12 through which infrared light IR (an example of light) can propagate, and a support layer 20 that connects at least a portion of the substrate 19 to at least a portion of the core layer 12 and supports the core layer 12 relative to the substrate 19. The core layer 12 and the substrate 19 are made of, for example, silicon (Si), and the support layer 20 is made of, for example, silicon dioxide (SiO2). The substrate 19 and the support layer 20 have, for example, a plate shape. As shown in FIG. 1, the support layer 20 may support the entire core layer 12, or may support at least a portion of the core layer 12; for example, the support layer 20 may support the entire diffraction grating portions 11, 13 and a portion of the light propagation portion 10 intermittently in the extension direction (as a result, the light propagation portion 10 of the optical waveguide 15 is connected to the support layer 20 intermittently in the extension direction, and has an air gap between the light propagation portion 10 and the substrate 19 without having a specified layer such as a cladding layer, except for the region where the support layer 20 is provided).

[0079] As shown in the schematic diagram of FIG. 2 , which illustrates the schematic configuration of an optical waveguide 15 according to this embodiment, the core layer 12 has a first diffraction grating portion (a grating coupler, for example) 11 formed at one end in the extension direction and a second diffraction grating portion (a grating coupler, for example) 13 formed at the other end. The core layer 12 also has a light propagation portion 10 between the first diffraction grating portion 11 and the second diffraction grating portion 13 at both ends in the extension direction. In the optical waveguide 15 according to this embodiment, the light propagation portion 10 has a uniform film thickness. In the optical waveguide 15 according to this embodiment, the light propagation portion 10 has a uniform width. The width direction is a direction perpendicular to the extension direction and the thickness direction. The thickness direction is a direction parallel to the stacking direction in which the substrate 19, the support layer 20, and the core layer 12 are stacked.

[0080] The first diffraction grating unit 11 is disposed in the emission direction of the light source 17. In this embodiment, the optical waveguide 15 is disposed so that the stacking direction is parallel to the vertical direction and the main surface of the substrate 19 is perpendicular to the vertical downward direction. The main surface of the substrate 19 is the surface perpendicular to the thickness direction of the substrate 19. In other words, in this embodiment, it is the surface with the largest area among the six surfaces forming the substrate 19. In other words, the emission direction of the light source 17 is the vertical downward direction of the light source 17 when the optical waveguide 15 is disposed in this manner. The first diffraction grating unit 11 introduces infrared light IR incident from the light source 17 into the core layer 12. Therefore, light propagating through the core layer 12 is input from the thickness direction of the first diffraction grating unit 11. The second diffraction grating unit 13 is disposed in a direction facing the photodetector 18. The direction facing the photodetector 18 is the vertical downward direction of the photodetector 18 when the optical waveguide 15 is disposed as described above. This second diffraction grating portion 13 extracts infrared light IR propagating through the core layer 12 and emits it toward the photodetector 18. Therefore, the light propagating through the core layer 12 is output in the thickness direction of the second diffraction grating portion 13.

[0081] Thus, the core layer 12 arranged on the light source 17 side (light incident side) has the first diffraction grating portion 11 at one end, and the core layer 12 arranged on the photodetector 18 side (light exit side) has the second diffraction grating portion 13 at the other end. Furthermore, the core layer 12 has, between the center and both ends in the extension direction, light propagation portions 10 through which infrared light IR incident from the first diffraction grating portion 11 and emitted from the second diffraction grating portion 13 propagates. The evanescent waves EW emanating from the core layer 12 are mainly absorbed in the light propagation portions 10 by the substance to be measured present in the external space 16.

[0082] The optical waveguide 15 according to the first embodiment will now be described in more detail.

[0083] In a sensor using the ATR method, as shown in FIG. 1, the sensitivity of the sensor can be improved by expanding the interaction region between the evanescent wave EW seeping out from the core layer 12 and the substance to be measured (i.e., by expanding the exposed portion of the core layer 12). Furthermore, in a sensor using the ATR method, as described above, the light introduced into the core layer needs to seep out of the light propagation section 10 as an evanescent wave and be absorbed by the external substance to be measured. This requires a long propagation distance of the light in the light propagation section 10 (propagation path 101). Furthermore, the diffraction grating section that inputs and outputs light also needs to be structured to match the size and shape of the light source and photodetector in order to efficiently input light into the optical waveguide or output light from the optical waveguide. Therefore, in such a sensor, the diffraction grating section and the light propagation section 10, both of which are core layers, have different required functions, and it is desirable to form them in sizes, shapes, and with materials that match their respective functions.

[0084] 3 , the first diffraction grating unit 11 has a diffraction grating region 111 and an extension region 111a connected to the diffraction grating region 111, and the diffraction grating region 111 and the extension region 111a are all made of a different material from the light propagation unit 10. The first optical coupling region 111b of the extension region 111a and the second optical coupling region 101a of the light propagation unit 10 are optically coupled to light propagating through the core layer 12. The optical coupling plane between the first optical coupling region 111b and the second optical coupling region 101a is exemplified as being not perpendicular to the main surface of the substrate 19. For example, the optical coupling plane may be parallel to the main surface of the substrate 19. Although not shown in the figure, the second diffraction grating section 13 also has a diffraction grating region 131 and an extension region 131a connected to the diffraction grating region 131, and the diffraction grating region 131 and the extension region 131a are all made of a material different from that of the light propagation section 10, and the first optical coupling region 131b of the extension region and the second optical coupling region 101a of the light propagation section 10 are optically coupled to the light propagating through the core layer 12.

