Optical multiplexer

Abstract

To provide a small-sized optical multiplexer capable of obtaining output light capable of displaying a high quality image obtained by improving light intensity and reducing speckle noise on a screen.SOLUTION: An optical multiplexer for outputting multiplexed light from at least two waveguides, respectively. Each multiplexed light is multiplexed by joining the at least two waveguides propagating monochromatic light into one waveguide.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an optical multiplexer that outputs multiplexed light from at least two waveguides, each of which is characterized in that each of the multiplexed lights is multiplexed by merging at least two waveguides that propagate monochromatic light into one waveguide. [Background technology]

[0002] In recent years, image display devices have been known that use multiple laser diodes as light sources as light source circuits for small image projection devices such as eyeglass-type terminals and portable projectors, and that are equipped with optical multiplexers that perform optical coupling using directional couplers made of waveguides (see Patent Document 1). The waveguides in 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 known chemical vapor deposition (CVD) or sputtering methods, and then patterned by photolithography using a photomask, and a low-refractive index silicon oxide film is further laminated.

[0003] Also known is an image display device that controls light intensity by changing and time-shifting the output times of the respective light beams output from a plurality of laser diodes, and is equipped with a scanning mirror that reflects the light in horizontal and vertical directions to project an image (see Patent Document 2).The image display device described in Patent Document 2 has a blue light source, a green light source, and two red light sources as light sources, but in order to eliminate the problem that one of the red light sources reduces its output when the temperature is high, the other red light source that can be driven even at high temperatures is used, and thus essentially one red light source is used.

[0004] In the light source section of the image display device in the above-mentioned conventional technology, since only one blue light source, one green light source, and one red light source are used in practice, there is a limit to improving the brightness (light intensity) of the output light. In addition, when the output light using one each of the above-mentioned light sources of each color is projected onto a screen, the image displayed on the screen generates speckle noise that causes a variation in the light intensity distribution, and the image quality is degraded, making it difficult to obtain a high-quality image. Therefore, it is conceivable to improve the brightness of the output light and reduce the speckle noise by increasing the number of light sources to six in total, that is, two each of the above-mentioned three colors, but this increases the size of the device in the light source section, which makes it difficult to miniaturize the image display device, and in addition, when raster scanning of a two-dimensional image is performed using a scanning mirror using a dichroic mirror, MEMS mirror, or the like, the driving operation of the scanning mirror in accordance with the light emission timing of the above-mentioned six light sources to correct color shift becomes complicated and difficult to control. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2013-195603 A [Patent Document 2] JP 2009-258207 A Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a small-sized optical multiplexer which is capable of obtaining output light capable of displaying a high-quality image on a screen with improved light intensity and reduced speckle noise.

[0007] A further object of the present invention is to provide an image display device which uses the optical multiplexer of the present invention, thereby making it easy to drive the scanning mirror and easy to control. [Means for solving the problem]

[0008] The present invention provides an optical multiplexer that outputs multiplexed light from at least two waveguides, each of which is characterized in that each multiplexed light is multiplexed by merging at least two waveguides that propagate monochromatic light into one waveguide.

[0009] Preferably, the width of said one waveguide is greater than the width of each of said at least two waveguides propagating said monochromatic light.

[0010] It is preferable that the width of the one waveguide is greater than or equal to the sum of the widths of the at least two waveguides that propagate the monochromatic light.

[0011] It is preferable that the optical multiplexer that outputs multiplexed light from each of the at least two waveguides is an optical multiplexer that outputs multiplexed light from each of at least three waveguides, and that the monochromatic light propagating through the at least two waveguides in each of the multiplexed light is monochromatic light of the same color.

[0012] In the optical multiplexer that outputs multiplexed light from each of the at least three waveguides, the monochromatic light of the same color preferably includes at least blue light, green light, and red light.

[0013] It is preferable that the monochromatic lights propagating through at least two of the waveguides in each of the multiplexed lights are monochromatic lights of different colors.

[0014] It is preferable that each of the multiplexed lights is a multiplexed light obtained by combining two waveguides propagating monochromatic light of different colors into one waveguide, and then combining the two waveguides with one other waveguide propagating monochromatic light of a different color.

[0015] Preferably, the different colored monochromatic lights are selected from at least blue light, green light, and red light.

