Diffraction grating coupler

Abstract

A diffraction grating coupler (10) is provided with: a diffraction grating (12) having a plate-shaped base material (121) and different refractive index regions (122) that are periodically arranged in a one-dimensional or two-dimensional manner within a predetermined range of the base material (121) and have a refractive index different from that of the base material (121); and a light reflecting section (14) provided at an end of the range on the opposite side from the light input section (13) side, the different refractive index region (122) having a planar shape in which the absolute value of the direct coupling coefficient (kappa 1D) is less than 1 / L, the direct coupling coefficient (kappa 1D) is an index indicating the intensity of light traveling from the light input unit (13) in a first direction (positive x-direction) parallel to the base material (121) reflected in the different refractive index region (122) in a second direction (negative x-direction) that differs by 180 DEG from the first direction (positive x-direction) without any radiation loss. The 1 / L is the reciprocal of the span length (L) of the range in relation to the first direction (positive x direction), and the light input portion (13) is a part of the end portion of the range.

Description

Technical Field

[0001] This invention relates to a diffraction grating coupler, which uses a diffraction grating to optically couple optical components such as integrated circuits and optical fibers to each other or to optical components to free space. Background Technology

[0002] Conventionally, diffraction grating couplers have been used, which are formed by periodically arranging regions with refractive indices different from those of the base material (regions of different refractive indices) on a plate-shaped base material. These regions of different refractive indices are typically formed using slots or apertures. In such a diffraction grating coupler, light with a specific wavelength corresponding to the arrangement period of the regions of different refractive indices, which is input from the end face of the base material, is diffracted and output from the surface of the diffraction grating coupler (more precisely, the surface of the base material containing the regions of different refractive indices). Conversely, light with a specific wavelength input from the surface can also be output from the end face. By arranging optical elements towards the surface and end face of such a diffraction grating coupler respectively, light of a specific wavelength input from one optical element can be input to the other optical element. Alternatively, after placing the optical element on the end face of the diffraction grating coupler, light of a specific wavelength input from the optical element can be output from the surface of the diffraction grating coupler into free space, or light of a specific wavelength input from free space to the surface can be input into the optical element. Such output of light into free space and input of light from free space can be used for optical communication with other optical elements separated from the diffraction grating coupler by free space, sensing of objects separated from the diffraction grating coupler by free space, etc.

[0003] In conventional diffraction grating couplers, when light is input from the end face, a portion of the input light is reflected in the anisotropic region, thereby generating reflected light whose direction of travel has changed by 180°. This reflected light exits from the light input section (the end face). Thus, when the reflected light exits from the light input section, the efficiency of light output from the surface of the diffraction grating decreases, and light enters (reverses) into the optical elements located on the light input side, potentially causing malfunctions. Therefore, in the diffraction grating coupler described in Patent Document 1, by using anisotropic regions with a planar shape without 180° rotational symmetry, the proportion of light traveling in a first direction parallel to the base material reflected in the anisotropic region in a second direction 180° different from the first direction is suppressed. In this diffraction grating coupler, by designating the end face of the base material on the side where light is input along the first direction as the light input section, light entry (reverses) into this light input section can be suppressed.

[0004] It is known that the larger the emanating area of ​​light emitted from the surface of a diffraction grating coupler, the smaller the diffusion angle. A smaller diffusion angle reduces the area where the emitted light is incident on other optical elements separated from the diffraction grating coupler by free space, or on the object being sensed, thereby increasing the light intensity per unit area in the incident region. However, conventional diffraction grating couplers, including the one described in Patent Document 1, exhibit an exponential decrease in light intensity emitted from the surface as it moves away from the light input section. Therefore, even within the region containing the heterorefringent region (in other words, the region where the diffraction grating is formed), almost no light is emitted from the portion far from the light input section. As a result, the actual emanating area is smaller than the entire surface of the diffraction grating (the region containing the heterorefringent region), and the diffusion angle becomes larger.

[0005] To prevent such a substantial reduction in the emission area, a diffraction grating coupler is sought that can emit light with a near-uniform intensity regardless of the distance from the light input unit. Non-Patent Document 1 describes a diffraction grating coupler in which multiple slots are equally spaced on a plate. When the ratio of the width of the slot to the width of the portion outside the slot (duty cycle) is a specific value, two wavenumber regions with repetitive energy bands of light within the diffraction grating are formed. When light with a wavelength having energy equivalent to the end (singularity) of this wavenumber region is input into the diffraction grating, light can be emitted from the entire surface of the diffraction grating regardless of the distance from the light input unit.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: International Publication No. WO2023 / 026712

[0009] Non-patent literature

[0010] Non-patent literature 1: Alexander Yulaev (6th author), "Exceptional points in lossy medialead to deep polynomial wave penetration with spatially uniform power loss", Nature Nanotechnology (UK), Nature Research, April 21, 2022, Vol. 17, pp. 583-589.

[0011] Non-Patent Literature 2: Yong Liang (4 authors), "Three-dimensional coupled-wave model for square-lattice photonic crystal lasers with transverse electric polarization: A general approach", Physical Review B, (USA), American Physical Society, November 22, 2011, Vol. 84, p. 195119 Summary of the Invention

[0012] The problem the invention aims to solve

[0013] In the diffraction grating coupler described in Non-Patent Document 1, more than half of the light input from the light input section is lost because it is not output in a direction perpendicular to the surface of the diffraction grating, resulting in low light extraction efficiency.

[0014] The problem to be solved by the present invention is to provide a diffraction grating coupler that enables light to be emitted from the entire surface of the diffraction grating and has high light extraction efficiency.

[0015] Solution for solving the problem

[0016] The diffraction grating coupler of the present invention, which addresses the above-mentioned problems, is characterized by comprising:

[0017] A diffraction grating having a plate-shaped base material and regions of different refractive indices, wherein the regions of different refractive indices are periodically arranged in a one-dimensional or two-dimensional manner within a defined range of the base material and have a refractive index different from that of the base material; and

[0018] A light-reflecting portion is disposed at the end of the range on the side opposite to the light input portion side.

[0019] This region of different refractive indices has a direct coupling coefficient κ. 1D For planar shapes with an absolute value less than 1 / L, the direct coupling coefficient κ... 1D It is an index representing the intensity of light traveling from the light input section along a first direction parallel to the base material, reflected without radiation loss in the region of different refractive indices into a second direction 180° different from the first direction, where 1 / L is the reciprocal of the span length L of the range related to the first direction, and the light input section is part of the end of the range.

[0020] As mentioned above, an anisotropic region refers to a region whose refractive index differs from that of the base material, typically consisting of air (voids, slots). As an alternative example, anisotropic regions can also be formed by embedding an object made of a different material into the base material. Anisotropic regions can be formed either entirely along the thickness direction of the base material (through the entire base material) or only within a portion of the base material's thickness direction. In the latter case, the anisotropic region can be formed either on one surface of the base material (appearing only on that surface) or only within the interior of the base material (not visible on either surface).

[0021] Direct coupling coefficient κ 1D This is an index indicating the intensity of light (hereinafter referred to as "directly reflected light") produced by the direct 180° change in the direction of light traveled along the first direction within a diffraction grating (i.e., reflection). The meaning of "direct" will be explained later. Furthermore, the direct coupling coefficient κ... 1D It is a complex number, and the coefficients of its real and imaginary parts have a dimension equal to the reciprocal of its length. Furthermore, κ... 1D complex conjugate This becomes an indicator of the intensity of light traveling in the second direction that is directly reflected in the first direction. Direct coupling coefficient κ 1D It is determined by the planar shape of the region of different refractive indices and can be obtained based on the method described in Non-Patent Document 2. As also described in Patent Document 1, in the light reflected in the 180° direction by the light traveling in the diffraction grating, in addition to the directly reflected light, there is also light generated due to radiation loss and a 180° change in the direction of travel due to interaction with the light output in the direction perpendicular to the surface of the diffraction grating (90° different from the direction of travel). However, the directly reflected light plays a dominant role in the reflection in the 180° direction.

[0022] If the intensity of the directly reflected light is too high, the light is locally blocked in the direction parallel to the base material. Consequently, the intensity of the light within the diffraction grating decreases sharply (exponentially) as it moves away from the light input section, and therefore the intensity of the emitted light also decreases sharply as it moves away from the light input section. Therefore, in this invention 1, by making |κ... 1D | By reducing the intensity of directly reflected light to less than 1 / L, the degree to which the light intensity decreases with distance from the light input section is made more gradual (a linear function) than before.

[0023] However, if the intensity of directly reflected light is suppressed, the proportion of incident light from the light input section that passes through the diffraction grating instead of being emitted as outgoing light in a direction perpendicular to the surface of the diffraction grating increases, thus reducing the extraction efficiency of the emitted light. In Non-Patent Document 1, the fact that a portion of the incident light passes through the diffraction grating instead of being emitted as outgoing light in a direction perpendicular to the surface of the diffraction grating is also considered a reason for the reduced extraction efficiency of the emitted light.

[0024] Therefore, in this invention, a light reflecting section is also provided at the end of the range (the range in which the heterorefringent region is configured) on the side opposite to the light input section. This causes incident light that enters from the light input section and propagates along the first direction to be reflected in the light reflecting section and returned to the diffraction grating side, thus preventing the incident light from passing through the diffraction grating and thereby improving the extraction efficiency of the emitted light.

[0025] The light reflected in the light reflector travels in the second direction, but like the light traveling in the first direction, the intensity decreases gradually with distance from the light reflector. Furthermore, when the intensity of the light traveling in the second direction is observed relative to the distance from the light input unit, the intensity increases slowly with distance from the light input unit. Therefore, if the light input from the light input unit and traveling in the first direction is mixed with the light reflected in the light reflector and traveling in the second direction, the intensity change of the light depending on its position within the diffraction grating becomes more gradual, thereby allowing the light to exit entirely from the surface of the diffraction grating.

[0026] Using the span length L of the region configured with different refractive indices (in other words, the region where the diffraction grating is formed), which is related to the first direction, so that |κ 1D |×L is less than 1, that is, |κ 1D |Determined by method less than 1 / L|κ 1D The value of |κ is adjusted to reduce the effect of light being confined within the diffraction grating in the direction parallel to the parent material. To suppress radiation loss of directly reflected light as much as possible, |κ 1D The value of | is preferably less than 1 / (2L), and most preferably 0. Furthermore, in |κ 1D When |=0, the intensity distribution of light within the diffraction grating is closest to uniform. For example, a region of heterorefractive index is a region obtained by combining two sub-regions with the same shape and refractive index, and regarding a region of heterorefractive index obtained by arranging these two sub-regions at a distance of 1 / 4 times the wavelength of the light within the diffraction grating in a first direction, it can be set as |κ. 1D |=0.

[0027] As described above, in the light reflected in a 180° direction from the light traveling within the diffraction grating, directly reflected light plays a dominant role, but the influence of indirect reflected light also exists to a certain extent. Therefore, it is preferable to position the light reflecting section such that the indirect reflected light and the light reflected in the light reflecting section are out of phase or nearly out of phase. This eliminates indirect reflected light, thus suppressing radiation loss from indirect reflected light.

[0028] In the diffraction grating coupler of the present invention, the following structure can be adopted: regardless of the periodic arrangement of the positions of the heterorefringent regions, the indirect coupling coefficient (non-Hermitian coupling coefficient) μ is the same value, which is an index indicating the intensity of light (i.e., the indirect reflected light) that has radiation loss due to the interaction between light traveling along the first direction or the second direction and light emitted in a direction perpendicular to the base material and the light whose travel direction changes by 180°.

