Patent Description:
As disclosed in Patent Document <NUM> (<CIT>), for example, an illumination device including a light source and a hologram element is known. In the illumination device disclosed in Patent Document <NUM>, the hologram element diffracts a light (light beam) from the light source, so that a road surface can be illuminated with a desired pattern. In the illumination device disclosed in Patent Document <NUM>, a laser light generated by the single light source is diffracted by the single hologram element.

When a light source that projects a laser light is used, an area to be illuminated can be brightly illuminated. However, when a person looks straight at the illumination light from the illumination device, his/her eyes may be damaged. In consideration of safety, a hologram element preferably has a large planar dimension so that the hologram element can have a large incident area (spot area) for a light-source light. However, the large planar dimension of the hologram element disadvantageously enlarges a size of the illumination device as a whole. The problem of enlargement in size of the illumination device becomes more serious in an illumination device that performs illumination with a specific color by means of additive color mixture using lights of various wavelength ranges.

Document <CIT> discloses an optical pickup device comprising a first light source emitting a first light beam, a second light source emitting a second light beam, a third light source emitting a third light beam, and an objective optical element, wherein the optical surface of the objective optical element has at least a central region and a peripheral region, the central region has a first optical path difference imparting structure and the peripheral region has a second optical path difference imparting structure, first best focus and second best focus are formed by the third light beam passed through the first optical path difference imparting structure, a spot central part, a spot middle part and a spot peripheral part are formed in a spot which is formed on the information recording surface of a third optical disk by the third light beam passed through the objective optical element, the spot central part is used for recording and/or reproducing the information on the third optical disk but the spot middle part and the spot peripheral part are not used for recording and/or reproducing the information on the third optical disk, and the spot peripheral part is formed on the information recording surface of the third optical disc by the third light beam passed through the second optical path difference imparting structure.

Document <CIT> discloses a vehicle lighting fixture configured to form a predetermined light distribution pattern by superimposing N partial light distribution patterns, wherein N is a natural number of <NUM> or more. The vehicle lighting fixture can include a light intensity changing unit configured to change a light intensity of at least one partial light distribution pattern out of the N partial light distribution patterns.

Document <CIT> discloses an imaging apparatus including: an imaging device that images an infrared image using reflected light from a subject to which infrared light is irradiated, and, in addition, images a color image using the reflected light from the subject to which patterns formed by combining a plurality of colors of visible laser light are projected; and a signal processing unit that colors the infrared image using color information which is determined depending on an intensity of the reflected light of the plurality of colors of visible laser light from the color image.

Document <CIT> discloses an optical device having: a laser light source for emitting a laser light; a scanning unit for reflecting the laser light emitted from the laser light source and emitting a scanning light; an optical element on which the scanning light is incident, the optical element illuminating a road by emitting a light; an imaging unit for capturing an image of the conditions around a vehicle; and a determining unit for determining whether a unique structure is present by analyzing the image captured by the imaging unit, the optical device suppressing or increasing illumination toward the unique structure after it is determined that a unique structure is present using the determination unit.

Document <CIT> discloses a laser lighting optical system composed of, at least, a laser array light source and a fly's-eye lens integrator, wherein the number of divides of the fly's-eye lenses is the divisor of the number of laser arrays in the direction of the laser array.

Document <CIT> discloses an optical device mounted to a movable body for providing light on a road surface. The optical device includes: a laser source for emitting a laser light; an optical element for receiving the laser light emitted from the laser source and emitting the light to the road surface; and a navigation unit for acquiring a route for the movable body to a destination on the basis of the current position of the movable body and map information.

The embodiment of the disclosure has been made in consideration of the above circumstances. The object of the present invention is to reduce a size of an illumination device while considering safety.

An illumination device according to the embodiment of the disclosure comprises:.

In the illumination device according to the embodiment of the disclosure, after the lights emitted from the respective laser light sources have been diffracted by the diffractive optical elements corresponding to the respective laser light sources, the lights may illuminate areas that are at least partially overlapped.

In the illumination device according to the embodiment of the disclosure, after the lights emitted from the respective laser light sources have been diffracted by the diffractive optical elements corresponding to the respective laser light sources, the lights may illuminate the same area to be illuminated.

