Light source unit, and optical engine, smart glasses, optical communication transmission device, optical communication system including the same

Abstract

The present invention provides a small and low-power light source unit, and an optical engine including the light source, smart glasses, a transmitting device for optical communication, and an optical communication system. The light source unit (1000) of the present invention includes: a light source section (10) having an optical semiconductor element (30); a first electrical signal generating element (40-1) for controlling the current driving the optical semiconductor element (30); an optical modulation element (200) having a Mach-Zehnder type optical waveguide (10) and electrodes for applying an electric field to the optical waveguide (10); and a second electrical signal generating element (40-2) for controlling the voltage that makes the optical modulation element (200) work. The optical semiconductor element (30) is optically connected to the optical modulation element (200). The first electrical signal generating element (40-1) and the second electrical signal generating element (40-2) can be connected synchronously. The intensity of the light emitted from the optical modulation element (200) is changed by the current controlled by the first electrical signal generating element (40-1) and the voltage controlled by the second electrical signal generating element (40-2).

Description

Technical Field

[0001] The present invention relates to a light source unit, and an optical engine including the same, smart glasses, a transmitting device for optical communication, and an optical communication system.

[0002] This application claims priority based on Japanese Patent Application No. 2022-005124 filed in Japan on January 17, 2022, the contents of which are incorporated herein by reference. Background Technology

[0003] AR (Augmented Reality) glasses and VR (Virtual Reality) glasses are anticipated as small, wearable devices. In such devices, a light-emitting element that emits full-color visible light is one of the central elements used to depict high-quality images. In such devices, the light-emitting element, for example, independently and rapidly modulates the intensity of each of the three colors of visible light (RGB) to represent dynamic images in the desired colors.

[0004] As such a light-emitting element, Patent Document 1 discloses a light-emitting element in which visible light laser light is incident onto a waveguide, and the emission intensity of each color laser chip is controlled by current, thereby emitting a color dynamic image. Additionally, Reference Document 2 discloses a modulator in which laser light is incident onto an external modulator having a waveguide via an optical fiber, and the intensity of each of the three colors (RGB) is independently modulated by the external modulator, wherein the waveguide is formed on a substrate having an electro-optical effect.

[0005] In wearable devices such as AR glasses and VR glasses, miniaturizing the light-emitting modules to house various functions within the size of typical eyeglasses is key to widespread adoption.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2021-86976

[0009] Patent Document 2: Japanese Patent No. 6728596

[0010] Patent Document 3: Japanese Patent Application Publication No. 2001-292107 Summary of the Invention

[0011] In the light-emitting element disclosed in Patent Document 1, the emitted intensity of the laser is directly controlled by current. However, in order to ensure the stability of the emitted intensity, current control needs to be performed in the linear region of the current-light output curve. Therefore, there are problems such as high power consumption and difficulty in reducing it.

[0012] Furthermore, Patent Document 2 discloses an optical modulator that uses a substrate made of materials such as lithium niobate, lithium tantalate, lead zirconate titanate, potassium titanate phosphate, polythiophene, liquid crystal materials, and various induced polymers with electro-optical effects, and an optical waveguide is provided on this substrate. Preferably, a method is disclosed that uses a single crystal or solid solution of lithium niobate, in particular, and a portion of it is modified by proton exchange or Ti diffusion to serve as the optical waveguide. However, the size of the modified waveguide portion (core) is determined by the distance of proton and Ti penetration and diffusion, making it difficult to reduce the diameter of the optical waveguide. Therefore, the size of the optical waveguide itself must be increased. In addition, because the diameter of the optical waveguide is large, it is difficult to concentrate the electric field of the modulation voltage. A large voltage needs to be applied for modulation, or the electrodes for applying the voltage need to be extended to operate with a smaller voltage, thus increasing the size of the device.

[0013] In addition, Figure 36 In the modulator shown in (a), where a portion of a bulk lithium niobate single crystal B1 is modified and used as an optical waveguide (B1-a), only a small amount of Ti is added to the bulk lithium niobate single crystal to create a refractive index difference Δn. Therefore, the refractive index difference between the modified waveguide portion (core) and the unmodified portion (cladding) is small. Consequently, the bending loss due to waveguide bending is large, and the waveguide cannot be bent at a high curvature. It is difficult to reduce the size of the device. Furthermore, for modulation light sources mounted on head-mounted displays such as AR glasses, a size that converges to the size of the glasses string is required. However, in the bulk crystal type optical modulator as shown in Patent Document 2, it is difficult to miniaturize the optical modulator to that size.

[0014] Compared to using a portion of modified lithium niobate single crystal B1 as a modulator for an optical waveguide, in Figure 36 As shown in (b), when a convex Fridge, which is processed from a single-crystal lithium niobate film F epitaxially grown on a substrate such as sapphire, is used as a modulator for an optical waveguide, it is suitable for miniaturization because the convex portion is smaller than that of a Ti diffused optical waveguide, the entire area around the convex portion is equivalent to a cladding, and if the surrounding material is appropriately selected, the refractive index difference Δn can be increased, and the light loss when the optical waveguide is bent into a curved shape is smaller than that of a bulk lithium niobate single crystal.

[0015] In addition, in patent document 2 Figure 7The present invention discloses an optical module 100, which modularizes a light source unit 311 and a modulator 30 as constituent units, and emits light that has been externally modulated by the modulator 30 without directly modulating the light source unit 311. As with the optical module 100 disclosed in Patent Document 2, when an optical module with a structure that combines red (R), green (G), and blue (G) lasers output from the modulator 30 is used as a constituent element of an optical engine, as will be described later, the optical system becomes larger, making it difficult to miniaturize the size of the optical engine.

[0016] In addition, in order to display an image in the desired color, the intensity of each of the three colors of visible light (RGB) needs to be modulated independently and at high speed. However, if this modulation is performed only by a light source or only by a light modulator, the load on the IC that controls these modulations will increase.

[0017] The present invention was made in view of the above-mentioned technical problems, and its object is to provide a small and low-power light source unit that can be mounted on AR glasses, VR glasses, etc., and an optical engine, smart glasses, optical communication transmitting device, and optical communication system including the light source.

[0018] In order to solve the above-mentioned technical problems, the present invention provides the following technical means.

[0019] A light source unit according to a first aspect of the present invention includes: a light source section having an optical semiconductor element; a first electrical signal generating element that generates an electrical signal for controlling the current driving the optical semiconductor element; an optical modulation element having a Mach-Zehnder type optical waveguide formed by processing a lithium niobate film into a convex shape, and electrodes for applying an electric field to the Mach-Zehnder type optical waveguide; and a second electrical signal generating element that generates an electrical signal for controlling the voltage that operates the optical modulation element. The optical semiconductor element is optically connected to the optical modulation element, and the first electrical signal generating element and the second electrical signal generating element are synchronously connected. The intensity of light emitted from the optical modulation element is varied by current modulation controlled by the first electrical signal generating element and voltage modulation controlled by the second electrical signal generating element.

[0020] In the light source unit described above, the first electrical signal generating element and the second electrical signal generating element may also be formed on a common semiconductor substrate.

[0021] In the light source unit described above, the minimum value of the change in light intensity caused by the first electrical signal generating element may be greater than the minimum value of the change in light intensity caused by the second electrical signal generating element.

[0022] In the light source unit described above, the minimum value of the change in light intensity caused by the second electrical signal generating element may be greater than the minimum value of the change in light intensity caused by the first electrical signal generating element.

[0023] In the light source unit described above, the peak wavelength of the optical semiconductor element can also be visible light ranging from 380 nm to 830 nm.

[0024] In the light source unit described above, the peak wavelength of the optical semiconductor element can also be near-infrared light of 830nm to 2000nm.

[0025] The light source unit described above can also have multiple optical modules formed by optically connecting the optical semiconductor element and the optical modulation element, and the multiple optical modules are controlled independently.

[0026] In the light source unit described above, light emitted from the light modulation elements of different optical modules of the plurality of optical modules may also be emitted from different outlets.

[0027] The light source unit described above can also have a multiplexing section for combining the light from different optical modules of the multiple optical modules, and the combined light from the multiplexing section is emitted from an outlet.

[0028] In the light source unit described above, the peak wavelength of the optical semiconductor element of the different optical modules can be visible light with a wavelength of 380nm to 830nm, and the light emitted from the emission port is visible light.

[0029] In the light source unit described above, the plurality of optical modules may include at least: a blue optical module with a peak wavelength of 380nm to 500nm for the optical semiconductor element; a green optical module with a peak wavelength of 500nm to 600nm for the optical semiconductor element; and a red optical module with a peak wavelength of 600nm to 830nm for the optical semiconductor element, having a visible light combining section where light from the red optical module, light from the green optical module, and light from the blue optical module are combined, and the combined visible light from the visible light combining section is emitted from a visible light emission port.

[0030] In the light source unit described above, it may also be a near-infrared light module that also has a near-infrared light with a peak wavelength of 830 nm or higher and a light semiconductor element, and has a near-infrared light emission port that emits the near-infrared light separately from the visible light emission port.

[0031] In the light source unit described above, it may also be a near-infrared light module with a peak wavelength of 830 nm or more for near-infrared light from a light semiconductor element, having a combining section for combining visible light emitted from the visible light combining section and near-infrared light emitted from the near-infrared light module, and the combined light from the combining section is emitted from an outlet.

[0032] The optical engine of the second aspect of the present invention comprises: a light source unit as described above; a light scanning mirror for scanning light emitted from the light source unit in different directions; and a control element for controlling the light scanning mirror.

[0033] The smart glasses of the third aspect of the present invention have the optical engine and eyeglass frame described above.

[0034] The optical communication transmitting device of the fourth aspect of the present invention has a light source unit of the above-described manner.

[0035] The optical communication system of the fifth aspect of the present invention includes: an optical communication transmitting device of the above-described aspect; and an optical communication receiving device having an optical signal receiving element for receiving light.

[0036] According to the present invention, a small and low-power light source unit that can be mounted on AR glasses, VR glasses, etc. can be provided. Attached Figure Description

[0037] Figure 1 This is a conceptual diagram of the light source unit in this embodiment.

[0038] Figure 2 This is a schematic top view of the light source unit in this embodiment.

[0039] Figure 3 Is Figure 2 A schematic diagram of the cross-section cut by the XX line.

[0040] Figure 4 Is Figure 2 A schematic diagram of the cross-section cut by the YY line.

[0041] Figure 5 This is a block diagram of the optical modulation element 200.

[0042] Figure 6 This is a graph showing the optical modulation curves in various Mach-Zehnder type optical waveguides.

[0043] Figure 7 This is a conceptual diagram illustrating two methods of adjusting light intensity by using current modulation of a light semiconductor element and voltage modulation of a light modulation element.

[0044] Figure 8This is a conceptual diagram of a control method in an image forming apparatus having a light source unit according to this embodiment, where image forming is performed.

[0045] Figure 9 This is a conceptual diagram of a control method in an image forming apparatus having a light source unit according to this embodiment, where image forming is performed.

[0046] Figure 10 This is a schematic top view of a light source unit with a wave combiner.

[0047] Figure 11 The diagrams schematically represent (a) an MMI type multiplexer, (b) a Y-type multiplexer, and (c) a directional coupler.

[0048] Figure 12 This is the first structural example used to make the output ratio of each color of light close to 1:1:1.

[0049] Figure 13 This is a second structural example used to make the ratio of light output of each color close to 1:1:1.

[0050] Figure 14 This is the third structural example used to make the output ratio of each color of light close to 1:1:1.

[0051] Figure 15 This is a schematic top view of a Mach-Zehnder type optical waveguide with a bend.

[0052] Figure 16 This is a top view schematically illustrating a light source unit in another embodiment.

[0053] Figure 17 This is a planar schematic diagram used to illustrate the stray light removal section.

[0054] Figure 18 It is along Figure 17 A cross-sectional view taken along line A-A'.

[0055] Figure 19 It is along Figure 17 A cross-sectional view taken along line B-B'.

[0056] Figure 20 This is a cross-sectional view showing another example of the shape of the groove.

