Optical multiplexer, optical multiplexing member, optical modulation functioning optical multiplexing member, visible light source module, optical engine and xr glass

Abstract

To provide an optical multiplexer which can be smaller than conventional one and reduces optical losses.SOLUTION: An optical multiplexer 100 multiplexes three laser beams of different wavelengths, and comprises: an MMI-coupled optical multiplexing section 50 obtained by coupling a first MMI-type optical multiplexing section (first MMI-type optical multiplexer element ) 50-1 for shifting an incident position from an input side to a second MMI-type optical multiplexing section (second MMI-type optical multiplexer element ) 50-2 having width W2 wider than width W1 of the first MMI-type optical multiplexing section 50-1; two first optical input side optical waveguides 21-1, 21-2 connected to the first MMI-type optical multiplexing section 50-1; one second optical input side optical waveguide 21-3 connected to the second MMI-type optical multiplexing section; and one optical output side optical waveguide 22 connected to the second MMI-type optical multiplexing section 50-2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical multiplexer, an optical multiplexing member, an optical multiplexing member with an optical modulation function, a visible light source module, an optical engine, and XR glasses. [Background technology]

[0002] Glasses-type devices are currently being considered for VR and AR. In particular, retinal scanning displays, which allow users to view images by focusing two-dimensionally scanned light on the user's retina, have been attracting attention in recent years. In retinal scanning displays, three colors of visible light, typically R (red), G (green), and B (blue), are emitted from light sources such as LEDs (Light Emitting Diodes) or LDs (Laser Diodes) and combined on a single optical axis. The combined three colors of visible light are transmitted to an image display unit. The image display unit then two-dimensionally scans the transmitted light and makes it incident on the user's pupil. The user perceives the image when this incident light forms an image on the user's retina.

[0003] For example, Patent Document 1 discloses the configuration of a retinal projection display using a Mach-Zehnder type optical modulator. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6728596 [Patent Document 2] Patent No. 6787397 [Patent Document 3] Patent No. 6572377 [Patent Document 4] Japanese Patent Application Laid-Open No. 2012-48071 [Patent Document 5] Japanese Patent Publication No. 2020-27170 Summary of the Invention [Problem to be solved by the invention]

[0005] In the retinal projection display disclosed in Patent Document 1, multiple optical waveguides are placed close to each other at the exit section, but they are not combined, so the optical axis for each wavelength is different, making it difficult to control the emitted light.

[0006] Furthermore, there is a demand for an optical multiplexer that can be connected to or integrated with a visible light modulator and that can adjust the RGB color balance, but this has not yet been considered.

[0007] However, in Patent Document 1, the light beams are simply placed close to each other at the exit section, without being multiplexed. As a result, the optical axes of the light beams differ for each wavelength, making it difficult to control the emitted light.

[0008] Furthermore, Patent Document 2 discloses a visible light modulator using a lithium niobate film. Although there is a demand for an RGB optical multiplexer that can be connected to or integrated with a visible light modulator using a lithium niobate film, this has not yet been studied.

[0009] Directional couplers are generally considered for combining visible light (see, for example, Patent Document 3). These are made of glass-based materials and have excellent stability, but when using a lithium niobate substrate with a large Δn, the coupling length becomes long and miniaturization is not possible.

[0010] Patent Documents 4 and 5 disclose the configuration of an RGB multiplexer using an MMI (multimode interferometer), but both use glass-based materials, and do not disclose any configuration using a lithium niobate film. An MMI optical multiplexer uses multiple waveguide ports on the optical input side to input multiple input signals, and on the optical output side, a single waveguide port is used for the output signal, with all input signals multiplexed and output as the output signal. An MMI optical multiplexer is an optical multiplexer that utilizes the property that, for each wavelength, multiple modes generated within the wide optical multiplexer interfere with each other and form an image (converge) at a specific position.

[0011] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide an optical multiplexer, an optical multiplexing member, an optical multiplexing member with optical modulation function, a visible light source module, and an optical engine that can be connected to or integrated with an optical modulator using a lithium niobate film, and that can be made smaller than conventional devices and have reduced optical loss. [Means for solving the problem]

[0012] The present disclosure provides the following means to solve the above problems.

[0013] A first aspect of the present disclosure is an optical multiplexer that multiplexes laser light of multiple different wavelengths, and includes: an MMI-coupled optical multiplexer formed by coupling, from an input side, a first MMI-type optical multiplexer that shifts the incident position and a second MMI-type optical multiplexer having a width wider than that of the first MMI-type optical multiplexer; one or more first optical input-side optical waveguides connected to the first MMI-type optical multiplexer; one or more second optical input-side optical waveguides connected to the second MMI-type optical multiplexer; and one optical output-side optical waveguide connected to the second MMI-type optical multiplexer.

[0014] A second aspect of the present disclosure is an optical multiplexer according to the first aspect, wherein the first optical input side optical waveguide, the second optical input side optical waveguide, and the optical output side optical waveguide all have tapered sections whose widths become continuously wider as they approach the MMI coupled optical multiplexer.

[0015] A third aspect of the present disclosure is an optical multiplexer according to either the first or second aspect, in which the number of the first optical input side optical waveguides is two.

[0016] A fourth aspect of the present disclosure is the optical multiplexer of any one of the first to third aspects, wherein the width of the first MMI type optical multiplexing section is ⅔ or less of the width of the second MMI type optical multiplexing section.

[0017] A fifth aspect of the present disclosure is the optical multiplexer of any one of the first to fourth aspects, wherein the length of the first MMI type optical multiplexing section is 2 μm or more.

[0018] A sixth aspect of the present disclosure is an optical multiplexer according to any one of the first to fifth aspects, wherein the plurality of different wavelengths are all visible light wavelengths.

[0019] A seventh aspect of the present disclosure is an optical multiplexing member comprising a substrate made of a material different from lithium niobate and a lithium niobate film formed on a main surface of the substrate, wherein an optical multiplexer according to any one of aspects 1 to 6 is formed in the lithium niobate film.

[0020] An eighth aspect of the present disclosure is a visible light source module including the optical multiplexing member of the seventh aspect and a plurality of visible laser light sources that emit visible light multiplexed by the optical multiplexing member.

[0021] A ninth aspect of the present disclosure is an optical multiplexing member with optical modulation function, comprising the optical multiplexing member of the seventh aspect and a Mach-Zehnder optical modulator connected to the optical multiplexing member and guiding multiple visible light beams emitted from multiple visible light laser light sources to the optical multiplexer.

[0022] A tenth aspect of the present disclosure is a visible light source module comprising an optical multiplexing element with optical modulation function of the ninth aspect and a plurality of visible light laser light sources that emit visible light that is multiplexed by the optical multiplexing element with optical modulation function, wherein the plurality of visible light laser light sources are visible light laser light sources of red light, green light, and blue light.

[0023] An eleventh aspect of the present disclosure is an optical engine including the visible light source module of the eighth aspect and a light scanning mirror that reflects light emitted from the visible light source module at different angles so as to display an image.

[0024] A twelfth aspect of the present disclosure is an optical engine including the visible light source module of the tenth aspect and a light scanning mirror that reflects light emitted from the visible light source module at different angles so as to display an image.

[0025] A thirteenth embodiment of the present disclosure is XR glasses equipped with the optical engine of the eleventh embodiment.

[0026] A fourteenth aspect of the present disclosure is XR glasses equipped with the optical engine of the twelfth aspect. [Effects of the Invention]

[0027] According to the present invention, it is possible to provide an optical multiplexer that can be connected to or integrated with an optical modulator using a lithium niobate film, can be made smaller than conventional ones, and has reduced optical loss. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a schematic plan view illustrating an example of an optical multiplexer according to the present disclosure. [Figure 2] FIG. 10 is a schematic plan view illustrating another example of an optical multiplexer according to the present disclosure. [Figure 3] FIG. 10 is a schematic plan view illustrating another example of an optical multiplexer according to the present disclosure. [Figure 4] FIG. 10 is a schematic plan view illustrating another example of an optical multiplexer according to the present disclosure. [Figure 5] FIG. 10 is a schematic plan view illustrating another example of an optical multiplexer according to the present disclosure. [Figure 6] FIG. 10 is a schematic plan view illustrating another example of an optical multiplexer according to the present disclosure. [Figure 7A] FIG. 1 is a diagram for explaining the principle of an MMI optical multiplexer, and is a conceptual diagram showing the relationship between the width WM and effective width We of the optical multiplexer and the single mode and higher-order modes. [Figure 7B] FIG. 1 is a diagram for explaining the principle of an MMI optical multiplexer, and is a diagram showing simulation results of electromagnetic field distribution in the cross section of each waveguide for a single mode (TM0), a higher-order mode (TM1), and a higher-order mode (TM2). [Figure 8A] FIG. 1 is a diagram for explaining the principle of an MMI optical multiplexer, showing the results of a simulation of the electromagnetic field distribution of red (R) light. [Figure 8B] 1 is a diagram for explaining the principle of an MMI optical multiplexer, showing the results of a simulation of the electromagnetic field distribution of green (G) light. [Figure 9A]10 is a graph showing the relationship between the lengths and beat length of the first MMI type optical multiplexing element and the second MMI type optical multiplexing element and the output intensity for each of red (R) laser beams. [Figure 9B] 10 is a graph showing the relationship between the lengths and beat length of the first MMI type optical multiplexing element and the second MMI type optical multiplexing element and the output intensity for each of green (G) laser beams. [Figure 10] 1 is a schematic plan view of an optical multiplexing member according to the present disclosure; [Figure 11] 11 is a cross-sectional view of the optical multiplexing member shown in FIG. 10 taken along line XX'. FIG. [Figure 12] FIG. 10 is a schematic cross-sectional view taken along the YZ plane when the cross section of the MMI type optical multiplexing section is trapezoidal and has a slab section on the substrate side. [Figure 13] 1 is a plan view schematically illustrating an optical multiplexing member with an optical modulation function according to the present disclosure. [Figure 14] 1 is a schematic plan view of a visible light source module according to the present disclosure. [Figure 15] 15 is a schematic cross-sectional view of a part of the light source module shown in FIG. 14 cut along the XZ plane, depicting only a part near the joint. [Figure 16A] FIG. 10 is a diagram for explaining an example of a method for driving an optical modulator. [Figure 16B] 10A and 10B are diagrams for explaining another example of a method for driving an optical modulator. [Figure 16C] 10A and 10B are diagrams for explaining another example of a method for driving an optical modulator. [Figure 17] 1 is a schematic plan view of a visible light source module according to the present disclosure. [Figure 18] FIG. 1 is a conceptual diagram for explaining an example of the XR glasses of the present invention. [Figure 19] FIG. 19 is a conceptual diagram showing how an image is projected directly onto the retina by laser light emitted from a light source module in the XR glasses shown in FIG. 18. [Figure 20] FIG. 10 is a diagram showing parameters of a model used in a simulation. [Figure 21]FIG. 10 is a diagram showing parameters of another model used in the simulation. [Figure 22A] 10 is a graph showing the example, with the horizontal axis representing the length L2 of the first MMI type optical multiplexing main portion, and the vertical axis representing the loss of light intensity after passing through the MMI coupling type optical multiplexing portion for each wavelength of RGB. [Figure 22B] 10 is a graph showing the comparative example, with the horizontal axis representing the length L2 of the first MMI type optical multiplexing main portion and the vertical axis representing the loss of light intensity after passing through the MMI coupling type optical multiplexing portion for each wavelength of RGB. DETAILED DESCRIPTION OF THE INVENTION

[0029] The present disclosure will be described in detail below with reference to the drawings as appropriate. The drawings used in the following description may show characteristic portions enlarged for the sake of clarity, and the dimensional ratios of each component may differ from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto. Appropriate modifications can be made within the scope of the effects of the present invention.

