Optical element and laser module

Abstract

The invention relates to an optical element and a laser module. In the optical element, a core layer is provided with a first conversion unit that converts a polarization mode of visible light between a TM0 mode and a TE1 mode, and the first conversion unit is provided with an upper tapered portion and a lower tapered portion that are stacked in a second direction. In the first region, the length of the upper tapered section in the third direction continuously increases from a first length to a second length that is longer than the first length as the length of the upper tapered section extends from the first end toward the intermediate position, and in the second region, the length of the lower tapered section in the third direction continuously increases from the first length to a third length that is longer than the second length as the length of the lower tapered section extends from the first end toward the intermediate position. The length of the upper tapered portion in the third direction continuously increases from a second length to a fourth length from the intermediate position toward the second end, the length of the lower tapered portion in the third direction continuously decreases from the third length to the fourth length from the intermediate position toward the second end, and the fourth length is longer than the second length and shorter than the third length.

Description

[0001] Cross-reference to related applications

[0002] This application is an application claiming the benefit of priority based on Japanese Patent Application No. 2023-184914 filed with the Japan Patent Office on October 27, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to an optical element and a laser module. Background Art

[0004] Among the polarization modes of light transmitted in an optical waveguide, there are a polarization mode having a main electric field in a horizontal direction relative to a substrate, namely a TE (Transverse Electric) mode, and a polarization mode having a main electric field in a vertical direction relative to the substrate, namely a TM (Transverse Magnetic) mode. An optical waveguide element that converts these polarization modes is known. For example, Japanese Patent Gazette No. 2023-34349 describes an optical waveguide element having a core, the core having a tapered shape whose width increases continuously from an input end toward an output end, and a groove having a V-shaped cross section formed on the upper surface. Summary of the invention

[0005] The optical waveguide element described in Japanese Patent Application Laid-Open No. 2023-34349 converts TM0 mode light having a wavelength of 1550 nm into TE1 mode light, but does not take visible light into consideration.

[0006] The present disclosure describes an optical element and a laser module that can convert the polarization mode of visible light.

[0007] 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 TM0 mode and a TE0 mode. The mode converter comprises: an incident portion, which is located at one end of the mode converter in the first direction, for incident visible light of a first polarization wave mode, which is one polarization wave mode of the TM0 mode and the TE0 mode; an emission portion, which is located at the other end of the mode converter in the first direction, for emitting visible light of a second polarization wave mode, which is the other polarization wave mode of the TM0 mode and the TE0 mode; a first conversion portion, which is arranged between the incident portion and the emission portion, for converting the polarization wave mode of the visible light between a TM0 mode and a TE1 mode; and a second conversion portion, which is arranged between the incident portion and the emission portion, for converting the polarization wave mode of the visible light between a TE0 mode and a TE1 mode. The first conversion portion includes two ends in the first direction, namely, a first end and a second end, and an upper tapered portion and a lower tapered portion stacked in a second direction intersecting the main surface. In a first region from the first end to a middle position between the first end and the second end of the first conversion portion, the length of the upper tapered portion in a third direction intersecting the first direction and the second direction continuously increases from a first length to a second length longer than the first length as it moves from the first end toward the middle position, and the length of the lower tapered portion in the third direction continuously increases from the first length to a third length longer than the second length as it moves from the first end toward the middle position. In a second region from the middle position to the second end of the first conversion portion, the length of the upper tapered portion in the third direction continuously increases from the second length to a fourth length as it moves from the middle position toward the second end, and the length of the lower tapered portion in the third direction continuously decreases from the third length to a fourth length as it moves from the middle position toward the second end, and the fourth length is longer than the second length and shorter than the third length.

[0008] In the optical element, the first conversion section converts the polarization wave mode of visible light between the TM0 mode and the TE1 mode. In the first conversion section, the upper tapered section and the lower tapered section are stacked in the second direction, and the first conversion section has asymmetry in the second direction. In the first conversion section, as the distance from the first end is increased, the effective refractive index of the TM0 mode and the effective refractive index of the TE1 mode approach each other, thereby causing conversion between the TM0 mode and the TE1 mode. For example, when visible light in the TM0 mode is incident on the first end of the first conversion section, the polarization wave mode of the visible light is converted from the TM0 mode to the TE1 mode in the first conversion section, and then converted from the TE1 mode to the TE0 mode in the second conversion section. Similarly, when visible light in the TE0 mode is incident on the second conversion section, the polarization wave mode of the visible light is converted from the TE0 mode to the TE1 mode in the second conversion section, and then converted from the TE1 mode to the TM0 mode in the first conversion section. As described above, the polarization wave mode of visible light can be converted between the TM0 mode and the TE0 mode.

[0009] The first polarization mode may be a TM0 mode, and the second polarization mode may be a TE0 mode. The first end may be connected to the incident portion. The second conversion portion may be provided between the first conversion portion and the emission portion. In this case, visible light incident in the TM0 mode may be emitted in the TE0 mode.

[0010] The first polarization mode may be a TE0 mode, and the second polarization mode may be a TM0 mode. The first end may be connected to the emission portion. The second conversion portion may be provided between the incident portion and the first conversion portion. In this case, visible light incident in the TE0 mode may be emitted in the TM0 mode.

[0011] The length of the first conversion portion in the first direction may also be greater than 360 μm and less than 1010 μm. The second length may also be greater than 0.5 μm and less than 1.0 μm. The third length may also be greater than 1.0 μm and less than 5.0 μm. In this case, the loss of light intensity in the conversion between the TM0 mode and the TE1 mode can be reduced. Therefore, the conversion efficiency between the TM0 mode and the TE1 mode can be improved.

[0012] Alternatively, the second conversion portion includes: a first asymmetric portion having an asymmetric shape in the third direction, the length of the first asymmetric portion in the third direction continuously increasing from a fifth length to a sixth length longer than the fifth length as the distance from the first conversion portion increases; a second asymmetric portion having an asymmetric shape in the third direction, the length of the second asymmetric portion in the third direction continuously decreasing from a sixth length to a seventh length shorter than the sixth length as the distance from the first conversion portion increases; and a connecting portion provided between the first asymmetric portion and the second asymmetric portion, the length of the connecting portion in the third direction being the sixth length within the entire length range of the first direction. In this case, the second conversion portion has asymmetry in the third direction. For example, when visible light in the TE1 mode is incident on the second conversion portion, two components of the TE1 mode with opposite phases are transmitted with different effective optical path lengths, and thus different phase changes are generated in the two components. By setting the length of the first asymmetric portion in the first direction, the length of the second asymmetric portion in the first direction, the length of the connecting portion in the first direction, the fifth length, the sixth length, and the seventh length, the phase matching condition that the two components are in the same phase is satisfied, thereby outputting visible light in TE0 mode from the second conversion portion. Similarly, when visible light in TE0 mode is incident on the second conversion portion, visible light in TE1 mode is emitted from the second conversion portion. As described above, the polarization wave mode of visible light can be converted between TE0 mode and TE1 mode.

[0013] The length of the second conversion portion in the first direction may also be greater than 40 μm and less than 100 μm. The length of the second conversion portion in the third direction may also be greater than 0.4 μm and less than 1.2 μm. In this case, the loss of light intensity in the conversion between the TE0 mode and the TE1 mode can be reduced. Therefore, the conversion efficiency between the TE0 mode and the TE1 mode can be improved.

[0014] The mode converter may also include a connecting portion connecting the first conversion portion and the second conversion portion. The length of the connecting portion in the third direction may also be constant over the entire length of the connecting portion in the first direction. In a structure in which the first conversion portion and the second conversion portion are connected by extending the upper conical portion of the first conversion portion, if the length of the upper conical portion in the third direction is too large, an unnecessary high-order mode is generated in the visible light, and the conversion efficiency is reduced. Therefore, in this structure, there are constraints on the design of the optical element, such as reducing the distance between the first conversion portion and the second conversion portion. On the other hand, in a structure in which the first conversion portion and the second conversion portion are connected by a connecting portion having a constant length in the third direction, by setting the length of the connecting portion in the third direction to a length that does not generate an unnecessary high-order mode, the distance between the first conversion portion and the second conversion portion can be adjusted to a desired length. Therefore, the degree of freedom in the design of the optical element can be increased.

[0015] The core layer may also include: a first mode converter, which is a 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 a 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 a 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. In this case, 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 TM0 mode and the TE0 mode as the second polarization mode, the combining efficiency can be improved.

[0016] The core layer may also 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 output full-color laser light by combining red light, green light, and blue light, it is necessary to adjust the intensity of each color of light according to the output color. According to the above structure, the intensity of red light, the intensity of green light, and the intensity of blue light are modulated, so that full-color laser light can be output.

[0017] A laser module according to another aspect of the present disclosure includes: the optical element described above; a first light source that emits red light in a first polarization mode; a second light source that emits green light in a first polarization mode; and a third light source that emits blue light in a first polarization mode. Since the laser module includes the optical element described above, it is possible to convert the polarization mode of visible light.

[0018] According to aspects and embodiments of the present disclosure, it is possible to convert a polarization wave mode of visible light. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] 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.

[0020] Figure 2 It roughly indicates Figure 1 The structural diagram of the retinal projection device shown.

[0021] Figure 3 yes Figure 2 A top view of the laser module is shown.