[0029] By setting μ to the same value regardless of position, light can be emitted from the surface of the diffraction grating with a near-uniform intensity. Typically, by making the shape and material (refractive index) of the heterorefractive index regions disposed at each position identical, μ can be set to the same value regardless of position. Furthermore, the term "identical value" here also includes cases where the value of μ at each position differs within ±20% due to unavoidable manufacturing errors in the heterorefractive index regions during the fabrication of the diffraction grating coupler.

[0030] On the other hand, μ can also be periodically configured to have different values ​​at at least two of the multiple locations in the heterorefringent region.

[0031] By varying the value of μ according to position, intentional variations in the intensity of light emitted from the surface of the diffraction grating can be achieved. To vary the value of μ according to position, the shape and / or material of the anisotropic regions disposed at each position can be varied according to position. For example, when each anisotropic region is defined as a region obtained by combining a first sub-region and a second sub-region, the further the ratio of the area S1 of the first sub-region to the area S2 of the second sub-region deviates from 1 (becomes larger or smaller), the larger the value of μ. Therefore, by arranging these anisotropic regions with different area ratios S1 / S2 at different positions, the value of μ can be varied according to position. The thickness of each anisotropic region can also be appropriately set along with or instead of the area.

[0032] In the diffraction grating coupler of this invention, the light reflecting section can be formed, for example, by placing a photonic crystal at a position outside the end of the range, where the energy of light of a predetermined wavelength is within the photonic bandgap. A photonic crystal is a structure whose refractive index changes periodically, and it is characterized by preventing the passage of light with wavelengths within a specific wavelength range (photonic bandgap) corresponding to the period of refractive index change. The formation of the photonic bandgap with respect to light within the photonic crystal is based on the same reasoning as the formation of the bandgap with respect to electrons in a solid having wave-like properties. Typically, similar to the diffraction grating of this invention, the photonic crystal is formed by periodically arranging regions of different refractive indices on a plate-shaped substrate. In other words, the diffraction grating of this invention is also a type of photonic crystal. The difference between the diffraction grating in this invention and the photonic crystal forming the light reflector is that, depending on the period of the configuration of the different refractive index regions, the energy of the light of the specified wavelength is set such that the light is within the photonic band that can propagate (diffraction grating), or is set such that the light is within the photonic band gap (light reflector).

[0033] In the diffraction grating coupler of the present invention, preferably, the indirect coupling coefficient μ(x) at each position x of the diffraction grating related to the first direction and the second direction is at the electric field intensity E of the light to be emitted at that position x. RAD (x) represents the range of the following expression

[0034] [Number 1]

[0035] .

[0036] Furthermore, the optimal choice is,

[0037] [Number 2]

[0038] .

[0039] The indirect coupling coefficient μ is determined by the planar shape of the region with different refractive indices and can be obtained based on the method described in Non-Patent Document 2. Since the magnitude of the interaction between the emitted light and the indirectly reflected light varies depending on the value of μ, by appropriately setting the value of μ, the proportion of light returning to the light input side due to indirect reflection can be reduced, thereby improving the extraction efficiency of emitted light emitted in a direction perpendicular to the substrate. For example, in the absolute value of the direct coupling coefficient |κ... 1D | is 0 and has the light-reflecting part, and μ is set to the same value regardless of its position (E) RADWhen (x) is set to a position-independent constant, the extraction efficiency of the emitted light exceeds 50% when the indirect coupling coefficient μ is in the range of 0.09 / L < μ < 2.91 / L, exceeds 90% when it is in the range of 0.25 / L < μ < 1 / L (equivalent to the aforementioned conditions), and becomes 100% when μ = 0.5 / L.

[0040] Furthermore, for convenience, the previous description described a portion of the end of a region (diffraction grating) with periodically arranged regions of different refractive indices as a light input section, and described light input from this light input section as being output from the surface of the diffraction grating. However, the diffraction grating coupler of the present invention can also be used to output light input from the surface of the diffraction grating from the light input section (the portion named for convenience).

[0041] In the diffraction grating coupler according to the present invention, the following structure can be adopted: an end-emitting laser is connected to the light input section with its light-emitting portion facing the light input section. This allows laser light excited by the end-emitting laser to be output from the surface of the diffraction grating coupler. The end-emitting laser can be integrally formed with the diffraction grating coupler or connected separately to it.

[0042] It can also be used as a diffraction grating coupler by configuring two diffraction grating couplers (excluding diffraction grating couplers where the end-emission laser is connected to the light input section) according to the present invention, such that their light input sections face each other and the first direction of one diffraction grating coupler coincides with the second direction of the other diffraction grating coupler. According to this structure, light input from the surface of the diffraction grating of one diffraction grating coupler can be output from the light input section (the part named for convenience) of one diffraction grating coupler and input to the light input section of another diffraction grating coupler, thereby being output from the surface of the diffraction grating of the other diffraction grating coupler. In this case, by making the areas of the diffraction gratings (the range) in the two diffraction grating couplers different from each other, it can be used as a converter to change the diameter of the beam.

[0043] Previously, it was explained that light incident from the light input section and traveling in the first direction was output from the surface of the diffraction grating in a direction perpendicular to the surface. However, depending on the shape of the region with different refractive indices, it is also possible to change the direction of light incident from the light input section and traveling in the first direction by 90° within the matrix (in a direction parallel to the matrix), so that it is emitted from the end of the diffraction grating outside the light input section.

[0044] Such an end-ejection type diffraction grating coupler is characterized by,

[0045] The device includes a diffraction grating having a plate-shaped base material and regions with different refractive indices. These regions are periodically arranged in a one-dimensional or two-dimensional pattern within a defined rectangular area of ​​the base material, and their refractive indices differ from those of the base material.

[0046] One side of the rectangular area is the light input section, and the side of the rectangular area perpendicular to this side is the light output section.

[0047] This region of heterorefractive index has a direct coupling coefficient κ. 1D For planar shapes with an absolute value less than 1 / L², the direct coupling coefficient κ... 1D This is an index representing the intensity of light traveling from the light input section along a first direction parallel to the base material, reflected without radiation loss in the region of varying refractive indices into a second direction parallel to the base material and 180° different from the first direction. 1 / L2 is the reciprocal of the span length L2 of the range related to the first direction. Therefore, light can be output with nearly uniform intensity from all positions of the linear light emitting section.

[0048] In such an end-emission diffraction grating coupler, it is preferable that the two sides of the rectangular area other than the light input section and the light emission section are light reflection sections. This prevents input light from the light input section and light that has been diffracted 90° and travels to the side opposite to the light emission section from being lost through the diffraction grating.

[0049] In such an end-emission diffraction grating coupler, the following structure can also be adopted: the end-emission laser is connected to the light input section in such a way that the light emitting part of the end-emission laser faces the light input section.

[0050] It can also be used as a diffraction grating coupler, as previously described, by combining a first diffraction grating coupler and an end-emission type diffraction grating coupler as a second diffraction grating coupler, wherein the first diffraction grating coupler causes the input light from the light input section to be emitted in a direction perpendicular to the surface of the diffraction grating. Specifically, the following structure can be adopted: the light input section of the first diffraction grating coupler has a straight shape perpendicular to the first direction, and the light input section of the first diffraction grating coupler and the light emission section of the second diffraction grating coupler face each other parallel to each other.

[0051] According to this structure, light input from the light input section of the second diffraction grating coupler is input to the light input section of the first diffraction grating coupler at approximately uniform intensity from each position of the light output section of the second diffraction grating coupler, which is a linear structure. Then, light input from each position of the light input section is output in a direction perpendicular to the diffraction grating of the first diffraction grating coupler at approximately uniform intensity in a first direction. Therefore, the output intensity of the light can be made approximately uniform throughout the planar range of the diffraction grating in the first diffraction grating coupler.

[0052] In a diffraction grating coupler obtained by combining a first diffraction grating coupler and a second emission type diffraction grating coupler, the following structure can also be adopted: an end-emission type laser is connected to the light input section in such a way that the light emitting part of the end-emission type laser faces the light input section of the second (end-emission type) diffraction grating coupler.

[0053] Invention Effects

[0054] According to the present invention, a diffraction grating coupler that enables light to be emitted entirely from the surface of the diffraction grating and has high light extraction efficiency can be obtained. Attached Figure Description

[0055] Figure 1 These are perspective views (a) and top views (b) of the diffraction grating coupler according to the first embodiment.

[0056] Figure 2 This is a top view showing a modified example of the diffraction grating coupler of the first embodiment.

[0057] Figure 3 This is a top view showing other variations of the diffraction grating coupler of the first embodiment.

[0058] Figure 4 These are longitudinal sectional views (a) and top views (b) illustrating the operation of the diffraction grating coupler according to the first embodiment.

[0059] Figure 5 This is a graph showing the results obtained by calculating the intensity distribution of the emitted light in a modified example of the diffraction grating coupler of the first embodiment.

[0060] Figure 6 These are top views (a) and (b) showing two further variations of the diffraction grating coupler of the first embodiment.

[0061] Figure 7 It is the shooting that allows light to enter. Figure 6The photograph (a) shows the emitted light when the light is input to the light input section of the diffraction grating coupler shown in (b), and the photograph (b) shows the emitted light when the light is input to the light input section of the diffraction grating coupler of the comparative example.

[0062] Figure 8 This is a top view showing the diffraction grating coupler of the second embodiment.

[0063] Figure 9 It is the shooting that allows light to enter. Figure 8 The photograph is obtained by taking the emitted light from the light input section of the diffraction grating coupler shown.

[0064] Figure 10 This is a top view showing the diffraction grating coupler of the third embodiment.

[0065] Figure 11 This is a top magnified view of the second heterorefractive index region of the second diffraction grating in the diffraction grating coupler of the third embodiment.

[0066] Figure 12 This is a graph showing the results obtained by calculating the intensity distribution of the emitted light for the diffraction grating coupler of the third embodiment.

[0067] Figure 13 This is a top view showing the diffraction grating coupler of the fourth embodiment.

[0068] Figure 14 This is a diagram showing the result obtained by calculating the intensity distribution of the emitted light for the diffraction grating coupler of the fourth embodiment.

[0069] Figure 15 This is a diagram showing the result obtained by calculating the far-field image of the emitted light for the diffraction grating coupler of the fourth embodiment.

[0070] Figure 16 These are a top view (a) showing the diffraction grating coupler of the fifth embodiment, and longitudinal sectional views (b) and (c) showing the operation of the diffraction grating coupler.

[0071] Figure 17 This is a top view showing the diffraction grating coupler of the sixth embodiment.

[0072] Figure 18 This is a top view showing the incident diffraction grating (a), the in-plane 90° diffraction grating (b), and the exit diffraction grating (c) in the diffraction grating coupler of the sixth embodiment.

[0073] Figure 19 This is a perspective view schematically illustrating the operation of the diffraction grating coupler according to the sixth embodiment.

[0074] Figure 20 The distribution of the design value of the indirect coupling coefficient μ calculated for the diffraction grating coupler of the sixth embodiment (a), and the 90° coupling coefficient κ 2D The distribution of design values ​​(b) and the graph (c) showing the results obtained by calculating the intensity distribution of the emitted light.