[0085] Therefore, in optical waveguide 15 of the first embodiment, diffraction grating regions 111, 131 and extension regions 111a, 131 connected to diffraction grating regions 111, 131 are all made of a material different from that of light propagation portion 10, so that first diffraction grating portion 11, second diffraction grating portion 13, and light propagation portion 10 as core layer 12 can be formed with sizes, shapes, and materials suited to their respective functions. Furthermore, at this time, first optical coupling regions 111b, 131b of extension regions 111a, 131a and second optical coupling region 101a of light propagation portion 10 are optically coupled to light propagating through core layer 12, so that light from a light source taken in by first diffraction grating portion 11 can be guided from first diffraction grating portion 11 to light propagation portion 10, and light propagating through light propagation portion 10 can be introduced from light propagation portion 10 to second diffraction grating portion 13.

[0086] 2, in optical waveguide 15 of the first embodiment, first diffraction grating portion 11 and second diffraction grating portion 13 each have one diffraction grating region 111, 131, and light propagation portion 10 having one propagation path 101 is present between first diffraction grating portion 11 and second diffraction grating portion 13. Also, first diffraction grating portion 11 and second diffraction grating portion 13 have extension regions 111a, 131a, respectively, as shown in FIG. 3 (second diffraction grating portion 13 is omitted), and each extension region 111a, 131a is made of the same material as one of the materials forming diffraction grating regions 111, 131, and all of diffraction grating regions 111, 131 and extension regions 111a, 131a are made of a different material from propagation path 101 of light propagation portion 10. Furthermore, each extension region 111a, 131a has a first optical coupling region 111b, 131b, and the propagation path 101 has a second optical coupling region 101a near both ends thereof, and the first optical coupling regions 111b, 131b and the second optical coupling region 101a are optically coupled to the light propagating through the first optical coupling regions 111b, 131b and the second optical coupling region 101a.

[0087] 3, the extension regions 111a, 131a and the light propagation portion 10 are located in the light waveguide 15 in a direction perpendicular to the extension direction of the light propagation portion 10 and at different positions in the thickness direction (in the illustrated example, the light propagation portion 10 is located closer to the substrate in the thickness direction than the extension region 111a). In other words, the extension regions 111a, 131a and the light propagation portion 10 overlap with each other in the extension direction of the light propagation portion 10 and are located in different layers. Furthermore, in the illustrated example, the extension regions 111a, 131a and the light propagation portion 10 are spaced apart from each other in the thickness direction in the light waveguide 15.

[0088] In the optical waveguide 15 of the first embodiment, the first optical coupling regions 111b, 131b of the extension regions 111a, 131a and the second optical coupling region 101a of the optical propagation unit 10 are not limited to a specific coupling form as long as they optically couple light propagating through the first optical coupling regions 111b, 131b and the second optical coupling region 101a, but as described above, the extension regions 111a, 131a and the optical propagation unit 10 are positioned in a direction perpendicular to the extension direction of the optical propagation unit 10 in the optical waveguide 15, so that the first optical coupling regions 111b, 131b and the second optical coupling region 101a can function as a directional coupler, as shown in Fig. 3. By functioning as a directional coupler, the two can be optically coupled with high efficiency.

[0089] Furthermore, in the first embodiment, by positioning the extension regions 111a, 131a and the light propagation portion 10 in a direction perpendicular to the extension direction of the light propagation portion 10 and at different positions in the thickness direction, portions having different functions that form the core layer 12 can be positioned in different layers, and the first diffraction grating portion 11, the second diffraction grating portion 13, and the light propagation portion 10 can be efficiently processed in accordance with their respective functions.

[0090] In the optical waveguide 15 of the first embodiment, the positional relationship between the extension region 111a of the first diffraction grating portion 11 and the extension region 131a of the second diffraction grating portion 13 and the light propagation portion 10 can be set arbitrarily as long as the first optical coupling regions 111b, 131b of the extension regions 111a, 131a and the second optical coupling region 101a of the light propagation portion 10 can be optically coupled. For example, unlike FIG. 3, the extension regions 111a, 131a and the light propagation portion 10 can be positioned at the same position in the thickness direction within the optical waveguide 15. Alternatively, as shown in FIG. 4, the extension regions 111a, 131a and the optical propagation portion 10 can be arranged so that the ends of the extension regions 111a, 131a and the optical propagation portion 10 are adjacent to each other (the first optical coupling regions 111b, 131b and the second optical coupling region 101a are adjacent to each other), and the ends of the extension regions 111a, 131a (the first optical coupling regions 111b, 131b) are located on the extension line of the optical propagation portion 10.

[0091] In addition, in the example shown in FIG. 3, the extension regions 111a, 131a and the light propagation portion 10 extend apart from each other, but the extension regions 111a, 131a and the light propagation portion 10, more specifically, the first optical coupling regions 111b, 131b and the second optical coupling region 101a may be in contact with each other.