In the illumination device according to the embodiment of the disclosure, after the lights emitted from the respective laser light sources have been diffracted by the diffractive optical elements corresponding to the respective laser light sources, the lights may illuminate only the whole area of the same area to be illuminated.

In the illumination device according to the embodiment of the disclosure, when the minimum radiant flux is represented as Wmin [W] and the maximum radiant flux is represented as Wmax [W], a planar dimension Amin [mm<NUM>] of the diffractive optical element, which corresponds to the laser light source that emits a laser light having the minimum radiant flux, and a planar dimension Amax [mm<NUM>] of the diffractive optical element, which corresponds to the laser light source that emits a laser light having the maximum radiant flux, may satisfy the following relationship: <MAT>.

In the illumination device according to the embodiment of the disclosure, a planar dimension of the diffractive optical element, which corresponds to one optionally selected laser light source, may be not more than a planar dimension of the diffractive optical element, which corresponds to another laser light source that emits a laser light having a radiant flux larger than that of a laser light emitted by the one laser light source.

The illumination device according to the embodiment of the disclosure further comprises a shaping optical system that expands laser lights emitted from the laser light sources, and guides the laser lights to the diffractive optical elements.

In the illumination device according to the embodiment of the disclosure, the laser light sources may emit laser lights of different wavelength ranges.

In the illumination device according to the embodiment of the disclosure,.

According to the embodiment of the disclosure, the illumination device can be reduced in size while considering the safety.

An embodiment of the disclosure is described herebelow with reference to the drawings. In the drawings attached to the specification, a scale size, an aspect ratio and so on are changed and exaggerated from the actual ones, for the convenience of easiness in illustration and understanding.

Further, terms specifying shapes, geometric conditions and their degrees, e.g., "parallel", "orthogonal", "same", etc. and a value of a length, an angle, etc., are not limited to their strict definitions, but are to be construed to include a range capable of exerting a similar function.

<FIG> is a perspective view schematically showing an overall structure of an illumination device <NUM>. The illumination device <NUM> is a device that illuminates an area to be illuminated Z. In the illustrated example, the area to be illuminated Z is an elongated area having a longitudinal direction dl. The area to be illuminated Z is, for example, an area to be illuminated Z in which a ratio of a length of the longitudinal direction dl with respect to a length of a width direction dw is not less than <NUM> or even not less than <NUM>. The area to be illuminated Z is typically a linear area to be illuminated Z. Such an illumination device can be applied to a vehicle such as an automobile or a ship. A vehicle needs to illuminate an area that extends forward a traveling direction. In particular, a headlight or a headlamp of an automobile that runs at a high speed is desired to brightly illuminate a forward road surface from near to far of the automobile.

As shown in <FIG>, the illumination device <NUM> has a light source device <NUM> that projects a light or light beam, and a diffractive optical element <NUM> that diffracts a light from the light source device <NUM> and directs the light to the area to be illuminated Z. The light source device <NUM> has a laser light source <NUM>, and a shaping optical system <NUM> that shapes a light emitted from the laser light source <NUM>.

As shown in <FIG>, the light source device <NUM> has a plurality of the laser light sources <NUM>. A laser light projected from the laser light source has excellent straightness and thus is suited to accurately illuminate the area to be illuminated Z. The laser light sources <NUM> may either be independently provided, or be a light source module in which the laser light sources <NUM> are arranged on a common substrate. For example, the laser light sources <NUM> have a first laser light source 20a that oscillates a light of a red emission wavelength range, a second laser light source 20b that oscillates a light of a green emission wavelength range, and a third laser light source 20c that oscillates a light of a blue emission wavelength range. According to this example, by superimposing three laser lights projected from the laser light sources <NUM>, the area to be illuminated Z can be illuminated with an illumination light of a desired color. By adjusting radiant fluxes [unit: W] of laser lights emitted from the laser light sources <NUM>, a color of the illumination light can be adjusted.

Note that, not limited to the above example, the light source device <NUM> may have two laser light sources <NUM> or not less than four laser light sources <NUM> having emission wavelength ranges different from one another. In addition, in order to increase a light intensity, a plurality of the laser light sources <NUM> may be provided for each of the emission wavelength ranges.

