Optical waveguides, optical circuits, and light source devices

Abstract

This makes it easier to increase the coupling efficiency of guiding incident light in an optical waveguide. [Solution] The optical waveguide (1) has an incident end (11) into which a predetermined input light is incident, and an exit end (12) into which the incident input light is emitted as guided light. The optical waveguide includes a first guide layer (31) having a first refractive index (n1) and extending from a first position at a predetermined distance (D1) from the incident end to the exit end in the guidance direction (Z) in which the guided light travels along the optical waveguide, and a second guide layer (32) having a second refractive index (n2) lower than the first refractive index. The first guide layer is not located within a predetermined distance from the incident end, but includes a comb-shaped region (31a) that branches out in a comb-like manner from a second position spaced apart from the exit end in the guidance direction toward the incident end and extends to the first position. The second waveguide layer is positioned adjacent to the first waveguide layer so as to extend a predetermined distance from the incident end in the waveguide direction and fill the comb-tooth region.

Description

[Technical Field]

[0001] This disclosure relates to optical waveguides, optical circuits, and light source devices. [Background technology]

[0002] Patent Document 1 discloses a multimode optical coupler for interfacing an optical fiber and an optical integrated circuit. The multimode optical coupler comprises a multimode input waveguide that receives optical signals from a single-mode optical fiber and a single-mode output waveguide that is optically coupled to the multimode input waveguide. The single-mode output waveguide receives excited multimodes caused by fiber misalignment. Such a multimode optical coupler can improve the tolerance of misalignment when a single-mode optical fiber is used as the input to the waveguide.

[0003] Patent Document 2 discloses a spot size converter utilizing an optical waveguide having the same functionality as a vertical tapered waveguide. In this spot size converter, the optical waveguide is connected to an optical fiber so that light is input from the optical fiber, and comprises a core region that confines and guides the incident light, and a cladding region. The core region comprises a first region and a second region having a lower refractive index than the first region. The first and second regions are arranged to have a period of approximately the same as, or smaller than, the wavelength of the incident light. This allows the effective refractive index to be continuously changed along the guidance direction of the core region, thereby realizing the above functionality. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Special Publication No. 2013-524262 [Patent Document 2] Japanese Patent Publication No. 2015-175902 [Overview of the project] [Problems that the invention aims to solve]

[0005] This disclosure provides an optical waveguide, an optical circuit, and a light source device that can easily increase the coupling efficiency of guiding incident light in an optical waveguide. [Means for solving the problem]

[0006] In this disclosure, an optical waveguide has an incident end into which a predetermined input light is incident and an exit end into which the incident input light is emitted as guided light. The optical waveguide includes a first waveguide layer having a first refractive index and extending from a first position at a predetermined distance from the incident end to the exit end in the guidance direction in which the guided light travels along the optical waveguide, and a second waveguide layer having a second refractive index lower than the first refractive index and extending from the incident end in the guidance direction. The first waveguide layer is not located within a predetermined distance from the incident end, but includes a comb-shaped region that branches out in a comb-like manner from a second position spaced apart from the exit end in the guidance direction toward the incident end and extends to the first position. The second waveguide layer is located adjacent to the first waveguide layer and extends over a predetermined distance from the incident end in the guidance direction to fill the comb-shaped region.

[0007] In this disclosure, the optical circuit comprises a plurality of optical waveguides. The optical circuit further comprises a wave-combining section that combines a plurality of guided light beams emitted from each of the plurality of optical waveguides.

[0008] In this disclosure, the light source device comprises a plurality of light sources, each emitting a plurality of input light having different wavelengths, and the optical circuit described above. The plurality of light sources are arranged facing each other at the input end of each optical waveguide so as to cause each input light to be incident on a plurality of optical waveguides in the optical circuit. [Effects of the Invention]

[0009] According to the optical waveguide, optical circuit, and light source device of this disclosure, it is possible to easily increase the coupling efficiency of guiding incident light in the optical waveguide. [Brief explanation of the drawing]

[0010] [Figure 1] Perspective view showing the outline of the optical waveguide in Embodiment 1 of the present disclosure [Figure 2] Cross-sectional view illustrating the configuration of the optical waveguide in Embodiment 1 [Figure 3] Enlarged view of the comb-tooth region in the optical waveguide [Figure 4] Graph showing the intensity distribution of the guided light in the width direction of the optical waveguide [Figure 5] Graph showing the intensity distribution of the guided light in the sub-core layer in the thickness direction of the optical waveguide [Figure 6] Graph showing the intensity distribution of the guided light in the core layer in the thickness direction of the optical waveguide [Figure 7] Table showing numerical examples of the optical waveguide in Embodiment 1 [Figure 8A] Table showing the simulation results of the coupling efficiency of the optical waveguides of the examples and Comparative Examples 1 to 4 [Figure 8B] Cross-sectional view illustrating the configuration of the optical waveguide of Comparative Example 1 [Figure 8C] Cross-sectional view illustrating the configuration of the optical waveguide of Comparative Example 2 [Figure 8D] Cross-sectional view illustrating the configuration of the optical waveguide of Comparative Example 3 [Figure 9] Graph showing the simulation results of the mounting error in the thickness direction of the optical waveguide of the example [Figure 10] Graph showing the simulation results of the mounting error in the width direction of the optical waveguide of the example [Figure 11] Graph showing the simulation results of the mounting error in the waveguide direction of the optical waveguide of the example [Figure 12] Graph showing the simulation results of the mounting error in the thickness direction of the optical waveguide of Comparative Example 1 [Figure 13] Graph showing the simulation results of the mounting error in the width direction of the optical waveguide of Comparative Example 1 [Figure 14] Graph showing the simulation results of the mounting error in the waveguide direction of the optical waveguide of Comparative Example 1 [Figure 15]Graph showing simulation results of the comb tooth shape for blue light in the optical waveguide of the embodiment. [Figure 16] Graph showing simulation results of the comb tooth shape for green light in the optical waveguide of the embodiment. [Figure 17] Graph showing simulation results of the comb tooth shape for red light in the optical waveguide of the embodiment. [Figure 18] Graph showing simulation results of the subcore layer for blue light in the optical waveguide of the example. [Figure 19] Graph showing simulation results of the subcore layer for green light in the optical waveguide of the example. [Figure 20] Graph showing simulation results of the subcore layer for red light in the optical waveguide of the example. [Figure 21] A diagram illustrating the configuration of the optical circuit in the light source device of Embodiment 2. [Figure 22] Cross-sectional diagram illustrating the configuration of the DBR section in an optical circuit. [Figure 23] Graph showing the relationship between the reflection band and refractive index ratio of the DBR section in the optical circuit of Embodiment 2. [Figure 24] A cross-sectional view illustrating the configuration of an optical waveguide in a modified example of Embodiment 1. [Modes for carrying out the invention]

[0011] The embodiments will be described in detail below, with reference to the drawings as appropriate. However, unnecessarily detailed explanations may be omitted. For example, detailed explanations of already well-known matters or redundant explanations of substantially identical configurations may be omitted. This is to avoid the following explanation becoming unnecessarily verbose and to facilitate understanding for those skilled in the art.

[0012] The inventors provide the accompanying drawings and the following description so that those skilled in the art may fully understand this disclosure, and not to limit the subject matter described in the claims.

[0013] (Embodiment 1) Hereinafter, Embodiment 1 of this disclosure will be described with reference to the drawings. In this embodiment, the configuration and operation of the optical waveguide will be described.

[0014] 1. Structure The configuration of the optical waveguide in Embodiment 1 will be explained using Figures 1 and 2.

[0015] Figure 1 is a perspective view showing an overview of the optical waveguide in Embodiment 1. Figure 2 is a cross-sectional view illustrating the configuration of the optical waveguide 1.

[0016] The optical waveguide 1 of this embodiment is an element structure that guides external input light L1, such as a laser light source, as guided light L2, as shown in Figure 1, for example. The optical waveguide 1 has an input end 11 into which the input light L1 is incident, where, for example, a laser light source is provided adjacent to it, and an output end 12 from which the guided light L2 that has traveled through the optical waveguide 1 from the input end 11 is emitted.