[0057] Figure 21 This is a cross-sectional view showing another example of the formation of the light-absorbing layer.

[0058] Figure 22 This is a top view of the optical modulation element in another embodiment, viewed from above.

[0059] Figure 23This is a top view of the optical modulation element in another embodiment, viewed from above.

[0060] Figure 24 This is a top view of the optical modulation element in another embodiment, viewed from above.

[0061] Figure 25 It is along Figure 24 A cross-sectional view taken along line C-C'.

[0062] Figure 26 This is a top view of the optical modulation element in another embodiment, viewed from above.

[0063] Figure 27 This is a conceptual diagram illustrating the optical engine used in this embodiment.

[0064] Figure 28 This is a conceptual diagram illustrating a scenario where an image is directly projected onto the retina using a laser emitted from the light source unit of this embodiment.

[0065] Figure 29 (a) is a schematic diagram of an optical engine without a combiner in the modulation element, and (b) is a schematic diagram of an optical engine of this embodiment with a combiner in the light source unit.

[0066] Figure 30 This is a conceptual diagram illustrating the optical communication transmitting device and the visible light signal generated by the transmitting device in this embodiment.

[0067] Figure 31 This is a block diagram of the optical communication system of this embodiment.

[0068] Figure 32 This is a block diagram illustrating a modified example of the communication system of this embodiment.

[0069] Figure 33 This is a diagram illustrating an example of the use of the information terminal in this embodiment.

[0070] Figure 34 This is another example of the use of the information terminal in this embodiment.

[0071] Figure 35 This is another example of the use of the information terminal in this embodiment.

[0072] Figure 36 (a) is a conceptual diagram illustrating a modulator that uses a modified portion of a single crystal of bulk lithium niobate as an optical waveguide, and (b) is a conceptual diagram illustrating a modulator that uses a protrusion formed by processing a single-crystal lithium niobate film as an optical waveguide.

[0073] Explanation of symbols

[0074] 10-1, 10-2, 10-3 Mach-Zehnder type optical waveguides

[0075] 11, 12 Optical waveguides

[0076] 30, 30-1, 30-2, 30-3, 6030 optical semiconductor components

[0077] 40-1, 40-2, and 6013 electrical signal generating elements

[0078] 50 Combined Wave Department

[0079] 100 Light Source Department

[0080] 115 groove section

[0081] 200, 201, 202, 203, 204, 205, 6200 optical modulation elements

[0082] 1000, 1000A, 1001, 1010 light source units

[0083] 2001 Optical System

[0084] 3001 optical scanning mirror

[0085] 5001 Optical Engine

[0086] 6001, 6001A, 6001a Optical Communication Transmitting Devices

[0087] 6002 and 6002A Optical Communication Receivers

[0088] 7001 and 7001A optical communication systems. Detailed Implementation

[0089] The present invention will now be described in detail with appropriate reference to the accompanying drawings. In the following description, the drawings used are sometimes enlarged representations of features for ease of understanding and convenience, and the dimensions and ratios of the constituent elements may differ from the actual dimensions. The materials, dimensions, etc., illustrated in the following description are examples, and the present invention is not limited thereto; it can be implemented with appropriate modifications within the scope of achieving the effects of the present invention.

[0090] [Light source unit]

[0091] Figure 1 This is a conceptual diagram of the light source unit in this embodiment. Figure 2 This is a schematic top view illustrating the light source unit of this embodiment. Figure 2 The image depicts only a portion of the electrodes used to impart a phase difference to the Mach-Zehnder type optical waveguide. Figure 3 Is Figure 2 A schematic diagram of the cross-section cut by the XX line. Figure 4 Is Figure 2 A schematic diagram of the cross-section cut by the YY line.

[0092] Figure 1 The light source unit 1000 shown includes: a light source section 100 having an optical semiconductor element 30; a first electrical signal generating element 40-1 that generates an electrical signal for controlling the current driving the optical semiconductor element 30; an optical modulation element 200 having an electrode formed by processing a lithium niobate film into a convex shape as an electrode, and applying an electric field to the Mach-Zehnder type optical waveguide 10; and a second electrical signal generating element 40-2 that generates an electrical signal for controlling the voltage that operates the optical modulation element 200. The optical semiconductor element 30 is configured such that emitted light can be incident on the entrance of the waveguide, that is, the optical semiconductor element 30 is optically connected to the optical modulation element 200, and the first electrical signal generating element 40-1 and the second electrical signal generating element 40-2 can be connected synchronously. Figure 1 The symbol A in the figure, through the current controlled by the first electrical signal generating element 40-1 and the voltage controlled by the second electrical signal generating element 40-2, causes the intensity of the light emitted from the optical modulation element 200 to change.

[0093] The first electrical signal generating element 40-1 and the second electrical signal generating element 40-2 can synchronize the timing of their respective modulation signals to control the modulation of the intensity of the light emitted from the optical modulation element 200.

[0094] In the light source unit 1000, the intensity of light emitted from the light modulation element 200 can be modulated by overlapping the current modulation of the driving light semiconductor element 30 performed by the first electrical signal generating element 40-1 and the voltage modulation of the light modulation element 200 operated by the second electrical signal generating element 40-2. Therefore, compared with a structure that changes the intensity of light emitted from the modulation element solely through current modulation of the driving light semiconductor element or solely through voltage modulation of the light modulation element, the load on each analog IC (electrical signal generating element) is suppressed. For example, when changing the color at a high frequency of 1 GHz to obtain a pixel resolution of 2560×1460, if this is handled by one analog IC (electrical signal generating element), modulation at a high frequency of GHz is required, but if two analog ICs (electrical signal generating elements) are used, modulation at frequencies of several tens of MHz is sufficient.

[0095] This structure requires two types of analog ICs (electrical signal generating elements), but if Figure 1 As shown, by having them on a common substrate 1 and assembling them into a single chip, the overall system can be simplified. Substrate 1 can be any substrate capable of forming an analog IC, such as a semiconductor substrate like silicon.

[0096] In order to stabilize the oscillation of the optical semiconductor element (laser), low-frequency modulation can be implemented using the first electrical signal generating element 40-1, and high-frequency modulation can be implemented using the second electrical signal generating element 40-2.

[0097] Figure 2 The light source unit 1000 shown includes three optical modules 500 formed by optical semiconductor element 30 and optical modulation element 200 optically connected. That is, the light source unit 1000 has an optical module 500-1 formed by optical semiconductor element 30-1 and optical modulation element 200-1 optically connected, an optical module 500-2 formed by optical semiconductor element 30-2 and optical modulation element 200-2 optically connected, and an optical module 500-3 formed by optical semiconductor element 30-3 and optical modulation element 200-3 optically connected.

[0098] Figure 2 The light source unit 1000 shown is a structure that includes 3 light modules 500, but the number is not limited; it can be 1, 2, or more than 4.

[0099] Optical modules 500-1, 500-2, and 500-3 can be controlled independently. Specifically, optical semiconductor elements 30-1, 30-2, and 30-3 can each control the current modulation driven independently by the first electrical signal generating element 40-1. Furthermore, optical modulation elements 200-1, 200-2, and 200-3 can each control the voltage modulation operated independently by the second electrical signal generating element 40-2. Moreover, in each of the optical modules 500-1, 500-2, and 500-3, modulation can be performed independently and synchronously by the first and second electrical signal generating elements 40-1 and 40-2, causing variations in the intensity of light emitted from each optical modulation element.

[0100] In addition, Figure 2 In order to facilitate the observation of features, only the optical modulation element 200-1 is depicted for the electrodes used to impart an electric field to the Mach-Zehnder type optical waveguide; the optical modulation elements 200-2 and 200-3 are not depicted.

[0101] In the light source unit 1000, optical semiconductor elements 30-1, 30-2, and 30-3 are mounted on a sub-carrier (base) 120, and Mach-Zehnder type optical waveguides 10-1, 10-2, and 10-3 are formed on a substrate 140 (see reference). Figure 4 ).

[0102] In the light source unit 1000, by using a convex optical waveguide formed from a single-crystal lithium niobate thin film, the size of the optical waveguide can be reduced to less than 1 mm, enabling miniaturization of the light source unit. Furthermore, since a highly insulating external modulator is controlled by voltage, almost no current is required for intensity modulation. It operates with the minimum necessary current for laser emission, resulting in low power consumption.

[0103] From the perspective of miniaturization, the advantages of using lithium niobate films in the fabrication of optical waveguides are further described compared to using bulk lithium niobate single crystals in the fabrication of optical waveguides.

[0104] When using bulk lithium niobate single crystals in the fabrication of optical waveguides, Ti-diffused waveguides diffuse Ti into the bulk lithium niobate single crystal, creating a portion with a higher refractive index than the surrounding original single crystal. In contrast, when using lithium niobate films in the fabrication of optical waveguides, the lithium niobate film is processed to create a convex portion of the optical waveguide. This convex portion is smaller in size compared to Ti-diffused waveguides.

[0105] Furthermore, when using bulk lithium niobate single crystals, the refractive index difference Δn between the Ti-diffused waveguide (core) and its surrounding single-crystal portion (cladding) is small. This is because the refractive index difference Δn is formed only by adding a small amount of Ti to the bulk lithium niobate single crystal. In contrast, when using a lithium niobate film, the entire periphery of the convex portion (core) corresponds to the cladding, so the refractive index difference Δn can be increased by appropriately selecting the surrounding materials (sapphire substrate and side / top surface materials of the waveguide). As a result, the optical waveguide can be bent with high curvature, and the length dimension can be further reduced through this bending. Moreover, the interaction length can be extended while reducing the overall size, thus reducing the driving voltage.

[0106] (Optical semiconductor devices)

[0107] As the optical semiconductor element 30, various laser elements can be used. For example, commercially available red, green, blue, and near-infrared laser diodes (LDs) can be used. Red light can use light with a peak wavelength of 600 nm or more and 830 nm or less; green light can use light with a peak wavelength of 500 nm or more and 600 nm or less; and blue light can use light with a peak wavelength of 380 nm or more and 500 nm or less. Furthermore, near-infrared light can use light with a peak wavelength of 830 nm or more and 2000 nm or less.

[0108] exist Figure 2In the light source unit 1000 shown, optical semiconductor elements 30-1, 30-2, and 30-3 are respectively configured as LDs emitting blue light, green light, and red light. LDs 30-1, 30-2, and 30-3 are arranged at intervals from each other in a direction approximately orthogonal to the emission direction of the light emitted from each LD, and are disposed on the upper surface 121 of the sub-carrier 120. Hereinafter, for any constituent element symbol Z, common content among constituent elements of symbols Z-1, Z-2, ..., ZK will sometimes be uniformly referred to as symbol Z. The aforementioned K is a natural number of 2 or greater.

[0109] exist Figure 2 The light source unit 1000 shown illustrates a case with three optical semiconductor elements, but it is not limited to three; two or more are acceptable. These optical semiconductor elements can be those emitting light with all different wavelengths, or they can be those emitting light with the same wavelength. Furthermore, the emitted light can be any light other than red (R), green (G), and blue (B). The arrangement order of red (R), green (G), and blue (B) shown in the accompanying drawings is not required and can be appropriately changed.

[0110] Optical semiconductor elements 30-1, 30-2, and 30-3 are each independently connected to the first electrical signal generating element 40-1, which generates an electrical signal for controlling the drive current.

[0111] The first electrical signal generating element 40-1 and the second electrical signal generating element 40-2, which generates an electrical signal for controlling the voltage that makes the optical modulation element 200 work, are connected together to the synchronization signal generating device 45. They can make the timing of each modulation signal consistent according to the synchronization signal emitted from the synchronization signal generating device 45, and make the intensity of the light emitted from the optical modulation element 200 change.

