Composite light generation device and image display device

Abstract

Provided is a composite light generation device that includes a photodetector and that is shaped such that the width is allowable to some extent and the length and the height can be reduced as much as possible. A composite light generation device (200) is provided with: a plurality of light sources (1, 2, 3) that output light having different wavelengths; an optical multiplexing circuit (100) that includes optical waveguides (4, 5, 6) through which light outputted from the plurality of light sources (1, 2, 3) propagates, an optical multiplexer (7), and an optical waveguide (8) that outputs multiplexed light (9) obtained by the optical multiplexer (7); and a photodetector (10). The composite light generation device (200) is characterized in that: the optical multiplexing circuit (100) has reflection grooves (11, 12) for reflecting, in one lateral surface direction, leakage light that does not propagate through the optical waveguides (4, 5, 6) among the light outputted from the plurality of light sources (1, 2, 3); and the photodetector (10) for detecting the reflected leakage light is disposed in the one lateral surface direction.

Description

Synthetic light generating device and image display device

[0001] The present invention relates to a composite light generating device for use in an image display device, which comprises a plurality of light sources that output light of different wavelengths, an optical multiplexing circuit including optical waveguides that receive the light output from the plurality of light sources, an optical multiplexer, and an optical waveguide that outputs multiplexed light obtained by the optical multiplexer, and a photodetector.

[0002] In recent years, optical multiplexers using multiple laser beams as light sources have become known in the field of composite light generating devices used in the light source portions of image display devices such as eyeglass-type terminals and portable projectors (see Patent Document 1). The optical multiplexers are manufactured through a process in which low-refractive index and high-refractive index silicon oxide films are laminated on a silicon substrate using a known method such as chemical vapor deposition (CVD) or sputtering, followed by patterning by photolithography using a photomask, and then laminating a low-refractive index silicon oxide film to form an overclad layer.

[0003] It is known that the laser diodes that generate the laser light change or deteriorate depending on the environment during use, such as temperature, humidity, static electricity, and power supply noise, and to address the problem of deterioration, an optical communication module is known in which a photodetector is provided on the back side of the laser diode opposite the light-emitting side, and the light emitted on the back side is detected and feedback-controlled to stabilize the output of the laser diode (see Patent Document 2). Also known is a combined light generating device that stabilizes the output of a laser diode by providing a photodetector above or below an optical waveguide in an optical multiplexer or the like into which light emitted from the laser diode is incident, and detecting and feedback-controlling the leaked light from the optical waveguide in the upward or downward direction (see Patent Documents 3 and 4).

[0004] However, when manufacturing a composite light generating device including a photodetector, for example, when the image display device is an eyeglass-type terminal and the composite light generating device is incorporated into temples with an approximately rectangular cross-sectional shape, there are various constraints on the shape of the composite light generating device.For example, the length of the composite light generating device corresponding to the output direction of the laser diode and the height of the composite light generating device (the vertical length of the composite light generating device) must be made as small as possible, but the width of the composite light generating device (the horizontal length of the composite light generating device) can be tolerated up to a certain size.Under these constraints, it has been difficult to address this issue using the technology of arranging a photodetector on the back side of the laser diode or above or below the optical waveguide in an optical multiplexer, etc.

[0005] JP 2013-195603 A JP 10-253857 A JP 2022-143133 A JP 2002-223027 A

[0006] The object of the present invention has been made in consideration of the above circumstances, and is to provide a synthetic light generating device including a photodetector, whose shape allows for a certain degree of tolerance in width, while making the length and height as small as possible.

[0007] The present invention provides a composite light generating device comprising a plurality of light sources that output light of different wavelengths, an optical multiplexing circuit including respective optical waveguides through which the light output from the plurality of light sources propagates, an optical multiplexer, and an optical waveguide that outputs multiplexed light obtained by the optical multiplexer, and a photodetector, wherein the optical multiplexing circuit has a reflective groove that reflects leakage light that does not propagate through the respective optical waveguides, among the light output from the plurality of light sources, toward one side, and the photodetector that detects the reflected leakage light is arranged toward the one side.

