Patent Application
20210149111
The present invention relates to an optical multiplexer, a light source module, a two-dimensional optical scanning device and an image projection device, and relates to, for example, the configuration for reducing the effects of stray light from a light source on the multiplexed output from an optical multiplexer.
Various forms of light beam multiplexing light sources have been known as conventional devices for multiplexing a plurality of light beams such as laser beams so as to radiate one light beam. From among these, light beam multiplexing light sources where semiconductor lasers and optical waveguide-type optical multiplexers are combined are characterized in that the device can be made compact and the power can be lowered, and thus are applied to a laser beam scanning-type color image projection device (see Patent Literature 1 through 6).
Conventional light beam multiplexing light sources where semiconductor lasers and optical waveguide-type optical multiplexers are combined include a light beam multiplexing light source for multiplexing laser beams of three primary colors as illustrated in Patent Literature 3, for example. As illustrated in FIGS. 3 and 10 in Patent Literature 3, a light beam multiplexing light source is formed of optical waveguides made of a core and a clad, and semiconductor lasers for generating light beams of red, blue and green are installed along the input ends of the optical waveguides that correspond to the respective colors. Here, the light beams propagate through the cores of the optical waveguides and are emitted from the output end of an optical multiplexer as a multiplexed light beam.
In this case, the entirety of the light beams that have been emitted from the semiconductor lasers for the respective colors is not guided into the core due to the difference in the form of the light beams emitted from the semiconductor lasers and the form of the cores, and part of the light beams leaks into a clad portion. Conventionally it has been said that the leaked light disseminates while progressing through the inside of an optical multiplexer or is radiated to the outside so as to be reduced to a neglectable degree.
It has become clear in the optical waveguide-type optical multiplexer that was diligently examined by the present inventors that the effects of the light that has leaked to a clad portion as described above cannot be neglected as compared to the light beam that has been multiplexed in the optical multiplexing unit. Part of the light that has leaked into a clad portion propagates through the clad portion at a certain efficiency, and therefore, the light that has failed to be guided into the core so as to propagate through a clad portion propagates up to an end surface of the optical multiplexer, particularly in the case where the optical multiplexer is small.
Such a light propagation through a clad portion is different from the propagation through the total reflections from the interface between the core layer and the clad layer, and is considered to be a propagation through reflections from the surface of the clad layer or the interface between the clad layer and the substrate even though the efficiency thereof is poor, and thus, this situation is described below in reference to
In the case of a conventional optical multiplexer having a problem as described above, the size thereof is relatively large, and therefore, the light beam that has failed to enter into the core layer from a light source has a small effect as stray light. As a result of diligent research by the present inventors, however, it was found for the first time that the effects of the stray light might cause a problem due to the miniaturization of the optical multiplexer.
In the case where the optical waveguide in the middle of the optical multiplexer is linear as illustrated in
In the case of a retina scanning display in particular, the negative effects as described above, that is to say, the effects of light that has propagated through the clad, cannot be neglected when it is necessary for the intensity of light with which a retina is irradiated to be lowered by approximately two digits relative to the light outputted from the semiconductor laser. As a result, such a problem arises when a light beam scanning-type image is formed by using a light beam emitted from an optical multiplexer that the light that has propagated through a clad portion mixes into the original multiplexed signal light so as to cause a color shift, a color irregularity and the like in the image which deteriorates the quality of the image.
An object of the present invention is to provide an optical multiplexer having input optical waveguides, an output optical waveguide and optical multiplexing units, where the effects of light that has failed to enter into the core layer from among light beams emitted from light sources for emitting light beams into the input ends of the input optical waveguides on the multiplexed output can be reduced.
According to one aspect of the invention, an optical multiplexer is provided with: a plurality of input optical waveguides for individually guiding light beams from a plurality of light sources; an optical multiplexing unit for multiplexing a plurality of light beams from the input optical waveguides; and an output optical waveguide for outputting multiplexed light that has been multiplexed in the optical multiplexing unit, wherein light that is in or below the range of 2.5 times greater than the full width at half maximum of the light intensity distribution of the light beam that has not entered into an input optical waveguide from among the respective light beams that have entered into the input ends of the plurality of input optical waveguides does not overlap with the multiplexed light outputted from the output optical waveguide in the output end of the output optical waveguide.
According to another aspect of the invention, a light source module has an optical multiplexer as described above and a plurality of light sources for entering light beams into the optical multiplexer as described above.
According to still another aspect of the invention, a two-dimensional optical scanning device has a light source module as described above and a two-dimensional optical scanning mirror device for two-dimensional scanning with multiplexed light emitted from the light source module as described above.
According to yet another aspect of the invention, an image projection device has a two-dimensional optical scanning device as described above and an image formation unit for projecting onto a projection plane an image scanned with multiplexed light by means of the two-dimensional optical scanning mirror device as described above.
As one effect of the invention, it becomes possible in an optical multiplexer having input optical waveguides, an output optical waveguide and an optical multiplexing unit to reduce the effects of a light beam that has failed to be inputted into an input optical waveguide from among the light beams that have been emitted from the light sources for emitting light beams into the input ends of the input optical waveguides on the multiplexed output.
An example of an optical multiplexer according to an embodiment of the present invention is described in reference to
The light intensity of a light beam that has failed to be inputted into an input optical waveguide 51 through 53 and that is prevented from overlapping with the multiplexed light that has been outputted from the output optical waveguide 9 depends on the sensitivity/tolerance of a target device. When the light intensity is in a range of full width at half maximum of the light intensity distribution at the output end of each input optical waveguide 51 through 53, for example, a clear image can be seen in practice. In the case where a higher definition image is required, the light intensity may be in a range from 1.5 times greater than the full width at half maximum so that the multiplexed output with less noise as compared to the case of full width at half maximum can be gained. Furthermore, the light intensity may be in or below a range of 2.5 times greater than the full width at half maximum, in which case multiplexed output with a further less noise as compared to the case where the range is 1.5 times greater than the full width at half maximum can be gained. Here, the light intensity distribution at the output end of each input optical waveguide 51 through 53 means the light intensity distribution of the spreading in the lateral direction of a light beam that has failed to be inputted into an input optical waveguide 51 through 53, namely, a light beam that has propagated through the clad, from among the respective input optical waveguides 51 through 53, that is to say, the intensity distribution that corresponds to the square of the electrical field intensity of the light beam.