[0016] The present invention also provides an image display device including, in addition to the optical multiplexer, a scanning mirror for scanning at least two multiplexed beams, and a laser diode as a light source of the monochromatic beam. Effect of the Invention

[0017] According to the present invention, it is possible to provide a small-sized optical multiplexer for use in an image display device used for image projection devices such as glasses-type terminals and portable projectors. The optical multiplexer of the present invention is an optical multiplexer that outputs multiplexed light from at least two waveguides, and can use two or more light sources of the same color, so that the light intensity is improved, it is possible to obtain a high-luminance image, and it is possible to display a high-quality image with reduced speckle noise on a screen. Furthermore, in an image display device using the optical multiplexer of the present invention, the scanning mirror can be easily driven and controlled without difficulty. [Brief description of the drawings]

[0018] [Figure 1] 1 is a top view of an optical multiplexer according to a first embodiment of the present invention. [Diagram 2] FIG. 11 is a top view of an optical multiplexer according to a second embodiment of the present invention. [Diagram 3] FIG. 11 is a top view of an optical multiplexer according to a third embodiment of the present invention. [Figure 4] 1 is a schematic diagram of an image display device using an optical multiplexer according to a first embodiment of the present invention. [Diagram 5] FIG. 11 is a schematic diagram of an image display device using an optical multiplexer according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, examples for carrying out the present invention will be described with reference to the drawings, however, the present invention is not limited to these examples.

[0020] FIG. 1 shows a top view of an optical multiplexer 100 according to a first embodiment. In the optical multiplexer 100, red light output from two red laser diodes, a first red laser diode 1 and a second red laser diode 2, arranged on the left side as light sources, is input to the respective waveguides 11 and 12 from the left end face, propagates, and is multiplexed by being merged as a waveguide 13, and after propagation, multiplexed light 20 is output from the right end face. Here, the widths of the waveguides 11, 12, and 13 are represented by waveguide widths W1, W2, and W3, respectively, and the waveguide width W3 is preferably larger than each of the waveguide widths W1 and W2, and more preferably is larger than the sum of the waveguide widths W1 and W2. If the waveguide width W3 is equal to or smaller than either of the waveguide widths W1 and W2, a loss of light may occur at the multiplexing stage.

[0021] In addition, in the optical multiplexer 100, green light output from two green laser diodes, a first green laser diode 3 and a second green laser diode 4, arranged on the left side as light sources, is input from the left end face to respective waveguides 14 and 15, propagates, and is combined by merging as waveguide 16, and after propagation, multiplexed light 21 is output from the right end face, and blue light output from two blue laser diodes, a first blue laser diode 5 and a second blue laser diode 6, arranged on the left side as light sources, is input from the left end face to respective waveguides 17 and 18, propagates, and is combined by merging as waveguide 19, and after propagation, multiplexed light 22 is output from the right end face. The widths of the waveguides 14 to 19 are represented by waveguide widths W4 to W9, respectively, and the relationship in size between the waveguide width W6 and the waveguide widths W4 and W5, and the relationship in size between the waveguide width W9 and the waveguide widths W7 and 8 are similar to the relationship in size between the waveguide width W3 and the waveguide widths W1 and W2. Therefore, the optical multiplexer 100 is an optical multiplexer that outputs multiplexed light beams 20, 21 and 22 of red light, green light and blue light, respectively, which are formed by multiplexing monochromatic light beams of the same color from the three waveguides on the right end face.

[0022] 2 shows a top view of an optical multiplexer 101 of Example 2. In the optical multiplexer 101, red light, green light, and blue light output from the first red laser diode 1, first green laser diode 3, and first blue laser diode 5, which are light sources arranged on the left side, are input from the left end face to the respective waveguides 31, 32, and 33, and after propagation, the red light and green light are first merged into each other by the waveguides 31 and 32, and after propagation, the waveguide 33 is added and merged as the waveguide 34, and the red light, green light, and blue light are multiplexed, and after propagation, multiplexed light 39 is output from the right end face. Here, the widths of the waveguides 31, 32, and 33 are represented by the waveguide widths W11, W12, and W13, respectively, and similarly to the contents described in FIG. 1, the waveguide width W14, which is the width of the waveguide where the waveguides 31 and 32 join together, is preferably larger than each of the waveguide widths W11 and W12, and more preferably is larger than the sum of the waveguide widths W11 and W12. If the waveguide width W14 is equal to or smaller than either of the waveguide widths W11 and W12, there is a possibility that optical loss will occur at the stage of combining. Furthermore, the waveguide width W15, which is the width of the waveguide 34, is preferably larger than each of the waveguide widths W13 and W14, and more preferably is larger than the sum of the waveguide widths W13 and W14. If the waveguide width W15 is equal to or smaller than either of the waveguide widths W13 and W14, there is a possibility that optical loss will occur at the stage of combining.