[0112] The LD30 can be mounted on the sub-carrier 120 via a bare die. The sub-carrier 120 is made of, for example, aluminum nitride (AlN), aluminum oxide (Al2O3), silicon (Si), etc. Figure 4As shown, metal layers 75 and 76 are provided between the sub-carrier 120 and the LD30. The sub-carrier 120 and the LD30 are connected via metal layers 75 and 76. Known methods can be used to form metal layers 75 and 76 without particular limitation; known methods such as sputtering, vapor deposition, and paste coating of metals can be employed. Metal layers 75 and 76 may contain, for example, one or more metals selected from gold (Au), platinum (Pt), silver (Ag), lead (Pb), indium (In), nickel (Ni), titanium (Ti) and tantalum (Ta), tungsten (W), alloys of gold (Au) and tin (Sn), tin (Sn)-silver (Ag)-copper (Cu) solder alloys (SAC), SnCu, InBi, SnPdAg, SnBiIn, and PbBiIn, or may be composed of one or more metals selected from the above.

[0113] As for substrate 140, there is no particular limitation as long as the substrate has a lower refractive index than the lithium niobate film constituting the Mach-Zehnder type optical waveguide, but a substrate capable of forming a single-crystal lithium niobate film as an epitaxial film is preferred, preferably a sapphire single-crystal substrate or a silicon single-crystal substrate. The crystal orientation of the single-crystal substrate is not particularly limited. For example, a c-axis oriented lithium niobate film has a 3-fold symmetry, so it is preferable that the single-crystal substrate of the substrate also has the same symmetry. In the case of a sapphire single-crystal substrate, a substrate with the c-plane is preferred, and in the case of a silicon single-crystal substrate, a substrate with the (111)-plane is preferred.

[0114] like Figure 4 As shown, the entrance port 61 of the incident path 13 of each Mach-Zehnder type optical waveguide 10 is opposite to the exit port 31-1 of each LD 30. Light emitted from the exit surface 31 of the LD 30 is positioned to be incident on the incident path 13. Each LD 30 is optically connected to each Mach-Zehnder type optical waveguide 10. The axis JX-1 of the incident path 13 approximately overlaps with the optical axis AXR of the laser LR emitted from the exit port 31-1 of the LD 30. With this structure and configuration, blue, green, and red light emitted from LD 30-1, 30-2, and 30-3 can be incident on the incident path 13 of each Mach-Zehnder type optical waveguide 10.

[0115] like Figure 4 As shown, the sub-carrier 120 can be configured to be directly bonded to the substrate 140 via metal layers 93 (first metal layer 71, second metal layer 72, and third metal layer 73). According to this structure, further miniaturization is possible by eliminating spatial coupling and fiber optic coupling.

[0116] In this embodiment, the side surface 122 of the sub-carrier 120 opposite to the substrate 140 (first side surface) and the side surface 42 of the substrate 140 opposite to the sub-carrier 120 (second side surface) are connected via a first metal layer 71, a second metal layer 72, a third metal layer 73, and an anti-reflective film 81. The melting point of the metal layer 75 is higher than that of the third metal layer 73.

[0117] The first metal layer 71 is formed in contact with the side surface 122 by sputtering or evaporation, and may contain one or more metals selected from gold (Au), platinum (Pt), silver (Ag), lead (Pb), indium (In), nickel (Ni), titanium (Ti), and tantalum (Ta), or may be composed of one or more metals selected from the above. Preferably, the first metal layer 71 contains at least one metal selected from gold (Au), platinum (Pt), silver (Ag), lead (Pb), indium (In), and nickel (Ni). The second metal layer 72 is formed in contact with the side surface 42 by sputtering or evaporation, and may contain one or more metals selected from, for example, titanium (Ti), tantalum (Ta), and tungsten (W), or may be composed of one or more metals selected from the above. Preferably, the second metal layer 72 is made of tantalum (Ta). The third metal layer 73 is located between the first metal layer 71 and the second metal layer 72, and may contain one or more metals selected from aluminum (Al), copper (Cu), AuSn, SnCu, InBi, SnAgCu, SnPdAg, SnBiIn, and PbBiIn, or may be composed of one or more metals selected from the above. Preferably, the third metal layer 73 uses AuSn, SnAgCu, or SnBiIn.

[0118] The thickness of the first metal layer 71, i.e., the magnitude of the first metal layer 71 in the y-direction, is, for example, 0.01 μm or more and 5.00 μm or less. The thickness of the second metal layer 72, i.e., the magnitude of the second metal layer 72 in the y-direction, is, for example, 0.01 μm or more and 1.00 μm or less. The thickness of the third metal layer 73, i.e., the magnitude of the third metal layer 73 in the y-direction, is, for example, 0.01 μm or more and 5.00 μm or less. Furthermore, the thickness of the third metal layer 73 is preferably greater than the thicknesses of the first metal layer 71 and the second metal layer 72. In this structure, the aforementioned effects of the first metal layer 71, the second metal layer 72, and the third metal layer 73 are well manifested, and the penetration of the material of the first metal layer 71 into the substrate 40 and the reduction of the adhesion strength between the metal layers can be suppressed. The thicknesses of the first metal layer 71, the second metal layer 72, and the third metal layer 73 are measured, for example, using a spectrophotometer.

[0119] The first metal layer 71, without contacting the metal layer 75, is disposed over approximately the entire area of ​​the side surface 122 opposite to the substrate 140 or the optical modulation structure layer 150. The front ends, i.e., the upper ends, of the second metal layer 72 and the third metal layer 73 in the z-direction reach, for example, the same position as the upper end of the first metal layer 71 in the z-direction. The rear ends, i.e., the lower ends, of the second metal layer 72 and the third metal layer 73 in the z-direction reach, for example, the same position as the lower ends of the sub-carrier 20, the first metal layer 71, and the substrate 140. When viewed along the y-direction, the first metal layer 71 is formed to be larger than the sub-carrier 20 in the x-direction.

[0120] As described above, it is preferable that the area of ​​the first metal layer 71, i.e., the size of the plane including the x and z directions, is approximately the same as the area of ​​the second metal layer 72 and the third metal layer 73, and its lower end reaches the same position as the lower end of the sub-carrier 120. In such a structure, the connection strength of the sub-carrier 120 relative to the substrate 140 can be maximized. That is, for example, even when the LD30 and the sub-carrier 120 are each connected to the internal electrode pads corresponding to each LD30 using wire bonding, the connection between the sub-carrier 120 and the substrate 140 can be prevented from being released. In addition, by making the lower ends of the sub-carrier 20, the first metal layer 71, the second metal layer 72, the third metal layer 73 and the substrate 140 reach the same position, the heat dissipation path from the sub-carrier 120 can be increased. Furthermore, the area of ​​the first metal layer 71 can also be smaller than the area of ​​the second metal layer 72 and the third metal layer 73.

[0121] In the light source unit 1000, an anti-reflective film 81 is provided between the LD30 and the light modulation structure layer 150. For example, the anti-reflective film 81 is integrally formed on the side surface 42 of the substrate 140 and the incident surface 151 of the light modulation structure layer 150. However, the anti-reflective film 81 may also be formed only on the incident surface 151 of the light modulation structure layer 150.

[0122] The antireflective film 81 is a film used to prevent incident light from the light modulation structure layer 150 from being reflected in a direction opposite to the direction it enters from the incident surface 151, and to improve the transmittance of the incident light. The antireflective film 81 is, for example, a multilayer film formed by alternately stacking various dielectrics at predetermined thicknesses corresponding to the wavelengths of red, green, and blue light, which are incident light. Examples of such dielectrics include titanium oxide (TiO2), tantalum oxide (Ta2O5), silicon oxide (SiO2), and aluminum oxide (Al2O3).

[0123] The exit surface 31 of the LD30 and the incident surface 151 of the light modulation structure layer 150 are arranged at a predetermined interval. The incident surface 151 and the exit surface 31 are opposite each other, and a gap 70 exists between the exit surface 31 and the incident surface 151 in the y-direction. Since the light source unit 1000 is exposed to air, the gap 70 is filled with air. Because the gap 70 is filled with the same gas (air), it is easy for light of various colors emitted from the LD30 to enter the incident path in a state that meets the predetermined coupling efficiency. When the light source unit 1000 is used for AR glasses or VR glasses, if the light intensity required by the AR glasses or VR glasses is changed, the size of the gap 70 in the y-direction is, for example, greater than 0 μm and less than 5 μm.

[0124] (Mach-Zehnder type optical waveguide)

[0125] In a Mach-Zehnder type optical waveguide, a beam with the same wavelength and phase is split (wave splitting) into two pairs of beams, each with a different phase, and then combined (wave combining). Depending on the phase difference, the intensity of the combined beam changes.

[0126] The optical modulation element 200 has three Mach-Zehnder type optical waveguides 10-1, 10-2, and 10-3, the same number as the optical semiconductor elements 30-1, 30-2, and 30-3. The optical semiconductor elements 30-1, 30-2, and 30-3 and the Mach-Zehnder type optical waveguides 10-1, 10-2, and 10-3 are positioned such that light emitted from the optical semiconductor elements is incident on the corresponding Mach-Zehnder type optical waveguides.

[0127] Figure 2 The Mach-Zehnder type optical waveguide 10 (10-1, 10-2, 10-3) shown has a first optical waveguide 11, a second optical waveguide 12, an input path 13, an output path 14, a branch 15, and a junction 16. Figure 2 The first optical waveguide 11 and the second optical waveguide 12 shown are linear structures extending in the x-direction, except near the branch portion 15 and the junction portion 16, but are not limited to such structures. Figure 2 The first optical waveguide 11 and the second optical waveguide 12 shown are approximately the same length. A branch 15 is located between the input path 13 and the first optical waveguide 11 and the second optical waveguide 12. The input path 13 is connected to the first optical waveguide 11 and the second optical waveguide 12 via the branch 15. A junction 16 is located between the first optical waveguide 11 and the second optical waveguide 12 and the output path 14. The first optical waveguide 11 and the second optical waveguide 12 are connected to the output path 14 via the junction 16.

[0128] The Mach-Zehnder type optical waveguide 10 includes ridges (convex shapes) protruding from the first surface 40a of a slab layer 40 made of lithium niobate, namely, a first optical waveguide 11 and a second optical waveguide 12. Hereinafter, the slab layer 40 made of lithium niobate and the ridges 11 and 12 made of lithium niobate are sometimes referred to together as a lithium niobate film. The first surface 40a is the upper surface of the lithium niobate film excluding the ridges. The two ridges (the first ridge and the second ridge) protrude from the first surface 40a in the z-direction and extend along the Mach-Zehnder type optical waveguide 10. In this embodiment, the first ridge functions as the first optical waveguide 11, and the second ridge functions as the second optical waveguide 12.

[0129] Figure 3 The XX cross section (the cross section perpendicular to the direction of light travel) of the ridge (first optical waveguide 11 and second optical waveguide 12) shown is rectangular in shape, and the width (Wridge) in the y direction is, for example, more than 0.3 μm and less than 5.0 μm, and the height of the ridge (the protrusion height H (=Tslab-TLN) protruding from the first surface 40a) is, for example, more than 0.1 μm and less than 1.0 μm.

[0130] The shape of the ridges (first optical waveguide 11 and second optical waveguide 12) can be any shape that can guide light, and their shape is not limited. For example, they can be dome-shaped or triangular.

[0131] The planar layer 40 made of lithium niobate is, for example, a lithium niobate film with a c-axis orientation. The planar layer 40 made of lithium niobate is, for example, an epitaxial film epitaxially grown on a substrate 140. An epitaxial film is a single-crystal film with a uniform crystal orientation across the substrate. An epitaxial film is a film with a single crystal orientation in the z-direction and xy-plane directions, with the crystal uniformly oriented in the x-axis, y-axis, and z-axis directions. Whether it is an epitaxial film can be confirmed, for example, by confirming the peak intensity and poles at the orientation position in 2θ-θ X-ray diffraction. Alternatively, the lithium niobate film 40 can also be a lithium niobate film disposed on a Si substrate with SiO2 as a barrier.

[0132] Lithium niobate is a compound represented by LixNbAyOz. A is an element other than Li, Nb, and O. Examples of elements represented by 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. These elements can be used individually or in combination of two or more. x represents a number between 0.5 and 1.2. x is preferably a number between 0.9 and 1.05. y represents a number between 0 and 0.5. z represents a number between 1.5 and 4.0. z is preferably a number between 2.5 and 3.5.