Next, the shaping optical system <NUM> is described. The shaping optical system <NUM> shapes a laser light emitted from the laser light sources <NUM>. In other words, the shaping optical system <NUM> shapes a shape of a laser light in a cross-section orthogonal to an optical axis, and a three-dimensional shape of a luminous flux of a laser light. In the illustrated example, the shaping optical system <NUM> shapes a laser light emitted from the laser light source <NUM> into a parallel luminous flux having a larger width. As shown in <FIG>, the shaping optical system <NUM> has a lens <NUM> and a collimation lens <NUM> in this order along an optical path of a laser light. The lens <NUM> shapes a laser light emitted from the laser light source <NUM> into a divergent luminous flux. The collimation lens <NUM> reshapes the divergent luminous flux generated by the lens <NUM> into a parallel luminous flux.

In the illustrated example, the light source device <NUM> has a first shaping optical system 30a, a second shaping optical system 30b and a third shaping optical system 30c, correspondingly to the first to third laser light sources 20a to 20c. The first shaping optical system 30a has a first lens 31a and a first collimation lens 32a. The second shaping optical system 30b has a second lens 31b and a second collimation lens 32b. The third shaping optical system 30c has a third lens 31c and a third collimation lens 32c.

Next, the diffractive optical element <NUM> is described. The diffractive optical element <NUM> is an element that performs a diffraction action on a light emitted from the light source device <NUM>. The illustrated diffractive optical element <NUM> diffracts a light from the light source device <NUM> and directs the light to the area to be illuminated Z. Thus, the area to be illuminated Z is illuminated with a light that is diffracted by the diffraction light source element <NUM>.

In the illustrated example, the illumination device <NUM> has a plurality of the diffractive optical elements <NUM>. To be more specific, the illumination device <NUM> has a first diffractive optical element 40a, a second diffractive optical element 40b and a third diffractive optical element 40c. The diffractive optical elements 40a, 40b and 40c are respectively provided to correspond to the laser light sources 20a, 20b and 20c that oscillate laser lights. According to this example, when the laser light sources 20a, 20b and 20c oscillate laser lights of different wavelength ranges, the diffractive optical elements 40a, 40b and 40c can respectively diffract corresponding laser lights of different wavelength ranges efficiently.

After the lights emitted respectively from the laser light sources 20a, 20b and 20c have been diffracted by the diffractive optical elements 40a, 40b and 40c corresponding to the respective laser light sources, the light illuminate areas that are at least partially overlapped. Particularly in the illustrated example, lights emitted respectively from the laser light sources 20a, 20b and 20c are diffracted by the diffractive optical elements 40a, 40b and 40c corresponding to the respective laser light sources, and then illuminate the same area to be illuminated Z. More strictly, the diffracted lights having been diffracted by the respective diffractive optical elements 40a, 40b and 40c illuminate only the whole area of the same area to be illuminated Z. Since each of the diffracted lights from each of the diffractive optical elements 40a, 40b and 40c illuminates only the area to be illuminated Z as a whole, non-uniformity in brightness and non-uniformity in color in the area to be illuminated Z can be efficiently made unnoticeable.

In the example shown in <FIG> and <FIG>, the diffractive optical elements <NUM> are arranged in a first direction da that is perpendicular to the longitudinal direction dl of the area to be illuminated Z. In addition, the first direction da along which the diffractive optical elements <NUM> are arranged is parallel with a normal direction nd that is normal to a plane pl which is a flat plane on which the area to be illuminated Z is positioned. Particularly in the illustrated example, the first direction da along which the diffractive optical elements <NUM> are arranged is a vertical direction perpendicular to a horizontal direction. Namely, in the illustrated specific example, the horizontal plane pl such as a ground or a water surface is illuminated by diffracted lights from the diffractive optical elements <NUM> that are disposed vertically above the ground or the water surface, so that the area to be illuminated Z is formed on the horizontal plane pl. The diffractive optical elements <NUM> are vertically displaced from one another.

