Composite light generation device and image display device

Abstract

Provided is a composite light generation device in which the shape of the composite light generation device can be a width size that is allowed to be at a certain degree while minimizing the length and height as much as possible in a composite light generation device including a light detector. A combined light generation device (200) is provided with: a plurality of light sources (1, 2, 3) that output light having different wavelengths; an optical multiplexer circuit (100) including optical waveguides (4, 5, 6) for propagating light output from the plurality of light sources (1, 2, 3), an optical multiplexer (7), and an optical waveguide (8) for outputting multiplexed light (9) obtained by the optical multiplexer (7); the combined light generation device (200) is characterized in that the light multiplexing circuit (100) has reflection grooves (11, 12) that reflect, in one side direction, leakage light that does not propagate through each of the optical waveguides (4, 5, 6) among light outputted from the plurality of light sources (1, 2, 3), and reflect, in the other side direction, leakage light that does not propagate through each of the optical waveguides (4, 5, 6) among the light outputted from the plurality of light sources (1, 2, 3). The combined light generation device (200) is provided with a light detector (10) for detecting reflected leakage light in one side surface direction.

Description

Synthetic light generation device and image display device Technical Field

[0001] This invention relates to a composite light generation apparatus for an image display device. The composite light generation apparatus includes: multiple light sources that output light of different wavelengths; a light combining circuit including individual optical waveguides receiving light output from the multiple light sources, an optical combiner, and an optical waveguide outputting multiplexed light obtained through the optical combiner; and a photodetector. Background Technology

[0002] In recent years, it has been known that in composite light generation devices used as light sources, multiple laser beams are employed as light combiners (see Patent Document 1) in the light source portion of image display devices such as eyeglass terminals and portable projectors. The light combiner is manufactured through the following steps: after forming silicon oxide films of low and high refractive indices on a silicon substrate using known chemical vapor deposition (CVD), sputtering, or other methods, a pattern is formed using photolithography with a photomask, and then a low-refractive-index silicon oxide film is formed and used as an outer cladding layer.

[0003] It is known that laser diodes that generate laser light can change or deteriorate depending on the operating environment, such as temperature, humidity, static electricity, and power supply noise. To address this deterioration, an optical communication module is known in which a photodetector is provided on the back side of the laser diode, opposite to the emitted light side, to detect light emitted to the back side and stabilize the output of the laser diode through feedback control (see Patent Document 2). A composite light generation device is also known in which a photodetector is provided above or below the optical waveguide in an optical combiner or similar device on which emitted light from the laser diode is incident, to detect leakage light from the optical waveguide upwards or downwards, and stabilize the output of the laser diode through feedback control (see Patent Documents 3 and 4).

[0004] However, in cases where the image display device is an eyeglass-type terminal and a light-generating device is assembled into a temple with a roughly rectangular cross-sectional shape, there are various limitations on the shape of the light-generating device, including the photodetector, during the manufacturing of the light-generating device. For example, the length and height (vertical length of the light-generating device) of the light-generating device corresponding to the output direction of the laser diode must be minimized as much as possible. However, it is difficult to match the width (horizontal length of the light-generating device) of the light-generating device with the limitation that it can be allowed to a certain size. This is because the photodetector is placed on the back side of the laser diode or above or below the optical waveguide in the optical combiner.

[0005] Previous technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2013-195603

[0008] Patent Document 2: Japanese Patent Application Publication No. 10-253857

[0009] Patent Document 3: Japanese Patent Application Publication No. 2022-143133

[0010] Patent Document 4: Japanese Patent Application Publication No. 2002-223027 Summary of the Invention

[0011] The technical problem that the invention aims to solve

[0012] In view of the above, the object of the present invention is to provide a synthetic light generating apparatus that, in a synthetic light generating apparatus including a photodetector, has a shape in which the width is allowed to a certain extent while the length and height are minimized as much as possible.

[0013] Technical means for solving technical problems

[0014] The present invention provides a composite light generating device comprising: multiple light sources outputting light of different wavelengths; a light combining circuit; and a photodetector. The light combining circuit includes optical waveguides for propagating light output from the multiple light sources, a light combiner, and an optical waveguide for outputting multiplexed light obtained through the light combiner. The composite light generating device is characterized in that the light combining circuit has a reflector groove, which reflects leaked light from the light output from the multiple light sources that does not propagate in the optical waveguides to a side direction. The composite light generating device is provided with a photodetector in the side direction for detecting the reflected leaked light.