[0008] It is preferable that the angles of incidence between the central axes of the light beams output from the plurality of light sources and the reflecting grooves are each 48 degrees or more.

[0009] It is preferable that the photodetector is disposed with its light-receiving surface facing upward.

[0010] The photodetector preferably includes a plurality of light-receiving regions.

[0011] It is preferable that the photodetector is provided for each of the reflected leaked lights.

[0012] It is preferable that the plurality of light sources include laser diodes of at least three colors: red, green, and blue.

[0013] The present invention also provides an image display device including the above-described composite light generating device.

[0014] According to the present invention, there is provided a combined light generating device comprising a plurality of light sources, an optical multiplexing circuit including optical waveguides to which the light output from the plurality of light sources is input, an optical multiplexer, and an optical waveguide to output multiplexed light obtained by the optical multiplexer, and a photodetector, wherein the optical multiplexing circuit has a reflective groove that reflects leakage light from the light output from the plurality of light sources that does not propagate through the optical waveguides toward one side, and a photodetector is disposed toward the one side for detecting the reflected leakage light, thereby allowing the shape of the combined light generating device to be as small as possible in length and height while allowing a certain degree of width. Furthermore, because the reflective groove reflects the leakage light toward one side, the leakage light output from the output end face of the optical multiplexing circuit as excess light that adversely affects image display can be reduced or eliminated. Here, the leaked light that does not propagate through the optical waveguide refers to both light that is output from the light source but cannot be input to the optical waveguide and leaks out, and light that is once input to the optical waveguide but leaks out of the optical waveguide during propagation.

[0015] Fig. 1 is a top view of a combined light generating device of Example 1 in the present invention. Fig. 2 is a top view of a combined light generating device of Example 2 in the present invention. Fig. 3 is a top view of a combined light generating device of Example 3 in the present invention. Fig. 4 is a diagram showing the angle between the central axis of light output from a light source and a reflective groove. Fig. 5 is a side view of the combined light generating device of Example 1 in the present invention. Fig. 6 is a top view of a combined light generating device of Comparative Example 1, which is prior art.

[0016] Hereinafter, examples for carrying out the present invention will be described with reference to the drawings, but the present invention is not limited to these examples.

[0017] FIG. 1 shows a top view of a combined light generating device 200 according to a first embodiment of the present invention. In combined light generating device 200, blue light, green light, and red light output from blue laser diode 1, green laser diode 2, and red laser diode 3, respectively, which are light sources arranged on the left side, are input to optical waveguides 4-6 from the left end face of optical multiplexing circuit 100, propagate, and are then combined by optical multiplexer 7. The combined multiplexed light 9 propagates through optical waveguide 8 and is then output from the right end face. Here, optical multiplexer 7 conceptually illustrates a part that combines the three types of light input through optical waveguides 4-6 into a single multiplexed light by known means or methods such as a directional coupler, and then outputs it to optical waveguide 8. There is no specific boundary defining optical multiplexer 7. The shapes of optical waveguides 4-6 are based on the optical waveguide shapes used in a combined light generating device described in Japanese Patent Application No. 2022-165691, previously filed by the applicant. The application describes a combined light generating device that can be miniaturized, and the contents of the application can be used not only for the shape of the optical waveguides but also for other shapes, such as the respective distances between the optical waveguides 4 to 6 at the left end face of the optical multiplexing circuit 100, as long as they do not interfere with solving the problem of the present invention.