The area to be illuminated Z can be considered as an area to be illuminated of a near field that is illuminated by the diffractive optical elements <NUM>. As described below, the area to be illuminated Z can be expressed not only by an actual planar dimension to be illuminated (illumination range) but also by a diffusion angle range in an angular space having certain coordinate axes.

For example, each diffractive optical element <NUM> may be constituted as a hologram recording medium that records an interference fringe pattern. By variously adjusting the interference fringe pattern, a traveling direction of a light that is diffracted by each diffractive optical element <NUM>, in other words, a traveling direction of a light that is diffused by each diffractive optical element <NUM> can be controlled.

For example, each diffractive optical element <NUM> can be produced by using, as an object light, a scattered light from an actual scattering plate. To be more specific, when a hologram photosensitive material, which is a matrix of the diffractive optical element <NUM>, is illuminated with a reference light, which is a coherent light, and an object light interfering with each other, an interference fringe by coherence of the lights is formed in the hologram photosensitive material, so that the diffractive optical element <NUM> is produced. As a reference light, a laser light which is a coherent light is used. On the other hand, as an object light, a scattered light scattered from an economically available isotropic scattering plate is used, for example.

By projecting a laser light toward the diffractive optical element <NUM> such that the laser light travels conversely to an optical path of the reference light used when the diffractive optical element <NUM> was produced, a reconstructed image of the scattering plate is generated at a position on which the scattering plate, which originated the object light used when the diffractive optical element <NUM> was produced, is located. When the scattering plate, which originated the object light used when the diffractive optical element <NUM> was produced, uniformly scattered the light planarly, the reconstructed image of the scattering plate, which is obtained by the diffractive optical element <NUM>, is also a uniform plane illumination. An area in which the reconstructed image of the scattering plate is generated can provide the area to be illuminated Z.

Instead of being formed by using a real object light and a reference light, a complicated interference fringe pattern formed on each diffractive optical element <NUM> can be designed by using a computer based on a wavelength and an incident direction of expected illumination light to be reconstructed as well as a shape and a position of an image to be reconstructed. The diffractive optical element <NUM> thus obtained is also referred to as computer generated hologram (CGH). For example, when the illumination device <NUM> is used for illuminating an area to be illuminated Z having a certain size on a ground or a water surface, it is difficult to generate an object light, and thus a computer generated hologram is preferably used as the diffractive optical element <NUM>.

In addition, a Fourier conversion hologram in which respective points on each diffractive optical element <NUM> have the same diffusion angle properties may be generated by a computer. Further, an optical member such as a lens may be disposed on the downstream side of the diffractive optical element <NUM>, in order that a diffracted light is incident on the overall area to be illuminated Z.

Specifically, the diffractive optical element <NUM> may be a volume type hologram recording medium using a photopolymer, a volume type hologram recording medium that uses a photosensitive medium containing a silver salt material for recording, or a relief type (emboss type) hologram recording medium. In addition, the diffractive optical element <NUM> may be of a transmission type or of a reflection type.

Next, an operation of the illumination device <NUM> having the above structure is described.

A laser light emitted from each laser light source <NUM> is firstly incident on the corresponding shaping optical system <NUM>. The shaping optical system <NUM> expands the laser light emitted from the laser light source <NUM>. Namely, the shaping optical system <NUM> shapes the laser light such that an area occupied by the light spreads in a cross-section perpendicular to the optical axis. In the illustrated example, the shaping optical system <NUM> includes the first shaping optical system 30a, the second shaping optical system 30b and the third shaping optical system 30c that are separately provided correspondingly to the respective laser light sources 20a, 20b and 20c. Each shaping optical system <NUM> has the lens <NUM> and the collimation lens <NUM>. As shown in <FIG>, the lens <NUM> of the shaping optical system <NUM> diverges the laser light emitted from the laser light source <NUM> into a divergent luminous flux. The collimation lens <NUM> of the shaping optical system <NUM> collimates the divergent luminous flux into a parallel luminous flux.