[0017] Hereinafter, in the optical waveguide 1, the direction in which the guided light L2 propagates from the input end 11 to the output end 12, i.e., the guidance direction, will be defined as the Z direction. In the optical waveguide 1, the width direction (long side direction) perpendicular to the Z direction will be defined as the Y direction, and the thickness direction (short side direction) perpendicular to both the Z and Y directions will be defined as the X direction. In addition, the +X side in the X direction of the optical waveguide 1 may be referred to as the upper side, and the -X side as the lower side. The various orthogonal relationships between the X, Y, and Z directions are not necessarily limited to 90-degree angles, and may have appropriate tolerances.

[0018] In this embodiment, the input light L1 is, for example, laser light in which the transverse mode of the laser oscillation is single-mode in the X direction and multi-mode in the Y direction. The input light L1 has an oscillation wavelength in the visible light band, for example, 400 to 800 nm (nanometers). The single-mode includes only the fundamental mode that exhibits the fundamental oscillation in the standing wave distribution on the beam cross-section. The multi-mode includes the fundamental mode and higher-order modes.

[0019] The optical waveguide 1 of this embodiment includes, for example, a core portion 13 extending from an input end 11 to an output end 12, and a cladding portion 14 provided so as to surround the outer circumference of the core portion 13, as shown in Figure 1. The core portion 13 of the optical waveguide 1 constitutes a core that confines the guided light L2 in the X,Y directions so that the guided light L2 propagates from, for example, the input end 11 side (i.e., the -Z side) to the output end 12 side (i.e., the +Z side).

[0020] The optical waveguide 1 of this embodiment employs a two-layer structure with different refractive indices in the core portion 13. This configuration of the core portion 13 makes it possible to provide an optical waveguide 1 that efficiently couples incident light L1 to guided light L2. The optical waveguide 1 of this embodiment can be manufactured, for example, by a film deposition process and a semiconductor process.

[0021] For example, Figure 2(A) illustrates the structure of optical waveguide 1 in the XZ cross-section of Figure 1. Figure 2(B) illustrates the structure of optical waveguide 1 in the YZ cross-section of Figure 1 within the range of the core layer 31 thickness T1, which will be described later.

[0022] In this embodiment, the core portion 13 of the optical waveguide 1 comprises a core layer 31 and a subcore layer 32 within a thickness T2, as shown in Figure 2(A), for example. In this embodiment, the core portion 13 is formed in a strip shape that has a predetermined core width W1 in the Y direction and extends in the Z direction, as shown in Figure 2(B), for example.

[0023] The core width W1 is set, for example, at the incident end 11 to suppress leakage of external input light L1, and is, for example, 10 to 100 μm (micrometers). Furthermore, the core width W1 is set to be larger than the cutoff length corresponding to the desired higher-order mode, from the viewpoint of guiding the guided light L2 in the Y direction in multimode. The cutoff length indicates the threshold at which the corresponding higher-order mode can propagate. Such higher-order modes may be the next (i.e., lowest-order) guided mode after the fundamental mode, or they may be higher-order guided modes than the lowest-order mode.

[0024] The core layer 31 is a waveguide layer that guides the guided light L2 on the +Z side of the optical waveguide 1 and emits it from the exit end 12. The core layer 31 is provided between the subcore layer 32 and the lower cladding layer 14b of the cladding layer 14 in the X direction, as shown in Figure 2(A). The core layer 31 extends in the Z direction from a position P1 in the middle of the optical waveguide 1 to the exit end 12 (hereinafter referred to as "tip position P1").

[0025] The leading edge position P1 of the core layer 31 is set in the Z direction with a predetermined approach distance D1 from the incident end 11 of the optical waveguide 1. The approach distance D1 is set, for example, from the viewpoint of stably propagating the input light L1 as guided light L2 to the subcore layer 32, and is, for example, 200 μm.

[0026] The core layer 31 has a thickness T1 in the X direction, for example, as shown in Figure 2(A). The thickness T1 of the core layer 31 is set to be less than or equal to the lowest-order cutoff length in the core layer 31 (e.g., 0.1 to 0.2 μm), from the point at which the guided light L2 is guided in single mode in the X direction. The thickness T1 of the core layer 31 is smaller than the size of the core layer 31 in the Y direction, i.e., the core width W1.

[0027] The core layer 31 has a relatively high refractive index n1 with respect to the wavelength band of the guided light L2. For example, the core layer 31 is constructed by stacking thin film materials such as SiN (silicon nitride) on the lower cladding layer 14b.

[0028] In the optical waveguide 1 of this embodiment, the core layer 31 includes, for example, a comb-tooth region 31a provided on the -Z side and a band-shaped region 31b provided on the +Z side, as shown in Figure 2(B). The comb-tooth region 31a is arranged in the Z direction from the tip position P1 to the root position P2, which has a predetermined comb tooth length D2. Details of the comb-tooth region 31a in the optical waveguide 1 of this embodiment will be described later.

[0029] The strip-shaped region 31b of the core layer 31 is connected to the comb-tooth region 31a at its root position P2 on the -Z side. The strip-shaped region 31b extends to the exit end 12 on the +Z side, for example, within a constant core width W1.

[0030] The subcore layer 32 is a waveguide layer that guides, for example, the input light L1 incident from the incident end 11 of the optical waveguide 1 as guided light L2, and couples the guided light L2 to the core layer 31. The subcore layer 32 extends in the Z direction from the incident end 11 to the exit end 12 of the optical waveguide 1, as shown in Figure 2(A). The subcore layer 32 has, for example, a run-up section 32a on the -Z side and a cover section 32b on the +Z side.

[0031] In the subcore layer 32, the approach section 32a is the section corresponding to the approach distance D1 in the Z direction from the incident end 11 of the optical waveguide 1 to the tip position P1 of the core layer 31. In the optical waveguide 1 of this embodiment, within the range of the approach distance D1, the core layer 31 is not arranged in the core section 13, but the subcore layer 32 is arranged therein.

[0032] The subcore layer 32 has a thickness T2 in the X direction, for example, in the run-up section 32a. The thickness T2 of the subcore layer 32 is greater than the thickness T1 of the core layer 31 and less than the core width W1. The thickness T2 is set considering, for example, the viewpoint of suppressing leakage of input light L1 incident on the optical waveguide 1 from a laser light source, and the viewpoint of propagating the guided light L2 in single mode in the X direction (for example, 0.5 to 1.0 μm). The thickness T2 may be less than the lowest-order cutoff length in the subcore layer 32, or it may be near the cutoff length.

[0033] The cover section 32b is a section in the Z direction from the leading edge P1 of the core layer 31 to the exit end 12 of the optical waveguide 1, in which the subcore layer 32 is provided to cover the core layer 31. For example, the thickness of the subcore layer 32 in the cover section 32b is smaller than the thickness T2 in the run-up section 32a by the thickness T1 of the core layer 31.

[0034] The subcore layer 32 has a refractive index n2 that is lower than the refractive index n1 of the core layer 31 with respect to the wavelength band of the guided light L2. For example, the subcore layer 32 is constructed by laminating a thin film material such as germanium-doped silicon dioxide (Ge-SiO2) on the cladding layer 14b on which the core layer 31 is stacked.

[0035] The clad portion 14 includes, for example, a clad layer 14a covering the upper side of the core portion 13 and a clad layer 14b covering the lower side, as shown in Figure 2(A). The clad portion 14 also includes side wall portions 14c provided adjacent to the core portion 13 on both sides in the Y direction, as shown in Figure 2(B).

[0036] The side wall portion 14c of the cladding portion 14 is connected, for example, to the upper cladding layer 14a and the lower cladding layer 14b in the X direction, and covers the core portion 13 on both sides in the Y direction. The side wall portion 14c is appropriately set to a width greater than, for example, the width at which the electromagnetic field of the guided light L2 is expected to seep out from the core portion 13 in the Y direction.

[0037] The cladding portion 14 has a refractive index n3 that is lower than the refractive index n2 of the subcore layer 32 with respect to the wavelength band of the guided light L2. For example, the cladding portion 14 is constructed by sequentially laminating thin film materials such as silicon dioxide (SiO2) in a manufacturing process in which the core portion 13 is formed on a substrate or the like.

[0038] 1.1. Regarding the comb-tooth region The details of the comb-tooth region 31a in the optical waveguide 1 of this embodiment will be explained using Figures 2(B) and 3.

