Optical element, laser module, and near-eye wearable device

Abstract

The invention relates to an optical element, a laser module, and a near-to-eye wearable device. This optical element is provided with: a substrate having a main surface; and a core layer that is provided on the main surface and is composed of a material having an electro-optical effect. The core layer is provided with a mode converter which extends in a first direction along the main surface and which converts the polarization mode of visible light between a TM mode and a TE mode. The mode converter has: a first waveguide into which visible light is incident in a first polarization mode, which is either a TE mode or a TM mode; a second waveguide that emits visible light in a second polarization mode, which is the other polarization mode of the TE mode and the TM mode; and a third waveguide that is provided between the first waveguide and the second waveguide and converts the visible light from the first polarization mode to the second polarization mode. The third waveguide has a shape that is asymmetric in a second direction along the main surface that intersects the first direction.

Description

[0001] Cross-reference to related applications

[0002] This application is based on Japanese Patent Application No. 2023-143080, filed on September 4, 2023, and claims the benefit of priority thereto, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to an optical element, a laser module, and a near-eye wearable device. Background Art

[0004] Laser modules are known to be applied to retinal projection devices mounted on near-eye wearable devices such as AR (Augmented Reality) glasses and MR (Mixed Reality) glasses. Such laser modules include a plurality of laser diodes and a combiner for combining laser beams emitted from the respective laser diodes into one laser beam.

[0005] The laser module described above sometimes includes an optical modulator (for example, Japanese Patent Publication No. 2022-36928). The optical modulator described in Japanese Patent Publication No. 2022-36928 receives visible light emitted from a laser light source and changes the intensity of the visible light to generate a visible light signal. In the optical modulator described in Japanese Patent Publication No. 2022-36928, the optical waveguide layer that guides the visible light is composed of a lithium niobate film. Summary of the invention

[0006] In materials having an electro-optical effect such as lithium niobate films, optical properties such as effective refractive index and modulation efficiency change for each mode, namely, a TE (Transverse Electric) mode in which the main component of the electric field is in the in-plane direction of the optical waveguide layer, and a TM (Transverse Magnetic) mode in which the main component of the electric field is in a perpendicular direction perpendicular to the in-plane direction (the main component of the magnetic field is in the in-plane direction). Therefore, in an optical modulator such as the above, the modulation efficiency changes depending on whether the polarization mode of visible light is a TE mode or a TM mode. In this way, it is sometimes desirable to set the polarization mode of visible light to a desired polarization mode.

[0007] On the other hand, the visible light emitted from the laser light source includes both TE mode visible light and TM mode visible light. Therefore, when the polarization mode of the visible light emitted from the laser light source is different from the desired polarization mode, it is necessary to convert the polarization mode of the visible light, and it is expected to improve the conversion efficiency of the polarization mode.

[0008] The present disclosure describes an optical element, a laser module, and a near-eye wearable device that can improve the conversion efficiency of polarization wave modes of visible light.

[0009] An optical element according to one aspect of the present disclosure comprises: a substrate having a main surface; and a core layer, which is arranged on the main surface and is composed of a material having an electro-optical effect. The core layer comprises a mode converter, which extends in a first direction along the main surface and converts the polarization wave mode of visible light between a TM mode and a TE mode. The mode converter comprises: a first waveguide, which inputs visible light in a first polarization wave mode, which is one of a TE mode and a TM mode; a second waveguide, which emits visible light in a second polarization wave mode, which is another of a TE mode and a TM mode; and a third waveguide, which is arranged between the first waveguide and the second waveguide and converts the visible light from the first polarization wave mode to the second polarization wave mode. The third waveguide has an asymmetric shape in a second direction along the main surface intersecting with the first direction.

[0010] In the above optical element, since the core layer is composed of a material having an electro-optical effect, optical properties such as the effective refractive index vary according to the shape of the waveguide for visible light transmission. The third waveguide has an asymmetric shape in the second direction along the main surface that intersects the first direction in which the mode converter extends. By having such a shape of the third waveguide, the first mixed mode and the second mixed mode in which the TE mode and the TM mode are mixed can be generated in the visible light transmitted in the third waveguide. In addition, the horizontal electric field component and the vertical electric field component of the first mixed mode are easy to become equal. Since the second mixed mode is in an orthogonal relationship with the first mixed mode, the horizontal electric field component and the vertical electric field component of the second mixed mode are easy to become equal, similar to the first mixed mode. Therefore, the polarization wave mode of the visible light transmitted in the third waveguide can be converted from the first polarization wave mode to the second polarization wave mode with high conversion efficiency. Due to the above structure, according to the above optical element, the conversion efficiency of the polarization wave mode of visible light can be improved.

[0011] Alternatively, the third waveguide may include: a bottom surface facing the main surface; a top surface arranged on the side opposite to the bottom surface in the third direction intersecting the first direction and the second direction; and an inclined surface connecting the top surface and the bottom surface. Alternatively, the third waveguide may have a columnar shape whose length in the second direction continuously increases from the top surface to the bottom surface. According to this structure, compared with the case where the length of the third waveguide in the second direction gradually increases as it approaches the main surface, the horizontal electric field component and the vertical electric field component of the first hybrid mode are easy to become equal. Since the second hybrid mode is in an orthogonal relationship with the first hybrid mode, the horizontal electric field component and the vertical electric field component of the second hybrid mode are easy to become equal, similar to the first hybrid mode. Therefore, the conversion efficiency from the first polarization wave mode to the second polarization wave mode can be further improved.

[0012] Alternatively, the inclination angle between the inclined plane and the main surface is greater than 71° and less than 85°. According to this structure, compared with the case where the inclination angle is less than 71° or greater than 85°, the horizontal electric field component and the vertical electric field component of the first hybrid mode are likely to become equal. Since the second hybrid mode is in an orthogonal relationship with the first hybrid mode, the horizontal electric field component and the vertical electric field component of the second hybrid mode are likely to become equal, similar to the first hybrid mode. Therefore, the conversion efficiency from the first polarization wave mode to the second polarization wave mode can be further improved.

[0013] Alternatively, the third waveguide has a stepped shape in which the length in the second direction gradually increases as it approaches the main surface. According to this structure, the horizontal electric field component and the vertical electric field component of the first hybrid mode are easy to become equal. Since the second hybrid mode is in an orthogonal relationship with the first hybrid mode, the horizontal electric field component and the vertical electric field component of the second hybrid mode are easy to become equal, similar to the first hybrid mode. Therefore, the conversion efficiency from the first polarization wave mode to the second polarization wave mode can be improved.

[0014] Alternatively, the third waveguide may include: a bottom surface facing the main surface; and a top surface provided on the opposite side of the bottom surface in a third direction intersecting the first direction and the second direction, wherein a groove extending in the first direction and recessed toward the bottom surface is provided on the top surface. According to this structure, compared with a case where the length of the third waveguide in the second direction gradually increases as it approaches the main surface, the conversion efficiency from the first polarization mode to the second polarization mode can be improved.

[0015] Alternatively, the length of the surface of the mode converter in contact with the main surface in the second direction is greater than 32% and less than 48% of the wavelength of visible light. According to this structure, the horizontal electric field component and the vertical electric field component of the first hybrid mode are more likely to become equal, compared with the case where the length in the second direction is less than 32% or greater than 48% of the wavelength of visible light. Since the second hybrid mode is in an orthogonal relationship with the first hybrid mode, the horizontal electric field component and the vertical electric field component of the second hybrid mode are more likely to become equal, similar to the first hybrid mode. Therefore, the conversion efficiency from the first polarization wave mode to the second polarization wave mode can be further improved.

[0016] Alternatively, the length of the mode converter in the third direction intersecting the first direction and the second direction is smaller than the wavelength of visible light. According to this structure, the length in the third direction is smaller than the wavelength of visible light, so that the horizontal electric field component and the vertical electric field component of the first hybrid mode are easily equalized. Since the second hybrid mode is in an orthogonal relationship with the first hybrid mode, the horizontal electric field component and the vertical electric field component of the second hybrid mode are easily equalized, similar to the first hybrid mode. Therefore, the conversion efficiency from the first polarization wave mode to the second polarization wave mode can be further improved.

[0017] Alternatively, the core layer may include: a first mode converter that converts the polarization mode of red light from the first polarization mode to the second polarization mode; a second mode converter that converts the polarization mode of green light from the first polarization mode to the second polarization mode; a third mode converter that converts the polarization mode of blue light from the first polarization mode to the second polarization mode; and a combiner that combines red light, green light, and blue light to emit laser light. According to this structure, the polarization modes of red light, green light, and blue light are converted from the first polarization mode to the second polarization mode. By using the polarization mode with higher combining efficiency of the combiner in the TM mode and the TE mode as the second polarization mode, the combining efficiency can be improved.

[0018] The first mode converter, the second mode converter, and the third mode converter may have the same length in the third direction intersecting the first direction and the second direction. According to this structure, the first mode converter, the second mode converter, and the third mode converter can be formed on the same substrate, and the lengths of the mode converters in the third direction can be made the same, so that the optical element can be easily manufactured.

[0019] Alternatively, the core layer may further include: a first modulator that modulates the intensity of red light; a second modulator that modulates the intensity of green light; and a third modulator that modulates the intensity of blue light. In order to combine red light, green light, and blue light to output full-color laser light, it is necessary to adjust the intensity of each color of light according to the output color. According to the above structure, since the intensity of red light, the intensity of green light, and the intensity of blue light are modulated, full-color laser light can be output.

[0020] A laser module according to another aspect of the present disclosure includes: the above-mentioned optical element; a first laser light source that emits red light in a first polarization mode; a second laser light source that emits green light in a first polarization mode; and a third laser light source that emits blue light in a first polarization mode. Since the laser module includes the above-mentioned optical element, the conversion efficiency of the polarization mode of visible light can be improved.

[0021] Another aspect of the present disclosure is a near-eye wearable device comprising: the above-mentioned laser module; a movable reflector that uses the laser light emitted from the laser module for scanning; and a reflector that reflects the laser light after passing through the movable reflector and guides the reflected light to the retina of the user wearing the near-eye wearable device, thereby projecting an image onto the retina. Since the near-eye wearable device comprises the above-mentioned optical element, it is possible to project an image onto the retina while improving the conversion efficiency of the polarization wave mode of visible light.

