Optical element and laser module

Abstract

The invention relates to an optical element and a laser module. A core layer of the optical element is provided with a first conversion unit for converting the polarization mode of light from a TM0 mode to a TE1 mode, and a second conversion unit for converting the polarization mode of light from the TE1 mode to the TE0 mode. A first branching unit that branches the TE1-mode light incident from the first conversion unit into a TE0-mode first branched light and a TE0-mode second branched light, which have opposite phases from each other; a first branch waveguide extending in the first direction and through which the first branch light is transmitted; a second branch waveguide extending in the first direction and through which the second branch light is transmitted; a coupling unit that couples the first branched light transmitted through the first branched waveguide and the second branched light transmitted through the second branched waveguide, and emits TE0-mode light; and a phase adjustment unit that adjusts a phase difference between the first branched light and the second branched light, the first branched waveguide and the second branched waveguide being arranged in the second direction.

Description

[0001] Cross-reference to related applications

[0002] This application is an application claiming the benefit of priority based on Japanese Patent Application No. 2023-184917 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 wave modes of light transmitted in the optical waveguide, there are a polarization wave mode having a main electric field in a horizontal direction relative to the substrate, namely a TE (Transverse Electric: transverse electric field) mode, and a polarization wave mode having a main electric field in a vertical direction relative to the substrate, namely a TM (Transverse Magnetic: transverse magnetic field) mode. An optical waveguide element that converts these polarization wave modes is known. For example, Japanese Patent Gazette No. 2021-196393 describes a mode conversion element, which includes: a polarization wave rotation unit that converts light in the TM0 mode into light in the TE1 mode; and a mode order conversion unit that converts light in the TE1 mode into light in the TE0 mode. Summary of the invention

[0005] In addition, there is known an optical modulator that converts an electrical signal into an optical signal by modulating the light intensity of a laser. For example, it is considered that an optical modulator is provided in the downstream section of the mode conversion element described in Japanese Patent Publication No. 2021-196393 to modulate the light intensity of the TE0 mode light converted by the mode conversion element. However, since an optical modulator is provided in addition to the mode conversion element, the device may be large-scale.

[0006] This disclosure describes optical components and laser modules that enable miniaturization.

[0007] An optical element of one aspect of the present disclosure comprises: a substrate having a main surface; and a core layer, which is provided on the main surface and is composed of a material having an electro-optical effect. The core layer comprises a mode converter that converts a polarization wave mode of light from a TM0 mode to a TE0 mode. The mode converter comprises: a first conversion section that converts a polarization wave mode of light from a TM0 mode to a TE1 mode; and a second conversion section that converts a polarization wave mode of light from a TE1 mode to a TE0 mode. The second conversion section includes: a branching section that branches the TE1 mode light incident from the first conversion section into a first branch light of a TE0 mode and a second branch light of a TE0 mode with opposite phases to each other; a first branch waveguide that extends in a first direction along the main surface for transmitting the first branch light; a second branch waveguide that extends in the first direction for transmitting the second branch light; a coupling section that couples the first branch light transmitted in the first branch waveguide with the second branch light transmitted in the second branch waveguide to emit light in the TE0 mode; and a phase adjustment section that adjusts the phase difference between the first branch light and the second branch light. The first branch waveguide and the second branch waveguide are arranged in a second direction intersecting the first direction.

[0008] In the optical element, the polarization wave mode of light is converted from TM0 mode to TE1 mode by the first conversion part, and the polarization wave mode of light is converted from TE1 mode to TE0 mode by the second conversion part. In the second conversion part, the light of TE1 mode incident from the first conversion part is branched into the first branch light and the second branch light of TE0 mode with opposite phases to each other, and the phase difference between the first branch light and the second branch light is adjusted so that the first branch light and the second branch light are coupled, thereby emitting light of TE0 mode. Since the light intensity of the light emitted from the coupling part can be changed according to the phase difference between the first branch light and the second branch light, the second conversion part can also function as an optical modulator. Therefore, it is not necessary to set up an optical modulator, so that the optical element can be miniaturized.