[0039] Figure 3 shows an enlarged view of the comb-tooth region 31a in the optical waveguide 1 shown in Figure 2(B), for example. In the optical waveguide 1 of this embodiment, the comb-tooth region 31a of the core layer 31 includes a plurality of comb teeth 3 that are periodically arranged in the Y direction.

[0040] The comb tooth region 31a has a period in which multiple comb teeth 3 are aligned in the Y direction, i.e., a comb tooth period C1. The comb tooth period C1 is, for example, 1 to 10 times the wavelength of the input light L1 or guided light L2, and for example, 2 to 3 times the wavelength.

[0041] The optical waveguide 1 is configured with a set number of comb teeth 3 in the comb tooth region 31a, i.e., the comb tooth count N. The comb tooth count N is set, for example, from the perspective of dividing the core width W1 range by the comb tooth period C1, and is, for example, 10 to 100 teeth.

[0042] The comb tooth length D2 is set appropriately, for example, from the viewpoint of transferring the waveguide light L2 from the subcore layer 32 to the core layer 31 (e.g., 100-200 μm). The comb tooth length D2 is greater than, for example, the core width W1 (Figure 2(B)) and smaller than the run-up distance D1 or the length D3 of the band-shaped region 31b.

[0043] In the comb tooth region 31a, each comb tooth 3 has a tapered shape, gradually narrowing in width from the root position P2 (+Z side) towards the tip position P1 (-Z side) where the comb tooth length D2 is located. Due to this tapered shape of the comb teeth 3, the spacing between adjacent comb teeth 3 gradually narrows towards the +Z side, and valleys are formed between the comb teeth 3 such that the spacing disappears or becomes nearly zero at the root position P2.

[0044] The subcore layer 32 includes a filling portion 30 that is positioned from the tip position P1 to the root position P2 of the comb tooth region 31a in the cover section 32b (Figure 2(A)) that covers the core layer 31. As shown in Figure 3, the filling portion 30 of the subcore layer 32 is the part that fills the valleys between the multiple comb teeth 3 in the comb tooth region 31a of the core layer 31. The filling portion 30 has a tapered shape that narrows in width from the tip position P1 to the root position P2 of the comb tooth region 31a.

[0045] The tips of the comb teeth 3 in the comb tooth region 31a may be sharply pointed or not. For example, as shown in Figure 3, the comb teeth 3 may have a blunt tip K1 at their tip. The blunt tip K1 is represented, for example, by the distance from the position in the Z direction where the tip of the comb teeth 3 would be pointed to the actual position of the comb teeth 3. The valleys between the comb teeth 3 may be more pointed than the tips of the comb teeth 3.

[0046] In the comb tooth region 31a, there may be various variations among the multiple comb teeth 3. For example, the comb tooth length D2 and each position P1, P2 may be set based on any one of the multiple comb teeth 3, or they may be set to various averages among the multiple comb teeth 3.

[0047] 2. Operation The operation of the optical waveguide 1, configured as described above, will be explained below.

[0048] In this embodiment, the optical waveguide 1 is supplied with input light L1 from an external light source, such as a laser light source, as shown in Figure 1. When the input light L1 from the laser light source enters the incident end 11 of the optical waveguide 1, it propagates through the optical waveguide 1 from the -Z side to the +Z side as guided light L2. At the incident end 11, coupling losses may occur that prevent the input light L1 from being obtained as guided light L2 due to Fresnel reflection or other factors.

[0049] Figure 4 shows the intensity distribution of the guided light L2 in the width direction (Y direction) of the optical waveguide 1. In the optical waveguide 1, the guided light L2 has a multimode intensity distribution across the core width W1 in the Y direction, for example, as shown in Figure 4.

[0050] Figure 5 shows the intensity distribution of guided light L2 in the subcore layer 32 in the thickness direction (X direction) of the optical waveguide 1. In the optical waveguide 1, guided light L2 first propagates through the preparatory section 32a of the subcore layer 32. At this time, guided light L2 has a single-mode intensity distribution over the thickness T2 of the subcore layer 32, as shown in Figure 5, for example. After passing through the preparatory section 32a of the subcore layer 32, guided light L2 reaches the comb-tooth region 31a of the core layer 31.

[0051] In the optical waveguide 1 of this embodiment, in the comb tooth region 31a, the guided light L2 gradually enters the core layer 31 from the subcore layer 32 towards the root position P2 of each comb tooth 3, and then continuously transitions to propagation to the core layer 31. In this way, the optical waveguide 1 of this embodiment can efficiently couple the guided light L2 from the subcore layer 32 to the core layer 31.

[0052] Figure 6 shows the intensity distribution of guided light L2 in the core layer 31 in the thickness direction (X direction) of the optical waveguide 1. The guided light L2 propagates through the comb-tooth region 31a in the optical waveguide 1, then propagates through the band-shaped region 31b of the core layer 31, and exits the optical waveguide 1 from the exit end 12. This exiting guided light L2 reaches a single-mode intensity distribution of the optical intensity distribution over the thickness T1 of the core layer 31, for example, as shown in Figure 6. In this case, the subcore layer 32 in the cover section 32b functions as part of the cladding for confining the guided light L2 in the core layer 31, for example.

[0053] As described above, according to the optical waveguide 1 of this embodiment, the subcore layer 32 and the comb-tooth region 31a of the core layer 31 efficiently couple the external input light L1 to the core layer 31 as guided light L2, and guide it, for example, from the output end 12 to the subsequent stage following the optical waveguide 1.

[0054] 2.1. Simulation of coupling efficiency The inventors of this invention confirmed through numerical simulation using beam propagation method (BPM) that the optical waveguide 1 of this embodiment has an effect that makes it easier to increase coupling efficiency. These simulation results will be explained with reference to Figures 7 to 20.

[0055] Figure 7 is a table showing numerical examples of the optical waveguide 1 of this embodiment. In this simulation, blue light with a wavelength of 450 nm, green light with a wavelength of 520 nm, and red light with a wavelength of 640 nm were used as input light L1. The light size w of each input light L1 incident on the incident end 11 x , w yThe dimensions of each laser light source were taken into consideration and set in the X and Y directions as shown in Figure 7. The light intensity distributions I(x) and I(y) in the X and Y directions for the input light L1 were set as shown in the following equations (1) and (2).

number

number

[0056] In equations (1) and (2) above, x represents the position in the X direction, y represents the position in the Y direction, and exp() represents the exponential function. Figure 7 shows numerical examples of the optical waveguide 1 of this embodiment for each input light L1 as described above. In this numerical example, separate optical waveguides 1 were constructed from the same material for each color of input light L1. The core layer 31, subcore layer 32, and cladding portion 14 of the optical waveguide 1 have different refractive indices n1, n2, and n3 for each color of light, respectively, due to the thin film material described above.

[0057] In this embodiment, the optical waveguides 1 for each color of light have different core widths W1, comb tooth counts N, and comb tooth periods C1, as shown in Figure 7. For example, the core width W1 is set according to the optical size in the Y direction of each color of light. Also in this embodiment, each optical waveguide 1 has a common approach distance D1, comb tooth length D2, core layer thickness T1, and subcore layer thickness T2, as shown in Figure 7.

[0058] Using the above-described embodiment of the optical waveguide 1, the coupling efficiency was measured in various simulations. In these measurements of coupling efficiency, the optical power obtained by subtracting the optical power of the input light L1 reflected by Fresnel reflection at the incident end 11 from the optical power of the input light L1 (i.e., optical energy per unit time) was used as the reference. That is, the ratio of the optical power coupled to the core layer 31 of the core portion 13 of the optical waveguide 1 to the reference optical power was measured as the coupling efficiency [%].

[0059] Figure 8A shows the first simulation results for the optical waveguide 1 of this embodiment. In the first simulation, the coupling efficiency of the input light L1 of each RGB color in the embodiment of the optical waveguide 1 of this embodiment was compared with the coupling efficiency of Comparative Examples 1 to 3.

[0060] Figures 8B to 8D show the configurations of the optical waveguides 1x to 1z of Comparative Examples 1 to 3 in the same YZ cross-section as in Figure 2(B). The optical waveguide 1 of this embodiment includes a comb-tooth region 31a of the core layer 31 and a subcore layer 32 (see Figure 2), but the optical waveguide 1x of Comparative Example 1 is constructed without both of these configurations. That is, the optical waveguide 1x of this comparative example includes only the core layer 31x as the core portion 13x, as shown in Figure 8B, for example.