[0022] According to aspects and embodiments of the present disclosure, it is possible to improve the conversion efficiency of the polarization wave mode of visible light. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a three-dimensional diagram showing the appearance of a near-eye wearable device to which a laser module according to one embodiment is applied.

[0024] Figure 2 It roughly indicates Figure 1 The structure diagram of the retinal projection device shown.

[0025] Figure 3 yes Figure 2 Block diagram of the laser module shown.

[0026] Figure 4 Yes means Figure 3 A perspective view of the structure of the mode converter is shown.

[0027] Figure 5 It is along Figure 4 A cross-sectional view of line VV.

[0028] Figure 6 It is along Figure 4 A cross-sectional view taken along line VI-VI.

[0029] Figure 7 It is along Figure 4 A cross-sectional view taken along line VII-VII.

[0030] Figure 8 It is used to illustrate Figure 4 A diagram showing the mode switching action of the mode converter shown.

[0031] Fig. 9 Yes means Figure 4 A graph showing an example of conversion efficiency of a mode converter shown in FIG.

[0032] Fig.10 (a) is a block diagram of a laser module according to another embodiment. Fig.10 (b) is a block diagram of a laser module according to still another embodiment.

[0033] Fig.11 This is a block diagram of a laser module according to still another embodiment.

[0034] Fig.12 (a) is a cross-sectional view of the waveguide of the first variant. Fig.12 (b) is a graph showing an example of the conversion efficiency of the mode converter including the waveguide of the first modification example.

[0035] Fig.13 (a) is a cross-sectional view of the waveguide of the second variant. Fig.13 (b) is a graph showing an example of the conversion efficiency of a mode converter including the waveguide of the second modification.

[0036] Fig.14 (a) is a cross-sectional view of the waveguide of the third variant. Fig.14 (b) is a graph showing an example of the conversion efficiency of a mode converter including a waveguide according to the third variation.

[0037] Fig.15 (a) is a graph showing the evaluation results of Example 1. Fig.15 (b) is a graph showing the evaluation results of Example 2. Fig.15 (c) is a graph showing the evaluation results of Example 3.

[0038] Fig.16 This is a diagram showing the evaluation results of Example 4.

[0039] Fig.17 (a) is a graph showing the evaluation results of Example 5. Fig.17 (b) is a graph showing the evaluation results of Example 6. Fig.17 (c) is a graph showing the evaluation results of Example 7. DETAILED DESCRIPTION

[0040] The embodiments of the present disclosure are described in detail below with reference to the accompanying drawings. In addition, the same reference numerals are used to mark the same elements in the description of the accompanying drawings, and repeated descriptions are omitted. An XYZ coordinate system is sometimes shown in each figure. The Y-axis direction (the second direction) is a direction that intersects (for example, is orthogonal to) the X-axis direction (the first direction) and the Z-axis direction (the third direction). The Z-axis direction is a direction that intersects (for example, is orthogonal to) the X-axis direction and the Y-axis direction. In this specification, the numerical range represented by "to" shows a range that includes the numerical values ​​recorded before and after the "to" as the minimum value and the maximum value, respectively. The upper limit value and the lower limit value recorded separately can be combined arbitrarily.

[0041] [Implementation Method]

[0042] Reference Figure 1 An application example of the laser module according to one embodiment will be described. Figure 1 This is a three-dimensional diagram showing the appearance of a near-eye wearable device to which a laser module according to one embodiment is applied. Figure 1 The near-eye wearable device 1 shown is a device that projects an image onto the retina of a user wearing the near-eye wearable device 1. The near-eye wearable device 1 is, for example, a head-mounted device (head-mounted device), which can be in the form of glasses, goggles, hats, and helmets. As examples of the near-eye wearable device 1, smart glasses such as AR (Augmented Reality) glasses, VR (Virtual Reality) glasses, and MR (Mixed Reality) glasses are listed. The near-eye wearable device 1 includes a frame 2, a lens 3, and a retinal projection device 10.

[0043] The frame 2 includes a pair of lens rings 2a, a nose bridge 2b, and a pair of temples 2c. The lens ring 2a is a portion that holds the lens 3. The nose bridge 2b is a portion that connects the pair of lens rings 2a. The temple 2c is a portion that extends from the lens ring 2a and hangs on the user's ear. The frame 2 may also be a frame without lens rings. The lens 3 includes an inner surface 3a (refer to Figure 2 ).

[0044] The retinal projection device 10 is a device that projects (draws) an image directly onto the retina of the user wearing the near-eye wearable device 1. The retinal projection device 10 is mounted on the near-eye wearable device 1. In the present embodiment, in order to project an image onto the retinas on the left and right sides, the near-eye wearable device 1 includes two retinal projection devices 10, but may include only one retinal projection device 10.

[0045] Next, refer to Figure 2 The retinal projection device 10 will be described in detail. Figure 2 It roughly indicates Figure 1The structure diagram of the retinal projection device is shown in FIG. Figure 2 As shown, the retinal projection device 10 includes an optical engine 20 and a reflector 30 .

[0046] The optical engine 20 is a device that generates laser light Ls of a color and light intensity corresponding to the pixel of the image projected onto the retina and emits the laser light Ls toward the reflector 30. The optical engine 20 is mounted on each temple 2c. The optical engine 20 includes a laser module 4, an optical component 5, a movable reflector 6, a laser driver 7, a reflector driver 8, and a controller 9.

[0047] The laser module 4 emits laser light La as visible light. For example, a full-color laser module is used as the laser module 4. The laser module 4 emits laser light La of a color and intensity corresponding to the pixel of the image projected onto the retina. The details of the laser module 4 will be described later.

[0048] The optical component 5 is a component that performs optical processing on the laser light La emitted from the laser module 4. In the present embodiment, the optical component 5 includes a collimating lens 5a, an aperture 5b, and a light reduction filter 5c. The collimating lens 5a, the aperture 5b, and the light reduction filter 5c are arranged in sequence along the optical path of the laser light La. The optical component 5 may also have other structures.

[0049] The movable reflector 6 is a member for scanning with the laser light Ls. The movable reflector 6 is provided in the emission direction of the laser light La processed by the optical component 5. The movable reflector 6 is configured to be able to swing around an axis extending in the lateral direction of the lens 3 and an axis extending in the longitudinal direction of the lens 3, and to change the angle in the lateral and longitudinal directions of the lens 3 to reflect the laser light La and emit the laser light Ls. As the movable reflector 6, for example, a MEMS (Micro Electro Mechanical Systems) reflector is used.

[0050] The laser driver 7 is a driving circuit for driving the laser module 4. The laser driver 7 drives the laser module 4 based on, for example, the light energy of the laser La and the temperature of the laser light sources 411, 412, 413 included in the laser module 4. The reflector driver 8 is a driving circuit for driving the movable reflector 6. The reflector driver 8 causes the movable reflector 6 to swing within a predetermined angle range and timing. The controller 9 is a device for controlling the laser driver 7 and the reflector driver 8.

[0051] In the optical engine 20, laser light La of a color and intensity corresponding to the pixel of the image projected onto the retina is emitted from the laser module 4, passes through the optical component 5, and is reflected by the movable mirror 6. The laser light La reflected by the movable mirror 6 is emitted toward the reflector 30 as laser light Ls.

[0052] The reflector 30 is a member that reflects the laser light Ls that has passed through the movable reflector 6 and irradiates the reflected light Lrf toward the retina of the user wearing the near-eye wearable device 1 to project an image onto the retina.

[0053] Next, refer to Figure 3 and Figure 4 The structure of the laser module 4 will be described. Figure 3 yes Figure 2 Block diagram of the laser module shown. Figure 4 Yes means Figure 3 The structure of the mode converter is shown in FIG. Figure 4 Only the peripheral portion of the mode converter 42 in the optical element 40 is shown in the figure.

[0054] like Figure 3 As shown, the laser module 4 includes an optical element 40, a laser light source 411 that emits red light Lr, a laser light source 412 that emits green light Lg, and a laser light source 413 that emits blue light Lb. The laser light source 411 is, for example, a red laser diode. The laser light source 412 is, for example, a green laser diode. The laser light source 413 is, for example, a blue laser diode. The peak wavelength of the red light Lr is, for example, in the range of 600nm to 830nm. The peak wavelength of the green light Lg is, for example, in the range of 500nm to 570nm. The peak wavelength of the blue light Lb is, for example, in the range of 380nm to 490nm.

[0055] In the present embodiment, the laser light source 411 emits red light Lr in TE mode. The laser light source 412 emits green light Lg in TE mode. The laser light source 413 emits blue light Lb in TE mode. Since the red light Lr, the green light Lg, and the blue light Lb are all visible light, in the following description, the red light Lr, the green light Lg, and the blue light Lb are sometimes referred to as visible light, and sometimes the red light Lr, the green light Lg, and the blue light Lb are collectively referred to as visible light.

[0056] The optical element 40 combines the visible light emitted from the laser light sources into a single laser beam La. The optical element 40 is, for example, a planar lightwave circuit (PLC). Figure 4 As shown, the optical element 40 includes a substrate S, a core layer C1 and a cladding layer C2.

[0057] The substrate S functions as a lower cladding. The substrate S is composed of a material having a refractive index lower than that of the constituent material of the core layer C1. Examples of constituent materials of the substrate S include sapphire, silicon, or aluminum oxide (Al2O3). The substrate S includes a main surface Sa and a back surface Sr on the side opposite to the main surface Sa. The main surface Sa and the back surface Sr are surfaces defined by the X-axis direction and the Y-axis direction, intersecting with the Z-axis direction (orthogonal in this embodiment). In other words, the X-axis direction and the Y-axis direction are directions along the main surface Sa.

[0058] The cladding C2 functions as an upper cladding. The cladding C2 covers the core C1 on the main surface Sa. The cladding C2 is made of a material having a refractive index lower than that of the constituent material of the core C1. Examples of constituent materials of the cladding C2 include silicon oxide (eg, SiO2).

[0059] The core layer C1 is provided on the main surface Sa. The core layer C1 is composed of a material having an electro-optic effect. The electro-optic effect refers to a phenomenon in which the refractive index of a material changes by applying an electric field to the material. As an example of a constituent material of the core layer C1, lithium niobate (LiNbO3) is cited. In the material having the electro-optic effect, for each mode of a TE (Transverse Electric) mode in which the main component of the electric field is in the in-plane direction of the optical waveguide layer and a TM (Transverse Magnetic) mode in which the main component of the electric field is in a perpendicular direction perpendicular to the in-plane direction (the main component of the magnetic field is in the in-plane direction), optical properties such as the effective refractive index and the modulation efficiency change.