[0075] Figure 21 This is a conceptual diagram illustrating the diffraction grating coupler of the seventh embodiment.

[0076] Figure 22 This is a top view showing the incident diffraction grating (a), the diffraction gratings (b) at 90° in the first and second planes, and the exit diffraction grating (c) in the diffraction grating coupler of the seventh embodiment.

[0077] Figure 23 These are top views ((a) to (c)) showing examples of connecting an end-emitting laser to a light incident section in each of the diffraction grating couplers in the first to fourth embodiments. Detailed Implementation

[0078] use Figures 1-23 The following describes the implementation of the diffraction grating coupler involved in this invention.

[0079] (1) First implementation method

[0080] exist Figure 1 The diffraction grating coupler 10 of the first embodiment is shown in (a) perspective view and (b) top view. The diffraction grating coupler 10 includes: a rectangular plate-shaped base 11; a rectangular plate-shaped parent material 121 formed on the surface of the base 11; a heterorefringent region 122 formed by a hole provided in the parent material 121; a light input section (input port) 13 provided on one of the shorter sides of the rectangle of the parent material 121; and a light reflecting section 14 provided within the parent material 121. The parent material 121 and the heterorefringent region 122 together constitute a diffraction grating 12. The surface of the parent material 121 opposite to the base 11 is space (air).

[0081] In this embodiment, the base 11 is made of silicon dioxide (SiO2), and the base material 121 is made of silicon (Si). However, the materials of the base 11 and the base material 121 are not limited to these, as long as the base material 121 is made of a material that allows light of the wavelength used in the diffraction grating coupler to pass through, and the base 11 is made of a material on which the base material 121 can be formed and whose refractive index is lower than that of the base material 121 (therefore, when light traveling within the base material 121 is incident at a shallow angle at the interface with the base 11, total internal reflection occurs). Furthermore, in this embodiment, the base 11 supports the entire lower surface of the base material 121, but it is also possible to use certain components to support a portion of the lower surface of the base material 121 (e.g., only near the two opposing sides of the rectangle of the base material 121). The anisotropic refractive index region 122 can also be replaced by a component with a refractive index different from that of the base material 121 instead of a hole.

[0082] In the first embodiment, such as Figure 1 As shown in (b), a plurality (N) of heterorefringent regions 122 are arranged in a one-dimensional manner with a periodic length a, extending in the direction of the long side of the rectangle towards the parent material 121 (the positive x-direction, equivalent to the first direction mentioned above). By arranging the heterorefringent regions 122 with a periodic length a, a diffraction grating 12 is formed throughout a length L = N × a, with a wavelength of a within the diffraction grating 12 (the wavelength in vacuum is a × n). eff。 Here, n eff The effective refractive index of the diffraction grating 12 is [value missing]. Light from [value missing] is diffracted in a direction perpendicular to the surface of the parent material 121. Furthermore, the anisotropic region 122 can also [value missing]. Figure 2 The arrangement is two-dimensional, as shown, instead of one-dimensional. Figure 2 In the example, N is arranged in a square lattice with a period length a along the direction from the light input section 13 toward the light reflection section 14 (positive x direction = first direction). x A region 122 of different refractive indices is arranged in a tetragonal lattice with a period length a along the y direction perpendicular to the x-direction. y One region with different refractive indices, 122.

[0083] Each anisotropic region 122 is formed by arranging a first anisotropic region 1221 and a second anisotropic region 1222 having the same shape and size as the first anisotropic region 1221, with a separation distance d = a / 4 in the direction (x direction) from the light input section toward the light reflection section 14. Therefore, the direct coupling coefficient κ... 1D It becomes 0 (details will be described later). Furthermore, in this embodiment, the planar shape of the first anisotropic region 1221 and the second anisotropic region 1222 is an ellipse with the x-direction as its minor axis, but this is not a limitation of this example. For example... Figure 3 As shown, a first part of the anisotropic refractive index region 1221 and a second part of the anisotropic refractive index region 1222 with a rectangular planar shape having the x-direction as the shorter side can also be used.

[0084] The light-reflecting section 14 is formed by periodically arranging a region of different refractive index (hereinafter referred to as the light-reflecting section different refractive index region 1411) consisting of holes in the base material 121 on the side opposite to the light input section 13 of the diffraction grating 12 at a period length of a / 2. This region, in which the light-reflecting section different refractive index region 1411 is arranged, functions as a photonic crystal 141. In the photonic crystal 141, by periodically arranging the light-reflecting section different refractive index region 1411, the refractive index undergoes a periodic change, thereby preventing light with wavelengths within a specific wavelength range (photonic bandgap) from passing through. In this embodiment, the period length of the arrangement of the light-reflecting section different refractive index region 1411 is a / 2, thus, since wavelength a within the photonic crystal 141 is contained within the photonic bandgap, light with wavelength a cannot pass through the photonic crystal. Therefore, light of wavelength a traveling within the diffraction grating 12 is reflected in the light reflecting section 14, which is the boundary between the diffraction grating 12 and the photonic crystal 141. Furthermore, the period length of the arrangement of the heterorefringent region 1411 of the light reflecting section is not limited to a / 2, as long as it is set such that wavelength a is contained within the photonic bandgap.

[0085] The operation of the diffraction grating coupler 10 in this embodiment will be explained. When using the diffraction grating coupler 10, the wavelength in vacuum emitted by a light source (not shown) is a×n. eff The input light is input from the light input section 13 in a direction parallel to the base material 121 (first direction). The light input to the diffraction grating coupler 10 is diffracted within the diffraction grating 12 by periodically arranged heterorefringent region 122. At this time, since the wavelength within the diffraction grating 12 is consistent with the period length a, the diffracted light diffracted in the direction perpendicular to the base material 121 is enhanced due to interference. As a result, the diffracted light diffracted in the direction perpendicular to the base material 121 is extracted from the surface of the base material 121 as emitted light. Figure 4 ).

[0086] In conventional diffraction grating couplers, light input in a direction parallel to the substrate is diffracted not only in a direction perpendicular to the substrate but also in a 180° direction (i.e., reflected) by periodically arranged heterorefringent region 122. However, in the diffraction grating coupler 10 of this embodiment, the first heterorefringent region 1221 and the second heterorefringent region 1222 have the same shape and size, and are separated by approximately d = a / 4. Therefore, the light directly reflected (without interaction other than reflection) in the 180° direction through the first heterorefringent region 1221 has the same intensity as the light directly reflected in the second heterorefringent region 1222, and an optical path difference of approximately a / 2 is formed between them. As a result, these two directly reflected lights are eliminated due to interference, thus no directly reflected light is generated. That is, in this embodiment, the direct coupling coefficient κ... 1D Become 0.

[0087] In the diffraction grating coupler 10 of this embodiment, by preventing direct reflection of light, it is possible to prevent light from being confined to a region near the light input section 13 in the direction parallel to the base material 121. This prevents the intensity of light within the diffraction grating from decreasing as it moves away from the light input section. As a result, it is also possible to prevent the intensity of light emitted in the direction perpendicular to the base material 121 from decreasing as it moves away from the light input section, thus ensuring that the intensity of the emitted light is nearly uniform regardless of its position.

[0088] Furthermore, in the diffraction grating coupler 10 of this embodiment, the direct coupling coefficient κ is... 1D Set to 0, but even if the absolute value of the direct coupling coefficient |κ 1D A value slightly larger than 0 can, to some extent, suppress the confinement of light to a region close to the light input section 13, thereby also suppressing the decrease in intensity of emitted light as it moves away from the light input section. Specifically, the length L in the x-direction of the diffraction grating 12 is such that |κ| < 0. 1D | A value less than 1 / L is allowed. If the distance d between the first anisotropic region 1221 and the second anisotropic region 1222 deviates from a / 4, or if the first anisotropic region 1221 and the second anisotropic region 1222 are different in size or shape, then the direct coupling coefficient |κ 1D | greater than 0, but as long as |κ can be 1D If the suppression is less than 1 / L, then slight deviations in these distances d, and differences in the size / shape of the first anisotropic region 1221 and the second anisotropic region 1222 are also allowed.

[0089] On the other hand, since no direct reflected light is generated, the proportion of the input light reaching the end of the diffraction grating 12 opposite to the light input section 13 is increased. If the light reaching this end passes directly, the intensity of the emitted light in the direction perpendicular to the base material 121 (although it is possible to achieve uniformity regardless of position) weakens. In contrast, in this embodiment, since a light reflecting section 14 is provided at this end to reflect light with wavelength α within the diffraction grating 12, input light with the same wavelength can be reflected back to the diffraction grating 12 side by the light reflecting section 14. As a result, a decrease in the extraction efficiency of the emitted light can be prevented.

[0090] In the light whose direction of travel changes by 180° from a direction parallel to the parent material 121, in addition to the directly reflected light described previously, there is also indirect reflected light. This indirect reflected light is light whose direction of travel changes by 180° due to radiation loss caused by interaction with the emitted light in a direction perpendicular to the parent material 121. The intensity of the indirect reflected light is determined based on the indirect coupling coefficient μ (which can be obtained based on the method described in Non-Patent Document 2), which is determined by the planar shape of the anisotropic refractive index region 122. By fine-tuning the position of the light reflecting section 14 related to the aforementioned direction, the aforementioned indirect reflected light and the light reflected in the light reflecting section 14 can be mutually canceled, thereby reducing the proportion of light returning to the light input section 13 and further improving the extraction efficiency of the emitted light.

[0091] Generally, when the direct coupling coefficient is κ 1D The indirect coupling coefficient is μ (in this embodiment, κ). 1D In a diffraction grating coupler where μ is independent of position x (i.e., the same in all regions of different refractive indices), the intensity R(x) of the traveling wave traveling in the same direction as the input light (positive x direction = first direction) from the light input section, and the intensity S(x) of the receding wave traveling in a direction 180° different from the traveling wave (negative x direction = second direction), are expressed by the following propagation equation (1), and the intensity E of the emitted light is expressed by the following equation (2). RAD (x).

[0092] [Number 3]

[0093]

[0094] [Number 4]

[0095]

[0096] In this embodiment, the direct coupling coefficient κ 1D (and its complex conjugate) Since ) is 0, the propagation equation (1) is expressed by the following equation (3).

[0097] [Number 5]

[0098]

[0099] If there is no light reflector 14, then the solution to equation (3) is as follows:

[0100] [Number 6]

[0101]

[0102] (E0 is a constant), the intensity E of the emitted light in this case RAD The following formula

[0103] [Number 7]

[0104] On the other hand, in the case where a light reflecting section 14 is provided as in this embodiment and the reflection phase is adjusted so that the light reflected in the light reflecting section 14 and the indirectly reflected light cancel each other out, the solution to equation (3) is as follows:

[0105] [Number 8]

[0106] ,

[0107] The intensity E of the emitted light under this condition RAD The following formula

[0108] [Number 9]

[0109] .

[0110] Thus, the intensity E of the emitted light RAD (x) is a constant that does not depend on x (regardless of whether there is a light reflector 14). That is, theoretically, the intensity of the emitted light is the same regardless of the position.