[0133] (electrode)

[0134] Electrodes 21 and 22 are electrodes for applying a modulation voltage Vm to each Mach-Zehnder type optical waveguide 10-1, 10-2, 10-3 (hereinafter sometimes simply referred to as "each Mach-Zehnder type optical waveguide 10"). Electrode 21 is an example of the first electrode, and electrode 22 is an example of the second electrode. The first end 21a of electrode 21 is connected to the second electrical signal generating element 40-2, and the second end 21b is connected to the terminating resistor 132. The first end 22a of electrode 22 is connected to the second electrical signal generating element 40-2, and the second end 22b is connected to the terminating resistor 132.

[0135] The second electrical signal generating element 40-2 is a driving circuit 210 that applies the modulation voltage Vm to each Mach-Zehnder type optical waveguide 10. Figure 5 Part of ).

[0136] The second electrical signal generating element 40-2, together with the first electrical signal generating element 40-1, is connected to the synchronization signal generating device 45. It can make the timing of each modulation signal consistent according to the synchronization signal emitted from the synchronization signal generating device 45, and make the intensity of the light emitted from the optical modulation element 200 change.

[0137] Electrodes 23 and 24 are electrodes for applying a DC bias voltage Vdc to each Mach-Zehnder type optical waveguide 10. The first terminal 23a of electrode 23 and the first terminal 24a of electrode 24 are connected to power supply 133. Power supply 133 is part of a DC bias application circuit 220 that applies the DC bias voltage Vdc to each Mach-Zehnder type optical waveguide 10.

[0138] exist Figure 2 In this design, for ease of observation, the linewidth and spacing of the parallel-configured electrodes 21 and 22 are made wider than they actually are. Therefore, the lengths (interaction lengths) of the portions where electrode 21 overlaps with the first optical waveguide 11 and the portions where electrode 22 overlaps with the second optical waveguide 12 appear different, but their lengths (interaction lengths) are approximately the same. Similarly, the lengths (interaction lengths) of the portions where electrode 23 overlaps with the first optical waveguide 11 and the portions where electrode 24 overlaps with the second optical waveguide 12 are approximately the same.

[0139] Alternatively, if a DC bias voltage Vdc is applied to electrodes 21 and 22, electrodes 23 and 24 may not be required. Alternatively, grounding electrodes may be provided around electrodes 21, 22, 23, and 24.

[0140] Electrodes 21, 22, 23, and 24 are located on the flat plate layer 40 and the ridges 11 and 12 made of lithium niobate, separated by a buffer layer 32. Electrodes 21 and 23 are capable of applying an electric field to the first optical waveguide 11. Electrodes 21 and 23 are located at positions that overlap with the first optical waveguide 11 when viewed from above in the z-direction. Electrodes 21 and 23 are located above the first optical waveguide 11. Electrodes 22 and 24 are capable of applying an electric field to the second optical waveguide 12. Electrodes 22 and 24 are located at positions that overlap with the second optical waveguide 12 when viewed from above in the z-direction. Electrodes 22 and 24 are located above the second optical waveguide 12.

[0141] A buffer layer 32 is located between each Mach-Zehnder type optical waveguide 10 and electrodes 21, 22, 23, and 24. The protective layer 31 and the buffer layer 32 cover and protect the ridges. Furthermore, the buffer layer 32 prevents light propagating in each Mach-Zehnder type optical waveguide 10 from being absorbed by electrodes 21, 22, 23, and 24. The refractive index of the buffer layer 32 is lower than that of the lithium niobate film 40. The protective layer 31 and the buffer layer 32 are, for example, SiInO, SiO2, Al2O3, MgF2, La2O3, ZnO, HfO2, MgO, Y2O3, CaF2, In2O3, or mixtures thereof. The protective layer 31 and the buffer layer 32 can be the same material or different materials. When different materials are used, appropriate selection can be made from the viewpoints of improving DC drift, reducing Vπ, and reducing propagation loss.

[0142] The size of the optical modulation element 200, including the Mach-Zehnder type optical waveguide 10, is, for example, 100 mm. 2 The following applies if the size of the optical modulation element 200 is 100mm. 2 The following are suitable for use as AR glasses or VR glasses.

[0143] The optical modulation element 200, including the Mach-Zehnder type optical waveguide 10, can be fabricated using known methods. For example, the optical modulation element 200 can be fabricated using semiconductor processes such as epitaxial growth, photolithography, etching, vapor phase growth, and metallization.

[0144] Figure 5 This is a block diagram of the optical modulation element 200.

[0145] The control unit 240 of the optical modulation element 200 includes a drive circuit 210, a DC bias application circuit 220, and a DC bias control circuit 230.

[0146] The driving circuit 210 applies a modulation voltage Vm corresponding to the modulation signal Sm to the Mach-Zehnder type optical waveguide 10. The DC bias application circuit 220 applies a DC bias voltage Vdc to the Mach-Zehnder type optical waveguide 10. The DC bias control circuit 230 monitors the output light Lout and controls the DC bias voltage Vdc output from the DC bias application circuit 220. The operating point Vd is controlled by adjusting this DC bias voltage Vdc.

[0147] The optical modulator 200 converts an electrical signal into an optical signal. The optical modulator 200 modulates the input light Lin, emitted from the optical semiconductor element 30 and input through the input path 13 of the Mach-Zehnder type optical waveguide 10, into an output light Lout. The modulation operation of the optical modulator 200 will be explained.

[0148] The input light Lin emitted from the optical semiconductor element 30 and input through the input path 13 branches into the first optical waveguide 11 and the second optical waveguide 12. The phase difference between the light propagating in the first optical waveguide 11 and the light propagating in the second optical waveguide 12 is zero at the time of branching.

[0149] Next, a voltage is applied between electrodes 21 and 22. For example, differential signals with the same absolute value, opposite signs, and no phase shift can also be applied to electrodes 21 and 22 respectively. The refractive indices of the first optical waveguide 11 and the second optical waveguide 12 vary according to electro-optical effects. For example, the refractive index of the first optical waveguide 11 changes by +Δn from the reference refractive index n, and the refractive index of the second optical waveguide 12 changes by -Δn from the reference refractive index n.

[0150] The difference in refractive index between the first optical waveguide 11 and the second optical waveguide 12 creates a phase difference between the light propagating in the first optical waveguide 11 and the light propagating in the second optical waveguide 12. The light propagating in the first optical waveguide 11 and the second optical waveguide 12 merges in the output path 14 and is output as the output light Lout. The output light Lout is the light resulting from the overlap of the light propagating in the first optical waveguide 11 and the light propagating in the second optical waveguide 12. The intensity of the output light Lout varies according to the odd multiple of the phase difference between the light propagating in the first optical waveguide 11 and the light propagating in the second optical waveguide 12. Through this process, the Mach-Zehnder type optical waveguide 10 modulates the input light Lin into the output light Lout according to an electrical signal.

[0151] Electrodes 21 and 22, used for applying the modulation voltage to the optical modulation element 200, apply a modulation voltage Vm corresponding to the modulation signal. The voltage applied to electrodes 23 and 24, used for applying the DC bias voltage, i.e., the DC bias voltage Vdc output from the DC bias application circuit 220, is controlled by the DC bias control circuit 230. The DC bias control circuit 230 adjusts the operating point Vd of the optical modulation element 200 by controlling the DC bias voltage Vdc. The operating point Vd is the voltage that forms the center of the modulation voltage amplitude.

[0152] use Figure 6 The optical modulation curves of each Mach-Zehnder type optical waveguide 10 are explained. Figure 6 This is a graph showing the relationship between DC bias voltage and output for Mach-Zehnder type optical waveguides that do not have a structure that generates a phase difference between the two optical waveguides (first optical waveguide 11 and second optical waveguide 12) and for Mach-Zehnder type optical waveguides that have a structure that generates a phase difference between the two optical waveguides. Figure 6 The horizontal axis represents the DC bias voltage applied to electrodes 23 and 24, and the vertical axis represents the normalized output value from the Mach-Zehnder type optical waveguide 10. The output is normalized to "1" when the phase difference between the light propagating in the first optical waveguide 11 and the light propagating in the second optical waveguide 12 is zero. Solid lines represent the characteristics of Mach-Zehnder type optical waveguides without a phase difference structure, while dashed lines represent the characteristics of Mach-Zehnder type optical waveguides with a phase difference structure.

[0153] In a Mach-Zehnder type optical waveguide that does not have a structure that generates a phase difference, when no voltage is applied (Vdc = 0), light of the same phase passing through the two optical waveguides interferes with each other at the junction 16 and enhances each other, so that the output of the Mach-Zehnder type optical waveguide becomes the maximum value.

[0154] (Methods for adjusting light intensity)

[0155] In this embodiment, the light source unit uses current modulation of the light-directing semiconductor element and voltage modulation of the light-directing modulation element to change the intensity of the emitted light.

[0156] Figure 7 This diagram conceptually illustrates two examples of methods for adjusting light intensity by using both current modulation of an optical semiconductor element and voltage modulation of an optical modulation element. In the diagram, the symbol LD represents the optical semiconductor element, and the symbol LN represents the optical modulation element. Figure 7 This is an example of two adjustment methods: coarse adjustment and fine adjustment, which are performed using LD and LN respectively.

[0157] Figure 7 The vertical axis of (a)(b) represents the light intensity emitted from the light source unit.

[0158] Figure 7 (a) is a method that combines adjusting large changes in light intensity by the LD and adjusting small changes in light intensity by the LN. That is, it is a coarse adjustment step that uses the current driving the LD to adjust the light intensity, and a fine adjustment step that uses the voltage that makes the LN work to adjust the light intensity. In this case, the minimum value of the change in light intensity caused by the first electrical signal generating element is greater than the minimum value of the change in light intensity caused by the second electrical signal generating element.

[0159] This situation involves coarse adjustments using current and fine adjustments using voltage.

[0160] on the other hand, Figure 7 (b) is a method that combines adjusting large changes in light intensity by the LN and adjusting small changes in light intensity by the LD. That is, it involves a coarse adjustment step using the voltage that operates the LN to adjust the light intensity, and a fine adjustment step using the current that drives the LD to adjust the light intensity. In this case, the minimum change in light intensity caused by the second electrical signal generating element is greater than the minimum change in light intensity caused by the first electrical signal generating element.

[0161] This situation involves coarse adjustments using voltage and fine adjustments using current.

[0162] Voltage-based fine-tuning offers good responsiveness, so it is the preferred choice when responsiveness is a key consideration. Figure 7 (a) is a method of using both.

[0163] On the other hand, when fine-tuning is done using current, a lower current is sufficient, thus suppressing power consumption. Therefore, when power consumption suppression is a priority, it is preferable to... Figure 7 (b) The method of using both.

[0164] Next, the control method of dividing coarse adjustment and fine adjustment into LD and LN for control will be explained in more detail using the attached diagram.

[0165] Figure 8 and Figure 9 This is a conceptual diagram of a control method in an image forming apparatus having a light source unit according to this embodiment, in which an image is formed by scanning a laser beam and changing the light intensity (hue) for each pixel.

[0166] like Figure 8As shown in (a), the laser beam (LB) is scanned over time to cover the entire image area. The laser beam moves across the image at various points (pixels) according to time, thus changing the color of the laser over time. Creating an image requires a specified amount of time, but since it cannot keep up with the speed of the human eye, it is perceived as an image. The scanning speed of the laser beam is generally around 100–500 MHz (a speed that switches the entire image about 60 times per second).

[0167] Hue is changed by altering the intensity of the three colors of light: red (R), green (G), and blue (B). For example, by changing the intensity of each color in 8-bit red, 8-bit green, and 8-bit blue, the resulting combined color is a 24-bit hue (approximately 16.77 million colors) (24-bit color scheme). That is, in 24-bit color, each of the RGB colors has 8 bits of information, capable of being reproduced to 256 gray levels. The total number of reproducible color combinations is 256 to the power of 3. In this scheme, the image for each of the RGB colors is a collection of pixels with 256 gray level data.

[0168] Figure 8 (b) is a graph with time on the horizontal axis and the hue of the combined RGB 3 colors on the vertical axis.