[0023] In addition, in the optical multiplexer 101, the red light, green light, and blue light output from the second red laser diode 2, second green laser diode 4, and second blue laser diode 6, which are light sources arranged on the left side, are input to the respective waveguides 37, 36, and 35 from the left end face, and after propagation, the waveguides 37 and 36 are first merged to multiplex the red light and green light, and after propagation, the waveguide 35 is added and merges as the waveguide 38 to multiplex the red light, green light, and blue light, and after propagation, the multiplexed light 40 is output from the right end face. The widths of the waveguides 35 to 38 are represented by the waveguide widths W16 to W20, respectively, and the magnitude relationship between the waveguide width W20 and the waveguide widths W16 to 19 is the same as the magnitude relationship between the waveguide width W15 and the waveguide widths W11 to 14. Therefore, the optical multiplexer 101 is an optical multiplexer that outputs multiplexed light beams 39, 40 of red light, green light and blue light, which are monochromatic lights of different colors, from two waveguides on the right end face.

[0024] 3 shows a top view of an optical multiplexer 102 of a third embodiment. In the optical multiplexer 102, red light, green light, and blue light output from the first red laser diode 1, the first green laser diode 3, and the first blue laser diode 5, which are light sources arranged on the left side, are input to the respective waveguides 41, 42, and 43 from the left end face, and after propagation, the red light, green light, and blue light are multiplexed, and after propagation, multiplexed light 49 is output from the right end face. Here, the widths of the waveguides 41, 42, and 43 are represented by the waveguide widths W21, W22, and W23, respectively, and similarly to the contents described in FIG. 1, the waveguide width W24, which is the width of the waveguide 44, is preferably larger than each of the waveguide widths W21, W22, and W23, and more preferably larger than the sum of the waveguide widths W21, W22, and W23. If the waveguide width W44 is equal to or smaller than any one of the waveguide widths W21, W22, and W23, there is a possibility that optical loss will occur at the multiplexing stage.

[0025] In addition, the optical multiplexer 102 is configured such that the red light, green light, and blue light output from the second red laser diode 2, the second green laser diode 4, and the second blue laser diode 6, which are light sources arranged on the left side, are input to the respective waveguides 45, 46, and 47 from the left end face, and after propagation, they are merged as the waveguide 48, so that the red light, the green light, and the blue light are multiplexed, and after propagation, the multiplexed light 50 is output from the right end face. The widths of the waveguides 45 to 48 are represented by the waveguide widths W25 to W28, respectively, and the magnitude relationship between the waveguide width W28 and the waveguide widths W25 to 27 is the same as the magnitude relationship between the waveguide width W24 and the waveguide widths W21 to 23. Therefore, the optical multiplexer 102 is an optical multiplexer that outputs multiplexed light 49, 50 of red light, green light, and blue light, which are monochromatic lights of different colors, from the two waveguides on the right end face.

[0026] Here, in the present invention, the two red lights output from the first red laser diode 1 and the second red laser diode 2, the two green lights output from the first green laser diode 3 and the second green laser diode 4, and the two blue lights output from the first blue laser diode 5 and the second blue laser diode 6 are monochromatic lights of the same color, red, green, and blue, respectively, but the main wavelengths that indicate the color of the light when actually viewed with the naked eye do not necessarily have to be strictly the same wavelengths, and as long as the wavelengths are generally recognized as the same color, they are treated as monochromatic lights of the same color. For example, blue light of 430 to 495 nm, green light of 495 to 570 nm, and red light of 610 to 770 nm are monochromatic lights of the same color, and further, yellow light of 570 to 595 nm, orange light of 595 to 610 nm, and purple light of 400 to 430 nm are monochromatic lights of the same color. The blue light, green light, red light, yellow light, orange light and purple light are treated as monochromatic lights of different colors.

