Optical modulator, light source module, optical engine and augmented reality glasses

Abstract

The invention relates to an optical modulator, a light source module, an optical engine and augmented reality glasses, and provides a small visible light modulator capable of being driven at a low voltage. The optical modulator includes: a substrate; an optical waveguide layer comprising lithium niobate and having a Mach-Zehnder waveguide including a first ridge waveguide and a second ridge waveguide that transmit visible light; a buffer layer formed on the optical waveguide layer; a signal electrode formed on the buffer layer; the signal electrode and the first ridge waveguide are disposed so as to be offset from each other such that the distance between the center of the signal electrode in the width direction and the center of the first ridge waveguide in the width direction in the horizontal direction is 0.5 [mu] m or less. The second ground electrode and the second ridge waveguide are disposed such that the distance in the horizontal direction between the side surface of the second ground electrode closer to the second ridge waveguide and the center of the second ridge waveguide in the width direction is 2 [mu] m or less.

Description

Technical Field

[0001] The present invention relates to an optical modulator, a light source module, an optical engine, and an extended reality glasses. Background Art

[0002] In recent years, light source modules having an optical modulator for light to enter from a laser diode (semiconductor laser) have attracted attention. Such light source modules can be used in optical engines of glasses-type terminals such as AR (Augmented Reality) glasses and VR (Virtual Reality) glasses, small projectors, and the like.

[0003] For example, Patent Document 1 describes an image display device including a light source unit that emits first light and second light, an optical modulator having a modulation unit with a Mach-Zehnder type modulation method, and an optical scanner that spatially scans the first light and the second light modulated by the optical modulator. In addition, in Patent Document 1, a head-mounted display worn on a user's head is described as an image display device.

[0004] In addition, although not an image display device, Patent Document 2 describes a transmission device including a laser source that emits visible light and an optical modulator that changes the intensity of the visible light to generate a visible light signal. Patent Document 2 describes a Mach-Zehnder type optical modulator having a substrate, an optical waveguide layer, a buffer layer, and an electrode layer, and the optical waveguide layer is made of a lithium niobate film. In addition, Patent Document 2 discloses using an electrode layer having a first signal electrode, a second signal electrode, a first ground electrode, a second ground electrode, and a third ground electrode as the electrode layer of the optical modulator. The optical modulator disclosed in Patent Document 2 is a so-called dual-drive type optical modulator having two signal electrodes.

[0005] Prior art documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent No. 6728596

[0008] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2022-036928 Summary of the Invention

[0009] Problems to be Solved by the Invention

[0010] In order to popularize glasses-type image display devices such as extended reality glasses, it is necessary to miniaturize and lower the drive voltage. In addition, in order to achieve mass production, it is sought to manufacture at as low a cost as possible.

[0011] The present invention has been completed in view of the above problems, and an object thereof is to provide a small-sized visible light modulator capable of being driven at a low voltage, a light source module, an optical engine equipped with the light source module, and an extended reality glasses.

[0012] Solution for Solving the Problem

[0013] In order to solve the above problems, the present invention provides the following solutions.

[0014] Solution 1 of the present invention is a light modulator, which includes: a substrate; an optical waveguide layer formed on the substrate, having a Mach-Zehnder waveguide including a first ridge waveguide and a second ridge waveguide for transmitting visible light, and is made of lithium niobate; a buffer layer formed on the optical waveguide layer; and a signal electrode formed on the buffer layer and a first ground electrode and a second ground electrode disposed on both sides of the signal electrode, the signal electrode is disposed above the first ridge waveguide, the second ground electrode is disposed above the second ridge waveguide, the signal electrode and the first ridge waveguide are disposed so as to be relatively offset with a horizontal distance between the center in the width direction of the signal electrode and the center in the width direction of the first ridge waveguide being 0.5 μm or less, and the second ground electrode and the second ridge waveguide are disposed so that the distance between the side surface of the two side surfaces of the second ground electrode closer to the second ridge waveguide and the center in the width direction of the second ridge waveguide in the horizontal direction is 2 μm or less.

[0015] Based on the light modulator of Solution 1, in Solution 2 of the present invention, the dielectric constant of the buffer layer is 7 or more, and the thickness of the buffer layer is 0.4 μm or more and 1 μm or less.

[0016] Solution 3 of the present invention is a light source module, which includes: the light modulator of Solution 1 or Solution 2; and a light source that emits visible light incident on the input waveguide of the light modulator.

[0017] Solution 4 of the present invention is an optical engine, which includes: the light source module of Solution 3; and a light scanning mirror that reflects the light emitted from the light source module at an angle to display an image.

[0018] Solution 5 of the present invention is an extended reality glasses equipped with the optical engine of Solution 4.

[0019] Effects of the Invention

[0020] According to the light modulator of the present invention, a small-sized visible light modulator capable of being driven at a low voltage can be provided. Description of the Drawings

[0021] Figure 1This is a top view schematic diagram showing an example of an optical modulator for explaining one embodiment.

[0022] Figure 2 It is a cross-sectional schematic diagram of the optical modulator taken along the Figure 1 A - A' line shown in the figure. Figure 1

[0023] Figure 3

[0024] Figure 4 It is a structure in which the center line of the first ridge waveguide is offset to the right with respect to the center line of the signal electrode.