[0022] Figure 4 It is along Figure 3 A cross-sectional view taken along line IV-IV.

[0023] Figure 5 Yes Figure 3A partially enlarged representation of the mode converter is shown.

[0024] Figure 6 It is along Figure 5 A cross-sectional view taken along line VI-VI.

[0025] Figure 7 Yes Figure 3 A partially enlarged representation of the mode converter is shown.

[0026] Figure 8 Yes Figure 3 A magnified representation of the modulator is shown.

[0027] Fig. 9 It is along Figure 8 A cross-sectional view taken along line IX-IX.

[0028] Fig.10 This is a top view of a laser module including an optical element according to another embodiment.

[0029] Fig.11 This is a top view of a laser module including an optical element according to still another embodiment.

[0030] Fig.12 This is a top view of a laser module including an optical element according to still another embodiment. DETAILED DESCRIPTION

[0031] 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 third direction) is a direction that intersects (for example, is orthogonal to) the X-axis direction (the first direction) and the Z-axis direction (the second 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.

[0032] 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 1The 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.

[0033] 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 has an inner surface 3a (see FIG. 1 ) that faces the eyeball of the user wearing the near-eye wearable device 1. Figure 2 ).

[0034] 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.

[0035] Next, refer to Figure 2 The retinal projection device 10 will be described in detail. Figure 2 It roughly indicates Figure 1 The structure diagram of the retinal projection device is shown in FIG. Figure 2 As shown, the retinal projection device 10 includes an optical engine 11 and a reflector 12 .

[0036] The optical engine 11 is a device that generates laser light Ls of a color and light intensity corresponding to the pixel of the image projected on the retina and emits the laser light Ls toward the reflector 12. The optical engine 11 is mounted on the temple 2c. The optical engine 11 includes a laser module 13, an optical component 14, a movable reflector 15, a laser driver 16, a reflector driver 17, and a controller 18.

[0037] The laser module 13 emits laser light. As the laser module 13, for example, a full-color laser module is used. The laser module 13 emits laser light of a color and intensity corresponding to the pixel of the image projected onto the retina. The laser module 13 will be described in detail later.

[0038] The optical component 14 is a component that performs optical processing on the laser light emitted from the laser module 13. In the present embodiment, the optical component 14 includes a collimating lens 14a, an aperture 14b, and a light reduction filter 14c. The collimating lens 14a, the aperture 14b, and the light reduction filter 14c are arranged in sequence along the optical path of the laser light. The optical component 14 may also have other structures.

[0039] The movable reflector 15 is a member for scanning with the laser light Ls. The movable reflector 15 is provided in the emission direction of the laser light processed by the optical component 14. The movable reflector 15 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, for example, and to change the angle in the lateral direction and the longitudinal direction of the lens 3 to reflect the laser light. As the movable reflector 15, for example, a MEMS (Micro Electro Mechanical Systems) reflector is used.

[0040] The laser driver 16 is a driving circuit for driving the laser module 13. The laser driver 16 is based on, for example, the light energy (light intensity) of the laser and the light source unit 20 (see Figure 3 ) temperature, drives the laser module 13. The mirror driver 17 is a driving circuit that drives the movable mirror 15. The mirror driver 17 causes the movable mirror 15 to swing within a predetermined angle range and timing. The controller 18 is a device that controls the laser driver 16 and the mirror driver 17.

[0041] In the optical engine 11, laser light of a color and intensity corresponding to the pixel of the image projected on the retina is emitted from the laser module 13, passes through the optical component 14, and is reflected by the movable mirror 15. The laser light reflected by the movable mirror 15 is emitted toward the reflector 12 as laser light Ls.

[0042] The reflector 12 is a member that reflects the laser light Ls after passing through the movable reflector 15 and irradiates the reflected light Lr toward the retina of the user wearing the near-eye wearable device 1, thereby projecting an image onto the retina.

[0043] Next, refer to Figure 3 and Figure 4 The laser module 13 will be described in detail. Figure 3 yes Figure 2 A top view of the laser module is shown. Figure 4 It is along Figure 3 In addition, Figure 3 In the figure, for the convenience of explanation, the cladding 33 is omitted. Figure 3 As shown, the laser module 13 includes a light source unit 20 and an optical element 30 .

[0044] The light source unit 20 emits visible light. The light source unit 20 includes a red laser diode 21 (first light source) that emits red light, a green laser diode 22 (second light source) that emits green light, and a blue laser diode 23 (third light source) that emits blue light. The peak wavelength of the red light is, for example, in the range of 600nm to 830nm. The peak wavelength of the green light is, for example, in the range of 500nm to 570nm. The peak wavelength of the blue light is, for example, in the range of 380nm to 490nm. The red laser diode 21, the green laser diode 22, and the blue laser diode 23 are arranged in sequence along the Y-axis direction.

[0045] In the present embodiment, the red laser diode 21 emits red light in a TM fundamental mode (hereinafter referred to as “TM0 mode”). The green laser diode 22 emits green light in the TM0 mode. The blue laser diode 23 emits blue light in the TM0 mode.

[0046] The optical element 30 combines the laser beams emitted from the laser diodes into one laser beam. The optical element 30 is, for example, a planar lightwave circuit (PLC). Figure 4 As shown, the optical element 30 includes a substrate 31 , a core layer 32 and a cladding layer 33 .

[0047] The substrate 31 functions as a lower cladding. The substrate 31 is made of a material having a refractive index lower than that of the constituent material of the core layer 32. Examples of constituent materials of the substrate 31 include sapphire, silicon oxide, and silicon stacked with silicon oxide. The substrate 31 has a main surface 31a and a back surface 31b on the side opposite to the main surface 31a. The main surface 31a and the back surface 31b are surfaces defined by the X-axis direction and the Y-axis direction, and intersect 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 31a.

[0048] The cladding 33 functions as an upper cladding. The cladding 33 covers the core layer 32 on the main surface 31a. The cladding 33 is provided over the entire surface of the main surface 31a. The cladding 33 is composed of a material having a refractive index lower than that of the constituent material of the core layer 32. As an example of a constituent material of the cladding 33, silicon oxide (e.g., SiO2) can be cited.

[0049] The core layer 32 is provided on the main surface 31a. The core layer 32 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 32, lithium niobate (LiNbO3) can be cited. In the present embodiment, the core layer 32 is composed of X-cut lithium niobate, and the optical axis (C-axis) of the lithium niobate extends along the Y-axis direction. The core layer 32 includes a mode converter 34R (a first mode converter), a mode converter 34G (a second mode converter), a mode converter 34B (a third mode converter), a modulator 35R (a first modulator), a modulator 35G (a second modulator), a modulator 35B (a third modulator), and a combiner 36.

[0050] The mode converter 34R is a mode converter that converts the polarization wave mode of red light between the TM0 mode and the TE basic mode (hereinafter referred to as "TE0 mode"). In the present embodiment, the mode converter 34R converts the polarization wave mode of red light from the TM0 mode (the first polarization wave mode) to the TE0 mode (the second polarization wave mode). The mode converter 34G is a mode converter that converts the polarization wave mode of green light between the TM0 mode and the TE0 mode. In the present embodiment, the mode converter 34G converts the polarization wave mode of green light from the TM0 mode to the TE0 mode. The mode converter 34B is a mode converter that converts the polarization wave mode of blue light between the TM0 mode and the TE0 mode. In the present embodiment, the mode converter 34B converts the polarization wave mode of blue light from the TM0 mode to the TE0 mode.

[0051] In addition, the polarization wave mode is also called a waveguide mode. The TM mode is a polarization wave mode in which the direction of the main component of the electric field in the section perpendicular to the direction of travel of the light is perpendicular to the main surface 31a of the substrate 31. The TE mode is a polarization wave mode in which the direction of the main component of the electric field in the section perpendicular to the direction of travel of the light is parallel to the main surface 31a of the substrate 31. The TM0 mode is a polarization wave mode with the largest effective refractive index in the TM mode. The TE0 mode is a polarization wave mode with the largest effective refractive index in the TE mode. The TE first mode (hereinafter referred to as the "TE1 mode") is a polarization wave mode with the second largest effective refractive index in the TE mode.

[0052] The mode converter 34R, the mode converter 34G, and the mode converter 34B extend in the X-axis direction, respectively. The mode converter 34R, the mode converter 34G, and the mode converter 34B are sequentially arranged in the Y-axis direction. The detailed structure of each mode converter will be described later.

[0053] The modulator 35R is a modulator that modulates the intensity of red light. The modulator 35R is disposed in the downstream section of the mode converter 34R, and modulates the intensity of the red light in the TE0 mode emitted from the mode converter 34R. The modulator 35G is a modulator that modulates the intensity of green light. The modulator 35G is disposed in the downstream section of the mode converter 34G, and modulates the intensity of the green light in the TE0 mode emitted from the mode converter 34G. The modulator 35B is a modulator that modulates the intensity of blue light. The modulator 35B is disposed in the downstream section of the mode converter 34B, and modulates the intensity of the blue light in the TE0 mode emitted from the mode converter 34B. The detailed structure of each modulator will be described later.