[0169] Figure 9 This diagram illustrates the concept of coarse and fine adjustments made using LD and LN, using the example of changing the hue of red (R) in 8 bits.

[0170] Figure 9 The three curves shown are all curves with time on the horizontal axis and the combined RGB 3 colors on the vertical axis. They represent coarse adjustment by each pixel through 4-bit current modulation of the LD and fine adjustment by 4-bit voltage modulation of the LN. By merging them, an 8-bit red hue can be obtained.

[0171] The same applies to green (G) and blue (B) hues. By merging the RGB light, a 24-bit color image can be obtained.

[0172] In addition, Figure 9 The control method uses LD for coarse adjustment and LN for fine adjustment. However, in principle, a color image can also be obtained using the control method of using LN for coarse adjustment and LD for fine adjustment.

[0173] The methods for sharing the burden of LD current modulation and LN voltage modulation through coarse and fine adjustments can be arbitrarily adopted.

[0174] For example, in the case of images with high contrast, it is preferable to perform coarse adjustments by LD current modulation and fine adjustments by LN voltage modulation.

[0175] On the other hand, in the case of monotonous images, from the viewpoint of power consumption, it is preferable to perform coarse adjustment by LN voltage modulation and fine adjustment by LD current modulation.

[0176] In addition, when there are both high-contrast and monotonous parts, a switching device can be provided to switch the adjustment mode between them, so that image formation can be performed while switching the adjustment mode.

[0177] (combination department)

[0178] like Figure 10 As shown, the light source unit 1010 may also have a combining section 50 in the optical modulation element 200 for combining the modulated light from the three Mach-Zehnder type optical waveguides. The combining section 50 combines the light propagating in the output path 14E-2 of the Mach-Zehnder type optical waveguide 10-2 and the light propagating in the output path 14E-3 of the Mach-Zehnder type optical waveguide 10-3, and emits the light from the output port 150a via the output waveguide 51. Since the structure is not separate from the modulator as in Patent Document 2, the resolution, color perception, etc. are improved. When the light emitted from each optical modulation element 200-1, 200-2, 200-3 is visible light, the combining section is sometimes referred to as a visible light combining section, and the output port after combining is sometimes referred to as a visible light output port.

[0179] In the case where the light source unit 1010 does not have a wave combiner 50, refer to Figure 1 In each of the Mach-Zehnder type optical waveguides 10-1, 10-2, and 10-3 of each optical modulation element 200-1, 200-2, and 200-3, the light combined by each junction 16 is emitted from its respective outlet.

[0180] The multiplexer 50 can be selected from an MMI (Multi-Mode Interferometer) type multiplexer (see reference). Figure 11 (a)(b)), Y-shaped combiner (see reference) Figure 11 (c)) and directional coupler (see reference) Figure 11 Any one of (d)).

[0181] Figure 11 (a) The multiplexing section 50 shown is a multiplexing section 50A that multiplexes the light propagating in the output path 14E-1 of the Mach-Zehnder type optical waveguide 10-1, the light propagating in the output path 14E-2 of the Mach-Zehnder type optical waveguide 10-2, and the light propagating in the output path 14E-3 of the Mach-Zehnder type optical waveguide 10-3. The light multiplexed by the multiplexing section 50A is output to the output waveguide 51.

[0182] in addition, Figure 11 (b) The multiplexing section 50 is composed of a multiplexing section 50B-1 that first multiplexes the light propagating in the output path 14E-1 of the Mach-Zehnder type optical waveguide 10-1 and the light propagating in the output path 14E-2 of the Mach-Zehnder type optical waveguide 10-2, and a multiplexing section 50B-2 that then multiplexes the light output from the multiplexing section 50B-1 and propagating in the output path 14E-3 of the Mach-Zehnder type optical waveguide 10-3. The light multiplexed from the multiplexing section 50B-2 is output to the output waveguide 51.

[0183] in addition, Figure 11 (c) The multiplexing section 50 is composed of a multiplexing section 50C-1 that first multiplexes the light propagating in the output path 14E-1 of the Mach-Zehnder type optical waveguide 10-1 and the light propagating in the output path 14E-2 of the Mach-Zehnder type optical waveguide 10-2, and a multiplexing section 50C-2 that then multiplexes the light output from the multiplexing section 50C-1 and propagating in the output path 14E-3 of the Mach-Zehnder type optical waveguide 10-3. The light multiplexed from the multiplexing section 50C-2 is output to the output waveguide 51.

[0184] in addition, Figure 11 (d) The wave combiner 50 is composed of a directional coupling section 50D-1 that first couples light propagating in the output path 14E-1 of the Mach-Zehnder type optical waveguide 10-1 with light propagating in the output path 14E-2 of the Mach-Zehnder type optical waveguide 10-2, and a directional coupling section 50D-2 that then couples the combined light with light propagating in the output path 14E-3 of the Mach-Zehnder type optical waveguide 10-3. The coupled and combined light is output from the directional coupling section 50C-2 to the output waveguide 51.

[0185] The light source unit 1010 may also have a controller (not shown) that controls the current value injected into each of the three optical semiconductor elements 30 so that the peak output of each wavelength in the light emitted to the outside through the three Mach-Zehnder type optical waveguides 10 is in a predetermined ratio. Since it also depends on the user, the application, and the sensitivity of human color perception (most sensitive to green), it is possible to appropriately select a method in which the peak output of each wavelength is in a predetermined ratio.

[0186] It is known that side surface roughness during the etching process is the primary cause of light loss in optical waveguides. Furthermore, it is known that the shorter the wavelength, the greater the light loss caused by this side surface roughness. That is, when the light propagating in the optical waveguide is blue (B), green (G), and red (R), the magnitude of the light loss is known to be B > G > R.

[0187] Therefore, the light source unit 1010 can also set the current values ​​injected into the three optical semiconductor elements 30 to constant values, so that the peak output of each wavelength in the light emitted to the outside through the three Mach-Zehnder optical waveguides 10 (10⁻¹, 10⁻², 10⁻³) is configured in a predetermined ratio. By setting the current driving the laser to the same value at each wavelength, a simple driver can be used, resulting in a simple circuit and further miniaturization.

[0188] Assuming that the three Mach-Zehnder waveguides have identical structures and the light loss caused by side roughness does not depend on the color of the light propagating in the waveguide, the output ratio of each color of light (or, in the case of a combiner, the output ratio of each color of light) is R:G:B = 1:1:1. However, since the light loss caused by side roughness depends on the color of the light propagating in the waveguide, the difference in light loss caused by side roughness can be compensated by making the structures of the three Mach-Zehnder waveguides different from each other.

[0189] In addition, depending on the application, sometimes it is not R:G:B = 1:1:1, but rather a desired ratio. However, in such cases, the structure of three Mach-Zehnder type optical waveguides can be determined in a way that is a prescribed ratio.

[0190] Figures 12-14 This represents a structural example used to make the output ratio of each color of light (or, in the case of a multiplexing section, the output ratio of each color of light that is multiplexed) approximately R:G:B = 1:1:1.

[0191] Figure 12 The structure shown is a three-wavelength Mach-Zehnder waveguide 10 (10-1, 10-2, 10-3) structure. The length of the waveguide from the incident end 13a to the exit end 14a is shorter for shorter wavelengths of light. Even if the side roughness of the ridges is the same, the propagation loss is greater for shorter wavelengths, which is a unique technical problem of ridge waveguide structures. By shortening the length of the waveguide of the shorter wavelength side, the propagation loss at all wavelengths can be made consistent.

[0192] According to this structure, the output ratio of each color of light (or, in the case of a multiplexing section, the output ratio of each color of light that is multiplexed) can be made close to R:G:B = 1:1:1.

[0193] exist Figure 12 In the structure shown, the output path 14 is set to different lengths, but the input path 13 can also be set to different lengths. Alternatively, the input path 13 and the output path 14 can be set to different lengths.

[0194] Figure 13 The structure shown is as follows: In each of the three Mach-Zehnder type optical waveguides 10 (10-1, 10-2, 10-3), the optical waveguide from the incident end 13a to the exit end 14a has a light-absorbing section 14A (14Aa, 14Ab, 14Ac) made of a material that absorbs the wavelength of the propagating light. The shorter the wavelength of the propagating light in the Mach-Zehnder type optical waveguide, the shorter the length of the light-absorbing section 14A in the longitudinal direction. According to this structure, the propagation loss at each wavelength can also be made uniform.

[0195] According to this structure, the output ratio of each color of light (or, in the case of a multiplexing section, the output ratio of each color of light that is multiplexed) can be made close to R:G:B = 1:1:1.

[0196] exist Figure 13 The structure shown has a light absorption section 14A in the output path 14, but it can also have a light absorption section 14A in the input path 13, or it can have a light absorption section 14A in both the input path 13 and the output path 14.

[0197] Figure 14 The structure shown is as follows: In each of the three Mach-Zehnder type optical waveguides 10 (10-1, 10-2, 10-3), the waveguide from the incident end 13a to the exit end 14a includes a curved portion 13B (13Ba, 13Bb, 13Bc). The shorter the wavelength of the propagating light in the Mach-Zehnder type optical waveguide, the greater the curvature of the curved portion 13B and the shorter the length of the curved portion 13B. According to this structure, the propagation loss at each wavelength can also be made uniform.

[0198] According to this structure, the output ratio of each color of light (or, in the case of a multiplexing section, the output ratio of each color of light that is multiplexed) can be made close to R:G:B = 1:1:1.

[0199] exist Figure 14 The structure shown is a Mach-Zehnder type optical waveguide where the curvature of the bent portion 13B is greater and the length of the bent portion 13B is shorter for shorter wavelengths of light. However, it can also be either a Mach-Zehnder type optical waveguide where the curvature of the bent portion 13B is greater or the length of the bent portion 13B is shorter for shorter wavelengths of light.

[0200] exist Figure 14The structure shown has a bend 13B in the input path 13, but it can also have a bend 13B in the output path 14. Alternatively, it can have a bend 13B in both the input path 13 and the output path 14.

[0201] The maximum value of each light output emitted through three Mach-Zehnder type optical waveguides 10 (10-1, 10-2, 10-3) can also be the same intensity.

[0202] like Figure 15 As shown, each Mach-Zehnder type optical waveguide 10' (10-1', 10-2', 10-3') may have a bend 10A, 10B, 10C. In the Mach-Zehnder type optical waveguide, the bend can be provided in any one of the following: a portion of the two-mode waveguides 11 and 12 (the portion shown by symbols 10B and 10C), the incident path (the portion shown by symbol 10A), or the exit path.

[0203] The structure of an optical waveguide formed by processing a single-crystal lithium niobate thin film formed on a substrate into a convex shape can impart a high refractive index difference between the core (single-crystal lithium niobate thin film) and the cladding (the side and top surface materials of the substrate and the optical waveguide), enabling the optical waveguide to be bent with high curvature. By bending, the length dimension can be further reduced. In addition, the interaction length can be extended while reducing the overall size, thus reducing the driving voltage.

[0204] Figure 16 This is a top view schematically illustrating a light source unit in another embodiment.

[0205] Figure 16 The light source unit 1020 shown is Figure 2 The light source unit 1000 shown Figure 10 The difference in the light source unit 1010 shown is that it also has an optical module 500-4, which has a light semiconductor element 30-4 that emits near-infrared light, for a total of 4 optical modules.

[0206] Figure 16 The light source unit 1020 shown includes: an optical module 500-1 formed by optically connecting a visible light semiconductor element 30-1 and an optical modulation element 200-1; an optical module 500-2 formed by optically connecting a visible light semiconductor element 30-2 and an optical modulation element 200-2; an optical module 500-3 formed by optically connecting a visible light semiconductor element 30-3 and an optical modulation element 200-3; and an optical module 500-4 formed by optically connecting a near-infrared light semiconductor element 30-4 and an optical modulation element 200-4.

[0207] Figure 16The light source unit 1020 shown has a structure with one optical module that emits near-infrared light, but the number is not limited and multiple modules can be used. In addition, when multiple optical modules emit near-infrared light, the peak wavelength of the near-infrared light emitted from each optical module can be different.