[0030] [Optical multiplexer] Fig. 1 is a schematic plan view showing an example of an optical multiplexer according to the present disclosure, and Fig. 2 is a schematic plan view showing another example of an optical multiplexer according to the present disclosure.

[0031] The optical multiplexer according to the present disclosure is a multi-mode interference (MMI) type optical multiplexer. In this specification, an optical multiplexer formed by coupling parts of different sizes (rectangular parts in plan view) as shown in Fig. 1 is referred to as an "MMI coupled optical multiplexer." Each part (rectangular part in plan view) that constitutes an MMI coupled optical multiplexer may be referred to as an "optical multiplexing element." In contrast, an optical multiplexer consisting of a single rectangular part may be referred to as an "MMI single type optical multiplexer." An MMI single type optical multiplexer consists of a single optical multiplexing element. An MMI coupled optical multiplexer and an MMI single type optical multiplexer may be collectively referred to as an MMI type optical multiplexer. Furthermore, an optical multiplexer in which MMI single-type optical multiplexers or MMI coupled-type optical multiplexers are connected via optical waveguides may be referred to as an "MMI coupled-type optical multiplexer." Furthermore, with regard to the "MMI coupled-type optical multiplexer," depending on the number of optical waveguides connected, a configuration in which two MMI single-type optical multiplexers or MMI coupled-type optical multiplexers are connected may be referred to as a two-stage MMI coupled-type optical multiplexer (or simply, a two-stage MMI optical multiplexer), a configuration in which three are connected may be referred to as a three-stage coupled-type optical multiplexer (or simply, a three-stage MMI optical multiplexer), and a configuration in which multiple units are connected may be referred to as a multi-stage coupled-type optical multiplexer (or simply, a multi-stage MMI optical multiplexer). Configurations in which no coupling occurs may be referred to as a single-stage MMI single-type optical multiplexer or a single-stage MMI coupled-type optical multiplexer. The single-stage MMI single-type optical multiplexer and the single-stage MMI coupled-type optical multiplexer are sometimes collectively referred to as a single-stage MMI type optical multiplexer.

[0032] The optical multiplexer 100 shown in FIG. 1 is an optical multiplexer that multiplexes laser light of three different wavelengths, and includes, from the input side, an MMI-coupled optical multiplexing section 50 formed by coupling a first MMI-type optical multiplexing section (first MMI-type optical multiplexing element) 50-1 that shifts the incident position and a second MMI-type optical multiplexing section (second MMI-type optical multiplexing element) 50-2 having a width W2 wider than the width W1 of the first MMI-type optical multiplexing section 50-1, two first optical input-side optical waveguides 21-1 and 21-2 connected to the first MMI-type optical multiplexing section 50-1, one second optical input-side optical waveguide 21-3 connected to the second MMI-type optical multiplexing section, and one optical output-side optical waveguide 22 connected to the second MMI-type optical multiplexing section 50-2.

[0033] The optical multiplexer 100 is a 3x1 type (3 input ports, 1 output port) optical multiplexer having three optical input ports (first optical input port 21-1i, second optical input port 21-2i, third optical input port 21-3i) and one optical output port 22o.

[0034] In FIG. 1, the X direction is the direction in which the first optical input side optical waveguide and the second optical input side optical waveguide extend, the Y direction is the direction perpendicular to the X direction, and the Z direction is the direction perpendicular to the plane formed by the X direction and the Y direction.

[0035] The first MMI type optical multiplexing section 50-1 is a section provided to shift the incident position of the laser light into the second MMI type optical multiplexing section 50-2 to the light input side. The first MMI type optical multiplexing section 50-1 can be rephrased as an MMI type optical multiplexing incident position shifting section, and the second MMI type optical multiplexing section 50-2 can be rephrased as an MMI type optical multiplexing main section. In this case, the MMI coupled optical multiplexing section 50 is an MMI type optical multiplexing main section coupled to an MMI type optical multiplexing incident position shifting section on the optical input side thereof. When laser light of different wavelengths is multiplexed from the same incident end face, the loss margin for the length and width of the MMI-type optical multiplexer depends on the wavelength, but the wavelength dependency of the loss margin can be improved by changing the position of the incident end face (sometimes simply called the "incident position").

[0036] A part of the laser beams input from the outside is incident on the first MMI type optical multiplexer, and the remaining laser beams are incident on the second MMI type optical multiplexer.

[0037] 1, two of the three laser beams (laser beams L1 and L2) enter the first MMI type optical multiplexing unit 50-1, and one laser beam (laser beam L3) enters the second MMI type optical multiplexing unit 50-2. Because laser beam L3 enters the second MMI type optical multiplexing unit 50-2, while laser beams L1 and L2 enter the first MMI type optical multiplexing unit 50-1, the entrance positions of laser beams L1 and L2 into the MMI type optical multiplexing unit 50 are shifted by the length L1 of the first MMI type optical multiplexing unit 50-1 relative to laser beam L3. By shifting the entrance positions of some of the laser beams among the multiple laser beams to be optically multiplexed, the wavelength dependence of the loss margin can be improved. 1 is configured to shift the incident positions of two of the three laser beams, L1 and L2, toward the optical input side, but it may also be configured to shift the incident position of only one laser beam toward the optical input side. The number of laser beams to be shifted among the multiple laser beams can be appropriately selected depending on the wavelength dependency of the loss margin for the length and width of the MMI optical multiplexer.

[0038] The first MMI type optical multiplexing section 50-1 as an MMI type optical multiplexing incident position shift section is an MMI single type optical multiplexing section consisting of a single rectangular section in a plan view, but may be an MMI coupled type optical multiplexing section formed by coupling sections of different sizes (rectangular sections in a plan view) (see FIG. 3). On the other hand, the second MMI type optical multiplexing section 50-2 as an MMI type optical multiplexing main section is an MMI single type optical multiplexing section consisting of a single rectangular section in a plan view in the optical multiplexer 100, but may be an MMI coupled type optical multiplexing section formed by coupling sections of different sizes (rectangular sections in a plan view).

[0039] The width W1 of the first MMI type optical multiplexing unit 50-1 can be set to 2 / 3 or less of the width W2 of the second MMI type optical multiplexing unit 50-2, and the width W1 of the first MMI type optical multiplexing unit 50-1 can be set to 1 / 3 or more of the width W2 of the second MMI type optical multiplexing unit 50-2.

[0040] The length L1 of the first MMI type optical multiplexing section 50-1 is preferably 2 μm or more. If it is 2 μm or more, the wavelength dependency of the loss margin can be improved. The upper limit of the length L1 of the first MMI type optical multiplexing section 50-1 can be set to, for example, 2 to 200 μm.

[0041] The length L2 of the second MMI type optical multiplexing section 50-2 is preferably 10 μm or more. The upper limit of the length of the second MMI type optical multiplexing section 50-2 can be set to, for example, 10 to 3000 μm.

[0042] The width W1 of the first MMI type optical multiplexing section 50-1 can be set to, for example, 1 to 10 μm.

[0043] The width W2 of the second MMI type optical multiplexing section 50-2 can be set to, for example, 3 to 20 μm.

[0044] 1, the two optical input side optical waveguides 21-1 and 21-2 have tapered portions 51-1 and 51-2 at their connecting portions to the first MMI type optical multiplexing unit 50-1, whose widths increase continuously toward the first MMI type optical multiplexing unit 50-1 and whose inclination angle can be defined, while the single optical input side optical waveguide 21-3 has a tapered portion 51-3 at its connecting portion to the second MMI type optical multiplexing unit 50-2, whose widths increase continuously toward the second MMI type optical multiplexing unit 50-2 and whose inclination angle can be defined. Furthermore, the single optical output side optical waveguide 22 has a tapered portion 52 at its connecting portion to the second MMI type optical multiplexing unit 50-2, whose widths increase continuously toward the second MMI type optical multiplexing unit 50-2 and whose inclination angle can be defined. When the cross sections of the optical input side optical waveguides 21-1, 21-2, 21-3 and the optical output side optical waveguide 22 perpendicular to the extension direction are rectangular or trapezoidal (the upper base is smaller than the lower base), for example, if the width of the upper surface of the optical input side optical waveguides 21-1, 21-2, 21-3 and the optical output side optical waveguide 22 is 0.3 to 1.2 μm, the tapered sections 51-1, 51-2, 51-3, 52 can have a starting width of 0.3 to 1.2 μm, a width of the portion connecting to the MMI type optical multiplexing element of 0.5 to 2.5 μm, and a length of 10 to 500 μm, for example.

[0045] Providing tapered sections at the input / output ports connected to the MMI optical multiplexing element provides the following benefits. The optical input and output waveguides connected to the MMI optical multiplexing element are configured to propagate single-mode (zeroth-order mode, fundamental mode) laser light, while the MMI optical multiplexing element is configured to propagate multimode (zeroth-order mode to higher-order modes) laser light. Therefore, when light is input from the optical input waveguide to the MMI optical multiplexing element and output from the MMI optical multiplexing element to the optical output waveguide, coupling loss occurs due to mode mismatch between the input single mode and multimode. In contrast, providing tapered sections at the input / output ports alleviates the mode mismatch between the single mode and multimode, thereby reducing coupling loss. The wider the tapered section, the more the mode mismatch is alleviated, resulting in a greater reduction in coupling loss.