[0024] Figure 4 It is a graph showing the relationship between the relative offset D CC of the signal electrode and the first ridge waveguide and the electric field efficiency VπL.

[0025] Figure 5A It is a graph showing the structures when the relative offset D is -0.5μm, 0μm, and +0.5μm, overlappingly depicted for a structure with a signal electrode width (We) of 1.0μm. CC

[0026] Figure 5B It is a graph showing the structures when the relative offset D is -0.5μm, 0μm, and +0.5μm, overlappingly depicted for a structure with a signal electrode width (We) of 2.0μm. CC

[0027] Figure 5C

[0028] It is a graph showing the structures when the relative offset D is -0.5μm, 0μm, and +0.5μm, overlappingly depicted for a structure with a signal electrode width (We) of 3.0μm. CC Figure 6

[0028] Figure 6 It is a graph showing the relationship between the dielectric constant ε_buffer of the dielectric constituting the buffer layer and the electric field efficiency VπL, obtained by simulating red light with a wavelength of 638nm in the case where the signal electrode width We is 3μm.

[0029] Figure 7 It is a graph showing the relationship between the thickness (T buffer ) of the buffer layer and the electric field efficiency VπL, obtained by simulating red light with a wavelength of 638nm in the case where the signal electrode width We is 3μm.

[0030] Figure 8 It is a graph showing the relationship between the thickness (T buffer ) of the buffer layer and the transmission loss (PL) caused by light absorption of the electrode, obtained by simulating red light with a wavelength of 638nm in the case where the signal electrode width We is 3μm.

[0031] Figure 9A top view schematic diagram of a light source module showing an embodiment of the present invention.

[0032] Figure 10 is a partial cross-sectional schematic diagram of the light source module shown, cut by the XZ plane, depicting only the part near the joint. Figure 9 A partial cross-sectional schematic diagram of the light source module shown, depicting only the part near the joint.

[0033] Figure 11A A diagram for explaining an example of the driving method of the optical modulator.

[0034] Figure 11B A diagram for explaining another example of the driving method of the optical modulator.

[0035] Figure 11C A diagram for explaining yet another example of the driving method of the optical modulator.

[0036] Figure 12 A conceptual diagram for explaining an example of the extended reality glasses of the present invention.

[0037] Figure 13 is for Figure 12 A conceptual diagram showing the case where an image is directly projected onto the retina using the laser light emitted from the light source module for the extended reality glasses shown.

[0038] Explanation of reference numerals

[0039] 1, optical modulator; 2, substrate; 3, optical waveguide layer; 32, ridge; 32b, second ridge waveguide path; 32c, first ridge waveguide path; 52, buffer layer; 61, ground electrode; 61A, first ground electrode; 61B, second ground electrode; 62, signal electrode; 100, light source module. Detailed description of the specific embodiment

[0040] The following describes the embodiments in detail with appropriate reference to the drawings. In the following description, the drawings used are sometimes enlarged for convenience to show the characteristic parts so that the characteristics are easy to understand, and the dimensional ratios of each component are sometimes different from the actual ones. The materials, dimensions, etc. exemplified in the following description are examples, and the present invention is not limited thereto, and can be appropriately changed within the range that can achieve the effects of the present invention for implementation.

[0041] [Optical modulator]

[0042] Figure 1 A top view schematic diagram for explaining an example of the optical modulator of an embodiment of the present invention. Figure 2 is along Figure 1 the A-A' line shown Figure 1 A cross-sectional schematic diagram of the optical modulator shown.

[0043] In Figure 1 andFigure 2 In this case, the X direction is the direction orthogonal to the side surface on which the light incident port is disposed, the Y direction is the direction orthogonal to the X direction, and the Z direction is the direction orthogonal to the plane formed by the X direction and the Y direction.

[0044] The optical modulator of the present embodiment is a Mach-Zehnder type (MZI type) optical modulator.

[0045] Figure 1 and Figure 2 The optical modulator 1 shown in FIG. includes: a substrate 2; an optical waveguide layer 3 formed on the substrate 2, having a Mach-Zehnder waveguide including a first ridge waveguide path 32c and a second ridge waveguide path 32b that transmit visible light, and made of lithium niobate; a buffer layer 52 formed on the optical waveguide layer 3; a signal electrode 62 formed on the buffer layer 52; and a first ground electrode 61A and a second ground electrode 61B disposed on both sides of the signal electrode 62. The signal electrode 62 is disposed above the first ground electrode 61A, the second ground electrode 61B is disposed above the second ridge waveguide path 32b, the signal electrode 62 and the first ridge waveguide path 32c are disposed so as to be relatively displaced with a distance in the horizontal direction between the center in the width direction of the signal electrode 62 and the center in the width direction of the first ridge waveguide path 32c being 0.5 μm or less, and the second ground electrode 61B and the second ridge waveguide path 32b are disposed such that the distance in the horizontal direction between the side surface 61Ba of the second ground electrode 61B that is closer to the second ridge waveguide path 32b among the two side surfaces of the second ground electrode 61B and the center in the width direction of the second ridge waveguide path 32b is 2 μm or less.

