Optical multiplexer

Abstract

Provided is a small-sized optical multiplexer capable of obtaining output light making it possible to display a high-quality image with improved light intensity and reduced speckle noise on a screen.　This optical multiplexer outputs multiplexed light from at least two waveguides, each multiplexed light being multiplexed by merging at least two waveguides propagating monochromatic light into one waveguide.

Description

optical multiplexer

[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 the multiplexed light is multiplexed by merging at least two waveguides that propagate monochromatic light into one waveguide.

[0002] In recent years, image display devices have been known that use a plurality of laser diodes as light sources as light source circuits in small image projection devices such as eyeglass-type terminals and portable projectors, and that include an optical multiplexer that performs optical coupling using a directional coupler made of a waveguide (see Patent Document 1).The waveguides in the optical multiplexer 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 a low-refractive-index silicon oxide film is laminated.

[0003] Also known is an image display device that controls light intensity by changing and time-shifting the output times of each light beam output from a plurality of laser diodes, and that includes a scanning mirror that reflects the beams horizontally and vertically to project an image (see Patent Document 2).The image display device described in Patent Document 2 includes a blue light source, a green light source, and two red light sources as light sources, but in order to overcome a problem in which one of the red light sources reduces its output at high temperatures, 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] The light source section of the image display device in the above-mentioned prior art essentially uses only one blue light source, one green light source, and one red light source, which limits the improvement in the brightness (light intensity) of the output light. Furthermore, when the output light using one light source each of the above colors is projected onto a screen, the image displayed on the screen suffers from speckle noise, which causes variations in the light intensity distribution, degrading the image quality, making it difficult to obtain a high-quality image. Therefore, it has been considered to improve the brightness of the output light and reduce the speckle noise by increasing the number of light sources to six, two of each of the three colors. However, this increases the size of the light source section, making it difficult to miniaturize the image display device. Furthermore, when raster scanning of a two-dimensional image is performed using a scanning mirror using a dichroic mirror, a MEMS mirror, or the like, the driving operation of the scanning mirror in accordance with the light emission timing of the six light sources to correct color shift becomes complicated and difficult to control.

[0005] JP 2013-195603 A JP 2009-258207 A

[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 optical multiplexer that can obtain output light with improved light intensity and reduced speckle noise, enabling high-quality images to be displayed on a screen.

[0007] A further object of the present invention is to provide an image display device that uses the optical multiplexer of the present invention, thereby facilitating the driving operation of the scanning mirror and making control easy.

[0008] The present invention provides an optical multiplexer that outputs multiplexed light from at least two waveguides, each of which is multiplexed light obtained by combining 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 that propagate 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 light beams propagating through at least two of the waveguides in each of the multiplexed light beams are monochromatic light beams of different colors.

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

[0015] Preferably, the monochromatic lights of different colors 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.

[0017] According to the present invention, a compact optical multiplexer can be provided for use in image display devices used in image projection devices such as eyeglass-type terminals and portable projectors. The optical multiplexer of the present invention outputs multiplexed light from at least two waveguides, and can use two or more light sources of the same color, thereby improving light intensity and enabling the production of high-brightness images, as well as the display of high-quality images 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.

[0018] Fig. 1 is a top view of an optical multiplexer according to a first embodiment of the present invention. Fig. 2 is a top view of an optical multiplexer according to a second embodiment of the present invention. Fig. 3 is a top view of an optical multiplexer according to a third embodiment of the present invention. Fig. 4 is a schematic diagram of an image display device using the optical multiplexer according to the first embodiment of the present invention. Fig. 5 is a schematic diagram of an image display device using the optical multiplexer according to the second embodiment of the present invention.

[0019] 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.