[0046] The optical multiplexer according to the present disclosure is not limited to a configuration in which the optical input side optical waveguide and the optical output side optical waveguide have tapered portions, and may have a configuration in which the optical input side optical waveguide and the optical output side optical waveguide do not have tapered portions, as in the optical multiplexer 101 shown in FIG.

[0047] FIG. 3 shows an optical multiplexer in which a first MMI type optical multiplexing section 50A-1 as an MMI type optical multiplexing incident position shift section is an MMI coupled type optical multiplexing section formed by coupling rectangular sections of different sizes in a plan view.

[0048] The optical multiplexer 102 shown in FIG. 3 is an optical multiplexer that multiplexes laser light of three different wavelengths, and includes, from the input side, an MMI coupled optical multiplexer 50A formed by coupling a first MMI type optical multiplexer 50A-1, which is an MMI coupled optical multiplexer that shifts the incident position, to a second MMI type optical multiplexer (second MMI type optical multiplexing element) 50-2 having a width W2 wider than the width W1 of the first MMI type optical multiplexer 50A-1, which is an MMI coupled optical multiplexer; two first optical input side optical waveguides 21-1 and 21-2 connected to the first MMI type optical multiplexer 50A-1, which is an MMI coupled optical multiplexer; one second optical input side optical waveguide 21-3 connected to the second MMI type optical multiplexer 50-2; and one optical output side optical waveguide 22 connected to the second MMI type optical multiplexer 50-2.

[0049] In the optical multiplexer 102 shown in FIG. 3, the MMI type optical multiplexing incident position shift section 50A-1, which is an MMI coupled type optical multiplexing section, is an optical multiplexing section formed by coupling, from the input side, a first MMI type optical multiplexing incident position shift section 50A-11 and a second MMI type optical multiplexing incident position shift section 50A-12 (illustrated as having the same length and width as the first MMI type optical multiplexing section 50-1 in the optical multiplexer 100 shown in FIG. 1) having a width W1 wider than the width W11 of the first MMI type optical multiplexing incident position shift section 50A-11.

[0050] The optical multiplexer 102 shown in Figure 3 is similar to the optical multiplexer 100 shown in Figure 1 in that the incident positions of two of the three laser beams, L1 and L2, are shifted toward the optical input side. However, the optical multiplexer 102 shown in Figure 3 differs from the optical multiplexer 100 shown in Figure 1 in that the incident position of one of the two laser beams, laser beam L2, is shifted further toward the optical input side than the incident position of laser beam L1. The optical multiplexer 102 shown in FIG. 3 is configured such that the three laser beams are incident at different positions. The different incident positions of the three laser beams can be set appropriately depending on the wavelength dependency of the loss margin relative to the length and width of the MMI type optical multiplexer.

[0051] The length L11 of the first MMI type optical multiplexing incident position shifting section 50A-11 is preferably 2 μm or more. If it is 2 μm or more, the wavelength dependency of the loss margin can be improved. The upper limit of the length L11 of the first MMI type optical multiplexing incident position shifting section 50A-11 can be set to, for example, 2 to 100 μm.

[0052] The width W11 of the first MMI type optical multiplexing incident position shifting section 50A-11 can be set to, for example, 1 to 10 μm.

[0053] The optical multiplexer 102 is a 3x1 type (3 input ports, 1 output port) optical multiplexer having three optical input ports (first optical input port 21-1i, second optical input port 21-2i, third optical input port 21-3i) and one optical output port 22o.

[0054] FIG. 4 is a schematic plan view of an optical multiplexer in which the second MMI type optical multiplexing section 50B-2 as the MMI type optical multiplexing main section is an MMI coupling type optical multiplexing section formed by coupling rectangular sections of different sizes in a plan view.

[0055] The optical multiplexer 103 shown in FIG. 4 is an optical multiplexer that multiplexes laser beams of three different wavelengths, and includes, from the input side, an MMI-coupled optical multiplexer 50B formed by coupling a first MMI-type optical multiplexer 50-1 that shifts the incident position with a second MMI-type optical multiplexer 50B-2 having a width W2 wider than the width W1 of the first MMI-type optical multiplexer 50A-1, two first optical-input-side optical waveguides 21-1 and 21-2 connected to the first MMI-type optical multiplexer 50-1, one second optical-input-side optical waveguide 21-3 connected to the second MMI-type optical multiplexer 50B-2, and one optical-output-side optical waveguide 22 connected to the second MMI-type optical multiplexer 50B-2.

[0056] In the optical multiplexer 103 shown in FIG. 4, the second MMI type optical multiplexing section 50B-2 as an MMI type optical multiplexing main section is an optical multiplexing section formed by coupling, from the input side, a first MMI type optical multiplexing main section 50B-21 and a second MMI type optical multiplexing main section 50B-22 having a width W22 narrower than the width W2 of the first MMI type optical multiplexing main section 50B-21 (a case where the length and width are the same as those of the second MMI type optical multiplexing section 50-2 in the optical multiplexer 100 shown in FIG. 1 is exemplified).

[0057] The optical multiplexer 103 shown in Fig. 4 has the same relationship as the optical multiplexer 100 shown in Fig. 1 regarding the incident positions of the three laser beams. That is, the incident positions of two of the three laser beams, laser beams L1 and L2, are shifted toward the optical input side.

[0058] The length L22 of the second MMI type optical multiplexing main portion 50B-22 is preferably 100 μm or more. The upper limit of the length L22 of the second MMI type optical multiplexing main portion 50B-22 can be set to, for example, 100 to 1000 μm.

[0059] The width W22 of the second MMI type optical multiplexing main portion 50B-22 can be set to, for example, 2 to 18 μm.

[0060] The optical multiplexer 103 is a 3x1 type (3 input ports, 1 output port) optical multiplexer having three optical input ports (first optical input port 21-1i, second optical input port 21-2i, third optical input port 21-3i) and one optical output port 22o.

[0061] FIG. 5 shows a schematic plan view of a 2×1 type (two input ports, one output port) optical multiplexer having two optical input ports (optical input ports 121-2i, 121-3i) and one optical output port 122o. The optical multiplexer 104 shown in FIG. 5 is an optical multiplexer that multiplexes laser light of two different wavelengths, and includes an MMI-coupled optical multiplexing section 150 formed by coupling, from the input side, a first MMI-type optical multiplexing section (first MMI-type optical multiplexing element) 150-1 that shifts the incident position and a second MMI-type optical multiplexing section (second MMI-type optical multiplexing element) 150-2 having a width W20 wider than the width W10 of the first MMI-type optical multiplexing section 150-1, one first optical input-side optical waveguide 121-2 connected to the first MMI-type optical multiplexing section 150-1, one second optical input-side optical waveguide 121-3 connected to the second MMI-type optical multiplexing section 150-2, and one optical output-side optical waveguide 122 connected to the second MMI-type optical multiplexing section 150-2.

[0062] The first optical input side optical waveguide 121-2, the second optical input side optical waveguide 121-3 and the optical output side optical waveguide 122 respectively have tapered portions 151-2, 151-3 and 152 having tapered shapes whose inclination angles can be defined.

[0063] The length L10 of the first MMI type optical multiplexing section 150-1 is preferably 2 μm or more. If it is 2 μm or more, the wavelength dependency of the loss margin can be improved. The upper limit of the length L1 of the first MMI type optical multiplexing section 150-1 can be set to, for example, 2 to 300 μm.

[0064] The length L20 of the second MMI type optical multiplexing section 150-2 is preferably 10 μm or more. The upper limit of the length of the second MMI type optical multiplexing section 150-2 can be set to, for example, 10 to 1000 μm.

[0065] The width W10 of the first MMI type optical multiplexing section 150-1 can be set to, for example, 1 to 10 μm.

[0066] The width W20 of the second MMI type optical multiplexing section 150-2 can be set to, for example, 3 to 20 μm.

[0067] FIG. 6 shows a schematic plan view of an optical multiplexer in the case of a 3×1 type MMI-connected optical multiplexing unit configuration including a 2×1 type MMI optical multiplexer such as the optical multiplexer 104 shown in FIG.

[0068] The optical multiplexer 110 shown in Fig. 6 is an optical multiplexer that multiplexes laser light of three different wavelengths, and in addition to the optical multiplexer 104 shown in Fig. 5, includes an output-side MMI type optical multiplexer 150T that is coupled to the MMI coupling-type optical multiplexer 150. Furthermore, the output-side MMI type optical multiplexer 150T is coupled to the MMI coupling-type optical multiplexer 150 (more specifically, the second MMI type optical multiplexer 150-2) via the optical output-side optical waveguide 122 that serves as a coupling optical waveguide.

[0069] The optical multiplexer 110 shown in FIG. 6 includes a first MMI type optical multiplexing section 150-1 as an MMI type optical multiplexing incident position shift section, and an MMI-coupled type optical multiplexing section including a second MMI type optical multiplexing section 150-2 and an output side MMI type optical multiplexing section 150T as an MMI type optical multiplexing main section. 6 includes a first optical input side optical waveguide 121-2 connected to a first MMI type optical multiplexing section 150-1 as an MMI type optical multiplexing incident position shift section, a second optical input side optical waveguide 121-3 connected to a second MMI type optical multiplexing section 150-2 which is a part of the MMI coupled type optical multiplexing section, the optical input side optical waveguide 121-1 as a second optical input side optical waveguide connected to an output side MMI type optical multiplexing section 150T which is a part of the MMI coupled type optical multiplexing section, and a optical output side optical waveguide 122T connected to the output side MMI type optical multiplexing section 150T which is a part of the MMI coupled type optical multiplexing section.

[0070] The two optical input side optical waveguides connected to the output side MMI type optical multiplexing unit 150T each have tapered portions 151T-1 and 151T-2 with tapered shapes that allow the inclination angle to be defined, and the one optical input side optical waveguide connected to the output side MMI type optical multiplexing unit 150T has tapered portion 152T with tapered shape that allows the inclination angle to be defined.

[0071] The optical multiplexer 110 shown in FIG. 6 is a 3×1 type (3 input ports, 1 output port) MMI optical multiplexer having three optical input ports (optical input ports 121-1i, 121-2i, 121-3i) and one optical output port 122To.

[0072] The length L10 of the first MMI type optical multiplexing section 150-1 is preferably 2 μm or more. If it is 2 μm or more, the wavelength dependency of the loss margin can be improved. The upper limit of the length L10 of the first MMI type optical multiplexing section 150-1 can be set to, for example, 2 to 300 μm.