[0060] In the present embodiment, the core layer C1 is a lithium niobate thin film formed on the main surface Sa of the substrate S by sputtering, and the optical axis (C axis) of the lithium niobate extends along the Z axis direction. In this case, the modulation efficiency of each modulator is improved in the TM mode. Therefore, in the present embodiment, each laser light source emits a TE mode visible light, each visible light is converted into a TM mode in each mode converter, and on this basis, each visible light is incident on each modulator. The core layer C1 can also be composed of Z-cut lithium niobate.

[0061] The core layer C1 includes a mode converter 42 , a mode converter 43 , a mode converter 44 , a modulator 45 , a modulator 46 , a modulator 47 and a combiner 48 .

[0062] The mode converter 42 is a mode converter that converts the polarization mode of the red light Lr between the TM mode and the TE mode. In the present embodiment, the mode converter 42 converts the polarization mode of the red light Lr from the TE mode (the first polarization mode) to the TM mode (the second polarization mode). The red light Lr is incident from the laser light source 411 to the incident end of the mode converter 42. The mode converter 43 is a mode converter that converts the polarization mode of the green light Lg between the TM mode and the TE mode. In the present embodiment, the mode converter 43 converts the polarization mode of the green light Lg from the TE mode to the TM mode. The green light Lg is incident from the laser light source 412 to the incident end of the mode converter 43. The mode converter 44 is a mode converter that converts the polarization mode of the blue light Lb between the TM mode and the TE mode. In the present embodiment, the mode converter 44 converts the polarization mode of the blue light Lb from the TE mode to the TM mode. The blue light Lb is incident from the laser light source 413 to the incident end of the mode converter 44.

[0063] The mode converter 42, the mode converter 43, and the mode converter 44 extend in the X-axis direction, respectively. The mode converter 42, the mode converter 43, and the mode converter 44 are arranged in sequence in the Y-axis direction. The lengths of the mode converter 42, the mode converter 43, and the mode converter 44 in the Z-axis direction are substantially equal. Hereinafter, the length in the Z-axis direction is sometimes referred to as "height". The height of the mode converter 42, the height of the mode converter 43, and the height of the mode converter 44 may also be different. The detailed structure of each mode converter will be described later.

[0064] The modulator 45 is a modulator that modulates the light intensity of the red light Lr. The incident end of the modulator 45 is optically connected to the emission end of the mode converter 42. The modulator 45 modulates the light intensity of the red light Lr in the TM mode emitted from the mode converter 42. The modulator 46 is a modulator that modulates the light intensity of the green light Lg. The incident end of the modulator 46 is optically connected to the emission end of the mode converter 43. The modulator 46 modulates the light intensity of the green light Lg in the TM mode emitted from the mode converter 43. The modulator 47 is a modulator that modulates the light intensity of the blue light Lb. The incident end of the modulator 47 is optically connected to the emission end of the mode converter 44. The modulator 47 modulates the light intensity of the blue light Lb in the TM mode emitted from the mode converter 44. Each modulator is, for example, a Mach-Zehnder type modulator.

[0065] The combiner 48 combines the red light Lr, green light Lg and blue light Lb modulated in each modulator into one visible light. The three input ends of the combiner 48 are optically connected to the output ends of the modulators 45, 46 and 47, respectively. The combiner 48 emits the combined visible light as laser light La from the output end of the combiner 48.

[0066] In the laser module 4, visible light is emitted from each laser light source in TE mode, and the polarization wave mode of the visible light is converted from TE mode to TM mode in each mode converter, and then the light intensity of each visible light is modulated in each modulator. Then, each modulated visible light is combined in the combiner 48, and the laser light La in TM mode is transmitted from the combiner 48 to the optical component 5 (refer to FIG. Figure 2 ) is ejected.

[0067] Next, refer to Figures 4 to 7 The specific configurations of the mode converters 42 , 43 , and 44 will be described. Figure 5 It is along Figure 4 A cross-sectional view of line VV. Figure 6 It is along Figure 4 A cross-sectional view taken along line VI-VI. Figure 7 It is along Figure 4 The cross-sectional view of the line VII-VII. Figure 4 As shown, each of the mode converters 42, 43 and 44 includes a waveguide 51, a waveguide 52 and a waveguide 53. Since the structures of the mode converters are the same, the mode converter 42 is taken as an example for description.

[0068] The waveguide 53 is provided between the waveguide 51 and the waveguide 52. Specifically, the waveguide 51, the waveguide 52, and the waveguide 53 are arranged linearly in the order of the waveguide 51, the waveguide 53, and the waveguide 52 in the traveling direction (X-axis direction) of the red light Lr.

[0069] The waveguide 51 is an optical waveguide located at one end (incident end) in the X-axis direction of the mode converter 42. The waveguide 51 has a columnar shape extending linearly along the X-axis direction. Specifically, the waveguide 51 has a rectangular parallelepiped shape with the X-axis direction as the length direction. The waveguide 51 includes an incident end 51a as one end in the X-axis direction and an emission end 51b as the other end in the X-axis direction. The red light Lr is incident from the laser light source 411 to the incident end 51a in the TE mode. The waveguide 51 transmits the red light Lr while maintaining the polarization wave mode of the red light Lr, and emits the red light Lr from the emission end 51b of the waveguide 51 to the waveguide 53 in the TE mode.

[0070] The waveguide 51 is symmetrical in the Z-axis direction and symmetrical in the Y-axis direction. Symmetrical in the Z-axis direction means that the waveguide 51 is symmetrical with respect to the center point passing through the Z-axis direction (in the case of the waveguide 51, Figure 5The two parts separated by the symmetry plane are symmetrical with respect to a symmetry plane orthogonal to the Z-axis direction (the center point CP of the cross section of the waveguide 51 shown in FIG. 1 ). Symmetry in the Y-axis direction means that the two parts separated by the symmetry plane are symmetrical with respect to a symmetry plane orthogonal to the Y-axis direction passing through the center point in the Y-axis direction (the center point CP in the case of the waveguide 51).

[0071] like Figure 5 As shown, the waveguide 51 includes: a bottom surface 51c, which faces the main surface Sa; a top surface 51d, which is provided on the side opposite to the bottom surface 51c in the Z-axis direction; and a side surface 51e and a side surface 51f, which are a pair of side surfaces connecting the bottom surface 51c and the top surface 51d. The bottom surface 51c is in contact with the main surface Sa over its entire surface. The bottom surface 51c and the top surface 51d are substantially parallel, and the side surface 51e and the side surface 51f are substantially parallel. The height and the length in the Y-axis direction of the waveguide 51 are constant from the incident end 51a to the emission end 51b. The length in the Y-axis direction is sometimes referred to as "width" hereinafter. The height of the waveguide 51 is the height T1, and the width of the waveguide 51 is the width W1. The height T1 is smaller than the wavelength of the red light Lr. The width W1 can be 20% to 60% of the wavelength of the red light Lr, or 32% to 48%.

[0072] The waveguide 53 is an optical waveguide that converts the polarization wave mode of the red light Lr between the TM mode and the TE mode. In the present embodiment, the waveguide 53 converts the polarization wave mode of the red light Lr from the TE mode to the TM mode. The waveguide 53 has a cylindrical shape extending linearly along the X-axis direction. Specifically, the waveguide 53 has a shape in which the corner formed by the top surface 51d and the side surface 51f of the waveguide 51 is missing. The waveguide 53 includes an incident end 53a as one end in the X-axis direction and an emission end 53b as the other end in the X-axis direction.

[0073] The incident end 53a is connected to the emission end 51b. The emission end 53b is connected to the waveguide 52. The red light Lr is incident on the incident end 53a from the waveguide 51 in the TE mode. The waveguide 53 converts the polarization wave mode of the red light Lr from the TE mode to the TM mode, and emits the red light Lr from the emission end 53b to the waveguide 52 in the TM mode. The length between the incident end 53a and the emission end 53b is defined as a conversion length Lc. Although the details will be described later, the conversion length Lc is a parameter that contributes to the conversion efficiency based on the conversion of the polarization wave mode of the red light Lr from the TE mode to the TM mode.

[0074] The waveguide 53 is asymmetric in the Z-axis direction and asymmetric in the Y-axis direction. The asymmetry in the Z-axis direction means that the waveguide 53 is asymmetric in the Y-axis direction with respect to the center point passing through the Z-axis direction (in the case of the waveguide 53, Figure 6In the embodiment of the present invention, the two parts separated by the symmetry plane are not plane-symmetrical with respect to the symmetry plane orthogonal to the Z-axis direction (the center point CP of the cross section of the waveguide 53 shown in the figure). Similarly, asymmetry in the Y-axis direction means that the two parts separated by the symmetry plane are not plane-symmetrical with respect to the symmetry plane orthogonal to the Y-axis direction passing through the center point in the Y-axis direction (the center point CP in the case of the waveguide 53).

[0075] like Figure 6 As shown, the waveguide 53 includes: a bottom surface 53c facing the main surface Sa; a top surface 53d provided on the side opposite to the bottom surface 53c in the Z-axis direction; a side surface 53e connecting the bottom surface 53c and the top surface 53d; and an inclined surface 53f connecting the bottom surface 53c and the top surface 53d. The bottom surface 53c is in contact with the main surface Sa over its entire surface. The bottom surface 53c and the top surface 53d are substantially parallel.

[0076] The angle between the side surface 53e and the bottom surface 53c (main surface Sa) is a right angle. The inclined surface 53f is inclined in a manner that moves away from the side surface 53e as it approaches the main surface Sa. The inclination angle θ between the inclined surface 53f and the bottom surface 53c (main surface Sa) is smaller than 90°. The inclination angle θ may be in the range of 71° to 83°, or in the range of 73° to 81°. That is, the cross-sectional shape of the waveguide 53 perpendicular to the X-axis direction is a right-angled trapezoid. The height of the waveguide 53, the width of the bottom surface 53c, and the width of the top surface 53d are constant from the incident end 53a to the emission end 53b. The height of the waveguide 53 is the same as the height of the waveguide 51, which is the height T1. The width of the bottom surface 53c of the waveguide 53 is the same as the width of the waveguide 51, which is the width W1. The width of the top surface 53d of the waveguide 53 is shorter than the width of the bottom surface 53c of the waveguide 53, which is the width W2.