[0111] Furthermore, when calculating the vertical diffraction efficiency η, which represents the extraction efficiency of the emitted light (the intensity of the emitted light relative to the intensity of the input light), if there is no light reflection section 14, then equation (4) is applied to η = 1 - (R(L) / E0). 2 -(S(0) / E0) 2 ((R(L) / E0) 2 This is due to the loss caused by traveling along the first direction and passing through the end opposite to the optical input section 13. (S(0) / E0) 2 This is due to the loss generated by traveling along the second direction and passing through the optical input section 13. Therefore, it becomes the following formula:

[0112] [Number 10]

[0113]

[0114] In the case where the light reflector 14 is provided as in this embodiment, equation (6) is applied to η=1-(S(0) / E0). 2 (Due to the presence of the light-reflecting part 14, therefore (R(L) / E0)) 2 =0), and becomes the following expression

[0115] [Number 11]

[0116] .

[0117] Equations (8) and (9) are functions with μL as the variable. However, if we subtract the left side of equation (8) from the right side of equation (9), we get the following equation.

[0118] [Number 12]

[0119]

[0120] Regardless of the value of μL, it is always positive (both μ and L are positive). That is, with respect to the value of η, the value of η in equation (9) is larger throughout the entire range of μL. Therefore, by providing the light reflection section 14, the diffraction grating coupler 10 of this embodiment can make the emitted light emit with a higher efficiency than when the light reflection section 14 is not present. For example, in the absence of the light reflection section 14, the vertical diffraction efficiency η is at most 0.5 (when μL=1, i.e., μ=1 / L), while in the case where the light reflection section 14 is provided as in this embodiment, the vertical diffraction efficiency η exceeds 0.5 when 0.09<μL<2.91 (0.09 / L<μ<2.91 / L), exceeds 0.9 when 0.25<μL<1 (0.25 / L<μ<1 / L), and becomes 1 when μL=0.5, i.e., μ=1 / 2L. Thus, by adjusting the value of μ (by setting the shape of the heterorefringence region 122), the diffraction grating coupler 10 of this embodiment can enable the emitted light to be emitted with a maximum efficiency of 100% (vertical diffraction efficiency η is 1).

[0121] For the diffraction grating coupler 10 of the first embodiment, the intensity distribution of the emitted light is calculated using the FDTD method. In this calculation, the diffraction grating coupler 10 having a heterorefringence region 122 is taken as the object, and this heterorefringence region 122 is composed of… Figure 3The rectangle shown is composed of a first anisotropic refractive index region 1221 and a second anisotropic refractive index region 1222. The period length a is set to 750 nm, and the distance d between the first anisotropic refractive index region 1221 and the second anisotropic refractive index region 1222 is set to 215 nm. Regarding the size of the rectangle in the planar shape of the first anisotropic refractive index region 1221 and the second anisotropic refractive index region 1222, the shorter side is 90 nm and the longer side is 220 nm. Forty-two (N=42) anisotropic refractive index regions 1222, composed of these first anisotropic refractive index regions 1221 and second anisotropic refractive index regions 1222, are arranged in the x-direction. In this example, the distance d is slightly larger than a / 4 (=187.5 nm) mentioned above, but the absolute value of the direct coupling coefficient |κ 1D | becomes approximately 0, and the indirect coupling coefficient μ becomes a value close to 0.5 / L. In the photonic crystal 141 used to form the light reflector 14, the shape and size of the anisotropic region 1411 of the light reflector are the same as those of the first anisotropic region 1221, and the period length is 375 nm (a / 2).

[0122] exist Figure 5 The calculation results are shown in the figure. It shows that the design values ​​are reproduced throughout the diffraction grating 12, and the emitted light is emitted with a near-uniform intensity regardless of the position.

[0123] exist Figure 6 Further variations of the diffraction grating coupler of the first embodiment are shown in the figure.

[0124] Figure 6 The diffraction grating coupler 10A shown in (a) has a diffraction grating 12A, which is obtained by periodically arranging a rectangular heterorefractive index region 122A with a side length of a / 2 in the x-direction at a period length a in the x-direction. The light reflecting part 14A is formed by periodically arranging a rectangular light reflecting heterorefractive index region 1411A with a period length of a / 2 in the x-direction. Other structures are the same as those of the diffraction grating coupler 10 in the first embodiment. According to this diffraction grating coupler 10A, by making the side length of the heterorefractive index region 122A in the x-direction a / 2, it has a structure equivalent to the structure formed by arranging two heterorefractive index regions with a width of a / 4 in the same direction at a interval of a / 4. Therefore, the absolute value of the direct coupling coefficient |κ| can be made more efficient. 1D |Sufficiently less than 1 / L.

[0125] Figure 6The diffraction grating coupler 10B shown in (b) in the first embodiment also includes a diffraction grating 12B, which is obtained by periodically arranging a sub-anisotropic region 122B with a shape or size different from that of the anisotropic region 122 at a position offset by a / 2 in the x-direction from the position of the anisotropic region 122 and with a period length a. In this modified example, the sub-anisotropic region 122B is arranged such that the first sub-anisotropic region 1221B and the second sub-anisotropic region 1222B, which have the same shape and size as each other and whose shape or size is different from that of the first sub-anisotropic region 1221 / the second sub-anisotropic region 1222, are arranged with a separation distance d = a / 4. Therefore, similarly to the first heterorefringence region 1221 / the second heterorefringence region 1222, the direct reflected light in the first heterorefringence region 1221B and the direct reflected light in the second heterorefringence region 1222B are eliminated due to interference. As a whole, the direct reflected light in the diffraction grating 12B is eliminated due to interference, thus the direct coupling coefficient κ... 1D It becomes 0. On the other hand, the indirect reflection coefficient μ can be appropriately adjusted based on the differences in shape and size between the first part of the anisotropic region 1221 / the second part of the anisotropic region 1222 and the first part of the subisotropic region 1221B / the second part of the subisotropic region 1222B.

[0126] Next, after making Figure 6Following the diffraction grating coupler 10B shown in (b), an experiment was conducted to capture the emitted light when light was input from the light input section 13. In the diffraction grating coupler 10B fabricated here, the diffraction grating 12B is set up by arranging the heterorefractive index region 122 and the sub-heterorefractive index region 122B, both composed of holes, over a length of 175 μm with a period length a of 875 nm, on a Si substrate 121 with a thickness of 220 nm and a waveguide width of 520 nm. The area S1 of the heterorefringent region 122 is set to 11.0% of the area of ​​the unit grating in the diffraction grating 12B (5.5% each for the first heterorefringent region 1221 and the second heterorefringent region 1222), and the area S2 of the sub-heterorefringent region 122B is set to 9.2% of the area of ​​the unit grating (4.6% each for the first sub-heterorefringent region 1221B and the second sub-heterorefringent region 1222B). For comparison, a conventional diffraction grating coupler was fabricated, and the same experiment as that of the diffraction grating coupler 10B was performed. This conventional diffraction grating coupler was obtained by arranging a planar heterorefringent region (with an area of ​​10% of the area of ​​the unit grating) with a period length of 750 nm and a length of 175 μm, as described in Patent Document 1, on a base material of the same material and size as the fabricated diffraction grating coupler 10B.

[0127] exist Figure 7 Experimental results for the diffraction grating coupler 10B are shown in (a). Figure 7 (b) shows experimental results for a conventional diffraction grating coupler. It is known that in conventional diffraction grating couplers, the input light is only applied at the end of the diffraction grating ( Figure 7 The light is output near the left end of (b), while the light is output throughout the diffraction grating 12B in the diffraction grating coupler 10B. Furthermore, when the efficiency of the light output from the diffraction grating coupler 10B (the ratio of the output light to the input light) is measured, a high value of approximately 85% is obtained.

[0128] (2) Second implementation method

[0129] In the first embodiment, the indirect coupling coefficient μ is set to a location-independent value, that is, the same value in all regions of different refractive indices. However, the indirect coupling coefficient μ can also be set to a value that varies depending on the location. An example of such a value is illustrated in the second embodiment.

[0130] For example, in a diffraction grating coupler having the same structure as the first embodiment except for the shape of the heterorefractive index region, the direct coupling coefficient κ... 1DWhen the value is 0, the indirect coupling coefficient μ is set to a value that varies depending on the position x, as expressed by a function μ(x) within the range of the inequality satisfying the following equation (10). This allows the emitted light to be emitted using the function E in the following equation (10). RAD (x) represents the electric field intensity emitted depending on the position x. Furthermore, the function μ(x) is preferably represented by the following equation (10A).

[0131] [Number 13]

[0132]

[0133] By making the shapes of the regions with different refractive indices different according to each of their locations, the value of μ(x) can be set to a value that varies depending on the location. For example, in the first embodiment, in such a way... Figure 6 When the anisotropic region 122 and the subisotropic region 122B are separated from each other by a / 2 and arranged with a period length a, as shown in (b) of the diffraction grating coupler 10B, the further the ratio S1 / S2 of the area S1 of the anisotropic region 122 to the area S2 of the subisotropic region 122B is from 1 (becoming larger or smaller), the larger the value of μ becomes. Therefore, by periodically arranging the anisotropic region 122 and the subisotropic region 122B with S1 / S2 set at each position so that the value of μ is consistent with Equation (10) (preferably Equation (10A)), it is possible to make the emitted light use the function E RAD (x) represents the electric field strength emitted depending on the position x.

[0134] As an example of the second implementation method, such as Figure 8 As shown, a diffraction grating coupler 10C, modified from the diffraction grating coupler 10B of the first embodiment, was fabricated. Specifically, in the one-dimensional diffraction grating 12C, a heterorefringence region 122 with area S1 and a secondary heterorefringence region 122B with area S2 are arranged in half of the region 12C1 located on the light input section 13 side in the x-direction. A heterorefringence region 122C with area S1C and a secondary heterorefringence region 122D with area S2C are arranged in half of the region 12C2 located on the light reflection section 14 side. The area of ​​each (secondary) heterorefringence region satisfies 1 < (S1 / S2) < (S1C / S2C), and the value of μ in the region 12C2 is set to twice the value of μ in the region 12C1. Specifically, S1 is set to 11.4%, S2 to 9.0% (S1 / S2 = 1.27), S1C to 11.8%, and S2C to 8.6% (S1C / S2C = 1.37). The thickness (220 nm) and width (520 nm) of the base material, as well as the period length (875 nm) of the configured (secondary) heterorefringent region, are the same as those in the first embodiment. Figure 7The values ​​used in the experiment shown in (a) are the same values.

[0135] exist Figure 9 The experimental results for the fabricated diffraction grating coupler 10C are shown. A unique intensity distribution, not seen in conventional diffraction grating couplers, was obtained, in which stronger light is emitted from a range 12C2 that is farther from the light input section 13 than from the light input section 13 side (the incident side of the light).

[0136] (3) Third implementation method

[0137] exist Figure 10 The diffraction grating coupler 20 of the third embodiment is shown in a top view. This diffraction grating coupler 20 includes: a rectangular plate-shaped base (not shown). It is disposed closer to the base material 221 described later. Figure 10 The position of the back side of the paper.); a rectangular plate-shaped base material 221, which is formed on the surface of the base; a region of different refractive indices 222, which is composed of periodically arranged holes within the range defined by a rectangle in the base material 221; a linear light input section 231, which is provided on one of the four sides of the rectangle; a linear light emitting section 232, which is provided on one of the two sides perpendicular to that side (described later); a linear first reflective section 241, which is provided on the side opposite to the side where the light input section 231 is provided; and a linear second reflective section 242, which is provided on the side opposite to the side where the light emitting section 232 is provided. The base material 221 and the base ( Figure 10 The surface opposite to the back side of the paper (the surface side of the paper) is space (air). A diffraction grating 22 is formed within the rectangular area where the heterorefractive index region 222 is configured. Hereinafter, the direction perpendicular to the linear light input section 231 is defined as the positive x-direction, and the direction 90° counterclockwise from the positive x-direction is defined as the positive y-direction. The light output section 232 is provided on one of the two sides located on the positive y-direction side.