[0046] The optical modulator of the present embodiment is small-sized and can be driven at a low voltage. In order to evaluate miniaturization and low driving voltage, VπL can be used. Vπ is the voltage required for phase modulation of a half wavelength (half wavelength voltage), and is defined by the difference between the voltage V1 at which the light output is maximum and the voltage V2 at which the light output is minimum. In addition, L is the length of the portion where the signal electrode overlaps with the optical waveguide path (ridge portion), that is, the length of the phase modulation region (interaction length, electrode length). If the interaction length L is long, the half wavelength voltage Vπ is small, and if the interaction length L is short, the half wavelength voltage Vπ is large. If the size of the optical modulator is to be reduced, the interaction length L is short and the half wavelength voltage Vπ is large.

[0047] The smaller VπL is, the smaller and the lower the driving voltage are shown. Hereinafter, VπL is sometimes referred to as the electric field efficiency.

[0048] (Substrate 2)

[0049] The substrate 2 only needs to have a refractive index lower than that of the lithium niobate film forming the optical waveguide layer 3, and there is no particular limitation. For example, sapphire substrates, Si substrates, thermally oxidized silicon substrates, etc. can be cited. The substrate 2 is preferably capable of forming the lithium niobate film as an epitaxial film.

[0050] Since the optical waveguide layer is composed of a lithium niobate (LiNbO3) film, the substrate 2 only needs to have a refractive index lower than that of the lithium niobate film, and there is no particular limitation. However, as a substrate capable of forming a single-crystal lithium niobate film as an epitaxial film, a sapphire single-crystal substrate or a silicon single-crystal substrate is preferred. The crystal orientation of the single-crystal substrate is not particularly limited. For example, since the lithium niobate film with c-axis orientation has three-fold symmetry, it is desirable that the single-crystal substrate of the substrate also has the same symmetry. In the case of a sapphire single-crystal substrate, a c-plane substrate is preferred, and in the case of a silicon single-crystal substrate, a (111) plane substrate is preferred.

[0051] (Optical waveguide layer 3)

[0052] The optical waveguide layer 3 is composed of a lithium niobate film. The lithium niobate forming the lithium niobate film may also contain elements other than lithium (Li), niobium (Nb), and oxygen (O).

[0053] Lithium niobate can also be, for example, a compound represented by the following formula (I).

[0054] Li x NbA y O z ···(I)

[0055] (In formula (I), A represents an element other than Li, Nb, and O. x represents a number of 0.5 or more and 1.2 or less. y represents a number of 0 or more and 0.5 or less. z represents a number of 1.5 or more and 4.0 or less.)

[0056] In formula (I), A only needs to be an element other than Li, Nb, and O. For example, K, Na, Rb, Cs, Be, Mg, Ca, Sr, Ba, Ti, Zr, Hf, V, Cr, Mo, W, Fe, Co, Ni, Zn, Sc, Ce, etc. can be cited. A can be either only one selected from these elements or two or more.

[0057] In formula (I), x is a number of 0.5 or more and 1.2 or less, preferably 0.9 or more and 1.05 or less. y is a number of 0 or more and 0.5 or less. z is a number of 1.5 or more and 4.0 or less, preferably 2.5 or more and 3.5 or less.

[0058] The lithium niobate film forming the optical waveguide layer 3 is preferably an epitaxial film.

[0059] The lithium niobate film is, for example, a c-axis oriented lithium niobate film. The lithium niobate film is, for example, an epitaxial film epitaxially grown on the substrate 2. The epitaxial film is a single crystal film in which the crystal orientation is aligned using the underlying substrate. The epitaxial film is a film having a single crystal orientation in the z direction and the in-plane direction of the xy plane, and the crystal is aligned and oriented in the x-axis direction, y-axis direction, and z-axis direction. Whether the film formed on the substrate 2 is an epitaxial film can be demonstrated, for example, by confirming the peak intensity and poles of the orientation positions of 2θ-θ X-ray diffraction.

[0060] The optical waveguide layer 3 has a plurality of flat portions 31 and ridge portions 32 disposed between adjacent flat portions 31 and having a shape that rises in a strip shape from the flat portion 31. In the optical modulator 1 of the present embodiment, the input waveguide path 32a, optical branching portion 4a, first ridge waveguide path 32c branched from the input waveguide path 32a, second ridge waveguide path 32b, optical multiplexing portion 4b that combines the first ridge waveguide path 32c and the second ridge waveguide path 32b, and output waveguide path 32d described later are collectively referred to as one ridge portion 32.

[0061] The number n of the ridge portions 32 is an integer of 2 or more. In Figure 1 an example of 3 (n = 3) is shown. Visible light with different wavelengths is incident on the three ridge portions 32R, 32G, and 32B, respectively.

[0062] In the present embodiment, for example, red light with a peak wavelength of 610 nm or more and 750 nm or less is incident on the ridge portion 32R. For example, green light with a peak wavelength of 500 nm or more and 560 nm or less is incident on the ridge portion 32G. For example, blue light with a peak wavelength of 435 nm or more and 480 nm or less is incident on the ridge portion 32B. Since the three ridge portions 32R, 32G, and 32B of the optical modulator 1 of the present embodiment are respectively irradiated with red light, green light, and blue light, it can be preferably used, for example, in extended reality glasses or the like that can display full-color images.