[0077] Waveguide 52 is an optical waveguide located at the other end (emitting end) in the X-axis direction of the mode converter 42. Waveguide 52 has a columnar shape extending linearly along the X-axis direction. Specifically, waveguide 52 has a rectangular parallelepiped shape with the X-axis direction as the length direction, and the cross-sectional shape of waveguide 52 orthogonal to the X-axis direction is the same as the cross-sectional shape of waveguide 51 orthogonal to the X-axis direction. Waveguide 52 includes an incident end 52a as one end in the X-axis direction and an emitting end 52b as the other end in the X-axis direction. The incident end 52a is connected to the emitting end 53b. The emitting end 52b is connected to the incident end of the modulator 45. Red light Lr is incident from waveguide 53 to the incident end 52a in the TM mode. Waveguide 52 transmits the red light Lr while maintaining the polarization wave mode of the red light Lr, and emits the red light Lr from the emitting end 52b to the modulator 45 in the TM mode.

[0078] The waveguide 52 is symmetrical in the Z-axis direction and symmetrical in the Y-axis direction. Figure 7As shown, the waveguide 52 includes: a bottom surface 52c, which faces the main surface Sa; a top surface 52d, which is provided on the side opposite to the bottom surface 52c in the Z-axis direction; and a side surface 52e and a side surface 52f, which are a pair of side surfaces connecting the bottom surface 52c and the top surface 52d. The bottom surface 52c is in contact with the main surface Sa over its entire surface. The bottom surface 52c and the top surface 52d are substantially parallel, and the side surface 52e and the side surface 52f are substantially parallel. The height and width of the waveguide 52 are constant from the incident end 52a to the emission end 52b. The height of the waveguide 52 is the same as the height of the waveguide 51, which is the height T1. The width of the waveguide 52 is the same as the width of the waveguide 51, which is the width W1.

[0079] The bottom surface 51c, the bottom surface 53c and the bottom surface 52c are connected in sequence and are located on the same plane. The side surface 51e, the side surface 53e and the side surface 52e are connected in sequence and are located on the same plane. The top surface 51d, the top surface 53d and the top surface 52d are connected in sequence and are located on the same plane.

[0080] The above-mentioned structure is the same in the mode converter 43 and the mode converter 44, but the optimal size is sometimes different in the mode converter 42, the mode converter 43 and the mode converter 44. The optimal size mentioned here refers to the optimal size based on maximizing the conversion efficiency of the polarization wave mode of each visible light. The tilt angle θ of the mode converter 42 can be in the range of 71° to 83°, or in the range of 73° to 81°. The tilt angle θ of the mode converter 43 can be in the range of 74° to 85°, or in the range of 77° to 83°. The tilt angle θ of the mode converter 44 can be in the range of 74° to 85°, or in the range of 77° to 83°. Therefore, the maximum range of the tilt angle θ of the mode converter 42, the mode converter 43 and the mode converter 44 is 71° to 85°.

[0081] The width (width W1) of the surface (bottom surface 51c, 52c, 53c) of each mode converter in contact with the main surface Sa may be 20% to 60% of the wavelength of the visible light transmitted in each mode converter, or 32% to 48%. The height T1 is smaller than the wavelength of the visible light transmitted in each mode converter. Specifically, the height T1 may be less than 1 μm, or less than 0.6 μm.

[0082] Next, refer to Figure 8 and Fig. 9 The operations of the mode converter 42 , the mode converter 43 , and the mode converter 44 will be described. Figure 8 It is a diagram for explaining the mode switching operation of the mode converter. Fig. 9 Yes means Figure 4 A graph showing an example of conversion efficiency of a mode converter shown in FIG. Fig. 9The horizontal axis of the graph represents the conversion length Lc [μm], and the vertical axis represents the conversion efficiency. Since the operations of each mode converter are the same, the mode converter 43 is used as an example for description.

[0083] like Figure 8 As shown, the mode converter 43 inputs the green light Lg in the TE mode into the waveguide 51, converts the polarization mode of the green light Lg from the TE mode to the TM mode in the waveguide 53, and emits the green light Lg in the TM mode from the waveguide 52. In this example, the wavelength of the green light Lg is set to 520 nm, the width W1 is set to 0.20 μm, the width W2 is set to 0.15 μm, and the height T1 is set to 0.30 μm.

[0084] like Figure 8 As shown, in the waveguide 51, since the polarization wave mode of the green light Lg is the TE mode, the vector of the electric field component is parallel to the Y-axis direction. When the green light Lg is incident on the waveguide 53, since the waveguide 53 is asymmetric in the Y-axis direction and asymmetric in the Z-axis direction, two mixed modes (the first mixed mode and the second mixed mode) in which the TE mode and the TM mode are mixed are excited as the polarization wave mode of the green light Lg. At this time, the horizontal electric field component of the first mixed mode and the horizontal electric field component of the second mixed mode will change depending on the shape and size of the waveguide 53.

[0085] In the present embodiment, the electric field component in the horizontal direction and the electric field component in the vertical direction of the first hybrid mode are easy to become equal. Since the second hybrid mode is in an orthogonal relationship with the first hybrid mode, the electric field component in the horizontal direction and the electric field component in the vertical direction of the second hybrid mode are easy to become equal, as with the first hybrid mode. For example, the electric field component in the horizontal direction of the first hybrid mode is 50% relative to the field of the first hybrid mode as a whole. Similarly, the electric field component in the horizontal direction of the second hybrid mode is 50% relative to the field of the second hybrid mode as a whole. In this case, the electric field vector of the first hybrid mode is rotated 45° from the Y-axis direction. The electric field vector of the second hybrid mode is rotated 45° from the Z-axis direction. The electric field vector of the first hybrid mode is orthogonal to the electric field vector of the second hybrid mode.

[0086] In the waveguide 53, since there is a difference between the transmission constant β1 of the first hybrid mode and the transmission constant β2 of the second hybrid mode, a phase difference is generated between the phase of the first hybrid mode and the phase of the second hybrid mode according to the length of the green light Lg transmitted in the waveguide 53. When the phase difference is π×(2n+1) (n is an integer greater than 0), when the green light Lg is transmitted from the emission end 53b of the waveguide 53 to the waveguide 52, the first hybrid mode and the second hybrid mode are coupled into one mode, and the polarization wave mode of the green light Lg is rotated 90° from the TE mode and converted into the TM mode.

[0087] The conversion efficiency (CE) of the mode converter is calculated using the rotation angle Convert length Lc to length L π It is represented by formula (1). In formula (1), the unit of CE is %. The tangent of the dielectric constant distribution ε(y,z), the electric field component Ey(y,z) of the horizontal mixed mode, and the electric field component Ez(y,z) of the vertical mixed mode are expressed by formula (2).

[0088] [Formula 1]

[0089]

[0090] [Formula 2]

[0091]

[0092] Here, the rotation angle It is the rotation angle between the optical axis of the hybrid mode and the plane parallel to the main surface Sa of the substrate S. The length L π The phase difference between the first mixed mode and the second mixed mode is π. The derived formula of the conversion length Lc will be described later. According to formula (1), at the rotation angle When the rotation angle is 45°, a conversion efficiency close to 100% can be obtained. According to formula (2), when the horizontal electric field component Ey(y, z) and the vertical electric field component Ez(y, z) of the first hybrid mode and the second hybrid mode are equal, the rotation angle According to the above, when the horizontal electric field component Ey(y,z) and the vertical electric field component Ez(y,z) of the first hybrid mode and the second hybrid mode are equal, a conversion efficiency close to 100% can be obtained.

[0093] like Fig. 9 As shown, the conversion efficiency CE1 represents the conversion efficiency when the polarization wave mode of the green light Lg incident as the TE mode is converted to the TM mode. The conversion efficiency CE2 represents the conversion efficiency when the polarization wave mode of the green light Lg incident as the TE mode is emitted as the TE mode. The conversion efficiency CE1 and the conversion efficiency CE2 vibrate periodically as the conversion length Lc increases, and the maximum value of the conversion efficiency CE1 and the maximum value of the conversion efficiency CE2 appear alternately every half period. It can be seen that the maximum value of either one is higher than 0.95, and high conversion efficiency can be achieved. In this embodiment, since the waveguide 53 converts the green light Lg in the TE mode into the green light Lg in the TM mode, the conversion length Lc is set to the length at which the conversion efficiency CE1 takes a maximum value. The conversion length Lc is calculated by formula (3).

[0094] [Formula 3]

[0095]

[0096] n eff1 represents the effective refractive index of the first mixed mode, n eff2 represents the effective refractive index of the second hybrid mode, and k0 represents the vacuum wave number. In this example, the conversion length Lc is calculated by formula (3) to be 17.44 μm. Fig. 9 As shown, when the conversion length Lc is 17.44 μm, the conversion efficiency when converting from the TE mode to the TM mode is 0.97.

[0097] In the laser module 4 and the optical element 40 described above, since the core layer C1 is composed of a material having an electro-optical effect, optical properties such as an effective refractive index vary according to the shape of the waveguide for visible light transmission. The waveguide 53 of each mode converter has an asymmetric shape in the Y-axis direction. By having such a shape of the waveguide 53, a first mixed mode and a second mixed mode in which a TE mode and a TM mode are mixed can be generated in the visible light transmitted in the waveguide 53. In addition, the horizontal electric field component and the vertical electric field component of the first mixed mode are easy to become equal. Since the second mixed mode is in an orthogonal relationship with the first mixed mode, the horizontal electric field component and the vertical electric field component of the second mixed mode are easy to become equal, similar to the first mixed mode. Therefore, the polarization wave mode of the visible light transmitted in the waveguide 53 can be converted from the TE mode to the TM mode with high conversion efficiency. Due to the above structure, according to the optical element 40, the conversion efficiency of the polarization wave mode of the visible light can be improved.