The laser light shaped by the shaping optical system <NUM> is then directed to the diffractive optical element <NUM>. The diffractive optical element <NUM> includes the first diffractive optical element 40a, the second diffractive optical element 40b and the third diffractive optical element 40c that are separately provided correspondingly to the respective laser light sources 20a, 20b and 20c. Each diffractive optical element <NUM> records an interference fringe corresponding to a center wavelength of the laser light emitted from the corresponding laser light source <NUM>, and can efficiently diffract the laser light that is incident thereon from a certain direction such that the laser light is directed in a desired direction. In the illustrated example, each diffractive optical element <NUM> diffuses the laser light over the same overall area to be illuminated Z positioned on the horizontal plane pl such as a ground or a water surface.

As a result, since the laser light emitted from the first laser light source 20a, the laser light emitted from the second laser light source 20b and the laser light emitted from the third light source 20c are superimposed, the area to be illuminated Z can be illuminated with a color that cannot be reproduced by a laser light emitted from a single laser light source. The illumination light can have a desired color, by suitably adjusting a radiant flux of the laser light emitted from the first laser light source 20a, a radiant flux of the laser light emitted from the second laser light source 20b and a radiant flux of the laser light emitted from the third laser light source 20c, in other words, by adjusting an output of each laser light source so as to adjust a radiant flux of a laser light emitted therefrom.

In the illumination device <NUM> described herein, an optical path of a laser light emitted from the laser light source <NUM> is adjusted by the diffractive optical element <NUM> so as to illuminate the area to be illuminated Z. One of the advantages of the use of the diffractive optical element <NUM> is that a light energy density of a light, such as a laser light from the light source device <NUM>, can be lowered by diffusion. In addition, another advantage is that the diffractive optical element <NUM> can serve as a directional surface light source. Namely, when a person looks straight at a laser light from the area to be illuminated Z, the laser light is emitted not from a point light source but from a surface light source having a size of the diffractive optical element <NUM>. Thus, a laser light of the same radiant flux can be converted by means of the diffractive optical element <NUM> to an illumination light emitted from a broader light emission surface. As a result, as compared with illumination by means of a point light source (lamp light source), a brightness, i.e., a power density at each position on the light source surface for achieving the same illumination distribution can be lowered. For this reason, when the laser light source <NUM> is used as a light source, the use of the diffractive optical element <NUM> can contribute to safety improvement of a laser light.

By increasing a planar dimension of the diffractive optical element <NUM>, an incident area for a laser light from the light source device <NUM>, i.e., a spot area can be increased. The laser light incident on the diffractive optical element <NUM> is diffracted by the diffractive optical element <NUM>, and emerges from the whole incident area on the diffractive optical element <NUM> toward the area to be illuminated Z. Thus, by increasing the planar dimensions of the incident surface and the emergent surface of the diffractive optical element <NUM>, a power density at each position on the diffractive optical element <NUM> can be lowered.

However, on the other hand, when the diffractive optical element <NUM> has an increased planar dimension, the illumination device <NUM> enlarges in size. In the aforementioned illumination device <NUM> which performs illumination with a specific color by means of additive color mixture using light of various wavelength ranges, the problem of enlargement in size of the illumination device becomes more serious.

In this embodiment, the lowering of a power density and the reduction in size of the illumination device <NUM>, which are in a trade-off relationship, can be made compatible. Namely, in this embodiment, depending on a value of a radiant flux of a laser light emitted by the laser light source <NUM>, a planar dimension of the diffractive optical element <NUM> corresponding to the laser light source <NUM> is varied, so as to make compatible the lowering of a power density and the reduction in size of the illumination device <NUM>. A specific structure is described herebelow.

The term "a radiant flux of a laser light" herein does not mean a maximum radiant flux that can be emitted by a laser light source. In other words, the term "a radiant flux of a laser light" does not mean a capacity of a laser light source. The term "a radiant flux of a laser light" herein means a radiant flux of a laser light that is actually emitted from a laser light source whose output is adjusted depending on an illumination purpose.

