Optical element, laser module, retinal projection device, and near-to-eye wearable device

Abstract

The invention relates to an optical element, a laser module, a retina projection device, and a near-to-eye wearable device. The optical element includes a mode converter that converts a polarization mode of visible light. The mode converter is provided with: a conversion unit that converts the polarization mode of visible light from a TM0 mode to a TE1 mode; and a branching unit that branches the visible light in the TE1 mode into first branched light in the TE0 mode and second branched light in the TE0 mode, and that adjusts the phase difference between the first branched light and the second branched light. The branching unit includes a first branching waveguide through which the first branching light is transmitted and a second branching waveguide through which the second branching light is transmitted. The optical path length of the first branched light in the first branched waveguide and the optical path length of the second branched light in the second branched waveguide are different from each other.

Description

[0001] Cross-reference to related applications

[0002] This application is based on Japanese Patent Application No. 2023-184920 filed with the Japan Patent Office on October 27, 2023, and claims the benefit of priority thereto, the entire contents of which are incorporated herein by reference. Technical Field

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

[0004] The polarization modes of light propagating in the optical waveguide include a polarization mode having a main electric field in a horizontal direction relative to the 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. Optical elements that convert the above polarization modes are known.

[0005] For example, Japanese Patent Publication No. 2017-181611 describes an optical element that converts the polarization mode of light from the TM0 mode to the TE0 mode. The optical element includes: a mode converter that converts the polarization mode of light from the TM0 mode to the TE1 mode; a mode branching unit that converts the polarization mode of light from the TE1 mode to two TE0 modes with different phases; a phase adjustment unit that adjusts the phases of the two TE0 mode lights; and a combining unit that combines the two TE0 mode lights with adjusted phases. Summary of the invention

[0006] The optical element described in Japanese Patent Publication No. 2017-181611 is an optical element used for optical communication, which converts light in the TM0 mode of the infrared band into light in the TE0 mode. However, in the optical element described in Japanese Patent Publication No. 2017-181611, the conversion efficiency when converting light in the TM0 mode into light in the TE0 mode is not considered, nor is the case of converting visible light in the TM0 mode into visible light in the TE0 mode considered.

[0007] The present disclosure describes an optical element, a laser module, a retinal projection device, and a near-eye wearable device that are capable of converting the polarization wave mode of visible light from the TM0 mode to the TE0 mode while suppressing a decrease in conversion efficiency.

[0008] 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 from the TM0 mode to the TE0 mode. The mode converter comprises: a conversion section, which converts the polarization wave mode of visible light from the TM0 mode to the TE1 mode; a branching section, which branches the visible light of the TE1 mode into a first branch light of the TE0 mode and a second branch light of the TE0 mode, and adjusts the phase difference between the first branch light and the second branch light; and a combining section, which combines the first branch light and the second branch light. The conversion section comprises a first end for incident visible light of the TM0 mode and a second end for emitting visible light of the TE1 mode, and the first end and the second end are two ends of the conversion section in the first direction. The length of the conversion section in the second direction increases continuously from the first end to the second end, and the second direction is along the main surface and intersects with the first direction. The phase difference is obtained by subtracting the phase of the first branch light when it is incident on the combining unit from the phase of the second branch light when it is incident on the combining unit. The branching unit includes a first branch waveguide for transmitting the first branch light and a second branch waveguide for transmitting the second branch light. The optical path length of the first branch light in the first branch waveguide and the optical path length of the second branch light in the second branch waveguide are different from each other.

[0009] In this optical element, since the length of the conversion section in the second direction increases continuously from the first end to the second end, the effective refractive index of the visible light transmitted in the conversion section changes. As a result, in the conversion section, the polarization wave mode of the visible light can be converted from the TM0 mode to the TE1 mode. Furthermore, in the branching section, the visible light in the TE1 mode emitted from the conversion section is branched into the first branch light in the TE0 mode and the second branch light in the TE0 mode, which have opposite phases to each other. Then, the first branch light is transmitted in the first branch waveguide, and the second branch light is transmitted in the second branch waveguide. Then, in the combining section, the first branch light and the second branch light are combined to emit visible light in the TE0 mode.

[0010] Here, when the optical path length in the first branch waveguide is the same as the optical path length in the second branch waveguide, the first branch light and the second branch light are incident on the combining section without changing from -π radians by the phase difference obtained by subtracting the phase when the first branch light is incident on the combining section from the phase when the second branch light is incident on the combining section. Therefore, the intensity of the visible light obtained by combining the first branch light and the second branch light is substantially half of the intensity of the visible light incident on the conversion section, and the conversion efficiency is reduced. On the other hand, in the optical element, since the optical path length in the first branch waveguide and the optical path length in the second branch waveguide are different from each other, the above-mentioned phase difference is a value different from -π radians. Thereby, it is possible to suppress the decrease in the intensity of the visible light obtained by combining the first branch light and the second branch light relative to the intensity of the visible light incident on the conversion section. According to the above, the above-mentioned optical element can convert the polarization wave mode of the visible light from the TM0 mode to the TE0 mode while suppressing the decrease in conversion efficiency.

[0011] The above-mentioned phase difference can be greater than -2π / 3+2nπ radians and less than -π / 3+2nπ radians. n can be an integer. When the above-mentioned phase difference is -π / 2+2nπ radians, the intensity of the visible light in the TE0 mode obtained by combining the first branch light and the second branch light is substantially the same as the intensity of the visible light in the TM0 mode incident on the conversion portion. As the above-mentioned phase difference moves away from -π / 2+2nπ radians, the intensity of the visible light in the TE0 mode obtained by combining the first branch light and the second branch light decreases. Since the above-mentioned range is a range of ±π / 6 centered on -π / 2+2nπ radians, the loss of the intensity of the visible light in the TE0 mode obtained by combining the first branch light and the second branch light can be further reduced. That is, the reduction in conversion efficiency from the TM0 mode to the TE0 mode can be further suppressed.

[0012] The core layer may further include a slab provided on the main surface. The mode converter may be provided on the slab in a third direction intersecting the first direction and the second direction. In this case, the waveguide formed by the conversion portion and the slab has an asymmetric shape in the third direction. Thus, the conversion efficiency of the conversion portion from the TM0 mode to the TE1 mode can be improved.

[0013] The length of the core layer in the third direction may be smaller than the wavelength of the visible light. In this case, the visible light easily leaks from the conversion part to the flat plate, thereby improving the conversion efficiency of the conversion part from the TM0 mode to the TE1 mode.

[0014] The combining unit may be formed of a multi-mode interferometer. In this case, the combining unit can be formed more simply than when the combining unit is formed of a Y-branch waveguide.

[0015] Alternatively, the length of the combining portion in the second direction may be greater than 2.0 μm. In this case, the interval between the first branch waveguide and the second branch waveguide can be ensured without reducing the width of the first branch waveguide and the second branch waveguide. Thus, the first branch waveguide and the second branch waveguide can be formed into a desired shape.

[0016] Alternatively, the length of the first branch waveguide in the second direction at the connection end of the first branch waveguide connected to the combiner is greater than 23% and less than 47% of the length of the combiner in the second direction. Alternatively, the length of the second branch waveguide in the second direction at the connection end of the second branch waveguide connected to the combiner is greater than 23% and less than 47% of the length of the combiner in the second direction. In this case, both the tolerance of the mode converter with respect to manufacturing errors and the interval between the first branch waveguide and the second branch waveguide can be ensured.

[0017] The core layer may include: a first mode converter, which is a mode converter that converts the polarization mode of red light from TM0 mode to TE0 mode; a second mode converter, which is a mode converter that converts the polarization mode of green light from TM0 mode to TE0 mode; a third mode converter, which is a mode converter that converts the polarization 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. According to this structure, the polarization mode of red light is converted from TM0 mode to TE0 mode, the polarization mode of green light is converted from TM0 mode to TE0 mode, and the polarization mode of blue light is converted from TM0 mode to TE0 mode. For example, when the combiner is designed so that the combining efficiency of the red light, green light, and blue light in the TE0 mode is higher than the combining efficiency of the red light, green light, and blue light in the TM0 mode, the combining efficiency of the combiner can be improved.

[0018] The length of the first mode converter in the third direction intersecting the first direction and the second direction, the length of the second mode converter in the third direction, and the length of the third mode converter in the third direction may be the same. In this case, the first mode converter, the second mode converter, and the third mode converter can be formed on the same substrate, and since the lengths of the mode converters in the third direction can be made the same, the optical element can be easily manufactured.

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

[0020] A laser module according to another aspect of the present disclosure includes: the above-mentioned optical element; a first laser light source that emits red light in TM0 mode; a second laser light source that emits green light in TM0 mode; and a third laser light source that emits blue light in TM0 mode. Since the laser module includes the above-mentioned optical element, it is possible to convert the polarization mode of visible light from TM0 mode to TE0 mode while suppressing a decrease in conversion efficiency.

[0021] A retinal projection device according to another aspect of the present disclosure is mounted on a near-eye wearable device, wherein the retinal projection device comprises: the above-mentioned laser module; a movable reflector that uses the laser emitted from the laser module for scanning; and a reflector that reflects the laser after passing through the movable reflector and guides the reflected light to the retina of the user wearing the near-eye wearable device, thereby projecting an image onto the retina. The retinal projection device comprises the above-mentioned optical element. Therefore, in the retinal projection device, the polarization wave mode of visible light can be converted from the TM0 mode to the TE0 mode while suppressing the reduction of conversion efficiency, and on this basis, the image is projected onto the retina.

[0022] A near-eye wearable device according to another aspect of the present disclosure includes: the above-mentioned retinal projection device; and a lens provided with the above-mentioned reflector. The near-eye wearable device includes a retinal projection device having the above-mentioned optical element. Therefore, in the near-eye wearable device, the polarization wave mode of visible light can be converted from the TM0 mode to the TE0 mode while suppressing the reduction of conversion efficiency, and on this basis, an image can be projected onto the retina.

[0023] According to aspects and embodiments of the present disclosure, it is possible to convert the polarization wave mode of visible light from the TM0 mode to the TE0 mode while suppressing a decrease in conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] 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.

[0025] Figure 2 It roughly indicates Figure 1 The structure diagram of the retinal projection device shown.

[0026] Figure 3 yes Figure 2 Block diagram of the laser module is shown.

[0027] Figure 4 Yes means Figure 3 A diagram showing the cross-sectional structure of an optical element.

[0028] Figure 5 Yes means Figure 3 A top view of the structure of the mode converter is shown.

[0029] Figure 6 It is a magnified representation Figure 5 A top view of the branch portion is shown.

[0030] Figure 7 is a block diagram of a laser module according to another embodiment.

[0031] Figure 8 is a block diagram of a laser module according to still another embodiment.

[0032] Fig. 9 This is a block diagram of a laser module according to still another embodiment.

[0033] Fig.10 (a) is a graph showing the evaluation results of Example 1.

[0034] Fig.10 (b) is a graph showing the evaluation results of Example 2.

[0035] Fig.10 (c) is a graph showing the evaluation results of Example 3.

[0036] Fig.11 (a) is a diagram showing the relationship between the length of the conversion section in the X-axis direction and the conversion loss.

[0037] Fig.11 (b) is a diagram showing the relationship between the length of the conversion section in the X-axis direction and the conversion loss.

[0038] Fig.11 (c) is a diagram showing the relationship between the length of the conversion section in the X-axis direction and the conversion loss.

[0039] Fig.12 (a) is a graph showing the evaluation results of Examples 10 to 13.

[0040] Fig.12 (b) is a graph showing the evaluation results of Examples 14 to 17.