[0009] The phase adjustment unit may include: a signal electrode, which is arranged between the first branch waveguide and the second branch waveguide; and a first ground electrode and a second ground electrode, which are arranged in a manner of sandwiching the first branch waveguide and the second branch waveguide in the second direction. The optical axis of the material constituting the core layer may extend along the second direction. According to the above structure, the first branch waveguide is arranged between the signal electrode and the first ground electrode, and the second branch waveguide is arranged between the signal electrode and the second ground electrode. Therefore, when a voltage is applied between the signal electrode and each ground electrode, a voltage is applied to the first branch waveguide and the second branch waveguide in the second direction. The polarization wave mode of the first branch light transmitted in the first branch waveguide is the TE0 mode, and the polarization wave mode of the second branch light transmitted in the second branch waveguide is the TE0 mode. Therefore, in the first branch waveguide, a voltage is applied in the direction of the optical axis of the material constituting the core layer, and the direction of the main electric field of the light transmitted in the first branch waveguide is consistent with the direction of the above optical axis, so that a larger electro-optical effect can be obtained. Similarly, in the second branch waveguide, a voltage is applied in the direction of the optical axis of the material constituting the core layer, and the direction of the main electric field of the light transmitted in the second branch waveguide is consistent with the direction of the optical axis, so a larger electro-optical effect can be obtained. Thus, the modulation efficiency of the second conversion unit can be improved.

[0010] The light may be visible light, in which case the polarization mode of the visible light can be converted from the TM0 mode to the TE0 mode.

[0011] The length of the branch portion in the first direction may be greater than 40 μm and less than 64 μm. The length of the branch portion in the second direction may be greater than 3.0 μm and less than 3.5 μm. In this case, the loss of light intensity in the conversion from the TE1 mode to the TE0 mode can be reduced. Therefore, the conversion efficiency of the conversion from the TE1 mode to the TE0 mode can be improved.

[0012] The core layer may also include: a first mode converter, which is a mode converter that converts the polarization wave mode of red light from TM0 mode to TE0 mode; a second mode converter, which is a mode converter that converts the polarization wave mode of green light from TM0 mode to TE0 mode; a third mode converter, which is a mode converter that converts the polarization wave mode of blue light from TM0 mode to TE0 mode; and a combiner that combines red light, green light, and blue light to emit laser 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 second conversion part of each mode converter is used to modulate the intensity of red light, the intensity of green light, and the intensity of blue light, so that full-color laser light can be output.

[0013] Another aspect of the present disclosure is a laser module comprising: the above-mentioned optical element; a first light source emitting red light in TM0 mode; a second light source emitting green light in TM0 mode; and a third light source emitting blue light in TM0 mode. Since the laser module comprises the above-mentioned optical element, the laser module can be miniaturized.

[0014] According to the aspects and embodiments of the present disclosure, it is possible to achieve miniaturization of an optical element and a laser module. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] 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.

[0016] Figure 2 It roughly indicates Figure 1 The structural diagram of the retinal projection device shown.

[0017] Figure 3 yes Figure 2 A top view of the laser module is shown.

[0018] Figure 4 It is along Figure 3 A cross-sectional view taken along line IV-IV.

[0019] Figure 5 Yes Figure 3 A partially enlarged representation of the mode converter is shown.

[0020] Figure 6 It is along Figure 5 A cross-sectional view taken along line VI-VI.

[0021] Figure 7 Yes Figure 3 A magnified representation of the modulator is shown.

[0022] Figure 8 It is along Figure 7 A cross-sectional view taken along line VIII-VIII. DETAILED DESCRIPTION

[0023] The following describes the embodiments of the present disclosure in detail with reference to the accompanying drawings. In addition, the same reference numerals are used to mark the same elements in the description of the accompanying drawings, and repeated descriptions are omitted. An XYZ coordinate system is sometimes shown in each figure. The Y-axis direction (the second direction) is a direction that intersects (for example, is orthogonal to) the X-axis direction (the first direction) and the Z-axis direction. The 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.

[0024] Reference Figure 1 An application example of the laser module according to one embodiment will be described. Figure 1 This is a three-dimensional diagram showing the appearance of a near-eye wearable device to which a laser module according to one embodiment is applied. Figure 1 The near-eye wearable device 1 shown is a device that projects an image onto the retina of a user wearing the near-eye wearable device 1. The near-eye wearable device 1 is, for example, a head-mounted device (head-mounted device), which can be in the form of glasses, goggles, hats, and helmets. As examples of the near-eye wearable device 1, smart glasses such as AR (Augmented Reality) glasses, VR (Virtual Reality) glasses, and MR (Mixed Reality) glasses are listed. The near-eye wearable device 1 includes a frame 2, a lens 3, and a retinal projection device 10.