[0208] Optical modules 500-1, 500-2, 500-3, and 500-4 can be controlled independently. Specifically, optical semiconductor elements 30-1, 30-2, 30-3, and 30-4 can each control the current modulation driven independently by the first electrical signal generating element 40-1A. Furthermore, optical modulation elements 200-1, 200-2, and 200-3 can each control the voltage modulation operated independently by the second electrical signal generating element 40-2A. Moreover, in each of the optical modules 500-1, 500-2, 500-3, and 500-4, modulation can be performed independently and synchronously by the first and second electrical signal generating elements 40-1A and 40-2A, causing variations in the intensity of light emitted from each optical modulation element.

[0209] In addition, Figure 16 In order to facilitate the observation of features, only the optical modulation element 200-1 is depicted for the electrodes used to impart an electric field to the Mach-Zehnder type optical waveguide; the optical modulation elements 200-2, 200-3, and 200-4 are not depicted.

[0210] exist Figure 16 In the light source unit 1020 shown, the light module 500-1 can be set as a blue light module with a light semiconductor element 30-1 having a peak wavelength of 380nm to 500nm, the light module 500-2 can be set as a green light module with a light semiconductor element 30-2 having a peak wavelength of 500nm to 600nm, and the light module 500-3 can be set as a red light module with a light semiconductor element 30-2 having a peak wavelength of 600nm to 830nm.

[0211] In this configuration, blue light from blue light module 500-1, green light from green light module 500-2, and red light from red light module 500-3 are combined at the visible light combining section 50, and the combined visible light is emitted from the visible light emission port 150a. Additionally, near-infrared light from light module 500-4 is emitted from another emission port (near-infrared light emission port) 150b.

[0212] Near-infrared light emitted from outlet 150b can, for example, be used as light for eye tracking in smart glasses equipped with light source unit 1020. In this case, the near-infrared light can be used without current modulation or voltage modulation.

[0213] Figure 16 The light source unit 1020 shown is configured to have an emission port for visible light and an emission port for near-infrared light, respectively, and emit visible light and near-infrared light from different emission ports. However, it can also be configured to include a wave combining section for combining visible light and near-infrared light, and emit visible light and near-infrared light from one emission port.

[0214] (Strray Light Propagation Prevention Department)

[0215] In the optical modulation element 200, a groove may be provided in a portion other than the Mach-Zehnder type optical waveguide, extending from the element surface to the substrate on which the Mach-Zehnder type optical waveguide is formed, and a light-absorbing layer is provided at least on the bottom and side surfaces of the groove. By preventing light from propagating to the cladding portion, stray light can be removed, and color perception can be improved, etc.

[0216] This is to prevent stray light propagating in the portion of the optical modulation element 200 containing the substrate from escaping to the outside. Although the optical modulation element 200 can be miniaturized, due to miniaturization, components of light not coupled to the optical waveguide are easily generated during the alignment process of the optical axis. Such light components propagate outside the optical waveguide within the optical modulation element 200, and after multiple reflections at the end face, a portion enters the photodetector, easily generating so-called stray light. Stray light propagating within the optical modulation element 200 hinders the alignment of the photodetector, potentially leading to increased connection loss and poor connection. Especially when using visible light as the light source, the optical waveguide becomes smaller, so the impact of stray light is significant. Therefore, as a stray light removal section, it is preferable to include a groove and a light-absorbing layer formed on its surface.

[0217] The stray light removal section will be described using a structure with a groove 115 near the optical waveguide 11 as an example. Figure 17 This is a schematic top view representing the structure. Figure 18 It is along Figure 17 A cross-sectional view taken along line A-A'. Figure 19 It is along Figure 17 A cross-sectional view taken along line B-B'.

[0218] like Figure 17As shown, in the optical modulation element 201, a groove 115 is formed near the optical waveguide 111. The groove 115 is formed on a portion of both sides of the optical waveguide 111. The groove 115 is rectangular, for example, a rectangle when viewed from above the substrate. In addition, the groove 115 is formed as an inverted trapezoidal shape in the cross-sectional shape of the thickness direction (stack direction) t of the light source unit 1000, and the side surface 115a of the groove 115 is formed as an inclined surface that is inclined relative to the thickness direction t.

[0219] The groove 115 is formed such that it extends from the surface 32a of the buffer layer 32 toward the substrate 140 to a depth greater than one side 140a of the substrate 140. That is, the bottom surface 115b of the groove 115 is formed at a position where it enters the interior of the substrate from one side 140a of the substrate 140, and the substrate 140 is recessed in the thickness direction t at the part where the groove 115 is formed.

[0220] Furthermore, in this embodiment, the side surface 115a of the groove 115 is an inclined surface that is inclined at a predetermined angle θ relative to the thickness direction t, but for example, it can also be as follows: Figure 20 As shown, the groove 115 is formed as a rectangle with a cross-sectional shape that is the thickness direction t of the light source unit 1000, and the side surface 115a of the groove 115 is formed as a vertical surface along the thickness direction t.

[0221] The depth of the portion of substrate 140 into the groove 115 cut from one side 140a of substrate 140 along the thickness direction t, i.e., the gap d between one side 140a of substrate 140 and the bottom surface of the groove 115, can be set according to the wavelength of the light propagating in the optical waveguide 111. That is, the gap d can be set to more than half the wavelength of the light propagating in the optical waveguide 111. For example, if the wavelength of the light propagating in the optical waveguide 111 is 520 nm, the groove 115 can be formed with a gap d of 260 nm or more.

[0222] Between the two grooves 115, a substrate 140, a lithium niobate layer with an optical waveguide 111 formed in a ridge shape, and a buffer layer 32 are formed extending from the bottom surface 115b of the groove 115 in a dike-like manner with a narrower width.

[0223] A light-absorbing layer 116 is formed in the groove 115, covering the bottom surface 115b and the side surface 115a of the groove 115. In this embodiment, the light-absorbing layer 116 is formed to cover not only the bottom surface 115b and the side surface 115a of the groove 115, but also the surface 32a of the buffer layer 32. Alternatively, the light-absorbing layer 116 may also have a structure that does not cover the surface 32a of the buffer layer 32.

[0224] The light-absorbing layer 116 is made of a material that absorbs light propagating in the optical waveguide 111. The material constituting the light-absorbing layer 116 is selected according to the wavelength of the light propagating in the optical waveguide 111. For example, when the light propagating in the optical waveguide 111 is visible light, a material capable of absorbing and blocking light in the visible light wavelength region can be used, such as a resin material including visible light absorbing pigments, a resin material containing visible light absorbing pigments such as C, Si, Ge, anthocyanin compounds, azo compounds, diphenylmethane compounds, and triphenylmethane compounds, or oxides or nitrides made of semiconductors such as In and Ga, Ti, Ni, Cr, Fe, Nb, Ta, Zn, W, Mo, or alloys thereof. Furthermore, for example, when the light propagating in the optical waveguide 111 is infrared light, a material capable of absorbing and blocking light in the infrared wavelength region can be used, such as a resin material containing infrared absorbing pigments such as anthocyanin compounds, diammonium compounds, and squaric acid compounds.

[0225] The light absorption layer 116 only needs to be formed to a thickness of, for example, more than 50% of the stray light P incident on the light absorption layer 116, so that the stray light P is absorbed during the passage of the light absorption layer 116 formed on one side 115a of the groove portion 115 and the light absorption layer 116 formed on the other side 115a.

[0226] In addition to being formed with a predetermined thickness on the bottom surface 115b and side surface 115a of the groove 115 as in this embodiment, the light absorption layer 116 can also be formed, for example, as in this embodiment. Figure 21 As shown in the diagram. In Figure 21 In this structure, a light-absorbing layer 116 is formed by filling the entire groove 115, which includes the bottom surface 115b and the side surface 115a. By adopting this structure, stray light P can be absorbed more reliably.

[0227] In the optical modulation element 201 according to the above-described structure, for example, during the alignment process of aligning the optical axis between the light source (light emitter) S that introduces light into the optical waveguide 111 and the input end IN of the optical waveguide 111, light components that are not coupled to the optical waveguide 111 are sometimes generated. These light components that are not coupled to the optical waveguide 111 become stray light P propagating in portions other than the optical waveguide 111 within the light source unit 1000, such as near one side 140a of the substrate 140 and in the buffer layer 32. In the optical modulation element 201 of this embodiment, when such stray light P reaches the formation position of the groove portion 115, the stray light P is absorbed by the light absorption layer 116.

[0228] In particular, stray light P propagating near one side 140a of the substrate 140 is reliably absorbed by the light absorption layer 116 formed therein because the groove 115 is formed along the thickness direction t to a position deeper than one side 140a of the substrate 140.

[0229] Stray light P is absorbed and blocked by the groove 115 and the light absorption layer 116 formed in the groove 115, so that stray light P will not enter the photodetector (not shown) disposed at the output end OUT of the optical waveguide 111. Therefore, in the alignment process, alignment that hinders the photodetector can be prevented, and connection loss and poor connection can be prevented.

[0230] Furthermore, stray light P can also be blocked by appropriately setting the tilt angle θ of the side surface 115a of the slot 115. For example, when stray light P is incident from the buffer layer 32 toward the space (air layer) of the slot 115, if the refractive index of air is set to 1 and the refractive index of the buffer layer 32 is set to approximately 3.5, due to this refractive index difference, total internal reflection occurs at the interface when the incident angle of stray light P at the interface between the buffer layer 32 and the air is approximately 15° or more. The case where the incident angle of stray light P toward the side surface 115a of the slot 115 is 15° or more is when the tilt angle θ of the side surface 115a is ±15° or more. In this case, the reflectivity of stray light P is 100%, and stray light P is completely emitted toward the upper or lower side of the light source unit 1000 and is removed.

[0231] Next, other embodiments of the optical modulation element 202 will be described. Furthermore, in the following embodiments, structures identical to those described above will be labeled with the same reference numerals, and repeated descriptions will be omitted.

[0232] Figure 22 This is a top view of the optical modulation element in another embodiment, viewed from above.

[0233] In this embodiment, the optical modulation element has multiple slots (five in this embodiment) 125A, 125B, 125C, 125D, and 125E formed separately on both sides of the optical waveguide 111 along its extension direction. On one side 140a of the substrate 140 (see reference 140a) viewed from above... Figure 19 When ), each groove 125A to 125E is formed into a rectangle (rectangle) with the same shape.

[0234] In this embodiment, the grooves 125A to 125E are formed in such a way that the intervals G1 between grooves 125A and grooves 125B, G2 between grooves 125B and grooves 125C, G3 between grooves 125C and grooves 125D, and G4 between grooves 125D and grooves 125E are all different.

[0235] Furthermore, the sum of the intervals between any two slots 125A to 125E is different from the sum of the intervals between any two slots 125A to 125E. For example, the sum of interval G1 + interval G3 is different from the sum of interval G2 + interval G4. Also, for example, the sum of interval G2 + interval G3 + interval G4 is different from the sum of interval G1 + interval G3 + interval G4.

[0236] If multiple slots 125A to 125E are arranged regularly at equal intervals, there is a concern that stray light will be enhanced by regular reflection. However, by making the intervals between adjacent slots 125A to 125E different as in this embodiment, it is possible to prevent stray light from being enhanced by regular reflection. The multiple slots 125A to 125E and the light absorption layer 116 covering them can reliably absorb and block stray light P.

[0237] Next, another embodiment of the optical modulation element 203 will be described. Furthermore, in the following embodiments, structures identical to those in the above embodiments will be labeled with the same reference numerals, and repeated descriptions will be omitted.

[0238] Figure 23 This is a top view of the optical modulation element in another embodiment, viewed from above.

[0239] In this embodiment, the optical modulation element 203 has multiple slots (five in this embodiment) 135A, 135B, 135C, 135D, and 135E formed at equal intervals on both sides of the optical waveguide 111 along its extension direction. Each slot 135A to 135E is located on one side 140a of the substrate 140 (see reference 140a). Figure 19 When it forms a rectangle, it becomes a rectangle.