[0092] In the optical waveguide 15 of the first embodiment, the shapes of the extension regions 111a and 131a are not particularly limited, but as shown in FIG. 3(a), one end of the extension region 111a of the first diffraction grating portion 11 is continuously connected to the diffraction grating region 111 without interruption, and the other end terminates without being connected to another core layer 12 (the second diffraction grating portion 13 is not shown). Furthermore, as shown in a cross-sectional view (in the illustrated example, a cross-sectional view in the thickness direction as shown in Figure 3(b)) of a plane including the first optical coupling regions 111b, 131b of the extension regions 111a, 131a and the second optical coupling region 101a of the propagation path 101, the shape of the extension regions 111a, 131a is such that the first distance change regions 111c, 131c of the extension regions 111a, 131a are curved toward the propagation path 101 so that the first optical coupling regions 111b, 131b of the extension regions 111a, 131a and the second optical coupling region 101a of the propagation path 101, which are optically coupled portions, approach each other. In the first distance change regions 111c and 131c (i.e., curved portions), the distance from the propagation path 101 gradually changes from a distance at which the extension region 111a and the propagation path 101 are not easily optically coupled (a distance greater than formula (2) or a distance greater than 0.7 μm) to a distance at which they are optically coupled (a distance equal to or less than formula (1) or a distance equal to or less than 0.7 μm). gap is the refractive index of the material present in the portion sandwiched between propagation path 101 and first distance change regions 111c, 131c. First distance change regions 111c, 131c are continuous with first optical coupling regions 111b, 131b. The maximum angle of this curved portion is preferably 45° or less, and more preferably 30° or less, with respect to the main surface of substrate 19 to avoid light loss. Furthermore, if the angle is too gentle, a large distance will be required before first optical coupling regions 111b, 131b and second optical coupling region 101a are brought closer together. Therefore, the maximum angle of the curved portion is preferably 10° or more, and more preferably 15° or more, with respect to the main surface of substrate 19.

[0093] Furthermore, the propagation path 101 and the extension regions 111a and 131a have portions that extend parallel to each other in a plan view. That is, the extension regions 111a, 131a have first distance change regions 111c, 131c that are curved from one end (the connection portion with the diffraction grating regions 111, 131) of the extension regions 111a, 131a toward the other end (terminal portion) so that the distance between the extension regions 111a, 131a and the propagation path 101 gradually decreases to a distance that allows optical coupling between the extension regions 111a, 131a and the propagation path 101, and then in the first optical coupling regions 111b, 131b, there is a portion where the extension regions 111a, 131a (first optical coupling regions 111b, 131b) and the propagation path 101 (second optical coupling region 101a) extend while maintaining a constant distance, and further there are second distance change regions 111d, 131d that are curved so that the distance between the extension regions 111a, 131a and the propagation path 101 gradually increases, and finally terminate at the other end.

[0094] In the above example, the propagation path 101 has a terminal portion, and the second optical coupling region 101a is located away from the terminal portion of the propagation path 101 (optical propagation section 10). However, the second optical coupling region 101a may be located at the terminal portion of the propagation path 101 (optical propagation section 10). However, it is more preferable that the second optical coupling region 101a is located away from the terminal portion of the propagation path 101 than that the second optical coupling region 101a is located at the terminal portion of the propagation path 101. By locating the second optical coupling region 101a away from the terminal portion of the propagation path 101, as shown in FIG. 3(b), the distance between the terminal portion of the propagation path 101 and the first diffraction grating section 11 and the second diffraction grating section 13 can be set to a distance at which they are unlikely to be optically coupled (a distance greater than Equation (2) or a distance greater than 0.7 μm). Here, n gap is the refractive index of the material present in the portion sandwiched between the terminal portion of the propagation path 101 and the first and second diffraction grating portions.

[0095] That is, in the above example, the propagation path 101 is separated in the thickness direction from the first diffraction grating portion 11 and the second diffraction grating portion 13 in the portion other than the second optical coupling region by a distance that makes it difficult to optically couple the propagation path 101 (a distance greater than the distance expressed by equation (2) or a distance greater than 0.7 μm).gap is the refractive index of the material present in the portion of the propagation path 101 other than the second optical coupling region and in the portion sandwiched between the first diffraction grating portion 11 and the second diffraction grating portion 13.

[0096] In the first embodiment, the positions of the first optical coupling regions 111b, 131b in the extension regions 111a, 131a can be arbitrary, and the first optical coupling regions 111b, 131b can be located at the other ends of the extension regions 111a, 131a. However, as shown in FIG. 3B and described above, it is preferable that the first optical coupling regions 111b, 131b are located midway between the extension regions 111a, 131a (between the first distance change regions 111c, 131c, where the distance between the extension region 111a and the propagation path 101 gradually decreases, and the second distance change regions 111d, 131d, where the distance gradually increases). In other words, it is preferable that the first optical coupling regions 111b, 131b are located between one end of the extension regions 111a, 131a that connects to the diffraction grating regions 111, 131 and the other end that terminates, away from the respective ends. By providing the first optical coupling regions 111b and 131b between the extension regions 111a and 131a, as shown in FIG. 3(b), the distance between the end portion of the extension region 111a and the propagation path can be set to a distance at which optical coupling between the two is difficult (a distance greater than equation (2) or a distance greater than 0.7 μm). Here, n gap is the refractive index of the material present in the portion sandwiched between the end portion of the extension region 111a and the propagation path 101. Furthermore, since the first optical coupling regions 111b and 131b are located between the extension regions 111a and 131a, the end portions of the extension regions 111a and 131a can be etched without damaging the propagation path 101, thereby improving the propagation efficiency of light in the propagation path 101.

[0097] In the first embodiment, the extension regions 111a and 131a are not limited to any particular form as long as they have at least the first optical coupling regions 111b and 131b.

[0098] Furthermore, in this embodiment, the extension regions 111a, 131a and the light propagation portion 10 are spaced apart from each other in the thickness direction, and a layer different from the extension regions 111a, 131a and the light propagation portion 10 exists between the extension regions 111a, 131a and the light propagation portion 10. However, a material (including air) having a relatively lower refractive index than the core layer 12 (including the extension regions 111a, 131a and the light propagation portion 10) can be interposed between the extension regions 111a, 131a and the light propagation portion 10, and in the illustrated example, a silicon oxide film (SiO2) exists between the first diffraction grating portion 11 and the light propagation portion 10.