[0027] The optical multiplexers 100, 101 and 102 can be manufactured by using known means and methods described in Patent Document 1 and the like. Although laser diodes are used as light sources in Examples 1 to 3, other light sources such as reflective light-emitting diodes may be used. Furthermore, in the examples, only two light sources of red light, green light and blue light are used as monochromatic light of the same color, but the above-mentioned yellow light, orange light and purple light may be used as necessary, and the number of light sources may be three or more for each color. Since cone cells in the human retina respond to red light, green light and blue light, it is preferable to include light sources of at least red light, green light and blue light, and it is also preferable to use at least two light sources for each color in order to enable the acquisition of a high-brightness image.

[0028] 4 is a schematic diagram of an image display device using the optical multiplexer 100 of the first embodiment. The multiplexed light beams 20 to 22 output from the optical multiplexer 100 are reflected by a scanning mirror 51 so as to overlap at a point 53 on a screen 52. The scanning mirror 51 is movable, and controls the multiplexed light beams 20 to 22 to overlap at a point 53 by changing the angle at which the multiplexed light beams 20 to 22 are reflected in response to a time shift that changes the output time of the multiplexed light beams 20 to 22. Furthermore, the point 53 is scanned in the horizontal and vertical directions, and an image is displayed on the screen 52.

[0029] The scanning mirror 51 can be controlled by using known means and methods described in Patent Document 2, etc. Also, for other components necessary for the image display device, such as a power supply and a driving circuit, which are omitted in Fig. 4, known components described in Patent Document 2, etc. can be used.

[0030] A known scanning mirror such as a mechanically rotating mirror using a motor or a Micro-Electro-Mechanical Systems (MEMS) mirror can be used as the scanning mirror 51. It is preferable to use a MEMS mirror because it consumes low power, has a wide optical deflection angle, and has a high mirror reflectance.

[0031] Fig. 5 shows a schematic diagram of an image display device using an optical multiplexer 101 according to the second embodiment. The same principle and configuration as those of the image display device shown in Fig. 4 can be used, except that multiplexed light beams 39 and 40 are output from the optical multiplexer 101. Moreover, instead of the optical multiplexer 101, the optical multiplexer 102 according to the third embodiment can also be used.

[0032] In the image display device in Fig. 4 and Fig. 5, two each of red laser diodes, green laser diodes, and blue laser diodes are used as light sources of the optical multiplexer of the present invention, and thus the light intensity is improved compared to the case where one each is used. Also, regarding the speckle noise that occurs when one each is used, by using two each, the variation in light intensity distribution is reduced, and a high quality image can be obtained. Furthermore, even if the number of laser diodes as the light source is six, the number of multiplexed lights output from the optical multiplexer is two or three, so that the driving operation of the scanning mirror 51 when raster scanning a two-dimensional image is easy and control is not difficult. [Industrial Applicability]

[0033] The optical multiplexer of the present invention can be used as a light source circuit for small image projection devices such as eyeglass-type terminals and portable projectors, and can obtain output light that has improved light intensity and reduced speckle noise, enabling a high-quality image to be displayed on a screen. [Explanation of symbols]