[0098] The waveguide 53 has a columnar shape whose length in the Y-axis direction continuously increases from the top surface 53d to the bottom surface 53c. According to this structure, compared with the case where the length of the waveguide 53 in the Y-axis direction gradually increases as it approaches the main surface Sa (waveguide 54 and waveguide 54A described later), the horizontal electric field component and the vertical electric field component of the first hybrid mode are easy to become equal. Since the second hybrid mode is in an orthogonal relationship with the first hybrid mode, the horizontal electric field component and the vertical electric field component of the second hybrid mode are easy to become equal, similar to the first hybrid mode. Therefore, the conversion efficiency from the TE mode to the TM mode can be further improved.

[0099] Furthermore, since the waveguide 53 has the inclined surface 53f, the waveguide 53 can be formed into an asymmetric shape in the Y-axis direction while suppressing the reduction of the cross-sectional area of ​​the waveguide 53 to a minimum. Therefore, it is possible to suppress the cross-sectional area of ​​the waveguide 53 from becoming extremely small relative to the cross-sectional areas of the waveguide 51 and the waveguide 52 connected to the waveguide 53. Thus, at the connection portion between the waveguide 51 and the waveguide 53 and the connection portion between the waveguide 53 and the waveguide 52, the difference in the mode field diameter of the mode propagating in the waveguide 51 and the waveguide 52 and the mode field diameter of the mixed mode propagating in the waveguide 53 can be suppressed to a minimum. Therefore, the coupling loss at the above-mentioned connection portion can be suppressed to a minimum, and as a result, the conversion efficiency can be improved.

[0100] The tilt angle θ is greater than 71° and less than 85°. According to this structure, compared with the case where the tilt angle θ is less than 71° or greater than 85°, the horizontal electric field component and the vertical electric field component of the first hybrid mode are easy to become equal. Since the second hybrid mode is in an orthogonal relationship with the first hybrid mode, the horizontal electric field component and the vertical electric field component of the second hybrid mode are easy to become equal, as with the first hybrid mode. Therefore, the conversion efficiency from the TE mode to the TM mode can be further improved. In addition, by making the tilt angle θ greater than 71° and less than 85°, the confinement of the visible light to the core layer C1 is weakened, and the visible light is easy to leak to the substrate S and the cladding C2. In this state, the waveguide 53 has an asymmetric shape in the Y-axis direction, so that the optical axis rotation of the polarization wave mode of the visible light is easy to occur, and as a result, the conversion efficiency can be improved.

[0101] The length (width W1) of the surface of each mode converter in contact with the main surface Sa in the Y-axis direction is greater than 32% and less than 48% of the wavelength of visible light. According to this structure, the horizontal electric field component and the vertical electric field component of the first hybrid mode are easy to become equal compared with the case where the width W1 is less than 32% or greater than 48% of the wavelength of visible light. Since the second hybrid mode is in an orthogonal relationship with the first hybrid mode, the horizontal electric field component and the vertical electric field component of the second hybrid mode are easy to become equal, as with the first hybrid mode. Therefore, the conversion efficiency from the TE mode to the TM mode can be further improved. In addition, by making the width W1 greater than 32% and less than 48% of the wavelength of visible light, the confinement of visible light to the core layer C1 is weakened, and visible light is easy to leak to the substrate S and the cladding C2. In this state, the waveguide 53 has an asymmetric shape in the Y-axis direction, so that the optical axis rotation of the polarization wave mode of visible light is easy to occur, and as a result, the conversion efficiency can be improved.

[0102] The length (height T1) of each mode converter in the Z-axis direction is smaller than the wavelength of visible light. According to this structure, by making the height T1 smaller than the wavelength of visible light, the horizontal electric field component and the vertical electric field component of the first hybrid mode are easily equalized. Since the second hybrid mode is in an orthogonal relationship with the first hybrid mode, the horizontal electric field component and the vertical electric field component of the second hybrid mode are easily equalized, as with the first hybrid mode. Therefore, the conversion efficiency from the TE mode to the TM mode can be further improved. In addition, by making the height T1 smaller than the wavelength of visible light, the confinement of visible light to the core layer C1 is weakened, and visible light is easily leaked to the substrate S and the cladding C2. In this state, the waveguide 53 has an asymmetric shape in the Y-axis direction, so that the optical axis rotation of the polarization wave mode of visible light is easily caused, and as a result, the conversion efficiency can be improved.

[0103] The combiner 48 is designed so that the combining efficiency when combining the red light, green light and blue light in the TM mode is higher than the combining efficiency when combining the red light, green light and blue light in the TE mode. In the laser module 4 and the optical element 40, the mode converter 42 converts the polarization mode of the red light Lr from the TE mode to the TM mode, the mode converter 43 converts the polarization mode of the green light Lg from the TE mode to the TM mode, and the mode converter 44 converts the polarization mode of the blue light Lb from the TE mode to the TM mode. Therefore, the combining efficiency of the combiner 48 can be improved.

[0104] The height of the mode converter 42 is the same as the height of the mode converter 43 and the height of the mode converter 44. According to this structure, the mode converter 42, the mode converter 43 and the mode converter 44 can be formed on the same substrate S and their respective heights can be made the same, so that the optical element 40 can be easily manufactured.

[0105] In order to output full-color laser light La by combining red light Lr, green light Lg, and blue light Lb, it is necessary to adjust the light intensity of each color of light according to the color of the output. In order to change the light intensity of each visible light in each laser light source, a large drive current is required. In the laser module 4 and the optical element 40, the light intensity of the red light Lr is modulated by the modulator 45, the light intensity of the green light Lg is modulated by the modulator 46, and the light intensity of the blue light Lb is modulated by the modulator 47. Therefore, full-color laser light La can be output without a large drive current.

[0106] Since the near-eye wearable device 1 includes the optical element 40 , it is possible to project an image onto the retina while improving the conversion efficiency of the polarization mode of visible light.

[0107] Alternatively, the laser module 4 (optical element 40) may emit laser light La in TE mode. For example, in the case where visible light in TM mode is emitted from each laser light source, each visible light is converted into TE mode in each mode converter. Specifically, the laser light source 411 emits red light Lr in TM mode, the laser light source 412 emits green light Lg in TM mode, and the laser light source 413 emits blue light Lb in TM mode. The mode converter 42 converts the polarization mode of the red light Lr from TM mode (first polarization mode) to TE mode (second polarization mode). The mode converter 43 converts the polarization mode of the green light Lg from TM mode to TE mode. The mode converter 44 converts the polarization mode of the blue light Lb from TM mode to TE mode. In this case, visible light in TE mode is incident on each modulator. In order to improve the modulation efficiency of each modulator, the core layer C1 can be composed of X-cut lithium niobate, and the optical axis (C-axis) of the lithium niobate can extend along the Y-axis direction.

[0108] The incident end and the emission end of each mode converter may also be swapped. That is, the waveguide 52 may also be an optical waveguide located at one end (incident end) of each mode converter in the X-axis direction, and the waveguide 51 may also be an optical waveguide located at the other end (emission end) of each mode converter in the X-axis direction. In this structure as well, the laser module 4 (optical element 40) may emit both TM mode laser La and TE mode laser La. For example, in the case where TE mode visible light is emitted from each laser light source, the visible light is converted into TM mode in each mode converter, and in the case where TM mode visible light is emitted from each laser light source, the visible light is converted into TE mode in each mode converter.

[0109] Next, refer to Fig.10 (a) illustrates a laser module according to another embodiment. Fig.10 (a) is a block diagram of a laser module according to another embodiment. Fig.10 The laser module 4A shown in (a) emits TE mode laser light La. The main difference between the laser module 4A and the laser module 4 is that the polarization wave mode of the visible light emitted by the laser light sources 411, 412, 413, and the positions of the modulators 45, 46, 47 and the mode converters 42, 43, 44 are reversed.

[0110] The laser light source 411 emits red light Lr in TM mode. The laser light source 412 emits green light Lg in TM mode. The laser light source 413 emits blue light Lb in TM mode. The red light Lr is incident from the laser light source 411 to the incident end of the modulator 45. The green light Lg is incident from the laser light source 412 to the incident end of the modulator 46. The blue light Lb is incident from the laser light source 413 to the incident end of the modulator 47. The emission end of the modulator 45 is optically connected to the incident end of the mode converter 42. The emission end of the modulator 46 is optically connected to the incident end of the mode converter 43. The emission end of the modulator 47 is optically connected to the incident end of the mode converter 44. The emission end of the mode converter 42, the emission end of the mode converter 43, and the emission end of the mode converter 44 are optically connected to the three incident ends of the combiner 48, respectively.

[0111] The mode converter 42 converts the polarization mode of the modulated red light Lr from the TM mode (first polarization mode) to the TE mode (second polarization mode). The mode converter 43 converts the polarization mode of the modulated green light Lg from the TM mode to the TE mode. The mode converter 44 converts the polarization mode of the modulated blue light Lb from the TM mode to the TE mode.

[0112] As described above, the core layer C1 is a lithium niobate thin film formed on the main surface Sa of the substrate S by sputtering, and the C-axis of the lithium niobate extends in the Z-axis direction. Therefore, the modulation efficiency of each modulator is improved in the TM mode. In the laser module 4A, since the visible light is emitted from each laser light source in the TM mode, after the light intensity of the visible light in the TM mode is modulated in each modulator, the polarization wave mode is converted from the TM mode to the TE mode in each mode converter. Then, each visible light with converted polarization wave mode is combined in the combiner 48, and the laser light La in the TE mode is transmitted from the combiner 48 to the optical component 5 (refer to Figure 2 ) is ejected.

[0113] Reference Fig.10 (b) illustrates a laser module according to still another embodiment. Fig.10 (b) is a block diagram of a laser module according to still another embodiment. Fig.10 The main difference between the laser module 4B shown in (b) and the laser module 4A is that the laser module 4B includes a mode converter 49 instead of the mode converter 42, the mode converter 43 and the mode converter 44, and a combiner 48 is arranged between each modulator and the mode converter 49.

[0114] Specifically, the emission ends of modulator 45, modulator 46 and modulator 47 are optically connected to the three incident ends of combiner 48. The emission end of combiner 48 is optically connected to the incident end of mode converter 49. The structure of mode converter 49 is the same as that of mode converter 42.

[0115] Similar to the laser module 4A, in the laser module 4B, since the visible light is emitted from each laser light source in the TM mode, the light intensity of the visible light in the TM mode is modulated in each modulator. Then, the visible light modulated in each modulator is combined in the combiner 48, and the polarization wave mode of the combined visible light is converted from the TM mode to the TE mode in the mode converter 49, and the laser light La in the TE mode is transmitted from the mode converter 49 to the optical component 5 (refer to FIG. 5 ). Figure 2 ) is ejected.