[0041] Fig.12 (c) is a graph showing the evaluation results of Examples 18 to 23. DETAILED DESCRIPTION

[0042] The embodiments of the present disclosure are described in detail below with reference to the accompanying drawings. In addition, the same reference numerals are used to mark the same elements in the description of the accompanying drawings, and repeated descriptions are omitted. An XYZ coordinate system is sometimes shown in each figure. The Y-axis direction (the second direction) is a direction that intersects (for example, is orthogonal to) the X-axis direction (the first direction) and the Z-axis direction (the third direction). The Z-axis direction is a direction that intersects (for example, is orthogonal to) the X-axis direction and the Y-axis direction. In this specification, the numerical range represented by "to" shows a range that includes the numerical values ​​recorded before and after the "to" as the minimum value and the maximum value, respectively. The upper limit value and the lower limit value recorded separately can be combined arbitrarily.

[0043] 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.

[0044] The frame 2 includes a pair of lens rings 2a, a nose bridge 2b, and a pair of temples 2c. The lens ring 2a is a portion that holds the lens 3. The nose bridge 2b is a portion that connects the pair of lens rings 2a. The temple 2c is a portion that extends from the lens ring 2a and hangs on the user's ear. The frame 2 may also be a frame without lens rings. The lens 3 includes an inner surface 3a (refer to Figure 2 ).

[0045] 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.

[0046] Next, refer to Figure 2 The retinal projection device 10 will be described in detail. Figure 2 It roughly indicates Figure 1 The structure of the retinal projection device is shown in FIG. Figure 2 As shown, the retinal projection device 10 includes an optical engine 20 and a reflector 30 .

[0047] The optical engine 20 is a device that generates laser light Ls of a color and light intensity corresponding to the pixel of the image projected onto the retina and emits the laser light Ls toward the reflector 30. The optical engine 20 is mounted on each temple 2c. The optical engine 20 includes a laser module 4, an optical component 5, a movable reflector 6, a laser driver 7, a reflector driver 8, and a controller 9.

[0048] The laser module 4 emits laser light La as visible light. For example, a full-color laser module is used as the laser module 4. The laser module 4 emits laser light La of a color and intensity corresponding to the pixel of the image projected onto the retina. The details of the laser module 4 will be described later.

[0049] The optical component 5 is a component that performs optical processing on the laser light La emitted from the laser module 4. In the present embodiment, the optical component 5 includes a collimating lens 5a, an aperture 5b, and a light reduction filter 5c. The collimating lens 5a, the aperture 5b, and the light reduction filter 5c are arranged in sequence along the optical path of the laser light La. The optical component 5 may also have other structures.

[0050] The movable reflector 6 is a member for scanning with the laser light Ls. The movable reflector 6 is provided in the emission direction of the laser light La processed by the optical component 5. The movable reflector 6 is configured to be able to swing around an axis extending in the lateral direction of the lens 3 and an axis extending in the longitudinal direction of the lens 3, and to change the angle in the lateral and longitudinal directions of the lens 3 to reflect the laser light La and emit the laser light Ls. As the movable reflector 6, for example, a MEMS (Micro Electro Mechanical Systems) reflector is used.

[0051] The laser driver 7 is a driving circuit for driving the laser module 4. The laser driver 7 drives the laser module 4 based on, for example, the light intensity of the laser La and the temperature of the laser light sources 411, 412, 413 included in the laser module 4. The reflector driver 8 is a driving circuit for driving the movable reflector 6. The reflector driver 8 causes the movable reflector 6 to swing within a predetermined angle range and timing. The controller 9 is a device for controlling the laser driver 7 and the reflector driver 8.

[0052] In the optical engine 20, laser light La of a color and intensity corresponding to the pixel of the image projected onto the retina is emitted from the laser module 4, passes through the optical component 5, and is reflected by the movable mirror 6. The laser light La reflected by the movable mirror 6 is emitted toward the reflector 30 as laser light Ls.

[0053] The reflector 30 is a member that projects an image onto the retina by reflecting the laser light Ls that has passed through the movable reflector 6 and guiding the reflected light Lrf toward the retina of the user wearing the near-eye wearable device 1 .

[0054] Next, refer to Figure 3 and Figure 4 The structure of the laser module 4 will be described. Figure 3 yes Figure 2 Block diagram of the laser module is shown. Figure 4 Yes means Figure 3 A diagram showing the cross-sectional structure of an optical element.

[0055] like Figure 3 As shown, the laser module 4 includes an optical element 40, a laser light source 411 (first laser light source) emitting red light Lr, a laser light source 412 (second laser light source) emitting green light Lg, and a laser light source 413 (third laser light source) emitting blue light Lb. The laser light source 411 is, for example, a red laser diode. The laser light source 412 is, for example, a green laser diode. The laser light source 413 is, for example, a blue laser diode. The peak wavelength of the red light Lr is, for example, in the range of 600nm to 830nm. The peak wavelength of the green light Lg is, for example, in the range of 500nm to 570nm. The peak wavelength of the blue light Lb is, for example, in the range of 380nm to 490nm.

[0056] In the present embodiment, the laser light source 411 emits red light Lr in the TM0 mode. The laser light source 412 emits green light Lg in the TM0 mode. The laser light source 413 emits blue light Lb in the TM0 mode. Since the red light Lr, the green light Lg, and the blue light Lb are all visible light, in the following description, the red light Lr, the green light Lg, and the blue light Lb are sometimes referred to as visible light, and sometimes the red light Lr, the green light Lg, and the blue light Lb are collectively referred to as visible light.

[0057] The optical element 40 combines the visible light emitted from the laser light sources into a single laser beam La. The optical element 40 is, for example, a planar lightwave circuit (PLC). Figure 4 As shown, the optical element 40 includes a substrate S, a core layer CA, and a cladding layer CB.

[0058] The substrate S functions as a lower cladding layer. The substrate S is made of a material having a refractive index lower than that of the material constituting the core layer CA. Examples of the constituent material of the substrate S include sapphire, silicon, or aluminum oxide (Al 2 O 3). The substrate S has a main surface Sa and a back surface Sb on the side opposite to the main surface Sa. The main surface Sa and the back surface Sb are surfaces defined by the X-axis direction and the Y-axis direction, and intersect the Z-axis direction. In this embodiment, the main surface Sa and the back surface Sb are orthogonal to the Z-axis direction. In other words, the X-axis direction and the Y-axis direction are directions along the main surface Sa.

[0059] The cladding CB functions as an upper cladding. The cladding CB covers the core CA on the main surface Sa. The cladding CB is composed of a material having a refractive index lower than that of the constituent material of the core CA. Examples of constituent materials of the cladding CB include silicon oxide (e.g., SiO 2 ).

[0060] The core layer CA is provided on the main surface Sa. The core layer CA 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. Examples of the constituent materials of the core layer CA include lithium niobate (LiNbO 3 In this embodiment, the core layer CA is a lithium niobate thin film formed on the main surface Sa of the substrate S by sputtering, and the optical axis (C axis) of the lithium niobate extends along the Z axis direction. The core layer CA may also be composed of Z-cut lithium niobate.

[0061] The core layer CA includes a flat plate 41, a modulator 42 (first modulator), a modulator 43 (second modulator), a modulator 44 (third modulator), a mode converter 45 (first mode converter), a mode converter 46 (second mode converter), a mode converter 47 (third mode converter) and a combiner 48.

[0062] like Figure 4 As shown, the flat plate 41 is provided on the main surface Sa. The flat plate 41 has a flat plate shape. The length of the flat plate 41 in the Z-axis direction is a height T11. Hereinafter, the length in the Z-axis direction may be referred to as "height". The height T11 is, for example, 0.1 μm to 0.7 μm.

[0063] In this embodiment, modulators 42, 43, 44, mode converters 45, 46, 47, and a combiner 48 are provided on one plate 41. Only mode converters 45, 46, 47 may be provided on one plate 41. That is, modulators 42, 43, 44 and combiner 48 may not be provided on the plate 41. A plate 41 may also be provided for each mode converter.

[0064] The modulator 42 is a modulator that modulates the light intensity of the red light Lr. The red light Lr in the TM0 mode is incident from the laser light source 411 to the incident end of the modulator 42. The modulator 42 modulates the light intensity of the red light Lr in the TM0 mode incident from the laser light source 411. The emission end of the modulator 42 is optically connected to the incident end of the mode converter 45.

[0065] The modulator 43 is a modulator that modulates the light intensity of the green light Lg. The green light Lg in the TM0 mode is incident from the laser light source 412 to the incident end of the modulator 43. The modulator 43 modulates the light intensity of the green light Lg in the TM0 mode incident from the laser light source 412. The emission end of the modulator 43 is optically connected to the incident end of the mode converter 46.

[0066] The modulator 44 is a modulator that modulates the light intensity of the blue light Lb. The blue light Lb in the TM0 mode is incident from the laser light source 413 to the incident end of the modulator 44. The modulator 44 modulates the light intensity of the blue light Lb in the TM0 mode incident from the laser light source 413. The emission end of the modulator 44 is optically connected to the incident end of the mode converter 47. Each modulator is, for example, a Mach-Zehnder type modulator.

[0067] The mode converter 45 is a mode converter that converts the polarization wave mode of the red light Lr from the TM0 mode to the TE0 mode. The red light Lr whose light intensity is modulated by the modulator 42 is incident on the incident end of the mode converter 45. The mode converter 46 is a mode converter that converts the polarization wave mode of the green light Lg from the TM0 mode to the TE0 mode. The green light Lg whose light intensity is modulated by the modulator 43 is incident on the incident end of the mode converter 46. The mode converter 47 is a mode converter that converts the polarization wave mode of the blue light Lb from the TM0 mode to the TE0 mode. The blue light Lb whose light intensity is modulated by the modulator 44 is incident on the incident end of the mode converter 47. The emission end of the mode converter 45, the emission end of the mode converter 46, and the emission end of the mode converter 47 are optically connected to the three incident ends of the combiner 48, respectively.

[0068] The mode converter 45 , the mode converter 46 , and the mode converter 47 extend in the X-axis direction, respectively. The mode converter 45 , the mode converter 46 , and the mode converter 47 are arranged in this order in the Y-axis direction.

[0069] The height of the mode converter 45, the height of the mode converter 46, and the height of the mode converter 47 are substantially the same, which is height T12. Height T12 is, for example, 0.1 μm to 0.7 μm. The height of the core layer CA is the sum of height T11 and height T12, which is height T1. Height T1 is smaller than the wavelength of visible light to be converted. Height T1 is, for example, 0.2 μm to 0.8 μm. The height of the mode converter 45, the height of the mode converter 46, and the height of the mode converter 47 may be different from each other. The detailed structure of each mode converter will be described later.

[0070] When the plate 41 is provided for each mode converter, the height T1 only needs to be smaller than the wavelength of the visible light to be converted in the corresponding mode converter. In the combination of the plate 41 and the mode converter 45, the height T1 only needs to be smaller than the wavelength of the red light Lr. In the combination of the plate 41 and the mode converter 46, the height T1 only needs to be smaller than the wavelength of the green light Lg. In the combination of the plate 41 and the mode converter 47, the height T1 only needs to be smaller than the wavelength of the blue light Lb.

[0071] The combiner 48 combines the red light Lr, green light Lg, and blue light Lb, whose polarization modes are converted in the respective mode converters, into one visible light. The three incident ends of the combiner 48 are optically connected to the emission ends of the mode converter 45, the mode converter 46, and the mode converter 47, respectively. The combiner 48 emits the combined visible light as laser light La from the emission end of the combiner 48.

[0072] In the laser module 4, visible light in TM0 mode is emitted from each laser light source, and the light intensity of each visible light is modulated in each modulator. Then, the polarization wave mode of the visible light is converted from TM0 mode to TE0 mode in each mode converter. Then, each visible light having its polarization wave mode converted is combined in the combiner 48, and the laser light La in TE0 mode is transmitted from the combiner 48 to the optical component 5 (refer to FIG. Figure 2 ) is ejected.