[0073] The length L20 of the second MMI type optical multiplexing section 150-2 is preferably 10 μm or more. The upper limit of the length of the second MMI type optical multiplexing section 150-2 can be set to, for example, 10 to 1000 μm.

[0074] The width W10 of the first MMI type optical multiplexing section 150-1 can be set to, for example, 1 to 10 μm.

[0075] The width W20 of the second MMI type optical multiplexing section 150-2 can be set to, for example, 3 to 20 μm.

[0076] The length L3 of the output side MMI type optical multiplexing section 150T is preferably 50 μm or more. The upper limit of the length L3 of the output side MMI type optical multiplexing section 150T can be set to, for example, 50 to 1000 μm.

[0077] The width W3 of the output-side MMI type optical multiplexing section 150T can be set to, for example, 3 to 20 μm.

[0078] The principle of the MMI type optical multiplexer will be explained with reference to FIGS. 7A, 7B, 8A, and 8B. FIG. 7A shows the width W M Figure 7 shows the single mode (v = 0) and higher-order modes (v ≥ 1) generated in the waveguide. We is the effective width of the MMI optical multiplexer, and is approximated by the effective width of the MMI optical multiplexer taking into account the optical mode bleeding and Goos-Henschen shift in the zeroth-order mode (fundamental mode). Figure 7B shows the simulation results of the electromagnetic field distribution in the cross section of the waveguide for the single mode (TM0), higher-order mode (TM1), and higher-order mode (TM2).

[0079] In an MMI optical multiplexer, multiple modes from the zeroth-order mode to higher-order modes interfere with each other and are characterized by forming an image (converging) at a specific position (a specified distance from the input end) of the MMI optical multiplexer. It is known that the distance or period (beat length) Lπ between adjacent convergence points roughly follows equation (1). Equation (1) is the beat length Lπ between the two lower-order modes, the zeroth-order mode and the first-order mode.

[0080]

number

[0081] In equation (1), We is the effective width of the MMI optical multiplexer, n is the effective refractive index of the MMI optical multiplexer, and λ is the wavelength of the input light. β0 and β1 are the propagation constants of the zeroth and first modes, respectively. From equation (1), we can see that the beat length depends on the width and wavelength of the MMI optical multiplexer.

[0082] When the electromagnetic field distribution undergoes a phase shift of 2π in all propagation modes generated within the MMI optical multiplexer, the optical intensity distribution coincides with the incident optical intensity distribution. The optical propagation distance required to achieve this coincidence (convergence) state is called the self-projection distance, and convergence is repeated at a period of Lπ after a certain propagation distance of 3Lπ / 4.

[0083] Figures 8A and 8B show the results of a simulation using simulation software (Photon Design's Fimmwave) of the electromagnetic field distribution at a cross section of a 2 × 1 MMI optical coupler (R / G coupler) along the light propagation direction (x direction). In the simulation model, the y-axis coordinate of the input waveguide where red (R) light with a wavelength of 638 nm enters the optical coupler is the same as the y-axis coordinate of the output waveguide of the optical coupler, while the y-axis coordinate of the input waveguide where green (G) light with a wavelength of 520 nm enters the optical coupler is separated by a predetermined distance. Lighter colors indicate areas where the modes interfere more strongly ("strong" in the figure), darker colors indicate areas where the modes do not interfere more strongly ("weak" in the figure), and intermediate colors indicate areas where the degree of interference between the modes is intermediate ("middle" in the figure).

[0084] FIG. 8A shows the results of a simulation of the electromagnetic field distribution of red (R) light, and FIG. 8B shows the results of a simulation of the electromagnetic field distribution of green (G) light. 8A and 8B, there is a strong interference portion near the output port of the optical multiplexer, and it is preferable to set the length (length in the X direction) of the MMI optical multiplexer so that this position coincides as closely as possible (i.e., so that it is as close as possible to an integer multiple (least common multiple) of the beat length of each input wavelength). However, because of the influence of the phase difference depending on the input position of each input wavelength to the optical multiplexer, the length of the MMI optical multiplexer cannot be determined solely by an integer multiple of the beat length of each input wavelength. Therefore, the length of the optical multiplexer should be set to an integer multiple (least common multiple) of the beat length of each input wavelength, and should be adjusted taking into account the phase effect of the input position of each input wavelength into the optical multiplexer.

[0085] 9A and 9B are graphs showing the relationship between the lengths and beat lengths of the first and second MMI-type optical multiplexing main sections and the output intensity for red (R) and green (G) laser light, respectively. The horizontal axis represents the lengths (L1, L2) of the MMI-type optical multiplexing sections, and the vertical axis represents the optical intensity.

[0086] The beat lengths of red (R) and green (G) are different. If the lengths of the first MMI-type optical multiplexing main section and the second MMI-type optical multiplexing main section are set to about 700 μm, both red (R) and green (G) can be multiplexed with an output intensity of 0.3. The design concept of the MMI optical multiplexer of the present disclosure is that the interference position of multiple modes is determined by equation (1), and the interference position is highly dependent on the wavelength and the width of the MMI optical multiplexer. π If the length of the MMI optical multiplexer is designed so that the wavelengths of the RGB colors are equal, it is possible to design the loss of each color to be small. However, this requires taking the least common multiple of the wavelengths of each color, which makes the length of the MMI optical multiplexer very long. Therefore, it is necessary to balance the loss of each RGB color with the length of the MMI optical multiplexer. If the MMI optical multiplexer is designed to be short, the loss margin for each color relative to the length of the MMI optical multiplexer will be narrow. If MMI optical multiplexers with different widths are installed at the input end, as shown in Figures 1, 2, 3, 4, 5, and 6 (also shown), or Figures 10, 13, 14, 17, 20, and 21 (described later), the side without the MMI optical multiplexer is not affected, while the length of the interference point for the light input from the side with the MMI optical multiplexer is corrected, improving loss. Therefore, balancing the lengths of the RGB colors makes it possible to reduce loss.

[0087] [Optical multiplexing member] The optical multiplexing member according to the present disclosure includes a substrate made of a material different from lithium niobate and a lithium niobate film formed on a main surface of the substrate, and the optical multiplexer according to the above embodiment is formed in the lithium niobate film. Regarding the components described below, components having the same functions as those in the above embodiment will be assigned the same reference numerals, and their description may be omitted. The lithium niobate film included in the optical multiplexing member according to the present disclosure may include an optical multiplexing section as shown in FIGS.

[0088] FIG. 10 is a schematic plan view of an optical multiplexing member according to the present disclosure. The optical multiplexing member 200 shown in Figure 10 has three light inlets 21-1i, 21-2i, and 21-2i on the first side surface 200A and one light outlet 22To on the third side surface 200C opposite the first side surface 200A, but the light outlet 22To may also be configured to be on the second side surface 200B or the fourth side surface 200D adjacent to the first side surface 200A.

[0089] FIG. 11 is a schematic cross-sectional view of the optical multiplexing member 200 shown in FIG. 10 taken along the YZ plane (XX' in FIG. 10).

[0090] The optical multiplexing member 200 shown in FIG. 11 includes a substrate 10 made of a material different from lithium niobate, and a lithium niobate film 24 formed on the main surface of the substrate 10, and an optical multiplexer such as that shown in FIGS. 1 to 6 is formed in the lithium niobate film 24.

[0091] 12, the lithium niobate film 24 may be configured to include a ridge 24-1 protruding from the first surface 24A and a slab layer 24-2 other than the ridge. The ridge constitutes the optical input side optical waveguides 21-1, 21-2, and 21-3, the first MMI type optical multiplexing element 50-1, the second MMI type optical multiplexing element 50-2, and the optical output side optical waveguide 22. The lithium niobate film 24 is covered with a buffer film 23. The lithium niobate film 24 and the buffer film 23 together are referred to as the optical multiplexing functional layer 20.

[0092] When the optical multiplexing member of this embodiment is used in an eyeglass-type image display device, the thickness (T slab ) is preferably 0.1 to 0.3 μm. When the optical multiplexing member of this embodiment is used in an eyeglass-type image display device, the thickness (T R The thickness (TR ) is small, light does not propagate, and if it is large, the propagating light becomes multimode. When the optical multiplexing member of this embodiment is used in an eyeglass-type image display device, the width (W R ) is preferably 0.3 to 1.2 μm. This is because if the waveguide width is small, light does not propagate, and if it is large, the propagating light becomes multimode. When the optical multiplexing member of this embodiment is used in an eyeglass-type image display device, the lower interior angle (α) of the ridge 24-1 having a trapezoidal cross section is 65° or more, because as the lower interior angle (inclination angle) becomes smaller, the propagating light becomes multimode.

[0093] In the optical multiplexing member 200, when the refractive index difference between the lithium niobate film and the buffer film is Δn, if the lithium niobate film is made of lithium niobate, Δn can be designed to be a larger value than when using materials such as glass, and the radius of curvature of the optical waveguide can be made smaller.Furthermore, by using a multimode interference optical multiplexing section, an increase in the coupling length can be prevented compared to when a directional coupler is used, thereby achieving both improved design freedom and miniaturization.

[0094] Examples of the substrate 10 include a sapphire substrate, a Si substrate, and a thermally oxidized silicon substrate. The substrate 10 is not particularly limited as long as it has a refractive index lower than that of a lithium niobate (LiNbO3) film, but a sapphire single crystal substrate or a silicon single crystal substrate is preferred as a substrate on which a single crystal lithium niobate film can be formed as an epitaxial film. The crystal orientation of the single crystal substrate is not particularly limited, but for example, since a c-axis oriented lithium niobate film has three-fold symmetry, it is desirable that the underlying single crystal substrate also has the same symmetry, and a c-plane substrate is preferred for a sapphire single crystal substrate, and a (111) plane substrate is preferred for a silicon single crystal substrate.

[0095] The lithium niobate film is, for example, a c-axis oriented lithium niobate film. The lithium niobate film is, for example, an epitaxial film epitaxially grown on a substrate 10. An epitaxial film is a single-crystal film whose crystal orientation is aligned by the underlying substrate. An epitaxial film is a film with a single crystal orientation in the z direction and the xy in-plane direction, and the crystals are aligned in the x-axis, y-axis, and z-axis directions. Whether the film formed on the substrate 10 is an epitaxial film can be verified, for example, by checking the peak intensity and poles at the orientation position in 2θ-θ X-ray diffraction.