[0138] The anisotropic refractive index region 222 is disposed at an angle of 45° relative to the x and y directions and has a period length of 2. -1 / 2 The lattice points of a square lattice are arranged at intervals of a in the x and y directions, respectively. Generally, it is known that in a two-dimensional photonic crystal with such square lattice lattice points arranged with regions of different refractive indices, the wavelength within the two-dimensional photonic crystal is a (the wavelength in vacuum is n). eff ×a. Here n eff(This is the effective refractive index of the diffraction grating 22.) Light traveling along the x and y directions is not emitted in directions perpendicular to the base material, but is diffracted in 180° and 90° directions respectively within planes parallel to the base material. The same applies to the diffraction grating 22 in this embodiment.

[0139] Each region with different refractive indices 222 is as follows Figure 11 As shown in the enlarged image, a square is obtained by tilting each side by 45° relative to the x and y directions. Figure 11 The square is formed by placing four circular planar holes at each vertex of the thin dashed line (in the diagram) and four circular planar holes at the midpoints of each side of the square. By adjusting the x- and y-direction spacing d2 of the holes positioned at the midpoints of each side of the square within a heterorefringent region 222, the direct coupling coefficient κ can be adjusted. 1D The value of κ changes. In this embodiment, the direct coupling coefficient κ is... 1D The value is set to be less than 1 / L², where 1 / L² is the reciprocal of the span length L² of the diffraction grating 22 in the x-direction. For example, when d² is set to 0.254a and the radius r of each aperture in the anisotropic region 222 is set to 0.035a, κ 1D Become 0.

[0140] In addition, the direct 90° diffraction coefficient κ is an index that represents the intensity of light diffracted in a 90° direction within a plane parallel to the parent material. 2D The value is also determined based on the shape of the anisotropic refractive index region 222. In the example above, the direct 90° diffraction coefficient κ can be adjusted by the radius r. 2D The value of . Furthermore, in this example, the radius r of the heterorefringent region 222 is set to an equal value throughout the diffraction grating 22.

[0141] Furthermore, in the diffraction grating coupler 20 of the third embodiment, corresponding to the indirect reflected light in the diffraction grating coupler 10 of the first embodiment, indirect reflected light is generated, which is accompanied by loss due to the interaction between light traveling in the positive or negative x-direction and light traveling in the y-direction, and whose travel direction changes by 180°. Similar to the indirect coupling coefficient μ in the first embodiment, the indirect coupling coefficient μ, which is an indicator of the intensity of this indirect reflected light, is... 2D Preferably 0.09 / L2 < μ 2D <2.91 / L2, more preferably 0.25 / L2<μ 2D <1 / L2, the optimal value is μ 2D =1 / 2L². Using the direct 90° diffraction coefficient κ. 2D and the span length L1 in the y-direction of the diffraction grating 22, expressed in μ 2D =2(κ2D ) 2 L1 represents μ 2D The value of .

[0142] The first reflective portion 241 is formed by placing a photonic crystal at a position outside the diffraction grating 22 (on the positive x-direction side) that prevents light of wavelength a within the diffraction grating 22 from passing through (this wavelength is contained within the photonic bandgap). The second reflective portion 242 is formed by placing a photonic crystal at a position outside the diffraction grating 22 (on the negative y-direction side) that is similar to that of the first reflective portion 241.

[0143] Furthermore, the anisotropic region 222 can also be replaced by a component with a refractive index different from that of the base material 221 instead of a void. In addition, the planar shape of the anisotropic region 222 is not limited to the example above, and can be set to any shape, but in order to achieve the same diffraction intensity, it needs to be a shape with four-fold rotational symmetry.

[0144] The operation of the diffraction grating coupler 20 according to the third embodiment will be explained. When light of wavelength α is input into the diffraction grating coupler 20 in the positive x-direction from the light input section 231, a portion of this light is diffracted in the positive or negative y-direction within the diffraction grating 22 (as described above, it is not diffracted in the direction perpendicular to the base material 221). Furthermore, light that is not diffracted in the y-direction but travels in the positive x-direction is reflected in the first reflection section 241, changing its travel direction to the negative x-direction, and thus, during its travel in the negative x-direction, is partially or completely diffracted in the positive or negative y-direction. The light diffracted in the positive y-direction then directly faces the light emission section 232. Conversely, light diffracted in the negative y-direction is reflected in the second reflection section 242, changing its travel direction to the positive y-direction, and then faces the light emission section 232.

[0145] In this way, light is emitted from the light emission section 232. At this time, by adjusting the direct coupling coefficient κ... 1D The light intensity is sufficiently small compared to 1 / L2, thereby preventing light from being locally present near the light input section 231 (near the negative x-direction) within the diffraction grating 22. This allows light to be emitted from the entire linear light emission section 232 with a nearly uniform intensity. Furthermore, by including the first reflector 241 and the second reflector 242, the extraction efficiency of the emitted light can be improved.

[0146] For the diffraction grating coupler 20 in the third embodiment, the intensity distribution of the emitted light is calculated using the FDTD method. In this calculation, the period length a is set to 460 nm, d2 is set to 0.254a (=117 nm), and r is set to 0.035a (=16.1 nm). 200 anisotropic regions 222 are arranged in the x-direction (L2=460 nm × 200 = 92 μm) and 60 are arranged in the y-direction. The direct coupling coefficient κ in this example... 1D The direct 90° diffraction coefficient κ is 0. 2D The absolute value is 95cm -1 Indirect coupling coefficient μ 2D The absolute value is μ 2D =2(κ 2D ) 2 L1=49cm -1 (=0.46 / L2).

[0147] exist Figure 12 The calculation results are shown below. It is known that the light is emitted with a nearly uniform intensity throughout the linear light emitting section 232. When the extraction efficiency of the emitted light is calculated, a high value of 96%, close to 100%, is obtained.

[0148] (4) Fourth Implementation Method

[0149] exist Figure 13 The diffraction grating coupler 30 of the fourth embodiment is shown in a top view. This diffraction grating coupler 30 is used to... Figure 2 The first embodiment shown has a diffraction grating coupler 10 (a structure obtained by arranging heterorefractive index regions 122 in a two-dimensional manner) and Figure 10 The diffraction grating coupler 20 of the third embodiment shown is combined. Specifically, the diffraction grating coupler 10 and the diffraction grating coupler 20 are formed on a single (shared) base material 321 such that the light emitting portion 232 of the diffraction grating coupler 20 of the third embodiment is aligned with or parallel to the light input portion 13 of the diffraction grating coupler 10 of the first embodiment. In this diffraction grating coupler 30, the light input portion 231 of the diffraction grating coupler 20 of the third embodiment functions as a light input portion, and the entire upper surface of the diffraction grating 12 of the first embodiment functions as a light emitting portion.

[0150] The operation of the diffraction grating coupler 30 according to the fourth embodiment will be explained. When light of wavelength α is input into the diffraction grating coupler 30 in the positive x-direction from the light input section 231, similarly to the diffraction grating coupler 20 of the third embodiment, the light is diffracted within the diffraction grating 22, and thus the light is input from the light input section 13 into the diffraction grating 12 with a nearly uniform intensity throughout the linear light emission section 232. Within the diffraction grating 12, similarly to the diffraction grating coupler 10 of the first embodiment, the light is diffracted in a direction perpendicular to the base material 321, and is emitted from the entire planar area of ​​the diffraction grating 12 with a nearly uniform intensity.

[0151] Regarding the diffraction grating coupler 30 of the fourth embodiment, the intensity distribution of light emitted from the upper surface of the diffraction grating 12 and the far-field image of the emitted light are calculated using the three-dimensional coupled-wave theory described in Non-Patent Document 2. In this calculation, a = 280 nm (common in diffraction grating couplers 10 and 20), L = 2.8 mm (10,000 heterorefractive index regions 122 are arranged in the y-direction of the diffraction grating 12), and L2 = 2.8 mm (10,000 heterorefractive index regions 222 are arranged in the x-direction of the diffraction grating 22). To make κ... 1D The planar shape of the anisotropic refractive index region 122 was determined by setting κ to 0 and μ to 0.5 / L. Furthermore, to make κ... 1D =0, μ 2D The planar shape of the anisotropic refractive index region 222 was determined using a ratio of 0.5 / L2.

[0152] exist Figure 14 The calculation results of the intensity distribution of the emitted light on the upper surface of the diffraction grating 12 are shown in the figure. Figure 15 The image shown is the calculated result of the far-field image of the emitted light. Based on... Figure 14 It can be seen that regardless of the position within the diffraction grating 12, the emitted light exits from the upper surface of the diffraction grating 12 with approximately uniform intensity. Furthermore, according to... Figure 15 It can be seen that the diffusion angle of the emitted light is less than 0.05°. The reason for the smaller diffusion angle of the emitted light is that, regardless of the position within the diffraction grating 12, the light is emitted with approximately uniform intensity, thereby substantially increasing the emission area.

[0153] (5) Fifth Implementation

[0154] exist Figure 16 (a) shows a top view of the diffraction grating coupler 40 of the fifth embodiment. This diffraction grating coupler 40 consists of two (these two are designated as partial diffraction grating couplers 10α and 10β, respectively). Figure 2The diffraction grating coupler 10 of the first embodiment shown (a structure obtained by arranging heterochromatic regions 122 in a two-dimensional manner) is formed on a single (shared) base material 421 such that the linear light input portions 13α and 13β of both are arranged in a consistent or parallel manner. However, these light input portions 13α and 13β are used to input light emitted from the other light input portion 13β and 13α, rather than to input light from the outside of the diffraction grating coupler 40.

[0155] The diffraction grating 12α of the partial diffraction grating coupler 10α and the diffraction grating 12β of the partial diffraction grating coupler 10β are composed of heterorefractive index regions 122 of the same shape and size arranged with the same period length a, but the areas of the diffraction gratings are different. Specifically, both diffraction gratings 12α and 12β are rectangular and have the same size in the y-direction (the direction parallel to the light input sections 13α and 13β), but their lengths L1 and L2 in the x-direction are different. Correspondingly, the number N1 and N2 of heterorefractive index regions 122 arranged in the x-direction are different between the two.

[0156] A light-reflecting portion 14α is provided at the end opposite to the light input portion 13α of the partial diffraction grating coupler 10α, and a light-reflecting portion 14β is provided at the end opposite to the light input portion 13β of the partial diffraction grating coupler 10β. These light-reflecting portions 14α and 14β have the same structure as the light-reflecting portion 14 in the diffraction grating coupler 10 of the first embodiment.