[0018] Then, the leakage light of the three light beams with different wavelengths output from the blue laser diode 1, the green laser diode 2, and the red laser diode 3 that could not enter the optical waveguides 4 to 6 is reflected toward the lower side surface by the reflecting grooves 11 and 12, and the reflected leakage light is detected by the photodetector 10 disposed on the lower side surface. The reflecting groove 11 reflects the leakage light that could not enter the optical waveguides 4 and 5, and the reflecting groove 12 reflects the leakage light that could not enter the optical waveguide 6. Here, the angle of incidence θ between the central axis of the light output from the light source and the reflecting surfaces of the reflecting grooves 11 and 12 is both 45 degrees. The definition of the angle of incidence θ will be described later. Furthermore, according to the law of light reflection, the angle of incidence and the angle of reflection are equal, so the central axis of the reflected leakage light is perpendicular to the central axis of the light output from the light source, and the leakage light is reflected directly downward. Since the photodetector 10 is disposed on the lower side of the optical multiplexing circuit 100, it is difficult to make the width of the combined light generating device 200 as small as possible, and therefore the width must be tolerable to a certain extent.

[0019] FIG. 2 shows a top view of a combined light generating device 201 according to a second embodiment of the present invention. The configuration of the combined light generating device 201 is the same as that of the combined light generating device 200 shown in FIG. 1, except for the shape and angle of the reflecting grooves. The reflecting grooves 13, 14, and 15 reflect the leaked light that could not enter the optical waveguides 4, 5, and 6, respectively. The angles of incidence between the central axis of the light output from the light source and the reflecting surfaces of the reflecting grooves 13, 14, and 15 are 55 degrees, 45 degrees, and 35 degrees, respectively. Since the angles of incidence and reflection are equal, the reflecting groove 13 reflects the leaked light slightly to the right of directly below, the reflecting groove 14 reflects the leaked light directly below, and the reflecting groove 15 reflects the leaked light slightly to the left of directly below. By using reflecting grooves corresponding to the leaked light that could not enter the optical waveguides, the degree of freedom of the angle θ relative to the photodetector 10 is increased. Furthermore, compared to Example 1, by optimally setting an arbitrary incident angle for each reflective groove, it is possible to reflect the leakage light from each of the blue laser diode 1, green laser diode 2, and red laser diode 3 onto a narrow region in the lower side surface direction of the optical multiplexing circuit 101. Therefore, the size of the photodetector 10 can be reduced, and the manufacturing cost of the photodetector 10 can be reduced. Even if the size of the photodetector 10 cannot be reduced, the accuracy error in the position where the photodetector 10 is disposed can be increased, so that manufacturing defects when disposing the photodetector 10 can be reduced and manufacturing costs can be reduced.

[0020] FIG. 3 shows a top view of a combined light generating device 202 according to a third embodiment of the present invention. The configuration of the combined light generating device 202 is the same as that of the combined light generating device 200 shown in FIG. 1, except for the shape of the reflecting grooves and the shape of the photodetectors. The reflecting grooves 16, 17, and 18 reflect the leaked light that could not enter the optical waveguides 4, 5, and 6, respectively. Since the angle of incidence θ between the central axis of the light output from the light source and the reflecting surfaces of the reflecting grooves 16, 17, and 18 is all 45 degrees, the leaked light is reflected directly downward, as in the combined light generating device 200. The leaked light reflected by the reflecting grooves 16, 17, and 18 is detected using photodetectors 19, 20, and 21, respectively. By providing a photodetector corresponding to each reflected leaked light, precise control of each laser diode can be performed, improving the output stability of the laser diode.

[0021] FIG. 4 shows the angle of incidence θ between the central axis of light output from the light source and the reflecting surface of the reflecting groove. Here, as an example, the angle of incidence θ between the central axis light 22 (not shown in FIG. 1) output from the blue laser diode 1 in FIG. 1 and the reflecting surface of the reflecting groove 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 reflecting groove 11. Regarding the reflected light 23 of the light 22 output from the light source, since the law of light reflection dictates that the angle of reflection is equal to the angle of incidence, it is reflected at a reflection angle θ that is symmetrical to the angle of incidence with respect to the normal. Furthermore, although the transmitted light 24 that could not be reflected by the reflecting surface is shown for the light 22 output from the light source, if total reflection occurs under the conditions described below, the transmitted light 24 is not generated, and only the reflected light 23 is generated.