[0096] Specifically, when measured by 2θ-θ X-ray diffraction, all peak intensities other than the target plane are 10% or less, preferably 5% or less, of the maximum peak intensity of the target plane. For example, when the lithium niobate film is a c-axis oriented epitaxial film, the peak intensities other than the (00L) plane are 10% or less, preferably 5% or less, of the maximum peak intensity of the (00L) plane. Here, (00L) is a general term for equivalent planes such as (001) and (002).

[0097] Furthermore, the conditions for confirming the peak intensity at the orientation position described above only indicate orientation in one direction. Therefore, even if the above conditions are met, if the crystal orientation is not uniform within the plane, the X-ray intensity will not increase at a specific angular position, and no pole points will be observed. For example, in the case of a lithium niobate film, because LiNbO3 has a trigonal crystal structure, there will be three pole points of LiNbO3 (014) in the single crystal. In the case of lithium niobate, it is known that epitaxial growth occurs in a so-called twin state, in which crystals rotated 180° around the c-axis are symmetrically bonded. In this case, three pole points are symmetrically bonded to two, resulting in six pole points. Furthermore, when a lithium niobate film is formed on a silicon single crystal substrate with a (100) plane, the substrate has four-fold symmetry, so 4 x 3 = 12 pole points are observed. Note that in this disclosure, lithium niobate films epitaxially grown in a twin state are also included in the term epitaxial film.

[0098] The composition of lithium niobate is Li x NbA y O z where A is an element other than Li, Nb, and O. x is 0.5 or more and 1.2 or less, and preferably 0.9 or more and 1.05 or less. y is 0 or more and 0.5 or less. z is 1.5 or more and 4.0 or less, and preferably 2.5 or more and 3.5 or less. Examples of the element A include K, Na, Rb, Cs, Be, Mg, Ca, Sr, Ba, Ti, Zr, Hf, V, Cr, Mo, W, Fe, Co, Ni, Zn, Sc, and Ce, and two or more of these elements may be combined. Furthermore, the lithium niobate film may be a lithium niobate single crystal thin film bonded onto a substrate.

[0099] [Optical multiplexing component with optical modulation function] The optical multiplexing member with optical modulation function according to this embodiment includes a substrate made of a material different from lithium niobate and a lithium niobate film formed on the main surface of the substrate, and the lithium niobate film is integrated with the optical multiplexer according to the above embodiment and a Mach-Zehnder optical modulator connected to the optical multiplexer and guiding multiple visible light beams emitted from multiple visible light laser light sources to the optical multiplexer. Regarding the components described below, components having the same functions as those in the above embodiment will be assigned the same reference numerals, and their description may be omitted. The lithium niobate film included in the optical multiplexing member with optical modulation function according to this embodiment may include any of the optical multiplexers shown in FIGS.

[0100] FIG. 13 is a schematic plan view of the optical multiplexing member with optical modulation function according to this embodiment. The optical multiplexing element 300 with optical modulation function shown in Figure 13 comprises a substrate 10 (see Figure 11) made of a material other than lithium niobate, and a lithium niobate film 24 formed on the main surface of the substrate 10, and an optical multiplexer provided in the optical multiplexing element 300 with optical modulation function is formed within the lithium niobate film 24.

[0101] The optical multiplexing member 300 with optical modulation function includes, for example, the 3×1 optical multiplexer 100 according to the above embodiment (see FIG. 1) and a Mach-Zehnder optical modulator 40.

[0102] A known Mach-Zehnder optical modulator or an optical waveguide can be used as the Mach-Zehnder optical modulator 40. It splits (demultiplexes) an optical beam with a uniform wavelength and phase into two paired beams, gives each beam a different phase, and then combines them. The intensity of the combined optical beam changes depending on the phase difference.

[0103] Each of the Mach-Zehnder optical waveguides 40-1, 40-2, and 40-3 shown in FIG. 13 includes a first optical waveguide 41, a second optical waveguide 42, an input path 43, an output path 44, a branching portion 45, and a coupling portion 46. The output path 44 of the Mach-Zehnder optical waveguide 40-1 is connected to the optical input side optical waveguide 21-1 of the first MMI optical multiplexing element 50-1. The output path 44 of the Mach-Zehnder optical waveguide 40-2 is connected to the optical input side optical waveguide 21-2 of the first MMI optical multiplexing element 50-1. The output path 44 of the Mach-Zehnder optical waveguide 40-3 is connected to the optical input side optical waveguide 21-3 of the first MMI optical multiplexing element 50-1. The first optical waveguide 41 and the second optical waveguide 42 shown in FIG. 13 extend linearly in the x direction except near the branching portion 45 and the coupling portion 46, but are not limited to this configuration. The first optical waveguide 41 and the second optical waveguide 42 shown in FIG. 13 have approximately the same length. The branching portion 45 is located between the input path 43 and the first optical waveguide 41 and the second optical waveguide 42. The input path 43 is connected to the first optical waveguide 41 and the second optical waveguide 42 via the branching portion 45. The coupling portion 46 is located between the first optical waveguide 41 and the second optical waveguide 42 and the output path 44. The first optical waveguide 41 and the second optical waveguide 42 are connected to the output path 44 via the coupling portion 46.

[0104] The electrodes 25 and 26 are electrodes that apply a modulation voltage to each of the Mach-Zehnder optical waveguides 40-1, 40-2, and 40-3 (hereinafter, sometimes simply referred to as "each Mach-Zehnder optical waveguide 40"). The electrode 25 is an example of a first electrode, and the electrode 26 is an example of a second electrode. One end of the electrode 25 is connected to a power supply 131, and the other end is connected to a termination resistor 132. One end of the electrode 26 is connected to the power supply 131, and the other end is connected to the termination resistor 132. The power supply 131 is a part of a drive circuit that applies a modulation voltage to each Mach-Zehnder optical waveguide 40. For simplicity of illustration, the electrodes 25 and 26 are only drawn in the area of ​​the Mach-Zehnder optical waveguide 40-3.

[0105] The electrodes 27 and 28 are electrodes that apply a DC bias voltage to each Mach-Zehnder optical waveguide 40. One end of the electrode 27 and one end of the electrode 28 are connected to a power supply 133. The power supply 133 is a part of a DC bias application circuit that applies a DC bias voltage to each Mach-Zehnder optical waveguide 40. When a DC bias voltage is superimposed on the electrodes 25 and 26, the electrodes 27 and 28 may not be provided. Also, ground electrodes may be provided around the electrodes 25, 26, 27, and 28.

[0106] Visible Light Source Module (First Embodiment) A visible light source module according to a first embodiment of the present disclosure includes an optical multiplexer according to the present disclosure and a plurality of visible laser light sources that emit visible light that is multiplexed by the optical multiplexer. FIG. 14 is a schematic plan view of a visible light source module according to the present disclosure.

[0107] 14 includes an optical multiplexing member 200 having an MMI coupled optical multiplexing section 50 in which a first MMI type optical multiplexing element 50-1 and a second MMI type optical multiplexing element 50-2 are connected, and three visible laser light sources 30 (30-1, 30-2, 30-3) that emit visible light multiplexed in the optical multiplexing member 200. The optical multiplexing member 200 includes a substrate 10 (see FIG. 11) made of a material different from lithium niobate, and a lithium niobate film 24 (see FIG. 11) formed on the main surface of the substrate 10, and has a first side surface 200A. Regarding the components shown in FIG. 14, components having the same functions as those described above are given the same reference numerals, and the description thereof may be omitted.

[0108] Various laser elements can be used as the visible light laser light source 30. For example, commercially available laser diodes (LDs) that emit red, green, blue, etc. can be used. For red light, light with a peak wavelength of 610 nm or more and 750 nm or less can be used, for green light, light with a peak wavelength of 500 nm or more and 560 nm or less can be used, and for blue light, light with a peak wavelength of 435 nm or more and 480 nm or less can be used. In the visible light source module 1000, the visible light laser light sources 30-1, 30-2, and 30-3 are an LD that emits green light, an LD that emits blue light, and an LD that emits red light, respectively. The visible light laser light sources 30-1, 30-2, and 30-3 are arranged at intervals from each other in a direction substantially perpendicular to the emission direction of the light emitted from each LD, and are provided on the upper surface of a light source base 60 (see FIG. 15).

[0109] In the visible light source module 1000, two and three visible light laser light sources are exemplified, but the number is not limited to two or three, and may be four or more. The multiple visible light laser light sources may all emit light with different wavelengths, or some visible light laser light sources may emit light with the same wavelength. Furthermore, light other than red (R), green (G), and blue (B) can be used for the emitted light, and the mounting order of red (R), green (G), and blue (B) described using the drawings does not have to be this order and can be changed as appropriate.

[0110] Fig. 15 is a schematic cross-sectional view of a part of the light source module 1000 shown in Fig. 14 cut along the XZ plane, depicting only a part near the joint. The light source 30 is mounted on the upper surface of a light source base 60. The light source base 60 may be common to all the light sources or may be separate for each light source. The light source base 60 is made of, for example, aluminum nitride (AlN), aluminum oxide (Al2O3), silicon (Si), or the like.

[0111] The light source base 60 and the optical waveguide substrate 10 on which the optical multiplexing function layer 20 is formed can be directly bonded via a metal layer 70. This configuration makes it possible to further reduce the size by eliminating spatial coupling or fiber coupling. By configuring the bonding surface 60A of the light source base 60 and the bonding surface 10A of the optical waveguide substrate 10 to be bonded via the metal layer 70, the relative positions of the light source base 60 and the optical waveguide substrate 10 can be adjusted during manufacturing, and the optical axis position of the laser light can be aligned so that the optical axis of each light source 30 coincides with the axis of the input waveguide (active alignment).

[0112] Metal layer 70 may consist of multiple metal layers.

[0113] When the light source module of this embodiment is used in XR glasses, taking into consideration the amount of light required in the XR glasses, etc., it is preferable that the gap (spacing) S (see Figure 14) between the bonding surface 60A of the light source base 60 and the bonding surface 10A of the optical waveguide substrate 10 be, for example, greater than 0 μm and not greater than 5 μm.

[0114] (Drive method) An optical modulator can modulate input light into output light using a high-frequency modulation voltage and a DC bias voltage. The operating point Vd of the optical modulator is adjusted by controlling the DC bias voltage Vdc. The operating point Vd is the voltage at the center of the modulation voltage amplitude Vpp. The half-wave voltage of the high-frequency modulation voltage is defined as Vπ(RF).