[0240] In this embodiment, the grooves 135A to 135E are formed in such a way that the widths W1 to W5 of each groove 135A to groove 135E along the extension direction of the optical waveguide 111 are all different.

[0241] Furthermore, the sum of the widths W1 to W5 of any of the slots 135A to 135E is different from the sum of the widths W1 to W5 of any other slot 135A to 135E. For example, the sum of width W1 + width W3 is different from the sum of width W2 + width W4. Also, for example, the sum of width W1 + width W3 + width W5 is different from the sum of width W1 + width W2 + width W4.

[0242] If the widths of the multiple slots 135A to 135E are equal, there is a concern that stray light will be amplified by regular reflection. However, as in this embodiment, by making the widths of adjacent slots 135A to 135E different, it is possible to prevent stray light from being amplified by regular reflection. The multiple slots 135A to 135E and the light absorption layer 116 covering them can reliably absorb and block stray light P.

[0243] Next, another embodiment of the optical modulation element 204 will be described. Furthermore, in the following embodiments, structures identical to those in the above embodiments will be labeled with the same reference numerals, and repeated descriptions will be omitted.

[0244] Figure 24 This is a top view of the optical modulation element in another embodiment, viewed from above. Figure 25 It is along Figure 24 A cross-sectional view taken along line C-C'.

[0245] In the optical modulation element 204 of this embodiment, the optical waveguide 111 is composed of a straight portion 111L extending in a straight line and a bent portion 111R bending from the straight portion 111L.

[0246] Therefore, in the two straight sections 111L, a plurality of grooves 145, 145... are formed on both sides of the straight section 111L, and the inner surface (side surface, bottom surface) of the groove 145 is covered by the light absorption layer 116.

[0247] Furthermore, at the connection between the straight portion 111L and the curved portion 111R of the optical waveguide 111, a plurality of grooves 145, 145... are also formed on the imaginary extension line Q1 of the straight portion 111L extending in a direction separate from the bending direction of the curved portion 111R. The inner surface (side surface, bottom surface) of the groove 145 is covered by the light absorption layer 116.

[0248] According to the optical modulation element 204 with such a structure, when light propagating in the optical waveguide 111 enters the curved portion 111R from the straight portion 111L, it bends along the curved portion 111R. Conversely, stray light P propagating in the substrate 140 and the buffer layer 32 does not bend at the formation position of the curved portion 111R and travels straight. Then, the straight stray light P is absorbed by a plurality of slots 145, 145... formed on the imaginary extension line Q1 of the straight portion 111L and the light absorption layer 116 covering them. Therefore, according to the optical modulation element 204 of this embodiment, the stray light P traveling straight at the formation position of the curved portion 11R of the optical waveguide 111 will not exit to the outside of the optical modulation element 204. For example, in the alignment process, it is possible to prevent obstruction of the alignment of the photodetector and prevent increased connection loss and poor connection.

[0249] Next, another embodiment of the optical modulation element 205 will be described. Furthermore, in the following embodiments, structures identical to those of the optical modulation element 204 described above will be labeled with the same reference numerals, and repeated descriptions will be omitted.

[0250] Figure 26 This is a top view of the optical modulation element 205 as seen from above.

[0251] In the optical modulation element 205 of this embodiment, the optical waveguide 111 is composed of a straight portion 111L extending in a straight line and a bent portion 111R bending from the straight portion 111L.

[0252] Therefore, in the two straight sections 111L, a plurality of grooves 155, 155... are formed on both sides of the straight section 111L, and the inner surface (side surface, bottom surface) of the groove 155 is covered by the light absorption layer 116.

[0253] Furthermore, a plurality of curved grooves 155, 155... are formed along the curved outer periphery of the curved portion 111R of the optical waveguide 111, and the inner surface (side and bottom surface) of the groove 155 is covered by the light absorption layer 116.

[0254] According to the optical modulation element 205 with such a structure, when light propagating in the optical waveguide 111 enters the curved portion 111R from the straight portion 111L, it bends along the curved portion 111R. In contrast, stray light P propagating in the substrate 110 and the buffer layer 32 does not bend at the formation position of the curved portion 111R and travels straight. Then, the straight stray light P is absorbed by a plurality of curved grooves 155, 155... formed along the curved outer periphery of the curved portion 111R and the light absorption layer 116 covering them.

[0255] As an example, according to the structure of this embodiment, for example, when the wavelength of the light incident on the optical waveguide 111 is 520 nm and the light absorption layer 116 is formed from a Si film, the light absorption coefficient of Si is 1.35 × 10⁵ cm⁻¹. Therefore, even if the thickness of the light absorption layer 116 is 100 nm, by arranging five slots 155, it is possible to attenuate the stray light to about 26% of its intensity before incident during the period when the stray light passes through all the light absorption layers 116 formed in the five slots 155 respectively.

[0256] Therefore, according to the optical modulation element 205 of this embodiment, stray light P traveling straight at the formation position of the bend 111R of the optical waveguide 111 will not be emitted to the outside of the optical modulation element 204. For example, in the core-aligning process, it can prevent the core-aligning of the photodetector from being obstructed, and prevent the increase of connection loss and the occurrence of poor connection.

[0257] (Optical engine)

[0258] In this specification, the optical engine is a device comprising: multiple light sources; an optical system including a combiner that combines multiple light rays emitted from the multiple light sources into a single light ray; a light scanning mirror that reflects light by changing its angle in a manner that displays an image of the light emitted from the optical system; and a control element that controls the light scanning mirror.

[0259] Figure 27 This is a conceptual diagram illustrating the optical engine 5001 used to explain this embodiment. The diagram shows the optical engine 5001 mounted on the frame 10010 of the glasses 10000. The symbol L represents image display light.

[0260] The optical engine 5001 includes a light source unit 1001 and a light scanning mirror 3001. The light source unit 1001 included in the optical engine 5001 is the light source unit of the embodiment described above.

[0261] As a light source unit 1001, it is a light source unit that can use three RGB light modules, including a red light module, a green light module, and a blue light module, and has a built-in wave combiner that makes the RGB light emitted from the RGB light modules a single beam.

[0262] like Figure 28 As shown, the laser light emitted from the light source unit 1001 mounted on the eyeglass frame is reflected by the light scanning mirror and enters the human eye, and the image is directly projected onto the retina.

[0263] In addition, as a light source unit 1001, in addition to the three RGB light modules (red light module, green light module, and blue light module), a light source unit with a built-in wave combiner can also be used. This wave combiner has a near-infrared light module, so that the RGB light emitted from the RGB light module and the light emitted from the near-infrared light module are combined into one.

[0264] In this structure, eye tracking is performed while the image is projected directly onto the retina.

[0265] The optical scanning mirror 3001 is, for example, a MEMS mirror. In order to project a 2D image, a 2-axis MEMS mirror that vibrates in a manner that reflects the laser by changing the angle in the horizontal direction (X direction) and the vertical direction (Y direction) is preferred.

[0266] The optical engine 5001 includes a collimating lens 2001a, a slit 2001b, and an ND filter 2001c, serving as an optical system for optically processing the laser emitted from the light source unit 1001. This optical system is one example, and other structures are also possible.

[0267] The optical engine 5001 has a laser driver 1100, an optical scanning mirror driver 1200, and a video controller 1300 that controls these drivers.

[0268] Figure 29 (a) is a schematic diagram of an optical engine A5001 (see Patent Document 2) that does not have a multiplexing section or multiplexer in the modulation element A1001. Figure 29 (b) is a schematic diagram of the optical engine 5001 of this embodiment, which has a wave combiner in the light source unit 1001.

[0269] exist Figure 29 In the optical engine 5001 shown in (b), three wavelengths are combined and output from the light source unit 1001, so each optical component is a single unit and can be miniaturized. In addition, since white is produced by a single beam point, it is easy to improve the resolution.

[0270] In contrast, Figure 29 In the optical engine A5001 shown in (a), there is no beam combiner or combiner in the modulation element A1001. Therefore, in order to emit white light, a beam point of 3 colors is required, which increases the size of the beam point and makes it difficult to improve the resolution. In addition, since a beam point of 3 colors is required, the design of the collimating lens A2001a, slit (or aperture) A2001b, ND filter A2001c, and 2-axis MEMS mirror A3001 becomes larger and more numerous, making it unsuitable for miniaturization.

[0271] (Transmitting device for optical communication)

[0272] One embodiment of the optical communication transmitting apparatus includes the light source unit of the above embodiment.

[0273] In this case, miniaturization and cost reduction can be achieved.

[0274] As light emitted from the light source unit, visible light and near-infrared light can be used.

[0275] When using visible light as the light emitted from the light source unit, it is possible to achieve a high speed in generating visible light signals.

[0276] With the increasing processing speed of computers and the accompanying improvement in information data processing capabilities, there is a desire for further high-speed communication in optical communication systems. However, in transmitting devices that generate visible light signals through internal modulation, there is a limit to shortening the switching time of the visible light source, making it difficult to achieve a high-speed generation of visible light signals.

[0277] Furthermore, as described in Patent Document 3, arranging visible light sources in an array increases the size of the device, making it potentially difficult to use in small information terminals such as smartphones. Additionally, arranging visible light sources in an array can complicate data processing. Moreover, using multiple light sources to improve data processing capabilities complicates the device's structure, resulting in very high costs. Therefore, applying such a structure to civilian transmission devices is impractical.

[0278] When using the optical communication transmitting apparatus of this embodiment, if visible light is used as the light emitted from the light source unit, the visible light signal can be generated quickly, and miniaturization and low cost can be achieved.

[0279] Figure 30 This is a conceptual diagram illustrating the optical communication transmitting apparatus and the visible light signal generated by the transmitting apparatus in this embodiment. The transmitting apparatus in this embodiment is a transmitting apparatus that transmits a visible light signal to a receiving apparatus.

[0280] The optical communication transmitting device 6001 of this embodiment includes a light source unit 1000A having an optical semiconductor element (laser) 6030 and an optical modulation element 6200, and an electrical signal generating element 6013. Hereinafter, the optical semiconductor element (laser) will sometimes be referred to as LD, and the optical modulation element as LN.

[0281] Laser 6030 emits visible light 1. Laser 6030 is set to a continuously on state. Furthermore, "continuous" means that laser 6030 is on while transmitting a visible light signal to the receiving device. The wavelength of the visible light 1 emitted by laser 6030 is typically in the range of 380 nm or higher and 830 nm or lower.

[0282] The electrical signal generating element 6013 receives the transmitted information data and outputs the information data as an electrical signal to the light source unit 1000A.

[0283] The light source unit 1000A generates a visible light signal 2 based on the electrical signal received from the electrical signal generating element 6013, through current modulation of the LD and voltage modulation of the LN. Alternatively, either current modulation of the LD or voltage modulation of the LN can be used to generate the visible light signal 2.

[0284] The optical modulator of the optical modulation element 6200 is a Mach-Zehnder type optical modulator. When generating the visible light signal 2 solely through voltage modulation of LN, the time required to modulate the visible light 1 into bright light 1a or dark light 1b using the Mach-Zehnder type optical modulator is shorter than the switching time of the visible light source. Therefore, the generation speed of the visible light signal 2 by the transmitting device 6001 is faster.

[0285] (Optical communication system)

[0286] Figure 31 This is a block diagram of an optical communication system according to one implementation method.

[0287] Figure 31 The optical communication system 7001 shown transmits the visible light signal 2 generated by the optical communication transmitting device 6001 to the optical communication receiving device 6002 via external space.

[0288] The transmitting device 6001 includes a laser 6030, an optical modulation element 6200, an electrical signal generating element 6013, and a visible light signal emission port 6014. In addition to the visible light signal emission port 6014, the transmitting device 6001 also includes... Figure 30 The transmitting device 6001 shown is the same. The visible light signal output port 6014 is connected to the optical modulation element 6200 and is used to radiate the visible light signal 2 generated by the optical modulation element 6200 into the external space.