[0015] Preferably, the incident angle formed by the central axis of the light output from the plurality of light sources and the reflecting surface of the reflective groove is 48 degrees or more.

[0016] Preferably, the photodetector is configured with the light-receiving surface facing upwards.

[0017] Preferably, the photodetector includes multiple light-receiving areas.

[0018] Preferably, each of the reflected leaked light rays is equipped with a photodetector.

[0019] Preferably, the plurality of light sources include at least three laser diodes of red, green and blue colors.

[0020] In addition, the present invention also provides an image display device including the aforementioned synthetic light generation device.

[0021] Invention Effects

[0022] According to the present invention, a composite light generating apparatus includes: a plurality of light sources; a light combining circuit; and a photodetector. The light combining circuit includes individual optical waveguides receiving light output from the plurality of light sources, a light combiner, and an optical waveguide outputting multiplexed light obtained through the light combiner. The light combining circuit has a reflective groove that reflects leaked light from the light output from the plurality of light sources that does not propagate in the individual optical waveguides to a side direction. The composite light generating apparatus is provided with a photodetector in the side direction to detect the reflected leaked light. Thus, the shape of the composite light generating apparatus allows for a certain degree of allowable width while minimizing the length and height. Furthermore, since the leaked light is reflected to a side direction by the reflective groove, the leaked light output from the output end face of the light combining circuit as residual light that adversely affects image display can be reduced or eliminated. Here, leaked light that does not propagate in the optical waveguide means both light that leaks from the light source but cannot be input into the optical waveguide, and light that leaks from the optical waveguide during propagation but is temporarily input into it. Attached Figure Description

[0023] Figure 1 is a top view of the synthetic light generation apparatus of Embodiment 1 of the present invention.

[0024] Figure 2 is a top view of the synthetic light generation apparatus of Embodiment 2 of the present invention.

[0025] Figure 3 is a top view of the synthetic light generation apparatus of Embodiment 3 of the present invention.

[0026] Figure 4 is a schematic diagram showing the angle formed between the central axis of the light output from the light source and the reflector groove.

[0027] Figure 5 is a side view of the synthetic light generation device of Embodiment 1 of the present invention.

[0028] Figure 6 is a top view of the synthetic light generation device as a comparative example 1 of the prior art. Detailed Implementation

[0029] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to these embodiments.

[0030] Figure 1 is a top view of the composite light generating apparatus 200 according to Embodiment 1 of the present invention. In the composite light generating apparatus 200, blue laser diode 1, green laser diode 2, and red laser diode 3, which are arranged on the left side as light sources, output blue light, green light, and red light, respectively. These lights are input from the left end face of the optical wave combiner circuit 100 to optical waveguides 4 to 6 and propagate therethrough. They are then combined by optical wave combiner 7, and the resulting multiplexed light 9 propagates in optical waveguide 8 and is output from the right end face. It should be noted that the optical wave combiner 7 is a conceptual element. Its function is to combine the three types of light input from optical waveguides 4 to 6 into a single multiplexed light using known means and methods such as directional couplers, and then output the multiplexed light to optical waveguide 8. Specifically, there is no boundary line defining the optical wave combiner 7. The shapes of optical waveguides 4 to 6 adopt the shapes of the optical waveguides in the composite light generating apparatus described in the applicant's earlier Japanese Patent Application 2022-165691. This application describes a miniaturized synthetic light generation device. Not only the shape of the optical waveguide, but also the various distances between optical waveguides 4 and 6 on the left end face of the optical wave combiner circuit 100, and other shapes, can be referenced as long as they do not hinder the solution of the problem of the present invention.