Typically, the wavelengths of light emitted from a plurality of light sources 121 through 123 are different from each other as those of the three primary colors, R (red light), G (green light) and B (blue light), and at least two wavelengths from among the wavelengths emitted from the plurality of light sources 121 through 123 may be the same.
As for the concrete configuration of the optical multiplexing unit 7, as illustrated in
Concretely, an optical waveguide 52 in linear form for guiding green light, an optical waveguide 51 for guiding blue light which optically couples with the optical waveguide 52 for guiding green light through two optical coupling parts 81 and 83, and an optical waveguide 53 for guiding red light which optically couples with the optical waveguide 52 for guiding green light through the portion (82) between the two optical coupling parts 81 and 83 form the optical coupling part (7). In this case, the output end of the optical waveguide 52 for guiding green light is connected to the output optical waveguide 9 so as to output multiplexed light.
Alternatively, as illustrated in
Alternatively, as shown in
The configuration for preventing the outer periphery of the light beam of which the light intensity distribution is in or below a range of at least 2.5 times greater than the full width at half maximum of that of the light beam that has failed to be inputted into the input optical waveguides 51 through 53 from overlapping with the multiplexed light is described again in reference to
Alternatively, the output end 11 of the output optical waveguide 9 may be arranged in the direction of 85° to 95° relative to the optical axis of the optical waveguide in linear form in the optical multiplexing unit 7. In this case, a light beam that has failed to be inputted into the input optical waveguides 51 through 53 and stray light that has leaked out from the optical coupling units 81 through 83 in the optical multiplexing unit 7 so as to propagate through the clad portion 6 can surely be prevented from overlapping. Here, the output end 11 of the output optical waveguide 9 may be inclined by 90° relative to the optical axis of the optical waveguide in linear form in the optical multiplexing unit 7; however, the angle is set to 85° through 95° taking an error in the manufacture or the like into consideration.
Alternatively, the direction in which the light beams are guided in proximity to the input ends of the plurality of input optical waveguides 51 through 53 may be arranged so as to be directed at an angle of 85° through 95° relative to the optical axis of the optical waveguide in linear form in the optical multiplexing unit 7. In this case, the plurality of light sources 121 through 123 may be arranged along one side of the substrate 1 so that the direction in which the light beams are guided in proximity to the input ends of the plurality of input optical waveguides 51 through 53 is at an angle of 85° through 95° relative to the optical axis of the optical waveguide in linear form in the optical multiplexing unit 7. Alternatively, at least one from among the plurality of light sources 121 through 123 may be arranged along a first side of the substrate 1, and the remaining light sources may be arranged along a second side that faces the first side of the remaining input optical waveguides so that the direction in which the light beams are guided in proximity to the input ends of the plurality of input optical waveguides 51 through 53 is at an angle of 85° through 95° relative to the optical axis of the optical waveguide in linear form in the optical multiplexing unit 7.
As for the concrete configuration of the optical waveguides, as illustrated in
Furthermore, a light shielding film for reflecting or absorbing clad mode light may be provided in a location where the multiplexed light from the output end 11 of the output optical waveguide 9 is not shielded in order to more surely prevent a light beam that has failed to be inputted into the input optical waveguides 51 through 53, that is to say, the clad mode light, from overlapping with the output light.
Here, any substrate such as an Si substrate, a glass substrate, a metal substrate or a plastic substrate may be used as the substrate 1. As for the material for the lower clad layer 2, the core layer 31 through 33 and the upper clad layer 4, an SiO2 glass-based material can be used; however, a material other than these, for example, a transparent plastic such as an acrylic resin or other transparent materials, may be used.
In order to form a light source module, as illustrated in
In order to form a two-dimensional optical scanning device, an optical multiplexing unit 27 in the two-dimensional optical scanning device as illustrated in
Here, the optical multiplexer in Example 1 of the present invention is described in reference to
As illustrated in
The wavelength of light emitted from the blue semiconductor laser chip 32 is 450 nm, the total angle of the spread of the beam in the lateral direction (full width at half maximum) is 5 degrees, and the output is 10 mW. The wavelength of light emitted from the green semiconductor laser chip 33 is 520 nm, the total angle of the spread of the beam in the lateral direction is 7 degrees, and the output is 10 mW. The wavelength of light emitted from the red semiconductor laser chip 34 is 638 nm, the total angle of the spread of the beam in the lateral direction is 8 degrees, and the output is 10 mW. Here, the full width at half maximum (FWHM) is an angle at which the light intensity becomes half the intensity of the peak intensity.
The blue semiconductor laser chip 32, the green semiconductor laser chip 33 and the red semiconductor laser chip 34 are mounted in such a manner that the emission areas thereof are respectively matched with the entrance areas of the input optical waveguides 23 through 25 in the lateral direction and in the height direction with a gap vis-a-vis the input ends of the input optical waveguides 23 through 25 being 10 μm.
The structure of the optical multiplexing unit 27 is the same as that illustrated in
Here, all the light beams emitted from the respective semiconductor lasers (32 through 34) are not guided into the core layer due to the difference in the shape between the light beams emitted from the semiconductor lasers (32 through 34) and the cores of the input optical waveguides 23 through 25 in the core layer, and partially leak into the clad portion made of the lower clad layer 22 and the upper clad layer so as to spread at a certain angle and propagate through the clad portion as illustrated in the figure. Concretely, light radiated from the blue semiconductor laser chip 32 propagates through the clad portion while spreading at an angle θB. Light radiated from the green semiconductor laser chip 33 propagates through the clad portion while spreading at an angle θG. In addition, light radiated from the red semiconductor laser chip 34 propagates through the clad portion while spreading at an angle θR.