[0054] The combiner 36 combines the red light, the green light, and the blue light. The combiner 36 combines the red light emitted from the modulator 35R, the green light emitted from the modulator 35G, and the blue light emitted from the modulator 35B into one laser light, and emits the laser light. The laser light includes a component having a red wavelength (red component), a component having a green wavelength (green component), and a component having a blue wavelength (blue component).

[0055] Next, refer to Figure 5 to Figure 7 , describing the detailed structure of the mode converters 34R, 34G, and 34B. Figure 5 Yes Figure 3 A partially enlarged representation of the mode converter is shown. Figure 6 It is along Figure 5 A cross-sectional view taken along line VI-VI. Figure 7 Yes Figure 3 FIG. 1 is a partial enlarged representation of the mode converter shown. Figure 3 As shown, each of the mode converter 34R, the mode converter 34G, and the mode converter 34B includes an end portion 41, a conversion portion 42 (first conversion portion), a connecting portion 43, a conversion portion 44 (second conversion portion), and an end portion 45. The mode converter 34R, the mode converter 34G, and the mode converter 34B have the same structure, and therefore, the structure of the mode converter 34R will be described here.

[0056] like Figure 3 and Figure 5 As shown, the end portion 41 is an optical waveguide located at one end (incident end) in the X-axis direction of the mode converter 34R. The end portion 41 functions as an incident portion. The end portion 41 is provided on the main surface 31a and extends in the X-axis direction. Red light in the TM0 mode is incident from the red laser diode 21 to one end in the X-axis direction of the end portion 41. The end portion 41 transmits the red light while maintaining the polarization wave mode of the red light, and emits the red light in the TM0 mode to the converter 42.

[0057] The cross section of the end 41 that intersects (is perpendicular to) the X-axis direction has a rectangular shape. The cross section may also have a trapezoidal shape. The length of the end 41 in the X-axis direction is, for example, 50 μm. The length of the end 41 in the Y-axis direction is substantially constant over the entire length of the end 41 in the X-axis direction. Hereinafter, the length in the Y-axis direction is sometimes referred to as "width". The width of the end 41 is width W0 (first length). Width W0 is, for example, 0.45 μm. The length of the end 41 in the Z-axis direction is substantially constant over the entire length of the end 41 in the X-axis direction. Hereinafter, the length in the Z-axis direction is sometimes referred to as "height". The height of the end 41 is height T0. Height T0 is, for example, 0.7 μm.

[0058] like Figure 3 , Figure 5 as well as Figure 6 As shown, the conversion portion 42 is provided between the end 41 and the end 45, and is a portion that converts the polarization wave mode of visible light between the TM0 mode and the TE1 mode. In the present embodiment, the conversion portion 42 is provided between the end 41 and the connecting portion 43, and converts the polarization wave mode of visible light from the TM0 mode to the TE1 mode. The conversion portion 42 is provided on the main surface 31a. The conversion portion 42 has two ends in the X-axis direction, namely, a connecting end 42a (first end) and a connecting end 42b (second end). The connecting end 42a is connected to the other end in the X-axis direction of the end 41. The connecting end 42b is connected to one end in the X-axis direction of the connecting portion 43.

[0059] The conversion section 42 is divided into a conversion region 42d (first region) and a conversion region 42e (second region) at the middle position 42c. The middle position 42c is a position between the connection end 42a and the connection end 42b in the X-axis direction. The conversion region 42d is a region from the connection end 42a to the middle position 42c in the conversion section 42. The conversion region 42e is a region from the middle position 42c to the connection end 42b in the conversion section 42. The length L11 of the conversion region 42d in the X-axis direction is, for example, 350 μm to 1000 μm. The length L12 of the conversion region 42e in the X-axis direction is, for example, 10 μm to 80 μm. The length L1 of the conversion section 42 in the X-axis direction is the sum of the length L11 and the length L12, and is, for example, 360 μm to 1010 μm.

[0060] The conversion portion 42 includes an upper tapered portion 46 and a lower tapered portion 47. The upper tapered portion 46 and the lower tapered portion 47 are stacked in the Z-axis direction. Specifically, the lower tapered portion 47 is provided on the main surface 31a, and the upper tapered portion 46 is provided on the lower tapered portion 47. The height of the upper tapered portion 46 is substantially constant over the entire length of the upper tapered portion 46 in the X-axis direction. The height of the upper tapered portion 46 is height T11. The height T11 is, for example, 0.5 μm. The height of the lower tapered portion 47 is substantially constant over the entire length of the lower tapered portion 47 in the X-axis direction. The height of the lower tapered portion 47 is height T12. The height T12 is, for example, 0.2 μm. The height of the conversion portion 42 is the sum of the height of the upper tapered portion 46 and the height of the lower tapered portion 47, which is height T0.

[0061] In the conversion region 42d, the width of the upper tapered portion 46 increases continuously from the width W0 to the width Wt (the second length) as it moves from the connection end 42a toward the middle position 42c. The width Wt is greater than the width W0. The width Wt is, for example, 0.5 μm to 1.0 μm. The rate of increase of the width of the upper tapered portion 46 in the conversion region 42d may also be substantially constant. In the conversion region 42e, the width of the upper tapered portion 46 increases continuously from the width Wt to ​​the width W1 (the fourth length) as it moves from the middle position 42c toward the connection end 42b. The width W1 is greater than the width Wt and less than the width Ws described later. The width W1 is, for example, 0.85 μm. The rate of increase of the width of the upper tapered portion 46 in the conversion region 42e may also be substantially constant. The upper tapered portion 46 has a shape that is plane-symmetrical with respect to the symmetry plane SP defined by the X-axis direction and the Z-axis direction.

[0062] In the transition region 42d, the width of the lower tapered portion 47 continuously increases from the width W0 to the width Ws (third length) as it moves from the connection end 42a toward the middle position 42c. The width Ws is greater than the width Wt. The width Ws is, for example, 1.0 μm to 5.0 μm. The rate of increase of the width of the lower tapered portion 47 in the transition region 42d may also be substantially constant. In the transition region 42e, the width of the lower tapered portion 47 continuously decreases from the width Ws to the width W1 as it moves from the middle position 42c toward the connection end 42b. The rate of decrease of the width of the lower tapered portion 47 in the transition region 42e may also be substantially constant. The lower tapered portion 47 has a shape that is plane-symmetrical with respect to the symmetry plane SP.

[0063] In the conversion portion 42 configured as described above, the upper tapered portion 46 and the lower tapered portion 47 are stacked in the Z-axis direction, so the conversion portion 42 has asymmetry in the Z-axis direction. Here, the asymmetry in the Z-axis direction means that the two portions separated by the symmetry plane are not plane-symmetrical with respect to the symmetry plane that passes through the center of the conversion portion 42 in the Z-axis direction and is orthogonal to the Z-axis direction.

[0064] In the conversion section 42, as the distance from the connection end 42a in the X-axis direction increases, the effective refractive index of the TM0 mode and the effective refractive index of the TE1 mode approach and cross each other, thereby causing conversion between the TM0 mode and the TE1 mode. Therefore, when red light in the TM0 mode is incident on the connection end 42a, the polarization wave mode of the red light is converted from the TM0 mode to the TE1 mode in the conversion section 42. In the conversion region 42d, as the distance from the connection end 42a increases, the increase in the width of the lower tapered portion 47 is greater than the increase in the width of the upper tapered portion 46. According to this structure, the conversion efficiency can be improved while shortening the length of the conversion section 42 in the X-axis direction. In the conversion region 42e, as the distance from the connection end 42b increases, the width of the lower tapered portion 47 decreases, and at the connection end 42b, the width of the upper tapered portion 46 is equal to the width of the lower tapered portion 47. According to this structure, the conversion efficiency can be further improved.

[0065] For example, in the conversion region 42d, the conversion from the TM0 mode to the TE1 mode is about 50% to 60%, and in the conversion region 42e, the conversion from the TM0 mode to the TE1 mode is about 20% to 30%. On the other hand, over the entire length of the conversion portion 42 in the X-axis direction, the effective refractive index of the TE0 mode is sufficiently far from the effective refractive indexes of the TM0 mode and the TE1 mode. Therefore, when red light in the TE0 mode is incident on the connection end 42a, the polarization wave mode of the red light is maintained in the TE0 mode.

[0066] like Figure 3 and Figure 5 As shown, the connecting portion 43 is an optical waveguide that connects the conversion portion 42 and the conversion portion 44. The connecting portion 43 is provided on the main surface 31a and extends in the X-axis direction. One end of the connecting portion 43 in the X-axis direction is connected to the connection end 42b, and the other end of the connecting portion 43 in the X-axis direction is connected to the conversion portion 44. The red light in TE1 mode is incident on the connecting portion 43 from the conversion portion 42. The connecting portion 43 transmits the red light while maintaining the polarization wave mode of the red light, and emits the red light in TE1 mode to the conversion portion 44.

[0067] The cross section of the connecting portion 43 that intersects (is perpendicular to) the X-axis direction has a rectangular shape. The cross section may also have a trapezoidal shape. The length of the connecting portion 43 in the X-axis direction is, for example, 50 μm. The width of the connecting portion 43 is substantially constant over the entire length of the connecting portion 43 in the X-axis direction. The width of the connecting portion 43 is width W1. The height of the connecting portion 43 is substantially constant over the entire length of the connecting portion 43 in the X-axis direction. The height of the connecting portion 43 is height T0.