[0020] FIG. 1 shows a top view of an optical multiplexer 100 according to a first embodiment. In the optical multiplexer 100, red light beams 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 are input to respective waveguides 11 and 12 from the left end face, propagate, and merge into waveguide 13, where they are multiplexed. After propagation, multiplexed light beams 20 are output from the right end face. Here, the widths of waveguides 11, 12, and 13 are represented by waveguide widths W1, W2, and W3, respectively. The waveguide width W3 is preferably larger than each of the waveguide widths W1 and W2, and more preferably is greater than or equal to the sum of the waveguide widths W1 and W2. If the waveguide width W3 is smaller than either of the waveguide widths W1 and W2, optical loss may occur during 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 the 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 the 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 W8 are the same as 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, 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 optical multiplexer 101 of Example 2. In optical multiplexer 101, red light, green light, and blue light output from 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 respective waveguides 31, 32, and 33, and after propagation, the red light and green light are first merged into waveguides 31 and 32, whereby the red light and green light are multiplexed, and after propagation, waveguide 33 is added and the red light, green light, and blue light are merged, whereby 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 waveguide widths W11, W12, and W13, respectively. As described with reference to FIG. 1 , the waveguide width W14, which is the width of the waveguide where the waveguides 31 and 32 merge, is preferably larger than each of the waveguide widths W11 and W12, and more preferably is greater than or equal to 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, optical loss may occur during the multiplexing stage. 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 greater than or equal to 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, optical loss may occur during the multiplexing stage.

[0023] In addition, in the optical multiplexer 101, 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 from the left end face to the respective waveguides 37, 36, and 35, and after propagation, the red light and green light are first merged into waveguides 37 and 36, whereby the red light and green light are multiplexed, and after propagation, waveguide 35 is added and the lights are merged to form waveguide 38, whereby the red light, green light, and blue light are multiplexed, and after propagation, multiplexed light 40 is output from the right end face. The widths of the waveguides 35 to 38 are represented by waveguide widths W16 to W20, respectively, and the relationship in magnitude between the waveguide width W20 and the waveguide widths W16 to W19 is the same as the relationship in magnitude between the waveguide width W15 and the waveguide widths W11 to W14. 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 light beams of different colors, from the two waveguides on the right end face.

[0024] 3 shows a top view of an optical multiplexer 102 according to a third embodiment. In the optical multiplexer 102, 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 to respective waveguides 41, 42, and 43 from the left end face, propagate, and then merge to form waveguide 44, where the red light, green light, and blue light are multiplexed and propagate, and then multiplexed light 49 is output from the right end face. Here, the widths of the waveguides 41, 42, and 43 are represented by waveguide widths W21, W22, and W23, respectively. As described with reference to 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 is larger than or equal to 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 receives 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, and enters the respective waveguides 45, 46, and 47 from the left end face. After propagating, the light beams merge into waveguide 48, whereby the red light, green light, and blue light are multiplexed and propagated, and multiplexed light 50 is output from the right end face. The widths of the waveguides 45 to 48 are represented by waveguide widths W25 to W28, respectively, and the relationship in magnitude between the waveguide width W28 and the waveguide widths W25 to W27 is the same as the relationship in magnitude between the waveguide width W24 and the waveguide widths W21 to W23. Therefore, the optical multiplexer 102 outputs multiplexed light beams 49 and 50 of red light, green light, and blue light, which are monochromatic light 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. However, the dominant wavelengths that indicate the color of the light when actually viewed with the naked eye do not need to be strictly the same wavelengths. Light of wavelengths that are generally recognized as the same color is 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 all monochromatic lights of the same color. Furthermore, yellow light of 570 to 595 nm, orange light of 595 to 610 nm, and violet light of 400 to 430 nm are all monochromatic lights of the same color. The blue light, green light, red light, yellow light, orange light, and violet light are treated as monochromatic lights of different colors.

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

[0028] 4 is a schematic diagram of an image display device using the optical multiplexer 100 of the first embodiment. The multiplexed 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 beams 20 to 22 so as to overlap at the point 53 by changing the angle at which the beams are reflected in accordance with a time shift that changes the output time of the multiplexed beams 20 to 22. Furthermore, the point 53 is scanned horizontally and vertically to display an image on the screen 52.

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

[0030] A known scanning mirror such as a mechanically rotating mirror using a motor or a MEMS (Micro-Electro-Mechanical Systems) 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 high mirror reflectivity.