[0116] Next, refer to Fig.11 A laser module according to still another embodiment will be described. Fig.11 This is a block diagram of a laser module according to still another embodiment. Fig.11 The laser module 4C shown emits TE mode laser light La. The laser module 4C is mainly different from the laser module 4 in that the laser module 4C further includes a mode converter 42A, a mode converter 43A, and a mode converter 44A.

[0117] The mode converter 42A is provided between the modulator 45 and the combiner 48. The incident end of the mode converter 42A is optically connected to the emission end of the modulator 45, and the emission end of the mode converter 42A is optically connected to the incident end of the combiner 48. The mode converter 42A converts the polarization wave mode of the modulated red light Lr from the TM mode to the TE mode.

[0118] The mode converter 43A is provided between the modulator 46 and the combiner 48. The incident end of the mode converter 43A is optically connected to the emission end of the modulator 46, and the emission end of the mode converter 43A is optically connected to the other incident end of the combiner 48. The mode converter 43A converts the polarization mode of the modulated green light Lg from the TM mode to the TE mode.

[0119] The mode converter 44A is provided between the modulator 47 and the combiner 48. The incident end of the mode converter 44A is optically connected to the emission end of the modulator 47, and the emission end of the mode converter 44A is optically connected to another incident end of the combiner 48. The mode converter 44A converts the polarization wave mode of the modulated blue light Lb from the TM mode to the TE mode.

[0120] In the laser module 4C, since the visible light is emitted from each laser light source in the TE mode, after the polarization wave mode of each visible light emitted from each laser light source is converted from the TE mode to the TM mode in each mode converter, the light intensity of the visible light in the TM mode is modulated in each modulator. Then, the polarization wave mode of each modulated visible light is converted from the TM mode to the TE mode in each mode converter. Then, each visible light is combined in the combiner 48, and the laser light La in the TE mode is transmitted from the combiner 48 to the optical component 5 (refer to FIG. 5 ). Figure 2 ) is ejected.

[0121] In the laser modules 4A, 4B, and 4C, the core layer C1 may also be composed of X-cut lithium niobate, and the optical axis (C-axis) of the lithium niobate may also extend in the Y-axis direction. In this case, the modulation efficiency of each modulator is improved in the TE mode. In the laser modules 4A and 4B, visible light may be emitted from each laser light source in TE mode, and the light intensity of the visible light in the TE mode may be modulated in each modulator. In the laser module 4C, visible light may be emitted from each laser light source in TM mode, and converted into TE mode in each mode converter, and then the light intensity of the visible light in the TE mode may be modulated in each modulator.

[0122] [Modifications]

[0123] As mentioned above, although embodiment of this disclosure was described, this disclosure is not necessarily limited to the said embodiment, Various changes can be made within the range which does not deviate from the summary.

[0124] The shape of the waveguide 53 is not limited to Figure 4 and Figure 6 For example, a waveguide 53 may be replaced by a Fig.12 The waveguide 54 is a waveguide 54 having a cross section shown in (a). The waveguide 54 is mainly different from the waveguide 53 in its shape. The waveguide 54 has a two-step stepped shape in which the length in the Y-axis direction gradually increases as it approaches the main surface Sa. Like the waveguide 53, the waveguide 54 is asymmetric in the Z-axis direction and asymmetric in the Y-axis direction.

[0125] Specifically, the waveguide 54 includes a bottom surface 54c, a top surface 54d, a side surface 54e, a step surface 54f, a stepped surface 54g, and a step surface 54h. The bottom surface 54c is a surface facing the main surface Sa, and is in contact with the main surface Sa over its entire surface. The top surface 54d is a surface that is located on the side opposite to the bottom surface 54c in the Z-axis direction and is substantially parallel to the bottom surface 54c. The side surface 54e is a surface that connects one end of the bottom surface 54c and one end of the top surface 54d. The stepped surface 54g is a surface that is located closer to the main surface Sa than the top surface 54d and is substantially parallel to the top surface 54d. The step surface 54f is a surface that connects the other end of the top surface 54d and one end of the stepped surface 54g. The step surface 54h is a surface that connects the other end of the stepped surface 54g and the other end of the bottom surface 54c.

[0126] The side surface 54e, the step surface 54f, and the step surface 54h are respectively set to form an angle of substantially 90° with respect to the bottom surface 54c (main surface Sa). The top surface 54d and the step surface 54f form a stepped shape of one step. The step surface 54g and the step surface 54h form a stepped shape of another step. The length obtained by adding the width of the top surface 54d and the width of the step surface 54g is equal to the width of the bottom surface 54c.

[0127] In the waveguide 54, for example, the horizontal electric field component of the first hybrid mode accounts for about 45% of the entire field of the first hybrid mode, and the horizontal electric field component of the second hybrid mode accounts for about 55% of the entire field of the second hybrid mode.

[0128] For example, the waveguide 54 that converts the polarization mode of the red light Lr from the TE mode to the TM mode is used for explanation. When the wavelength of the red light Lr is set to 638nm, the height of the side surface 54e is set to 560nm, the width of the bottom surface 54c is set to 280nm, the height of the step surface 54f is set to 380nm, and the width of the step surface 54g is set to 90nm, the following is obtained: Fig.12 The conversion efficiency CE1 and the conversion efficiency CE2 shown in (b) are shown in FIG. Fig.12 As shown in (b), the maximum value of conversion efficiency CE1 is about 0.75, and the maximum value of conversion efficiency CE2 is about 0.9. In this case, the conversion length Lc is calculated as 20.5 μm by formula (3). When the conversion length Lc is 20.5 μm, the conversion efficiency when converting from TE mode to TM mode is 0.74.

[0129] Instead of the waveguide 54, a Fig.13The waveguide 54A has a cross-section shown in (a). The waveguide 54A has a three-step stepped shape whose length in the Y-axis direction gradually increases as it approaches the main surface Sa. In other words, the waveguide 54A has a shape in which one step of stepped shape is added to the step shape included in the waveguide 54. Like the waveguides 53 and 54, the waveguide 54A is asymmetric in the Z-axis direction and asymmetric in the Y-axis direction.

[0130] Specifically, in addition to the various surfaces of the waveguide 54, the waveguide 54A also includes a step surface 54i and a step difference surface 54j. The step surface 54i is a surface that is located closer to the main surface Sa than the step surface 54g and is substantially parallel to the top surface 54d. The step difference surface 54j is a surface that connects the other end of the step surface 54i with the other end of the bottom surface 54c. In the waveguide 54A, the step difference surface 54h connects the other end of the step surface 54g with one end of the step surface 54i. The step difference surface 54j is set to be substantially at an angle of 90° relative to the bottom surface 54c (main surface Sa). The step surface 54i and the step difference surface 54j form another step shape. The length obtained by adding the width of the top surface 54d, the width of the step surface 54g, and the width of the step surface 54i is equal to the width of the bottom surface 54c.

[0131] In the waveguide 54A, for example, the horizontal electric field component of the first hybrid mode accounts for about 57% of the entire field of the first hybrid mode, and the horizontal electric field component of the second hybrid mode accounts for about 55% of the entire field of the second hybrid mode.

[0132] For example, the waveguide 54A that converts the polarization mode of the red light Lr from the TE mode to the TM mode is used for explanation. When the wavelength of the red light Lr is set to 638nm, the height of the side surface 54e is set to 560nm, the width of the bottom surface 54c is set to 280nm, the height of the step surface 54f is set to 150nm, the width of the step surface 54g is set to 120nm, the height of the step surface 54h is set to 260nm, and the width of the step surface 54i is set to 80nm, the following is obtained: Fig.13 The conversion efficiency CE1 and the conversion efficiency CE2 shown in (b) are shown in FIG. Fig.13 As shown in (b), the maximum value of conversion efficiency CE1 is about 0.6, and the maximum value of conversion efficiency CE2 is about 0.55. In this case, the conversion length Lc is calculated as 16.0 μm by formula (3). When the conversion length Lc is 16.0 μm, the conversion efficiency when converting from TE mode to TM mode is 0.61.

[0133] According to the mode converter including the waveguide 54 or the waveguide 54A, the polarization wave mode of visible light can be converted from the TE mode to the TM mode. According to this structure, the horizontal electric field component and the vertical electric field component of the first hybrid mode are easy to become equal. Since the second hybrid mode is in an orthogonal relationship with the first hybrid mode, the horizontal electric field component and the vertical electric field component of the second hybrid mode are easy to become equal, similar to the first hybrid mode. Therefore, the conversion efficiency from the TE mode to the TM mode can be improved.

[0134] It can also be used instead of waveguide 53 Fig.14 The waveguide 55 is shown in (a). The waveguide 55 is mainly different from the waveguide 53 in its shape. Like the waveguide 53, the waveguide 55 is asymmetric in the Z-axis direction and asymmetric in the Y-axis direction.

[0135] Specifically, the waveguide 55 includes a bottom surface 55c, a top surface 55d, and a pair of side surfaces 55e and 55f connecting the bottom surface 55c and the top surface 55d. The bottom surface 55c is a surface facing the main surface Sa, and is in contact with the main surface Sa over its entire surface. The top surface 55d is a surface provided on the side opposite to the bottom surface 55c in the Z-axis direction and substantially parallel to the bottom surface 55c. The pair of side surfaces 55e and 55f are surfaces connecting the bottom surface 55c and the top surface 55d, and are substantially parallel to each other.

[0136] The top surface 55d is provided with a groove Cv1 and a groove Cv2 extending in the X-axis direction and recessed toward the bottom surface 55c. The groove Cv1 and the groove Cv2 are arranged in sequence from the side surface 55e toward the side surface 55f. The cross-sectional shape of each of the groove Cv1 and the groove Cv2 intersecting (orthogonal to) the X-axis direction is a rectangular shape. The length (depth) of the groove Cv1 in the Z-axis direction is shorter than the length (depth) of the groove Cv2 in the Z-axis direction.

[0137] In the waveguide 55, for example, the horizontal electric field component of the first hybrid mode accounts for about 40% of the entire field of the first hybrid mode, and the horizontal electric field component of the second hybrid mode accounts for about 60% of the entire field of the second hybrid mode.