[0034] 1. First red laser diode 2. Second red laser diode 3. First green laser diode 4. 2nd Green Laser Diode 5. First blue laser diode 6. Second Blue Laser Diode 11: Waveguide into which the output light of the first red laser diode 1 in FIG. 1 is input 12 Waveguide into which the output light of the second red laser diode 2 in FIG. 1 is input 13 Waveguide where waveguides 11 and 12 join 14: Waveguide into which the output light of the first green laser diode 3 in FIG. 1 is input 15 Waveguide into which the output light of the second green laser diode 4 in FIG. 1 is input 16 Waveguide where the waveguides 14 and 15 join 17 Waveguide into which the output light of the first blue laser diode 5 in FIG. 1 is input 18: Waveguide into which the output light of the second blue laser diode 6 in FIG. 1 is input 19 Waveguide where the waveguides 17 and 18 join 20 Red multiplexed light output from the waveguide 13 21 Green multiplexed light output from the waveguide 16 22 Blue multiplexed light output from the waveguide 19 31: Waveguide into which the output light of the first red laser diode 1 in FIG. 2 is input 32 Waveguide into which the output light of the first green laser diode 3 in FIG. 2 is input 33: Waveguide into which the output light of the first blue laser diode 5 in FIG. 2 is input 34 Waveguide where the waveguides 31, 32 and 33 join 35 Waveguide into which the output light of the second blue laser diode 6 in FIG. 2 is input 36 Waveguide into which the output light of the second green laser diode 4 in FIG. 2 is input 37 Waveguide into which the output light of the second red laser diode 2 in FIG. 2 is input 38 Waveguide where the waveguides 35, 36 and 37 join 39 Multiplexed light output from the waveguide 34 40 Multiplexed light output from the waveguide 38 41: Waveguide into which the output light of the first red laser diode 1 in FIG. 3 is input 42 Waveguide into which the output light of the first green laser diode 3 in FIG. 3 is input 43 Waveguide into which the output light of the first blue laser diode 5 in FIG. 3 is input 44 Waveguide where the waveguides 41, 42 and 43 join 45 Waveguide into which the output light of the second red laser diode 2 in FIG. 3 is input 46 Waveguide into which the output light of the second green laser diode 4 in FIG. 3 is input 47 Waveguide into which the output light of the second blue laser diode 6 in FIG. 3 is input 48 Waveguide where the waveguides 45, 46 and 47 join 49 Multiplexed light output from the waveguide 44 50 Multiplexed light output from the waveguide 48 51 Scanning mirror 52 screens 53 Point on screen 52 100 Optical multiplexer of the first embodiment 101 Optical multiplexer of the second embodiment 102 Optical multiplexer of the third embodiment W1: Waveguide width of the waveguide 11 W2: Waveguide width of the waveguide 12 W3: Waveguide width of waveguide 13 W4: Waveguide width of the waveguide 14 W5: Waveguide width of waveguide 15 W6: Waveguide width of waveguide 16 W7: Waveguide width of waveguide 17 W8 Waveguide width of waveguide 18 W9 Waveguide width of waveguide 19 W11: Waveguide width of the waveguide 31 W12: Waveguide width of waveguide 32 W13 Waveguide width of waveguide 33 W14: The width of the waveguide where the waveguides 31 and 32 join W15 Waveguide width of waveguide 34 W16 Waveguide width of waveguide 35 W17 Waveguide width of waveguide 36 W18 Waveguide width of waveguide 37 W19: Waveguide width of the waveguide where waveguides 36 and 37 join W20 Waveguide width of waveguide 38 W21: Waveguide width of the waveguide 41 W22: Waveguide width of waveguide 42 W23 Waveguide width of waveguide 43 W24: Waveguide width of waveguide 44 W25 Waveguide width of waveguide 45 W26 Waveguide width of waveguide 46 W27 Waveguide width of waveguide 47 W28 Waveguide width of waveguide 48

Claims

1. An optical multiplexer which outputs multiplexed light from at least two waveguides, each of which is a multiplexed light obtained by combining at least two waveguides propagating monochromatic light into one waveguide.

2. 2. The optical multiplexer of claim 1, wherein the width of said one waveguide is greater than the width of each of said at least two waveguides that propagate said monochromatic light.

3. 2. The optical multiplexer according to claim 1, wherein the width of said one waveguide is greater than or equal to the sum of the widths of at least two waveguides that propagate said monochromatic light.

4. 2. The optical multiplexer according to claim 1, wherein the optical multiplexer that outputs multiplexed light from each of the at least two waveguides is an optical multiplexer that outputs multiplexed light from each of at least three waveguides, and the monochromatic light propagating through the at least two waveguides in each of the multiplexed light is monochromatic light of the same color.

5. 5. The optical multiplexer according to claim 4, wherein said monochromatic light of the same color includes at least blue light, green light and red light, in said optical multiplexer outputting multiplexed light from each of said at least three waveguides.

6. 2. An optical multiplexer according to claim 1, wherein the monochromatic light propagating through at least two of said respective multiplexed lights is monochromatic light of a different color.

7. 2. The optical multiplexer according to claim 1, wherein each of the multiplexed lights is a multiplexed light obtained by combining two waveguides propagating monochromatic light of different colors into one waveguide, and then combining the combined light with another waveguide propagating monochromatic light of a different color.

8. 8. The optical multiplexer according to claim 6, wherein the monochromatic lights of different colors are selected from at least blue light, green light, and red light.

9. 2. An image display device comprising: an optical multiplexer according to claim 1; a scanning mirror for scanning at least two multiplexed beams; and a laser diode as a light source of the monochromatic beam.

Images