[0289] The receiving device 6002 includes a visible light signal receiving unit 6021, a photoelectric conversion element 6022, and a visible light signal entrance 6024. The visible light signal entrance 6024 is used to receive the visible light signal 2 transmitted from the transmitting device 6001. The visible light signal receiving unit 6021 is connected to the visible light signal entrance 6024, receives the visible light signal 2 incident at the entrance 6024, and illuminates the photoelectric conversion element 6022. The photoelectric conversion element 6022 converts the visible light signal 2 into an electrical signal. The photoelectric conversion element 6022 can be any element capable of high-speed detection of the visible light signal 2 and conversion into an electrical signal; there are no particular limitations, and any type of element can be used.

[0290] The 7001 optical communication system performs visible light communication as follows.

[0291] In the transmitting device 6001, as described above, a visible light signal 2 is generated by the optical modulation element 6200. The generated visible light signal 2 is emitted into the external space via the visible light signal emission port 6014.

[0292] The emitted visible light signal 2 is received by the visible light signal receiving unit 6021 via the visible light signal input port 6024 of the receiving device 6002. The received visible light signal 2 is converted into an electrical signal by the photoelectric conversion element 6022, and the information data assigned to the visible light signal 2 is extracted.

[0293] According to the optical communication system 7001 of this embodiment, configured as described above, the intensity of the visible light signal 2 transmitted from the transmitting device 6001 is high, making it easy to visually confirm the communication path of the visible light signal 2. Therefore, data mistransmission can be prevented. In the case of communication systems using infrared light, it is impossible to visually confirm whether the visible light signal has been received in the receiving device at the destination. Therefore, there is a risk of transmitting to an unintended recipient. According to the optical communication system 7001 of this embodiment, which can achieve a data transmission rate of 10 Gbit / s or more per second, ranging from hundreds of Gbit / s to 1 Tbib / s, the amount of data that can be transmitted per second is also large, which is very convenient. On the other hand, the risk of transmitting data to the wrong recipient also increases. Therefore, visible light communication, which allows visual confirmation of whether a visible light signal has been transmitted to the destination, is a significant advantage from the viewpoint of preventing data mistransmission. In infrared light, which is not visible to the naked eye, there is always a sense of unease when transmitting data.

[0294] Furthermore, as an advantage of using visible light, its shorter wavelength compared to infrared light allows for a reduction in the size of the optical waveguide. This also allows for a reduction in the size of the optical modulator. Compared to infrared waveguides, visible light waveguides can reduce the size of each side by approximately 1 / 3 to 1 / 4, resulting in a reduction of the area by 1 / 9 to 1 / 16. This means that the number of components obtained on each substrate can be approximately 10 times greater, thus reducing the manufacturing cost of the optical modulator to 1 / 9 to 1 / 16. This enables consumer applications such as smartphones and other information terminals. Using infrared light, however, prevents a reduction in chip size. This increases the cost of the modulation element, making its use in consumer applications very difficult and impractical.

[0295] As mentioned above, the advantages of using visible light in high-speed optical communication can be summarized in the following two points.

[0296] (1) In high-speed optical communication, it is possible to send data after visually confirming the destination, and to safely send and receive large amounts of data.

[0297] (2) It can reduce the size of optical modulator components. As a result, the manufacturing cost of optical modulators can be reduced to less than 1 / 10. As a result, even in civilian applications, the advantages of ultra-high-speed communication can be enjoyed.

[0298] In the optical communication system of this embodiment, visible light signals can also use optical transmission units such as optical fibers.

[0299] Figure 32 This is a block diagram illustrating a variation of an optical communication system implemented in other ways.

[0300] Figure 32 The optical communication system 7001A shown is Figure 31 The difference in the communication system 7001 shown is that the visible light signal 2 generated by the transmitting device 6001A is transmitted to the receiving device 6002A via the optical fiber 6070.

[0301] exist Figure 32 In the optical communication system 7001A shown, the transmitting device 6001A includes a laser 6030, an optical modulation element 6200, an electrical signal generating element 6013, and an output optical fiber connector 6015. The output optical fiber connector 6015 is connected to the optical modulation element 6200 and the optical fiber 6070, and outputs the visible light signal 2 generated by the optical modulation element 6200 to the connector of the optical fiber 6070.

[0302] The receiving device 6002A includes a visible light signal receiving unit 6021, a photoelectric conversion element 6022, and an input optical fiber connector 6025. The input optical fiber connector 6025 is connected to the optical fiber 6070 and the visible light signal receiving unit 6021, and inputs the visible light signal 2 transmitted in the optical fiber 6070 to the visible light signal receiving unit 6021.

[0303] The 7001A optical communication system performs visible light communication as follows.

[0304] In the transmitting device 6001A, as described above, a visible light signal 2 is generated by the optical modulation element 6200. The generated visible light signal 2 is output to the optical fiber 6070 via the output optical fiber connector 6015. The output visible light signal 2 propagates in the optical fiber 6070 and is received by the visible light signal receiving unit 6021 via the input optical fiber connector 6025 of the receiving device 6002A. The received visible light signal 2 is converted into an electrical signal by the photoelectric conversion element 6022, and the information data assigned to the visible light signal 2 is extracted.

[0305] According to the communication system 7001A of this embodiment configured as described above, the visible light signal 2 generated by the transmitting device 6001A is transmitted to the receiving device 6002A via the optical fiber 6070, so for example, the visible light signal 2 can be transmitted to places where light does not pass through, such as rooms separated by walls.

[0306] Figure 33 This is a diagram illustrating an example of the use of the information terminal in this embodiment.

[0307] exist Figure 33 The internal components of smartphones 6091a and 6091b respectively include Figure 10The transmitting device 6001a and receiving device 6002 are shown. Smartphones 6091a and 6091b include a flat surface with a display and a side surface. The visible light signal output port 6014 of the transmitting device 6001a is exposed on one side surface, and the visible light signal input port 6024 of the receiving device 6002 is included on the flat surface with the display.

[0308] When transmitting data from smartphone 6091a to smartphone 6091b, a visible light signal 2 is transmitted with the visible light signal output port 6014 of smartphone 6091a facing the visible light signal input port 6024 of smartphone 6091b. Conversely, when transmitting data from smartphone 6091b to smartphone 6091a, a visible light signal 2 is transmitted with the visible light signal output port 6014 of smartphone 6091b facing the visible light signal input port 6024 of smartphone 6091a.

[0309] Figure 34 This is another example of the use of the information terminal in this embodiment.

[0310] exist Figure 34 The internal components of smartphones 6091c and 6091d respectively include Figure 10 The transmitting device 6001a and the receiving device 6002 are shown. Smartphones 6091c and 6091d include a flat surface and a side surface with a display, and the visible light signal output port 6014 of the transmitting device 6001a and the visible light signal input port 6024 of the receiving device 6002 are exposed on one side surface.

[0311] When data is transmitted between smartphones 6091c and 6091d, visible light signal 2 is transmitted when the visible light signal output port 6014 and visible light signal input port 6024 of smartphone 6091c are opposite to the visible light signal output port 6014 and visible light signal input port 6024 of smartphone 6091d.

[0312] Figure 35 This is another example of the use of the information terminal in this embodiment.

[0313] exist Figure 35 The 6091 smartphone contains the following components: Figure 10 The transmitting device 6001a and receiving device 6002 are shown. The smartphone 6091 includes a flat surface with a display and a side surface. The visible light signal emission port 6014 of the transmitting device 6001a is exposed on one side, and the visible light signal inlet port 6024 of the receiving device 6002 is included on the flat surface with the display. On the other hand, the personal computer 6092 includes... Figure 10The receiving device 6002 is shown. The visible light signal input port 6024 is exposed near the display of the personal computer 6092.

[0314] When transmitting data from smartphone 6091a to personal computer 6092, visible light signal 2 is transmitted while the visible light signal output port 6014 of smartphone 6091a is facing the visible light signal input port 6024 of personal computer 6092.

[0315] Figures 33-35 This is one example of the use of the information terminal in this embodiment, but the information terminal in this embodiment is not limited to this. For example, the information terminal may also be a tablet computer.

Claims

1. A light source unit, in, include: The light source section includes optical semiconductor elements; The first electrical signal generating element generates an electrical signal for controlling the current driving the optical semiconductor element; An optical modulation element comprising a Mach-Zehnder type optical waveguide formed by processing a lithium niobate film into a convex shape and electrodes for applying an electric field to the Mach-Zehnder type optical waveguide; and The second electrical signal generating element generates an electrical signal for controlling the voltage that operates the optical modulation element. The optical semiconductor element is optically connected to the optical modulation element. The first electrical signal generating element and the second electrical signal generating element can be connected synchronously. By switching between coarse and fine adjustments to share the current modulation controlled by the first electrical signal generating element and the voltage modulation controlled by the second electrical signal generating element, the intensity of the light emitted from the optical modulation element is varied. Coarse adjustment is performed by current modulation controlled by the first electrical signal generating element, and fine adjustment is performed by voltage modulation controlled by the second electrical signal generating element; or, fine adjustment is performed by current modulation controlled by the first electrical signal generating element, and coarse adjustment is performed by voltage modulation controlled by the second electrical signal generating element.

2. The light source unit as described in claim 1, wherein, The first electrical signal generating element and the second electrical signal generating element are formed on a common semiconductor substrate.

3. The light source unit as described in claim 1 or 2, wherein, The minimum change in light intensity caused by the first electrical signal generating element is greater than the minimum change in light intensity caused by the second electrical signal generating element.

4. The light source unit as described in claim 1 or 2, wherein, The minimum change in light intensity caused by the second electrical signal generating element is greater than the minimum change in light intensity caused by the first electrical signal generating element.

5. The light source unit as described in any one of claims 1 to 4, wherein, The peak wavelength of the optical semiconductor element is visible light with a wavelength of 380nm to 830nm.

6. The light source unit as described in any one of claims 1 to 4, wherein, The peak wavelength of the optical semiconductor element is near-infrared light with a wavelength of 830nm to 2000nm.

7. The light source unit as described in any one of claims 1 to 6, wherein, Multiple optical modules are formed by optically connecting the aforementioned optical semiconductor element and the aforementioned optical modulation element. The multiple optical modules are controlled independently.

8. The light source unit as described in claim 7, wherein, Light emitted from the optical modulation elements of different optical modules of the plurality of optical modules is emitted from different outlets.

9. The light source unit as described in claim 7, wherein, The light from the different optical modules of the plurality of optical modules is combined by a multiplexing section. The combined light, after passing through the combined section, is emitted from an outlet.

10. The light source unit as claimed in claim 9, wherein, The peak wavelength of the optical semiconductor element in the different optical modules is visible light in the range of 380nm to 830nm, and the light emitted from the outlet is visible light.

11. The light source unit as claimed in claim 7, wherein, The plurality of optical modules have at least: Blue light module with peak wavelength of 380nm~500nm for optical semiconductor elements; Green light modules with peak wavelengths of 500nm~600nm for optical semiconductor elements; and A red optical module with a peak wavelength of 600nm~830nm, a semiconductor optical element. The visible light from the red light module, the green light module, and the blue light module are combined by a visible light combining section, and the combined visible light from the visible light combining section is emitted from a visible light outlet.

12. The light source unit as claimed in claim 11, wherein, It also features a near-infrared light module with a peak wavelength of 830nm or higher for optical semiconductor elements. It has a near-infrared light emission port that emits near-infrared light, separate from the visible light emission port.

13. The light source unit as claimed in claim 11, wherein, It also features a near-infrared light module with a peak wavelength of 830nm or higher for optical semiconductor elements. A beam combining section that combines visible light emitted from the visible light combining section and near-infrared light emitted from the near-infrared light module, and the combined light from the beam combining section is emitted from an outlet.

14. An optical engine, wherein, have: The light source unit according to any one of claims 1 to 13; A light scanning mirror is used to scan the light emitted from the light source unit in different directions; and A control element for controlling the optical scanning mirror.

15. A type of smart glasses, wherein, It has the optical engine and eyeglass frame as described in claim 14.

16. A transmitting device for optical communication, wherein, Includes the light source unit according to any one of claims 1 to 13.

17. An optical communication system, in, include: The optical communication transmitting apparatus according to claim 16; and A receiving device for optical communication, which has an optical signal receiving element for receiving light.

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