[0022] Here, assuming that the refractive index of silicon dioxide, a common cladding material, is 1.46 and the refractive index of the air medium of the reflecting groove is 1.0, Snell's law calculates that the condition for total reflection of light 22 output from the light source on the reflecting surface of reflecting groove 11 is an incident angle θ of 43 degrees or greater. Therefore, in order for light 22 output from the light source to generate only reflected light 23 toward photodetector 10 without generating transmitted light 24, it is preferable that the incident angle θ be 43 degrees or greater. Furthermore, since light output from a laser diode generally has a radiation angle spread of approximately ±5 degrees, it is even more preferable that the incident angle θ be 48 degrees or greater if the spread of the radiation angle is taken into consideration.

[0023] FIG. 5 shows a side view of the combined light generating device 200 of Example 1 shown in FIG. 1 , viewed from the photodetector 10 side. The light sources arranged on the left side include a red laser diode 3 at the front, a green laser diode 2, and a blue laser diode 1 arranged from front to back. Leaked light that fails to enter the optical waveguides 4-6 is reflected toward the front by reflective grooves 11 and 12 (not shown). The optical multiplexing circuit 100 includes a silicon substrate 27 on which a cladding layer 26 is stacked (the optical waveguides 4-6, which are core layers, are not shown). The photodetector 10 is disposed with its light-receiving surface 25 facing upward. Instead of disposing the light-receiving surface 25 facing upward, the photodetector 10 may be disposed vertically so that the light-receiving surface 25 directly faces the reflected light beams 28-30. While a vertical arrangement has the advantage of being able to receive a larger amount of reflected light, the height of the photodetector 10 may be greater than the height of the light sources 1-3 and the optical multiplexing circuit 100. Therefore, in order to reduce the overall height of the combined light generating device 200, it is preferable to arrange the light-receiving surface 25 facing upward. When the light-receiving surface 25 faces upward, the amount of light received is reduced compared to when the light-receiving surface 25 is arranged vertically facing the reflected light 28-30, but it is still possible to receive the reflected light 28-30. The photodetector may be a known photodiode or the like, and feedback control is performed in response to changes in the detected leakage light to stabilize the output of each laser diode, which serves as the light source. The feedback control is not particularly limited, and known methods described in Patent Documents 2-4, etc., may be used.

[0024] FIG. 6 shows a top view of a combined light generating device 203 conforming to Patent Document 2 as Comparative Example 1. The configuration of the combined light generating device 203 is the same as that of the combined light generating device 200 of FIG. 1 , except that the photodetector 31 is disposed on the rear side opposite the laser diode output light side, and the optical multiplexer 103 does not have a reflective groove. Because the photodetector is not disposed on the side of the optical multiplexer 103, the combined light generating device 203 can be made smaller in width compared to the combined light generating device 200 of FIG. 1 , but it is clear that the length is increased. Furthermore, leakage light that could not enter the optical waveguides 4 to 6 is output from the right end face of the optical multiplexing circuit 103 as excess light that adversely affects image display. In contrast, the present invention has the effect of reflecting the leakage light toward one side using a reflective groove, thereby reducing or eliminating the excess light output from the right end face of the optical multiplexing circuit 103.

[0025] The optical multiplexing circuits 100 to 102 described in Examples 1 to 3 can be manufactured using known means and methods described in Patent Document 1, etc., and the reflecting grooves can be processed using known methods such as etching. Although only a parallelogram shape is described for the reflecting grooves in Examples 1 to 3, this is not limiting and known shapes such as a triangle can also be used. It is preferable to form a metal thin film on the bottom surface of the reflecting groove, as this can improve reflection performance. Furthermore, either a single-mode optical waveguide or a multi-mode optical waveguide may be used as the optical waveguide.

[0026] Regarding the three light beams of different wavelengths output from the blue laser diode 1, green laser diode 2, and red laser diode 3 described in Examples 1 to 3, it is preferable to include light sources of at least blue, green, and red light, since cone cells in the human retina respond to red, green, and blue light. However, it is also possible to include only two types of light sources if necessary. Laser diodes that output yellow, orange, and violet light may also be used. For example, the wavelength ranges of blue light are 430 to 495 nm, green light is 495 to 570 nm, red light is 610 to 770 nm, yellow light is 570 to 595 nm, orange light is 595 to 610 nm, and violet light is 400 to 430 nm. Furthermore, other light sources, such as reflective light-emitting diodes, may be used instead of laser diodes.