[0099] In the first embodiment, the distance between the first optical coupling region 111b, 131b and the second optical coupling region 101a is preferably equal to or less than the above formula (1), or 0.7 μm or less. Here, λ0 is the average wavelength in a vacuum of light propagating through the core layer 12, and n coup is the refractive index of the material forming the first optical coupling region 111b, 131b or the second optical coupling region 101a, and n mid is the refractive index of the material present in the portion sandwiched between the first optical coupling regions 111b, 131b and the second optical coupling region 101a. By setting the distance between the first optical coupling regions 111b, 131b and the second optical coupling region 101a to the above distance, optical coupling between the first optical coupling regions 111b, 131b and the second optical coupling region 101a can be efficiently performed over a short distance.

[0100] Furthermore, the length in the extension direction where the first optical coupling regions 111b, 131b and the second optical coupling region 101a are optically coupled is preferably 20 μm or less, and more preferably 10 μm or less. This length allows the first optical coupling regions 111b, 131b and the second optical coupling region 101a to be optically coupled in a space-saving manner. The length in the extension direction where the first optical coupling regions 111b, 131b and the second optical coupling region 101a are optically coupled refers to the length of the portion where the distance between the extension regions 111a, 131a and the propagation path 101 is equal to or less than the above formula (1) or 0.7 μm or less, i.e., the portion defined as the first optical coupling regions 111b, 131b and the second optical coupling region 101a.

[0101] Furthermore, in the first embodiment, the diffraction grating portions 11 and 13 having the extension regions 111a and 131a are made of different materials from the light propagation portion 10. While any specific material can be used, in the illustrated example, the diffraction grating portions 11 and 13 are made of polycrystalline silicon, and the light propagation portion 10 is made of single-crystal silicon. Note that the material used to form the diffraction grating portions 11 and 13 and the light propagation portion 10 can also be amorphous silicon.

[0102] Furthermore, in the first embodiment, the equivalent refractive index of the first optical coupling regions 111b and 131b to light propagating through the first optical coupling regions 111b and 131b and the second optical coupling region 101a is preferably 0.7 to 1.3 times, more preferably 0.8 to 1.2 times, and even more preferably 0.9 to 1.1 times, the equivalent refractive index of the second optical coupling region 101a being equal to that of the first optical coupling regions 111b and 131b and the second optical coupling region 101a. The more equal the equivalent refractive indexes of the first optical coupling regions 111b and 131b and the second optical coupling region 101a to light propagating through the first optical coupling regions 111b and 131b and the second optical coupling region 101a, the more efficiently they can be optically coupled to each other.

[0103] In this embodiment, the refractive index of the material forming the first optical coupling regions 111b and 131b is preferably 0.9 to 1.1 times, and more preferably 0.95 to 1.05 times, the refractive index of the material forming the second optical coupling region 101a. The more similar the refractive indexes of the materials forming the first optical coupling regions 111b and 131b and the second optical coupling region 101a are, the easier it is to match the equivalent refractive indexes of the first optical coupling regions 111b and 131b and the second optical coupling region 101a for light propagating through the first optical coupling regions 111b and 131b and the second optical coupling region 101a, thereby improving optical coupling efficiency.

[0104] 3(b), the film thickness of the first optical coupling regions 111b and 131b is preferably 0.7 to 1.3 times, more preferably 0.8 to 1.2 times, and even more preferably 0.9 to 1.1 times that of the second optical coupling region 101a. More specifically, the film thickness of the extension regions 111a and 131a including the first optical coupling regions 111b and 131b is preferably 0.7 to 1.3 times, more preferably 0.8 to 1.2 times, and even more preferably 0.9 to 1.1 times that of the propagation path 101 including the second optical coupling region 101a. The more equal the film thicknesses of the first optical coupling regions 111b, 131b and the second optical coupling region 101a are, the easier it is to match the equivalent refractive indexes of the first optical coupling regions 111b, 131b and the second optical coupling region 101a with respect to light propagating through the first optical coupling regions 111b, 131b and the second optical coupling region 101a, thereby improving the optical coupling efficiency.

[0105] In the first embodiment, when the film thickness of the first optical coupling regions 111b, 131b or the film thickness of the second optical coupling region 101a varies within the first optical coupling regions 111b, 131b or within the second optical coupling region 101a, the film thickness refers to the film thickness at the portion where the distance between the first optical coupling regions 111b, 131b and the second optical coupling region 101a is shortest.

[0106] From the viewpoint of manufacturing and optical characteristics, the film thickness of the first optical coupling regions 111b and 131b and the second optical coupling region 101a is preferably 0.2 to 1.0 μm.

[0107] 3A, the width of the first optical coupling regions 111b and 131b is preferably 0.7 to 1.3 times, more preferably 0.8 to 1.2 times, and even more preferably 0.9 to 1.1 times the width of the second optical coupling region 101a. The more equal the widths of the first optical coupling regions 111b and 131b and the second optical coupling region 101a, the easier it is to match the equivalent refractive indexes of the first optical coupling regions 111b and 131b and the second optical coupling region 101a for light propagating through the first optical coupling regions 111b and 131b and the second optical coupling region 101a, thereby improving optical coupling efficiency.

[0108] In the first embodiment, when the width of the first optical coupling regions 111b, 131b or the width of the second optical coupling region 101a varies within the first optical coupling regions 111b, 131b or the second optical coupling region 101a, the widths of the first optical coupling regions 111b, 131b and the second optical coupling region 101a refer to the respective widths at the portions where the distance between the first optical coupling regions 111b, 131b and the second optical coupling region 101a is shortest.