Firstly, a planar dimension of a diffractive optical element, which corresponds to a laser light source that emits a laser light having a minimum radiant flux among laser lights emitted respectively by the laser light sources <NUM> included in the illumination device <NUM>, is smaller than a planar dimension of a diffractive optical element, which corresponds to a laser light source that emits a laser light having a maximum radiant flux among laser lights emitted respectively by the laser light sources <NUM> included in the illumination device <NUM>. In the illustrated example, a radiant flux of a laser light of a red wavelength range, which is emitted from the first laser light source 20a, is the largest, and a radiant flux of a laser light of a blue wavelength range, which is emitted from the third laser light source 20c, is the smallest. Thus, planar dimensions of the incident surface and the emergent surface of the third diffractive optical element 40c, which corresponds to the third laser light source 20c that oscillates a laser light having a minimum radiant flux, is smaller than planar dimensions of the incident surface and the emergent surface of the first diffractive optical element 40a, which corresponds to the first laser light source 20a that oscillates a laser light having a maximum radiant flux.

As described above, when the emergent area on the emergent surface of the diffractive optical element <NUM> is increased, a power density can be lowered. Thus, by deciding sizes of the emergent surface of the diffractive optical element <NUM> and the incident surface thereof, which is generally the same area as the emergent surface, in consideration of a value of a radiant flux of the laser light source <NUM>, the safety of the illumination device <NUM> can be enhanced. On the other hand, when a radiant flux of a laser light emitted from the third laser light source 20c is smaller than a radiant flux of a laser light emitted from the first laser light source 20a, from the viewpoint of lowering a power density at a position on the diffractive optical element, it is not necessary for the third diffractive optical element 40c corresponding to the third laser light source 20c to have a planar dimension that is about the same as a planar dimension of the first diffractive optical element 40a corresponding to the first laser light source 20a. Since the planar dimensions of the incident surface and the emergent surface of the third diffractive optical element 40c are reduced, in other words, since a planar dimension of the planar shape of the third diffractive optical element 40c is reduced, the illumination device <NUM> can be reduced in size, avoiding its unnecessary enlargement in size.

Further, when the minimum radiant flux of a laser light emitted from the third laser light source 20c is represented as Wmin [W], and the maximum radiant flux of a laser light emitted from the first laser light source 20a is represented as Wmax [W], a planar dimension Amin [mm<NUM>] of the third diffractive optical element 40c, which corresponds to the third laser light source 20c that emits a laser light having the minimum radiant flux, and a planar dimension Amax [mm<NUM>] of the first diffractive optical element 40a, which corresponds to the first laser light source 20a that emits a laser light having the maximum radiant flux, satisfy the following relationship: <MAT>.

Namely, on the assumption that the whole area of the first diffractive optical element 40a is effectively used, i.e., on the assumption that a laser light is expanded over the whole area of the incident surface of the first diffractive optical element 40a and is incident thereon at a uniform intensity, a value of a power density at each position on the first diffractive optical element 40a is represented by (Wmax/Amax) as an index. Thus, the planar dimension Amax of the first diffractive optical element 40a should be decided such that the index (Wmax/Amax) has a sufficient value. As described above, the third diffractive optical element 40c has a planar dimension smaller than that of the first diffractive optical element 40a. It is preferable that a power density at each position on the third diffractive optical element 40c is set to be not more than a power density at each position on the first diffractive optical element 40a. A value of a power density at each position on the third diffractive optical element 40c on which a laser light having a minimum radiant flux is incident is represented by (Wmin/Amin) as an index. When the planar dimension Amin of the third diffractive optical element 40c satisfies the aforementioned condition so as to be not less than "Amax × (Wmin/Wmax)", a power density at each position on the third diffractive optical element 40c can be made not more than a power density at each position on the first diffractive optical element 40a. Namely, when the aforementioned condition is satisfied, the first diffractive optical element 40a, which corresponds to the first laser light source 20a having a maximum radiant flux and thus has relatively a larger planar dimension, can have a planar dimension that is reduced as much as possible, and simultaneously therewith, the third diffractive optical element 40c, which corresponds to the third laser light source 20c having a minimum radiant flux and thus has relatively a smaller planar dimension, can have a sufficiently lowered power density.