[0061] The optical waveguide 1y in Comparative Example 2 does not have the comb-tooth region 31a in the optical waveguide 1 of this embodiment, and instead comprises a core layer 31y without a comb-tooth portion and a subcore layer 32y as the core portion 13y, as shown in Figure 8C, for example. The subcore layer 32y of this Comparative Example includes, for example, a portion similar to the cover section 32b of the subcore layer 32 of the optical waveguide 1 described above (see Figure 2(A)). The subcore layer 32y of this Comparative Example may or may not include, for example, a portion similar to the run-up section 32a of the subcore layer 32 of the optical waveguide 1 described above (see Figure 2(A)).

[0062] The optical waveguide 1z in Comparative Example 3 does not have the subcore layer 32 in the optical waveguide 1 of this embodiment, and instead has a core layer 31z having a comb-like portion as the core portion 13z, as shown in Figure 8C, for example.

[0063] According to the first simulation, as shown in Figure 8A, it was confirmed that the optical waveguide 1 of this embodiment can achieve significantly higher coupling efficiency than comparative examples 1 to 3.

[0064] For example, the coupling efficiency of red light is lower in Comparative Example 2, which has only the subcore layer 32, and in Comparative Example 2, which has only the comb-tooth region 31a, than in Comparative Example 1, which lacks both the comb-tooth region 31a and the subcore layer 32. In contrast, the optical waveguide 1 of this embodiment, by having both the comb-tooth region 31a and the subcore layer 32, achieves a coupling efficiency that is unexpectedly high compared to Comparative Examples 1 to 3, as shown in Figure 8A.

[0065] Furthermore, the coupling efficiency for green or blue light was below 70% in comparative examples 1 and 2. In contrast, it was confirmed that the optical waveguide 1 of this embodiment could achieve a high coupling efficiency of over 99%.

[0066] Figures 9 to 14 are graphs showing the results of the second simulation, respectively. In the second simulation, the variation in coupling efficiency with respect to the mounting errors Δx, Δy, and Δz of the laser light source was compared between this embodiment and Comparative Example 1. The mounting errors Δx, Δy, and Δz of the laser light source relative to the optical waveguide 1 are expressed, for example, as the distance between the center position of the incident end 11 and the center position of the laser light source in the X, Y, and Z directions.

[0067] Figure 9 shows the simulation results of the mounting error Δx in the X direction (i.e., thickness direction) of optical waveguide 1 in this embodiment. Figures 10 and 11 show the simulation results of the mounting errors Δy and Δz in the Y direction (i.e., width direction) and Z direction (i.e., guidance direction) of optical waveguide 1 in this embodiment, respectively. Figures 12 to 14 show the mounting errors Δx, Δy, and Δz in the X, Y, and Z directions of the optical waveguide in Comparative Example 1, respectively.

[0068] According to the second simulation, for example, as shown in Figures 9 to 14, it was confirmed that the optical waveguide 1 of this embodiment is more likely to maintain a higher coupling efficiency than Comparative Example 1 with respect to various mounting errors Δx, Δy, and Δz.

[0069] For example, when the mounting position error Δx = 0.5 μm in the X direction, Comparative Example 1 had a coupling efficiency of less than 10% (Figure 12), while the optical waveguide 1 of this embodiment had a coupling efficiency of 40% or more (Figure 9). Furthermore, even when there were mounting position errors Δy and Δz in the Y and Z directions, the coupling efficiency of the optical waveguide 1 of this embodiment (Figures 10 and 11) was significantly higher than that of Comparative Example 1 (Figures 13 and 14).

[0070] Figures 15 to 17 are graphs showing the results of a third simulation in the optical waveguide 1 of this embodiment. In the third simulation, the relationship between the shape change of the comb-tooth region 31a in the optical waveguide 1 and the coupling efficiency of the input light L1 of each RGB color was analyzed.

[0071] Figure 15 shows the simulation results of the comb tooth shape for blue light in the optical waveguide 1 of this embodiment. Figures 16 and 17 show the simulation results of the comb tooth shape for green light and red light, respectively, in this embodiment. The graphs in Figures 15 to 17 show the relationship between the comb tooth period C1 and the coupling efficiency of each color of light when the comb tip bluntness K1 (Figure 3) of the comb teeth 3 is set in increments of 10 μm from 0 μm to 50 μm.

[0072] According to the third simulation, it was confirmed that in the optical waveguide 1 of this embodiment, by setting the comb tooth period C1 to, for example, two to three times the wavelength of the input light L1, it is easy to obtain a high coupling efficiency of over 90% even if there is comb tip dulling K1.

[0073] For example, as shown in Figure 15, when a comb tip blunting K1 is present, the coupling efficiency for blue light decreases sharply around 0.5 μm (slightly exceeding 1x wavelength ratio) when the comb tooth period C1 is present, and then increases, with a stable coupling efficiency of over 90% being obtained for C1 = 0.7 to 2.0 μm. Furthermore, as the comb tooth period C1 increases, the coupling efficiency for blue light gradually decreases regardless of the presence or absence of comb tip blunting K1. For a comb tooth period C1 corresponding to 2 to 3x wavelength ratio of blue light, a coupling efficiency of over 94% is obtained for 0.90 to 1.35 μm.

[0074] The relationship between coupling efficiency and comb tooth shape, as described above, was also confirmed for green and red light. For example, as shown in Figure 16, the coupling efficiency for green light shows a sharp decline when the comb tooth period C1 is around 0.6 μm in the case of comb tip blunting K1, but stabilizes at over 90% for C1 = 0.8 to 3.0 μm. For the comb tooth period C1, which corresponds to 2 to 3 times the wavelength ratio of green light, a coupling efficiency of over 95% is obtained at 1.04 to 1.56 μm.

[0075] Furthermore, as shown in Figure 17, the coupling efficiency of red light drops sharply when the comb tooth period C1 is around 0.8 μm, then stabilizes at over 90% when C1 = 1.1 to 2.2 μm, which corresponds to a wavelength ratio of 1.7 to 3 times that of red light. In the optical waveguide 1 of this embodiment, the comb tooth period C1 is not limited to the above, and may exceed, for example, a wavelength ratio of 3 times. For example, the comb tooth period C1 may be 5 μm or less, and even in this case, high coupling efficiencies such as 85% or more for each color can be obtained, as shown in the examples in Figures 15 to 17. Also, from this viewpoint, the comb tooth period C1 may be 1.5 times or more that of a wavelength ratio.

[0076] Figures 18 to 20 are graphs showing the results of the fourth simulation in the optical waveguide 1 of this embodiment. In the fourth simulation, the relationship between detailed changes such as the refractive index n2 and thickness T2 of the subcore layer 32 in the optical waveguide 1 and the coupling efficiency of the input light L1 of each RGB color was analyzed.

[0077] Figures 18 to 20 show the simulation results of the subcore layer 32 for blue light, green light, and red light in the optical waveguide 1 of this embodiment, respectively. The graphs in Figures 18 to 20 show the relationship between the thickness T2 of the subcore layer 32 and the coupling efficiency of each color of light when the refractive index n2 of the subcore layer 32 is varied from 1.02 times to 1.40 times the refractive index n3 of the cladding portion 14.

[0078] According to the fourth simulation, it was confirmed that in the optical waveguide 1, the subcore layer 32 can easily achieve a high coupling efficiency of 90% or more when the refractive index n2 is 1.05 to 1.15 times that of the cladding portion 14's refractive index n3, and the thickness T2 is 0.5 to 1.0 μm.

[0079] For example, in the example shown in Figure 20, the red light coupling efficiency increases as the refractive index ratio n2 / n3 of the subcore layer 32 to the cladding 14 increases, within the range of 1.02 to 1.10 times n2 / n3. At a refractive index ratio n2 / n3 = 1.05, the coupling efficiency exceeds 90% when the thickness T2 of the subcore layer 32 is 1 μm or less. Furthermore, for example, a coupling efficiency exceeding 90% is obtained even at refractive index ratios n2 / n3 = 1.06 to 1.10.

[0080] Furthermore, in the example shown in Figure 20, the red light coupling efficiency increases as the refractive index ratio n2 / n3 decreases within the range of 1.15 to 1.40 times. At a refractive index ratio n2 / n3 = 1.15, a coupling efficiency of over 90% is obtained when the thickness T2 of the subcore layer 32 is 1 μm or less.