[0063] As Figure 1 shown, the three ridge portions 32R, 32G, and 32B each have an input waveguide path 32a, an optical branching portion 4a, a first ridge waveguide path 32c, a second ridge waveguide path 32b, an optical multiplexing portion 4b, and an output waveguide path 32d.

[0064] In the three ridge portions 32R, 32G, and 32B of the optical waveguide layer 3, the input waveguide path 32a is, for example, substantially rectangular in cross-section and receives visible light generated by a light source such as a laser element. As Figure 1 shown, the input waveguide path 32a branches into a first ridge waveguide path 32c and a second ridge waveguide path 32b by the optical branching portion 4a. As Figure 2As shown, the first ridge waveguide path 32c and the second ridge waveguide path 32b are trapezoidal in cross-section, for example. The first ridge waveguide path 32c and the second ridge waveguide path 32b of the present embodiment have the same shape in cross-section. As Figure 1 shown, the first ridge waveguide path 32c and the second ridge waveguide path 32b are combined by the optical multiplexing section 4b to form the output waveguide path 32d. The output waveguide path 32d is substantially rectangular in cross-section, for example, and emits the visible light signal generated in the optical multiplexing section 4b.

[0065] The cross-sectional shapes of the input waveguide path 32a and the output waveguide path 32d are not limited to rectangular shapes, and may be trapezoidal shapes or semi-circular shapes, for example.

[0066] In addition, the cross-sectional shapes of the first ridge waveguide path 32c and the second ridge waveguide path 32b are not limited to trapezoidal shapes, and may be rectangular shapes or semi-circular shapes, for example.

[0067] In addition, the cross-sectional shapes of the input waveguide path 32a, the output waveguide path 32d, the first ridge waveguide path 32c, and the second ridge waveguide path 32b may or may not have symmetry.

[0068] When the optical modulator of the present embodiment is used in a glasses-type image display device, the thickness (T slab ) of the flat portion 31 of the optical waveguide layer 3 is preferably 0.1 μm to 0.3 μm. In addition, the thickness (T R ) of the ridge portion 32 of the optical waveguide layer 3 is preferably 0.5 μm to 1.0 μm.

[0069] The reason is that if the thickness (T R ) of the ridge portion 32 is small, light cannot be transmitted. If the thickness (T R ) of the ridge portion 32 is large, the transmitted light becomes multimode.

[0070] When the optical modulator of the present embodiment is used in a glasses-type image display device, the distance (S) between the ridge portions 32 is preferably 2 μm to 12 μm.

[0071] The reason is that by reducing S, the distance between the signal electrode and the ground electrode can be shortened, and the electric field efficiency applied to the ridge portion 32 can be improved.

[0072] Figure 2 The ridge portion 32 shown is an example of a trapezoid that is symmetric with respect to the center lines L 1C , L 2C . When the optical modulator of the present embodiment is used in a glasses-type image display device, in this example of the shape, the inclination angle (α) of the ridge portion 32 is preferably 60 degrees to 90 degrees. The reason is that if the inclination angle is small, the transmitted light becomes multimode.

[0073] In addition, the width (W R ) of the upper surface of the ridge portion 32 is preferably 0.3 μm to 1.2 μm.

[0074] The reason is that if the waveguide width is small, light cannot be transmitted, and if the waveguide width is large, the transmitted light will become multimode.

[0075] (Protective layer 51)

[0076] As Figure 2 shown, the protective layer 51 is disposed between the flat portion 31 of the optical waveguide layer 3 and the buffer layer 52. The protective layer 51 is made of a dielectric having a refractive index smaller than that of the optical waveguide layer 3. As the material of the protective layer 51, for example, silicon oxide (SiO2), aluminum oxide (Al2O3), lanthanum oxide (La2O3), or a composite of these oxides can be used. As the composite of the above oxides, for example, LaAlSiInO can be cited. As the material of the protective layer 51, silicon oxide (SiO2) is preferably used among the above materials.

[0077] (Buffer layer 52)

[0078] The buffer layer 52 is formed on the optical waveguide layer 3 and the protective layer 51 to prevent the visible light transmitted in the optical waveguide layer 3 from being absorbed by the electrode layer 6.

[0079] The buffer layer 52 is made of a dielectric having a refractive index smaller than that of the optical waveguide layer 3.

[0080] The dielectric constant of the dielectric constituting the buffer layer 52 is preferably 7 or more. The reason is that the electric field efficiency VπL can be reduced.

[0081] As specific materials for the buffer layer 52, aluminum oxide (Al2O3, dielectric constant 7), LaAlSiInO (dielectric constant 11) can be exemplified.

[0082] The material of the buffer layer 52 can be either the same as that of the protective layer 51 or different from that of the protective layer 51.

[0083] The thickness (T buffer ) of the buffer layer 52 is preferably 0.4 μm or more and 1 μm or less. The reason is that the electric field efficiency VπL can be reduced.

[0084] (Electrode layer 6)

[0085] The electrode layer 6 is formed on the buffer layer 52 and includes a signal electrode 62, a first ground electrode 61A and a second ground electrode 61B disposed on both sides of the signal electrode 62.