The blue semiconductor laser chip 32, the green semiconductor laser chip 33, and the red semiconductor laser chip 34 are installed in such a manner that the output end 29 of the output optical waveguide 28 is not irradiated with all of the light radiated from the respective semiconductor laser chips, that is to say, the outer periphery of the entire radiated light does not overlap with the output end 29. Here, the blue semiconductor laser chip 32 and the green semiconductor laser chip 33 are arranged above the center line of the optical multiplexing unit 27, while the red semiconductor laser chip 34 is arranged beneath the center line.
As for the spread of the beam in the lateral direction in the clad portion after entering into the optical multiplexing unit 27, the total angle θR of the spread of the red laser beam in the lateral direction is 5.5 degrees, the total angle 6G of the spread of the green laser beam in the lateral direction is 4.8 degrees, and the total angle θB of the spread of the blue laser beam in the lateral direction is 3.5 degrees. Here, the total angle of the spread of the beam in the lateral direction, that is to say, the full width at half maximum, of the clad mode light is the outer periphery of the radiated light, and thus, this outer periphery of the radiated light is prevented from overlapping with the output end 29.
Incidentally, the relationship between the point at which the light beam from each semiconductor laser reaches an end portion of the substrate and the location of the output end 29 of the output optical waveguide 28 is as follows, taking the length of the Si substrate 21 being 10 mm into consideration. In the case of the red laser beam, it is necessary for the output end 29 to be away from the center of the red laser beam by dR=10 mm×tan (θR/2) or more. In the case of the green laser beam, it is necessary for the output end 29 to be away from the center of the green laser beam by dG=10 mm×tan (θG/2) or more. In the case of the blue laser beam, it is necessary for the output end 29 to be away from the center of the blue laser beam by dB=10 mm×tan (θB/2) or more. In reality, the relationship with the arrangement of the lasers is also involved, and as for the relationship between the point at which the light beam from each semiconductor laser reaches an end portion of the substrate and the location of the output end 29 of the output optical waveguide 28, the output end 29 is at 0.8 mm away from the center of the red laser beam in the case of the red laser beam, the output end 29 is at 0.8 mm away from the center of the green laser beam in the case of the green laser beam, and the output end 29 is at 1.3 mm away from the center of the blue laser beam in the case of the blue laser beam. Here, there is a gap vis-a-vis the end surface (this is set at 10 μm), and therefore, the size of a light beam in the input end is not a point and has a finite size; however, the size is so small as to be negligible as compared to the size of the optical multiplexing unit 27, and thus is regarded as a point for calculating dR, dG and dB.
In this manner, the outer periphery of each radiated beam can be prevented from overlapping with the output end 29 so that the ratio of the clad mode light that has mixed with the multiplexed signal light and propagated through the clad portion can be suppressed to 1% or less. Here, the outer periphery is at the full width at half maximum; however, in the case where it is necessary to further reduce noise light in order to gain an image with high definition, the outer periphery may be at 1.5 times greater than the full width at half maximum, and furthermore, in the case where an image with higher definition is necessary, the outer periphery may be 2.5 times greater than the full width at half maximum, and thus, the greater the outer periphery is as compared to the full width at half maximum, the smaller the effects of noise light become.
Next, the optical multiplexer in Example 2 of the present invention is described in reference to
Here, an Si substrate having a thickness of 1 mm, a length of 10 mm, a width of 5.3 mm and a (100) surface is used as the Si substrate 21. The wavelength of light emitted from the red LED chip is 640 nm with the total angle of the spread of the beam in the lateral direction being 16 degrees and the output being 5 mW. The wavelength of light emitted from the green LED chip is 530 nm with the total angle of the spread of the beam in the lateral direction being 14 degrees and the output being 5 mW. The wavelength of light emitted from the blue LED chip is 450 nm with the total angle of the spread of the beam in the lateral direction being 10 degrees and the output being 5 mW.
As for the spread of the beam in the lateral direction in the clad portion after entering into the optical multiplexing unit 27, the total angle θR of the spread of the red beam in the lateral direction is 11 degrees, the total angle θG of the spread of the green beam in the lateral direction is 9.6 degrees, and the total angle θB of the spread of the blue beam in the lateral direction is 6.9 degrees. Here, the total angle of the spread of the beam in the lateral direction, that is to say, the full width at half maximum, of the clad mode light is the outer periphery of the radiated light, and this outer periphery of the radiated light is prevented from overlapping with the output end 29.
Incidentally, the relationship between the point at which the light beam from each LED reaches an end portion of the substrate and the location of the output end 29 of the output optical waveguide 28 is as follows, taking the length of the Si substrate 21 being 10 mm into consideration. In the case of the red beam, it is necessary for the output end 29 to be away from the center of the red beam by dR=10 mm×tan (θR/2) or more. In the case of the green beam, it is necessary for the output end 29 to be away from the center of the green beam by dG=10 mm×tan (θG/2) or more. In the case of the blue beam, it is necessary for the output end 29 to be away from the center of the blue beam by dB=10 mm×tan (θB/2) or more. In reality, the relationship with the arrangement of LEDs is also involved, and thus, as for the relationship between the point at which the light beam from each LED reaches an end portion of the substrate and the location of the output end 29 of the output optical waveguide 28, the output end 29 is away from the center of the red beam by 1.6 mm in the case of the red beam, away from the center of the green beam by 1.6 mm in the case of the green beam, and away from the center of the blue beam by 2.1 mm in the case of the blue beam.
As described above, the outer periphery of each radiated beam is prevented from overlapping with the output end 29 in the case where light-emitting diodes are used as the light sources, and as a result, the ratio of the clad mode light that has mixed with the multiplexed signal light and propagated through the clad portion can be suppressed to 1% or less. Here, the outer periphery is the full width at half maximum; however, the outer periphery may be 1.5 times greater than the full width at half maximum of the clad mode light in the case where it is necessary to further reduce the noise light in order to gain an image with high definition, and furthermore, in the case where an image with higher definition is necessary, the outer periphery may be 2.5 times greater than the full width at half maximum, and thus, the greater the outer periphery is as compared to the full width at half maximum, the smaller the effects of noise light become.