[0025] 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 ).

[0026] 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.

[0027] 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 .

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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 3In addition, Figure 3 In the figure, for the sake of convenience, the cladding 33 is omitted. Figure 3 As shown, the laser module 13 includes a light source unit 20 and an optical element 30 .

[0036] 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.

[0037] 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.

[0038] 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 .

[0039] 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.

[0040] 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 with a lower refractive index than the material constituting the core layer 32. Examples of the constituent material of the cladding 33 include silicon oxide (e.g., SiO 2 ).

[0041] The core layer 32 is provided on the main surface 31a. The core layer 32 is made 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. Examples of the constituent material of the core layer 32 include lithium niobate (LiNbO 3 In the present embodiment, the core layer 32 is made 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), and a combiner 36.

[0042] The mode converter 34R is a mode converter that converts the polarization wave mode of red light from the TM0 mode to the TE fundamental mode (hereinafter referred to as "TE0 mode"). The mode converter 34G is a mode converter that 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 from the TM0 mode to the TE0 mode.

[0043] 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.

[0044] 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.

[0045] The combiner 36 combines the red light, the green light, and the blue light. The combiner 36 combines the red light emitted from the mode converter 34R, the green light emitted from the mode converter 34G, and the blue light emitted from the mode converter 34B 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).

[0046] Next, refer to Figures 5 to 8 , describing the detailed structure of the mode converters 34R, 34G, and 34B. Figure 5 Yes Figure 3A 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 A magnified representation of the modulator is shown. Figure 8 It is along Figure 7 A cross-sectional view of the line VIII-VIII. Figure 3 As shown, each of the mode converter 34R, the mode converter 34G, and the mode converter 34B includes an incident portion 41 into which visible light is incident, a conversion portion 42 (first conversion portion) that converts the polarization wave mode of the visible light from the TM0 mode to the TE1 mode, and a conversion portion 43 (second conversion portion) that converts the polarization wave mode of the visible light from the TE1 mode to the TE0 mode. 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 is described here.

[0047] like Figure 3 and Figure 5 As shown, the incident portion 41 is an optical waveguide located at one end (incident end) in the X-axis direction of the mode converter 34R. The incident 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 incident portion 41. The incident 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.

[0048] The cross section of the incident portion 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 incident portion 41 in the X-axis direction is, for example, 50 μm. The length of the incident portion 41 in the Y-axis direction is substantially constant over the entire length of the incident portion 41 in the X-axis direction. Hereinafter, the length in the Y-axis direction is sometimes referred to as the "width". The width of the incident portion 41 is the width W0. The width W0 is, for example, 0.45 μm. The length of the incident portion 41 in the Z-axis direction is substantially constant over the entire length of the incident portion 41 in the X-axis direction. Hereinafter, the length in the Z-axis direction is sometimes referred to as the "height". The height of the incident portion 41 is the height T0. The height T0 is, for example, 0.7 μm.

[0049] like Figure 3 , Figure 5 as well as Figure 6As shown, the conversion section 42 is provided between the incident section 41 and the conversion section 43, and is a part that converts the polarization wave mode of visible light from the TM0 mode to the TE1 mode. The conversion section 42 is provided on the main surface 31a. The conversion section 42 has two ends in the X-axis direction, namely, a connection end 42a and a connection end 42b. The connection end 42a is connected to the other end in the X-axis direction of the incident section 41. The connection end 42b is connected to one end (incident end) in the X-axis direction of the conversion section 43.

[0050] The conversion portion 42 is divided into a conversion region 42d and a conversion region 42e 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 portion 42. The conversion region 42e is a region from the middle position 42c to the connection end 42b in the conversion portion 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 portion 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.

[0051] 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.

[0052] In the conversion region 42d, the width of the upper tapered portion 46 increases continuously from the width W0 to the width Wt 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 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.