[0081] Furthermore, in the example in Figure 19, the coupling efficiency for green light increases with increasing subcore layer thickness T2 at a refractive index ratio n2 / n3 = 1.15, reaching approximately 90% at a thickness T2 = 5 μm. In this example, the coupling efficiency exceeds 90% within the refractive index ratio range of n2 / n3 = 1.04 to 1.15. Also, in the example in Figure 18, the coupling efficiency for blue light exceeds 90% within the refractive index ratio range of n2 / n3 = 1.05 to 1.20.

[0082] 3. Summary As described above, the optical waveguide 1 of this embodiment has an incident end 11 into which a predetermined input light L1 is incident, and an exit end 12 into which the incident input light L1 is emitted as guided light L2. The optical waveguide 1 comprises a core layer 31 which is an example of a first waveguide layer, and a subcore layer 32 which is an example of a second waveguide layer. The core layer 31 extends from the tip position P1 to the exit end 12 in the waveguide direction (Z direction) in which the guided light L2 travels through the optical waveguide 1, with an example of a predetermined run-up distance D1 from the incident end 11, and has a refractive index n1 which is an example of a first refractive index. The tip position P1 is an example of a first position with a run-up distance D1 from the incident end 11. The subcore layer 32 extends from the incident end 11 in the Z direction and has a refractive index n2 which is an example of a second refractive index lower than the refractive index n1. The core layer 31 includes a comb-shaped region 31a that branches out in a comb-like manner from a root position P2, an example of a second position spaced apart from the exit end 12 in the Z direction, toward the entrance end 11. The subcore layer 32 is positioned adjacent to the core layer 31 so as to extend a run-up distance D1 from the entrance end 11 in the Z direction and fill the comb-shaped region 31a.

[0083] According to the optical waveguide 1 described above, by providing a subcore layer 32 in addition to the core layer 31 and a comb-tooth region 31a between them, it is possible to easily increase the coupling efficiency of guiding the input light L1 incident on the optical waveguide 1 as guided light L2.

[0084] In the optical waveguide 1 of this embodiment, the subcore layer 32 extends from the incident end 11 to the exit end 12 in the Z direction and is laminated to cover the core layer 31. As a result, the subcore layer 32 propagates the guided light L2 on the -Z side of the optical waveguide 1 and functions as cladding near the core layer 31 on the +Z side, making it easier to increase the coupling efficiency of the optical waveguide 1.

[0085] In the optical waveguide 1 of this embodiment, the input light L1 is multimode in the width direction (Y direction) of the optical waveguide 1 and single-mode in the thickness direction (X direction) of the optical waveguide 1. The core layer 31 and subcore layer 32 have a core width W1 in the Y direction that is greater than or equal to the multimode cutoff length, and thicknesses T1 and T2 in the X direction that are smaller than the core width W1. As a result, the optical waveguide 1 of this embodiment can easily guide the guided light L2 in the same mode as the input light L1, thereby increasing its coupling efficiency.

[0086] In the optical waveguide 1 of this embodiment, the comb-tooth region 31a includes a plurality of comb teeth 3 arranged in the Y direction of the optical waveguide 1. Each of the plurality of comb teeth 3 has a tapered shape in which the spacing between adjacent teeth gradually narrows from the incident end 11 to the exit end 12. As a result, in the optical waveguide 1 of this embodiment, the guided light L2 gradually enters the core layer 31 from the subcore layer 32 from the incident end 11 to the exit end 12, making it easier to increase the coupling efficiency to the core layer 31.

[0087] In the optical waveguide 1 of this embodiment, the comb tooth region 31a has a comb tooth period C1, which is an example of a predetermined period in which a plurality of comb teeth 3 are arranged in the Y direction of the optical waveguide 1. The comb tooth period C1 may be twice or more the wavelength of the input light L1. This makes it easier to increase the coupling efficiency to the core layer 31 in the optical waveguide 1 of this embodiment, even if, for example, the comb tip blunts K1 on the comb teeth 3. Alternatively, the comb tooth period C1 may be three times or less the wavelength of the input light L1.

[0088] In the optical waveguide 1 of this embodiment, the refractive index n2 may be 1.05 times or more and 1.15 times or less the refractive index n2 of an example of the third refractive index n2 of the cladding portion 14 that covers at least a part of the outer circumference of the subcore layer 32. The thickness of the subcore layer 32 may be 0.5 μm or more and 1.0 μm or less. By using such a subcore layer 32, the optical waveguide 1 of this embodiment can more easily achieve higher coupling efficiency.

[0089] In this embodiment, the optical waveguide 1 further comprises a cladding portion 14 having a refractive index n3 smaller than the refractive index n2. The cladding portion 14 includes sidewall portions 14c that cover both sides of the outer periphery of the core layer 31 and subcore layer 32 in the Y direction of the optical waveguide 1. The sidewall portions 14c of the cladding portion 14 make it easier to confine the guided light L2 in the Y direction within the optical waveguide 1 and improve coupling efficiency.

[0090] (Embodiment 2) Hereinafter, Embodiment 2 of this disclosure will be described with reference to Figures 21 to 23. Embodiment 2 will describe an optical circuit and light source device using the optical waveguide described in Embodiment 1.

[0091] Hereinafter, descriptions of the configuration and operation similar to that of the optical waveguide 1 in Embodiment 1 will be omitted as appropriate, and the optical circuit and light source device according to this embodiment will be described.

[0092] 1. About optical circuits Figure 21 illustrates the configuration of the optical circuit 5 in the light source device 20 of Embodiment 2. The light source device 20 of this embodiment comprises, for example, three laser light sources 2A to 2C corresponding to the three RGB colors, and the optical circuit 5, as shown in Figure 21. The light source device 20 is a device that outputs white light or various colored light, and is used for image display applications such as video projection devices. The light source device 20 may also be used in lighting devices, etc. Hereinafter, the laser light sources 2A to 2C will be collectively referred to as "laser light source 2".

[0093] The optical circuit 5 in the light source device 20 realizes a wave combining function that coaxially combines the three colored guided rays L2a to L2c, which are generated by guiding the laser light from each laser light source 2, and outputs them as combined light L20. In this embodiment, the optical circuit 5 can efficiently couple to the laser light from each laser light source 2A to 2C by employing the optical waveguide 1 of Embodiment 1.

[0094] The three laser light sources 2A to 2C include, for example, a red laser light source 2A, a green laser light source 2B, and a blue laser light source 2C, each emitting laser light of the corresponding color as input light. The laser light from the red laser light source 2A is red light with an oscillation wavelength in the red wavelength band, for example, 600 to 650 nm. The laser light from the green laser light source 2B is green light with an oscillation wavelength in the green wavelength band, for example, 500 to 550 nm. The blue laser light source 2C is blue light with an oscillation wavelength in the blue wavelength band, for example, 400 to 490 nm.

[0095] Each laser light source 2 is a semiconductor laser element, such as a laser diode. Each laser light source 2A to 2C is arranged adjacent to its corresponding optical waveguide 1A to 1C in the optical circuit 5. For example, each laser light source 2 generates laser light in single mode in the X direction and in multimode in the Y direction, and supplies it to the optical waveguide 1A to 1C as input light. Each laser light source 2 has, for example, a larger output port in the Y direction than in the X direction. In the light source device 20 illustrated in Figure 21, the red laser light source 2A, the green laser light source 2B, and the blue laser light source 2C are arranged in order from the -Y side in the Y direction.

[0096] The optical circuit 5 of this embodiment includes, for example, an incident section 51, a multiplexing section 52, and an output section 53, as shown in Figure 21. The optical circuit 5 is provided on a circuit substrate 50, such as silicon. The circuit substrate 50 of the optical circuit 5 has a hexagonal shape that is easily formed by utilizing the cleavage properties of silicon, for example. The optical circuit 5 is manufactured by, for example, a semiconductor process and a film deposition process. The optical circuit 5 of this embodiment can be manufactured with a simple circuit configuration by employing, for example, an optical waveguide 1 in which the functions are concentrated in the incident section 51.