[0138] For example, the waveguide 55 that converts the polarization mode of the red light Lr from the TE mode to the TM mode is used for explanation. When the wavelength of the red light Lr is set to 638nm, the width of the bottom surface 55c is set to 280nm, the separation distance between the side surface 55e and the groove Cv1 is set to 170nm, the separation distance between the groove Cv1 and the groove Cv2 is set to 40nm, the width of the groove Cv1 is set to 20nm, the width of the groove Cv2 is set to 20nm, the height of the side surface 55e is set to 400nm, the depth of the groove Cv1 is set to 250nm, and the depth of the groove Cv2 is set to 300nm, the following is obtained: Fig.14The conversion efficiency CE1 and the conversion efficiency CE2 shown in (b) are shown in FIG. Fig.14 As shown in (b), the maximum value of conversion efficiency CE1 is about 0.9, and the maximum value of conversion efficiency CE2 is about 0.95. In this case, the conversion length Lc is calculated as 33.5 μm by formula (3). When the conversion length Lc is 33.5 μm, the conversion efficiency when converting from TE mode to TM mode is 0.87.

[0139] According to the mode converter including the waveguide 55 described above, the conversion efficiency of the polarization wave mode of visible light can be improved compared with the mode converter including the waveguide 54 or the waveguide 54A. In addition, since the groove Cv1 and the groove Cv2 are provided in the waveguide 55, the waveguide 55 can be formed into an asymmetric shape in the Y-axis direction while suppressing the reduction of the cross-sectional area of ​​the waveguide 55 compared with the waveguide 54 and the waveguide 54A. Therefore, it is possible to suppress the cross-sectional area of ​​the waveguide 55 from becoming extremely small relative to the cross-sectional areas of the waveguides 51 and 52 connected to the waveguide 55. As a result, at the connection portion between the waveguide 51 and the waveguide 55 and the connection portion between the waveguide 55 and the waveguide 52, the difference in the mode field diameter of the mode transmitted in the waveguide 51 and the waveguide 52 and the mode field diameter of the mixed mode transmitted in the waveguide 55 can be suppressed to a minimum. Therefore, the coupling loss of the above-mentioned connection portion can be suppressed to a minimum, and as a result, the conversion efficiency can be improved.

[0140] [Example]

[0141] In order to illustrate the above effects, the present disclosure is described in more detail below through examples. The present disclosure is not limited to these examples.

[0142] <Evaluation of conversion loss based on the ratio of width W1 to wavelength λ of visible light>

[0143] The effect of the ratio of the width W1 to the wavelength λ of visible light on the conversion loss was evaluated. Figure 3 The maximum conversion efficiency for each value of the width W1 is calculated by changing the value of the width W1 by changing the value of the width W1. The maximum conversion efficiency when the polarization wave mode of the visible light is converted from the TE basic mode to the TM basic mode is calculated by setting the height T1 to 0.3 μm, the wavelength λ of the red light to 638 nm, the wavelength λ of the green light to 520 nm, and the wavelength λ of the blue light to 455 nm. The conversion efficiency represents the light intensity of the visible light in the TM basic mode when the light intensity of the visible light in the TE basic mode is set to 1. The conversion loss [dB] is obtained by converting the maximum conversion efficiency into the dB unit.

[0144] The calculation results for red light are shown in Table 1 and Fig.15Table 1 shows the width W1, the maximum conversion efficiency and the conversion loss, and also shows the width W2 [μm] and the conversion length Lc [μm] when the maximum conversion efficiency is obtained at each value of the width W1, and the ratio W1 / λ [%]. Fig.15 The horizontal axis of (a) represents the ratio W1 / λ [%], Fig.15 The vertical axis of (a) represents conversion loss [dB]. This indicates that high conversion efficiency is achieved when the maximum conversion efficiency is higher than 0.60 or the conversion loss is lower than 2.2 dB.

[0145] [Table 1]

[0146] W1 / λ[%] W1[μm] W2[μm] Lc[μm] Maximum conversion efficiency Conversion loss [dB] 25 0.16 0.11 47 0.53 2.7 28 0.18 0.09 31 0.50 3.0 31 0.20 0.07 23 0.47 3.3 34 0.22 0.19 33 0.78 1.1 38 0.24 0.17 17 0.96 0.2 41 0.26 0.15 12 0.88 0.5 44 0.28 0.13 9 0.77 1.2 47 0.30 0.11 8 0.65 1.9 50 0.32 0.09 7 0.53 2.7 53 0.34 0.09 6 0.44 3.6

[0147] According to Table 1 and Fig.15 (a) shows that when the ratio W1 / λ is in the range of 34% to 47%, the maximum conversion efficiency is higher than 0.60 and the conversion loss is lower than 2.2dB. Based on the change in conversion loss (slope) relative to the ratio W1 / λ per unit when the ratio W1 / λ changes from 31% to 34%, it can be inferred that the conversion loss is lower than 2.2dB when the ratio W1 / λ is 32%. Similarly, based on the change in conversion loss (slope) relative to the ratio W1 / λ per unit when the ratio W1 / λ changes from 47% to 50%, it can be inferred that the conversion loss is lower than 2.2dB when the ratio W1 / λ is 48%. Based on the above, it can be said that high conversion efficiency can be achieved when the ratio W1 / λ is in the range of 32% to 48%.

[0148] The calculation results of green light are shown in Table 2 and Fig.15 Table 2 shows the width W1, the maximum conversion efficiency and the conversion loss, and also shows the width W2 [μm] and the conversion length Lc [μm] when the maximum conversion efficiency is obtained at each value of the width W1, and the ratio W1 / λ [%]. Fig.15 The horizontal axis of (b) represents the ratio W1 / λ[%], Fig.15 The vertical axis of (b) represents conversion loss [dB].

[0149] [Table 2]

[0150] W1 / λ[%] W1[μm] W2[μm] Lc[μm] Maximum conversion efficiency Conversion loss [dB] 19 0.10 0.07 32 0.03 15.8 24 0.13 0.06 25 0.14 8.6 29 0.15 0.05 21 0.20 7.0 34 0.18 0.02 23 0.36 4.4 38 0.20 0.15 18 0.96 0.2 43 0.23 0.12 8 0.85 0.7 48 0.25 0.10 6 0.64 2.0 53 0.28 0.07 5 0.45 3.4

[0151] According to Table 2 and Fig.15 (b) shows that when the ratio W1 / λ is in the range of 38% to 48%, the maximum conversion efficiency is higher than 0.60 and the conversion loss is lower than 2.2 dB. Therefore, it can be said that when the ratio W1 / λ is in the range of 38% to 48%, high conversion efficiency can be achieved.

[0152] The calculation results of blue light are shown in Table 3 and Fig.15 Table 3 shows the width W1, the maximum conversion efficiency and the conversion loss, and also shows the width W2 [μm] and the conversion length Lc [μm] when the maximum conversion efficiency is obtained at each value of the width W1, and the ratio W1 / λ [%]. Fig.15 The horizontal axis of (c) represents the ratio W1 / λ[%], Fig.15 The vertical axis of (c) represents conversion loss [dB].

[0153] [Table 3]

[0154] W1 / λ[%] W1[μm] W2[μm] Lc[μm] Maximum conversion efficiency Conversion loss [dB] 22 0.10 0.03 41 0.15 8.3 27 0.13 0.04 3 0.13 8.9 33 0.15 0.04 10 0.29 5.4 38 0.18 0.13 14 0.86 0.6 44 0.20 0.09 8 0.78 1.1 49 0.23 0.08 5 0.39 4.1 55 0.25 0.06 4 0.13 8.9

[0155] According to Table 3 and Fig.15 (c) shows that when the ratio W1 / λ is in the range of 38% to 44%, the maximum conversion efficiency is higher than 0.60 and the conversion loss is lower than 2.2 dB. Therefore, it can be said that when the ratio W1 / λ is in the range of 38% to 44%, high conversion efficiency can be achieved.

[0156] <Evaluation of conversion loss at height T1>

[0157] The effect of height T1 on conversion loss was evaluated. Figure 3 The maximum conversion efficiency for each value of the height T1 was calculated by changing the value of the height T1 of the mode converter having the same structure as the mode converter 42 shown. The maximum conversion efficiency when the polarization mode of red light is converted from the TE fundamental mode to the TM fundamental mode was calculated by setting the wavelength λ to 638 nm.

[0158] The calculation results are shown in Table 4 and Fig.16 Table 4 shows the height T1, the maximum conversion efficiency, and the conversion loss, and also shows the width W1 [μm], the width W2 [μm], and the conversion length Lc [μm] when the maximum conversion efficiency is obtained at each value of the height T1. Fig.16 The horizontal axis represents the waveguide height T1 [μm], Fig.16 The vertical axis represents conversion loss [dB].

[0159] [Table 4]

[0160] T1[μm] W1[μm] W2[μm] Lc[μm] Maximum conversion efficiency Conversion loss [dB] 0.3 0.24 0.17 17 0.96 0.2 0.4 0.25 0.20 31 0.98 0.1 0.5 0.25 0.20 19 0.81 0.9 0.6 0.25 0.20 53 0.47 3.3

[0161] According to Table 4 and Fig.16 When the height T1 is less than 0.5 μm, the maximum conversion efficiency is higher than 0.6 and the conversion loss is lower than 2.2 dB. Based on the above, it can be said that high conversion efficiency can be achieved when the height T1 is smaller than the wavelength λ (638 nm) of the visible light used in this calculation.

[0162] <Evaluation of conversion loss at tilt angle θ>

[0163] The effect of the tilt angle θ on the conversion loss was evaluated. Figure 3 The mode converter having the same structure as the mode converter 42 shown in the figure was used to change the value of the tilt angle θ, and the conversion loss at each value of the tilt angle θ was calculated. In the evaluation of red light, a mode converter having a conversion length Lc of 16 μm and a mode converter having a conversion length Lc of 18 μm were used, and the wavelength λ of the red light was set to 638 nm, the height T1 was set to 0.3 μm, and the width W1 was set to 0.24 μm. By changing the width W2, the conversion loss when the polarization wave mode of the red light was converted from the TE basic mode to the TM basic mode at each value of the tilt angle θ was calculated.