[0068] like Figure 3 and Figure 7As shown, the conversion portion 44 is provided between the end portion 41 and the end portion 45, and is a portion that converts the polarization wave mode of visible light between the TE0 mode and the TE1 mode. In the present embodiment, the conversion portion 44 is provided between the connecting portion 43 and the end portion 45, and converts the polarization wave mode of visible light from the TE1 mode to the TE0 mode. The conversion portion 44 is provided on the main surface 31a. The conversion portion 44 has two ends in the X-axis direction, namely, a connecting end 44a and a connecting end 44b. The connecting end 44a is connected to the other end in the X-axis direction of the connecting portion 43. The connecting end 44b is connected to one end in the X-axis direction of the end portion 45. The conversion portion 44 includes an asymmetric portion 48 (the first asymmetric portion), an asymmetric portion 49 (the second asymmetric portion) and a connecting portion 50.

[0069] The asymmetric portion 48 is an optical waveguide having an asymmetric shape in the Y-axis direction when viewed from the Z-axis direction (overhead view). The asymmetric portion 48 includes a connection end 44a. The width of the asymmetric portion 48 increases continuously from width W1 (5th length) to width W2 (6th length) as it moves from the connection end 44a toward the connection end 44b. In other words, the width of the asymmetric portion 48 increases continuously from width W1 to width W2 as it moves away from the connecting portion 43. The width W2 is greater than the width W1. The width W2 is, for example, 1.2 μm. The rate of increase of the width of the asymmetric portion 48 may also be substantially constant. The height of the asymmetric portion 48 is substantially constant over the entire length of the asymmetric portion 48 in the X-axis direction. The height of the asymmetric portion 48 is height T0. The length L21 of the asymmetric portion 48 in the X-axis direction is, for example, 13 μm to 37 μm.

[0070] The asymmetric portion 48 has two side surfaces in the Y-axis direction, namely, a side surface 48 a and a side surface 48 b. The side surface 48 a extends in the X-axis direction. The side surface 48 b is inclined so as to be separated from the side surface 48 a as it is separated from the connecting portion 43 .

[0071] The asymmetric portion 49 is an optical waveguide having an asymmetric shape in the Y-axis direction when viewed from the Z-axis direction (viewed from above). The asymmetric portion 49 includes a connecting end 44b. The width of the asymmetric portion 49 continuously decreases from width W2 to width W3 (the 7th length) as it moves away from the connecting portion 43. Width W3 is smaller than width W2. Width W3 is, for example, 0.4 μm. The reduction rate of the width of the asymmetric portion 49 may also be substantially constant. The height of the asymmetric portion 49 is substantially constant over the entire length of the asymmetric portion 49 in the X-axis direction. The height of the asymmetric portion 49 is height T0. The length L23 of the asymmetric portion 49 in the X-axis direction is, for example, 13 μm to 37 μm.

[0072] The asymmetric portion 49 has two side surfaces in the Y-axis direction, namely, a side surface 49a and a side surface 49b. The side surface 49a extends in the X-axis direction. The side surface 49b is inclined so as to approach the side surface 49a as it moves away from the connection portion 43.

[0073] The connecting portion 50 is provided between the asymmetric portion 48 and the asymmetric portion 49, and is an optical waveguide connecting the asymmetric portion 48 and the asymmetric portion 49. The width of the connecting portion 50 is substantially constant over the entire length of the connecting portion 50 in the X-axis direction. The width of the connecting portion 50 is width W2. The height of the connecting portion 50 is substantially constant over the entire length of the connecting portion 50 in the X-axis direction. The height of the connecting portion 50 is height T0. The length L22 of the connecting portion 50 in the X-axis direction is, for example, 14 μm to 26 μm. The connecting portion 50 has two side surfaces in the Y-axis direction, namely, the side surface 50a and the side surface 50b. The side surface 50a and the side surface 50b extend in the X-axis direction and are substantially parallel. The side surface 48a, the side surface 50a, and the side surface 49a are located on the same plane.

[0074] The length L2 of the conversion portion 44 in the X-axis direction is the sum of the length L21, the length L22, and the length L23, and is, for example, 40 μm to 100 μm. The width of the conversion portion 44 is, for example, 0.4 μm to 1.2 μm.

[0075] In the conversion section 44 constructed as described above, the asymmetric section 48, the connecting section 50 and the asymmetric section 49 are arranged in sequence in the X-axis direction, and therefore, the conversion section 44 has asymmetry in the Y-axis direction. Here, the asymmetry in the Y-axis direction means that, relative to a symmetry plane passing through the center of the conversion section 44 in the Y-axis direction and orthogonal to the Y-axis direction, the two parts separated by the symmetry plane are not plane-symmetrical. When red light in the TE1 mode is incident on the connecting end 44a, the two components of the TE1 mode with opposite phases to each other are transmitted with different effective optical path lengths, and therefore, different phase changes are generated in the two components. The width W1, the width W2, the width W3, the length L21, the length L22 and the length L23 are set to satisfy the phase matching condition that the two components become the same phase, and therefore, the red light in the TE0 mode is output from the connecting end 44b.

[0076] like Figure 3 and Figure 7 As shown, the end portion 45 is an optical waveguide located at the other end (emitting end) in the X-axis direction of the mode converter 34R. The end portion 45 functions as an emitting portion. The end portion 45 is provided on the main surface 31a and extends in the X-axis direction. One end of the end portion 45 in the X-axis direction is connected to the connection end 44b, and the other end of the end portion 45 in the X-axis direction is connected to the modulator 35R. The red light in the TE0 mode is incident from the converter 44 to one end of the end portion 45 in the X-axis direction. The end portion 45 transmits the red light while maintaining the polarization wave mode of the red light, and emits the red light in the TE0 mode to the modulator 35R.

[0077] The cross section of the end portion 45 that intersects (is perpendicular to) the X-axis direction has a rectangular shape. The cross section may also have a trapezoidal shape. The length of the end portion 45 in the X-axis direction is, for example, 50 μm. The width of the end portion 45 is substantially constant over the entire length of the end portion 45 in the X-axis direction. The width of the end portion 45 is width W3. The height of the end portion 45 is substantially constant over the entire length of the end portion 45 in the X-axis direction. The height of the end portion 45 is height T0.

[0078] Next, refer to Figure 3 , Figure 8 as well as Fig. 9 , the detailed structure of modulators 35R, 35G, and 35B is explained. Figure 8 Yes Figure 3 A magnified representation of the modulator is shown. Fig. 9 It is along Figure 8 The cross-sectional view of the IX-IX line. Figure 3 As shown, the modulator 35R, the modulator 35G and the modulator 35B are Mach-Zehnder type optical waveguides, including an input waveguide 51, a branching portion 52, a branch waveguide 53, a branch waveguide 54, a coupling portion 55, an output waveguide 56, a signal electrode 57, a ground electrode 58, a ground electrode 59, and a plate 60 (see Fig. 9 ), a signal source SS and a terminal resistor TR. The modulator 35R, the modulator 35G and the modulator 35B have the same structure, so the structure of the modulator 35R is described here.

[0079] like Fig. 9 As shown, the flat plate 60 is provided on the main surface 31a. The flat plate 60 has a flat plate shape. The height of the flat plate 60 is a height T22. The height T22 is, for example, 0.2 μm.

[0080] The input waveguide 51 is an optical waveguide located at one end (incident end) in the X-axis direction of the modulator 35R. The input waveguide 51 is provided on the flat plate 60 and extends in the X-axis direction. One end of the input waveguide 51 in the X-axis direction is connected to the other end of the end portion 45 in the X-axis direction. The other end of the input waveguide 51 in the X-axis direction is connected to the branch portion 52.

[0081] The cross section of the input waveguide 51 that intersects (is perpendicular to) the X-axis direction has a rectangular shape. The cross section may also have a trapezoidal shape. The width of the input waveguide 51 is substantially constant over the entire length of the input waveguide 51 in the X-axis direction. The width of the input waveguide 51 is width W3. The height of the input waveguide 51 is substantially constant over the entire length of the input waveguide 51 in the X-axis direction. The height of the input waveguide 51 is height T21. The height T21 is, for example, 0.5 μm.

[0082] The branching portion 52 branches the red light incident from the input waveguide 51 into two red lights. In the present embodiment, the branching portion 52 is formed by a multimode interferometer (MMI). The branching portion 52 can be formed by a Y-branch waveguide or a directional coupler. The branching portion 52 emits the two branched red lights to the branch waveguide 53 and the branch waveguide 54. The branching portion 52 is provided on the plate 60.

[0083] The cross section of the branch portion 52 that intersects (is perpendicular to) the X-axis direction has a rectangular shape. The cross section may also have a trapezoidal shape. The branch portion 52 has a rectangular shape when viewed from the Z-axis direction. The length of the branch portion 52 in the X-axis direction is, for example, 140 μm. The width of the branch portion 52 is substantially constant over the entire length of the branch portion 52 in the X-axis direction. The width of the branch portion 52 is, for example, 10 μm. The height of the branch portion 52 is substantially constant over the entire length of the branch portion 52 in the X-axis direction. The height of the branch portion 52 is height T21.