[0053] In the transition region 42d, the width of the lower tapered portion 47 continuously increases from the width W0 to the width Ws 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] like Figure 7As shown, the conversion section 43 is a Mach-Zehnder type optical waveguide, including an input waveguide 51, a branching section 52, a branch waveguide 53 (a first branch waveguide), a branch waveguide 54 (a second branch waveguide), a coupling section 55, an output waveguide 56, a phase adjustment section 57, and a plate 58 (see Figure 8 ).

[0058] like Figure 8 As shown, the flat plate 58 is provided on the main surface 31a. The flat plate 58 has a flat plate shape. The height of the flat plate 58 is a height T22. The height T22 is, for example, 0.2 μm.

[0059] The input waveguide 51 is an optical waveguide located at one end (incident end) in the X-axis direction of the conversion section 43. The input waveguide 51 is provided on the flat plate 58 and extends in the X-axis direction. One end of the input waveguide 51 in the X-axis direction is connected to the connection end 42b. The other end of the input waveguide 51 in the X-axis direction is connected to the input end of the branch section 52. Red light in TE1 mode (hereinafter sometimes referred to as "light Lin") is incident from the conversion section 42 to the input waveguide 51. The input waveguide 51 transmits the light Lin while maintaining the polarization wave mode of the light Lin, and emits the light Lin in TE1 mode to the branch section 52.

[0060] 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 length of the input waveguide 51 in the X-axis direction is, for example, 50 μm. 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 W1. 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. Height T21 is, for example, 0.5 μm.

[0061] The branching portion 52 branches the TE1 mode light Lin incident from the input waveguide 51 into a TE0 mode branched light Ld1 (first branched light) and a TE0 mode branched light Ld2 (second branched light). The branched light Ld1 and the branched light Ld2 are in opposite phases to each other. The light intensity of the branched light Ld1 and the light intensity of the branched light Ld2 are substantially half (50%) of the light intensity of the light Lin. In the present embodiment, the branching portion 52 is formed by a multimode interferometer (MMI). The branching portion 52 can be formed by either a Y-branch waveguide or a directional coupler. The branching portion 52 is disposed on a flat plate 58. The branching portion 52 emits the branched light Ld1 to the branching waveguide 53 and emits the branched light Ld2 to the branching waveguide 54.

[0062] 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 length L21 of the branch portion 52 in the X-axis direction is, for example, 40 μm to 64 μm. The branch portion 52 has a rectangular shape when viewed from the Z-axis direction. 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 width W21. The width W21 is, for example, 3.0 μm to 3.5 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.

[0063] The branch waveguide 53 is an optical waveguide for transmitting the branch light Ld1. The branch waveguide 54 is an optical waveguide for transmitting the branch light Ld2. The branch waveguide 53 and the branch waveguide 54 extend from the branch portion 52 to the coupling portion 55 along the X-axis direction, respectively. The branch waveguide 53 and the branch waveguide 54 are provided on the flat plate 58 and arranged along 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.

[0064] One end of the branch waveguide 53 in the X-axis direction is connected to the emission end of the branch portion 52. The other end of the branch waveguide 53 in the X-axis direction is connected to the incident end of the coupling portion 55. The branch light Ld1 in the TE0 mode is incident from the branch portion 52 to one end of the branch waveguide 53. The branch waveguide 53 transmits the branch light Ld1 while maintaining the polarization mode of the branch light Ld1, and emits the branch light Ld1 in the TE0 mode from the other end to the coupling portion 55.

[0065] One end of the branch waveguide 54 in the X-axis direction is connected to the other emission end of the branch portion 52. The other end of the branch waveguide 54 in the X-axis direction is connected to the other incident end of the coupling portion 55. The branch light Ld2 in the TE0 mode is incident on one end of the branch waveguide 54 from the branch portion 52. The branch waveguide 54 transmits the branch light Ld2 while maintaining the polarization mode of the branch light Ld2, and emits the branch light Ld2 in the TE0 mode from the other end to the coupling portion 55.

[0066] 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, 0.8 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.

[0067] The coupling unit 55 couples the branch light Ld1 transmitted in the branch waveguide 53 with the branch light Ld2 transmitted in the branch waveguide 54 to emit red light in the TE0 mode (hereinafter sometimes referred to as "light Lout"). In this embodiment, the coupling unit 55 is composed of MMI. The coupling unit 55 can be composed of a Y-branch waveguide or a directional coupler. The coupling unit 55 is provided on the plate 58. The coupling unit 55 emits the light Lout to the output waveguide 56.