[0086] The optical modulator of the present embodiment is a so-called single-drive type optical modulator having one signal electrode. In the case of a so-called dual-drive type optical modulator having two signal electrodes, since the electrode structure is complex and it is necessary to control the two signal electrodes while applying electrical signals with inverted data phases, there is a problem of complication of the circuit structure of the drive system. Since the optical modulator of the present embodiment is of the single-drive type, there is no such problem.

[0087] When the optical modulator of the present embodiment is used in a glasses-type image display device, the width (We) of the signal electrode 62 is preferably 1.0 μm to 4.0 μm.

[0088] The reason is that the electric field efficiency VπL can be reduced.

[0089] When the optical modulator of the present embodiment is used in a glasses-type image display device, the widths of the first ground electrode 61A and the second ground electrode 61B are preferably 50 μm to 1000 μm.

[0090] The reason is that if the ground electrode is thin, the voltage is not 0 V and the electric field efficiency VπL increases.

[0091] When the optical modulator of the present embodiment is used in a glasses-type image display device, the thickness (Te) of the electrode layer 6 is preferably 0.1 μm to 5 μm.

[0092] The reason is that when the modulation frequency is large, microwaves are transmitted with high efficiency in an electrode layer having a large electrode cross-sectional area.

[0093] When the optical modulator of the present embodiment is used in a glasses-type image display device, the distance (G) between the signal electrode 62 and the ground electrode 61 is preferably 1 μm to 12 μm.

[0094] The reason is that the electric field efficiency VπL can be reduced.

[0095] (Position relationship between the electrode and the ridge waveguide)

[0096] The signal electrode 62 is disposed above the first ridge waveguide 32c (in the direction parallel to the Z direction), and the center in the width direction of the signal electrode 62 (the center line L extending along the Z direction through the center in the width direction of the signal electrode 62 SC ) and the center in the width direction of the first ridge waveguide 32c (the center line L extending along the Z direction through the center in the width direction of the first ridge waveguide 32c 1C ) are arranged in a positional relationship such that the distance D CC in the horizontal direction (in the direction parallel to the Y direction) is 0.5 μm or less. Sometimes the center-to-center distance D CC is referred to as the relative offset.

[0097] In the structure where the relative positional relationship between the signal electrode 62 and the first ridge waveguide path 32c is such that the relative offset D between the signal electrode 62 and the first ridge waveguide path 32c is 0.5 μm or less, the first ridge waveguide path 32c is arranged in a range where the electric field strength is relatively large to reduce the electric field efficiency VπL. CC In the structure where the relative positional relationship between the signal electrode 62 and the first ridge waveguide path 32c is such that the relative offset D between the signal electrode 62 and the first ridge waveguide path 32c is 0.5 μm or less, the first ridge waveguide path 32c is arranged in a range where the electric field strength is relatively large to reduce the electric field efficiency VπL.

[0098] In addition, by allowing the relative offset D CC , the manufacturing difficulty is reduced and mass production becomes easier.

[0099] In Figure 2 , regarding the relative position (offset between centers) of the signal electrode 62 and the first ridge waveguide path 32c, the center line L of the first ridge waveguide path 32c SC is offset to the left with respect to the center line L of the signal electrode 62. In 1C , an example is shown in which the first ground electrode 61A and the second ground electrode 61B are also offset to the left in the same manner as the signal electrode 62, that is, an example of offset in such a way that the distance G between the side surface 62a of the signal electrode 62 and the side surface 61Ab of the first ground electrode 61A and the distance G between the side surface 62b of the signal electrode 62 and the side surface 61Ba of the second ground electrode 61B remain unchanged. Figure 2 An example is shown in which the first ground electrode 61A and the second ground electrode 61B are also offset to the left in the same manner as the signal electrode 62, that is, an example of offset in such a way that the distance G between the side surface 62a of the signal electrode 62 and the side surface 61Ab of the first ground electrode 61A and the distance G between the side surface 62b of the signal electrode 62 and the side surface 61Ba of the second ground electrode 61B remain unchanged.

[0100] In contrast, Figure 3 is a case where the center line L of the first ridge waveguide path 32c SC is offset to the right with respect to the center line L of the signal electrode 62. 1C

[0101] Figure 3 is a case where the relative position (offset between centers) of the signal electrode 62 and the first ridge waveguide path 32c is the opposite of the case shown in Figure 2 . For convenience, the offset of the signal electrode 62 and the first ridge waveguide path 32c shown in Figure 2 is set to be positive, and the offset of the signal electrode 62 and the first ridge waveguide path 32c shown in Figure 3 is set to be negative. The signs of "-1 μm to +1 μm" for the center distance (D CC ) between the signal electrode 62 and the ridge described later represent this positive and negative.

[0102] The second ground electrode 61B is arranged above (in the Z direction) the second ridge waveguide path 32b, and the distance D in the horizontal direction (direction parallel to the Y direction) between the side surface 61Ba of the second ground electrode 61B, which is the side closer to the second ridge waveguide path 32b among the two side surfaces of the second ground electrode 61B, and the center in the width direction of the second ridge waveguide path 32b (center line L passing through the center in the width direction of the second ridge waveguide path 32b and extending in the Z direction) 2C )cE is 2 μm or less.

[0103] When viewed from above in the Z direction, the second ground electrode 61B is disposed at a position that at least partially overlaps with the second ridge waveguide 32b.