[0115] 16A to 16C are diagrams for explaining three examples of a method for driving an optical modulator. 16A to 16C, the horizontal axis represents the DC bias voltage applied to the optical modulator, and the vertical axis represents the intensity of the optical output at the applied voltage. The applied voltage width Vpp is the difference between the minimum value (Vmin) and the maximum value (Vmax) of the applied voltage.

[0116] 16A shows an example in which the DC bias voltage can be set to approximately 0 V by setting the operating point Vd' so that the shift amount of the operating point voltage is (Vn-0.5Vπ). For example, if the applied voltage width Vpp of the modulation voltage Vm is the half-wave voltage Vπ(RF), then a modulation voltage Vm in the range of (-1 / 2)Vπ(RF) to (1 / 2)Vπ(RF) is applied to the optical modulator. As shown in FIG. 16A, the optical output from the optical modulator is maximum when the modulation voltage Vm is (-1 / 2)Vπ(RF), minimum when the modulation voltage Vm is (1 / 2)Vπ(RF), and the optical output when the modulation voltage Vm is 0 V is 50% of the maximum output.

[0117] Similarly, using Figure 16B, we will explain the optical modulation of an optical modulator in which the operating point Vd' is set so that the shift amount of the operating point voltage is (Vn-0.25Vπ) and the applied voltage width Vpp of the modulation voltage Vm is controlled as a (1 / 4) wavelength voltage (1 / 2)Vπ(RF). In this case, if the shift amount of the operating point voltage is set to (Vn-0.25Vπ), the operating point Vd' can be set to a DC bias voltage of approximately 0 (V). A modulation voltage Vm corresponding to the range from (-1 / 4)Vπ(RF) to (1 / 4)Vπ(RF) is applied to the optical modulator. As shown in Figure 16B, the optical output from the optical modulator is maximum when the modulation voltage Vm is (-1 / 4)Vπ(RF) and minimum when the modulation voltage Vm is (1 / 4)Vπ(RF). When the modulation voltage Vm is 0V(Vd'), the optical output is 15% of the maximum output.

[0118] Similarly, using Figure 16C, we will explain the optical modulation of an optical modulator in which the operating point Vd' is set so that the shift amount of the operating point voltage is (Vn-0.75Vπ) and the applied voltage width Vpp of the modulation voltage Vm is controlled as a (1 / 4) wavelength voltage (1 / 2)Vπ(RF). In this case, if the operating point voltage shift is set to (Vn-0.75Vπ), the operating point Vd' can be set to a DC bias voltage of approximately 0 (V). A modulation voltage Vm corresponding to the range from (-1 / 4)Vπ(RF) to (1 / 4)Vπ(RF) is applied to the optical modulator. As shown in Figure 16C, the optical output from the optical modulator is maximum when the modulation voltage Vm is (-1 / 4)Vπ(RF) and minimum when the modulation voltage Vm is (1 / 4)Vπ(RF). When the modulation voltage Vm is 0V(Vd'), the optical output is 85% of the maximum output.

[0119] [Visible Light Source Module (Second Embodiment)] FIG. 17 is a schematic plan view of a visible light source module according to the second embodiment of the present disclosure. 17 includes the optical multiplexing member with optical modulation function 300 shown in Fig. 13, and a plurality of visible laser light sources 30 (30-1, 30-2, 30-3) that emit visible light that is multiplexed in the optical multiplexing member with optical modulation function 300. The optical multiplexing member with optical modulation function 300 includes a substrate 10 (see Fig. 11) made of a material different from lithium niobate, and a lithium niobate film 24 (see Fig. 11) formed on the main surface of the substrate 10, and has a side surface 300A. Regarding the components shown in FIG. 17, components having the same functions as those described above are given the same reference numerals, and the description thereof may be omitted.

[0120] The visible light source module 2000 has three Mach-Zehnder optical waveguides 40-1, 40-2, 40-3, the same number as the visible light laser light sources 30-1, 30-2, 30-3. The visible light laser light sources 30-1, 30-2, 30-3 and the Mach-Zehnder optical waveguides 40-1, 40-2, 40-3 are positioned so that light emitted from the visible light laser light sources enters the corresponding Mach-Zehnder optical waveguide.

[0121] The light source base 60 on which the visible light laser light sources 30-1, 30-2, and 30-3 are mounted can be directly bonded via a metal bonding layer to the substrate 10 on which the optical multiplexing function layer 20 having the optical multiplexing member 300 with optical modulation function is formed. This configuration makes it possible to further reduce the size by eliminating spatial coupling or fiber coupling. Furthermore, during manufacturing, the relative positions of the light source base 60 and the substrate 10 can be adjusted to align the optical axis position of the laser light so that the optical axis of each visible light laser coincides with the axis of the input path 43 of each of the Mach-Zehnder optical waveguides 40-1, 40-2, and 40-3 (active alignment).

[0122] The size of the optical multiplexing functional layer 20 is, for example, 100 mm 2 The size of the optical multiplexing functional layer 20 is 100 mm or less. 2 If it meets the following criteria, it is suitable for use with XR glasses such as AR glasses and VR glasses.

[0123] The optical multiplexing functional layer 20 can be fabricated by a known method, for example, by using semiconductor processes such as epitaxial growth, photolithography, etching, vapor phase growth, and metallization.

[0124] When the visible light source module according to the present invention is applied to XR glasses such as AR glasses or VR glasses, the width of the first MMI type optical multiplexing element and the second MMI type optical multiplexing element constituting the optical multiplexer is preferably, for example, about 5 to 15 μm, and the length thereof is preferably, for example, about 100 to 1000 μm.

[0125] For example, in a retinal projection display, to display an image in the desired color, it is necessary to independently and quickly modulate the intensity of each of the three colors (RGB) that represent visible light. Performing such modulation solely with a visible laser light source (current modulation) places a heavy load on the IC controlling the modulation. However, it is possible to also use modulation (voltage modulation) with a Mach-Zehnder optical modulator 40 (optical combining component 300 with optical modulation function). In this case, coarse adjustment can be performed with current (visible laser light source) and fine adjustment with voltage (Mach-Zehnder optical modulator 40). Alternatively, coarse adjustment can be performed with voltage (Mach-Zehnder optical modulator 40) and fine adjustment with current (visible laser light source). Since fine adjustment with voltage provides better responsiveness, the former is preferred when responsiveness is important. However, fine adjustment with current requires less current and therefore reduces power consumption, so the latter is preferred when power consumption is important.

[0126] [Optical engine and XR glasses] In this specification, an optical engine is a device that includes a plurality of light sources, an optical system including a multiplexing unit that combines the plurality of light beams emitted from the plurality of light sources into a single beam of light, an optical scanning mirror that reflects the light emitted from the optical system at a different angle so as to display an image, and a control element that controls the optical scanning mirror.

[0127] Fig. 18 is a conceptual diagram for explaining an example of the XR glasses of the present invention. Fig. 19 is a conceptual diagram showing how an image is projected directly onto the retina by laser light emitted from the light source module in the XR glasses shown in Fig. 18. Symbol L is image display light.

[0128] The XR glasses (eyeglasses) 10000 of this embodiment are glasses-type terminals. XR is a general term for virtual reality (VR), augmented reality (AR), and mixed reality. The symbol L shown in FIG. 19 denotes image display light.

[0129] The XR glasses 10000 of this embodiment shown in FIG. 18 are configured such that the light source module 1000 according to the above-described embodiment is mounted on an optical engine 5001 installed in a frame 1010. As shown in FIG. 18, the optical engine 5001 includes a light source module 1000, an optical scanning mirror 3001, an optical system 2001 connecting the light source module 1000 and the optical scanning mirror 3001, a laser driver 1100, an optical scanning mirror driver 1200, and a video controller 1300 that controls these drivers.

[0130] For example, a MEMS mirror can be used as the optical scanning mirror 3001. In order to project a 2D image, it is preferable to use, as the optical scanning mirror 3001, a two-axis MEMS mirror that vibrates so as to reflect laser light while changing the angle in the horizontal direction (X direction) and the vertical direction (Y direction).

[0131] The optical system 2001 optically processes the laser light emitted from the light source module 1000. The optical system 2001 may include, for example, a collimator lens 2001a, a slit 2001b, and an ND filter 2001c. The optical system 2001 shown in Fig. 18 is an example, and other configurations may also be used.

[0132] In the XR glasses 10000 of this embodiment shown in Figure 18, as shown in Figure 19, laser light R emitted from the light source module 1000 attached to the frame 1010 is reflected by the optical scanning mirror 3001, and further reflected by the lens 4001 of the XR glasses 10000, enters the human eyeball E as image display light L, and an image (video) can be projected directly onto the retina M.

[0133] The XR glasses 10000 of this embodiment are equipped with the light source module 1000 of this embodiment, and therefore have reduced electric field efficiency.

[0134] The above describes the embodiments of the present invention in detail with reference to the drawings. However, each configuration and combination thereof in each embodiment is an example, and additions, omissions, substitutions, and other modifications of the configurations are possible within the scope that does not deviate from the spirit of the present invention. [Example]

[0135] The present invention will be described in more detail below using examples, but the present invention is not limited to the examples shown below.

[0136] <3-input, 1-output MMI-coupled optical multiplexer (1-stage shift)> Simulations were conducted to compare the coupling losses of the three RGB color lights (loss of light intensity at output after the light intensity at input passes through the MMI coupled optical multiplexer) between an example model corresponding to the 3-input 1-output MMI coupled optical multiplexer shown in Figure 1 and a comparative example model of a 3-input 1-output MMI coupled optical multiplexer that differs only in that it does not have the first MMI optical multiplexer as the MMI optical multiplexing incident position shifter. Fimmwave (Photon Design) was used as the simulation software.