[0031] Furthermore, for the leakage light that cannot be input into optical waveguides 4 to 6 from the three wavelengths of light output from blue laser diode 1, green laser diode 2, and red laser diode 3, respectively, reflective grooves 11 and 12 in the downward side direction, and detect the reflected leakage light using a photodetector 10 disposed on the lower side. Reflective groove 11 reflects the leakage light that cannot be input into optical waveguides 4 and 5, and reflective groove 12 reflects the leakage light that cannot be input into optical waveguide 6. Here, the incident angle θ between the central axis of the light output from the light source and the reflection from the reflective grooves 11 and 12 is 45 degrees. The definition of this incident angle θ will be described later. In addition, according to the law of reflection of light, the incident angle and the reflection angle are equal, so the central axis of the reflected leakage light forms a right angle with the central axis of the light output from the light source, therefore, the leakage light is reflected directly downwards. Since the photodetector 10 is disposed on the side below the optical wave combining circuit 100, it is difficult to minimize the width of the synthesized light generating device 200. Therefore, the width needs to be allowed to a certain extent.

[0032] Figure 2 is a top view of the composite light generating apparatus 201 of Embodiment 2 of the present invention. The composite light generating apparatus 201 has the same configuration as the composite light generating apparatus 200 of Figure 1, except for the shape and angle of the reflector slots. Reflector slots 13, 14, and 15 reflect leakage light that cannot be input into optical waveguides 4, 5, and 6, respectively. The incident angles of the central axis of the light output from the light source with the reflecting surfaces of reflector slots 13, 14, and 15 are 55 degrees, 45 degrees, and 35 degrees, respectively. Since the incident angle is equal to the reflection angle, reflector slot 13 reflects leakage light slightly to the right and directly downward, reflector slot 14 reflects leakage light directly downward, and reflector slot 15 reflects leakage light slightly to the left and directly downward. By using reflector slots corresponding to leakage light that cannot be input into the optical waveguides, the degree of freedom of angle θ relative to the photodetector 10 is increased. Furthermore, compared to Embodiment 1, by optimally setting an arbitrary incident angle for each reflector, the leakage light from the blue laser diode 1, the green laser diode 2, and the red laser diode 3 can be reflected into a small area in the lateral direction below the optical wave combining circuit 101. Therefore, the size of the photodetector 10 can be reduced, and its manufacturing cost can be lowered. Moreover, even if the size of the photodetector 10 cannot be reduced, the accuracy of its placement can be increased, thus reducing manufacturing defects during placement and lowering manufacturing costs.

[0033] Figure 3 is a top view of the composite light generating apparatus 202 according to Embodiment 3 of the present invention. The composite light generating apparatus 202 has the same configuration as the composite light generating apparatus 200 in Figure 1, except for the shape of the reflector grooves and the shape of the photodetectors. Reflector grooves 16, 17, and 18 reflect leakage light that cannot be input into optical waveguides 4, 5, and 6, respectively. The incident angle θ between the central axis of the light output from the light source and the reflecting surfaces of reflector grooves 16, 17, and 18 is 45 degrees, so, similar to the composite light generating apparatus 200, the leakage light is reflected directly downwards. The leakage light reflected by reflector grooves 16, 17, and 18 is detected by photodetectors 19, 20, and 21, respectively. By setting photodetectors corresponding to the reflected leakage light, precise control of each laser diode can be achieved, thus improving the output stability of the laser diodes.

[0034] Figure 4 is a diagram showing the angle of incidence θ between the central axis of the light output from the light source and the reflecting surface of the reflector. Here, as an example, the angle of incidence θ between the light 22 (not shown in Figure 1) output from the central axis of the blue laser diode 1 and the reflecting surface of the reflector 11 is shown. The angle of incidence θ is defined as the angle between the light 22 output from the light source and the normal to the reflecting surface of the reflector 11. For the reflected light 23 of the light 22 output from the light source, according to the law of reflection, the angle of reflection equals the angle of incidence; therefore, it is reflected relative to the normal at a reflection angle θ symmetrical to the angle of incidence. Additionally, for the light 22 output from the light source, transmitted light 24 that cannot be reflected by the reflecting surface is shown; however, under the conditions described later for total internal reflection, the transmitted light 24 is not generated, and only the reflected light 23 is generated.

[0035] Here, with the refractive index of silicon dioxide, the general cladding material, set to 1.46, and the refractive index of air, the medium of the reflector, set to 1.0, according to Snell's law, the condition for total internal reflection of the light 22 output from the light source at the reflecting surface of the reflector 11 is an incident angle θ of 43 degrees or more. Therefore, in order to generate only reflected light 23 towards the photodetector 10 in the light 22 output from the light source without generating transmitted light 24, it is preferable that the incident angle θ is 43 degrees or more. Furthermore, the light output from the laser diode generally has a radiation angle spread of ±5 degrees; therefore, considering the radiation angle spread, it is further preferable that the incident angle θ is 48 degrees or more.