[0068] 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 length L22 of the coupling portion 55 in the X-axis direction is, for example, 63 μm to 100 μm. The coupling portion 55 has a rectangular shape when viewed from the Z-axis direction. 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 width W22. The width W22 is, for example, 6 μm to 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.

[0069] The output waveguide 56 is an optical waveguide located at the other end (emitting end) in the X-axis direction of the conversion section 43. The output waveguide 56 is provided on the flat plate 58 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 section 55. The other end of the output waveguide 56 in the X-axis direction is connected to the incident end of the combiner 36. The light Lout in the TE0 mode is incident from the coupling section 55 to the output waveguide 56. The output waveguide 56 transmits the light Lout while maintaining the polarization mode of the light Lout, and emits the light Lout in the TE0 mode to the combiner 36.

[0070] 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 length of the output waveguide 56 in the X-axis direction is, for example, 50 μm. 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.

[0071] The phase adjustment unit 57 adjusts the phase difference between the branched light Ld1 and the branched light Ld2 . In this embodiment, the phase adjustment unit 57 includes a signal electrode 71 , a ground electrode 72 (first ground electrode), a ground electrode 73 (second ground electrode), a signal source 74 , and a terminal resistor 75 .

[0072] The signal electrode 71, the ground electrode 72, and the ground electrode 73 are electrodes provided on the flat plate 58 and extending in the X-axis direction. The signal electrode 71 is arranged between the branch waveguide 53 and the branch waveguide 54. The ground electrode 72 and the ground electrode 73 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 72, the branch waveguide 53, the signal electrode 71, the branch waveguide 54, and the ground electrode 73 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 71, a part of the ground electrode 72, and a part of the ground electrode 73, and a part of the upper surface of the signal electrode 71, a part of the upper surface of the ground electrode 72, and a part of the upper surface of the ground electrode 73 are exposed.

[0073] The cross-section of the signal electrode 71, the ground electrode 72, and the ground electrode 73 that intersects (is perpendicular to) the X-axis direction has a rectangular shape. The length of the signal electrode 71 in the X-axis direction is, for example, 10 mm. The width of the signal electrode 71 is substantially constant over the entire length of the signal electrode 71 in the X-axis direction. The width of the signal electrode 71 is, for example, 5 μm. The height of the signal electrode 71 is substantially constant over the entire length of the signal electrode 71 in the X-axis direction. The height of the signal electrode 71 is height T21.

[0074] The length of the ground electrode 72 in the X-axis direction is, for example, 10 mm. The width of the ground electrode 72 is substantially constant over the entire length of the ground electrode 72 in the X-axis direction. The width of the ground electrode 72 is, for example, 200 μm. The height of the ground electrode 72 is substantially constant over the entire length of the ground electrode 72. The height of the ground electrode 72 is height T21. The length of the ground electrode 73 in the X-axis direction is substantially the same as the length of the ground electrode 72 in the X-axis direction. The width of the ground electrode 73 is substantially the same as the width of the ground electrode 72, and is substantially constant over the entire length of the ground electrode 73 in the X-axis direction. The height of the ground electrode 73 is substantially the same as the height of the ground electrode 72, and is substantially constant over the entire length of the ground electrode 73.

[0075] Signal source 74 supplies a modulation signal for modulating the intensity of red light transmitted in conversion section 43. One end of signal source 74 is electrically connected to one end of signal electrode 71, and the other end of signal source 74 is electrically connected to one end of ground electrode 72 and one end of ground electrode 73.

[0076] The modulation signal is electrically terminated by the terminal resistor 75 , and one end of the terminal resistor 75 is electrically connected to the other end of the signal electrode 71 , and the other end of the terminal resistor 75 is electrically connected to the other end of the ground electrode 72 and the other end of the ground electrode 73 .