[0104] (simulation)

[0105] As an index for evaluating miniaturization and low driving voltage, VπL is used. Vπ is the voltage required for phase modulation of a half wavelength (half wavelength voltage), which is defined by the difference between the voltage V1 at which the light output is maximum and the voltage V2 at which the light output is minimum, and refers to the driving voltage. In addition, L is the length of the phase modulation region (interaction length, electrode length). The smaller VπL is, the smaller and the lower the driving voltage.

[0106] In the simulation, the calculation of the light transmission efficiency uses the FDM (Finite Difference Method) Solver of Fimmwave of Photon Design, and the calculation of VπL uses Maxwell of Ansys.

[0107] In the simulation, Figure 1 and Figure 2 a model with the structure shown in the figure is used, and the materials of the components forming the optical modulator 1 are as follows.

[0108] The substrate 2 is a sapphire single crystal substrate, the optical waveguide layer 3 is a lithium niobate film directly epitaxially grown on the sapphire single crystal substrate, the protective layer 51 is made of silicon dioxide (SiO2), the buffer layer 52 is made of LaAlSiInO, and the electrode layer 6 is made of gold.

[0109] In addition, in the simulation, the dimensions of each part are as follows.

[0110] The thickness (T slab ) of the flat portion 31 of the optical waveguide layer 3: 0.15 μm

[0111] The shape of the ridge 32 is symmetric with respect to the center lines L 1C , L 2C .

[0112] The thickness (T R ) of the ridge 32: 0.7 μm

[0113] The width (W R ) of the upper surface of the ridge 32: 0.8 μm

[0114] The tilt angle (α) of the ridge 32: 80°

[0115] The distance (S) between the ridges 32: 4 μm

[0116] Thickness (T buffer ) of the buffer layer 52: 0.7 μm

[0117] Thickness (Te) of the electrode layer 6: 2 μm

[0118] Width (We) of the signal electrode 62: 1 μm, 2 μm, 3 μm

[0119] Distance (G) between the signal electrode 62 and the ground electrode 61: 2 μm

[0120] Distance (D CC ) between the signal electrode 62 and the center of the ridge: -1 μm to +1 μm

[0121] Distance (D CE ) between the second ground electrode 61B and the center of the ridge: 0 to 2 μm

[0122] Regarding the sign of "-1 μm to +1 μm" of the distance (D CC ) between the signal electrode 62 and the center of the ridge, it exactly refers to Figure 2 the offset shown, and negative refers to Figure 3 the offset shown.

[0123] Figure 4 It is a graph showing the relationship between the distance (D CC ) between the signal electrode 62 and the center of the first ridge waveguide 32c and the electric field efficiency VπL obtained by simulating red light with a wavelength of 638 nm for each structure where the width (We) of the signal electrode 62 is 1.0 μm, 2 μm, 3 μm.

[0124] According to Figure 4 the graph shown, in each case of We = 1 μm, 2 μm, 3 μm, within the range of relative offset D CC from -0.5 μm to +0.5 μm, the range of the electric field efficiency VπL is as follows:

[0125] When We = 1 μm: 0.98 [Vcm] ≤ VπL ≤ 1.13 [Vcm]

[0126] When We = 2 μm: 0.95 [Vcm] ≤ VπL ≤ 1.02 [Vcm]

[0127] When We = 3 μm: 0.92 [Vcm] ≤ VπL ≤ 0.96 [Vcm]

[0128] In the relative offset D CCIn the range of -0.5 μm to +0.5 μm, when the minimum value of the electric field efficiency VπL is set as VπL(min) and the maximum value of the electric field efficiency VπL is set as VπL(max), in each case of We = 1 μm, 2 μm, and 3 μm, the variation range ({VπL(max) / VπL(min)} × 100) [%] is as follows:

[0129] When We = 1 μm: 15%

[0130] When We = 2 μm: 7%

[0131] When We = 3 μm: 4%

[0132] Figures 5A to 5C is a diagram depicting the structure when the distance (D CC ) between the center of the signal electrode 62 and the first ridge waveguide 32c is -0.5 μm, 0 μm, and +0.5 μm, overlappingly for each structure with the width (We) of the signal electrode 62 being 1 μm, 2 μm, and 3 μm. Sometimes the distance between the centers D CC is called the relative offset. For the signal electrode 62, when the relative offset D CC is 0 μm, it is depicted by a solid line, and in addition, when the relative offset D CC is -0.5 μm and +0.5 μm, it is depicted by a dashed line.

[0133] Figure 6 is a graph showing the relationship between the dielectric constant of the dielectric constituting the buffer layer 52 and the electric field efficiency VπL obtained by simulating red light with a wavelength of 638 nm in the case where the width (We) of the signal electrode 62 is 3 μm.

[0134] According to Figure 6 the graph, it can be seen that as the dielectric constant increases from 7 to 11, the electric field efficiency VπL decreases.

[0135] Figure 7 is a graph showing the relationship between the thickness (T buffer ) of the buffer layer 52 and the electric field efficiency VπL obtained by simulating red light with a wavelength of 638 nm in the case where the width (We) of the signal electrode 62 is 3 μm.

[0136] According to Figure 7 the graph, it can be seen that as the thickness of the buffer layer 52 decreases from 1 μm to 0.5 μm, the electric field efficiency VπL decreases.