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

[0032] 4 and 5, two red laser diodes, two green laser diodes, and two blue laser diodes are used as light sources for the optical multiplexer of the present invention, thereby improving light intensity compared to when one of each is used. Furthermore, by using two of each, the variation in light intensity distribution, which would otherwise occur when one of each is used, is reduced, resulting in a high-quality image. Furthermore, even if the number of laser diodes serving as light sources is six, the number of multiplexed beams output from the optical multiplexer is two or three, so driving the scanning mirror 51 when raster scanning a two-dimensional image is easy and not difficult to control.

[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 high-quality images to be displayed on a screen.

[0034] 1 First red laser diode 2 Second red laser diode 3 First green laser diode 4 Second green laser diode 5 First blue laser diode 6 Second blue laser diode 11 Waveguide to which output light of the first red laser diode 1 in FIG. 1 is input 12 Waveguide to which output light of the second red laser diode 2 in FIG. 1 is input 13 Waveguide where waveguides 11 and 12 join 14 Waveguide to which output light of the first green laser diode 3 in FIG. 1 is input 15 Waveguide to which output light of the second green laser diode 4 in FIG. 1 is input 16 Waveguide where waveguides 14 and 15 join 17 Waveguide to which output light of the first blue laser diode 5 in FIG. 1 is input 18 Waveguide to which output light of the second blue laser diode 6 in FIG. 1 is input 19 Waveguide where waveguides 17 and 18 join 20 Red multiplexed light output from the waveguide 13 21 2 36 Waveguide to which output light of the second green laser diode 4 in FIG. 2 is input 37 Waveguide to which output light of the second red laser diode 2 in FIG. 2 is input 38 Waveguide to which waveguides 35, 36 and 37 are input 39 Multiplexed light output from waveguide 34 40 Multiplexed light output from waveguide 38 41 Waveguide to which output light of the first red laser diode 1 in FIG. 3 is input 42 3. Waveguide 43 into which output light from the first blue laser diode 5 in FIG. 3 is input. 44. Waveguide where the waveguides 41, 42, and 43 join together.3 to which output light of the second red laser diode 2 in FIG. 3 is input 46 Waveguide to which output light of the second green laser diode 4 in FIG. 3 is input 47 Waveguide to which output light of the second blue laser diode 6 in FIG. 3 is input 48 Waveguide where waveguides 45, 46, and 47 join 49 Multiplexed light output from waveguide 44 50 Multiplexed light output from waveguide 48 51 Scanning mirror 52 Screen 53 Point on screen 52 100 Optical multiplexer of Example 1 101 Optical multiplexer of Example 2 102 Optical multiplexer of Example 3 W1 Waveguide width of waveguide 11 W2 Waveguide width of waveguide 12 W3 Waveguide width of waveguide 13 W4 Waveguide width of 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 waveguide 31 W12 Waveguide width of waveguide 32 W13 Waveguide width of waveguide 33 W14 Waveguide width of the waveguide where 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 waveguide 41 W22 Waveguide width of waveguide 42 W23 Waveguide width of the waveguide 43 W24 Waveguide width of the waveguide 44 W25 Waveguide width of the waveguide 45 W26 Waveguide width of the waveguide 46 W27 Waveguide width of the waveguide 47 W28 Waveguide width of the waveguide 48

Claims

1. 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 combining at least two waveguides that propagate monochromatic light into one waveguide.

2. An optical multiplexer according to claim 1, wherein the width of said one waveguide is greater than the width of each of said at least two waveguides propagating said monochromatic light.

3. An 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. An optical multiplexer as described in claim 1, wherein the optical multiplexer which outputs multiplexed light from each of said at least two waveguides is an optical multiplexer which outputs multiplexed light from each of at least three waveguides, and the monochromatic light in each of said multiplexed light propagating through at least two waveguides is monochromatic light of the same color.

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

6. 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. An optical multiplexer as described in 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. An optical multiplexer according to claim 6 or 7, wherein the monochromatic lights of different colors are selected from at least blue light, green light, and red light.

9. An image display device comprising the 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.

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