[0073] Next, refer to Figure 4 and Figure 5 The specific configurations of the mode converters 45 , 46 , and 47 will be described. Figure 5 Yes means Figure 3 The top view of the structure of the mode converter is shown. Figure 5 As shown, each of the mode converters 45, 46 and 47 includes a conversion unit 51, a branching unit 52 and a combining unit 53. Since the structures of the mode converters are the same, the mode converter 45 is taken as an example for description.

[0074] The conversion section 51 is a part that converts the polarization mode of visible light from the TM0 mode to the TE1 mode. Figure 5As shown, the conversion section 51 is located at one end of the mode converter 45 in the X-axis direction. The conversion section 51 includes an incident end 51a (first end) and an emission end 51b (second end) as two ends in the X-axis direction. Red light in the TM0 mode is incident on the incident end 51a from the laser light source 411. The red light incident on the incident end 51a is sometimes referred to as "light Lin" hereinafter. The emission end 51b emits light Lin in the TE1 mode. The emission end 51b emits the light Lin in the TE1 mode toward the branching section 52. The length L1 of the conversion section 51 in the X-axis direction is, for example, 10 μm to 10000 μm.

[0075] The length of the conversion portion 51 in the Y-axis direction increases continuously from the incident end 51a to the emission end 51b. The length in the Y-axis direction is sometimes referred to as "width" below. The width of the conversion portion 51 increases continuously from the width W1 to the width W2 as it moves from the incident end 51a toward the emission end 51b. The width W1 is smaller than the width W2. The width W1 is, for example, 0.3μm to 1.0μm. The width W2 is, for example, 0.4μm to 1.2μm. The rate of increase of the width of the conversion portion 51 may be constant.

[0076] In the conversion section 51, as the distance from the incident end 51a in the X-axis direction is increased, the effective refractive index of the TM0 mode and the effective refractive index of the TE1 mode approach each other and cross each other, thereby causing conversion between the TM0 mode and the TE1 mode. Therefore, when the light Lin in the TM0 mode is incident on the incident end 51a, the polarization wave mode of the light Lin is converted from the TM0 mode to the TE1 mode in the conversion section 51. On the other hand, within the entire length range of the conversion section 51 in the X-axis direction, the effective refractive index of the TE0 mode is sufficiently away from the effective refractive index of the TM0 mode and the effective refractive index of the TE1 mode. Therefore, when the light Lin in the TE0 mode is incident on the incident end 51a, the polarization wave mode of the light Lin is maintained as the TE0 mode.

[0077] The branching unit 52 is configured to branch the TE1 mode light Lin incident from the emission end 51b of the conversion unit 51 into a TE0 mode branched light LA ​​(first branched light) and a TE0 mode branched light LB (second branched light) and adjust the phase difference between the branched light LA ​​and the branched light LB. Phase difference It is the phase difference obtained by subtracting the phase of the branch light LA ​​when it is incident on the combining section 53 from the phase of the branch light LB when it is incident on the combining section 53. The branch section 52 branches the TE1 mode light Lin into the TE0 mode branch light LA ​​and the TE0 mode branch light LB which have opposite phases to each other. The light intensity of the branch light LA ​​and the light intensity of the branch light LB are substantially half (50%) of the light intensity of the TE1 mode light Lin incident from the emission end 51b. In the present embodiment, the branch section 52 is composed of a Y-branch waveguide. The length L2 of the branch section 52 in the X-axis direction is, for example, 10μm to 1000μm. The branch section 52 includes a branch waveguide 52A (first branch waveguide) and a branch waveguide 52B (second branch waveguide).

[0078] The branch waveguide 52A is a waveguide for transmitting the branch light LA. The branch waveguide 52A is disposed between the conversion unit 51 and the combining unit 53, and includes a connection end (end 521a described later) connected to the conversion unit 51 and a connection end (end 522b described later) connected to the combining unit 53. The branch waveguide 52A emits the branch light LA ​​of the TE0 mode branched from the light Lin of the TE1 mode to the combining unit 53.

[0079] The branch waveguide 52B is a waveguide for transmitting the branch light LB. The branch waveguide 52B is arranged between the conversion unit 51 and the combining unit 53, and includes a connection end (end 523a described later) connected to the conversion unit 51 and a connection end (end 526b described later) connected to the combining unit 53. The branch waveguide 52B emits the branch light LB of the TE0 mode branched from the light Lin of the TE1 mode to the combining unit 53.

[0080] The branch waveguide 52A and the branch waveguide 52B extend so as to be separated from each other in the Y-axis direction as they are separated from the conversion section 51 in the X-axis direction, and then extend substantially parallel to each other to the combining section 53 .

[0081] The combining unit 53 combines the branched light LA ​​and the branched light LB. The combining unit 53 combines the branched light LA ​​incident from the branch waveguide 52A and the branched light LB incident from the branch waveguide 52B to emit red light in the TE0 mode. The red light emitted from the combining unit 53 is sometimes referred to as "light Lout" below. When the combining unit 53 emits the light Lout, the light intensity of the light Lout is adjusted according to the phase difference. For example, the phase difference When the phase difference is -π / 2 radians, the intensity of the light Lout is substantially the same (100%) as the intensity of the light Lin in the TE1 mode emitted from the emission end 51b. Described later.

[0082] In the present embodiment, the combining unit 53 is composed of a multimode interferometer. Specifically, the combining unit 53 is composed of a dual-input dual-output multimode interferometer. That is, the combining unit 53 includes an incident end 53a, an incident end 53b, an emission end 53c, and an emission end 53d. The incident end 53a is connected to the connection end (end 522b described later) of the branch waveguide 52A. The incident end 53b is connected to the connection end (end 526b described later) of the branch waveguide 52B. In the present embodiment, since the mode converter 45 is used as a mode converter that converts the polarization wave mode of the red light Lr from the TM0 mode to the TE0 mode, the emission end 53c is connected to the incident end of the combiner 48 to emit the light Lout of the TE0 mode. The length L3 of the combining unit 53 in the X-axis direction is, for example, 2.0μm to 1000μm. The width W3 of the combining unit 53 is, for example, 1.0μm to 10μm.

[0083] Next, refer to Figure 5 and Figure 6 The structure of the branch portion 52 will be described in more detail. Figure 6 It is a magnified representation Figure 5 A top view of the branch portion shown. In the branch portion 52, the optical path length OL1 of the branch light LA ​​in the branch waveguide 52A and the optical path length OL2 of the branch light LB in the branch waveguide 52B are different from each other. In the present embodiment, the physical length of the branch waveguide 52A along the optical path of the branch light LA ​​and the physical length of the branch waveguide 52B along the optical path of the branch light LB are equal to each other. The width of the branch waveguide 52A is constant over the entire length of the branch waveguide 52A, while the width of the branch waveguide 52B is smaller than the width of the branch waveguide 52A in a part of the branch waveguide 52B. This is described in detail below.

[0084] The branch waveguide 52A includes a waveguide 521 and a waveguide 522. The waveguide 521 and the waveguide 522 are sequentially arranged in the X-axis direction. In the present embodiment, the waveguide 521 extends obliquely with respect to the X-axis direction, and the waveguide 522 extends substantially parallel to the X-axis direction.

[0085] The waveguide 521 includes an end 521a and an end 521b as two ends in the X-axis direction. The waveguide 522 includes an end 522a and an end 522b as two ends in the X-axis direction. The end 521a is connected to the emission end 51b. The end 521b and the end 522a are connected to each other. The end 522b is connected to the incident end 53a. In this way, in the present embodiment, the branch waveguide 52A is formed by connecting the waveguide 521 and the waveguide 522. In the present embodiment, the end 521a is the connection end of the branch waveguide 52A connected to the conversion unit 51, and the end 522b is the connection end of the branch waveguide 52A connected to the combining unit 53.

[0086] The width of the waveguide 521 at the end 521a is, for example, less than 50% of the width W2, and in the present embodiment, is smaller than 50% of the width W2. The width of the waveguide 521 between the end 521a and the end 521b is the width W4, which is substantially constant. The width of the waveguide 522 between the end 522a and the end 522b is the width W4, which is substantially constant. Therefore, in the present embodiment, the width W4 is also smaller than 50% of the width W2. Furthermore, in the present embodiment, the width W4 is 23% to 47% of the width W3. Therefore, the width of the waveguide 522 (branch waveguide 52A) at the end 522b is also 23% to 47% of the width W3. The width W4 is, for example, 0.4 μm to 4.0 μm.

[0087] The length L21 of the waveguide 521 in the X-axis direction is, for example, 1.0 μm to 100 μm. The length L22 of the waveguide 522 in the X-axis direction is, for example, 1.0 μm to 300 μm. In the present embodiment, the total value of the length L21 and the length L22 is the length L2.

[0088] The branch waveguide 52B includes a waveguide 523, a waveguide 524, a waveguide 525, and a waveguide 526. The waveguide 523, the waveguide 524, the waveguide 525, and the waveguide 526 are arranged in the X-axis direction in sequence. In the present embodiment, the waveguide 523 extends obliquely with respect to the X-axis direction, and the waveguide 524, the waveguide 525, and the waveguide 526 extend substantially parallel to the X-axis direction. The waveguide 521 and the waveguide 523 are inclined so as to move away from each other in the Y-axis direction as they move away from the emission end 51b.

[0089] The waveguide 523 includes an end 523a and an end 523b as two ends in the X-axis direction. The waveguide 524 includes an end 524a and an end 524b as two ends in the X-axis direction. The waveguide 525 includes an end 525a and an end 525b as two ends in the X-axis direction. The waveguide 526 includes an end 526a and an end 526b as two ends in the X-axis direction. The end 523a is connected to the emission end 51b. The end 523b and the end 524a are connected to each other. The end 524b and the end 525a are connected to each other. The end 525b and the end 526a are connected to each other. The end 526b is connected to the incident end 53b. In this way, in the present embodiment, the branch waveguide 52B is formed by connecting the waveguide 523, the waveguide 524, the waveguide 525, and the waveguide 526. In the present embodiment, the end portion 523 a is a connection end of the branch waveguide 52B connected to the conversion unit 51 , and the end portion 526 b is a connection end of the branch waveguide 52B connected to the combining unit 53 .

[0090] The width of the waveguide 523 decreases continuously from the end 523a to the end 523b. The width of the waveguide 523 decreases from the width W5 to the width W6 as it moves from the end 523a toward the end 523b. The width W5 is, for example, less than 50% of the width W2, and in the present embodiment, is smaller than 50% of the width W2. The width W5 may be substantially the same as the width of the waveguide 521 at the end 521a, or may be different from the width of the waveguide 521 at the end 521a. In the present embodiment, the width W5 is substantially the same as the width W4, and the width W6 is smaller than the width W2 and the width W5. The width W6 may be larger than the width W5, or may be larger than the width W2. The width W6 is, for example, 0.2 μm to 3.0 μm. The width of the waveguide 524 between the end 524a and the end 524b is the width W6, which is substantially constant.

[0091] The width of the waveguide 525 increases continuously from the end 525a to the end 525b. The width of the waveguide 525 increases from the width W6 to the width W4 as it moves from the end 525a toward the end 525b. The width of the waveguide 526 between the end 526a and the end 526b is the width W4, which is substantially constant. As described above, since the width W4 is 23% to 47% of the width W3, the width of the waveguide 526 (branch waveguide 52B) at the end 526b is also 23% to 47% of the width W3. In addition, the width of the waveguide 526 at the end 526b may be different from the width of the waveguide 522 at the end 522b.

[0092] The length of the waveguide 523 in the X-axis direction is length L21. The length L23 of the waveguide 524 in the X-axis direction is, for example, 0 μm to 100 μm. The length L24 of the waveguide 525 in the X-axis direction is, for example, 1.0 μm to 100 μm. The length L25 of the waveguide 526 in the X-axis direction is, for example, 0 μm to 100 μm. In the present embodiment, the total value of the length L21, the length L23, the length L24, and the length L25 is the length L2.