[0097] The incident section 51 of the optical circuit 5 includes, for example, three optical waveguides 1A to 1C. Each optical waveguide 1A to 1C in the incident section 51 is configured in the same way as optical waveguide 1 in Embodiment 1. The incident section 51 inputs laser light from each laser light source 2A to 2C as input light to the corresponding optical waveguides 1A to 1C and guides it as guided light L2a to L2c toward the combined section 52. Hereinafter, the optical waveguides 1A to 1C will be collectively referred to as "optical waveguide 1," and the guided light L2a to L2c will be collectively referred to as "guided light L2."

[0098] The incident section 51 is provided such that, for example, the incident ends 11 of each optical waveguide 1 are sequentially aligned in the Y direction on one of the six end faces of the circuit board 50. In the incident section 51, each optical waveguide 1A to 1C is arranged parallel to each other in the Z direction, for example. The lengths of each optical waveguide 1A to 1C in the Z direction are set, for example, from the viewpoint of ensuring that the optical path length of the guided light L2a to L2c emitted from each is the same until it reaches the output section 53 of the optical circuit 5. For example, in the example in Figure 21, the length of the optical waveguide 1 is shorter for the optical waveguide 1 located on the -Y side.

[0099] Multiple optical waveguides 1A to 1C are formed integrally on a circuit board 50 using the same process, for example, in an optical circuit 5. This simplifies the manufacturing process of the optical circuit 5. The thicknesses T1, T2, etc., of each core layer 31, 32 among the multiple optical waveguides 1A to 1C may be set commonly within an appropriate tolerance range. For example, if the spacing between optical waveguides 1A to 1C is about 3 mm, the tolerance may be about 0.1%. On the other hand, the core width W1, for example, can be set individually among the corresponding optical waveguides 1A to 1C according to the dimensions of the output ports of each color laser light source 2A to 2C.

[0100] For example, in the optical circuit 5, the side wall portion 14c of the cladding portion 14 (Figure 2(A)) is not provided on the +Z side of the output end 12 of each optical waveguide 1, while the core layer 31 and subcore layer 32 and the cladding layers 14a and 14b above and below them may be provided as appropriate. In the optical circuit 5, the region where the guided light L2a to L2c propagates between the incident portion 51 and the multiplexing portion 52 is provided, for example, the core layer 31 and subcore layer 32 and the cladding layers 14a and 14b above and below them.

[0101] The wave-combining section 52 includes, for example, three DBR (Distributed Bragg Reflector) sections 6A to 6C, which combine the three colored waveguide rays L2a to L2c from the incident section 51 coaxially and emit the combined light L20 to the emission section 53. Hereinafter, the DBR sections 6A to 6C will be collectively referred to as "DBR section 6".

[0102] The DBR section 6 is an example of a reflector that selectively reflects light in a specific wavelength band and transmits light in other wavelength bands using a diffraction grating provided for Bragg reflection in the optical circuit 5. In the following, the longitudinal direction of the DBR section 6 will be referred to as the V direction, and the direction perpendicular to the V and X directions will be referred to as the U direction. Details of the DBR section 6 will be described later.

[0103] Each DBR section 6A to 6C of the wave multiplexing section 52 is positioned, for example, on the extension line on the +Z side in the Z direction from each optical waveguide 1A to 1C of the incident section 51, and is sequentially arranged along the extension of a predetermined optical axis from the incident side of the exit section 53. For example, the orientation of each DBR section 6A to 6C is parallel to each other and set to reflect the incident waveguide light L2 toward the exit section 53.

[0104] Each DBR section 6A to 6C is configured to reflect red, green, and blue light, respectively, and transmit light of other wavelengths. Thus, for example, in the example shown in Figure 21, the guided light L2a from the red laser light source 2A, guided into the optical waveguide 1A, is reflected in one DBR section 6A and transmitted through two DBR sections 6B and 6C. Similarly, the guided green and blue light L2b and L2c are reflected / transmitted in the DBR sections 6B and 6C. In this way, in the combined section 52, the reflected light of the three colored guided lights L2a to L2c from the DBR sections 6A to 6C is superimposed coaxially to form combined light L20.

[0105] The emission section 53 is composed of an optical waveguide provided on, for example, a circuit board 50, and emits the combined light L20 from the combined section 52 to the outside of the optical circuit 5 (and consequently the light source device 20). The emission section 53 is configured such that, for example, the emission end of the optical waveguide is located on one end face of the circuit board 50, and the incidence end is positioned toward the combined section 52. The optical waveguide of the emission section 53 is configured similarly to the optical waveguide 1 of Embodiment 1, for example, by omitting the comb-tooth region 31a of the core layer 31, the run-up section 32a of the subcore layer 32, and the filling section 30.

[0106] The lengths of the waveguides in the output section 53 and the optical waveguides 1 in the input section 51 are set such that the distance from the output end 12 of each optical waveguide 1 in the input section 51 to the corresponding reflection position in the DBR section 6 is the same as the distance from the reflection position to the input end of the output section 53. Furthermore, the DBR sections 6A, 6B, and 6C are each provided in the shape of an aspherical curve, for example given by the following equation (3), with the point where the optical axes (parallel to the Z direction) of the guided light L2a, L2b, and L2c intersect with the input surface (output surface) of each DBR section 6A, 6B, and 6C in the UV plane as their respective origins (for convenience of explanation, they are shown as straight lines in Figure 21). With this configuration, the beam of the guided light L2 from the output end 12 of each optical waveguide 1 in the input section 51 can be considered, and the beam of the combined light L20 from the combined light section 52 can be focused into the output section 53. [Math 3] U(V) = V 2 / R(1-(1+K)(V / R) 2 ) 1 / 2 +B4V 4 +B6V 6 +B8V 8 +B 10 V 10 …(3) In the above formula (3), R is the radius of curvature, and K, B4, B6, B8, B 10 are aspherical coefficients.

[0107] 2. Regarding the DBR section Details of the DBR section 6 in the optical circuit 5 of this embodiment will be described using FIGS. 22 to 23.

[0108] FIG. 22 is a cross-sectional view illustrating the configuration of the DBR section 6 in the optical circuit 5. FIG. 22(A) illustrates the structure of the DBR section 6 in the UX cross-section of FIG. 21 near the origin described above. FIG. 22(B) illustrates the structure of the DBR section 6 in the UV cross-section of FIG. 21 within the range of the high refractive index layer 61 described later.

[0109] The DBR section 6 includes, for example, a diffraction grating 60 composed of a high refractive index layer 61 and a low refractive index layer 62 as shown in FIG. 22(A). For example, the diffraction grating 60 of the DBR section 6 is formed by periodically providing groove portions in the high refractive index layer 61 in the U direction and filling the groove portions with the low refractive index layer 62. The groove portions of the diffraction grating 60 extend in the V direction as shown in FIG. 22(B), for example. [[ID=3-1]]

[0110] In the optical circuit 5 of this embodiment, the high refractive index layer 61 of the DBR section 6 is formed integrally with the core layer 31 of the optical waveguide 1 of the incident portion 51, for example, and has the same refractive index n1 as the core layer 31. Also, the low refractive index layer 62 is formed integrally with the core layer 31 of the optical waveguide 1 of the incident portion 51 in the optical circuit 5, for example, and has the same refractive index n2 as the sub-core layer 32. With such a configuration, the manufacturing of the optical circuit 5 can be facilitated.

[0111] The diffraction grating 60 of the DBR section 6 has, for example, a DBR period C6, a duty ratio H6, and a DBR length L6 as shown in FIG. 22(A).

[0112] The DBR period C6 is, for example, the period during which the grooves of the diffraction grating 60 are aligned in the U direction. The DBR period C6 is set separately in each DBR section 6, for example, from the viewpoint of setting the reflection band corresponding to each color of light. For example, in the DBR section 6A for reflecting red light, C6 = 243 nm, in the DBR section 6B for green light, C6 = 198 nm, and in the DBR section 6C for blue light, C6 = 175 nm. The duty cycle H6 is the proportion occupied by the high refractive index layer 61 within one period of the DBR period C6 of the diffraction grating 60, for example, H6 = 0.8.

[0113] The DBR length L6 is the length over which the diffraction grating 60 is positioned in the U direction in the DBR section 6, and is set separately for each color-specific DBR section 6A to 6C. For example, L6 = 25 μm in the DBR section 6A for red light, L6 = 20 μm in the DBR section 6B for green light, and L6 = 15 μm in the DBR section 6C for blue light.