Next, the optical multiplexer in Example 3 of the present invention is described in reference to
As illustrated in
The wavelength of light emitted from the blue semiconductor laser chip 32 is 450 nm, the total angle of the spread of the beam in the lateral direction (full width at half maximum) is 5 degrees, and the output is 10 mW. The wavelength of light emitted from the green semiconductor laser chip 33 is 520 nm, the total angle of the spread of the beam in the lateral direction is 7 degrees, and the output is 10 mW. The wavelength of light emitted from the red semiconductor laser chip 34 is 638 nm, the total angle of the spread of the beam in the lateral direction is 8 degrees, and the output is 10 mW. Here, the full width at half maximum (FWHM) is an angle at which the light intensity becomes half the intensity of the peak intensity.
The blue semiconductor laser chip 32, the green semiconductor laser chip 33 and the red semiconductor laser chip 34 are mounted in such a manner that the emission areas thereof are respectively matched with the entrance areas of the input optical waveguides 23 through 25 in the lateral direction and in the height direction with a gap vis-a-vis the input ends of the input optical waveguides 23 through 25 being 10 μm. Here, a light shielding film 35 is provided so that a window of 4 μm×4 μm is created over the core of 2 μm×2 μm in the core layer on the output end 29 of the output optical waveguide 28 in the optical multiplexer. The light shielding film 35 is formed by applying a lift-off method to a vapor-deposited Al film having a thickness of 100 nm. In the case where the light shielding film 35 is formed as a reflection film, the material thereof is not limited to an Al film and a film of various types of metals can be used, or a light-absorbing film such as a resin film that includes carbon black may be used in place of the reflection film. Here, the structure of the optical multiplexing unit 27 is exactly the same as in Example 1.
In this case as well, the outer periphery of each radiated beam can be prevented from overlapping with the output end 29 so that the ratio of the clad mode light that has mixed with the multiplexed signal light and propagated through the clad portion can be suppressed to 1% or less. Here, the outer periphery is the full width at half maximum; however, the outer periphery may be 1.5 times greater than the full width at half maximum of the clad mode light in the case where it is necessary to further reduce the noise light in order to gain an image with high definition, and furthermore, in the case where an image with higher definition is necessary, the outer periphery may be 2.5 times greater than the full width at half maximum, and thus, the greater the outer periphery is as compared to the full width at half maximum, the smaller the effects of noise light become.
Next, the optical multiplexer in Example 4 of the present invention is described in reference to
As illustrated in
The wavelength of light emitted from the blue semiconductor laser chip 32 is 450 nm, the total angle of the spread of the beam in the lateral direction (full width at half maximum) is 5 degrees, and the output is 10 mW. The wavelength of light emitted from the green semiconductor laser chip 33 is 520 nm, the total angle of the spread of the beam in the lateral direction is 7 degrees, and the output is 10 mW. The wavelength of light emitted from the red semiconductor laser chip 34 is 638 nm, the total angle of the spread of the beam in the lateral direction is 8 degrees, and the output is 10 mW.
The structure of the optical multiplexing unit 36 is the same as that illustrated in
In this case as well, in the same manner as in Example 2, LED chips may be used as the light sources instead of the semiconductor laser diode chips, or in the same manner as in Example 3, a light shielding film may be provided in proximity to the output end 29 of the output optical waveguide 28.
Next, the following description relates to the optical multiplexer in Example 5 of the present invention, which is the same as the above-described optical multiplexer in Example 4 except that the light beams inputted into the optical multiplexing unit are modified.
As illustrated in
The wavelength of light emitted from the blue semiconductor laser chip 32 is 450 nm, the total angle of the spread of the beam in the lateral direction (full width at half maximum) is 5 degrees, and the output is 10 mW. The wavelength of light emitted from the green semiconductor laser chip 33 is 520 nm, the total angle of the spread of the beam in the lateral direction is 7 degrees, and the output is 10 mW. The wavelength of light emitted from the red semiconductor laser chip 34 is 638 nm, the total angle of the spread of the beam in the lateral direction is 8 degrees, and the output is 10 mW.
The structure of the optical multiplexing unit 36 is the same as that illustrated in
In this case as well, in the same manner as in Example 2, LED chips may be used as the light sources instead of the semiconductor laser diode chips, or in the same manner as in Example 3, a light shielding film may be provided in proximity to the output end 29 of the output optical waveguide 28.
Next, the optical multiplexer in Example 6 of the present invention is described in reference to
In each optical waveguide in Example 6 of the present invention, as illustrated in
In this case as well, the outer periphery of each radiated beam is prevented from overlapping with the output end 29, and as a result, the ratio of the clad mode light that has mixed with the multiplexed signal light and propagated through the clad portion can be suppressed to 1% or less. Here again, the outer periphery may be defined as being 1.5 times greater than the full width at half maximum of the clad mode light or 2.5 times greater than the full width at half maximum, and thus, the greater the outer periphery is as compared to the full width at half maximum, the smaller the effects of noise light become. In addition, in the same manner as in Example 2, LED chips may be used as the light sources instead of the semiconductor laser diode chips; in the same manner as in Example 3, a light shielding film may be provided in proximity to the output end 29 of the output optical waveguide 28; or the optical multiplexing unit may have the same structure as in Example 4 or 5.
Next, the optical multiplexer in Example 7 of the present invention is described in reference to
As illustrated in
In Example 7 of the present invention, the optical axis of the green semiconductor laser chip 33 is made to agree with the center axis of the optical multiplexing unit 27, and at the same time, the output optical waveguide 28 is bent so that the gap between the input optical waveguide 24 and the output optical waveguide 28 in proximity to the output end 29 is set to 1.0 mm, and thus, the location of the output end 29 is prevented from overlapping with the outer peripheries of the respective beams of clad mode light.