[0109] In the first embodiment, in the example shown in FIGS. 2 and 3, the diffraction grating region 111 of the first diffraction grating portion 11 and the diffraction grating region 131 of the second diffraction grating portion 13 both have a fan shape, but in the present embodiment, the diffraction grating regions 111 and 131 can have any shape in plan view.

[0110] <Method for manufacturing optical waveguide> Next, an example of a method for manufacturing the optical waveguide 15 according to the first embodiment will be described with reference to Figures 5 to 12. Figures 5 to 12 are cross-sectional views showing an example of a method for manufacturing the portion shown in Figure 3(b).

[0111] 5 to 12 are simplified schematic diagrams focusing on one diffraction grating region 111 of the first diffraction grating portion 11 to facilitate the explanation of the manufacturing method of the optical waveguide 15. Figures 5 to 12 show cross-sectional views of the manufacturing process of the optical waveguide 15 cut at a position corresponding to line AA in Figure 3(a).

[0112] First, as shown in Figure 5, an SiO2 film is formed on either or both of support substrate 19a, which is made of silicon and will eventually become substrate 19, and active substrate 12a, which is made of silicon and will have core layer 12 formed thereon. Support substrate 19a and active substrate 12a are then bonded together with this SiO2 film sandwiched between them, and then bonded by heat treatment. Thereafter, the film thickness of active substrate 12a is adjusted by grinding and polishing it to a predetermined thickness. This results in an SOI substrate 15a having a "silicon-insulating layer-silicon" structure, which includes support substrate 19a, BOX layer 20a formed on support substrate 19a, and active substrate 12a formed on BOX layer 20a.

[0113] Next, the active substrate 12a of the SOI substrate 15a is etched using lithography and etching techniques to form the light propagation portion 10. As a result, as shown in Fig. 6, an optical waveguide main portion is formed, which includes a support substrate 19a, a BOX layer 20a formed on the support substrate 19a, and the light propagation portion 10 formed on the BOX layer 20a.

[0114] Next, as shown in Fig. 7, a separating film 15c for separating the extension region 111a of the first diffraction grating portion 11, which will be formed later, from the light propagation portion 10 is formed by depositing an SiO2 film made of, for example, TEOS (Tetraethyl orthosilicate). After this separating film 15c is formed on the BOX layer 20a and the light propagation portion 10, the surface is flattened using CMP (Chemical Mechanical Polishing), etc., to realize the structure shown in Fig. 7. The separating film 15c can separate the light propagation portion 10 from the first diffraction grating portion 11 in the thickness direction.

[0115] Next, as shown in FIG. 8, photoresist is patterned on the separating film 15c, and the separating film 15c is partially etched using the photoresist as a mask layer M1. At this time, wet etching is performed using BHF (Buffered Hydrofluoric Acid) or the like to form as gentle a slope as possible. In the wet etching, a gentler slope can be formed by adjusting the adhesion of the interface between the separating film 15c and the mask layer M1. By doing so, as shown in FIG. 8, holes are formed in the separating film 15c to optically couple the extension region 111a of the first diffraction grating portion 11, which will be formed later, to the vicinity of the end of the light propagation portion 10 (propagation path 101).

[0116] Next, after etching and removing the mask layer M1, an SiO2 film is formed to a thickness of, for example, about 30 nm on the surface of the light propagation portion 10 exposed by forming the hole in the separation film 15c, as shown in Fig. 9. This film can be formed by any method such as CVD (Chemical vapor deposition) or oxidation. Furthermore, this film does not necessarily have to be an SiO2 film, and can also be, for example, an SiN film.

[0117] Next, as shown in FIG. 10, a three-layer structure of a polysilicon film (upper layer) 21a / SiO2 film 21b / polysilicon film (lower layer) 21c is formed on the entire surface. The two polysilicon films 21a and 21c are formed by, for example, CVD. The middle SiO2 film 21b is formed by oxidation, CVD, or the like. The film thickness of the lower polysilicon film 21c is preferably approximately equal to the film thickness of the light propagation portion 10 (propagation path 101). By having the film thickness approximately equal to that of the propagation path 101, optical coupling between the first diffraction grating portion 11 formed by the polysilicon film 21c and the light propagation portion 10 can be performed with high efficiency. For example, the film thickness of the lower polysilicon film 21c and the propagation path 101 are both 0.6 μm.

[0118] 11, the upper polysilicon film 21a is etched using lithography and etching techniques to form a concave-convex pattern for forming the first diffraction grating portion 11. In this process, the SiO2 film 21b formed between the two polysilicon films 21a and 21c acts as a stopper film during etching, allowing the concave-convex pattern to be formed with high precision and protecting the lower polysilicon film 21c from over-etching. After forming the concave-convex pattern, only the exposed portions of the SiO2 film 21b used as a stopper are removed by dry etching or wet etching.

[0119] 12, the underlying polysilicon film 21c is etched using lithography and etching techniques to form the outline of the first diffraction grating portion 11. Subsequently, although not shown, lithography and etching techniques are used to remove a portion of the separating film 15c so as to expose a portion of the surface of the light propagation portion 10 that performs gas sensing, thereby obtaining an optical waveguide main portion 15b having a structure corresponding to the optical waveguide 15 of the first embodiment.

[0120] Next, the support substrate 19a is cut at predetermined regions to separate the optical waveguide main portions 15b, thereby completing the optical waveguide 15 according to the first embodiment.

[0121] In the above description, the first diffraction grating portion 11 has been focused on as the diffraction grating portion, but the second diffraction grating portion 13 can also be formed in the same manner.

[0122] Second Embodiment Next, an optical waveguide according to a second embodiment of the present invention will be described with reference to Figures 13 and 14. Note that components common to the first embodiment are given the same reference numerals and descriptions thereof will be omitted.