[0036] Figure 5 is a side view of the synthesized light generation apparatus 200 of Embodiment 1 shown in Figure 1, viewed from the photodetector 10 side. The light source positioned on the left consists of a red diode 3 arranged near the front, a green diode 2 arranged from the front towards the inside, and a blue diode 1. Leakage light that cannot be input to the optical waveguides 4 to 6 is reflected near the front through reflector slots 11 and 12 (not shown) as reflected light 28 to 30. In the optical wave combiner circuit 100, a cladding layer 26 is stacked on a silicon substrate 27 (optical waveguides 4 to 6, serving as the core layer, are not shown), and the photodetector 10 is configured with its light-receiving surface 25 facing upwards. Alternatively, the photodetector 10 may be configured with the light-receiving surface 25 not facing upwards, but rather with the light-receiving surface 25 vertically aligned with the reflected light 28 to 30. When vertically arranged, it has the advantage of receiving a larger amount of reflected light. However, there is a possibility that the height of the photodetector 10 is larger than the height of the light sources 1-3 and the light combining circuit 100. Therefore, in order to reduce the overall height of the synthesized light generation device 200, it is preferable to arrange the light-receiving surface 25 facing upwards. When the light-receiving surface 25 is arranged facing upwards, the amount of light received is reduced compared to the case where the light-receiving surface 25 is vertically arranged so that it faces the reflected light 28 to 30 directly. However, the light received from the reflected light 28 to 30 can still be received. The photodetector can be a known photodiode or the like, and feedback control is performed based on the detected changes in leakage light, thereby stabilizing the output of each laser diode that serves as the light source. The feedback control is not particularly limited, and known controls described in Patent Documents 2-4, etc., can be used.

[0037] Figure 6 is a top view of a composite light generating apparatus 203 based on Patent Document 2, as Comparative Example 1. The composite light generating apparatus 203 has the same configuration as the composite light generating apparatus 200 in Figure 1, except that the photodetector 31 is disposed on the back side of the laser diode opposite to the emitted light side, and the optical combiner 103 does not have a reflective groove. Since the photodetector is not disposed on the side of the optical combiner 103, the composite light generating apparatus 203 can be narrower in width than the composite light generating apparatus 200 in Figure 1, but its length is significantly longer. Furthermore, leakage light that cannot be input to the optical waveguides 4 to 6 is output as residual light that adversely affects image display from the right end face of the optical combiner circuit 103. In this invention, the leakage light is reflected to one side using a reflective groove, thus also having the effect of reducing or eliminating the residual light output from the right end face of the optical combiner circuit 103.

[0038] The optical waveguides 100 to 102 in Examples 1 to 3 can be manufactured using known means and methods described in Patent Document 1, etc. Furthermore, the reflective groove can be processed using known methods such as etching. Regarding the shape of the reflective groove, only a parallelogram shape is described in Examples 1 to 3, but it is not limited to this; a known shape such as a triangle can also be used. Because it can improve reflection performance, it is preferable to form a thin metal film on the bottom surface of the reflective groove. Furthermore, any single-mode or multimode optical waveguide can be used.

[0039] For the three wavelengths of light output by the blue laser diode 1, green laser diode 2, and red laser diode 3 described in Examples 1 to 3, since cone cells in the human retina respond to red, green, and blue light, it is preferable to include a light source containing at least blue, green, and red light; however, it is also permissible to include only two types of light source as needed. Alternatively, other laser diodes that output yellow, orange, and violet light can also be used. For each wavelength range, for example, blue light is 430nm to 495nm, green light is 495nm to 570nm, red light is 610nm to 770nm, yellow light is 570nm to 595nm, orange light is 595nm to 610nm, and violet light is 400nm to 430nm. Furthermore, other light sources such as reflective light-emitting diodes can be used instead of laser diodes.

[0040] Industrial applicability

[0041] The synthetic light generating device of the present invention can be used as a light source for small image projection devices such as eyeglasses terminals and portable projectors, and its shape allows for a certain degree of reduction in width while minimizing length and height.