In this case as well, the outer periphery of each radiated beam can be prevented from overlapping with the output end 29 so that the ratio of the clad mode light that has mixed with the multiplexed signal light and propagated through the clad portion can be suppressed to 1% or less. In this case, the light that has leaked out from an optical coupling unit in the optical multiplexing unit 27 does not overlap with the multiplexed light emitted from the output end 29, and therefore, the effects of noise light can further be reduced. Here again, the outer periphery may be defined as being 1.5 times greater than the full width at half maximum of the clad mode light or 2.5 times greater than the full width at half maximum, and thus, the greater the outer periphery is as compared to the full width at half maximum, the smaller the effects of noise light become. In addition, in the same manner as in Example 2, LED chips may be used as the light sources instead of the semiconductor laser diode chips; in the same manner as in Example 3, a light shielding film may be provided in proximity to the output end 29 of the output optical waveguide 28; or the optical multiplexing unit may have the same structure as in Example 4 or 5.
Next, the optical multiplexer in Example 8 of the present invention is described in reference to
As illustrated in
In Example 8, as for the size of the Si substrate 21, the length is 13.5 mm and the width is 4 mm. In this case, the outer periphery of the clad mode light from the blue semiconductor laser chip 32 is prevented from overlapping with the output end 29 of the output optical waveguide 28. Here, the gap between the input end of the input optical waveguide 23 and the output end 29 of the output optical waveguide 28 is 1.0 mm in the arrangement, the gap between the input end of the input optical waveguide 24 and the output end 29 of the output optical waveguide 28 is 2.0 mm in the arrangement, and the gap between the input end of the input optical waveguide 25 and the output end 29 of the output optical waveguide 28 is 3.0 mm in the arrangement.
In this case as well, the outer periphery of each radiated beam can be prevented from overlapping with the output end 29 so that the ratio of the clad mode light that has mixed with the multiplexed signal light and propagated through the clad portion can be suppressed to 1% or less. In this case, the light that has leaked out from an optical coupling unit in the optical multiplexing unit 27 does not overlap with the multiplexed light emitted from the output end 29, and therefore, the effects of noise light can further be reduced. Here again, the outer periphery may be defined as being 1.5 times greater than the full width at half maximum of the clad mode light or 2.5 times greater than the full width at half maximum, and thus, the greater the outer periphery is as compared to the full width at half maximum, the smaller the effects of noise light become. In addition, in the same manner as in Example 2, LED chips may be used as the light sources instead of the semiconductor laser diode chips; in the same manner as in Example 3, a light shielding film may be provided in proximity to the output end 29 of the output optical waveguide 28 by way of precaution; or the optical multiplexing unit may have the same structure as in Example 4 or 5.
Next, the optical multiplexer in Example 9 of the present invention is described in reference to
As illustrated in
In Example 9 of the present invention, as illustrated in
In the case where each clad portion surrounds a core and lies only in proximity to the lower clad layer, light that has failed to enter into the input optical waveguides 23 through 25 propagates through the lower clad layer so as to be guided to the optical multiplexing unit 27 together with light in the core layer. This takes place because the amount of light that propagates through this clad layer cannot be neglected in the case where the size of the optical multiplexer is small, even when the substrate beneath the lower clad layer has a refractive index that is greater than that of the lower clad layer or is a light absorbing layer.
Accordingly, light leaks out to the clad portion having layers in the connection portion between an upper clad layer 37 through 39 and the upper clad layer 26 so as to disseminate, and the shape of the lower clad in the lower clad layer is determined so that the output end 29 of the output optical waveguide 28 is not irradiated with the outer periphery of the radiated light that has disseminated. That is to say, light that was emitted from each semiconductor laser and has propagated through an individual clad portion spreads in the lateral direction at a certain angle θ in the connection portion between an upper clad layer 37 through 39 and the upper clad layer 26 after the upper clad layer 37 through 39 and the upper clad layer 26 are connected so as to provide layers in the clad portion. Accordingly, in this case as well, the optical coupling unit 27 is arranged so that the outer periphery of each light beam radiated from the connection portion between the upper clad layer 37 through 39 and the upper clad layer 26 does not overlap with the multiplexed light emitted from the output end 29 of the output optical waveguide 28. Here, the length of the perpendicular from the output end 29 to the center axis of the blue laser beam that spreads from the connection portion between the upper clad layer 37 through 39 and the upper clad layer 26 is 1.75 mm. The length of the perpendicular from the output end 29 to the center axis of the green laser beam that spreads from the connection portion between the upper clad layer 37 through 39 and the upper clad layer 26 is 1.75 mm. The length of the perpendicular from the output end 29 to the center axis of the red laser beam that spreads from the connection portion between the upper clad layer 37 through 39 and the upper clad layer 26 is 0.8 mm.
In this case as well, the outer periphery of each radiated beam is prevented from overlapping with the output end 29, and as a result, the ratio of the clad mode light that has mixed with the multiplexed signal light and propagated through the clad portion can be suppressed to 1% or less. Here again, the outer periphery may be defined as being 1.5 times greater than the full width at half maximum of the clad mode light or 2.5 times greater than the full width at half maximum, and thus, the greater the outer periphery is as compared to the full width at half maximum, the smaller the effects of noise light become. In addition, in the same manner as in Example 2, LED chips may be used as the light sources instead of the semiconductor laser diode chips; in the same manner as in Example 3, a light shielding film may be provided in proximity to the output end 29 of the output optical waveguide 28; or the optical multiplexing unit may have the same structure as in Example 4 or 5.
Next, the optical multiplexer in Example 10 of the present invention is described in reference to
As illustrated in
In Example 10 of the present invention, as illustrated in
In this case, it is desirable for the active layer portion of a first semiconductor laser chip to be prevented from being irradiated with the light beam emitted from a second semiconductor laser chip, where the first and second semiconductor laser chips are any two from among the blue semiconductor laser chip 32, the green semiconductor laser chip 33 and the red semiconductor laser chip 34 that face each other. The configuration where the active layer portion of a first semiconductor laser chip that faces a second semiconductor laser chip is prevented from being irradiated with the light beam emitted from the second semiconductor laser chip is more desirable because such a configuration makes the oscillation of each semiconductor laser chip stable, and thus makes the semiconductor laser chips function as multiplexing light sources providing a high-speed, stable signal operation. Here, even in the case where the active layer portion of a first semiconductor laser chip is irradiated with the light beam emitted from a second semiconductor laser chip, the oscillations of the semiconductor lasers are still stable, and thus, the semiconductors function as multiplexing light sources providing a high-speed, stable signal operation at least when the wavelength of the second semiconductor laser is longer than the wavelength of the first semiconductor laser. Here, the gap between the input end of the input optical waveguide 23 and the output end 29 of the output optical waveguide 28 is 6.0 mm in the arrangement, the gap between the input end of the input optical waveguide 24 and the output end 29 of the output optical waveguide 28 is 6.5 mm in the arrangement, and the gap between the input end of the input optical waveguide 25 and the output end 29 of the output optical waveguide 28 is 5.5 mm in the arrangement.