[0084] The branch waveguide 53 is an optical waveguide for transmitting one red light branched from the branch portion 52. The branch waveguide 54 is an optical waveguide for transmitting another red light branched from the branch portion 52. The branch waveguide 53 and the branch waveguide 54 extend from the branch portion 52 to the coupling portion 55 in the X-axis direction, respectively. The branch waveguide 53 and the branch waveguide 54 are provided on the flat plate 60 and arranged in the Y-axis direction. The branch waveguide 53 and the branch waveguide 54 extend in the vicinity of the branch portion 52 so as to be separated from each other in the Y-axis direction as they are separated from the branch portion 52, and extend in the vicinity of the coupling portion 55 so as to be close to each other in the Y-axis direction as they are close to the coupling portion 55. The branch waveguide 53 and the branch waveguide 54 extend substantially in parallel between the vicinity of the branch portion 52 and the vicinity of the coupling portion 55.

[0085] The cross-sections of the branch waveguide 53 and the branch waveguide 54 that intersect (are orthogonal to) the X-axis direction have a rectangular shape. The cross-section may also have a trapezoidal shape. The length of the branch waveguide 53 in the X-axis direction is, for example, 11 mm. The width of the branch waveguide 53 is substantially constant over the entire length of the branch waveguide 53. The width of the branch waveguide 53 is, for example, 0.7 μm. The height of the branch waveguide 53 is substantially constant over the entire length of the branch waveguide 53. The height of the branch waveguide 53 is height T21. The length of the branch waveguide 54 in the X-axis direction is substantially the same as the length of the branch waveguide 53 in the X-axis direction. The width of the branch waveguide 54 is substantially the same as the width of the branch waveguide 53, and is substantially constant over the entire length of the branch waveguide 54. The height of the branch waveguide 54 is substantially the same as the height of the branch waveguide 53, and is substantially constant over the entire length of the branch waveguide 54.

[0086] The coupling unit 55 couples the red light incident from the branch waveguide 53 with the red light incident from the branch waveguide 54. In the present embodiment, the coupling unit 55 is formed by MMI. The coupling unit 55 can be formed by a Y-branch waveguide or a directional coupler. The coupling unit 55 emits the coupled red light to the output waveguide 56. The coupling unit 55 is provided on the plate 60.

[0087] The cross section of the coupling portion 55 that intersects (is perpendicular to) the X-axis direction has a rectangular shape. The cross section may also have a trapezoidal shape. The coupling portion 55 has a rectangular shape when viewed from the Z-axis direction. The length of the coupling portion 55 in the X-axis direction is, for example, 140 μm. The width of the coupling portion 55 is substantially constant over the entire length of the coupling portion 55 in the X-axis direction. The width of the coupling portion 55 is, for example, 10 μm. The height of the coupling portion 55 is substantially constant over the entire length of the coupling portion 55 in the X-axis direction. The height of the coupling portion 55 is height T21.

[0088] The output waveguide 56 is an optical waveguide located at the other end (emitting end) of the modulator 35R in the X-axis direction. The output waveguide 56 is provided on the plate 60 and extends in the X-axis direction. One end of the output waveguide 56 in the X-axis direction is connected to the emission end of the coupling unit 55. The other end of the output waveguide 56 in the X-axis direction is connected to the incident end of the combiner 36.

[0089] The cross section of the output waveguide 56 that intersects (is perpendicular to) the X-axis direction has a rectangular shape. The cross section may also have a trapezoidal shape. The width of the output waveguide 56 is substantially constant over the entire length of the output waveguide 56 in the X-axis direction. The width of the output waveguide 56 is substantially the same as the width of the branch waveguide 53. The height of the output waveguide 56 is substantially constant over the entire length of the output waveguide 56 in the X-axis direction. The height of the output waveguide 56 is height T21.

[0090] The signal electrode 57, the ground electrode 58, and the ground electrode 59 are electrodes provided on the flat plate 60 and extending in the X-axis direction. The signal electrode 57 is arranged between the branch waveguide 53 and the branch waveguide 54. The ground electrode 58 and the ground electrode 59 are arranged so as to sandwich the branch waveguide 53 and the branch waveguide 54 in the Y-axis direction. In other words, the ground electrode 58, the branch waveguide 53, the signal electrode 57, the branch waveguide 54, and the ground electrode 59 are arranged in this order at substantially equal intervals in the Y-axis direction. The cladding 33 does not cover a part of the signal electrode 57, a part of the ground electrode 58, and a part of the upper surface of the signal electrode 57, a part of the upper surface of the ground electrode 58, and a part of the upper surface of the ground electrode 59 are exposed.

[0091] The cross section of the signal electrode 57, the ground electrode 58, and the ground electrode 59 that intersects (is perpendicular to) the X-axis direction has a rectangular shape. The length of the signal electrode 57 in the X-axis direction is, for example, 10 mm. The width of the signal electrode 57 is substantially constant over the entire length of the signal electrode 57 in the X-axis direction. The width of the signal electrode 57 is, for example, 5 μm. The height of the signal electrode 57 is substantially constant over the entire length of the signal electrode 57 in the X-axis direction. The height of the signal electrode 57 is height T21.

[0092] The length of the ground electrode 58 in the X-axis direction is, for example, 10 mm. The width of the ground electrode 58 is substantially constant over the entire length of the ground electrode 58 in the X-axis direction. The width of the ground electrode 58 is, for example, 200 μm. The height of the ground electrode 58 is substantially constant over the entire length of the ground electrode 58. The height of the ground electrode 58 is height T21. The length of the ground electrode 59 in the X-axis direction is substantially the same as the length of the ground electrode 58 in the X-axis direction. The width of the ground electrode 59 is substantially the same as the width of the ground electrode 58, and is substantially constant over the entire length of the ground electrode 59 in the X-axis direction. The height of the ground electrode 59 is substantially the same as the height of the ground electrode 58, and is substantially constant over the entire length of the ground electrode 59.

[0093] The signal source SS supplies a modulation signal for modulating the red light transmitted in the modulator 35R. One end of the signal source SS is electrically connected to one end of the signal electrode 57 , and the other end of the signal source SS is electrically connected to one end of the ground electrode 58 and one end of the ground electrode 59 .

[0094] The terminal resistor TR electrically terminates the modulated signal. One end of the terminal resistor TR is electrically connected to the other end of the signal electrode 57 , and the other end of the terminal resistor TR is electrically connected to the other end of the ground electrode 58 and the other end of the ground electrode 59 .

[0095] In the modulator 35R configured as described above, when red light in the TE0 mode is incident on the input waveguide 51, it is branched into two red lights of the same phase in the TE0 mode by the branching portion 52, and the two red lights are emitted and propagated to the branch waveguide 53 and the branch waveguide 54, respectively. When a modulation signal is output from the signal source SS to the signal electrode 57, the ground electrode 58, and the ground electrode 59, a potential difference corresponding to the modulation signal is generated between the signal electrode 57 and the ground electrode 58 and between the signal electrode 57 and the ground electrode 59, and a voltage in the Y-axis direction is applied to the branch waveguide 53 and the branch waveguide 54. As a result, a phase difference is generated between the red light propagating in the branch waveguide 53 and the red light propagating in the branch waveguide 54.

[0096] Then, the red light transmitted in the branch waveguide 53 and the red light transmitted in the branch waveguide 54 are coupled in the coupling section 55. At this time, the light intensity of the coupled red light varies according to the phase difference between the red light transmitted in the branch waveguide 53 and the red light transmitted in the branch waveguide 54. Then, the coupled red light is emitted toward the combiner 36 through the output waveguide 56.

[0097] In the laser module 13 and the optical element 30 described above, the conversion section 42 converts the polarization wave mode of visible light between the TM0 mode and the TE1 mode. In the conversion section 42, the upper tapered section 46 and the lower tapered section 47 are stacked in the Z-axis direction, and the conversion section 42 has asymmetry in the Z-axis direction. In the conversion section 42, as the distance from the connection end 42a approaches, the effective refractive index of the TM0 mode and the effective refractive index of the TE1 mode approach each other, thereby causing a conversion between the TM0 mode and the TE1 mode. Therefore, when the visible light of the TM0 mode is incident on the connection end 42a of the conversion section 42, the polarization wave mode of the visible light is converted from the TM0 mode to the TE1 mode in the conversion section 42, and then converted from the TE1 mode to the TE0 mode in the conversion section 44. Therefore, the visible light incident in the TM0 mode can be emitted in the TE0 mode. As described above, the polarization wave mode of the visible light can be converted from the TM0 mode to the TE0 mode.

[0098] The length L1 may be greater than 360 μm and less than 1010 μm. The width Wt may be greater than 0.5 μm and less than 1.0 μm. The width Ws may be greater than 1.0 μm and less than 5.0 μm. In this case, the loss of light intensity in the conversion between the TM0 mode and the TE1 mode can be reduced. Therefore, the conversion efficiency between the TM0 mode and the TE1 mode can be improved.

[0099] The conversion section 44 has asymmetry in the Y-axis direction. When the visible light of the TE1 mode is incident on the connection end 44a of the conversion section 44, the two components of the TE1 mode with opposite phases are transmitted with different effective optical path lengths. Therefore, different phase changes are generated in these two components. The width W1, width W2, width W3, length L21, length L22 and length L23 are set to meet the phase matching condition that the two components become the same phase. Therefore, the visible light of the TE0 mode is output from the connection end 44b of the conversion section 44. As described above, the polarization wave mode of the visible light can be converted from the TE1 mode to the TE0 mode.