[0077] In the conversion section 43 configured as described above, when the TE1 mode light Lin is incident on the input waveguide 51, it is branched into the branch light Ld1 and the branch light Ld2 of the TE0 mode with opposite phases to each other by the branching section 52, and the branch light Ld1 and the branch light Ld2 are emitted and transmitted to the branch waveguide 53 and the branch waveguide 54, respectively. When the modulation signal is supplied from the signal source 74 to the signal electrode 71, the ground electrode 72, and the ground electrode 73, a potential difference corresponding to the modulation signal is generated between the signal electrode 71 and the ground electrode 72 and between the signal electrode 71 and the ground electrode 73, and a voltage in the Y-axis direction is applied to the branch waveguide 53 and the branch waveguide 54.

[0078] Thus, the refractive index of the branch waveguide 53 changes according to the voltage applied to the branch waveguide 53, and the refractive index of the branch waveguide 54 changes according to the voltage applied to the branch waveguide 54. In the present embodiment, the voltage applied to the branch waveguide 54 has a polarity opposite to that of the voltage applied to the branch waveguide 53, and has the same magnitude. Therefore, a difference is generated between the refractive index of the branch waveguide 53 and the refractive index of the branch waveguide 54, and the phase difference between the branch light Ld1 and the branch light Ld2 changes from 180° according to the difference between the above refractive indices. Then, the branch light Ld1 after being transmitted in the branch waveguide 53 and the branch light Ld2 after being transmitted in the branch waveguide 54 are coupled in the coupling section 55.

[0079] At this time, the intensity of the coupled light Lout varies according to the phase difference between the branched light Ld1 and the branched light Ld2. For example, when the phase difference between the branched light Ld1 and the branched light Ld2 is 180°, the intensity of the light Lout is 0%, and the light Lout is not output. When the branched light Ld1 and the branched light Ld2 are in the same phase, the intensity of the light Lout is substantially the same as the intensity of the light Lin (100%). Therefore, the intensity of the light Lout can be adjusted within the range of 0% to 100% of the intensity of the light Lin. Then, the light Lout is emitted to the combiner 36 via the output waveguide 56.

[0080] In the laser module 13 and the optical element 30 described above, the polarization mode of the visible light is converted from the TM0 mode to the TE1 mode by the conversion section 42, and the polarization mode of the visible light is converted from the TE1 mode to the TE0 mode by the conversion section 43. Therefore, the polarization mode of the visible light can be converted from the TM0 mode to the TE0 mode. In addition, in the conversion section 43, the light Lin of the TE1 mode incident from the conversion section 42 is branched into branch lights Ld1 and Ld2 of the TE0 mode with opposite phases to each other, and the phase difference between the branch lights Ld1 and the branch lights Ld2 is adjusted to couple the branch lights Ld1 and Ld2, thereby emitting light Lout of the TE0 mode. Since the light intensity of the light Lout emitted from the coupling section 55 can be changed according to the phase difference between the branch lights Ld1 and the branch lights Ld2, the conversion section 43 can also function as an optical modulator. Therefore, there is no need to provide an optical modulator, so that the laser module 13 and the optical element 30 can be miniaturized.

[0081] 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.

[0082] On the other hand, a branch waveguide 53 is arranged between the signal electrode 71 and the ground electrode 72, and a branch waveguide 54 is arranged between the signal electrode 71 and the ground electrode 73. Therefore, when a voltage is applied between the signal electrode 71 and the ground electrode 72, a voltage is applied in the Y-axis direction to the branch waveguide 53. Similarly, when a voltage is applied between the signal electrode 71 and the ground electrode 73, a voltage is applied in the Y-axis direction to the branch waveguide 54. Furthermore, the light Lin in the TE1 mode is branched into the branch light Ld1 and the branch light Ld2 in the TE0 mode by the branching portion 52, and the branch light Ld1 is emitted to the branch waveguide 53, and the branch light Ld2 is emitted to the branch waveguide 54.

[0083] Therefore, in the branch waveguide 53, a voltage is applied in the C-axis direction of the material constituting the core layer 32, and the direction of the main electric field of the branch light Ld1 transmitted in the branch waveguide 53 is consistent with the C-axis direction, so a large electro-optical effect can be obtained. Similarly, in the branch waveguide 54, a voltage is applied in the C-axis direction of the material constituting the core layer 32, and the direction of the main electric field of the branch light Ld2 transmitted in the branch waveguide 54 is consistent with the C-axis direction, so a large electro-optical effect can be obtained. As a result, the modulation efficiency of the conversion unit 43 can be improved.