[0157] use Figure 16 (b) will be used to explain the operation of the diffraction grating coupler 40 of the fifth embodiment. Light with wavelength a is input into the diffraction grating coupler 40 from the upper surface of the diffraction grating 12α. The light is then diffracted 90° in a direction parallel to the base material 421 within the diffraction grating 12α. The light directed towards the light input section 13α and the light directed towards the light reflection section 14α and reflected in the light reflection section 14α pass through the light input section 13α (in this case, the light is actually output from the light input section 13α, but it is named as such for convenience), and is thus input from the light input section 13β into the diffraction grating 12β of the partial diffraction grating coupler 10β. The light is then diffracted 90° in a direction perpendicular to the base material 421 within the diffraction grating 12β, and thus emitted with a nearly uniform intensity throughout the planar area of ​​the diffraction grating 12β. Here, since the areas of diffraction grating 12α and diffraction grating 12β are different, light exits from diffraction grating 12β with a diameter different from the diameter input to diffraction grating 12α. That is, the diffraction grating coupler 40 of the fifth embodiment functions as a converter that transforms the diameter of light.

[0158] exist Figure 16 (b) shows an example where light enters from the upper surface of diffraction grating 12α and exits from the upper surface of diffraction grating 12β, but it can also be done as follows: Figure 16 As shown in (c), light enters from the upper surface of diffraction grating 12β and exits from the upper surface of diffraction grating 12α. Figure 16 In example (b), the light path is expanded. Figure 16 In example (c), the light is reduced in diameter.

[0159] (6) Sixth Implementation Method

[0160] The diffraction grating coupler 30 of the fourth embodiment described above has a structure obtained by combining a diffraction grating 22 (the diffraction grating in the third embodiment) and a diffraction grating 12 (the diffraction grating in the first embodiment). The diffraction grating 22 diffracts light input from the outside in the x-direction towards the y-direction (directions differing by 90° in-plane), and the diffraction grating 12 diffracts light input from the diffraction grating 22 in the y-direction towards a direction perpendicular to the surface. In such a structure, in order to allow light to be input into the diffraction grating 22 in the x-direction, a diffraction grating for diffracting light input from a direction perpendicular to the surface in the x-direction can also be provided. Such an example will be described in the sixth embodiment. Furthermore, in the following description, diffraction gratings having structures different from those used in the fourth embodiment are used, but these diffraction gratings 22 and 12 can also be used if it is not necessary for light to be incident with different intensities depending on the incident and exit positions as described later.

[0161] like Figure 17As shown, the diffraction grating coupler 60 of the sixth embodiment has an incident diffraction grating 62A, an in-plane 90° diffraction grating 62B, and an exit diffraction grating 62C. These three diffraction gratings are respectively disposed within a rectangular region within the plate-shaped substrate 621. One short side of the rectangular region where the incident diffraction grating 62A is disposed functions as a linear first light output section 65A that outputs light from the incident diffraction grating 62A to the in-plane 90° diffraction grating 62B. A short side of the rectangular region containing the in-plane 90° diffraction grating 62B functions as a linear second light input section 63B, allowing light to enter from the incident diffraction grating 62A into the in-plane 90° diffraction grating 62B. A long side functions as a linear second light output section 65B, allowing light to exit from the in-plane 90° diffraction grating 62B into the exit diffraction grating 62C. A long side of the rectangular region containing the exit diffraction grating 62C functions as a linear third light input section 63C, allowing light to enter from the in-plane 90° diffraction grating 62B into the exit diffraction grating 62C. The first light output section 65A and the second light input section 63B face each other approximately parallel to each other, and the second light output section 65B and the third light input section 63C face each other approximately parallel to each other. Furthermore, a light reflecting section 64 is provided around these three diffraction gratings. The structure of the light reflecting part 64 is the same as that of the light reflecting part 14 in the above embodiments.

[0162] exist Figure 18 The diagram shows the structure of the incident diffraction grating 62A, the in-plane 90° diffraction grating 62B, and the exit diffraction grating 62C. Figure 18 As shown in (a), the incident diffraction grating 62A is formed by arranging any one of the first incident anisotropic refractive index regions 6221A and the second incident anisotropic refractive index region 6222A with different areas at each lattice point of a square lattice. The first incident anisotropic refractive index region 6221A and the second incident anisotropic refractive index region 6222A are arranged in a manner parallel to the y-direction (parallel to the first light output section 65A), and two rows of each region are alternately arranged in the x-direction (a direction that differs from the y-direction by 90° in-plane). The spacing between the lattice points in the x-direction of the square lattice is 1 / 4 of the wavelength of the light incident on the diffraction grating coupler 60 within the incident diffraction grating 62A. According to the above structure, a periodic structure of four lattice points is formed in the x-direction, and the period length 'a' of this periodic structure is consistent with the wavelength.

[0163] like Figure 18As shown in (b), the in-plane 90° diffraction grating 62B is formed by arranging either a first in-plane 90° diffraction region of different refractive index 6221B or a second in-plane 90° diffraction region of different refractive index 6222B at each lattice point of a square lattice having the same period length as the incident diffraction grating 62A. In each column in the x and y directions, the first in-plane 90° diffraction region of different refractive index 6221B and the second in-plane 90° diffraction region of different refractive index 6222B are arranged alternately with two of each. As a result, in a direction tilted at 45° relative to the x and y directions, columns consisting only of the first in-plane 90° diffraction region of different refractive index 6221B are formed in every four columns. Figure 18 (The column shown by the dotted line in (b)) and the column that only contains the anisotropic refractive index region 6222B of the 90° diffraction section in the second plane (the column shown by the dashed line in the figure).

[0164] like Figure 18 As shown in (c), the emission diffraction grating 62C has a structure that expands its range after the incident diffraction grating 62A is rotated 90° about an axis perpendicular to the parent material 621. That is, the first emission region with different refractive index 6221C and the second emission region with different refractive index 6222C are arranged in an x-direction arrangement, with two rows of each arranged alternately in the y-direction. Furthermore, for convenience, the incident diffraction grating 62A is referred to as the "first light output section 65A," and the emission diffraction grating 62C as the "third light input section 63C." However, the first light output section 65A can also function as a "light input section," and the third light input section 63C can function as a "light output section."

[0165] The diffraction grating coupler 60 of the sixth embodiment is as follows: Figure 19 The operation is as shown in the schematic diagram. That is, when incident light is incident from the surface of the incident diffraction grating 62A, the light propagating in the incident diffraction grating 62A in the x-direction, having wavelengths corresponding to the four lattice points, is suppressed from being reflected 180° in the x-direction by two first incident anisotropic refractive index regions 6221A arranged adjacent to each other in the x-direction at a spacing of 1 / 4 of the wavelength (adjacent lattice points to each other) and having the same area, and also by two second incident anisotropic refractive index regions 6222A that are similarly adjacent in the x-direction. The light is then input to the in-plane 90° diffraction grating 62B through the first light output section 65A and the second light input section 63B.

[0166] In the in-plane 90° diffraction grating 62B, the reflection of light propagating in the x-direction by 180° is suppressed for the same reason as in the incident diffraction grating 62A. On the other hand, when light propagating in the x-direction is reflected (diffracted) 90° in the y-direction in the first in-plane 90° diffraction region 6221B, its phase differs by 180° from the phase of light reflected 90° in the y-direction in the second in-plane 90° diffraction region 6222B (which is located at a position that is necessarily present at this position in the above-described structure of the in-plane 90° diffraction grating 62B) by half a wavelength (the amount of two lattice points). Therefore, it interferes with the light, causing mutual attenuation. However, since the areas of the anisotropic refractive index region 6221B of the 90° diffraction section in the first plane and the anisotropic refractive index region 6222B of the 90° diffraction section in the second plane are different, even if such mutually weakening interference occurs, the light propagating along the y-direction will not disappear, but will be input to the emission diffraction grating 62C through the second light output section 65B and the third light input section 63C.

[0167] In the emission diffraction grating 62C, the light from the light input from the third light input section 63C, which is reflected in the first emission section anisotropic region 6221C or the second emission section anisotropic region 6222C in a direction perpendicular to the parent material 621, is emitted outward from the surface of the emission diffraction grating 62C.

[0168] Furthermore, within the incident diffraction grating 62A, the in-plane 90° diffraction grating 62B, and the exit diffraction grating 62C, light propagating in directions other than those described above is reflected in the light reflection section 64 and thus remains within these diffraction gratings. Moreover, if the propagation direction changes to the aforementioned direction due to diffraction at 90° or the like in the region of opposite refractive index, then propagation continues as described above.

[0169] Through the above actions, light incident from the surface of the incident diffraction grating 62A can be emitted from the surface of the exit diffraction grating 62C. At this time, by providing two regions of different refractive indices with different areas in the incident diffraction grating 62A and the exit diffraction grating 62C, the intensity of the emitted light can vary according to its position in the exit diffraction grating 62C.

[0170] The intensity of the emitted light from the emission diffraction grating 62C can be set as follows. Here, the electric field intensity distribution E of the incident light that is to be incident on the incident diffraction grating 62A is set. IN Let (X, Y) be E. IN(x,y)=a(x)b(y)…(11), where E is the electric field intensity distribution of the emitted light that is to be emitted from the diffraction grating 62C at the emission point. RAD Let (X, Y) be E. RAD (x,y)=c(x)d(y)…(12). Based on this, the shape of each region with different refractive indices is determined so that the direct coupling coefficient κ 1D All become 0, and the indirect coupling coefficient μ related to the x-direction in the incident diffraction grating 62A is... a (x) Direct 90° diffraction coefficient κ in the in-plane 90° diffraction section of diffraction grating 62B 2D (x, y) and the indirect coupling coefficient μ related to the y-direction in the exit diffraction grating 62C. c (y) becomes the value obtained by the following formulas (13) to (15).

[0171] [Number 14]

[0172]

[0173] Here, L is the length of the incident diffraction grating 62A in the x direction, L1 and L2 are the lengths of the in-plane 90° diffraction grating 62B in the y and x directions, respectively, and L3 is the length of the exit diffraction grating 62C in the y direction. When this condition is satisfied, the incident light is made to satisfy the electric field intensity distribution E of equation (11). IN (X, Y) is incident on the incident diffraction grating 62A, thereby enabling the emitted light to satisfy the electric field intensity distribution E of equation (12). RAD (X, Y) are emitted from the diffraction grating 62C of the emission section.

[0174] After setting the shapes of the regions with different refractive indices such that a(x) is a function with one peak, b(y) is a function with one peak, c(x) is a function with three peaks, and d(y) is a function with three peaks, the electric field intensity distribution E of the emitted light emitted from the surface of the diffraction grating 62C at the emission section is calculated. RAD (x, y). In Figure 20 (a) shows the indirect coupling coefficient μ calculated using equations (13) and (15) based on a(x) and d(y) used herein. a (x) and μ c (y), in figure (b), shows the direct 90° diffraction coefficient κ calculated using equation (14) based on b(y) and c(x). 2D (x, y), the electric field intensity distribution E of the emitted light is shown in (c) of the figure. RAD(x, y). According to (c) of the figure, according to this example, incident light with an intensity distribution having only one peak in the x direction is incident from the surface of the incident diffraction grating 62A, thereby emitting light consisting of a total of nine beams arranged in three in the x direction and three in the y direction is emitted from the surface of the emitting diffraction grating 62C.