In this case as well, the outer periphery of each radiated beam is prevented from overlapping with the output end 29, and as a result, the ratio of the clad mode light that has mixed with the multiplexed signal light and propagated through the clad portion can be suppressed to 1% or less. In this case, the light that has leaked out from an optical coupling unit in the optical multiplexing unit 27 does not overlap with the multiplexed light emitted from the output end 29, and therefore, the effects of noise light can further be reduced. In addition, the modulation of each semiconductor laser was increased as high as 100 MHz without causing a signal distortion. Here again, the outer periphery may be defined as being 1.5 times greater than the full width at half maximum of the clad mode light or 2.5 times greater than the full width at half maximum, and thus, the greater the outer periphery is as compared to the full width at half maximum, the smaller the effects of noise light become. Furthermore, in the same manner as in Example 2, LED chips may be used as the light sources instead of the semiconductor laser diode chips; in the same manner as in Example 3, a light shielding film may be provided in proximity to the output end 29 of the output optical waveguide 28; or the optical multiplexing unit may have the same structure as in Example 4 or 5.
Next, the optical multiplexer in Example 11 of the present invention is described in reference to
As illustrated in
In Example 11 of the present invention as well, as illustrated in
In Example 11 of the present invention, the optical axis of the output optical waveguide 28 is inclined by 85° to 95° relative to the center axis of the optical multiplexing unit 27 by means of a waveguide-type reflection mirror at 0.5 mm to the rear of the output end of the optical multiplexing unit 27. Here, the inclination is 90°. In this case, the waveguide is bent at a right angle by using a waveguide-type reflection mirror; however, a bent waveguide having a curvature may of course be used. Here, the gap between the input end of the input optical waveguide 23 and the output end 29 of the output optical waveguide 28 is 6.0 mm in the arrangement, the gap between the input end of the input optical waveguide 24 and the output end 29 of the output optical waveguide 28 is 6.5 mm in the arrangement, and the gap between the input end of the input optical waveguide 25 and the output end 29 of the output optical waveguide 28 is 5.5 mm in the arrangement.
In the same manner as in Example 10, it is desirable for the active layer portion of a first semiconductor laser chip to be prevented from being irradiated with the light beam emitted from a second semiconductor laser chip, where the first and second semiconductor laser chips are any two from among the blue semiconductor laser chip 32, the green semiconductor laser chip 33 and the red semiconductor laser chip 34 that face each other. The configuration where the active layer portion of a first semiconductor laser chip that faces a second semiconductor laser chip is prevented from being irradiated with the light beam emitted from the second semiconductor laser chip is more desirable because such a configuration makes the oscillation of each semiconductor laser chip stable, and thus makes the semiconductor laser chips function as multiplexing light sources providing a high-speed, stable signal operation. Here, even in the case where the active layer portion of a first semiconductor laser chip is irradiated with the light beam emitted from a second semiconductor laser chip, the oscillations of the semiconductor lasers are still stable, and thus, the semiconductors function as multiplexing light sources providing a high-speed, stable signal operation at least when the wavelength of the second semiconductor laser is longer than the wavelength of the first semiconductor laser.
In this case as well, the outer periphery of each radiated beam is prevented from overlapping with the output end 29, and as a result, the ratio of the clad mode light that has mixed with the multiplexed signal light and propagated through the clad portion can be suppressed to 1% or less. In this case, the light that has leaked out from an optical coupling unit in the optical multiplexing unit 27 does not overlap with the multiplexed light emitted from the output end 29, and therefore, the effects of noise light can further be reduced. In addition, the modulation of each semiconductor laser was increased as high as 100 MHz without causing a signal distortion. Here again, the outer periphery may be defined as being 1.5 times greater than the full width at half maximum of the clad mode light or 2.5 times greater than the full width at half maximum, and thus, the greater the outer periphery is as compared to the full width at half maximum, the smaller the effects of noise light become. Furthermore, in the same manner as in Example 2, LED chips may be used as the light sources instead of the semiconductor laser diode chips; in the same manner as in Example 3, a light shielding film may be provided in proximity to the output end 29 of the output optical waveguide 28; or the optical multiplexing unit may have the same structure as in Example 4 or 5.
Next, the optical multiplexer in Example 12 of the present invention is described in reference to
As illustrated in
In Example 12 of the present invention, as illustrated in
In this case, the blue semiconductor laser chip 32, the green semiconductor laser chip 33 and the red semiconductor laser chip 34 are arranged along the same side of the substrate, and therefore, the active layer portion of a first semiconductor laser chip is not irradiated with the light beam emitted from a second semiconductor laser chip, where the first and second semiconductor laser chips are any two of the blue semiconductor laser chip 32, the green semiconductor laser chip 33 and the red semiconductor laser chip 34 that face each other. Accordingly, a more desirable configuration is gained where the oscillations of the respective semiconductor laser chips are stable, and the semiconductor laser chips function as multiplexed light sources providing a high-speed, stable signal operation.
In this case as well, the outer periphery of each radiated beam is prevented from overlapping with the output end 29, and as a result, the ratio of the clad mode light that has mixed with the multiplexed signal light and propagated through the clad portion can be suppressed to 1% or less. In this case, the light that has leaked out from an optical coupling unit in the optical multiplexing unit 27 does not overlap with the multiplexed light emitted from the output end 29, and therefore, the effects of noise light can further be reduced. In addition, the modulation of each semiconductor laser was increased as high as 100 MHz without causing a signal distortion. Here again, the outer periphery may be defined as being 1.5 times greater than the full width at half maximum of the clad mode light or 2.5 times greater than the full width at half maximum, and thus, the greater the outer periphery is as compared to the full width at half maximum, the smaller the effects of noise light become. Furthermore, in the same manner as in Example 2, LED chips may be used as the light sources instead of the semiconductor laser diode chips.