Further, in this embodiment, a planar dimension of the diffractive optical element <NUM>, which corresponds to one optionally selected laser light source <NUM>, is not more than a planar dimension of the diffractive optical element <NUM>, which corresponds to another laser light source <NUM> having a radiant flux larger than that of the one laser light source <NUM>. Namely, as a radiant flux of the laser light source <NUM> becomes smaller, a planar dimension of the corresponding diffractive optical element <NUM> becomes smaller. In other words, as a radiant flux of the laser light source <NUM> becomes larger, a planar dimension of the corresponding diffractive optical element <NUM> becomes larger.

In the illustrated example, a radiant flux of a laser light emitted from the second laser light source 20b is smaller than a radiant flux of a laser light emitted from the first laser light source 20a, and is larger than a radiant flux of a laser light emitted from the third laser light source 20c. Namely, the radiant flux of a laser light decreases in the order of the first laser light source 20a, the second laser light source 20b and the third laser light source 20c. As shown in <FIG> and <FIG>, in the illustrated example, the planar dimension decreases in the order of the first diffractive optical element 40a, the second diffractive optical element 40b and the third diffractive optical element 40c. According to such an illumination device <NUM>, a power density at each position on each diffractive optical element <NUM> can be sufficiently lowered, and simultaneously therewith, a planar dimension of each diffractive optical element <NUM> can be effectively reduced.

Further, a radiant flux Wa of a laser light emitted from the first laser light source 20a, a radiant flux Wb of a laser light emitted from the second laser light source 20b, a radiant flux Wc of the third laser light source 20c, a planar dimension Aa of the first diffractive optical element 40a, a planar dimension Ab of the second diffractive optical element 40b and a planar dimension Ac of the third diffractive optical element 40c ideally satisfy the following relationship: <MAT> As a specific example, in the illustrated illumination device <NUM>, a radiant flux Wa of a laser light emitted from the first laser light source 20a, a radiant flux Wb of a laser light emitted from the second laser light source 20b and a radiant flux Wc of the third laser light source 20c have a relationship of <NUM>:<NUM>:<NUM>. A planar dimension ratio of the first diffractive optical element 40a, the second diffractive optical element 40b and the third diffractive optical element 40c is <NUM>:<NUM>:<NUM>. As shown in <FIG>, the first diffractive optical element 40a, the second diffractive optical element 40b and the third diffractive optical element 40c have the same length in a second direction db that is parallel with the width direction dw of the area to be illuminated Z. On the other hand, as shown in <FIG>, a ratio of the lengths along the first direction da of the first diffractive optical element 40a, the second diffractive optical element 40b and the third diffractive optical element 40c is <NUM>:<NUM>:<NUM>. According to such an illumination device <NUM>, the diffractive optical elements <NUM> have a uniform power density. Thus, by allowing the power density to have a sufficient value, the planar dimensions of the diffractive optical elements <NUM> included in the illumination device <NUM> can be reduced.

In the aforementioned embodiment described above, the illumination device <NUM> has the laser light sources <NUM> that emit laser lights of different radiant fluxes, and the diffractive optical elements <NUM> provided correspondingly to the respective laser light sources. A planar dimension of the diffractive optical element <NUM>, which corresponds to the laser light source <NUM> that emits a laser light having a minimum radiant flux, is smaller than a planar dimension of the diffractive optical element <NUM>, which corresponds to the laser light source <NUM> that emits a laser light having a maximum radiant flux. Namely, in the illumination device <NUM>, depending on a radiant flux of a laser light emitted by the laser light source <NUM>, a planar dimension of the diffractive optical element <NUM> corresponding thereto is varied. Thus, a power density at each position of each diffractive optical element <NUM> can be effectively lowered. In addition, unnecessary increase in planar dimension of the diffractive optical element <NUM>, which corresponds to the laser light source <NUM> that emits a laser light having a lower radiant flux, can be effectively avoided. As a result, the illumination device <NUM> can be effectively reduced in size, while ensuring the safety. As particularly in the illustrated example, when the area to be illuminated Z is illuminated with a specific color by means of additive color mixture, a radiant flux of a laser light emitted by each laser light source <NUM> is suitably adjusted, depending on a wavelength range of a laser light to be generated. When including the laser light sources <NUM> of a plurality of wavelength ranges, the illumination device <NUM> according to this embodiment is particularly useful.