[0100] The length L2 may be 40 μm or more and 100 μm or less. The width of the conversion portion 44 may be 0.4 μm or more and 1.2 μm or less. In this case, the loss of light intensity in the conversion between the TE0 mode and the TE1 mode can be reduced. Therefore, the conversion efficiency between the TE0 mode and the TE1 mode can be improved.

[0101] Consider a structure in which the conversion section 42 is connected to the conversion section 44 without using the connecting section 43 by extending the upper tapered section 46 of the conversion section 42. In this structure, if the width of the upper tapered section 46 is too wide, an unnecessary high-order mode is generated in the visible light, and the conversion efficiency is reduced. Therefore, in this structure, there is a restriction on the design of the optical element 30, such as the need to reduce the distance between the conversion section 42 and the conversion section 44. On the other hand, in the laser module 13 and the optical element 30, the conversion section 42 and the conversion section 44 are connected by the connecting section 43, and the width of the connecting section 43 is constant over the entire length of the connecting section 43 in the X-axis direction. Therefore, by setting the width (width W1) of the connecting section 43 to a width that does not generate an unnecessary high-order mode, the distance between the conversion section 42 and the conversion section 44 can be adjusted to a desired length. Therefore, the degree of freedom in the design of the optical element 30 can be improved.

[0102] It is known that the electro-optical properties of a device made of a material having an electro-optical effect such as lithium niobate depend on the direction of voltage application and the polarization direction of light. For example, when a voltage is applied in the C-axis direction of a material having an electro-optical effect and the direction of the main electric field of light transmitted in the device is consistent with the C-axis direction, a greater electro-optical effect can be obtained. In the laser module 13 and the optical element 30, the core layer 32 is made of X-cut lithium niobate, and the C-axis of the lithium niobate extends in the Y-axis direction.

[0103] On the other hand, the red laser diode 21 emits red light in the TM0 mode, the green laser diode 22 emits green light in the TM0 mode, and the blue laser diode 23 emits blue light in the TM0 mode, so the direction of the main electric field of each light is orthogonal to the C-axis direction of the lithium niobate constituting the core layer 32. The mode converters 34R, 34G, and 34B convert the polarization wave modes of the red light, the green light, and the blue light from the TM0 mode to the TE0 mode, respectively. As a result, the direction of the main electric field of each light is consistent with the C-axis direction, so the modulation efficiency of the modulators 35R, 35G, and 35B can be improved.

[0104] The core layer 32 is composed of X-cut lithium niobate, and the C-axis of the lithium niobate extends along the Y-axis direction. Therefore, the combiner 36 is designed to have a higher combining efficiency when combining red light, green light and blue light in the TE0 mode than when combining red light, green light and blue light in the TM0 mode. In the laser module 13 and the optical element 30, the mode converter 34R converts the polarization wave mode of the red light from the TM0 mode to the TE0 mode, the mode converter 34G converts the polarization wave mode of the green light from the TM0 mode to the TE0 mode, and the mode converter 34B converts the polarization wave mode of the blue light from the TM0 mode to the TE0 mode. Therefore, the combining efficiency in the combiner 36 can be improved.

[0105] In order to output full-color laser light by combining red light, green light, and blue light, 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 color of light in the light source unit 20, a large driving current is required. In the laser module 13 and the optical element 30, the light intensity of the red light is modulated by the modulator 35R, the light intensity of the green light is modulated by the modulator 35G, and the light intensity of the blue light is modulated by the modulator 35B. Therefore, full-color laser light can be output without a large driving current.

[0106] Next, refer to Fig.10 A laser module including an optical element according to another embodiment will be described. Fig.10 FIG. 1 is a top view of a laser module including an optical element of another embodiment. Fig.10 In the figure, for the convenience of explanation, the cladding 33 is omitted. Fig.10 The laser module 13A shown is different from the laser module 13 mainly in that it includes an optical element 30A instead of the optical element 30. The optical element 30A is different from the optical element 30 mainly in that it does not include modulators 35R, 35G, and 35B.

[0107] The laser module 13A has the same structure as the laser module 13 and has the same effect as the laser module 13. The optical element 30A has the same structure as the optical element 30 and has the same effect as the optical element 30. The laser module 13A and the optical element 30A do not include the modulators 35R, 35G, and 35B, so the laser module 13A and the optical element 30A can be miniaturized.

[0108] Next, refer to Fig.11 A laser module including an optical element according to still another embodiment will be described. Fig.11 FIG. 1 is a top view of a laser module including an optical element according to another embodiment. Fig.11 In the figure, for the convenience of explanation, the cladding 33 is omitted. Fig.11 The illustrated laser module 13B is different from the laser module 13 mainly in that it includes a light source unit 20B and an optical element 30B instead of the light source unit 20 and the optical element 30 .

[0109] The light source unit 20B is different from the light source unit 20 mainly in that it includes a red laser diode 21B, a green laser diode 22B, and a blue laser diode 23B instead of the red laser diode 21, the green laser diode 22, and the blue laser diode 23. The red laser diode 21B is different from the red laser diode 21 mainly in the polarization wave mode of the emitted red light. The red laser diode 21B emits red light in the TE0 mode. The green laser diode 22B is different from the green laser diode 22 mainly in the polarization wave mode of the emitted green light. The green laser diode 22B emits green light in the TE0 mode. The blue laser diode 23B is different from the blue laser diode 23 mainly in the polarization wave mode of the emitted blue light. The blue laser diode 23B emits blue light in the TE0 mode.

[0110] The optical element 30B is different from the optical element 30 mainly in the constituent material of the core layer 32 and in that the core layer 32 includes mode converters 61R, 61G, 61B and modulators 62R, 62G, 62B instead of the mode converters 34R, 34G, 34B and the modulators 35R, 35G, 35B. In the present embodiment, the core layer 32 is made of Z-cut lithium niobate, and the C-axis of the lithium niobate extends in the Z-axis direction.

[0111] The mode converter 61R (first mode converter) converts the polarization wave mode of red light from the TE0 mode (first polarization wave mode) to the TM0 mode (second polarization wave mode). The mode converter 61G (second mode converter) converts the polarization wave mode of green light from the TE0 mode to the TM0 mode. The mode converter 61B (third mode converter) converts the polarization wave mode of blue light from the TE0 mode to the TM0 mode. The mode converter 61R, the mode converter 61G, and the mode converter 61B extend in the X-axis direction, respectively. The mode converter 61R, the mode converter 61G, and the mode converter 61B are arranged in sequence in the Y-axis direction.

[0112] The mode converter 61R, the mode converter 61G, and the mode converter 61B each include an end portion 41, a conversion portion 42, a connecting portion 43, a conversion portion 44, and an end portion 45. The mode converter 61R, the mode converter 61G, and the mode converter 61B have the same structure, so the structure of the mode converter 61R is described here. In the mode converter 61R, the end portion 45, the conversion portion 44, the connecting portion 43, the conversion portion 42, and the end portion 41 are arranged in this order along the traveling direction of the red light. That is, the mode converter 61R has a structure in which the mode converter 34R is inverted in the X-axis direction.

[0113] The end portion 45 is located at one end (incident end) in the X-axis direction of the mode converter 61R, and functions as an incident portion. Red light in the TE0 mode is incident from the red laser diode 21B to one end in the X-axis direction of the end portion 45. The end portion 45 transmits the red light while maintaining the polarization mode of the red light, and emits the red light in the TE0 mode to the converter 44.

[0114] The conversion section 44 is provided between the end 45 and the connecting section 43, and converts the polarization wave mode of the visible light from the TE0 mode to the TE1 mode. In the conversion section 44, an asymmetric section 49, a connecting section 50, and an asymmetric section 48 are sequentially arranged from the end 45 toward the connecting section 43. The connecting end 44b is connected to the end 45, and the connecting end 44a is connected to the connecting section 43.

[0115] The connecting portion 43 is an optical waveguide that connects the conversion portion 44 and the conversion portion 42. One end of the connecting portion 43 in the X-axis direction is connected to the connection end 44a, and the other end of the connecting portion 43 in the X-axis direction is connected to the connection end 42b. The red light in TE1 mode is incident on the connecting portion 43 from the conversion portion 44. The connecting portion 43 transmits the red light while maintaining the polarization mode of the red light, and emits the red light in TE1 mode to the conversion portion 42.

[0116] The conversion section 42 is provided between the connection section 43 and the end 41, and converts the polarization mode of the visible light from the TE1 mode to the TM0 mode. The connection end 42b is connected to the connection section 43, and the connection end 42a is connected to the end 41. That is, the conversion region 42e and the conversion region 42d are sequentially arranged from the connection section 43 toward the end 41.

[0117] The end portion 41 is located at the other end (emitting end) in the X-axis direction of the mode converter 61R, and functions as an emitting portion. Red light in the TM0 mode is incident from the converter 42 to the end portion 41. The end portion 41 transmits the red light while maintaining the polarization mode of the red light, and emits the red light in the TM0 mode to the modulator 62R (first modulator).