[0137] Example 1 The dimensions of the example model of the 3-input 1-output MMI coupled optical multiplexing unit shown in Fig. 20 are as follows: The first MMI type optical multiplexing element 50-1 is described as an MMI type optical multiplexing incident position shift unit, and the second MMI type optical multiplexing element 50-2 is described as an MMI type optical multiplexing main unit. (length and width of each component) Length of MMI type optical multiplexing incident position shift part L1: 60 μm Width of MMI type optical multiplexing incident position shift part W1: 8μm Length of MMI type optical multiplexer main part L2: 2600 μm Width of MMI type optical multiplexer main part W2: 13 μm Maximum width W1 of the tapered part on the optical input side in , W2 in :2μm Maximum width W2 of the tapered part on the optical output side out :2μm Length of the optical input and output taper sections: 50 μm (common) Width of the optical waveguide other than the tapered portion W0: 0.8 μm (common) The maximum width of the tapered portion on the optical input side and the maximum width of the tapered portion on the optical output side are the widths of the portions where the tapered portions connect to the optical multiplexing portion. (Wavelength of laser light propagating through the optical waveguide on the optical input side) L1 wavelength: 637 μm (red R) L2 wavelength: 455 μm (blue B) L3 wavelength: 520 μm (green G) (distance between adjacent optical input waveguides) Distance between the top surfaces of adjacent tapered sections d1: 1.5 μm As shown in the figure, the distance d1 between the upper surfaces is the distance between the upper surfaces of the connecting portions of adjacent tapered portions to the first MMI type optical multiplexing portion 50-1.

[0138] Comparative Example 1 The model of the MMI coupled optical multiplexing unit according to Comparative Example 1 is the same model as that of Example 1, and has the same parameters, except that the MMI coupled optical multiplexing unit corresponding to the MMI coupled optical multiplexing unit 50 of Example 1 is an MMI coupled optical multiplexing unit that does not include a first MMI type optical multiplexing unit as an MMI type optical multiplexing incident position shift unit.

[0139] The coupling losses of the RGB three-color light in Example 1 and Comparative Example 1 (loss of light intensity at output after the light intensity at input passes through the MMI coupling type optical multiplexing section) were as follows. The coupling losses of Example 1 were 5 dB, 4 dB, and 4 dB for R, G, and B, respectively. The coupling losses of Comparative Example 1 were 12 dB, 4 dB, and 2 dB for R, G, and B, respectively. The coupling loss of green G remained unchanged, and the coupling loss of blue B in Example 1 was slightly worse than that in Comparative Example 1, but the coupling loss of red R in Example 1 was significantly improved compared to that in Comparative Example 1.

[0140] <3-input, 1-output MMI-coupled optical multiplexer (one-stage shift, different RGB arrangement)> Example 2 In Example 2, the length L1 of the first MMI type optical multiplexing element and the length L2 of the second MMI type optical multiplexing element are as follows, and the model and parameters are the same as those of Example 1 except that the arrangement of the incident light for the three RGB colors is different. (length of each component) Length of MMI type optical multiplexing incident position shift part L1: 50 μm Length of MMI type optical multiplexer main part L2: 300 μm (RGB input arrangement and wavelength of laser light propagating through the optical input side optical waveguide) L1 wavelength: 520 μm (green G) L2 wavelength: 455 μm (blue B) L3 wavelength: 637 μm (red R)

[0141] Comparative Example 2 Comparative Example 2 was the same model as Example 2, and had the same parameters, except that it was an MMI coupling type optical multiplexing section that did not include a first MMI type optical multiplexing section.

[0142] The coupling losses of the RGB three-color light in Example 2 and Comparative Example 3 were as follows. The coupling losses in Example 2 were 4 dB, 5 dB, and 6 dB for R, G, and B, respectively. The coupling losses of Comparative Example 2 were 4 dB, 13 dB, and 6 dB for R, G, and B, respectively. The coupling loss of red R and green G remained unchanged, but the coupling loss of blue B in Example 2 was significantly improved compared to Comparative Example 2.

[0143] <3-input, 1-output MMI-coupled optical multiplexer (2-stage shift)> Simulations were conducted to compare the coupling losses of the three RGB color lights (loss of light intensity at the time of output after the light intensity at the time of input has passed through the MMI coupled optical multiplexer) between an example model corresponding to a three-input one-output type MMI coupled optical multiplexer that combines the MMI coupled optical multiplexers shown in FIGS. 3 and 4, and a comparative example model that differs only in that it does not have the first MMI optical multiplexer as an MMI optical multiplexing incident position shift unit.

[0144] Example 3 The dimensions of the example model of the 3-input 1-output MMI coupled optical multiplexer shown in Fig. 21 are as follows: The width of the tapered section on the optical input side, the width of the tapered section on the optical output side, the width of the optical waveguide other than the tapered section, and the distance between the upper surfaces of adjacent tapered sections are the same as the dimensions of the example model shown in Fig. 20. (length and width of each component) Length of the first MMI type optical multiplexing incident position shift part L11: 40 μm Width W11 of the first MMI type optical multiplexing incident position shift part: 3 μm Length of the second MMI type optical multiplexing incident position shift part L1: 25 μm Width W1 of the second MMI type optical multiplexing incident position shift part: 8 μm Length of the first MMI type optical multiplexer main part L2: 320 μm Width of the first MMI type optical multiplexer main part W2: 13 μm Length of the second MMI type optical multiplexer main part L22: 685 μm Width of the second MMI type optical multiplexer main part W22: 7 μm (Wavelength of laser light propagating through the optical waveguide on the optical input side) L1 wavelength: 637 μm (red R) L2 wavelength: 455 μm (blue B) L3 wavelength: 520 μm (green G)

[0145] Comparative Example 3 The comparative example model of the 3-input 1-output MMI coupled optical multiplexer according to Comparative Example 3 was the same model as that of Example 3, and had the same parameters, except that it was an MMI coupled optical multiplexer that did not include the first MMI type optical multiplexing incident position shift unit and the second MMI type optical multiplexing incident position shift unit.

[0146] The coupling losses of the RGB three-color light in Example 3 and Comparative Example 3 (loss of light intensity at output after the light intensity at input passes through the MMI coupling type optical multiplexing section) were as follows. The coupling losses of Example 3 were 3.7 dB, 3.7 dB, and 3.7 dB for R, G, and B, respectively. The coupling losses of Comparative Example 3 were 3.7 dB, 6.2 dB, and 6.2 dB for R, G, and B, respectively. Although the coupling loss of red R remained unchanged, the coupling losses of blue B and green G in Example 3 were significantly improved compared to Comparative Example 3.

[0147] Examples 4 to 12 In Examples 4 to 6, the lengths and widths of the first MMI type optical multiplexing main portion and the second MMI type optical multiplexing main portion are fixed to the dimensions of Example 3, and the lengths and widths of the first MMI type optical multiplexing incident position shift portion and the second MMI type optical multiplexing incident position shift portion are changed from those of Example 3.

[0148] In Examples 4 to 6, the length L1 of the second MMI type optical multiplexing incident position shifting portion was set to 2 μm, 15 μm, and 65 μm, respectively. In Example 7, the length L1 of the second MMI type optical multiplexing incident position shifting section and the length L11 of the first MMI type optical multiplexing incident position shifting section are set to 30 μm and 40 μm, respectively. In Example 8, the length L1 of the second MMI type optical multiplexing incident position shifting section and the length L11 of the first MMI type optical multiplexing incident position shifting section are set to 7 μm and 55 μm, respectively. In Example 9, the length L1 of the second MMI type optical multiplexing incident position shifting section and the length L11 of the first MMI type optical multiplexing incident position shifting section are set to 7 μm and 55 μm, respectively, and further, the length W11 of the first MMI type optical multiplexing incident position shifting section is set to 3.4 μm. In Example 10, the length L1 of the second MMI type optical multiplexing incident position shifting section and the length L11 of the first MMI type optical multiplexing incident position shifting section are set to 7 μm and 55 μm, respectively, and further, the length W11 of the first MMI type optical multiplexing incident position shifting section is set to 2.7 μm. In Example 11, the length L1 of the second MMI type optical multiplexing incident position shifting section and the length L11 of the first MMI type optical multiplexing incident position shifting section are set to 7 μm and 55 μm, respectively, and further, the width W1 of the second MMI type optical multiplexing incident position shifting section and the width W11 of the first MMI type optical multiplexing incident position shifting section are set to 5.6 μm and 3.4 μm, respectively. In Example 12, the length L1 of the second MMI type optical multiplexing incident position shifting section and the length L11 of the first MMI type optical multiplexing incident position shifting section are set to 7 μm and 55 μm, respectively, and further, the width W1 of the second MMI type optical multiplexing incident position shifting section and the width W11 of the first MMI type optical multiplexing incident position shifting section are set to 4.7 μm and 2.7 μm, respectively. Table 1 shows the dimensions and RGB coupling losses of each of Examples 3 to 12 and Comparative Example 3. In Table 1, the first MMI type optical multiplexing incident position shift section is abbreviated as the first shift section, the second MMI type optical multiplexing incident position shift section is abbreviated as the second shift section, the first MMI type optical multiplexing main section is abbreviated as the first main section, and the second MMI type optical multiplexing main section is abbreviated as the second shift section.

[0149] [Table 1]

[0150] In all of Examples 3 to 12, the coupling loss of red R remained unchanged, but the coupling loss of light intensity of blue B and green G was significantly improved compared to Comparative Example 3. It was found that the length and width of the first MMI type optical multiplexing incident position shift section and the second MMI type optical multiplexing incident position shift section can be appropriately selected so as to reduce the coupling loss of the light intensities of the three colors of RGB.

[0151] In Example 4, L11 is 2 μm, but for green G, the same improvement in coupling loss as in Example 3, where L11 is 40 μm, is obtained, and for blue G, an improvement in coupling loss similar to that in Example 3 is obtained. It was found that the coupling loss can be improved when the length L11 of the first MMI type optical multiplexing incident position shift portion is 2 μm or more.

[0152] In Examples 5 and 6, L11 was changed from Example 3 (L11=40 μm) to 15 μm and 65 μm, respectively, and the same improvement in coupling loss as in Example 3 was achieved for both RGB.

[0153] In Example 7, L1 was changed to 30 μm compared to Example 3 (L1 = 25 μm), but the red R showed the same improvement in coupling loss as Example 3, and the GB also showed almost the same improvement in coupling loss as Example 3.

[0154] In Example 8, L11 was changed to 55 μm and L1 to 7 μm compared to Example 3 (L11 = 40, L1 = 25 μm). Red R showed the same improvement in coupling loss as Example 3, and blue B showed almost the same improvement in coupling loss as Example 3. For green G, the improvement was smaller than for RB, but a significant improvement in coupling loss was achieved compared to Comparative Example 3.

[0155] In Examples 9 and 10, W11 was changed to 3.4 μm and 2.7 μm, respectively, compared to Example 8 (W11 = 3 μm). Red R showed the same improvement in coupling loss as Example 8 (the same improvement as Example 3), green G showed the same improvement in coupling loss as Example 8, and while the improvement in blue B was smaller than that of RG, a significant improvement in coupling loss was achieved compared to Comparative Example 3.