[0084] The length of the branch portion 52 in the X-axis direction may be greater than 40 μm and less than 64 μm. The width of the branch portion 52 may be greater than 3.0 μm and less than 3.5 μm. In this case, the loss of light intensity in the conversion from the TE1 mode to the TE0 mode can be reduced. Therefore, the conversion efficiency from the TE1 mode to the TE0 mode can be improved.

[0085] 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 conversion section 43 of the mode converter 34R, the light intensity of the green light is modulated by the conversion section 43 of the mode converter 34G, and the light intensity of the blue light is modulated by the conversion section 43 of the mode converter 34B. Therefore, full-color laser light can be output without a large driving current.

[0086] In addition, the optical element and the laser module disclosed in the present invention are not limited to the above-mentioned embodiments.

[0087] For example, the laser module 13 may also be applied to devices other than the near-eye wearable device 1 .

[0088] The optical element 30 may not include the cladding 33. In this case, the air layer can function as the upper cladding.

[0089] The optical element 30 only needs 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 from the TM0 mode to the TE0 mode.

[0090] The light emitted from the light source unit 20 is not limited to visible light. In this case, the core layer 32 includes a mode converter that converts the polarization mode of light from the TM0 mode to the TE0 mode.

[0091] The structure of the conversion portion 42 is not limited to the structure in which the upper tapered portion 46 and the lower tapered portion 47 are stacked in the Z-axis direction. The conversion portion 42 only needs to be able to convert the polarization mode of light from the TM0 mode to the TE1 mode.

[0092] Example

[0093] 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.

[0094] <Evaluation of Conversion Loss in Mode Converters>

[0095] The conversion loss in the mode converters having the structures of Examples 1 to 7 was calculated. Figure 3 The mode converter 34R, the mode converter 34G, and the mode converter 34B shown in the figure have the same structure. As shown in Table 1, the width W0, the width Wt, the width Ws, the width W1, the width W21, the width W22, the length L11, the length L12, the length L21, and the length L22 are set for the wavelength of each color. In addition, in Examples 1 to 7, the height T11 is set to 0.5 μm, the height T12 is set to 0.2 μm, the height T21 is set to 0.5 μm, and the height T22 is set to 0.2 μm. A voltage is applied between the signal electrode 71 and the ground electrode 72 so that the branched light Ld1 and the branched light Ld2 are in the same phase. The calculation results of the conversion loss are shown in Table 1.

[0096] [Table 1]

[0097]

[0098] In Examples 1 to 7, relatively small losses of about 2.6 dB to 3.4 dB were generated. It can be seen that the conversion loss is suppressed and the conversion efficiency is improved. The branching efficiency depends on the dimensions of the branch portion 52 (length L21 and width W21), and the coupling (combining) efficiency depends on the dimensions of the coupling portion 55 (length L22 and width W22). In Examples 1 to 7, the length L21 is in the range of 40 μm to 64 μm, and the width W21 is in the range of 3.0 μm to 3.5 μm. The length L22 is in the range of 63 μm to 100 μm, and the width W22 is in the range of 6 μm to 10 μm. It can be seen that the conversion efficiency is improved in this case.

[0099] (Note)

[0100]

Project 1

[0101] An optical element, wherein

[0102] The optical component has:

[0103] a substrate having a main surface; and

[0104] The core layer is disposed on the main surface and is composed of a material having an electro-optical effect.

[0105] The core layer has a mode converter for converting the polarization mode of light from TM0 mode to TE0 mode.

[0106] The mode converter comprises:

[0107] A first converter that converts the polarization mode of the light from the TM0 mode to the TE1 mode; and

[0108] a second conversion section that converts the polarization mode of the light from the TE1 mode to the TE0 mode,

[0109] The second conversion unit comprises:

[0110] a branching section that branches the light in the TE1 mode incident from the first conversion section into a first branched light in the TE0 mode and a second branched light in the TE0 mode having opposite phases to each other;

[0111] a first branch waveguide extending in a first direction along the main surface for transmitting the first branch light;

[0112] a second branch waveguide extending in the first direction for transmitting the second branch light;

[0113] a coupling section that couples the first branch light transmitted through the first branch waveguide and the second branch light transmitted through the second branch waveguide to emit the light in the TE0 mode; and

[0114] a phase adjustment unit for adjusting a phase difference between the first branched light and the second branched light,

[0115] The first branch waveguide and the second branch waveguide are arranged in a second direction intersecting the first direction.