[0093] Next, the optical path length difference ΔOL between the optical path length OL1 and the optical path length OL2 and the phase difference In the following, the wavelength of the branched light LA ​​and the wavelength of the branched light LB are referred to as wavelength λ, and the effective refractive index of the branched light LA ​​is referred to as effective refractive index n effA , the effective refractive index of the branched light LB is set to the effective refractive index n effB (s). Since the width of the branch waveguide 52A is constant over the entire length of the branch waveguide 52A, the effective refractive index n effA The effective refractive index n is constant over the entire length of the branch waveguide 52A. Since the width of the branch waveguide 52B is not constant over the entire length of the branch waveguide 52B, the effective refractive index n is effB(s) is expressed as a function of the position s along the optical path of the branched light LB. Here, for convenience of description, the position s of the end portion 523a is set to 0.

[0094] First, the optical path length difference ΔOL will be described. In the present embodiment, the optical path length difference obtained by subtracting the optical path length OL1 from the optical path length OL2 is defined as the optical path length difference ΔOL (= OL2 - OL1). As described above, in the waveguide 523 and the waveguide 525 whose widths vary, the branched light LB propagates in the waveguide 523 and the waveguide 525 while changing its effective refractive index. Moreover, the width of the portion of the waveguide 523 other than the end 523a, the width of the waveguide 524, and the width of the portion of the waveguide 525 other than the end 525b are smaller than the widths of the waveguides 521 and 522. Therefore, in the portion of the waveguide 523 other than the end 523a, and the portions of the waveguide 524 and the waveguide 525 other than the end 525b, the effective refractive index n effB (s)<effective refractive index n effA The relationship is established.

[0095] Furthermore, for the optical path length OL1, the physical length PL2 of the branch waveguide 52A along the optical path of the branch light LA ​​and the effective refractive index n effA It is expressed by formula (1).

[0096] [Formula 1]

[0097] OL1=n effA ×PL2 (1)

[0098] The optical path length OL2 uses an effective refractive index n effB (s) is expressed by equation (2). The physical length of the branch waveguide 52B along the optical path of the branch light LB is the same as the physical length of the branch waveguide 52A along the optical path of the branch light LA, that is, length PL2.

[0099] [Formula 2]

[0100]

[0101] As described above, in the portion of the waveguide 523 other than the end 523a, the waveguide 524, and the portion of the waveguide 525 other than the end 525b, due to the effective refractive index n effB (s)<effective refractive index n effA The relationship holds, so the optical path length difference ΔOL is a negative value. As described above, by adopting a structure in which the width of the waveguide 523 and the width of the waveguide 525 are changed in the branch waveguide 52B, an optical path length difference ΔOL is generated between the optical path length OL1 and the optical path length OL2.

[0102] Next, the phase difference In this embodiment, the phase difference obtained by subtracting the phase of the branched light LA ​​when incident on the branching portion 52 from the phase of the branched light LB when incident on the branching portion 52 is defined as the initial phase difference When the light Lin in the TM0 mode is incident on the mode converter 45, the phase of the branched light LB when incident on the branching portion 52 is delayed by π radians compared to the phase of the branched light LA ​​when incident on the branching portion 52. Therefore, the initial phase difference When the light Lin in TE0 mode is incident on the mode converter 45, the initial phase difference is is 0 radians.

[0103] As described above, in the branching portion 52, the optical path length difference ΔOL is a negative value. From the initial phase difference Here, the phase difference The relationship between the optical path length difference ΔOL and the wavelength λ is expressed as In the multiplexing unit 53, the phase difference at which the intensity of the light Lout is the largest That is, the phase difference with the maximum conversion efficiency from TM0 mode to TE0 mode = -π / 2+2nπ radians (n ​​is an integer). Therefore, according to the above relationship, the optical path length difference ΔOL that maximizes the conversion efficiency is -λ / 4+nλ. In addition, the conversion efficiency represents the ratio of the intensity of the visible light in the TE0 mode emitted from the mode converter 45 to the intensity of the visible light in the TM0 mode incident on the mode converter 45.

[0104] In this embodiment, the phase difference The conversion efficiency is set to be 86.6% or more. The phase difference is set within the range of -2π / 3+2nπ radians to -π / 3+2nπ radians, and the optical path length difference ΔOL is set within the range of -λ / 3+nλ to -λ / 6+nλ. To make the phase difference In the present embodiment, the length and width W6 of the waveguides 524, 525, 526 in the X-axis direction are set so that the optical path length difference ΔOL is in the range of -λ / 3+nλ to -λ / 6+nλ.

[0105] In this embodiment, the light Lin of the TM0 mode is incident on the mode converter 45. In this case, in the conversion section 51, the polarization wave mode of the light Lin is converted from the TM0 mode to the TE1 mode, and the light Lin of the TE1 mode is emitted from the emission end 51b to the branch section 52. Then, in the branch section 52, the light Lin of the TE1 mode is branched into the branch light LA ​​of the TE0 mode and the branch light LB of the TE0 mode, which have opposite phases to each other. Then, the branch light LA ​​is transmitted in the branch waveguide 52A, and the branch light LB is transmitted in the branch waveguide 52B. The light intensity of the branch light LA ​​and the light intensity of the branch light LB are substantially half of the light intensity of the light Lin.

[0106] For example, when the optical path length OL1 of the branch waveguide 52A and the optical path length OL2 of the branch waveguide 52B are the same, the phase difference Not from -π radians (initial phase difference ) The branched light LA ​​and the branched light LB are incident on the combining unit 53. In this case, the light Lout of the TE0 mode with opposite phases is emitted from the emission end 53c and the emission end 53d. The light intensity of the light Lout emitted from the emission end 53c and the light intensity of the light Lout emitted from the emission end 53d are substantially half of the light intensity of the light Lin.

[0107] On the other hand, in this embodiment, since the optical path length OL1 of the branch waveguide 52A and the optical path length OL2 of the branch waveguide 52B are different from each other, the phase difference is a value different from -π radians. For example, in the phase difference When the angle is -π / 2 radians, the branched light LA ​​and the branched light LB are combined in the combining unit 53, and the light Lout in the TE0 mode is emitted from the emission end 53c. The light intensity of the light Lout emitted from the emission end 53c is substantially the same as the light intensity of the light Lin.

[0108] When the light Lin in TE0 mode is incident on the mode converter 45, the polarization wave mode of the light Lin is not converted in the conversion section 51, and the light Lin in TE0 mode is emitted from the emission end 51b to the branch section 52. Then, in the branch section 52, the light Lin in TE0 mode is branched into branch light LA ​​in TE0 mode and branch light LB in TE0 mode, which have the same phase as each other. Then, the branch light LA ​​is transmitted in the branch waveguide 52A, and the branch light LB is transmitted in the branch waveguide 52B. The light intensity of the branch light LA ​​and the light intensity of the branch light LB are substantially half of the light intensity of the light Lin. At this time, since the optical path length OL1 of the branch waveguide 52A and the optical path length OL2 of the branch waveguide 52B are different from each other, the phase difference is the initial phase difference from 0 radians ) different values. For example, in the phase difference When the angle is π / 2 radians, the branched light LA ​​and the branched light LB are combined in the combining unit 53, and the light Lout of the TE0 mode is emitted from the emission end 53d. The light intensity of the light Lout emitted from the emission end 53d is substantially the same as the light intensity of the light Lin.

[0109] In the laser module 4 and the optical element 40 described above, since the width of the conversion section 51 increases continuously from the incident end 51a to the emission end 51b, the effective refractive index of the visible light transmitted in the conversion section 51 changes. As a result, in the conversion section 51, the polarization wave mode of the visible light can be converted from the TM0 mode to the TE1 mode. Furthermore, in the branching section 52, the visible light in the TE1 mode emitted from the conversion section 51 is branched into branch lights LA and LB in the TE0 mode with opposite phases to each other. Then, the branch light LA ​​is transmitted in the branch waveguide 52A, and the branch light LB is transmitted in the branch waveguide 52B. Then, in the combining section 53, the branch lights LA and the branch lights LB are combined to emit visible light in the TE0 mode.

[0110] Here, when the optical path length OL1 in the branch waveguide 52A and the optical path length OL2 in the branch waveguide 52B are the same, the phase difference Not from -π radians (initial phase difference ) The branched light LA ​​and the branched light LB are incident on the combining unit 53. Therefore, the intensity of the visible light obtained by combining the branched light LA ​​and the branched light LB is substantially half of the intensity of the visible light incident on the conversion unit 51, and the conversion efficiency is reduced. On the other hand, in the laser module 4 and the optical element 40, since the optical path length OL1 and the optical path length OL2 are different from each other, the phase difference is a value different from -π radians. This can suppress the decrease in the intensity of the visible light obtained by combining the branched light LA ​​and the branched light LB relative to the intensity of the visible light incident on the conversion unit 51. Based on the above, the optical element 40 can convert the polarization mode of the visible light from the TM0 mode to the TE0 mode while suppressing the decrease in conversion efficiency.

[0111] In phase difference When the phase difference is -π / 2+2nπ radians, the intensity of the visible light in the TE0 mode obtained by combining the branched light LA ​​and the branched light LB is substantially the same as the intensity of the visible light in the TM0 mode incident on the conversion unit 51. As the angle moves away from -π / 2+2nπ radians, the intensity of the visible light in the TE0 mode obtained by combining the branched light LA ​​and the branched light LB decreases. It is -2π / 3+2nπ radians to -π / 3+2nπ radians. Since this range is a range of ±π / 6 centered on -π / 2+2nπ radians, the loss of light intensity of the visible light in the TE0 mode obtained by combining the branched light LA ​​and the branched light LB can be further reduced. That is, the reduction in conversion efficiency from the TM0 mode to the TE0 mode can be further suppressed.

[0112] The mode converters 45, 46, and 47 are arranged on the plate 41 in the Z-axis direction. According to this structure, the waveguide formed by the conversion part 51 and the plate 41 has an asymmetric shape in the Z-axis direction. Therefore, the conversion efficiency of the conversion part 51 from the TM0 mode to the TE1 mode can be improved. Here, asymmetry in the Z-axis direction means that the two parts separated by the symmetry plane are not plane-symmetrical with respect to the symmetry plane orthogonal to the Z-axis direction passing through the center of the Z-axis direction of the part formed by the combination of the conversion part 51 and the plate 41. In addition, if the conversion efficiency of the conversion part 51 from the TM0 mode to the TE1 mode is improved, the length L1 required to obtain the desired conversion efficiency can be shortened. Therefore, the optical element 40 can be miniaturized.

[0113] The height T1 of the core layer CA is smaller than the wavelength of visible light. According to this structure, visible light easily leaks from the conversion part 51 to the flat plate 41. As a result, the effect of the flat plate 41 can be well exerted, and the conversion efficiency of the conversion part 51 from the TM0 mode to the TE1 mode can be improved. In addition, by improving the conversion efficiency of the conversion part 51 from the TM0 mode to the TE1 mode, the length L1 required to obtain the desired conversion efficiency can be shortened. Therefore, the optical element 40 can be miniaturized.

[0114] The multiplexing unit 53 is formed of a multi-mode interferometer. According to this configuration, the multiplexing unit 53 can be manufactured more simply than when the multiplexing unit 53 is manufactured by a Y-branch waveguide.