Next, the optical multiplexer in Example 13 of the present invention is described in reference to
As illustrated in
The structure of the optical multiplexing unit in Example 13 of the present invention is the same that is illustrated in
In Example 13 of the present invention, light beams having the same wavelength can be multiplexed so as to increase the output, and therefore, the optical multiplexer can be applied to an image formation device that requires intense light such as an HUD (head-up display).
In this case as well, the outer periphery of each radiated beam is prevented from overlapping with the output end 29, and as a result, the ratio of the clad mode light that has mixed with the multiplexed signal light and propagated through the clad portion can be suppressed to 1% or less. In this case, the light that has leaked out from an optical coupling unit in the optical multiplexing unit 27 does not overlap with the multiplexed light emitted from the output end 29, and therefore, the effects of noise light can further be reduced. Here again, the outer periphery may be defined as being 1.5 times greater than the full width at half maximum of the clad mode light or 2.5 times greater than the full width at half maximum, and thus, the greater the outer periphery is as compared to the full width at half maximum, the smaller the effects of noise light become. Furthermore, in the same manner as in Example 2, LED chips may be used as the light sources instead of the semiconductor laser diode chips; in the same manner as in Example 3, a light shielding film may be provided in proximity to the output end 29 of the output optical waveguide 28.
Next, the light source module in Example 14 of the present invention is described in reference to
The wavelength of light emitted from the blue semiconductor laser chip 32 is 450 nm, the total angle of the spread of the beam in the lateral direction (full width at half maximum) is 5 degrees, and the output is 10 mW. The wavelength of light emitted from the green semiconductor laser chip 33 is 520 nm, the total angle of the spread of the beam in the lateral direction is 7 degrees, and the output is 10 mW. The wavelength of light emitted from the red semiconductor laser chip 34 is 638 nm, the total angle of the spread of the beam in the lateral direction is 8 degrees, and the output is 10 mW. Here, the full width at half maximum (FWHM) is an angle at which the light intensity becomes half the intensity of the peak intensity.
The blue semiconductor laser chip 32, the green semiconductor laser chip 33 and the red semiconductor laser chip 34 are mounted in such a manner that the emission areas thereof are respectively matched with the entrance areas of the input optical waveguides 23 through 25 in the lateral direction and in the height direction with a gap vis-a-vis the input ends of the input optical waveguides 23 through 25 being 10 μm.
The structure of the optical multiplexing unit 27 is the same as that illustrated in
Here, all the light beams emitted from the respective semiconductor lasers (32 through 34) are not guided into the core layer due to the difference in the shape between the light beams emitted from the semiconductor lasers (32 through 34) and the cores of the input optical waveguides 23 through 25 in the core layer, and partially leak into the clad portion made of the lower clad layer 22 and the upper clad layer so as to spread at a certain angle and propagate through the clad portion as illustrated in the figure. Concretely, light radiated from the blue semiconductor laser chip 32 propagates through the clad portion while spreading at an angle θB. Light radiated from the green semiconductor laser chip 33 propagates through the clad portion while spreading at an angle θG. In addition, light radiated from the red semiconductor laser chip 34 propagates through the clad portion while spreading at an angle θR.
The blue semiconductor laser chip 32, the green semiconductor laser chip 33, and the red semiconductor laser chip 34 are installed in such a manner that the output end 29 of the output optical waveguide 28 is not irradiated with all of the light radiated from the respective semiconductor laser chips, that is to say, the outer periphery of the entire radiated light does not overlap with the output end 29. Here, the blue semiconductor laser chip 32 and the green semiconductor laser chip 33 are arranged above the center line of the optical multiplexing unit 27, while the red semiconductor laser chip 34 is arranged beneath the center line.
As for the spread of the beam in the lateral direction in the clad portion after entering into the optical multiplexing unit 27, the total angle θR of the spread of the red laser beam in the lateral direction is 5.5 degrees, the total angle θG of the spread of the green laser beam in the lateral direction is 4.8 degrees, and the total angle θB of the spread of the blue laser beam in the lateral direction is 3.5 degrees. Here, the total angle of the spread of the beam in the lateral direction, that is to say, the full width at half maximum, of the clad mode light is the outer periphery of the radiated light, and thus, this outer periphery of the radiated light is prevented from overlapping with the output end 29.
Incidentally, the relationship between the point at which the light beam from each semiconductor laser reaches an end portion of the substrate and the location of the output end 29 of the output optical waveguide 28 is as follows, taking the length of the Si substrate 21 being 10 mm into consideration. In the case of the red laser beam, it is necessary for the output end 29 to be away from the center of the red laser beam by dR=10 mm×tan (θR/2) or more. In the case of the green laser beam, it is necessary for the output end 29 to be away from the center of the green laser beam by dG=10 mm×tan (θG/2) or more. In the case of the blue laser beam, it is necessary for the output end 29 to be away from the center of the blue laser beam by dB=10 mm×tan (θB/2) or more. In reality, the relationship with the arrangement of the lasers is also involved, and as for the relationship between the point at which the light beam from each semiconductor laser reaches an end portion of the substrate and the location of the output end 29 of the output optical waveguide 28, the output end 29 is at 0.8 mm away from the center of the red laser beam in the case of the red laser beam, the output end 29 is at 0.8 mm away from the center of the green laser beam in the case of the green laser beam, and the output end 29 is at 1.3 mm away from the center of the blue laser beam in the case of the blue laser beam. Here, there is a gap vis-a-vis the end surface (this is set at 10 μm), and therefore, the size of a light beam in the input end is not a point and has a finite size; however, the size is so small as to be negligible as compared to the size of the optical multiplexing unit 27, and thus is regarded as a point for calculating dR, dG and dB.