[0175] (7) Seventh Implementation

[0176] In the diffraction grating coupler 70 of the seventh embodiment, as Figure 21 and Figure 22 As shown, the parent material 721 is divided into four regions: two regions in the x-direction and two regions in the y-direction. An incident diffraction grating 72A is provided in one of these four regions. An exit diffraction grating 72C is provided in the region located diagonally opposite to this region. A first in-plane 90° diffraction grating 72B1 is provided in the region adjacent to the incident diffraction grating 72A in the x-direction, and a second in-plane 90° diffraction grating 72B2 is provided in the region adjacent to the incident diffraction grating 72A in the y-direction. Furthermore, a phase adjustment section 77 is provided between the incident diffraction grating 72A and the second in-plane 90° diffraction grating 72B2, and between the second in-plane 90° diffraction grating 72B2 and the exit diffraction grating 72C. Furthermore, in this embodiment, a phase adjustment section 77 is provided at both of the aforementioned locations, but it is also possible to provide a phase adjustment section 77 at only one of them. Additionally, although not shown, a light-reflecting section is provided around the area formed by combining the aforementioned four regions.

[0177] like Figure 22 As shown in (a), the incident diffraction grating 72A is formed by arranging any one of the following regions—a first incident anisorefractive index region 7221A, a second incident anisorefractive index region 7222A, and a third incident anisorefractive index region 7223A—with different areas on each lattice point of a square lattice. Two adjacent first incident anisorefractive index regions 7221A and two adjacent second incident anisorefractive index regions 7222A are alternately arranged in the x-direction. Two adjacent second incident anisorefractive index regions 7222A and two adjacent third incident anisorefractive index regions 7223A are alternately arranged in the y-direction. The spacing between the lattice points is 1 / 4 of the wavelength of the light incident on the diffraction grating coupler 70 within the incident diffraction grating 72A. Based on the above structure, a periodic structure of four lattice points is formed in both the x-direction and y-direction, and the period length 'a' of this periodic structure is consistent with the wavelength.

[0178] like Figure 22As shown in (b), both the first in-plane 90° diffraction grating 72B1 and the second in-plane 90° diffraction grating 72B2 have the same structure as the in-plane 90° diffraction grating 62B in the sixth embodiment. In this embodiment, the two different refractive index regions with different areas are referred to as "the first in-plane 90° diffraction region with different refractive index 7221B and the second in-plane 90° diffraction region with different refractive index 7222B".

[0179] like Figure 22 As shown in (c), the emission diffraction grating 72C has a structure obtained by rotating the incident diffraction grating 72A by 90° about an axis perpendicular to the parent material 721. In the emission diffraction grating 72C, three different anisotropic refractive index regions with different areas are referred to as the first emission anisotropic refractive index region 7221C, the second emission anisotropic refractive index region 7222C, and the third emission anisotropic refractive index region 7223C.

[0180] The phase adjustment unit 77 has a phase adjustment region formed by a portion of the base material 721 and a heater for heating the phase adjustment region. By heating the phase adjustment region with the heater, the temperature of the phase adjustment region changes, thereby changing the refractive index within the phase adjustment region, and thus the phase of light passing through the phase adjustment region at that point in time can be altered.

[0181] The operation of the diffraction grating coupler 70 according to the seventh embodiment will be explained. Linearly polarized light having the aforementioned wavelength and tilted at 45° relative to both the x and y directions is incident on the surface of the incident diffraction grating 72A. Consequently, within the incident diffraction grating 72A, the linearly polarized light in the y direction (referred to as "y-polarized light") propagates along the x direction, and the linearly polarized light in the x direction (referred to as "x-polarized light") propagates along the y direction. The y-polarized light propagating along the x direction within the incident diffraction grating 72A is suppressed from reflection in the 180° direction, similar to other embodiments, and is input to the first in-plane 90° diffraction grating 72B1. Passing through the heterorefringent region within the first in-plane 90° diffraction grating 72B1, it is reflected 90°, similar to the sixth embodiment, becoming x-polarized light with a 90° change in polarization direction, and is then input to the exit diffraction grating 72C. On the other hand, the x-polarized light propagating in the y-direction within the incident diffraction grating 72A is suppressed and reflected in the 180° direction. After passing through the phase adjustment section 77, it is input into the second-plane 90° diffraction grating 72B2. It is reflected by 90° through the heterorefractive index region within the second-plane 90° diffraction grating 72B2, becoming y-polarized light with a polarization direction changed by 90°. After passing through the phase adjustment section 77, it is input into the exit diffraction grating 72C.

[0182] In the emission diffraction grating 72C, x-polarized light that has passed through the first in-plane 90° diffraction grating 72B1 and y-polarized light that has passed through the second in-plane 90° diffraction grating 72B2 and the two phase adjustment sections 77 are combined. If there is no phase difference between these two polarized lights, the combined light becomes linearly polarized light tilted by 45° relative to both the x and y directions. On the other hand, if a phase difference is formed between the two polarized lights by the phase adjustment section 77, the combined light becomes polarized light reflecting that phase difference. For example, if a 90° phase difference is formed between the x-polarized and y-polarized lights, the combined light becomes circularly polarized light. Furthermore, if a 180° phase difference is formed between the x-polarized and y-polarized lights, the combined light becomes linearly polarized light tilted by 90° relative to the polarization direction when there is no phase difference. As described above, the diffraction grating coupler 70 of the seventh embodiment functions as a polarization control element for controlling the polarization of the incident light.

[0183] The above describes several embodiments of the diffraction grating coupler involved in the present invention, but the present invention is not limited to these embodiments and can be modified in various ways.

[0184] For example, in the diffraction grating coupler 10 of the first embodiment and the diffraction grating coupler 10C of the second embodiment, the end 511 of a known end-face (end-face) emitting laser 51 can be connected to the light input section 13. Figure 23 (a)). The light input section 231 of the diffraction grating coupler 20 in the third embodiment and the light input section 231 of the diffraction grating coupler 30 in the fourth embodiment can also be connected to the end 511 of the end-emitting laser 51. Figure 23 (b) and (c)). According to this structure, the laser excited by the end-emitting laser 51 is emitted from the surface of the diffraction grating couplers 10 and 30 and the end face of the diffraction grating coupler 20, so the emission direction can be switched (in all the examples listed here), or the emission area can be made larger than the end (end face) of the end-emitting laser 51 (in the case of the diffraction grating couplers 10 and 30).

[0185] The end-emitting laser 51 can be integrally formed with the diffraction grating couplers 10, 20, and 30 by being formed on the base material 121, 221. Alternatively, the end 511 of the end-emitting laser 51, which is separate from the diffraction grating couplers 10, 20, and 30, can be connected to the light input section 13, 231. Furthermore, while each embodiment has been shown as an example of an embodiment with an end-emitting laser 51, the end-emitting laser can also be connected to the light input section in other examples of the first to fourth embodiments.

[0186] [Way]

[0187] It will be apparent to those skilled in the art that the above exemplary embodiments are specific examples of the following methods.

[0188] (First item) One aspect of the present invention relates to a diffraction grating coupler comprising:

[0189] A diffraction grating having a plate-shaped base material and regions of different refractive indices, wherein the regions of different refractive indices are periodically arranged in a one-dimensional or two-dimensional manner within a defined range of the base material and have a refractive index different from that of the base material; and

[0190] A light-reflecting portion is disposed at the end of the range on the side opposite to the light input portion side.

[0191] This region of different refractive indices has a direct coupling coefficient κ. 1D For planar shapes with an absolute value less than 1 / L, the direct coupling coefficient κ... 1D It is an index representing the intensity of light traveling from the light input section along a first direction parallel to the base material, reflected without radiation loss in the region of different refractive indices into a second direction 180° different from the first direction, where 1 / L is the reciprocal of the span length L of the range related to the first direction, and the light input section is part of the end of the range.

[0192] (Second item) The diffraction grating coupler involved in the second item is the same as that involved in the diffraction grating coupler involved in the first item, in which the indirect coupling coefficient μ is the same regardless of how the positions of the different refractive index regions are periodically arranged. The indirect coupling coefficient μ is an index representing the intensity of light that has radiation loss and a 180° change in the direction of travel due to the interaction between light traveling along the first direction or the second direction and light emitted in a direction perpendicular to the parent material.

[0193] (Third item) The diffraction grating coupler involved in the third item is, in the diffraction grating coupler involved in the first item, the indirect coupling coefficient μ is different at at least two of the multiple positions where the heterorefractive index region is periodically arranged, the indirect coupling coefficient μ is an index representing the intensity of light that has radiation loss due to the interaction between light traveling along the first direction or the second direction and light emitted in a direction perpendicular to the parent material and the direction of travel changes by 180°.

[0194] (Fourth item) The diffraction grating coupler involved in the fourth item is, in any one of the diffraction grating couplers involved in the first to the third items, the light reflecting part is formed by a photonic crystal having light energy of a predetermined wavelength within the photonic bandgap at a position outside the end of the range.

[0195] (Fifth Item) The diffraction grating coupler involved in the fifth item is one in which the indirect coupling coefficient μ(x) is at the electric field intensity E of the light to be emitted at each position x of the diffraction grating related to the first direction and the second direction. RAD Within the range of the following formula (x), where the indirect coupling coefficient μ(x) is an index representing the intensity of light that has undergone radiation loss and a 180° change in direction of travel due to the interaction between light traveling at position x along the first or second direction and light output in a direction perpendicular to the parent material.

[0196] .

[0197] (Sixth item) The diffraction grating coupler involved in the sixth item is, in any one of the diffraction grating couplers involved in the first to fifth items, an end-emitting laser is connected to the light input section in such a way that the light emitting part of the end-emitting laser faces the light input section.

[0198] (Seventh item) In the diffraction grating coupler involved in the seventh item, two diffraction grating couplers involved in any one of the first to fifth items are configured such that their optical input sections face each other and the first direction of one diffraction grating coupler coincides with the second direction of the other diffraction grating coupler.

[0199] (Eighth) Another aspect of the present invention relates to a diffraction grating coupler comprising a diffraction grating having a plate-shaped base material and a region of different refractive indices, the region of different refractive indices being a region periodically arranged in a one-dimensional or two-dimensional shape within a predetermined rectangular area of ​​the base material, and having a refractive index different from that of the base material.

[0200] One side of the rectangular area is the light input section, and the side of the rectangular area perpendicular to this side is the light output section.

[0201] This region of heterorefractive index has a direct coupling coefficient κ. 1D For planar shapes with an absolute value less than 1 / L², the direct coupling coefficient κ... 1DIt is an index representing the intensity of light traveling from the light input section along a first direction parallel to the base material and reflected in the region of different refractive indices without radiation loss into a second direction parallel to the base material and 180° different from the first direction, where 1 / L2 is the reciprocal of the span length L2 of the range related to the first direction.

[0202] (Item 9) The diffraction grating coupler involved in Item 9 is, in the diffraction grating coupler involved in Item 6, an end-emitting laser is connected to the light input section in such a way that the light emitting part of the end-emitting laser faces the light input section.

[0203] (Item 10) The diffraction grating coupler involved in Item 10 has the following features:

[0204] A first diffraction grating coupler, which is a diffraction grating coupler according to any one of the first to fifth items, wherein the light input section of the first diffraction grating coupler is linear; and

[0205] The second diffraction grating coupler is based on the diffraction grating coupler described in item eight or nine.

[0206] The light input section of the first diffraction grating coupler and the light output section of the second diffraction grating coupler are parallel to each other and face each other.

[0207] (Item 11) The diffraction grating coupler involved in Item 11 has the following features:

[0208] The first diffraction grating coupler is a diffraction grating coupler according to any one of the first to fifth items, wherein the light input section is linear;

[0209] The second diffraction grating coupler is the diffraction grating coupler according to item eight or nine; and

[0210] The third diffraction grating coupler is a diffraction grating coupler according to any one of the first to fifth items, wherein the light input section is linear.