In addition, in the aforementioned embodiment, when the minimum radiant flux is represented as Wmin [W], and the maximum radiant flux is represented as Wmax [W], a planar dimension Amin [mm<NUM>] of the diffractive optical element <NUM>, which corresponds to the laser light source <NUM> that emits a laser light having the minimum radiant flux, and a planar dimension Amax [mm<NUM>] of the diffractive optical element <NUM>, which corresponds to the laser light source <NUM> that emits a laser light having the maximum radiant flux, satisfy the following relationship: <MAT> According to this illumination device <NUM>, a power density at each position of the diffractive optical element <NUM>, which corresponds to the laser light source <NUM> that emits a laser light of a minimum radiant flux, and thus has a smaller planer dimension, can be lowered down to a power density not more than a power density at each position of the diffractive optical element <NUM>, which corresponds to the laser light source <NUM> that emits a laser light of a maximum radiant flux, and thus has a larger planar dimension. Namely, a power density at each position of the diffractive optical element <NUM> having a smaller planar dimension can be sufficiently lowered, whereby the illumination device <NUM> can be effectively reduced in size while ensuring the safety.

Further, in the aforementioned embodiment, a planar dimension of the diffractive optical element <NUM>, which corresponds to one optionally selected laser light source <NUM>, is not more than a planar dimension of the diffractive optical element <NUM>, which corresponds to another laser light source <NUM> that emits a laser light having a radian flux larger than that of a laser light emitted by the one laser light source <NUM>. According to this illumination device <NUM>, depending on values of radiant fluxes of laser lights emitted by the laser light sources <NUM>, the diffractive optical elements <NUM> corresponding to the respective laser light sources <NUM> have different sizes. Thus, a power density can be made uniform to some extent among the respective diffractive optical elements <NUM>. As a result, the planar dimension of the diffractive optical element <NUM> can be reduced as much as possible.

Further, in the aforementioned embodiment, the illumination device <NUM> further has the shaping optical system <NUM> that expands laser lights emitted from the laser light sources <NUM>, and guides the laser lights to the diffractive optical elements <NUM>. According to this illumination device <NUM>, the lights emitted from the laser light sources <NUM> are expanded, and are then incident on the diffractive optical elements <NUM>. Thus, a power density at each position of the diffractive optical element <NUM> can be effectively lowered, whereby the safety can be improved,.

The aforementioned embodiment can be variously modified. A modification example is described herebelow with reference to the drawings. In the below description, a component that can be similarly structured as that of the above embodiment has the same reference number as the number used for the corresponding component of the above embodiment, and redundant description is omitted.

For example, in the aforementioned embodiment, the shaping optical systems <NUM> independent of one another are provided for the respective laser light sources <NUM>. However, not falling under the scope of the claimed invention, the shaping optical system <NUM>, or one or more elements of the lens <NUM> and the collimation lens <NUM> included in the shaping optical system <NUM> may be shared by the laser optical sources <NUM>.

Claim 1:
An illumination device (<NUM>) comprising:
a plurality of laser light sources (<NUM>) that emit laser lights of different radiant fluxes;
a plurality of diffractive optical elements (<NUM>) separately provided correspondingly to the respective laser light sources (<NUM>); and
a plurality of shaping optical systems (<NUM>, 31a-31c, 32a-32c) separately provided correspondingly to the respective laser light sources (<NUM>);
wherein each shaping optical system of the plurality of shaping optical systems is configured to expand laser light emitted from a corresponding laser light source of the plurality of laser light sources over a whole area of an incident surface of the corresponding diffractive optical element, and to guide the laser light to the corresponding diffractive optical element of the plurality of diffractive optical elements, wherein a planar dimension of one diffractive optical element (40c) of the plurality of diffractive optical elements (<NUM>), which corresponds to one laser light source (20c) of the plurality of laser light sources (<NUM>) that emits a laser light having a minimum radiant flux, is smaller than a planar dimension of another diffractive optical element (40a) of the plurality of diffractive optical elements (<NUM>), which corresponds to another laser light source (20a) of the plurality of laser light sources (<NUM>) that emits a laser light having a maximum radiant flux.