In this manner, the outer periphery of each radiated beam can be prevented from overlapping with the output end 29 so that the ratio of the clad mode light that has mixed with the multiplexed signal light and propagated through the clad portion can be suppressed to 1% or less. Here, the outer periphery is at the full width at half maximum; however, in the case where it is necessary to further reduce noise light in order to gain an image with high definition, the outer periphery may be at 1.5 times greater than the full width at half maximum, and furthermore, in the case where an image with higher definition is necessary, the outer periphery may be 2.5 times greater than the full width at half maximum, and thus, the greater the outer periphery is as compared to the full width at half maximum, the smaller the effects of noise light become.
In this case as well, in the same manner as in Example 2, LED chips may be used as the light sources instead of the semiconductor laser diode chips; in the same manner as in Example 3, a light shielding film may be provided in proximity to the output end 29 of the output optical waveguide 28; or the optical multiplexing unit may have the same structure as in Example 4 or 5.
Next, the light source module in Example 15 of the present invention is described in reference to
In this case, microscopic sphere lenses having a focal distance of 0.54 mm and a sphere diameter of 1 mm are used as the lenses 46 through 48. Light beams that have been condensed by the microscopic sphere lenses are inputted into input optical waveguides 23 through 25. The condenser lenses are not limited to microscopic sphere lenses, and GRIN (gradient index type) lenses may be used.
In Example 15 as well, the outer periphery of each radiated beam is prevented from overlapping with the output end 29, and as a result, the ratio of the clad mode light that has mixed with the multiplexed signal light and propagated through the clad portion can be suppressed to 1% or less. In this case as well, in the same manner as in Example 2, LED chips may be used as the light sources instead of the semiconductor laser diode chips; in the same manner as in Example 3, a light shielding film may be provided in proximity to the output end 29 of the output optical waveguide 28; or the optical multiplexing unit may have the same structure as in Example 4 or 5.
Next, the light source module in Example 16 of the present invention is described in reference to
At the output ends of the optical fibers 53 through 55, the wavelength of light emitted as a red beam is 640 nm with the total angle of the spread of the beam in the lateral direction being 5 degrees and the output being 5 mW. The wavelength of light emitted as a green beam is 530 nm with the total angle of the spread of the beam in the lateral direction being 5 degrees and the output being 5 mW. The wavelength of light emitted as a blue beam is 450 nm with the total angle of the spread of the beam in the lateral direction being 5 degrees and the output being 5 mW.
After the respective beams have entered into the optical multiplexer, the total angle θR of the spread of the red beam in the lateral direction, the total angle θG of the spread of the green beam in the lateral direction and the total angle θB of the spread of the blue beam in the lateral direction are all 3.5 degrees in the clad portion. Here, the gap between the input end of the input optical waveguide 23 and the output end 29 of the output optical waveguide 28 is 1.3 mm in the arrangement, the gap between the input end of the input optical waveguide 24 and the output end 29 of the output optical waveguide 28 is 0.8 mm in the arrangement, and the gap between the input end of the input optical waveguide 25 and the output end 29 of the output optical waveguide 28 is 0.8 mm in the arrangement.
In Example 16 as well, the outer periphery of each radiated beam is prevented from overlapping with the output end 29, and as a result, the ratio of the clad mode light that has mixed with the multiplexed signal light and propagated through the clad portion can be suppressed to 1% or less. In this case as well, in the same manner as in Example 2, LED chips may be used as the light sources instead of the semiconductor laser diode chips; in the same manner as in Example 3, a light shielding film may be provided in proximity to the output end 29 of the output optical waveguide 28; the optical multiplexing unit may have the same structure as in Example 4 or 5; or condenser lenses may be provided between the optical fibers 53 through 55 and the input optical waveguides 23 through 25.
Next, the two-dimensional optical scanning device in Example 17 of the present invention is described in reference to
Next, the image formation device in Example 18 of the present invention is described in reference to
In this image formation device, in the same manner as in the prior art, a control unit 70 has a sub-control unit 71, an operation unit 72, an external interface (I/F) 73, an R laser driver 74, a G laser driver 75, a B laser driver 76 and a two-dimensional scanning driver 77. The sub-control unit 71 is formed of a microcomputer that includes a CPU, a ROM, a RAM and the like. The sub-control unit 71 generates an R signal, a G signal, a B signal, a horizontal signal and a vertical signal that become elements for synthesizing an image on the basis of the image data supplied from an external apparatus such as a PC via the external I/F 73. The sub-control unit 71 transmits the R signal to the R laser driver 74, the G signal to the G laser driver 75, and the b signal to the B laser driver 76, respectively. In addition, the sub-control unit 71 transmits the horizontal signal and the vertical signal to the two-dimensional scanning driver 77, and controls the current to be applied to the electromagnetic coil 64 so as to control the operation of the movable mirror unit 63.
The R laser driver 74 drives the red semiconductor laser chip 34 so that a red laser beam of which the optical quantity corresponds to the R signal from the sub-control unit 71 is generated. The G laser driver 75 drives the green semiconductor laser chip 33 so that a green laser beam of which the optical quantity corresponds to the G signal from the sub-control unit 71. The B laser driver 76 drives the blue semiconductor laser chip 32 so that a blue laser beam of which the optical quantity corresponds to the B signal from the sub-control unit 71 is generated. It becomes possible to synthesize a laser beam having a desired color by adjusting the intensity ratio between the laser beams of the respective colors.
The respective laser beams generated in the blue semiconductor laser chip 32, the green semiconductor laser chip 33 and the red semiconductor laser chip 34 are multiplexed in the optical multiplexing unit 27 in the optical multiplexer, and after that reflected from the movable mirror unit 63 for two-dimensional scanning. An image is formed on a retina 80 as a result of scanning with the multiplexed laser beam that has been reflected from a concave reflection mirror 78 and passed through a pupil 79.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-196990 | Oct 2018 | JP | national |
This application is a continuation of International Application No. PCT/JP2019/003660, filed on Feb. 1, 2019, now pending, herein incorporated by reference. Further, this application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2018-196990, filed on Oct. 18, 2018, the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2019/003660 | Feb 2019 | US |
| Child | 17159643 | US |