[0116]

Project 2

[0117] The optical element according to item 1, wherein:

[0118] The phase adjustment unit comprises:

[0119] a signal electrode disposed between the first branch waveguide and the second branch waveguide; and

[0120] a first ground electrode and a second ground electrode arranged so as to sandwich the first branch waveguide and the second branch waveguide in the second direction;

[0121] An optical axis of the material constituting the core layer extends along the second direction.

[0122]

Project 3

[0123] The optical element according to item 1 or 2, wherein:

[0124] The light is visible light.

[0125]

Project 4

[0126] The optical element according to item 3, wherein:

[0127] The length of the branch portion in the first direction is not less than 40 μm and not more than 64 μm,

[0128] The length of the branch portion in the second direction is greater than or equal to 3.0 μm and less than or equal to 3.5 μm.

[0129]

Project 5

[0130] The optical element according to item 3 or item 4, wherein:

[0131] The core layer also has:

[0132] a first mode converter, which is the mode converter that converts the polarization wave mode of red light from the TM0 mode to the TE0 mode;

[0133] a second mode converter, which is the mode converter that converts the polarization wave mode of green light from the TM0 mode to the TE0 mode;

[0134] a third mode converter, which is the mode converter that converts the polarization wave mode of blue light from the TM0 mode to the TE0 mode; and

[0135] A combiner combines the red light, the green light, and the blue light to emit laser light.

[0136]

Project 6

[0137] A laser module, wherein:

[0138] The laser module has:

[0139] The optical component described in item 5;

[0140] a first light source emitting the red light in the TM0 mode;

[0141] a second light source that emits the green light in the TM0 mode; and a third light source that emits the blue light in the TM0 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 has a mode converter for converting the polarization mode of light from TM0 mode to TE0 mode. The mode converter comprises: A first converter that converts the polarization mode of the light from the TM0 mode to the TE1 mode; and a second conversion section that converts the polarization mode of the light from the TE1 mode to the TE0 mode, The second conversion unit comprises: a branching section that branches the light in the TE1 mode incident from the first conversion section into a first branched light in the TE0 mode and a second branched light in the TE0 mode having opposite phases to each other; a first branch waveguide extending in a first direction along the main surface for transmitting the first branch light; a second branch waveguide extending in the first direction for transmitting the second branch light; a coupling section that couples the first branch light transmitted through the first branch waveguide with the second branch light transmitted through the second branch waveguide to emit the light in the TE0 mode; as well as a phase adjustment unit for adjusting a phase difference between the first branched light and the second branched light, The first branch waveguide and the second branch waveguide are arranged in a second direction intersecting the first direction.

2. The optical element according to claim 1, wherein The phase adjustment unit comprises: a signal electrode disposed between the first branch waveguide and the second branch waveguide; and a first ground electrode and a second ground electrode arranged so as to sandwich the first branch waveguide and the second branch waveguide in the second direction; An optical axis of the material constituting the core layer extends along the second direction.

3. The optical element according to claim 1 or 2, wherein: The light is visible light.

4. The optical element according to claim 3, wherein: The length of the branch portion in the first direction is not less than 40 μm and not more than 64 μm, The length of the branch portion in the second direction is greater than or equal to 3.0 μm and less than or equal to 3.5 μm.

5. The optical element according to claim 3 or 4, wherein: The core layer also has: a first mode converter, which is the mode converter that converts the polarization wave mode of red light from the TM0 mode to the TE0 mode; a second mode converter, which is the mode converter that converts the polarization wave mode of green light from the TM0 mode to the TE0 mode; a third mode converter, which is the mode converter for converting the polarization wave mode of the blue light from the TM0 mode to the TE0 mode; as well as A combiner combines the red light, the green light, and the blue light to emit laser light.

6. A laser module, wherein: The laser module has: The optical element according to claim 5; a first light source emitting the red light in the TM0 mode; a second light source that emits the green light in the TM0 mode; and The third light source emits the blue light in the TM0 mode.

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