[0114] The orientation of the DBR section 6 in the optical circuit 5 is set such that, for example, near the origin as described above, the normal direction (U direction) of the incident plane of the guided light L2 in the DBR section 6 has a predetermined angle A6 (e.g., 30 degrees) with respect to the guidance direction (Z direction) of the optical waveguide 1 of the incident section 51, as shown in Figure 22(B). As a result, the DBR section 6 reflects the guided light L2 incident from the optical waveguide 1 at an angle A6 with respect to the U direction. The angle A6 is set in common, for example, among multiple DBR sections 6A to 6C.

[0115] Figure 23 is a graph showing the relationship between the reflection bandwidth and refractive index ratio n1 / n2 of the DBR sections 6A to 6C for each color in the optical circuit 5 of this embodiment. The reflection bandwidth of the DBR section 6 is, for example, 90% of the total width of the reflection spectrum of the DBR section 6. In the optical circuit 5 of this embodiment, for example, the refractive index n1 of the high refractive index layer 61 is set to 1.26 to 1.29 times the refractive index n2 of the low refractive index layer 62. As a result, the DBR sections 6A to 6C of this embodiment can obtain a reflection bandwidth of 15 nm to 20 nm for the guided light L2a to L2c of each RGB color, as shown in Figure 23. In this way, the wavelength selectivity characteristics of each DBR section 6A to 6C in the optical circuit 5 can be improved.

[0116] 3. Summary As described above, in this embodiment, the optical circuit 5 comprises a plurality of optical waveguides 1 similar to those in Embodiment 1. The optical circuit 5 further comprises a wave-combining unit 52 that combines the plurality of guided light L2 emitted from the plurality of optical waveguides 1A to 1C with each other. In this embodiment, the optical circuit 5 makes it easy to increase the coupling efficiency of each guided light L2 by each optical waveguide 1, and makes it easy to obtain combined light L20 with high efficiency.

[0117] In the optical circuit 5 of this embodiment, a plurality of DBR sections 6, which are an example of reflectors, are provided. Each of the plurality of DBR sections 6A to 6C is composed of a diffraction grating 60 that selectively reflects light of different wavelength bands. With the DBR sections 6, the optical circuit 5 of this embodiment can easily obtain a combined wave light L20 with high efficiency by selectively reflecting and transmitting, for example, multiple colored guided lights L2a to L2c.

[0118] In the optical circuit 5 of this embodiment, the diffraction grating 60 of the DBR section 6 periodically includes a high refractive index layer 61 having a refractive index n1 and a low refractive index layer 62 having a refractive index n2. As a result, the optical waveguide 1 and the DBR section 6 of the optical circuit 5 of this embodiment can be constructed from the same material, and the manufacturing of the optical circuit 5 can be simplified.

[0119] In the optical circuit 5 of this embodiment, the refractive index n1 may be 1.29 times or less of the refractive index n2. This makes it easier to limit the reflection bandwidth of the DBR section 6 to 20 nm or less. The refractive index n1 may be 1.26 times or more of the refractive index n2. This makes it easier to secure a reflection bandwidth of 15 nm or more of the DBR section 6.

[0120] In the optical circuit 5 of this embodiment, multiple optical waveguides 1A to 1C are integrally formed on a common circuit board 50. The optical circuit 5 of this embodiment allows for the integral formation of multiple optical waveguides 1A to 1C, thereby facilitating the manufacturing of the optical circuit 5.

[0121] In this embodiment, the light source device 20 includes laser light sources 2A to 2C, which are an example of a plurality of light sources. Each of the plurality of laser light sources 2A to 2C emits a plurality of input light having different wavelengths. The plurality of laser light sources 2A to 2C are arranged facing each other at the incident end 11 of each optical waveguide 1 so that each input light is incident on a plurality of optical waveguides 1A to 1C in the optical circuit 5. In this embodiment, the light source device 20 makes it easier to increase the coupling efficiency of guiding the input light from the laser light sources 2A to 2C as guided light L2a to L2c using the optical waveguide 1 of the optical circuit 5.

[0122] (Other embodiments) As described above, Embodiments 1 and 2 have been explained as examples of the technology disclosed in this application. However, the technology in this disclosure is not limited thereto and can be applied to embodiments that have been modified, substituted, added, or omitted as appropriate. Furthermore, it is possible to create new embodiments by combining the components described in each of the above embodiments. Therefore, other embodiments will be illustrated below.

[0123] In the above embodiment 2, an optical circuit 5 that combines laser light from three laser light sources 2 was described, but the optical circuit 5 in this embodiment is not particularly limited to this. In this embodiment, the optical circuit 5 may be equipped with two optical waveguides 1 to combine laser light from two laser light sources 2, or it may be configured to combine laser light from four or more laser light sources 2. Furthermore, the optical circuit 5 in this embodiment may be equipped with optical waveguides 1 to realize various functions, not just the combining function.

[0124] In embodiments 1 and 2 described above, examples were explained in which a light source, such as a laser light source, is placed at the incident end 11 of the optical waveguide 1. In this embodiment, the light source used in the optical waveguide 1 is not limited to a laser light source; various other light sources may be used. Furthermore, various optical elements, such as optical fibers, may be placed between the incident end 11 of the optical waveguide 1 and the light source.

[0125] In each of the embodiments described above, an optical waveguide 1 that guides single-mode guided light L2 in the Y direction was described. In the optical waveguide 1 of this embodiment, the guided light L2 does not necessarily have to be single-mode in the Y direction. For example, in the optical waveguide 1 of this embodiment, the guided light L2c of a relatively short wavelength, such as blue light or green light, may allow the next guided mode after the fundamental mode in multimode. In the optical waveguide 1 of this embodiment, the guided light L2 may have a smaller number of modes in the Y direction than the number of multimode modes in the X direction.

[0126] In each of the embodiments described above, an optical waveguide 1 comprising a cladding portion 14 surrounding a core portion 13 was described. In the optical waveguide 1 of this embodiment, part or all of the cladding portion 14 may be omitted as appropriate, and for example, the optical waveguide 1 may consist of a core portion 13. In such an optical waveguide 1, an external medium such as the surrounding air may function as the cladding portion.

[0127] In each of the embodiments described above, an optical waveguide 1 was described in which the subcore layer 32 in the core portion 13 extends from the input end 11 to the output end 12. In the optical waveguide 1 of this embodiment, the subcore layer 32 does not necessarily have to extend to the output end 12. Such modifications will be explained with reference to Figure 24.

[0128] Figure 24(A) illustrates the structure of an optical waveguide 1D of a modified embodiment of Embodiment 1 in an XZ cross-section, similar to Figure 2(A). Figure 24(B) illustrates the structure of the optical waveguide 1 in a YZ cross-section, similar to Figure 2(B). In this modified optical waveguide 1D, the thickness T2 of the subcore layer 32 may be the same as the thickness T1 of the core layer 31. For example, if the thickness T2 of the subcore layer 32 is about the same as the thickness T1 of the core layer 31, the subcore layer 32 may be composed of a run-up section 32a and a filling section 30, as shown in Figures 24(A) and (B), by omitting the cover section 32b (see Figure 2(A)). Alternatively, the cover section 32b of the subcore layer 32 does not have to cover the entire core layer 31 in the Z direction; for example, it may cover the comb-tooth region 31a and not cover part or all of the band-shaped region 31b.

[0129] In the embodiments described above, an optical waveguide 1 in which the core layer 31 and the subcore layer 32 have the same core width W1 has been described, but the disclosure is not particularly limited thereto. For example, in the optical waveguide 1 of this embodiment, the subcore layer 32 may have a tapered shape in which the width is greater at the input end 11 than the width of the core layer 31 at the output end 12, and then narrows in the approach section 32a. In addition, the core layer 31 may also have various shapes such as such a tapered shape.

[0130] In each of the embodiments described above, an example of a thin-film material for manufacturing the optical waveguide 1 was explained. However, the optical waveguide 1 of this embodiment may be composed of a material other than the thin-film material described above. For example, an additive other than germanium may be used in the subcore layer 32 of the optical waveguide 1. The optical waveguide 1 of this embodiment may be composed of various inorganic or organic materials. Each layer 31, 32, 14a, and 14b in the optical waveguide 1 does not necessarily have to be a thin film. Furthermore, the optical waveguide 1 of this embodiment may be manufactured using various manufacturing processes that are not limited to film deposition processes or semiconductor processes.