[0123] 13, the first diffraction grating unit 11 has a plurality of diffraction grating regions 111. Furthermore, at least two of the plurality of diffraction grating regions 111 in the first diffraction grating unit 11 receive light emitted from the same light-emitting surface of the light source 17. Specifically, a range R1 in FIG. 13 is a range obtained by projecting, in a plan view, a range of the light-emitting surface of the arranged light source 17 that can be considered as the same light-emitting surface onto the diffraction grating unit 11 along a direction perpendicular to the light-emitting surface, and at least two diffraction grating regions 111 exist within the range R1.

[0124] Conventionally, when light from a light-emitting element is received by one large diffraction grating region, there has been a problem in that the light cannot be introduced from the light-emitting element into the optical waveguide (core layer 12) with high efficiency. However, as shown in Fig. 13, by having at least two of the multiple diffraction grating regions 111 receive light emitted from the same light-emitting surface of the light source 17, the diffraction grating region 111 can be made relatively small, the efficiency decrease that occurs with a large diffraction grating region is suppressed, and the light from the light-emitting element can be introduced into the optical waveguide with high efficiency.

[0125] Note that the range that can be considered to be the same light-emitting surface does not necessarily have to be one light-emitting surface. Even if there are multiple light-emitting surfaces, if the light output from each of the multiple light-emitting surfaces is synchronously controlled by a common driving system, the total range of the multiple light-emitting surfaces is considered to be the same light-emitting surface.

[0126] 13, all of the diffraction grating regions 111 of the first diffraction grating portion 11 are present within range R1, but there may also be diffraction grating regions 111 formed outside range R1. Even if the diffraction grating region 111 is located outside range R1, or even if part of the diffraction grating region 111 is outside range R1, light spreads from the light emitting surface of the light source 17, so that light can be taken into the core layer 12 even from the diffraction grating region 111 located outside or the part located outside.

[0127] 14 , in the second embodiment, the diffraction grating region 111 of the first diffraction grating unit 11 has an extension region 111a, and the diffraction grating region 111, the extension region 111a connected to the diffraction grating region 111, and each propagation path 101 are made of a different material. The extension region 111a and the propagation path 101 are spaced apart in the thickness direction. As a result, as shown in the figure, another diffraction grating region 111 can be formed on the surface side in the thickness direction of one propagation path 101 that is optically coupled to the extension region 111a of one diffraction grating region 111, spaced apart from the one propagation path 101. By forming another diffraction grating region 111 on the surface side in the thickness direction of one propagation path 101, the diffraction grating regions 111 in the first diffraction grating unit 11 can be arranged more densely, and light from the light emitting element can be introduced into the optical waveguide with high efficiency.

[0128] 13, all of the propagation paths 101 of the optical propagation unit 10 are located closer to the substrate in the thickness direction than the diffraction grating regions 111 of the first diffraction grating unit 11, and the second optical coupling regions 101a of all of the propagation paths 101 are optically coupled to the first optical coupling regions 111b of the extension regions 111a that are connected to the diffraction grating regions 111. Similarly to the first diffraction grating unit 11, the diffraction grating regions 131 of the second diffraction grating unit 13 are also optically coupled to all of the propagation paths 101 and all of the diffraction grating regions 131 via the first optical coupling regions 131b and the second optical coupling regions 101a.

[0129] However, in the second embodiment, even if the diffraction grating section has a plurality of diffraction grating regions, in some of the diffraction grating regions, the diffraction grating regions are connected to the extension region so that the first optical coupling region of the extension region and the second optical coupling region 101a of the propagation path 101 are optically coupled, and the remaining diffraction grating regions may be directly connected to the propagation path 101 without going through the first optical coupling region and the second optical coupling region 101a of the propagation path 101.

[0130] 13, in the optical waveguide 15 of the second embodiment, the optical propagation section 10 of the optical waveguide 15 has a plurality of propagation paths 101 that introduce and propagate light received by one diffraction grating region 111 and that guide the light to one diffraction grating region 131. This allows the diffraction grating regions 111 in the first diffraction grating section 11 and the diffraction grating regions 131 in the second diffraction grating section 13 to be arranged more densely, thereby enabling efficient use of light from the light emitting element.

[0131] In the illustrated example, all of the multiple propagation paths 101 are arranged in parallel between the diffraction grating region 111 and the diffraction grating region 131, but in this embodiment, the multiple propagation paths 101 do not need to be arranged in parallel, and the multiple propagation paths 101 can merge or branch between the diffraction grating region 111 and the diffraction grating region 131, and the form of the propagation paths 101 can be any form.

[0132] In the second embodiment, the diffraction grating regions 111 in the first diffraction grating unit 11 all have the same size and the same shape, but diffraction grating regions 111 of different sizes and shapes may be provided. By providing diffraction grating regions 111 of different sizes and shapes, it is possible to impart multiple functions to the optical waveguide 15. A specific example of multiple functions is, for example, making the period of the concaves and convexes forming the diffraction grating region 111 different for each diffraction grating region 111, so that multiple wavelengths can be selected.

[0133] In this embodiment, at least two of the diffraction grating regions 111 have a size of 5×5 mm 2 It is preferable that the thickness is within the range of 1×1 mm 2 and more preferably within a range of 500 × 500 μm 2 This allows the light emitting element and the optical waveguide 15 to be coupled with high efficiency. 2 ) or within the range (1 x 1 mm 2) or within the range (500 × 500 μm 2 ) is preferably 30% or more, and more preferably 60% or more, thereby enabling the light emitting element and the optical waveguide 15 to be coupled with each other with high efficiency.