[0164] In the evaluation of green light, a mode converter having a conversion length Lc of 14 μm and a mode converter having a conversion length Lc of 16 μm were used, and the wavelength λ of the green light was set to 520 nm, the height T1 was set to 0.3 μm, and the width W1 was set to 0.20 μm. By changing the width W2, the conversion loss when the polarization wave mode of the green light is converted from the TE basic mode to the TM basic mode at each value of the tilt angle θ was calculated. In the evaluation of blue light, a mode converter having a conversion length Lc of 12 μm and a mode converter having a conversion length Lc of 14 μm were used, and the wavelength λ of the blue light was set to 455 nm, the height T1 was set to 0.3 μm, and the width W1 was set to 0.18 μm. By changing the width W2, the conversion loss when the polarization wave mode of the blue light is converted from the TE basic mode to the TM basic mode at each value of the tilt angle θ was calculated.

[0165] The calculation results for red light are Fig.17 is shown in (a). Fig.17 The horizontal axis of (a) represents the tilt angle θ [°], Fig.17 The vertical axis of (a) represents conversion loss [dB]. Fig.17 (a) shows that when the conversion length Lc is 16 μm, when the tilt angle θ is 73° to 81°, the conversion loss is less than 2.2 dB, and high conversion efficiency can be achieved. It can be seen that when the conversion length Lc is 18 μm, when the tilt angle θ is 74° to 81°, the conversion loss is less than 2.2 dB, and high conversion efficiency can be achieved.

[0166] The calculation results for green light are Fig.17 is shown in (b). Fig.17 The horizontal axis of (b) represents the tilt angle θ [°], Fig.17The vertical axis of (b) represents conversion loss [dB]. Fig.17 (b) shows that when the conversion length Lc is 14 μm, when the tilt angle θ is 77° to 82°, the conversion loss is less than 2.2 dB, and high conversion efficiency can be achieved. It can be seen that when the conversion length Lc is 16 μm, when the tilt angle θ is 78° to 83°, the conversion loss is less than 2.2 dB, and high conversion efficiency can be achieved.

[0167] The calculation results for blue light are Fig.17 As shown in (c). Fig.17 The horizontal axis of (c) represents the tilt angle θ [°], Fig.17 The vertical axis of (c) represents conversion loss [dB]. Fig.17 (c) shows that when the conversion length Lc is 12 μm, when the tilt angle θ is 77° to 82°, the conversion loss is less than 2.2 dB, and high conversion efficiency can be achieved. It can be seen that when the conversion length Lc is 14 μm, when the tilt angle θ is 78° to 82°, the conversion loss is less than 2.2 dB, and high conversion efficiency can be achieved.

[0168] According to the above evaluation results, as an example of the range of the tilt angle θ that can achieve high conversion efficiency, Fig.17 (a)~ Fig.17 Alternatively, from the viewpoint of increasing the degree of freedom in waveguide design, the range of the tilt angle θ may be 71° to 85°, which is an increase of ±2° from the above range.

[0169] (Note)

[0170] [Project 1]

[0171] An optical element, wherein

[0172] The optical component has:

[0173] a substrate having a main surface; and

[0174] The core layer is disposed on the main surface and is composed of a material having an electro-optical effect.

[0175] The core layer includes a mode converter extending in a first direction along the main surface and converting a polarization mode of visible light between a TM mode and a TE mode.

[0176] The mode converter has:

[0177] a first waveguide for injecting the visible light in a first polarization mode, which is one of the TE mode and the TM mode;

[0178] a second waveguide configured to emit the visible light in a second polarization mode which is the other polarization mode of the TE mode and the TM mode; and

[0179] a third waveguide provided between the first waveguide and the second waveguide, and converting the visible light from the first polarization mode to the second polarization mode,

[0180] The third waveguide has an asymmetric shape in a second direction along the main surface intersecting the first direction.

[0181] [Project 2]

[0182] The optical element according to item 1, wherein:

[0183] The third waveguide has: a bottom surface facing the main surface; a top surface provided on the opposite side of the bottom surface in a third direction intersecting the first direction and the second direction; and an inclined surface connecting the top surface and the bottom surface.

[0184] The third waveguide has a columnar shape in which the length in the second direction continuously increases from the top surface to the bottom surface.

[0185] [Item 3]

[0186] The optical element according to item 2, wherein:

[0187] An inclination angle between the inclined surface and the main surface is greater than or equal to 71° and less than or equal to 85°.

[0188] [Item 4]

[0189] The optical element according to item 1, wherein:

[0190] The third waveguide has a stepped shape in which the length in the second direction gradually increases as it approaches the main surface.

[0191] [Item 5]

[0192] The optical element according to item 1, wherein:

[0193] The third waveguide has a bottom surface facing the main surface and a top surface provided on a side opposite to the bottom surface in a third direction intersecting the first direction and the second direction.

[0194] The top surface is provided with a groove extending in the first direction and recessed toward the bottom surface.

[0195] [Item 6]

[0196] The optical element according to any one of items 1 to 5, wherein

[0197] A length of a surface of the mode converter in contact with the main surface in the second direction is not less than 32% and not more than 48% of a wavelength of the visible light.

[0198] [Item 7]

[0199] The optical element according to any one of items 1 to 6, wherein

[0200] The length of the mode converter in a third direction intersecting the first direction and the second direction is smaller than the wavelength of the visible light.

[0201] [Item 8]

[0202] The optical element according to any one of items 1 to 7, wherein

[0203] The core layer has:

[0204] a first mode converter, which is the mode converter that converts the polarization mode of red light from the first polarization mode to the second polarization mode;

[0205] a second mode converter, which is the mode converter that converts the polarization mode of green light from the first polarization mode to the second polarization mode;

[0206] a third mode converter, which is the mode converter that converts the polarization mode of blue light from the first polarization mode to the second polarization mode; and

[0207] A combiner combines the red light, the green light, and the blue light to emit laser light.

[0208] [Item 9]

[0209] The optical element according to item 8, wherein:

[0210] The first mode converter, the second mode converter, and the third mode converter have the same length in a third direction intersecting the first direction and the second direction.

[0211] [Item 10]

[0212] The optical element according to item 8 or item 9, wherein:

[0213] The core layer also has:

[0214] a first modulator, which modulates the intensity of the red light;

[0215] a second modulator for modulating the intensity of the green light; and

[0216] The third modulator modulates the intensity of the blue light.

[0217] [Item 11]

[0218] A laser module, wherein:

[0219] The laser module has:

[0220] The optical element according to any one of items 8 to 10;

[0221] a first laser light source that emits the red light in the first polarization mode;

[0222] a second laser light source that emits the green light in the first polarization mode; and

[0223] The third laser light source emits the blue light in the first polarization mode.

[0224] [Item 12]

[0225] A near-eye wearable device, wherein:

[0226] The near-eye wearable device has:

[0227] The laser module as described in item 11;

[0228] a movable reflecting mirror for scanning using the laser light emitted from the laser module; and

[0229] A reflector projects an image onto the retina by reflecting the laser light after passing through the movable reflector and guiding the reflected light toward the retina of a user wearing the near-eye wearable device.

Claims

1. An optical element, wherein: The optical component has: a substrate having a main surface; and The core layer is disposed on the main surface and is composed of a material having an electro-optical effect. The core layer includes a mode converter extending in a first direction along the main surface and converting a polarization mode of visible light between a TM mode and a TE mode. The mode converter has: a first waveguide for injecting the visible light in a first polarization mode, which is one of the TE mode and the TM mode; a second waveguide configured to emit the visible light in a second polarization mode which is the other polarization mode of the TE mode and the TM mode; as well as a third waveguide provided between the first waveguide and the second waveguide, and converting the visible light from the first polarization mode to the second polarization mode, The third waveguide has an asymmetric shape in a second direction along the main surface intersecting the first direction.

2. The optical element according to claim 1, wherein The third waveguide has: a bottom surface facing the main surface; a top surface provided on the opposite side of the bottom surface in a third direction intersecting the first direction and the second direction; and an inclined surface connecting the top surface and the bottom surface. The third waveguide has a columnar shape in which the length in the second direction continuously increases from the top surface to the bottom surface.

3. The optical element according to claim 2, wherein: An inclination angle between the inclined surface and the main surface is greater than or equal to 71° and less than or equal to 85°.

4. The optical element according to claim 1, wherein The third waveguide has a stepped shape in which the length in the second direction gradually increases as it approaches the main surface.

5. The optical element according to claim 1, wherein The third waveguide has: a bottom surface facing the main surface; and a top surface disposed on a side opposite to the bottom surface in a third direction intersecting the first direction and the second direction, The top surface is provided with a groove extending in the first direction and recessed toward the bottom surface.

6. The optical element according to any one of claims 1 to 5, wherein A length of a surface of the mode converter in contact with the main surface in the second direction is not less than 32% and not more than 48% of a wavelength of the visible light.

7. The optical element according to any one of claims 1 to 6, wherein The length of the mode converter in a third direction intersecting the first direction and the second direction is smaller than the wavelength of the visible light.

8. The optical element according to any one of claims 1 to 7, wherein The core layer has: a first mode converter, which is the mode converter that converts the polarization mode of red light from the first polarization mode to the second polarization mode; a second mode converter, which is the mode converter that converts the polarization mode of green light from the first polarization mode to the second polarization mode; a third mode converter, which is the mode converter for converting the polarization mode of blue light from the first polarization mode to the second polarization mode; as well as A combiner combines the red light, the green light, and the blue light to emit laser light.

9. The optical element according to claim 8, wherein: The first mode converter, the second mode converter, and the third mode converter have the same length in a third direction intersecting the first direction and the second direction.

10. The optical element according to claim 8 or claim 9, wherein: The core layer also has: a first modulator, which modulates the intensity of the red light; a second modulator for modulating the intensity of the green light; and The third modulator modulates the intensity of the blue light.

11. A laser module, wherein: The laser module has: The optical element according to any one of claims 8 to 10; a first laser light source that emits the red light in the first polarization mode; a second laser light source that emits the green light in the first polarization mode; and The third laser light source emits the blue light in the first polarization mode.

12. A near-eye wearable device, wherein: The near-eye wearable device has: The laser module according to claim 11; a movable reflecting mirror for scanning using the laser light emitted from the laser module; and A reflector projects an image onto the retina by reflecting the laser light after passing through the movable reflector and guiding the reflected light toward the retina of a user wearing the near-eye wearable device.

Images