[0115] The width W3 of the combining section 53 is greater than or equal to 2.0 μm. The size of the width W3 affects the spacing between the branch waveguide 52A and the branch waveguide 52B. When manufacturing the mode converters 45, 46, and 47, for example, anisotropic etching such as dry etching is used. At this time, if the spacing between the branch waveguide 52A and the branch waveguide 52B cannot be ensured, it is possible that the side surfaces of each waveguide are excessively cut and the branch waveguide 52A and the branch waveguide 52B cannot be formed into the desired shape. In contrast, in the laser module 4 and the optical element 40, since the width W3 of the combining section 53 is greater than or equal to 2.0 μm, the spacing between the branch waveguide 52A and the branch waveguide 52B can be ensured without reducing the width W4 of the branch waveguides 52A and 52B. Therefore, the branch waveguide 52A and the branch waveguide 52B can be formed into the desired shape.

[0116] When width W4 is less than 23% of width W3, the tolerance of mode converters 45, 46, 47 becomes small due to manufacturing errors, etc. When width W4 is greater than 47% of width W3, the interval between branch waveguide 52A and branch waveguide 52B may not be sufficiently ensured.

[0117] Here, for the tolerance ΔL3 of the length L3 in the combining unit 53, the refractive index n of the constituent material of the core layer CA is used. r , the wavelength λ of the visible light to be converted by the mode converter including the multiplexing unit 53 0 and the Gaussian beam waist w of the polarization wave mode of visible light 0 , expressed by formula (3).

[0118] [Formula 3]

[0119]

[0120] Furthermore, the tolerance ΔW3 of the width W3 corresponding to the tolerance ΔL3 and the wavelength λ 0 The bandwidth Δλ 0 They are represented by equation (4) and equation (5) respectively.

[0121] [Formula 4]

[0122]

[0123] [Formula 5]

[0124]

[0125] For example, in the Gaussian beam waist w 0 is 1000nm, refractive index n r is 2.38, wavelength λ 0 In the case where the length L3 is 638 nm, the tolerance ΔL3 is 2930 nm. In this case, if the length L3 is 64.5 μm and the width W3 is 3.0 μm, the tolerance ΔW3 is 68 nm and the bandwidth Δλ is 0 The width W3 is the largest among the widths of all the components of the mode converter. Therefore, the deviation tolerance Δw of the width of the mode converters 45, 46, and 47 as a whole is device is equal to the tolerance ΔW3. Therefore, the bandwidth Δλ 0 The deviation tolerance Δw of the entire mode converter 45, 46, 47 is 29 nm. device It is 68nm.

[0126] Gaussian beam waist w 0Proportional to the width W4. For example, when the width W3 is 3.0 μm and the width W4 is 23% of the width W3, the width W4 is about 0.7 μm. In this case, the Gaussian beam waist w 0 is about 0.5 μm. Moreover, in this case, if the refractive index n r is 2.38, wavelength λ 0 is 638nm, and the length L3 is 64.5μm, and the width W3 is 3.0μm, then the deviation tolerance Δw device On the other hand, a distance of about 1.6 μm can be ensured as the distance between the branch waveguide 52A and the branch waveguide 52B.

[0127] Furthermore, for example, when the width W3 is 3.0 μm and the width W4 is 47% of the width W3, the width W4 is approximately 1.4 μm. In this case, the Gaussian beam waist w 0 is about 1.0 μm. Moreover, in this case, if the refractive index n r is 2.38, wavelength λ 0 is 638nm, and the length L3 is 64.5μm, and the width W3 is 3.0μm, then the deviation tolerance Δw device On the other hand, as the interval between the branch waveguide 52A and the branch waveguide 52B, a distance of about 0.2 μm can be ensured.

[0128] Here, when the width W4 is less than 23% of the width W3, the interval between the branch waveguide 52A and the branch waveguide 52B can be sufficiently ensured, but the deviation tolerance Δw device will become smaller. Within the deviation tolerance Δw device If the width W4 is smaller than 47% of the width W3, the tolerance of the mode converters 45, 46, and 47 becomes smaller relative to the manufacturing error, and the difficulty of manufacturing increases. On the other hand, when the width W4 is larger than 47% of the width W3, the deviation tolerance Δw can be increased. device , but the interval between the branch waveguide 52A and the branch waveguide 52B cannot be sufficiently ensured. In the case where the interval between the branch waveguide 52A and the branch waveguide 52B cannot be sufficiently ensured, as described above, the branch waveguide 52A and the branch waveguide 52B may not be formed into a desired shape. Therefore, by setting the width W4 to be greater than 23% and less than 47% of the width W3, both the tolerance of the mode converters 45, 46, and 47 relative to manufacturing errors and the interval between the branch waveguide 52A and the branch waveguide 52B can be ensured.

[0129] The combiner 48 is designed so that the combining efficiency when combining the red light Lr, green light Lg and blue light Lb in the TE0 mode is higher than the combining efficiency when combining the red light Lr, green light Lg and blue light Lb in the TM0 mode. In the laser module 4 and the optical element 40, the mode converter 45 converts the polarization mode of the red light Lr from the TM0 mode to the TE0 mode, the mode converter 46 converts the polarization mode of the green light Lg from the TM0 mode to the TE0 mode, and the mode converter 47 converts the polarization mode of the blue light Lb from the TM0 mode to the TE0 mode. Therefore, the combining efficiency of the combiner 48 can be improved.

[0130] The height of the mode converter 45, the height of the mode converter 46, and the height of the mode converter 47 are the same. According to this structure, the mode converter 45, the mode converter 46, and the mode converter 47 can be formed on the same substrate S, and since the heights of the respective mode converters can be made the same, the optical element 40 can be easily manufactured.

[0131] In order to output full-color laser light La by combining red light Lr, green light Lg, and blue light Lb, it is necessary to adjust the light intensity of each color of light according to the color of the output. In order to change the light intensity of the corresponding color of light in each laser light source, a large drive current is required. In the laser module 4 and the optical element 40, the light intensity of the red light Lr is modulated by the modulator 42, the light intensity of the green light Lg is modulated by the modulator 43, and the light intensity of the blue light Lb is modulated by the modulator 44. Therefore, full-color laser light La can be output without a large drive current.

[0132] The near-eye wearable device 1 includes a retinal projection device 10, and the retinal projection device 10 includes an optical element 40. Therefore, in the near-eye wearable device 1 and the retinal projection device 10, the polarization wave mode of visible light can be converted from the TM0 mode to the TE0 mode while suppressing the reduction in conversion efficiency, and on this basis, the image is projected onto the retina.

[0133] Reference Figure 7 A laser module according to another embodiment will be described. Figure 7 is a block diagram of a laser module according to another embodiment. Figure 7 The laser module 4A shown mainly differs from the laser module 4 in that the laser module 4A includes a mode converter 49 instead of the mode converters 45 , 46 and 47 , and a combiner 48 is arranged between each modulator and the mode converter 49 .

[0134] Specifically, the emission ends of modulator 42, modulator 43 and modulator 44 are optically connected to the three input ends of combiner 48. The emission end of combiner 48 is optically connected to the input end of mode converter 49. The structure of mode converter 49 is the same as that of mode converter 45.

[0135] In the laser module 4A, since visible light in the TM0 mode is emitted from each laser light source, the light intensity of the visible light in the TM0 mode is modulated in each modulator. Then, the visible light modulated in each modulator is combined in the combiner 48. Then, the polarization wave mode of the combined visible light is converted from the TM0 mode to the TE0 mode in the mode converter 49, and the laser light La in the TE0 mode is transmitted from the mode converter 49 to the optical component 5 (refer to FIG. 5 ). Figure 2 ) is ejected.

[0136] Next, refer to Figure 8 A laser module according to still another embodiment will be described. Figure 8 is a block diagram of a laser module according to still another embodiment. Figure 8 The laser module 4B shown is different from the laser module 4 mainly in the polarization modes of visible light emitted by the laser light sources 411 , 412 , 413 and in that the laser module 4B further includes a mode converter 45A, a mode converter 46A, and a mode converter 47A.

[0137] The laser light source 411 emits red light Lr in TE0 mode. The laser light source 412 emits green light Lg in TE0 mode. The laser light source 413 emits blue light Lb in TE0 mode.

[0138] The mode converter 45A is a mode converter that converts the polarization wave mode of the red light Lr from the TE0 mode to the TM0 mode. The mode converter 45A is provided between the laser light source 411 and the modulator 42. The red light Lr in the TE0 mode is incident from the laser light source 411 to the incident end of the mode converter 45A, and the emission end of the mode converter 45A is optically connected to the incident end of the modulator 42. The mode converter 45A converts the polarization wave mode of the red light Lr incident from the laser light source 411 from the TE0 mode to the TM0 mode, and emits the red light Lr in the TM0 mode to the modulator 42.

[0139] In the mode converter 45A, for example, a structure is adopted in which the incident end and the emission end of the mode converter 45 are reversed. In this structure, the red light Lr of the TE0 mode is incident from the laser light source 411 to the emission end 53c of the combiner 53, the incident end 53a of the combiner 53 emits the red light Lr of the TE0 mode to the branch waveguide 52A, and the incident end 53b of the combiner 53 emits the red light Lr of the TE0 mode to the branch waveguide 52B. The phase difference obtained by subtracting the phase of the red light Lr at the incident end 53a from the phase of the red light Lr at the incident end 53b is -π / 2 radians.

[0140] Then, a red light Lr is transmitted in the branch waveguide 52A and is incident on the emission end 51b of the conversion section 51. Another red light Lr is transmitted in the branch waveguide 52B and is incident on the emission end 51b of the conversion section 51. The optical path length difference ΔOL between the optical path length OL1 in the branch waveguide 52A and the optical path length OL2 in the branch waveguide 52B is -λ / 4+nλ. Therefore, the phase difference obtained by subtracting the phase of the above-mentioned one red light Lr at the emission end 51b from the phase of the above-mentioned other red light Lr at the emission end 51b is -π+2nπ radians. Therefore, at the emission end 51b, the red light Lr in the TE1 mode is coupled by two TE0 modes, and the red light Lr in the TE1 mode is transmitted from the emission end 51b toward the incident end 51a in the conversion section 51. At this time, in the conversion section 51, the polarization wave mode of the red light Lr is converted from the TE1 mode to the TM0 mode.

[0141] The mode converter 46A is a mode converter that converts the polarization wave mode of the green light Lg from the TE0 mode to the TM0 mode. The mode converter 46A is provided between the laser light source 412 and the modulator 43. The green light Lg in the TE0 mode is incident from the laser light source 412 to the incident end of the mode converter 46A, and the emission end of the mode converter 46A is optically connected to the incident end of the modulator 43. The mode converter 46A converts the polarization wave mode of the green light Lg incident from the laser light source 412 from the TE0 mode to the TM0 mode, and emits the green light Lg in the TM0 mode to the modulator 43.

[0142] The mode converter 46A also adopts a configuration in which the incident end and the output end of the mode converter 46 are reversed, for example. In this case, the mode converter 46A also converts the polarization mode of the green light Lg from the TE0 mode to the TM0 mode, similarly to the mode converter 45A.

[0143] The mode converter 47A is a mode converter that converts the polarization wave mode of the blue light Lb from the TE0 mode to the TM0 mode. The mode converter 47A is provided between the laser light source 413 and the modulator 44. The blue light Lb in the TE0 mode is incident from the laser light source 413 to the incident end of the mode converter 47A, and the emission end of the mode converter 47A is optically connected to the incident end of the modulator 44. The mode converter 47A converts the polarization wave mode of the blue light Lb incident from the laser light source 413 from the TE0 mode to the TM0 mode, and emits the blue light Lb in the TM0 mode to the modulator 44.

[0144] The mode converter 47A also adopts a configuration in which the incident end and the output end of the mode converter 47 are reversed, for example. In this case, the mode converter 47A also converts the polarization mode of the blue light Lb from the TE0 mode to the TM0 mode, similarly to the mode converter 45A.