[0027] The composite light generating device of the present invention can be used as a light source for small image projection devices such as eyeglass-type terminals and portable projectors, and its shape allows for a certain degree of width tolerance while allowing for the length and height to be made as small as possible.

[0028] 1 Blue laser diode 2 Green laser diode 3 Red laser diode 4 Optical waveguide into which output light of blue laser diode 1 is input 5 Optical waveguide into which output light of green laser diode 2 is input 6 Optical waveguide into which output light of red laser diode 3 is input 7 Optical multiplexer 8 Optical waveguide through which multiplexed light propagates 9 Multiplexed light 10 Photodetector in Figures 1 and 2 11 Reflecting groove that reflects leaked light from optical waveguides 4 and 5 in Figure 1 12 Reflecting groove that reflects leaked light from optical waveguide 6 in Figure 1 13 Reflecting groove that reflects leaked light from optical waveguide 4 in Figure 2 14 Reflecting groove that reflects leaked light from optical waveguide 5 in Figure 2 15 Reflecting groove that reflects leaked light from optical waveguide 6 in Figure 2 16 Reflecting groove that reflects leaked light from optical waveguide 4 in Figure 3 17 Reflecting groove that reflects leaked light from optical waveguide 5 in Figure 3 18 Reflecting groove reflecting leaked light from optical waveguide 6 in FIG. 3 19 Photodetector of leaked light reflected by reflecting groove 16 in FIG. 3 20 Photodetector of leaked light reflected by reflecting groove 17 in FIG. 3 21 Photodetector of leaked light reflected by reflecting groove 18 in FIG. 3 22 Central axis of light output from blue laser diode 1 in FIG. 4 23 Reflected light of light output from blue laser diode 1 reflected by reflecting surface in FIG. 4 24 Transmitted light of light output from blue laser diode 1 transmitted through reflecting surface in FIG. 4 25 Light receiving surface 26 Cladding layer 27 Silicon substrate 28 Reflected light of leaked light that could not be input to optical waveguide 4 29 Reflected light of leaked light that could not be input to optical waveguide 5 30 Reflected light of leaked light that could not be input to optical waveguide 6 31 Photodetector in FIG. 6 100 Optical multiplexing circuit in combined light generating device of embodiment 1 101 Optical multiplexing circuit in combined light generating device of embodiment 2 102 Optical multiplexing circuit in the combined light generating device of Example 3 200 Combined light generating device of Example 1 201 Combined light generating device of Example 2 202 Combined light generating device of Example 3 203 Combined light generating device of Comparative Example 1

Claims

1. A composite light generating device comprising a plurality of light sources outputting light of different wavelengths, an optical multiplexing circuit including respective optical waveguides through which the light output from the plurality of light sources propagates, an optical multiplexer, and an optical waveguide that outputs the multiplexed light obtained by the optical multiplexer, and a photodetector, wherein the optical multiplexing circuit has a reflective groove that reflects leakage light that does not propagate through each of the optical waveguides among the light output from the plurality of light sources toward one side, and the photodetector that detects the reflected leakage light is disposed toward the one side.

2. A composite light generating device as described in claim 1, wherein the angles of incidence between the central axes of the light beams output from said plurality of light sources and the reflecting surface of said reflecting groove are each 48 degrees or more.

3. A composite light generating device according to claim 1 or 2, wherein said photodetector is disposed with its light receiving surface facing upward.

4. A device for generating composite light as claimed in claim 1 or 2, wherein said photodetector includes a plurality of light receiving regions.

5. A composite light generating device according to claim 1 or 2, wherein a photodetector is provided for each of the reflected leak lights.

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

7. An image display device comprising the composite light generating device according to claim 6.

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