[0211] In this configuration, the light input section of the first diffraction grating coupler and the light input section of the second diffraction grating coupler are parallel and face each other.

[0212] The light input section of the third diffraction grating coupler is parallel to and faces the light output section of the second diffraction grating coupler.

[0213] Furthermore, in the diffraction grating coupler involved in the eleventh item, the "light input section of the first diffraction grating coupler" is structurally identical to the light input section specified in any of the first to fifth items, but actually functions as a light output section that outputs light toward the light input section of the second diffraction grating coupler (refer to the first light output section 65A in the sixth embodiment). In the sixth embodiment, the region where the incident diffraction grating 62A is formed corresponds to the first diffraction grating coupler, the region where the in-plane 90° diffraction diffraction grating 62B is formed corresponds to the second diffraction grating coupler, and the region where the exit diffraction grating 62C is formed corresponds to the third diffraction grating coupler.

[0214] (Item 12) The diffraction grating coupler involved in Item 12 has the following features:

[0215] The first diffraction grating coupler is a diffraction grating coupler according to any one of the first to fifth items. In the first diffraction grating coupler, the different refractive index regions are arranged in a two-dimensional shape, the light input section is linear, and a linear second light input section is provided along a direction that is 90° different from the light input section.

[0216] The second diffraction grating coupler is the diffraction grating coupler according to the eighth or ninth item, wherein the light input section of the second diffraction grating coupler is arranged facing the light input section of the first diffraction grating coupler;

[0217] The third diffraction grating coupler is the diffraction grating coupler according to the eighth or ninth item, wherein the light input section is arranged facing the second light input section of the first diffraction grating coupler;

[0218] A fourth diffraction grating coupler, which is a diffraction grating coupler according to any one of the first to fifth claims, wherein the heterorefractive index regions are arranged in a two-dimensional manner, the light input section is linear, and a linear second light input section is provided along a direction 90° different from the light input section. This light input section is arranged facing the light emission section of the second diffraction grating coupler, and the second light input section is arranged facing the light emission section of the diffraction grating coupler of the third diffraction grating coupler; and

[0219] A phase adjustment unit is disposed between the second light input section of the first diffraction grating coupler and the light input section of the third diffraction grating coupler, and between the light emission section of the third diffraction grating coupler and the light input section of the fourth diffraction grating coupler, or both of these locations, and the phase adjustment unit changes the phase of the transmitted light.

[0220] Furthermore, the light input section and the second light input section of the first diffraction grating coupler involved in the twelfth item are structurally identical to the light input sections specified in any of the first to fifth items, but actually function as light output sections that output light toward the light input sections of the second and third diffraction grating couplers (in the seventh embodiment, this corresponds to the ends of the incident diffraction grating 72A facing the first in-plane 90° diffraction grating 72B1 and the second in-plane 90° diffraction grating 72B2). In the seventh embodiment, the region where the incident diffraction grating 72A is formed corresponds to the first diffraction grating coupler, the region where the first in-plane 90° diffraction grating 72B1 is formed corresponds to the second diffraction grating coupler, the region where the second in-plane 90° diffraction grating 72B2 is formed corresponds to the third diffraction grating coupler, and the region where the exit diffraction grating 72C is formed corresponds to the fourth diffraction grating coupler.

[0221] Explanation of reference numerals in the attached figures

[0222] 10, 10A, 10B, 20, 30, 40, 60, 70… Diffraction grating couplers

[0223] 10α, 10β… partial diffraction grating couplers

[0224] 11…base

[0225] 12, 12A, 12B, 12α, 12β, 22… diffraction gratings

[0226] 121, 221, 321, 421, 621, 721… base material

[0227] 122, 122A, 222… regions of different refractive indices

[0228] 1221…First Part: Region with Different Refractive Indices

[0229] 1221B… Part One: Sub-isorefractive index region

[0230] 1222… Part Two: Region with Different Refractive Indices

[0231] 1222B… Part Two: Sub-isorefractive index region

[0232] 122B… Sub-isorefractive index region

[0233] 13, 13α, 13β, 231… Optical Input Section

[0234] 14, 14A, 14α, 14β… Light reflecting parts

[0235] 141…Photonic Crystal

[0236] 1411, 1411A… Different refractive index regions of the light reflecting part

[0237] 232…Light Emission Section

[0238] 241…First Reflector

[0239] 242…Second Reflector

[0240] 51…End-face emission type laser

[0241] 511…End face of an end-emitting laser

[0242] 6221A, 7221A… First incident region with different refractive indices

[0243] 6221B, 7221B… Different refractive index regions in the 90° diffraction section within the first plane

[0244] 6221C, 7221C… First ejection section, heterorefringent region

[0245] 6222A…Second incident region with different refractive index

[0246] 6222B, 7222B… Different refractive index regions in the 90° diffraction section within the second plane

[0247] 6222C, 7222C… Second ejection section anisotropic refractive index region

[0248] 62A, 72A... Incident diffraction gratings

[0249] 62B…In-plane 90° diffraction grating

[0250] 62C, 72C... Exit section diffraction gratings

[0251] 63B…Second Optical Input Section

[0252] 63C…Third Optical Input Section

[0253] 64…Light Reflector

[0254] 65A…First Optical Output Section

[0255] 65B…Second Optical Output Section

[0256] 72B1… Diffraction grating for the first in-plane 90° diffraction section

[0257] 72B2… Diffraction grating for the 90° inner section of the second plane

[0258] 7223A… Third incident region with different refractive index

[0259] 7223C… Third ejection section, heterorefringent region

[0260] 77… Phase adjustment section.

Claims

1. A diffraction grating coupler, characterized in that, have: A diffraction grating having a plate-shaped base material and a region with different refractive indices, wherein the region with different refractive indices is a region that is periodically arranged in a one-dimensional or two-dimensional shape within a specified range of the base material and has a refractive index different from that of the base material. as well as A light-reflecting portion is disposed at the end of the range on the side opposite to the light input portion side. This region of different refractive indices has a direct coupling coefficient κ. 1D For planar shapes with an absolute value less than 1 / L, the direct coupling coefficient κ... 1D It is an index representing the intensity of light traveling from the light input section along a first direction parallel to the base material, reflected without radiation loss in the region of different refractive indices into a second direction 180° different from the first direction, where 1 / L is the reciprocal of the span length L of the range related to the first direction, and the light input section is part of the end of the range.

2. The diffraction grating coupler according to claim 1, characterized in that, Regardless of how the positions of the different refractive index regions are periodically configured, the indirect coupling coefficient μ is always the same. The indirect coupling coefficient μ is an index representing the intensity of light that has radiation loss due to the interaction between light traveling along the first direction or the second direction and light emitted in a direction perpendicular to the substrate, and whose direction of travel changes by 180°.

3. The diffraction grating coupler according to claim 1, characterized in that, The indirect coupling coefficient μ has different values ​​at at least two of the multiple locations where the heterorefringent regions are periodically configured. The indirect coupling coefficient μ is an index representing the intensity of light that has radiation loss due to the interaction between light traveling along the first direction or the second direction and light emitted in a direction perpendicular to the base material, and whose direction of travel changes by 180°.

4. The diffraction grating coupler according to claim 1, characterized in that, The light-reflecting section is formed by a photonic crystal that has light energy of a specified wavelength within the photonic bandgap at a position outside the end of the range.

5. The diffraction grating coupler according to claim 1, characterized in that, The indirect coupling coefficient μ(x) is the electric field intensity E of the light emitted at each position x of the diffraction grating relative to the first and second directions. RAD Within the range of the following formula (x), where the indirect coupling coefficient μ(x) is an index representing the intensity of light that has undergone radiation loss and a 180° change in direction of travel due to the interaction between light traveling at position x along the first or second direction and light output in a direction perpendicular to the parent material. 。 6. The diffraction grating coupler according to claim 1, characterized in that, An end-emitting laser is connected to the light input section such that the light emitting part of the end-emitting laser faces the light input section.

7. A diffraction grating coupler, characterized in that, Two diffraction grating couplers according to claim 1 are configured such that their optical input sections face each other and the first direction of one diffraction grating coupler coincides with the second direction of the other diffraction grating coupler.

8. A diffraction grating coupler, characterized in that, The device includes a diffraction grating having a plate-shaped base material and regions with different refractive indices. These regions are periodically arranged in a one-dimensional or two-dimensional pattern within a defined rectangular area of ​​the base material, and their refractive indices differ from those of the base material. One side of the rectangular area is the light input section, and the side of the rectangular area perpendicular to this side is the light output section. This region of heterorefractive index has a direct coupling coefficient κ. 1D For planar shapes with an absolute value less than 1 / L², the direct coupling coefficient κ... 1D It is an index representing the intensity of light traveling from the light input section along a first direction parallel to the base material and reflected in the region of different refractive indices without radiation loss into a second direction parallel to the base material and 180° different from the first direction, where 1 / L2 is the reciprocal of the span length L2 of the range related to the first direction.

9. The diffraction grating coupler according to claim 8, characterized in that, An end-emitting laser is connected to the light input section such that the light emitting part of the end-emitting laser faces the light input section.

10. A diffraction grating coupler, characterized in that, have: A first diffraction grating coupler, which is a diffraction grating coupler according to any one of claims 1 to 5, wherein the light input portion of the first diffraction grating coupler is linear; and The second diffraction grating coupler is the diffraction grating coupler according to claim 8 or 9. The light input section of the first diffraction grating coupler and the light output section of the second diffraction grating coupler are parallel to each other and face each other.

11. A diffraction grating coupler, characterized in that, have: The first diffraction grating coupler is a diffraction grating coupler according to any one of claims 1 to 5, wherein the light input section is linear; The second diffraction grating coupler is the diffraction grating coupler according to claim 8 or 9; and The third diffraction grating coupler is a diffraction grating coupler according to any one of claims 1 to 5, wherein the light input section is linear. In this configuration, the light input section of the first diffraction grating coupler and the light input section of the second diffraction grating coupler are parallel and face each other. The light input section of the third diffraction grating coupler is parallel to and faces the light output section of the second diffraction grating coupler.

12. A diffraction grating coupler, characterized in that, have: The first diffraction grating coupler is a diffraction grating coupler according to any one of claims 1 to 5, wherein the heterorefractive index regions are arranged in a two-dimensional manner, the light input section is linear, and a linear second light input section is provided along a direction 90° different from the light input section; The second diffraction grating coupler is the diffraction grating coupler according to claim 8 or 9, wherein the light input section of the second diffraction grating coupler is arranged facing the light input section of the first diffraction grating coupler; The third diffraction grating coupler is the diffraction grating coupler according to claim 8 or 9, wherein the light input section is arranged facing the second light input section of the first diffraction grating coupler; A fourth diffraction grating coupler, as described in any one of claims 1 to 5, wherein the heterorefractive index regions are arranged in a two-dimensional manner, the light input section is linear, and a linear second light input section is provided along a direction 90° different from the light input section, the light input section is arranged facing the light emission section of the second diffraction grating coupler, and the second light input section is arranged facing the light emission section of the diffraction grating coupler of the third diffraction grating coupler; as well as A phase adjustment unit is disposed between the second light input section of the first diffraction grating coupler and the light input section of the third diffraction grating coupler, and between the light emission section of the third diffraction grating coupler and the light input section of the fourth diffraction grating coupler, or both of these locations, and the phase adjustment unit changes the phase of the transmitted light.

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