[0145] In the laser module 4B, since each laser light source emits visible light in TE0 mode, the polarization wave mode of each visible light emitted from each laser light source is first converted from TE0 mode to TM0 mode in each mode converter 45A, 46A, 47A. Then, the light intensity of the visible light in TM0 mode is modulated in each modulator, and then the polarization wave mode of each modulated visible light is converted from TM0 mode to TE0 mode in each mode converter 45, 46, 47. Then, each visible light is combined in the combiner 48 and transmitted as laser light La in TE0 mode from the combiner 48 to the optical component 5 (refer to FIG. 5 ). Figure 2 ) is ejected.

[0146] Next, refer to Fig. 9 A laser module according to still another embodiment will be described. Fig. 9 Laser module 4C is different from laser module 4 mainly in that the orientation of the C-axis of lithium niobate constituting core layer CA and the positions of modulators 42, 43, 44 and mode converters 45, 46, 47 are reversed.

[0147] In this embodiment, the C-axis of lithium niobate extends in the Y-axis direction. The core layer CA is composed of X-cut lithium niobate.

[0148] The red light Lr in TM0 mode is incident from the laser light source 411 to the incident end of the mode converter 45, and the emission end of the mode converter 45 is optically connected to the incident end of the modulator 42. The mode converter 45 converts the polarization wave mode of the red light Lr incident from the laser light source 411 from TM0 mode to TE0 mode, and emits the red light Lr in TE0 mode to the modulator 42.

[0149] The green light Lg in TM0 mode is incident from the laser light source 412 to the incident end of the mode converter 46, and the emission end of the mode converter 46 is optically connected to the incident end of the modulator 43. The mode converter 46 converts the polarization wave mode of the green light Lg incident from the laser light source 412 from the TM0 mode to the TE0 mode, and emits the green light Lg in TE0 mode to the modulator 43.

[0150] The blue light Lb in TM0 mode is incident from the laser light source 413 to the incident end of the mode converter 47, and the emission end of the mode converter 47 is optically connected to the incident end of the modulator 44. The mode converter 47 converts the polarization wave mode of the blue light Lb incident from the laser light source 413 from the TM0 mode to the TE0 mode, and emits the blue light Lb in TE0 mode to the modulator 44.

[0151] The emission ends of modulator 42, modulator 43 and modulator 44 are optically connected to the three input ends of combiner 48. As described above, the C axis of lithium niobate extends in the Y axis direction. Therefore, the modulation efficiency of each modulator is improved in the TE mode.

[0152] In the laser module 4C, since each laser light source emits visible light in TM0 mode, the polarization wave mode of each visible light emitted from each laser light source is converted from TM0 mode to TE0 mode in each mode converter. Then, the light intensity of the visible light in TE0 mode is modulated in each modulator, and then the modulated visible light is combined in the combiner 48 and transmitted as laser light La in TE0 mode from the combiner 48 to the optical component 5 (refer to FIG. Figure 2 ) is ejected.

[0153] As mentioned above, although embodiment of this disclosure was described, this disclosure is not necessarily limited to the said embodiment, Various changes can be made within the range which does not deviate from the summary.

[0154] For example, the laser module 4 may also be applied to devices other than the near-eye wearable device 1 .

[0155] The optical element 40 may not include the cladding CB. In this case, the air layer can function as the upper cladding.

[0156] The optical element 40 only needs to include one mode converter. In other words, the core layer CA only needs to include one mode converter that converts the polarization mode of visible light from the TM0 mode to the TE0 mode.

[0157] The core layer CA may not include the flat plate 41 . In this case, the mode converters 45 , 46 , and 47 may be directly provided on the main surface Sa of the substrate S.

[0158] The width of the conversion portion 51 only needs to increase continuously. The increasing rate of the width of the conversion portion 51 does not need to be constant.

[0159] To adjust the phase difference The structure is not limited to the above structure. For example, the phase difference may be adjusted by the difference in physical length between the branch waveguide 52A having a constant width over the entire length and the branch waveguide 52B having the same width as the branch waveguide 52A over the entire length. For example, the physical length can be changed by providing a bend in one of the branch waveguide 52A and the branch waveguide 52B. Alternatively, the phase difference can be adjusted by changing both the waveguide width and the physical length of the waveguide between the branch waveguide 52A and the branch waveguide 52B. It is also possible to adopt a structure in which the width of the waveguide 523 increases continuously from the end 523a to the end 523b and the width of the waveguide 525 decreases continuously from the end 525a to the end 525b. Moreover, the widths of the waveguides 521 and 522 may not be constant. For example, it is possible to adopt a structure in which the width of the waveguide 521 increases continuously from the end 521a to the end 521b, or it is possible to adopt a structure in which the width of the waveguide 521 decreases continuously from the end 521a to the end 521b. It is possible to adopt a structure in which the width of the waveguide 522 increases continuously from the end 522a to the end 522b, or it is possible to adopt a structure in which the width of the waveguide 522 decreases continuously from the end 522a to the end 522b.

[0160] Another example of the specific structure of each waveguide of the branch portion 52 is described below. In this other example, the width of the waveguide 521 may be continuously increased from the end 521a to the end 521b. Alternatively, the width of the waveguide 521 may be increased from 50% of the width W2 to the width W4, for example, as it moves from the end 521a toward the end 521b. Alternatively, the width of the waveguide 522 may be substantially constant at the width W4 between the end 522a and the end 522b. Alternatively, the width of the waveguide 523 may be continuously increased from the width W5 to the width W6, for example, as it moves from the end 523a toward the end 523b. In this case, the width W5 may also be 50% of the width W2. Alternatively, the width of the waveguide 524 may be substantially constant at the width W6 between the end 524a and the end 524b. In this other example as well, the same structure as that in the above-mentioned embodiment may be adopted in the waveguide 525 and the waveguide 526.

[0161] Alternatively, in another example, in addition to the structure of the above-mentioned other example, a structure in which the width of the waveguide 525 decreases continuously from the end 525a to the end 525b may be adopted. In this case, the width of the waveguide 525 may decrease from the width W6 to the width W4 as it moves from the end 525a toward the end 525b. That is, the width W6 may be larger than the width W4.

[0162] The combining unit 53 may be formed of a Y-branch waveguide or a directional coupler instead of the multi-mode interferometer.

[0163] Example

[0164] 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.

[0165] <Evaluation of the relationship between length PL2 and conversion efficiency>

[0166] In the mode converters having the structures of Examples 1 to 3, the relationship between the length PL2 and the conversion efficiency was evaluated. As the mode converters of Examples 1 to 3, the following mode converters were used: In addition to adopting a structure in which the width of the waveguide 521 increases from the end 521a toward the end 521b and a structure in which the width of the waveguide 523 increases from the end 523a toward the end 523b, the mode converter has the same structure as Figures 4 to 6 The structure is the same as the structure shown in the embodiment 1 to the embodiment 3. Moreover, in the mode converter of the embodiment 1 to the embodiment 3, the width W5 is set to 50% of the width W2, and the width of the waveguide 521 at the end 521a is set to be substantially the same as the width W5. In the embodiment 1 to the embodiment 3, while changing the length L24 of the waveguide 525 in the X-axis direction, the conversion efficiency when each polarization wave mode of the red light, the green light, and the blue light of each length L24 is converted from the TM0 mode to the TE0 mode is calculated. In the embodiment 1 to the embodiment 3, the length L22 of the waveguide 522 in the X-axis direction is also changed by the same amount as the length L24. That is, in the embodiment 1 to the embodiment 3, the conversion efficiency of each length L24 is calculated in the state where the physical length of the branch waveguide 52A and the physical length of the branch waveguide 52B are the same. Here, since the length PL2 is the physical length of the branch waveguide 52B along the optical path of the branch light LB, the length PL2 is changed by changing the length L24. Therefore, the conversion efficiency calculated while changing the length L24 can also be referred to as the conversion efficiency calculated while changing the length PL2.

[0167] In Examples 1 to 3, height T1, height T11, length L1, length L21, length L22, length L23, length L25, length L3, width W1, width W2, width W3, width W4, width W5 and width W6 are set for the wavelength of each color as shown in Table 1.

[0168] [Table 1]

[0169] Example 1 Example 2 Example 3 color R G B Wavelength [nm] 638 520 455 T1[μm] 0.30 0.30 0.30 T11[μm] 0.10 0.10 0.10 L1[μm] 225 212 570 L21[μm] 31.0 32.0 34.0 L23[μm] 10.0 10.0 10.0 L25[μm] 10.0 10.0 10.0 L3[μm] 64.5 81.0 95.0 W1[μm] 0.65 0.52 0.43 W2[μm] 0.75 0.62 0.53 W3[μm] 3.00 3.00 3.00 W4[μm] 1.00 1.00 1.00 W5[μm] 0.375 0.31 0.265 W6[μm] 0.80 0.80 0.80

[0170] exist Fig.10 (a) shows the calculation results for red light. Fig.10 (b) shows the calculation result of green light. Fig.10 (c) shows the calculation result of blue light. Fig.10 (a) Fig.10 (b) Fig.10 The vertical axis of (c) represents the conversion efficiency normalized by the ideal value (100%) of the conversion efficiency, and the unit is an arbitrary unit. Fig.10 (a) Fig.10 (b) and Fig.10 The horizontal axis of (c) represents the length L24 [μm].

[0171] according to Fig.10 (a) Fig.10 (b) and Fig.10 As can be seen from (c), in red light, green light, and blue light, the conversion efficiency changes periodically with respect to the length L24 (length PL2). This is because when the length L22 and the length L24 are increased by the same amount, the effective refractive index n of the waveguide 522 is effA and the effective refractive index n of the waveguide 525 effB Therefore, it can be seen that when the optical path length difference ΔOL is in the range of -λ / 3+nλ to -λ / 6+nλ, in other words, when the phase difference In the range of -2π / 3+2nπ radians to -π / 3+2nπ radians, a high conversion efficiency of 86.6% or more was obtained.

[0172] <Evaluation of Conversion Loss Due to the Presence of Flat Plate 41 and Evaluation of Length L1 of Conversion Section 51>

[0173] In the conversion section 51 having the structure of Examples 4 to 9, the influence of the presence or absence of the plate 41 on the conversion loss of TM0-TE1 conversion and the length L1 of the conversion section 51 was evaluated. Figure 4 and Figure 5 As the optical elements of Examples 7 to 9, a conversion unit 51 having the same structure as that of the embodiment 1 is used except that the core layer CA does not include the flat plate 41. Figure 4 and Figure 5 The structure shown is the same as the conversion part 51.

[0174] In Examples 4 to 9, the height T1, height T11, length L1, width W1, and width W2 are set for the wavelength of each color as shown in Table 2. The height T11 of 0 μm indicates the case where the core layer CA does not include the flat plate 41. In Examples 4 to 9, in the conversion unit 51 in which the parameters shown in Table 2 are set, the conversion loss when the polarization wave mode of each of the red light, the green light, and the blue light is converted from the TM0 mode to the TE1 mode is calculated. The calculation results of the conversion loss are shown in Table 2.

[0175] [Table 2]

[0176] Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 color R G B R G B Wavelength [nm] 638 520 455 638 520 455 T1[μm] 0.30 0.30 0.30 0.30 0.30 0.30 T11[μm] 0.10 0.10 0.10 0.00 0.00 0.00 L1[μm] 1000 1000 1000 1000 1000 1000 W1[μm] 0.65 0.50 0.40 0.65 0.50 0.40 W2[μm] 0.85 0.70 0.60 0.85 0.70 0.60 Conversion loss [dB] 0.01 0.00 0.15 5.76 7.69 9.63

[0177] Then, in the conversion section 51 set to the height T1, height T11, width W1, and width W2 shown in Table 2, the conversion loss was calculated while changing the length L1. The calculation results for red light are Fig.11 The calculation result of green light is shown in (a). Fig.11 (b) shows that the calculation results of blue light are Fig.11 As shown in (c). Fig.11 (a) Fig.11 (b) and Fig.11 The vertical axis of (c) represents conversion loss [dB]. Fig.11 (a) Fig.11 (b) and Fig.11 The horizontal axis of (c) represents the length L1 [μm].