[0156] In Example 11, W1 was changed to 5.6 μm compared to Example 9 (W1 = 8 μm), but the red R showed the same improvement in coupling loss as Example 9 (also the same improvement as Example 3), the green G showed almost the same improvement in coupling loss as Example 9, and the blue B showed the same improvement in coupling loss as Example 9.

[0157] In Example 12, W1 was changed to 4.7 μm compared to Example 10 (W1 = 8 μm), but the red R showed an improvement in coupling loss of the same magnitude as Example 10 (the same magnitude as Example 3), the green G showed an improvement in coupling loss of approximately the same magnitude as Example 9, and the blue B showed an improvement in coupling loss of the same magnitude as Example 9.

[0158] FIG. 22A is a graph showing the loss of optical intensity after transmission through the MMI coupled optical multiplexer for each wavelength of RGB on the vertical axis, where the horizontal axis represents the length L2 of the first MMI type optical multiplexer main part and the vertical axis represents the loss of optical intensity after transmission through the MMI coupled optical multiplexer for each wavelength of RGB, in a case where the first MMI type optical multiplexer incident position shift part and the second MMI type optical multiplexer incident position shift part have the same structure as the example model (model of Example 3) shown in FIG. 21, but only the lengths L11 and L1 of the first MMI type optical multiplexer incident position shift part are different. The lengths L11 and L1 of the first MMI type optical multiplexing incident position shifting section and the second MMI type optical multiplexing incident position shifting section are as follows: Length of the first MMI type optical multiplexing incident position shift part L11: 44 μm Length of the second MMI type optical multiplexing incident position shift part L1: 27 μm

[0159] FIG. 22B is a graph similar to FIG. 22A for a model of the MMI coupling type optical multiplexing unit of Comparative Example 3 (an MMI coupling type optical multiplexing unit not including a first MMI type optical multiplexing incident position shifting unit and a second MMI type optical multiplexing incident position shifting unit).

[0160] Comparing Figures 22A and 22B, it can be seen that the deviation in the RGB multiplexing loss margin in the example equipped with an MMI-type optical multiplexing incident position shifting unit is significantly improved compared to the comparative example not equipped with an MMI-type optical multiplexing incident position shifting unit. In the example of Figure 22A, the minimum value of the loss in light intensity for each of the RGB colors is in the range of 320±12 μm, whereas in the comparative example of Figure 22B, the minimum value of the loss in light intensity for each of the RGB colors is 318±3 μm, so that L1 can be appropriately selected so as to reduce the loss in light intensity for the three RGB colors.

[0161] (Effect of tapered section) Example 13 Example 13 has the same structure as the example model of the MMI coupled optical multiplexing unit shown in Fig. 21 (the model of Example 3), except that only the lengths L11 and L1 of the first MMI type optical multiplexing incident position shifting unit and the second MMI type optical multiplexing incident position shifting unit and the width W1 of the second MMI type optical multiplexing incident position shifting unit are different, and the optical input side tapered unit and the optical output side tapered unit are not provided. The case where the optical input side tapered unit and the optical output side tapered unit are not provided refers to the case where all the optical waveguides have the same thickness (straight) and are connected to the MMI coupled optical multiplexing unit.

[0162] The lengths L11 and L1 of the first and second MMI type optical multiplexing incident position shifting sections and the width W1 of the second MMI type optical multiplexing incident position shifting section are as follows: Length of the first MMI type optical multiplexing incident position shift part L11: 44 μm Length of the second MMI type optical multiplexing incident position shift part L1: 27 μm Width W1 of the second MMI type optical multiplexing incident position shift part: 5 μm

[0163] Comparative Example 4 The model of Comparative Example 4 was the same model as that of Example 13, and had the same parameters, except that it was an MMI-coupled optical multiplexing section that did not have a first MMI-type optical multiplexing incident position shifting section and a second MMI-type optical multiplexing incident position shifting section.

[0164] The coupling losses of the RGB three-color light in Example 13 and Comparative Example 4 were as follows. The coupling losses of Example 13 were 6 dB, 6 dB, and 4 dB for R, G, and B, respectively. The coupling losses of Comparative Example 4 were 6 dB, 9 dB, and 7 dB for R, G, and B, respectively. Although the coupling loss of red R was the same as that of Comparative Example 4, the coupling loss of blue B and green G was improved by 4 dB compared to Comparative Example 4. As described above, it was confirmed that the effect of having an MMI-type optical multiplexing incident position shift section can be obtained even in a configuration without a tapered section.

[0165] (MMI-coupled optical multiplexer) Example 14 Example 14 is the structure of the example model of the MMI-connected optical multiplexer shown in Figure 6, where the dimensional parameters are as follows: Length L10 of the first MMI type optical multiplexing unit 150-1: 145 μm Width W10 of the first MMI type optical multiplexing section 150-1: 2.3 μm Length L20 of the second MMI type optical multiplexing unit 150-2: 525 μm Width W20 of the second MMI type optical multiplexing section 150-2: 6 μm Length L3 of output MMI type optical multiplexer 150T: 685 μm Width W3 of output MMI type optical multiplexer 150T: 5.6 μm Maximum width W1 of the tapered part on the optical input side in , W2 in (See Figure 20) :2μm Maximum width W2 of the tapered part on the optical output side out (See Figure 20) :2μm Length of the optical input and output taper sections: 50 μm (common) Width W0 of the optical waveguide other than the tapered portion (see Figure 21): 0.8 μm (common) (Wavelength of laser light propagating through the optical waveguide on the optical input side) L1 wavelength: 637 μm (red R) L2 wavelength: 455 μm (blue B) L3 wavelength: 520 μm (green G) (distance between adjacent optical input waveguides) Distance between the top surfaces of adjacent tapered sections d1: 1.5 μm

[0166] Example 15 Example 15 has the same model and parameters as Example 14, except that the length L10 of the first MMI type optical multiplexing section 150-1 is 62 μm.

[0167] Comparative Example 5 The model of Comparative Example 5 was the same model as that of Example 14, and had the same parameters, except that it was an MMI-coupled optical multiplexing section that did not include the first MMI type optical multiplexing section 150-1 as an MMI type optical multiplexing incident position shift section.

[0168] The coupling losses of the RGB three-color light in Examples 14 and 15 and Comparative Example 5 were as follows: The coupling losses of the RGB three-color light are the loss of light intensity at the time of output after the input light intensity has passed through the MMI-coupled optical multiplexer. The coupling losses of Example 14 were 3.2 dB, 1.5 dB, and 3.5 dB for R, G, and B, respectively. The coupling losses of Example 15 were 3.2 dB, 1.5 dB, and 3.7 dB for R, G, and B, respectively. The coupling losses of Comparative Example 5 were 3.2 dB, 1.5 dB, and 5.3 dB for R, G, and B, in that order.

[0169] Although the coupling loss of RG in Examples 14 and 15 was the same as that of Comparative Example 5, the coupling loss of blue B in Examples 14 and 15 was significantly improved compared to that of Comparative Example 5. As described above, it was confirmed that the effect of having an MMI-type optical multiplexing incident position shift section can be obtained even when the MMI-coupled optical multiplexing section is configured as an MMI-linked optical multiplexing section type. [Explanation of symbols]

[0170] 10 Substrate 20 Optical multiplexing functional layer 24 Lithium niobate film 30 Visible light laser light source 40 Mach-Zehnder optical modulator 50, 50A, 50B, 150 MMI combined optical multiplexer 50-1, 50A-1, 150-1 1st MMI type optical multiplexer (MMI type optical multiplexer input position shift unit) 50-2, 50B-2, 150-2 2nd MMI type optical multiplexing section (MMI type optical multiplexing main section) 100, 101, 102, 103, 104, 110 optical multiplexer 200 Optical multiplexing components 300 Optical multiplexer with optical modulation function 1000, 2000 Visible Light Source Module 10000 XR Glasses

Claims

1. An optical multiplexer that multiplexes laser beams of different wavelengths, an MMI-coupled optical multiplexing unit formed by coupling, from an input side, a first MMI-type optical multiplexing unit that shifts the incident position and a second MMI-type optical multiplexing unit having a width wider than that of the first MMI-type optical multiplexing unit; one or more first optical input side optical waveguides connected to the first MMI type optical multiplexing unit; one or more second optical input side optical waveguides connected to the second MMI type optical multiplexing unit; an optical output side optical waveguide connected to the second MMI type optical multiplexing section;

2. 2. The optical multiplexer according to claim 1, wherein each of the first optical input side optical waveguide, the second optical input side optical waveguide, and the optical output side optical waveguide has a tapered portion whose width continuously increases as it approaches the MMI coupled optical multiplexer.

3. 2. The optical multiplexer according to claim 1, wherein the number of said first optical input side optical waveguides is two.

4. 2. The optical multiplexer according to claim 1, wherein the width of said first MMI type optical multiplexing section is equal to or less than two-thirds of the width of said second MMI type optical multiplexing section.

5. 2. The optical multiplexer according to claim 1, wherein the length of said first MMI type optical multiplexing section is 2 [mu]m or more.

6. 2. The optical multiplexer according to claim 1, wherein the plurality of different wavelengths are all visible light wavelengths.

7. a substrate made of a material different from lithium niobate; a lithium niobate film formed on a main surface of the substrate, An optical multiplexing member, wherein the optical multiplexer according to any one of claims 1 to 6 is formed on the lithium niobate film.

8. A visible light source module comprising: the optical multiplexing member according to claim 7; and a plurality of visible laser light sources that emit visible light that is multiplexed by the optical multiplexing member.

9. 8. An optical multiplexing member with an optical modulation function, comprising: the optical multiplexing member according to claim 7; and a Mach-Zehnder optical modulator connected to the optical multiplexing member, which guides a plurality of visible light beams emitted from a plurality of visible light laser light sources to the optical multiplexer.

10. 10. A visible light source module comprising: an optical multiplexing member with optical modulation function according to claim 9; and a plurality of visible light laser light sources that emit visible light to be multiplexed by the optical multiplexer with optical modulation function, wherein the plurality of visible light laser light sources are visible light laser light sources of red light, green light, and blue light.

11. The visible light source module according to claim 8 ; an optical scanning mirror that reflects the light emitted from the visible light source module at different angles so as to display an image;

12. The visible light source module according to claim 10; an optical scanning mirror that reflects the light emitted from the visible light source module at different angles so as to display an image;

13. XR glasses equipped with the optical engine according to claim 11.

14. XR glasses equipped with the optical engine according to claim 12.

Images