[0134] In this embodiment, the structure of the second diffraction grating section 13 can be any desired structure. Specifically, in the illustrated example, the structure of the second diffraction grating section 13 is the same as the structure of the first diffraction grating section 11, but it can also be different. Furthermore, range R2 in FIG. 13 is the range of the detector arranged in a plan view of the substrate 19 of the optical waveguide 15 (when viewed toward the substrate 19), projected onto the second diffraction grating section 13 along a direction perpendicular to the detection surface of the detector. However, the size or arrangement of the diffraction grating region 131 of the second diffraction grating section 13 can be changed depending on the detector, for example.

[0135] <Method for manufacturing optical waveguide> The method for manufacturing the optical waveguide 15 according to the second embodiment is the same as the manufacturing method shown in the first embodiment except for changing the mask pattern used in lithography, and therefore a detailed description thereof will be omitted. [Industrial Applicability]

[0136] According to the present invention, it is possible to provide an optical concentration measuring device and an optical waveguide that can more easily form a diffraction grating portion and a light propagation portion as a core layer with high performance. [Explanation of symbols]

[0137] 10: Optical propagation section 101: Propagation path 101a: Second optical coupling region 11: First diffraction grating section 111: Diffraction grating region 111a: Extension area 111b: 1st optical coupling region 111c: First distance change area 111d: Second distance change area 12: Core layer 13: Second diffraction grating section 131: Diffraction grating area 131a: Extension area 131b: 1st optical coupling region 131c: First distance change area 131d: Second distance change area 14: Optical concentration measuring device 15: Optical waveguide 15a: SOI substrate 15b: Main part of optical waveguide 15c: Diaphragm 16:External Space 17:Light source 18: Photodetector 19: Circuit board 19a: Support board 20:Support layer 20a:BOX layer 21a: Polysilicon film (upper layer) 21b:SiO2 film 21c: Polysilicon film (lower layer) 51: Structure 52: Substance EW: Evanescent wave IR: Infrared L:Light M1: Mask layer R1, R2: Range

Claims

1. a light source capable of irradiating light onto the core layer; a detector capable of receiving light that has propagated through the core layer; An optical concentration measuring device for measuring the concentration of a gas or liquid to be measured, comprising: The optical waveguide is A substrate; the core layer having a light propagation portion through which light can propagate in the extending direction and a diffraction grating portion; Equipped with the light propagation unit has a first propagation path and a second propagation path that do not overlap at least in a plan view, the diffraction grating portion has at least a first diffraction grating and a second diffraction grating, the first propagation path is optically disconnected from the second diffraction grating and the second propagation path; the second propagation path is optically disconnected from the first diffraction grating and the first propagation path; the first diffraction grating has a diffraction grating region and an extension region connected to the diffraction grating region; the first diffraction grating is made of a material different from that of the first propagation path and the second propagation path; the second propagation path and the first diffraction grating overlap in a planar view, and the second propagation path and the first diffraction grating are spaced apart in a thickness direction of the optical waveguide, with a layer between the second propagation path and the first diffraction grating containing a material having a refractive index lower than that of the second propagation path and that of the first diffraction grating, a first optical coupling region of the extension region and a second optical coupling region of the first propagation path are optically coupled to light propagating through the core layer; An optical concentration measuring device, characterized in that the concentration is measured by causing the evanescent wave leaking from the light propagation portion to be absorbed by the gas or liquid to be measured.

2. 2. The optical concentration measurement device according to claim 1, wherein a material forming the light propagation portion includes one of single crystal silicon, polycrystalline silicon, amorphous silicon, silicon nitride, silicon germanium, germanium, gallium arsenide, indium phosphide, indium antimony, indium gallium arsenide, indium gallium phosphide, indium fluoride, diamond, sapphire, lithium niobate, and chalcogenide glass, and a material forming the diffraction grating portion includes another one of single crystal silicon, polycrystalline silicon, amorphous silicon, silicon nitride, silicon germanium, germanium, gallium arsenide, indium phosphide, indium antimony, indium gallium arsenide, indium gallium phosphide, indium fluoride, diamond, sapphire, lithium niobate, and chalcogenide glass.

3. 3. The optical concentration measurement device according to claim 1, wherein the material forming said light propagation portion is single crystal silicon, and the material forming said diffraction grating portion includes polycrystalline silicon or amorphous silicon.

4. 4. The optical concentration measurement device according to claim 1, wherein at least a part of the optical coupling surface of the first optical coupling region and the second optical coupling region is parallel to the main surface of the substrate.

5. 5. The optical concentration measurement device according to claim 1, wherein the direction of light propagating through the core layer does not change before and after a transition from the first optical coupling region to the second optical coupling region and / or before and after a transition from the second optical coupling region to the first optical coupling region.

6. 6. The optical concentration measurement device according to claim 1, wherein a distance between the first optical coupling region and the second optical coupling region is equal to or less than the following formula (1): [Equation 1] where λ ０ is the average wavelength in a vacuum of light propagating through the core layer, and n ｃｏｕｐ is the refractive index of the material forming the first optical coupling region or the second optical coupling region, and n ｍｉｄ is the refractive index of the material present in the portion sandwiched between the first optical coupling region and the second optical coupling region.

7. 7. The optical concentration measurement device according to claim 1, wherein the distance between the first optical coupling region and the second optical coupling region is 0.7 [mu]m or less.

8. 8. The optical concentration measurement device according to claim 1, wherein the equivalent refractive index of the first optical coupling region is 0.7 to 1.3 times the equivalent refractive index of the second optical coupling region for light propagating through the core layer.