[0118] The modulator 62R is a modulator that modulates the intensity of red light. The modulator 62R is provided at the downstream section of the mode converter 61R, and modulates the intensity of the red light of the TM0 mode emitted from the mode converter 61R. The modulator 62G (second modulator) is a modulator that modulates the intensity of green light. The modulator 62G is provided at the downstream section of the mode converter 61G, and modulates the intensity of the green light of the TM0 mode emitted from the mode converter 61G. The modulator 62B (third modulator) is a modulator that modulates the intensity of blue light. The modulator 62B is provided at the downstream section of the mode converter 61B, and modulates the intensity of the blue light of the TM0 mode emitted from the mode converter 61B.

[0119] The modulators 62R, 62G, and 62B are different from the modulators 35R, 35G, and 35B mainly in that they include a signal electrode 57B and a ground electrode 58B instead of the signal electrode 57 , the ground electrode 58 , and the ground electrode 59 .

[0120] The signal electrode 57B is provided on the branch waveguide 53 along the branch waveguide 53 via a buffer layer not shown. The ground electrode 58B is provided on the branch waveguide 54 along the branch waveguide 54 via a buffer layer not shown. The cladding 33 does not cover a part of the signal electrode 57B and a part of the ground electrode 58B, and a part of the upper surface of the signal electrode 57B and a part of the upper surface of the ground electrode 58B are exposed. One end of the signal source SS is electrically connected to one end of the signal electrode 57B, and the other end of the signal source SS is electrically connected to one end of the ground electrode 58B. One end of the terminal resistor TR is electrically connected to the other end of the signal electrode 57B, and the other end of the terminal resistor TR is electrically connected to the other end of the ground electrode 58B.

[0121] In the laser module 13B, the same effect as that of the laser module 13 is achieved with respect to the structure common to the laser module 13. In the optical element 30B, the same effect as that of the optical element 30 is achieved with respect to the structure common to the optical element 30. In the laser module 13B and the optical element 30B, visible light incident in the TE0 mode can be emitted in the TM0 mode. That is, the polarization mode of the visible light can be converted from the TE0 mode to the TM0 mode.

[0122] In the conversion section 44 of the present embodiment, the asymmetric section 49, the connecting section 50 and the asymmetric section 48 are arranged in sequence in the X-axis direction, so the conversion section 44 has asymmetry in the Y-axis direction. When the red light of the TE0 mode is incident on the connecting end 44b, the red light of the TE0 mode is transmitted with two different effective optical path lengths, and different phase changes are generated in the two components. The width W1, the width W2, the width W3, the length L21, the length L22 and the length L23 are set to meet the phase matching condition that the two components become opposite phases, so that the red light of the TE1 mode is output from the connecting end 44a. As described above, the polarization wave mode of the visible light can be converted from the TE0 mode to the TE1 mode.

[0123] In the conversion section 42 of the present embodiment, as the distance from the connection end 42b in the X-axis direction increases, the effective refractive index of the TM0 mode and the effective refractive index of the TE1 mode approach each other, thereby causing conversion between the TM0 mode and the TE1 mode. Therefore, when red light of the TE1 mode is incident on the connection end 42b, the polarization wave mode of the red light is converted from the TE1 mode to the TM0 mode in the conversion section 42, and the red light of the TM0 mode is output from the connection end 42a. As described above, the polarization wave mode of visible light can be converted from the TE1 mode to the TM0 mode.

[0124] In the laser module 13B and the optical element 30B, the core layer 32 is composed of Z-cut lithium niobate, and the C-axis of the lithium niobate extends along the Z-axis direction. On the other hand, the red laser diode 21B emits red light in TE0 mode, the green laser diode 22B emits green light in TE0 mode, and the blue laser diode 23B emits blue light in TE0 mode. Therefore, the direction of the main electric field of each light is orthogonal to the C-axis direction of the lithium niobate constituting the core layer 32. In contrast, the mode converters 61R, 61G, and 61B convert the polarization wave modes of the red light, green light, and blue light from TE0 mode to TM0 mode, respectively. As a result, the direction of the main electric field of each light is consistent with the C-axis direction, so the modulation efficiency of the modulators 62R, 62G, and 62B can be improved.

[0125] Furthermore, in the laser module 13B and the optical element 30B, the core layer 32 is made of Z-cut lithium niobate, and therefore the combiner 36 is designed to have a higher combining efficiency when combining the red light, green light, and blue light in the TM0 mode than when combining the red light, green light, and blue light in the TE0 mode. Therefore, the combining efficiency in the combiner 36 can be improved.

[0126] Next, refer to Fig.12 A laser module including an optical element according to still another embodiment will be described. Fig.12 FIG. 1 is a top view of a laser module including an optical element according to another embodiment. Fig.12 In the figure, for the convenience of explanation, the cladding 33 is omitted. Fig.12 The laser module 13C shown is different from the laser module 13B mainly in that it includes an optical element 30C instead of the optical element 30B. The optical element 30C is different from the optical element 30B mainly in that it does not include the modulator 62R, the modulator 62G, and the modulator 62B.

[0127] The laser module 13C has the same structure as the laser module 13B and has the same effect as the laser module 13B. The optical element 30C has the same structure as the optical element 30B and has the same effect as the optical element 30B. The laser module 13C and the optical element 30C do not include the modulators 62R, 62G, and 62B, so the laser module 13C and the optical element 30C can be miniaturized.

[0128] In addition, the optical element and the laser module disclosed in the present invention are not limited to the above-mentioned embodiments.

[0129] For example, the laser modules 13 , 13A, 13B, 13C may also be applied to devices other than the near-eye wearable device 1 .

[0130] The optical elements 30, 30A, 30B, and 30C may not include the cladding 33. In this case, the air layer can function as the upper cladding.

[0131] The optical elements 30 , 30A, 30B, and 30C only need to include one mode converter. In other words, the core layer 32 only needs to include one mode converter that converts the polarization mode of visible light between the TM0 mode and the TE0 mode.

[0132] The mode converters 34R, 34G, 34B, 61R, 61G, 61B may not include the connecting portion 43. In this case, the connecting end 42b is connected to the connecting end 44a. According to this structure, the length of the mode converters 34R, 34G, 34B, 61R, 61G, 61B in the X-axis direction can be shortened. Therefore, the laser modules 13, 13A, 13B, 13C and the optical elements 30, 30A, 30B, 30C can be miniaturized.

[0133] Example

[0134] Hereinafter, in order to illustrate the above-mentioned effects, the present disclosure will be described in more detail by way of examples, but the present disclosure is not limited to these examples.

[0135] <Evaluation of Conversion Loss in Converter 42>

[0136] The conversion loss in the converter 42 having the structures of Examples 1 to 12 and Comparative Examples 1 and 2 was calculated. Figure 5 The structure is a stacked structure of the upper tapered portion 46 and the lower tapered portion 47 shown in FIG. As shown in Table 1, the width W0, the width Wt, the width Ws, the width W1, the length L11, and the length L12 are set for the wavelength of each color. As Comparative Examples 1 and 2, only Figure 5The structure of the upper tapered portion 46 shown in FIG. As shown in Table 1, in Comparative Examples 1 and 2, the width W0, the width Wt (= the width Ws), the width W1, and the length L1 are set for the wavelength of red. In Examples 1 to 12, the height T11 is set to 0.5 μm, and the height T12 is set to 0.2 μm. In Comparative Examples 1 and 2, the height T0 is set to 0.7 μm. Table 1 shows the calculation results of the conversion loss.

[0137] [Table 1]

[0138]

[0139] In Examples 1 to 12, relatively small losses of about 1.0 dB to 1.7 dB were generated. In Comparative Examples 1 and 2, losses greater than 10 dB were generated. It can be seen that in the conversion portion 42, by setting the upper tapered portion 46 and the lower tapered portion 47 to be stacked in the Z-axis direction and having an asymmetric structure in the Z-axis direction, the conversion loss can be suppressed and the conversion efficiency can be improved. In Examples 1 to 12, the length L1 is within the range of 360 μm to 1010 μm, the width Wt is within the range of 0.5 μm to 1.0 μm, and the width Ws is within the range of 1.0 μm to 5.0 μm. It can be seen that in this case, the conversion efficiency is improved.

[0140] <Loss Evaluation in Converter 44>

[0141] The conversion loss in the converter 44 having the structures of Examples 13 to 17 and Comparative Example 3 was calculated. Figure 7 The asymmetric portion 48, the connecting portion 50, and the asymmetric portion 49 are arranged in the X-axis direction. Figure 7 The asymmetric portion 48 and the asymmetric portion 49 are arranged in the X-axis direction without including the connecting portion 50. As shown in Table 2, the width W1, the width W2, the width W3, the length L21, the length L22, and the length L23 are set for the wavelength of each color. In addition, in Examples 13 to 17 and Comparative Example 3, the height T0 is set to 0.7 μm. Table 2 shows the calculation results of the conversion loss.

[0142] [Table 2]

[0143]

[0144] In Examples 13 to 17, relatively small losses of about 0.6 dB to 1.0 dB were generated. In Comparative Example 3, losses greater than 10 dB were generated. It can be seen that in the conversion portion 44, by setting the asymmetric portion 48, the connecting portion 50, and the asymmetric portion 49 to be arranged in the X-axis direction and being asymmetric in the Y-axis direction, the conversion loss can be suppressed and the conversion efficiency can be improved. In Examples 13 to 17, the length L2 is within the range of 40 μm to 100 μm, and the width of the conversion portion 44 is within the range of 0.4 μm to 1.2 μm. It can be seen that in this case, the conversion efficiency is improved.