[0178] exist Fig.11 In (a), curve E4 shows the relationship between the length L1 of the conversion portion 51 and the conversion loss when the height T1, height T11, width W1, and width W2 in Example 4 are set. Fig.11 In (a), a curve E7 shows the relationship between the length L1 of the conversion portion 51 and the conversion loss when the height T1, the height T11, the width W1, and the width W2 in the seventh embodiment are set.

[0179] exist Fig.11 In (b), curve E5 shows the relationship between the length L1 of the conversion portion 51 and the conversion loss when the height T1, height T11, width W1, and width W2 in Example 5 are set. Fig.11In (b), a curve E8 shows the relationship between the length L1 of the conversion portion 51 and the conversion loss when the height T1, the height T11, the width W1, and the width W2 in the eighth embodiment are set.

[0180] exist Fig.11 In (c), curve E6 shows the relationship between the length L1 of the conversion portion 51 and the conversion loss when the height T1, height T11, width W1, and width W2 in Example 6 are set. Fig.11 In (c), a curve E9 shows the relationship between the length L1 of the conversion portion 51 and the conversion loss when the height T1, the height T11, the width W1, and the width W2 in the ninth embodiment are set.

[0181] According to Table 2, in Examples 4 to 6, the conversion loss is suppressed compared to the corresponding examples in Examples 7 to 9. Therefore, it is found that the inclusion of the slab 41 in the core layer CA suppresses the reduction in conversion efficiency in red light, green light, and blue light.

[0182] Moreover, according to Fig.11 (a) Fig.11 (b) and Fig.11 (c), in order to achieve the same conversion loss, compared with the corresponding embodiments in Examples 7 to 9, Examples 4 to 6 can reduce the length L1. Therefore, it can be seen that by including the flat plate 41 in the core layer CA, the length L1 for achieving a predetermined conversion loss can be reduced, thereby reducing the length of the mode converters 45, 46, and 47 in the X-axis direction.

[0183] <Evaluation of Conversion Loss at Height T1 of Core Layer CA and Evaluation of Length L1 of Conversion Portion 51>

[0184] The influence of the height T1 in red light on the conversion loss and the length L1 was evaluated using the mode converters having the structures of Examples 10 to 13. As the mode converter of Example 10, the following mode converter was used: in addition to adopting a structure in which the width of the waveguide 521 increases from the end 521a toward the end 521b and a structure in which the width of the waveguide 523 increases from the end 523a toward the end 523b, the mode converter has the same structure as Figures 4 to 6 As the mode converters of Examples 11 to 13, the following mode converters are used: the mode converter has the same structure as that of Example 10 except that the width of the waveguide 525 decreases from the width W6 to the width W4 as it moves from the end 525a toward the end 525b. In addition, in the mode converters of Examples 10 to 13, the width W5 is set to 50% of the width W2, and the width at the end 521a is set to be substantially the same as the width W5.

[0185] In Examples 10 to 13, height T1, height T11, length L21, length L22, length L23, length L24, length L25, length L3, width W1, width W2, width W3, width W4, width W5, and width W6 are set for red light as shown in Table 3. In addition, the wavelength of red light is 638 nm. In Examples 10 to 13, in the optical element in which the parameters shown in Table 3 are set, the conversion loss when the polarization wave mode of red light is converted from TM0 mode to TE0 mode is calculated. The length L1 with the minimum conversion loss and the calculation results of the minimum conversion loss are shown in Table 3.

[0186] [Table 3]

[0187] Example 10 Embodiment 11 Example 12 Embodiment 13 T1[μm] 0.30 0.45 0.80 0.90 T11[μm] 0.10 0.15 0.20 0.20 L21[μm] 31.0 39.0 28.0 23.0 L22[μm] 37.0 48.0 80.0 80.0 L23[μm] 10.0 10.0 10.0 10.0 L24[μm] 17.0 28.0 60.0 60.0 L25[μm] 10.0 10.0 10.0 1.0.0 L3[μm] 64.5 90.0 90.0 90.0 W1[μm] 0.65 0.70 0.80 0.80 W2[μm] 0.75 0.80 0.90 0.90 W3[μm] 3.00 2.00 2.00 2.00 W4[μm] 1.00 0.50 0.50 0.50 W5[μm] 0.375 0.40 0.45 0.45 W6[μm] 0.80 0.60 0.60 0.60 Conversion loss [dB] 0.31 0.57 3.71 4.00 L1[μm] 225 370 4700 12400

[0188] Moreover, among the parameters shown in Table 3, the relationship between the height T1 and the conversion loss and the relationship between the height T1 and the length L1 are Fig.12 is shown in (a). Fig.12 The left vertical axis of (a) represents conversion loss [dB], Fig.12 The right vertical axis of (a) represents the length L1 [μm], Fig.12 The horizontal axis of (a) represents the height T1 [μm].

[0189] Curve E10a shows the relationship between the height T1 and the conversion loss of Example 10. Curve E10b shows the relationship between the height T1 and the length L1 of Example 10. Curve E11a shows the relationship between the height T1 and the conversion loss of Example 11. Curve E11b shows the relationship between the height T1 and the length L1 of Example 11. Curve E12a shows the relationship between the height T1 and the conversion loss of Example 12. Curve E12b shows the relationship between the height T1 and the length L1 of Example 12. Curve E13a shows the relationship between the height T1 and the conversion loss of Example 13. Curve E13b shows the relationship between the height T1 and the length L1 of Example 13.

[0190] Hereinafter, when the conversion loss is smaller than 1.00 dB, it is assumed that high conversion efficiency is achieved, and when the length L1 is smaller than 1000 μm, it is assumed that the length L1 is suppressed.

[0191] According to Table 3 and Fig.12 (a), the conversion loss of Examples 10 and 11, where the height T1 is smaller than the wavelength of red light (638 nm), is 0.31 dB to 0.57 dB. On the other hand, the conversion loss of Examples 12 and 13, where the height T1 is greater than the wavelength of red light, is 3.71 dB to 4.00 dB. Therefore, it can be seen that in red light, high conversion efficiency is achieved when the height T1 is smaller than the wavelength of red light.

[0192] Furthermore, the length L1 of Example 10 and Example 11, in which the height T1 is smaller than the wavelength of red light, is 225 μm to 370 μm. On the other hand, the length L1 of Example 12 and Example 13, in which the height T1 is greater than the wavelength of red light, is 4700 μm to 12400 μm. Therefore, it can be seen that in red light, when the height T1 is smaller than the wavelength of red light, the length L1 can be reduced, thereby reducing the length of the mode converter 45 in the X-axis direction.

[0193] The influence of the height T1 in green light on the conversion loss and the length L1 was evaluated using the mode converters having the structures of Examples 14 to 17. As the mode converter of Example 14, the following mode converter was used: in addition to adopting a structure in which the width of the waveguide 521 increases from the end 521a toward the end 521b and a structure in which the width of the waveguide 523 increases from the end 523a toward the end 523b, the mode converter has the same structure as that of Example 14. Figures 4 to 6 As the mode converters of Examples 15 to 17, the following mode converters are used: the mode converter has the same structure as that of Example 14 except that the width of the waveguide 525 decreases from the end 525a toward the end 525b. In addition, in the mode converters of Examples 14 to 17, the width W5 is set to 50% of the width W2, and the width at the end 521a is set to be substantially the same as the width W5.

[0194] In Examples 14 to 17, height T1, height T11, length L21, length L22, length L23, length L24, length L25, length L3, width W1, width W2, width W3, width W4, width W5, and width W6 are set for green light as shown in Table 4. In addition, the wavelength of green light is 520 nm. In Examples 14 to 17, in the optical element in which the parameters shown in Table 4 are set, the conversion loss when the polarization mode of green light is converted from TM0 mode to TE0 mode is calculated. The length L1 with the minimum conversion loss and the calculation results of the minimum conversion loss are shown in Table 4.

[0195] [Table 4]

[0196] Embodiment 14 Embodiment 15 Example 16 Embodiment 17 T1[μm] 0.30 0.45 0.80 0.90 T11[μm] 0.10 0.15 0.20 0.20 L21[μm] 32.0 50.0 43.0 35.0 L22[μm] 36.0 28.0 80.0 80.0 L23[μm] 10.0 10.0 10.0 10.0 L24[μm] 16.0 8.0 60.0 60.0 L25[μm] 10.0 10.0 10.0 10.0 L3[μm] 81.0 112.0 112.0 112.0 W1[μm] 0.52 0.52 0.60 0.60 W2[μm] 0.62 0.62 0.80 0.80 W3[μm] 3.00 2.00 2.00 2.00 W4[μm] 1.00 0.50 0.50 0.50 W5[μm] 0.31 0.31 0.40 0.40 W6[μm] 0.80 0.60 0.60 0.60 Conversion loss [dB] 0.38 0.97 3.66 5.13 L1[μm] 212 614 2500 24100

[0197] Furthermore, the relationship between the height T1 and the conversion loss and the relationship between the height T1 and the length L1 in the various parameters shown in Table 4 are Fig.12 is shown in (b). Fig.12 The left vertical axis of (b) represents conversion loss [dB], Fig.12 The right vertical axis of (b) represents the length L1 [μm], Fig.12 The horizontal axis of (b) represents the height T1 [μm].

[0198] Curve E14a shows the relationship between the height T1 and the conversion loss of Example 14. Curve E14b shows the relationship between the height T1 and the length L1 of Example 14. Curve E15a shows the relationship between the height T1 and the conversion loss of Example 15. Curve E15b shows the relationship between the height T1 and the length L1 of Example 15. Curve E16a shows the relationship between the height T1 and the conversion loss of Example 16. Curve E16b shows the relationship between the height T1 and the length L1 of Example 16. Curve E17a shows the relationship between the height T1 and the conversion loss of Example 17. Curve E17b shows the relationship between the height T1 and the length L1 of Example 17.

[0199] According to Table 4 and Fig.12 (b) shows that the conversion loss of Examples 14 and 15, in which the height T1 is smaller than the wavelength of green light (520 nm), is 0.38 dB to 0.97 dB. On the other hand, the conversion loss of Examples 16 and 17, in which the height T1 is greater than the wavelength of green light, is 3.66 dB to 5.13 dB. Therefore, it can be seen that high conversion efficiency is achieved in green light when the height T1 is smaller than the wavelength of green light.

[0200] Furthermore, the length L1 of Example 14 and Example 15, in which the height T1 is smaller than the wavelength of green light, is 212 μm to 614 μm. On the other hand, the length L1 of Example 16 and Example 17, in which the height T1 is greater than the wavelength of green light, is 2500 μm to 24100 μm. Therefore, it can be seen that in green light, when the height T1 is smaller than the wavelength of green light, the length L1 can be reduced, thereby reducing the length of the mode converter 46 in the X-axis direction.

[0201] The influence of the height T1 in blue light on the conversion loss and the length L1 was evaluated using the mode converters having the structures of Examples 18 to 23. As the mode converter of Example 18, the following mode converter was used: in addition to adopting a structure in which the width of the waveguide 521 increases from the end 521a toward the end 521b and a structure in which the width of the waveguide 523 increases from the end 523a toward the end 523b, the mode converter has the same structure as Figures 4 to 6 As the mode converters of Examples 19 to 23, the following mode converters are used: the mode converter has the same structure as that of Example 18 except that the width of the waveguide 525 decreases from the end 525a toward the end 525b. In addition, in the mode converters of Examples 18 to 23, the width W5 is set to 50% of the width W2, and the width at the end 521a is set to be substantially the same as the width W5.