[0042] Symbol Explanation

[0043] 1 Blue laser diode

[0044] 2 Green laser diodes

[0045] 3 Red laser diodes

[0046] 4. Optical waveguide with output light from blue laser diode 1 input.

[0047] 5. Optical waveguide with output light from green laser diode 2 input.

[0048] 6. Optical waveguide with the output light from the input red laser diode 3

[0049] 7. Optical wave combiner

[0050] 8 Optical waveguide for multiplexed optical propagation

[0051] 9. Multiplexing light

[0052] 10. Photodetectors in Figures 1 and 2

[0053] 11. The leakage light reflection grooves of the reflected light waveguides 4 and 5 in Figure 1

[0054] 12. The leakage light reflection groove of the reflected light waveguide 6 in Figure 1

[0055] 13. The leakage light reflection groove of the reflected light waveguide 4 in Figure 2.

[0056] 14. The reflection groove of the leakage light of the reflected light waveguide 5 in Figure 2.

[0057] 15. The leakage light reflection groove of the reflected light waveguide 6 in Figure 2.

[0058] 16. The leakage light reflection groove of the reflected light waveguide 4 in Figure 3.

[0059] 17. The reflection groove of the leakage light in the reflected light waveguide 5 in Figure 3.

[0060] 18. The leakage light reflection groove of the reflected light waveguide 6 in Figure 3.

[0061] 19. The photodetector of the leaked light reflected by the reflector groove 16 in Figure 3.

[0062] 20 The photodetector of the leaked light reflected by the reflector groove 17 in Figure 3.

[0063] 21. Photodetector of leaked light reflected by reflector groove 18 in Figure 3

[0064] 22 The central axis of the light output from blue laser diode 1 in Figure 4

[0065] 23. The reflected light from the blue laser diode 1 reflected by the reflective surface in Figure 4.

[0066] 24. Transmitted light from blue laser diode 1 at the transmission and reflection surface in Figure 4.

[0067] 25 Light-receiving surface

[0068] 26 cladding layers

[0069] 27 Silicon substrate

[0070] 28. Reflected light from leakage that cannot be input into optical waveguide 4.

[0071] 29. Reflected light from leakage that cannot be input into optical waveguide 5

[0072] 30. Reflected light from leakage that cannot be input into optical waveguide 6.

[0073] 31 Photodetector in Figure 6

[0074] 100. Photosynthesizing circuit in the synthetic light generation device of Example 1

[0075] 101. Photosynthesizing circuit in the synthetic light generation device of Example 2

[0076] 102. Photosynthesis circuit in the synthetic light generation device of Example 3

[0077] 200 Synthetic Light Generation Apparatus of Example 1

[0078] 201 Synthetic Light Generation Apparatus of Example 2

[0079] 202 Synthetic Light Generation Apparatus of Example 3

[0080] 203 The synthetic light generation apparatus of Comparative Example 1.

Claims

1. A composite light generating apparatus comprising: a plurality of light sources outputting light of different wavelengths; a light combining circuit; and a photodetector, wherein the light combining circuit includes individual optical waveguides for propagating light output from the plurality of light sources, an optical combiner, and an optical waveguide for outputting multiplexed light obtained through the optical combiner, the composite light generating apparatus being characterized in that the light combining circuit has a reflective groove, the reflective groove reflecting leaked light from the light output from the plurality of light sources that does not propagate in the individual optical waveguides in a lateral direction, and the composite light generating apparatus is provided with the photodetector in the lateral direction for detecting the reflected leaked light.

2. The synthetic light generation device according to claim 1, wherein, The incident angle formed by the central axis of the light output from the plurality of light sources and the reflecting surface of the reflective groove is 48 degrees or more.

3. The synthetic light generating apparatus according to claim 1 or 2, wherein, The photodetector is configured with the light-receiving surface facing upwards.

4. The synthetic light generating apparatus according to claim 1 or 2, wherein, The photodetector includes multiple light-receiving areas.

5. The synthetic light generating apparatus according to claim 1 or 2, wherein, Each of the reflected leaked light rays is equipped with a photodetector.

6. The synthetic light generating apparatus according to claim 1 or 2, wherein, The plurality of light sources includes at least three laser diodes of red, green and blue colors.

7. An image display device comprising the synthetic light generating device of claim 6.

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