[0131] In each of the embodiments described above, an optical waveguide 1 used in the optical circuit 5 was explained. In this embodiment, the optical waveguide 1 may be applied to various applications, not limited to the optical circuit 5. In this embodiment, various optical devices comprising a light source that supplies input light to the optical waveguide 1 and the optical waveguide 1 may be provided. In such optical devices, an optical interface equipped with a configuration for inputting a predetermined input light to the incident end 11 of the optical waveguide 1 may be used instead of, or in addition to, the light source.

[0132] (Example of form) The various aspects of this disclosure are described below.

[0133] A first aspect of the present disclosure is an optical waveguide having an incident end into which a predetermined input light is incident and an exit end from which the incident input light is emitted as guided light. The optical waveguide comprises a first guide layer having a first refractive index and extending from a first position at a predetermined distance from the incident end to the exit end in the guidance direction in which the guided light travels through the optical waveguide, and a second guide layer having a second refractive index lower than the first refractive index and extending from the incident end in the guidance direction. The first guide layer is not located within a predetermined distance from the incident end, but includes a comb-shaped region that branches out in a comb-like manner from a second position spaced apart from the exit end in the guidance direction toward the incident end and extends to the first position. The second guide layer is located adjacent to the first guide layer and extends over a predetermined distance from the incident end in the guidance direction to fill the comb-shaped region.

[0134] In the second embodiment, in the optical waveguide described in the first embodiment, the second waveguide layer extends from the input end to the output end in the waveguide direction and is laminated to cover the first waveguide layer.

[0135] In the third embodiment, in the optical waveguide described in the first or second embodiment, the input light is multimode in the width direction of the optical waveguide and singlemode in the thickness direction of the optical waveguide, and the first and second waveguide layers have a width in the width direction that is greater than or equal to the multimode cutoff length and a thickness in the thickness direction that is less than the width.

[0136] In the fourth embodiment, in the optical waveguide described in any of the first to third embodiments, the comb region includes a plurality of comb teeth arranged in the width direction of the optical waveguide. Each of the plurality of comb teeth has a tapered shape in which the spacing between adjacent teeth gradually narrows from the input end to the output end.

[0137] In the fifth embodiment, in the optical waveguide described in any of the first to fourth embodiments, the comb-tooth region has a predetermined period in which a plurality of comb teeth are arranged in the width direction of the optical waveguide 1. The period of the comb-tooth region is at least twice the wavelength of the input light. The period of the comb-tooth region may be at least three times the wavelength of the input light.

[0138] In the sixth embodiment, in the optical waveguide described in any of the first to fifth embodiments, the second refractive index is 1.05 times or more and 1.15 times or less the third refractive index of the cladding portion covering at least a part of the outer circumference of the second waveguide layer. The thickness of the second waveguide layer is 0.5 μm or more and 1.0 μm or less.

[0139] In the seventh embodiment, the optical waveguide described in any of the first to sixth embodiments further comprises a cladding portion having a third refractive index smaller than the second refractive index, and covering at least both sides of the outer periphery of the first and second waveguide layers in the width direction of the optical waveguide.

[0140] The eighth aspect is an optical circuit comprising a plurality of optical waveguides described in any of the first to fifth aspects. The optical circuit further comprises a wave-combining section that combines a plurality of guided light beams emitted from each of the plurality of optical waveguides.

[0141] In the ninth aspect, the optical circuit described in the eighth aspect comprises a plurality of reflectors, each composed of a diffraction grating that selectively reflects light of different wavelength bands.

[0142] In the tenth aspect, in the optical circuit described in the ninth aspect, the diffraction grating periodically includes a portion having a first refractive index and a portion having a second refractive index. The first refractive index is 1.26 times or more and 1.29 times or less of the second refractive index.

[0143] In the eleventh embodiment, in the optical circuit described in any of the eighth to tenth embodiments, a plurality of optical waveguides are integrally formed on a common substrate.

[0144] The twelfth embodiment is a light source device comprising a plurality of light sources, each emitting a plurality of input light having different wavelengths, and an optical circuit as described in any of the eighth to tenth embodiments. The plurality of light sources are arranged facing each other at the input end of each optical waveguide so that each input light is incident on a plurality of optical waveguides in the optical circuit.

[0145] As described above, embodiments have been explained as examples of the technology in this disclosure. For this purpose, accompanying drawings and a detailed description have been provided.

[0146] Therefore, the components described in the attached drawings and detailed descriptions may include not only components essential for solving the problem, but also components that are not essential for solving the problem, provided that they illustrate the technology described above. For this reason, the mere presence of these non-essential components in the attached drawings and detailed descriptions should not be immediately assumed to mean that they are essential.

[0147] Furthermore, since the embodiments described above are for illustrative purposes of the technology described herein, various modifications, substitutions, additions, omissions, etc., can be made within the claims or their equivalents. [Industrial applicability]

[0148] This disclosure can be applied, for example, to optical waveguides in optical circuits. [Explanation of symbols]

[0149] 1 Optical waveguide 11 Incidence end 12 Output end 13 Core section 14 Clad section 3 Comb teeth 30 Filling section 31 Core Layers 31a Comb area 32 subcore layers 2. Laser light source 20 Light source device 5 Optical circuit 52 Wave-receiving section 6 DBR section

Claims

1. An optical waveguide having an input end into which a predetermined input light is incident, and an output end into which the incident input light is emitted as guided light, In the direction in which the guided light propagates through the optical waveguide, a first waveguide layer having a first refractive index extends from a first position at a predetermined distance from the incident end to the exit end, and comprises: The system comprises a second waveguide layer extending from the incident end in the waveguide direction and having a second refractive index lower than the first refractive index, The first waveguide layer is not located within the predetermined distance range from the incident end, but includes a comb-shaped region that branches out in a comb-like manner from a second position spaced apart from the exit end in the waveguide direction toward the incident end and extends to the first position. The second waveguide layer is positioned adjacent to the first waveguide layer so as to extend from the incident end over a predetermined distance in the waveguide direction and fill the comb-tooth region. optical waveguide.

2. The second waveguide layer extends from the input end to the output end in the waveguide direction and is laminated to cover the first waveguide layer. The optical waveguide according to claim 1.

3. The input light is multimode in the width direction of the optical waveguide and single-mode in the thickness direction of the optical waveguide. The first and second waveguide layers have a width in the width direction that is greater than or equal to the multimode cutoff length, and a thickness in the thickness direction that is less than the width. The optical waveguide according to claim 1.

4. The comb-tooth region includes a plurality of comb teeth arranged in the width direction of the optical waveguide, Each of the aforementioned comb teeth has a tapered shape, where the spacing between adjacent teeth gradually narrows from the input end to the output end. The optical waveguide according to claim 1.

5. The comb-tooth region has a predetermined period in which a plurality of comb teeth are arranged in the width direction of the optical waveguide. The period of the comb-tooth region is at least twice the wavelength of the input light. The optical waveguide according to claim 1.

6. The second refractive index is 1.05 times or more and 1.15 times or less the third refractive index of the cladding portion covering at least a part of the outer circumference of the second waveguide layer. The thickness of the second waveguide layer is 0.5 micrometers or more and 1.0 micrometer or less. The optical waveguide according to claim 1.

7. The present invention further comprises a cladding portion having a third refractive index smaller than the second refractive index, which covers at least both sides of the outer periphery of the first and second waveguide layers in the width direction of the optical waveguide. The optical waveguide according to claim 1.

8. A plurality of optical waveguides as described in claim 1, The system further comprises a wave-combining unit that combines multiple guided light waves emitted from each of the aforementioned multiple optical waveguides. optical circuit.

9. The multiplexing section comprises a plurality of reflectors, each composed of a diffraction grating that selectively reflects light of different wavelengths. The optical circuit according to claim 8.

10. The diffraction grating periodically includes a portion having a first refractive index and a portion having a second refractive index. The first refractive index is 1.26 times or more and 1.29 times or less than the second refractive index. The optical circuit according to claim 9.

11. The plurality of optical waveguides are integrally formed on a common substrate. The optical circuit according to claim 8.

12. Multiple light sources, each emitting multiple input light with different wavelengths, The optical circuit is as described in claim 8, The plurality of light sources are arranged opposite to the input end of each optical waveguide so as to cause each input light to be incident on the plurality of optical waveguides in the optical circuit. Light source device.

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