[0202] In Examples 18 to 23, height T1, height T11, length L21, length L22, length L23, length L24, length L25, length L3, width W1, width W2, width W3, width W4, width W5, and width W6 are set for blue light as shown in Table 5. In addition, in Examples 18 to 23, the wavelength of blue light is 455 nm. In Examples 18 to 23, in the optical element in which the parameters shown in Table 5 are set, the conversion loss when the polarization wave mode of blue light is converted from TM0 mode to TE0 mode is calculated. The length L1 with the minimum conversion loss and the calculation results of the minimum conversion loss are shown in Table 5.

[0203] [Table 5]

[0204] Embodiment 18 Embodiment 19 Embodiment 20 Embodiment 21 Embodiment 22 Embodiment 23 T1[μm] 0.30 0.45 0.60 0.70 0.80 0.90 T11[μm] 0.10 0.15 0.15 0.15 0.15 0.15 L21[μm] 34.0 37.0 32.0 32.0 32.0 49.0 L22[μm] 30.0 51.0 56.0 54.0 51.0 59.0 L23[μm] 10.0 10.0 10.0 10.0 10.0 10.0 L24[μm] 10.0 31.0 36.0 34.0 31.0 39.0 L25[μm] 10.0 10.0 10.0 10.0 10.0 10.0 L3[μm] 95.0 130.0 129.0 128.0 128.0 128.0 W1[μm] 0.43 0.40 0.50 0.50 0.50 0.50 W2[μm] 0.53 0.50 0.60 0.60 0.60 0.60 W3[μm] 3.00 2.00 2.00 2.00 2.00 2.00 W4[μm] 1.00 0.50 0.50 0.50 0.50 0.50 W5[μm] 0.265 0.25 0.30 0.30 0.30 0.30 W6[μm] 0.80 0.60 0.60 0.60 0.60 0.60 Conversion loss [dB] 0.31 0.89 3.37 4.26 4.94 5.16 L1[μm] 570 300 1800 2400 2650 14700

[0205] Furthermore, the relationship between the height T1 and the conversion loss and the relationship between the height T1 and the length L1 in the various parameters shown in Table 5 are Fig.12 As shown in (c). Fig.12 The left vertical axis of (c) represents conversion loss [dB], Fig.12 The right vertical axis of (c) represents the length L1 [μm], Fig.12 The horizontal axis of (c) represents the height T1 [μm].

[0206] Curve E18a represents the relationship between the height T1 and the conversion loss of Example 18. Curve E18b represents the relationship between the height T1 and the length L1 of Example 18. Curve E19a represents the relationship between the height T1 and the conversion loss of Example 19. Curve E19b represents the relationship between the height T1 and the length L1 of Example 19. Curve E20a represents the relationship between the height T1 and the conversion loss of Example 20. Curve E20b represents the relationship between the height T1 and the length L1 of Example 20. Curve E21a represents the relationship between the height T1 and the conversion loss of Example 21. Curve E21b represents the relationship between the height T1 and the length L1 of Example 21. Curve E22a represents the relationship between the height T1 and the conversion loss of Example 22. Curve E22b represents the relationship between the height T1 and the length L1 of Example 22. Curve E23a represents the relationship between the height T1 and the conversion loss of Example 23. Curve E23b represents the relationship between the height T1 and the length L1 of Example 23.

[0207] According to Table 5 and Fig.12(c) shows that the conversion loss of Examples 18 and 19, in which the height T1 is smaller than the wavelength of blue light (455 nm), is 0.31 dB to 0.89 dB. On the other hand, the conversion loss of Examples 20 to 23, in which the height T1 is greater than the wavelength of blue light, is 3.37 dB to 5.16 dB. Therefore, it can be seen that high conversion efficiency is achieved in the case of blue light when the height T1 is smaller than the wavelength of blue light.

[0208] Furthermore, the length L1 of Examples 18 and 19, in which the height T1 is smaller than the wavelength of blue light, is 300 μm to 570 μm. On the other hand, the length L1 of Examples 20 to 23, in which the height T1 is greater than the wavelength of blue light, is 1800 μm to 14700 μm. Therefore, it can be seen that in blue light, when the height T1 is smaller than the wavelength of blue light, the length L1 can be reduced, thereby reducing the length of the mode converter 47 in the X-axis direction.

[0209] In addition, in Examples 10 to 23, although parameters other than the height T1 also change, the parameters other than the height T1 shown in Tables 3, 4 and 5 are set to values ​​that minimize the conversion loss by making the optical path length difference ΔOL -λ / 4+nλ when the color of the visible light and the height T1 are changed. It is believed that the changes in parameters other than the height T1 have an effect on the conversion efficiency that is small enough to be ignored.

[0210] (Note)

[0211] [Project 1]

[0212] An optical element, wherein

[0213] The optical component has:

[0214] a substrate having a main surface; and

[0215] The core layer is disposed on the main surface and is composed of a material having an electro-optical effect.

[0216] The core layer includes a mode converter extending in a first direction along the main surface and converting a polarization mode of visible light from a TM0 mode to a TE0 mode.

[0217] The mode converter comprises:

[0218] A conversion unit, which converts the polarization wave mode of the visible light from the TM0 mode to the TE1 mode;

[0219] a branching unit that branches the visible light in the TE1 mode into a first branched light in the TE0 mode and a second branched light in the TE0 mode, and adjusts a phase difference between the first branched light and the second branched light; and

[0220] a combining unit that combines the first branched light and the second branched light,

[0221] The conversion portion includes a first end for the visible light in the TM0 mode to be incident and a second end for emitting the visible light in the TE1 mode, wherein the first end and the second end are both ends of the conversion portion in the first direction.

[0222] The length of the conversion portion in the second direction increases continuously from the first end to the second end, and the second direction is along the main surface and intersects the first direction.

[0223] The phase difference is a phase difference obtained by subtracting a phase of the first branched light when incident on the combining unit from a phase of the second branched light when incident on the combining unit.

[0224] The branching portion includes a first branch waveguide for transmitting the first branched light and a second branch waveguide for transmitting the second branched light.

[0225] An optical path length of the first branched light in the first branch waveguide and an optical path length of the second branched light in the second branch waveguide are different from each other.

[0226] [Project 2]

[0227] The optical element according to item 1, wherein:

[0228] The phase difference is greater than -2π / 3+2nπ radians and less than -π / 3+2nπ radians,

[0229] Said n is an integer.

[0230] [Item 3]

[0231] The optical element according to item 1 or 2, wherein:

[0232] The core layer further comprises a flat plate provided on the main surface,

[0233] The mode converter is provided on the plate in a third direction intersecting the first direction and the second direction.

[0234] [Item 4]

[0235] The optical element according to item 3, wherein:

[0236] The length of the core layer in the third direction is smaller than the wavelength of the visible light.

[0237] [Item 5]

[0238] The optical element according to any one of items 1 to 4, wherein

[0239] The combining unit is composed of a multi-mode interferometer.

[0240] [Item 6]

[0241] The optical element according to item 5, wherein:

[0242] The length of the multiplexing unit in the second direction is 2.0 μm or more.

[0243] [Item 7]

[0244] The optical element according to item 5 or 6, wherein:

[0245] The length of the first branch waveguide in the second direction at the connection end of the first branch waveguide connected to the coupling unit is not less than 23% and not more than 47% of the length of the coupling unit in the second direction.

[0246] A length of the second branch waveguide in the second direction at a connection end of the second branch waveguide connected to the coupling unit is not less than 23% and not more than 47% of a length of the coupling unit in the second direction.

[0247] [Item 8]

[0248] The optical element according to any one of items 1 to 7, wherein

[0249] The core layer has:

[0250] 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;

[0251] 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;

[0252] 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

[0253] A combiner combines the red light, the green light, and the blue light to emit laser light.

[0254] [Item 9]

[0255] The optical element according to item 8, wherein:

[0256] A length of the first mode converter in a third direction intersecting the first direction and the second direction, a length of the second mode converter in the third direction, and a length of the third mode converter in the third direction are the same.

[0257] [Item 10]

[0258] The optical element according to item 8 or 9, wherein:

[0259] The core layer also has:

[0260] a first modulator, which modulates the intensity of the red light;

[0261] a second modulator for modulating the intensity of the green light; and

[0262] The third modulator modulates the intensity of the blue light.

[0263] [Item 11]

[0264] A laser module, wherein:

[0265] The laser module has:

[0266] The optical element according to any one of items 8 to 10;

[0267] a first laser light source emitting the red light in the TM0 mode;

[0268] a second laser light source that emits the green light in the TM0 mode; and

[0269] The third laser light source emits the blue light in the TM0 mode.

[0270] [Item 12]

[0271] A retinal projection device is mounted on a near-eye wearable device, wherein:

[0272] The retinal projection device has:

[0273] The laser module as described in item 11;

[0274] a movable reflecting mirror for scanning using the laser light emitted from the laser module; and

[0275] A reflector projects an image onto the retina by reflecting the laser light after passing through the movable reflector and guiding the reflected light toward the retina of a user wearing the near-eye wearable device.

[0276] [Item 13]

[0277] A near-eye wearable device, wherein:

[0278] The near-eye wearable device has:

[0279] The retinal projection device of item 12; and

[0280] A lens is provided with the reflector.

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 from a TM0 mode to a TE0 mode. The mode converter comprises: A conversion unit, which converts the polarization wave mode of the visible light from the TM0 mode to the TE1 mode; a branching unit that branches the visible light in the TE1 mode into a first branched light in the TE0 mode and a second branched light in the TE0 mode, and adjusts a phase difference between the first branched light and the second branched light; as well as a combining unit that combines the first branched light and the second branched light, The conversion portion includes a first end for the visible light in the TM0 mode to be incident and a second end for emitting the visible light in the TE1 mode, wherein the first end and the second end are both ends of the conversion portion in the first direction. The length of the conversion portion in the second direction increases continuously from the first end to the second end, and the second direction is along the main surface and intersects the first direction. The phase difference is a phase difference obtained by subtracting a phase of the first branched light when incident on the combining unit from a phase of the second branched light when incident on the combining unit. The branching portion includes a first branch waveguide for transmitting the first branched light and a second branch waveguide for transmitting the second branched light. An optical path length of the first branched light in the first branch waveguide and an optical path length of the second branched light in the second branch waveguide are different from each other.

2. The optical element according to claim 1, wherein The phase difference is greater than -2π / 3+2nπ radians and less than -π / 3+2nπ radians, Said n is an integer.

3. The optical element according to claim 1 or 2, wherein: The core layer further comprises a flat plate provided on the main surface, The mode converter is provided on the plate in a third direction intersecting the first direction and the second direction.

4. The optical element according to claim 3, wherein: The length of the core layer in the third direction is smaller than the wavelength of the visible light.

5. The optical element according to any one of claims 1 to 4, wherein The combining unit is composed of a multi-mode interferometer.

6. The optical element according to claim 5, wherein: The length of the multiplexing unit in the second direction is 2.0 μm or more.

7. The optical element according to claim 5 or 6, wherein: The length of the first branch waveguide in the second direction at the connection end of the first branch waveguide connected to the coupling unit is not less than 23% and not more than 47% of the length of the coupling unit in the second direction. A length of the second branch waveguide in the second direction at a connection end of the second branch waveguide connected to the coupling unit is not less than 23% and not more than 47% of a length of the coupling unit in the second direction.

8. The optical element according to any one of claims 1 to 7, wherein The core layer has: a first mode converter, which is the mode converter that converts the polarization 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 that converts the polarization wave mode of 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.

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

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

11. A laser module, wherein: The laser module has: The optical element according to any one of claims 8 to 10; a first laser light source emitting the red light in the TM0 mode; a second laser light source that emits the green light in the TM0 mode; and The third laser light source emits the blue light in the TM0 mode.

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

13. A near-eye wearable device, wherein: The near-eye wearable device has: The retinal projection device of claim 12; and A lens is provided with the reflector.

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