[0137] Figure 8 is a graph showing the relationship between the thickness (T bufferA graph showing the relationship with transmission loss (PL) caused by light absorption of the electrode.

[0138] According to Figure 8 the graph, it can be seen that if the thickness of the buffer layer 52 is thinner than 0.4 μm, the transmission loss (PL) increases.

[0139] [Light source module]

[0140] In Figure 9 a top view schematic diagram of a light source module according to an embodiment of the present invention is shown.

[0141] The light source module includes the optical modulator of the above embodiment and a light source that emits visible light incident on the input waveguide path of the optical modulator.

[0142] Figure 9 The shown light source module 100 includes three light sources 7R, 7G, and 7B as the light source 7. Each of the light sources 7R, 7G, and 7B emits visible light incident on the input waveguide paths 32a of the respective ridge portions 32R, 32G, and 32B of the optical waveguide layer 3 of the optical modulator 14. For example, the light source 7R can emit red light, the light source 7G can emit green light, and the light source 7B can emit blue light. In addition, the arrangement of the light sources of each color is not limited. For example, the light source 7B can be connected to the central input waveguide path 32a, and the light sources 7R and 7G can be connected to the input waveguide paths 32a at both ends.

[0143] As the light sources 7R, 7G, and 7B, laser elements such as laser diodes (LDs) can be used, and various commercially available laser elements can be used.

[0144] Figure 10 It is a partial cross-sectional schematic diagram of the light source module 100 shown in Figure 9 sectioned by the XZ plane. Only the part near the joint is depicted.

[0145] The light source 7 is provided on the upper surface of the light source base 20. The light source base 20 can be shared by all the light sources or can be separate for each light source.

[0146] The light source base 20 is made of, for example, aluminum nitride (AlN), aluminum oxide (Al2O3), silicon (Si), etc.

[0147] The light source base 20 and the substrate 2 for the optical waveguide on which the optical waveguide layer is formed can be configured to be directly joined by a metal layer 70. With this structure, further miniaturization can be achieved without performing spatial bonding or fiber bonding.

[0148] By adopting a structure in which the joint surface 20A of the light source base 20 and the joint surface 2A of the substrate 2 for the optical waveguide are joined by means of the metal layer 70, the relative positions of the light source base 20 and the substrate 2 for the optical waveguide can be adjusted during manufacturing to calibrate the optical axis position of the laser, so that the optical axes of the respective light sources 7 are aligned with the axis of the input waveguide path (active calibration).

[0149] The metal layer 70 can be composed of a plurality of metal layers.

[0150] When the light source module of the present embodiment is used in an extended reality glasses, according to the light quantity and the like required by the extended reality glasses, the gap (spacing) S between the joint surface 20A of the light source base 20 and the joint surface 2A of the substrate 2 for the optical waveguide is preferably greater than 0 μm and less than or equal to 5 μm, for example.

[0151] (Driving method)

[0152] The optical modulator can modulate the input light into output light by using a high-frequency modulation voltage and a DC bias voltage. By controlling the DC bias voltage Vdc, the operating point Vd of the optical modulator is adjusted. The operating point Vd is the voltage that becomes the center of the modulation voltage amplitude Vpp. Let the half-wavelength voltage of the high-frequency modulation voltage be Vπ(RF).

[0153] Figures 11A to 11C They are diagrams for explaining three examples of the driving method of the optical modulator respectively.

[0154] In Figures 11A to 11C , the horizontal axis is the DC bias voltage applied to the optical modulator, and the vertical axis is the intensity of the optical output of the applied voltage. The applied voltage amplitude Vpp is the difference between the minimum value (Vmin) and the maximum value (Vmax) of the applied voltage.

[0155] In Figure 11A , it is an example in which the DC bias voltage can take a value of about 0 V if the operating point Vd' is set such that the offset of the operating point voltage is (Vn - 0.5Vπ). For example, if the applied voltage amplitude Vpp of the modulation voltage Vm is set to the half-wavelength voltage Vπ(RF), a modulation voltage Vm in the range of (-1 / 2)Vπ(RF) to (1 / 2)Vπ(RF) is applied to the optical modulator. As Figure 11A shows, the optical output from the optical modulator is maximum when the modulation voltage Vm is (-1 / 2)Vπ(RF), minimum when the modulation voltage Vm is (1 / 2)Vπ(RF), and the optical output when the modulation voltage Vm is 0 V is 50% of the maximum output.

[0156] Similarly, using Figure 11BDescribes the optical modulation of an optical modulator that sets the operating point Vd' in such a way that the offset of the operating point voltage is (Vn - 0.25Vπ) and controls the applied voltage amplitude Vpp of the modulation voltage Vm as a (1 / 4) wavelength voltage (1 / 2)Vπ(RF).

[0157] In this case, if the offset of the operating point voltage is set to (Vn - 0.25Vπ), the operating point Vd' can be taken as a DC bias voltage of approximately 0 (V). A modulation voltage Vm corresponding to the range of (-1 / 4)Vπ(RF) to (1 / 4)Vπ(RF) is applied to the optical modulator. As Figure 11B shown, the optical output from the optical modulator is maximum when the modulation voltage Vm is (-1 / 4)Vπ(RF), minimum when the modulation voltage Vm is (1 / 4)Vπ(RF), and the optical output when the modulation voltage Vm is 0 V (Vd') is 15% of the maximum output.