9. 9. The optical concentration measurement device according to claim 1, wherein at least a portion of the light propagation portion is spaced from the extension region by a distance greater than a distance between the first optical coupling region and the second optical coupling region.

10. 10. The optical concentration measurement device according to claim 1, wherein at least a portion of the light propagation portion is spaced from the extension region by a distance greater than the following formula (2): .times. ... [Equation 2] where λ ０ is the average wavelength in a vacuum of light propagating through the core layer, and n ｐｒｏ is the refractive index of the material forming the light propagating portion or the extension region, and n ｇａｐ is the refractive index of the material present in at least a part of the light propagating portion and the portion sandwiched between the extension region.

11. At least one of the light propagating portion and the extension region has a terminal portion; 11. The optical concentration measurement device according to claim 1, wherein a distance between the terminal portion of the light propagation portion and the diffraction grating portion, and / or a distance between the terminal portion of the extension region and the light propagation portion is greater than the following formula (3): [Equation 3] where λ ０ is the average wavelength in a vacuum of light propagating through the core layer, and n ｐｒｏ is the refractive index of the material forming the light propagating portion or the extension region, and n ｇａｐ is the refractive index of the material present in the portion sandwiched between the end portion of the light propagating portion and the diffraction grating portion, or the material present in the portion sandwiched between the end portion of the extension region and the light propagating portion.

12. at least a part of the diffraction grating portion is spatially separated from the light propagating portion; 12. The optical concentration measurement device according to claim 1, further comprising: a first distance change region in which a distance between the diffraction grating portion and the light propagation portion decreases in a direction from the diffraction grating region toward the first optical coupling region in a region where the diffraction grating portion and the light propagation portion overlap in a planar view.

13. 13. The optical concentration measurement device according to claim 12, wherein the distance from the first distance changing region to the light propagation portion gradually changes from a distance greater than the following formula (4) to a distance equal to or less than the following formula (5): [Equation 4] where λ ０ is the average wavelength in a vacuum of light propagating through the core layer, and n ｐｒｏ is the refractive index of the material forming the light propagating portion or the extension region, and n ｇａｐ is the refractive index of the material present in the portion sandwiched between the light propagation portion and at least a part of the diffraction grating portion. [Equation 5] where λ ０ is the average wavelength in a vacuum of light propagating through the core layer, and n ｃｏｕｐ is the refractive index of the material forming the first optical coupling region or the second optical coupling region, and n ｍｉｄ is the refractive index of the material present in the portion sandwiched between the first optical coupling region and the second optical coupling region.

14. 14. The optical concentration measurement device according to claim 12, wherein the maximum angle of the first distance change region relative to the light propagation portion is 45 degrees or less.

15. 15. The optical concentration measurement device according to claim 12, further comprising: a second distance change region in which the distance between the diffraction grating portion and the light propagation portion increases in a direction away from the first optical coupling region toward the diffraction grating portion, in a region where the diffraction grating portion and the light propagation portion overlap in a planar view.

16. An optical waveguide used in an optical concentration measuring device for measuring the concentration of a gas or liquid to be measured, A substrate; a core layer having a light propagation portion through which light can propagate in the extending direction and a diffraction grating portion; Equipped with the light propagation unit has a first propagation path and a second propagation path that do not overlap at least in a plan view, the diffraction grating portion has at least a first diffraction grating and a second diffraction grating, the first propagation path is optically disconnected from the second diffraction grating and the second propagation path; the second propagation path is optically disconnected from the first diffraction grating and the first propagation path; the first diffraction grating has a diffraction grating region and an extension region connected to the diffraction grating region; the first diffraction grating is made of a material different from that of the first propagation path and the second propagation path; the second propagation path and the first diffraction grating overlap in a planar view, and the second propagation path and the first diffraction grating are spaced apart in a thickness direction of the optical waveguide, with a layer between the second propagation path and the first diffraction grating containing a material having a refractive index lower than that of the second propagation path and that of the first diffraction grating, a first optical coupling region of the extension region and a second optical coupling region of the first propagation path are optically coupled to light propagating through the core layer; 1. An optical waveguide used in an optical concentration measuring device that measures concentration by causing the evanescent wave leaking from the light propagation portion to be absorbed by the gas or liquid to be measured.

17. 17. The optical waveguide according to claim 16, wherein a material forming the light propagation portion includes one of single crystal silicon, polycrystalline silicon, amorphous silicon, silicon nitride, silicon germanium, germanium, gallium arsenide, indium phosphide, indium antimony, indium gallium arsenide, indium gallium phosphide, indium fluoride, diamond, sapphire, lithium niobate, and chalcogenide glass, and a material forming the diffraction grating portion includes another one of single crystal silicon, polycrystalline silicon, amorphous silicon, silicon nitride, silicon germanium, germanium, gallium arsenide, indium phosphide, indium antimony, indium gallium arsenide, indium gallium phosphide, indium fluoride, diamond, sapphire, lithium niobate, and chalcogenide glass.

18. 18. The optical waveguide according to claim 16, wherein the material forming said light propagation portion is single crystal silicon, and the material forming said diffraction grating portion includes polycrystalline silicon or amorphous silicon.

19. 19. The optical waveguide according to claim 16, wherein at least a part of an optical coupling surface of the first optical coupling region and the second optical coupling region is parallel to a major surface of the substrate.

20. at least a part of the diffraction grating portion is spatially separated from the light propagating portion; 20. The optical waveguide according to claim 16, further comprising: a first distance change region in which a distance between the diffraction grating portion and the light propagation portion decreases in a direction from the diffraction grating region toward the first optical coupling region, in a region where the diffraction grating portion and the light propagation portion overlap in a planar view.

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