[0145] (Note)

[0146]

Project 1

[0147] An optical element, wherein

[0148] The optical component has:

[0149] a substrate having a main surface; and

[0150] The core layer is disposed on the main surface and is composed of a material having an electro-optical effect.

[0151] 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 TM0 mode and a TE0 mode.

[0152] The mode converter comprises:

[0153] an incident portion, which is located at one end of the mode converter in the first direction, for the visible light of a first polarization mode to be incident, wherein the first polarization mode is one of the TM0 mode and the TE0 mode;

[0154] an emission portion, which is located at the other end of the mode converter in the first direction, and emits the visible light in a second polarization mode, wherein the second polarization mode is the other polarization mode of the TM0 mode and the TE0 mode;

[0155] a first conversion section, which is provided between the incident section and the emitting section and converts the polarization mode of the visible light between the TM0 mode and the TE1 mode; and

[0156] a second conversion section, which is provided between the incident section and the emitting section and converts the polarization mode of the visible light between the TE0 mode and the TE1 mode;

[0157] The first conversion portion includes a first end and a second end which are both ends in the first direction, and an upper tapered portion and a lower tapered portion stacked in a second direction intersecting the main surface.

[0158] In a first region of the first conversion portion from the first end to a middle position between the first end and the second end, a length of the upper tapered portion in a third direction intersecting the first direction and the second direction continuously increases from a first length to a second length longer than the first length as it moves from the first end toward the middle position, and a length of the lower tapered portion in the third direction continuously increases from the first length to a third length longer than the second length as it moves from the first end toward the middle position,

[0159] In the second region from the middle position to the second end of the first conversion portion, the length of the upper tapered portion in the third direction continuously increases from the second length to the fourth length from the middle position toward the second end, and the length of the lower tapered portion in the third direction continuously decreases from the third length to the fourth length from the middle position toward the second end, and the fourth length is longer than the second length and shorter than the third length.

[0160]

Project 2

[0161] The optical element according to item 1, wherein:

[0162] The first polarization mode is the TM0 mode,

[0163] The second polarization mode is the TE0 mode,

[0164] The first end is connected to the incident portion,

[0165] The second conversion section is provided between the first conversion section and the emission section.

[0166]

Project 3

[0167] The optical element according to item 1, wherein:

[0168] The first polarization mode is the TE0 mode,

[0169] The second polarization mode is the TM0 mode,

[0170] The first end is connected to the emitting portion,

[0171] The second conversion section is provided between the incident section and the first conversion section.

[0172]

Project 4

[0173] The optical element according to any one of items 1 to 3, wherein

[0174] The length of the first conversion portion in the first direction is greater than or equal to 360 μm and less than or equal to 1010 μm.

[0175] The second length is greater than or equal to 0.5 μm and less than or equal to 1.0 μm,

[0176] The third length is greater than or equal to 1.0 μm and less than or equal to 5.0 μm.

[0177]

Project 5

[0178] The optical element according to any one of items 1 to 4, wherein

[0179] The second conversion unit comprises:

[0180] a first asymmetric portion having an asymmetric shape in the third direction, wherein a length of the first asymmetric portion in the third direction continuously increases from a fifth length to a sixth length longer than the fifth length as the length increases away from the first conversion portion;

[0181] a second asymmetric portion having an asymmetric shape in the third direction, wherein a length of the second asymmetric portion in the third direction continuously decreases from the sixth length to a seventh length shorter than the sixth length as it moves away from the first conversion portion; and

[0182] A connecting portion is provided between the first asymmetric portion and the second asymmetric portion, wherein a length of the connecting portion in the third direction is the sixth length within the entire length range of the first direction.

[0183]

Project 6

[0184] The optical element according to item 5, wherein:

[0185] The length of the second conversion portion in the first direction is not less than 40 μm and not more than 100 μm,

[0186] The length of the second conversion portion in the third direction is greater than or equal to 0.4 μm and less than or equal to 1.2 μm.

[0187]

Project 7

[0188] The optical element according to any one of items 1 to 6, wherein

[0189] The mode converter further includes a connecting portion connecting the first converting portion and the second converting portion.

[0190]

Project 8

[0191] The optical element according to item 7, wherein:

[0192] The length of the connection portion in the third direction is constant over the entire length of the connection portion in the first direction.

[0193]

Project 9

[0194] The optical element according to any one of items 1 to 8, wherein

[0195] The core layer also has:

[0196] 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;

[0197] a second mode converter, which is the mode converter that converts the polarization mode of the green light from the first polarization mode to the second polarization mode;

[0198] 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

[0199] A combiner combines the red light, the green light, and the blue light to emit laser light.

[0200]

Project 10

[0201] The optical element according to item 9, wherein:

[0202] The core layer also has:

[0203] a first modulator, which modulates the intensity of the red light;

[0204] a second modulator for modulating the intensity of the green light; and

[0205] The third modulator modulates the intensity of the blue light.

[0206]

Project 11

[0207] A laser module, wherein:

[0208] The laser module has:

[0209] An optical element as described in item 9 or item 10;

[0210] a first light source that emits the red light in the first polarization mode;

[0211] a second light source that emits the green light in the first polarization mode; and

[0212] A third light source emits the blue light in the first polarization mode.

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 TM0 mode and a TE0 mode. The mode converter comprises: an incident portion, which is located at one end of the mode converter in the first direction, for the visible light of a first polarization mode to be incident, wherein the first polarization mode is one of the TM0 mode and the TE0 mode; an emission portion, which is located at the other end of the mode converter in the first direction, and emits the visible light in a second polarization mode, wherein the second polarization mode is the other polarization mode of the TM0 mode and the TE0 mode; a first conversion section, which is provided between the incident section and the emitting section and converts the polarization wave mode of the visible light between the TM0 mode and the TE1 mode; as well as a second conversion section, which is provided between the incident section and the emitting section and converts the polarization mode of the visible light between the TE0 mode and the TE1 mode; The first conversion portion includes a first end and a second end which are both ends in the first direction, and an upper tapered portion and a lower tapered portion stacked in a second direction intersecting the main surface. In a first region of the first conversion portion from the first end to a middle position between the first end and the second end, a length of the upper tapered portion in a third direction intersecting the first direction and the second direction continuously increases from a first length to a second length longer than the first length as it moves from the first end toward the middle position, and a length of the lower tapered portion in the third direction continuously increases from the first length to a third length longer than the second length as it moves from the first end toward the middle position, In the second region from the middle position to the second end of the first conversion portion, the length of the upper tapered portion in the third direction continuously increases from the second length to the fourth length from the middle position toward the second end, and the length of the lower tapered portion in the third direction continuously decreases from the third length to the fourth length from the middle position toward the second end, and the fourth length is longer than the second length and shorter than the third length.

2. The optical element according to claim 1, wherein The first polarization mode is the TM0 mode, The second polarization mode is the TE0 mode, The first end is connected to the incident portion, The second conversion section is provided between the first conversion section and the emission section.

3. The optical element according to claim 1, wherein The first polarization mode is the TE0 mode, The second polarization mode is the TM0 mode, The first end is connected to the emitting portion, The second conversion section is provided between the incident section and the first conversion section.

4. The optical element according to any one of claims 1 to 3, wherein The length of the first conversion portion in the first direction is greater than or equal to 360 μm and less than or equal to 1010 μm. The second length is greater than or equal to 0.5 μm and less than or equal to 1.0 μm, The third length is greater than or equal to 1.0 μm and less than or equal to 5.0 μm.

5. The optical element according to any one of claims 1 to 4, wherein The second conversion unit comprises: a first asymmetric portion having an asymmetric shape in the third direction, wherein a length of the first asymmetric portion in the third direction continuously increases from a fifth length to a sixth length longer than the fifth length as the length increases away from the first conversion portion; a second asymmetric portion having an asymmetric shape in the third direction, wherein a length of the second asymmetric portion in the third direction continuously decreases from the sixth length to a seventh length shorter than the sixth length as it moves away from the first conversion portion; and A connecting portion is provided between the first asymmetric portion and the second asymmetric portion, wherein a length of the connecting portion in the third direction is the sixth length within the entire length range of the first direction.

6. The optical element according to claim 5, wherein: The length of the second conversion portion in the first direction is not less than 40 μm and not more than 100 μm, The length of the second conversion portion in the third direction is greater than or equal to 0.4 μm and less than or equal to 1.2 μm.

7. The optical element according to any one of claims 1 to 6, wherein The mode converter further includes a connecting portion connecting the first converting portion and the second converting portion.

8. The optical element according to claim 7, wherein: The length of the connection portion in the third direction is constant over the entire length of the connection portion in the first direction.

9. The optical element according to any one of claims 1 to 8, wherein The core layer also 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 the 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 the 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.

10. The optical element according to 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 claim 9; a first light source that emits the red light in the first polarization mode; a second light source that emits the green light in the first polarization mode; and A third light source emits the blue light in the first polarization mode.

12. A laser module, wherein: The laser module has: The optical element according to claim 10; a first light source that emits the red light in the first polarization mode; a second light source that emits the green light in the first polarization mode; and A third light source emits the blue light in the first polarization mode.

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