[0158] Similarly, using Figure 11C Describes the optical modulation of an optical modulator that sets the operating point Vd' in such a way that the offset of the operating point voltage is (Vn - 0.75Vπ) and controls the applied voltage amplitude Vpp of the modulation voltage Vm as a (1 / 4) wavelength voltage (1 / 2)Vπ(RF).

[0159] In this case, if the offset of the operating point voltage is set to (Vn - 0.75Vπ), the operating point Vd' can be taken as a DC bias voltage of approximately 0 (V). A modulation voltage Vm corresponding to the range of (-1 / 4)Vπ(RF) to (1 / 4)Vπ(RF) is applied to the optical modulator. As Figure 11C shown, the optical output from the optical modulator is maximum when the modulation voltage Vm is (-1 / 4)Vπ(RF), minimum when the modulation voltage Vm is (1 / 4)Vπ(RF), and the optical output when the modulation voltage Vm is 0 V (Vd') is 85% of the maximum output.

[0160] [Optical Engine and Extended Reality Glasses]

[0161] Figure 12 Is a conceptual diagram for explaining an example of the extended reality glasses of the present invention. Figure 13 Is for Figure 12 The shown extended reality glasses represent a conceptual diagram of the case where an image is directly projected onto the retina using laser light emitted from a light source module.

[0162] The extended reality glasses (glasses) 1000 of the present embodiment are glasses-type terminals. XR is a general term for virtual reality (VR: Virtual Reality), augmented reality (AR: Augmented Reality), and mixed reality (Mixed Reality). Figure 13The indicated marker L is the image display light.

[0163] In Figure 12 In the extended reality glasses 1000 of the present embodiment shown, the light source module 100 of the above-described embodiment is mounted on the optical engine 5001 provided in the frame 1010.

[0164] As Figure 12 As shown, the optical engine 5001 includes a light source module 100, an optical scanning mirror 3001, an optical system 2001 that connects the light source module 100 and the optical scanning mirror 3001, a laser driver 1100, an optical scanning mirror driver 1200, and a video controller 1300 that controls these drivers.

[0165] As the optical scanning mirror 3001, for example, a MEMS mirror can be used. In order to project a 2D image, as the optical scanning mirror 3001, a biaxial MEMS mirror that changes angles in the horizontal direction (X direction) and the vertical direction (Y direction) and vibrates to reflect the laser is preferably used.

[0166] The optical system 2001 optically processes the laser emitted from the light source module 100. As the optical system 2001, for example, an optical system having a collimating lens 2001a, a diaphragm 2001b, and an ND filter 2001c can be used. Figure 12 The optical system 2001 shown is an example, and other structures may also be used.

[0167] In Figure 12 In the extended reality glasses 1000 of the present embodiment shown, as Figure 13 As shown, the laser R irradiated from the light source module 100 mounted on the frame 1010 is reflected by the optical scanning mirror 3001, and then reflected by the lens 4001 of the extended reality glasses 1000, and enters the human eyeball E as the image display light L, so that an image (image) can be directly projected onto the retina M.

[0168] The extended reality glasses 1000 of the present embodiment have a reduced electric field efficiency because they are equipped with the light source module 100 of the present embodiment.

[0169] The embodiments of the present invention have been described in detail with reference to the accompanying drawings, but each structure and its combination of each embodiment are examples, and additional, omission, substitution, and other changes in the structure can be made without departing from the gist of the present invention.

[0170] For example, the number of ridges in the optical waveguide layer of the light modulator of the present invention may be two or more, and is not limited to three or four.

Claims

1. An optical modulator, wherein, the optical modulator includes: a substrate; an optical waveguide layer formed on the substrate, having a Mach-Zehnder waveguide including a first ridge waveguide and a second ridge waveguide for transmitting visible light, and made of lithium niobate; a buffer layer formed on the optical waveguide layer; and a signal electrode formed on the buffer layer and first and second ground electrodes disposed on both sides of the signal electrode, the signal electrode is disposed above the first ridge waveguide, the second ground electrode is disposed above the second ridge waveguide, the signal electrode and the first ridge waveguide are disposed so as to be relatively displaced with a horizontal distance between the center in the width direction of the signal electrode and the center in the width direction of the first ridge waveguide being 0.5 μm or less, the second ground electrode and the second ridge waveguide are disposed so that the horizontal distance between the side surface of the second ground electrode closer to the second ridge waveguide among the two side surfaces of the second ground electrode and the center in the width direction of the second ridge waveguide is 2 μm or less.

2. The optical modulator according to claim 1, wherein, the dielectric constant of the buffer layer is 7 or more, the thickness of the buffer layer is 0.4 μm or more and 1 μm or less.

3. A light source module, wherein, the light source module includes: the optical modulator according to claim 1 or 2; and a light source that emits visible light incident on the input waveguide of the optical modulator.

4. An optical engine, wherein, the optical engine includes: the light source module according to claim 3; and a light scanning mirror that reflects the light emitted from the light source module at an altered angle to display an image.

5. An extended reality glasses, wherein, the extended reality glasses are equipped with the optical engine according to claim 4.

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