Display device using coherent light beam and vehicle based thereon

A display device includes: a light source configured to generate a coherent light beam; and an optical plate including a plurality of microlenses arranged with a period larger than the diameter of the light beam, the optical plate being configured to control the divergence angle of the light beam.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2007-304030, filed on Nov. 26, 2007; the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a display device and a vehicle based thereon.

2. Background Art

To increase display brightness is important in improving display visibility. However, simply increasing display brightness incurs increased power consumption and hence may be impractical. Thus, it is investigated to improve brightness by limiting the display area, or the spatial region of visible display. For example, in a known display device using a high-brightness light source with low power consumption, such as a laser, the visible spatial region is limited by interposing a microlens array sheet, for example, between the laser light source and the viewer and suitably designing the optical characteristics of this microlens to control the divergence angle of laser light, control the visible spatial region, and improve display brightness without adversely affecting the power consumption. However, irradiation of a microlens array sheet with coherent light such as laser light causes speckles to be visible, and is impractical.

On the other hand, for example, head-up display (HUD) displays various traffic information through the windshield of a car on the external background field. For such a head-up display, JP-A 2-195388 (Kokai) (1990) proposes a technique to reduce speckles by vibrating a diffusion plate interposed in the optical path of laser light. However, this method involves a complicated structure because the diffusion plate is vibrated, and was unsuccessful in completely removing speckles. Furthermore, because the diffusion plate cannot control the divergence angle of laser light, this method of using the diffusion plate is not applicable to improving HUD visibility by controlling the spatial region of visible display for traffic information within a certain extent (for example, controlling it so that the display is visible to only one eye).

SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided a display device including: a light source configured to generate a coherent light beam; and an optical plate including a plurality of microlenses arranged with a period larger than the diameter of the light beam, the optical plate being configured to control the divergence angle of the light beam.

According to another aspect of the invention, there is provided A vehicle including: a display device including a light source configured to generate a coherent light beam and an optical plate including a plurality of microlenses arranged with a period larger than the diameter of the light beam, the optical plate being configured to control the divergence angle of the light beam; and a projection plate on which the light beam emitted from the display device is projected.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention will now be described in detail with reference to the drawings.

First Embodiment

FIG. 1schematically illustrates the configuration of a display device according to a first embodiment of the invention.

FIG. 1Ais a schematic view illustrating the configuration of the display device according to the first embodiment of the invention.

As shown inFIG. 1A, the display device10of the first embodiment of the invention includes a light source110for generating a coherent light beam112. The light source110can be based on any of various solid-state lasers and gas lasers, as well as semiconductor lasers and laser diodes (LD). The laser light (light beam112) generated by the light source110is coherent. The light beam112is emitted from the light source110, and then passes through a first mirror120, a projection lens130, and an optical plate140, travels to a second mirror (projection direction controller)150and a magnifying optical system160, and is emitted with a prescribed divergence angle.

Then, the light beam112having the prescribed divergence angle is emitted from the display device10and projected on a projection plate310, and reaches a viewer510. The projection plate310can be made of a mirror or a translucent plate, which can be illustratively configured as a transparent body having a surface partly reflecting light. The viewer510can view a virtual image350formed behind the projection plate310.

The light source110can include an optical system (not shown) for concentrating the light beam112.

FIG. 1Bis a partial schematic view illustrating the configuration of the display device according to the first embodiment of the invention.

As illustrated inFIG. 1B, in the optical plate140, for example, the first major surface141for receiving the light beam112is planar, and the opposite surface, or the second major surface142, is illustratively provided with microlenses145. A plurality of microlenses145are regularly arrayed with a spacing of pitch p. The optical characteristics of this microlens145allow the divergence angle of the incident light beam112to be controlled within a prescribed range. As illustrated inFIG. 1B, the optical plate140can be formed into a fly-eye structure in which microlenses are regularly arranged in a two-dimensional manner.

As described later, the optical plate140can be based on any of various configurations, such as a structure in which lenticular plates with a plurality of microlenses (cylindrical lenses) arrayed therein are placed so that the microlenses have generally orthogonal extending directions and are opposed to each other.

As shown inFIG. 1B, in the display device10, the pitch p of the microlens145of the optical plate140is designed to be substantially larger than the diameter φ of the light beam112. After being emitted from such an optical plate140, the light beam112passes through various optical elements and reaches the viewer. The right-side portion ofFIG. 1Bschematically shows the viewer's eye, where the light beam112passes through the lens410of the viewer's eye and reaches the viewer's retina420. As shown inFIG. 1B, because the diameter φ of the light beam112is smaller than the pitch p of the microlens145, the light beam112fits into the range of a single microlens145and causes no interference on the retina420, substantially avoiding speckles.

Thus, the display device10illustrated inFIG. 1is free from the occurrence of speckles and can realize a highly uniform display with a controlled divergence angle.

First Comparative Example

In the following, a display device of a first comparative example is described.

FIG. 2is a schematic view illustrating the configuration of the display device of the first comparative example.

As shown inFIG. 2, in the display device of the first comparative example, the diameter φ of the light beam812is larger than the pitch p of the microlens845of the optical plate840. In the example ofFIG. 2, the diameter φ of the light beam812is approximately three times the pitch p. As shown inFIG. 2, after being emitted from the optical plate840, the light beam812is split into three light beams812a,812b, and812c, which pass through the lens410of the viewer's eye and reaches the viewer's retina420. Here, because the three light beams812a,812b, and812care coherent, they interfere with each other and appear as speckles. Thus, if the diameter φ of the light beam812is larger than the pitch p of the microlens845, the microlens845produces a plurality of light beams, producing speckles.

In contrast, in the display device10of this embodiment, the diameter φ of the light beam112is designed to be smaller than the pitch of the microlens145. Hence, a display device substantially free from speckles can be realized with high display uniformity and a controlled divergence angle. Thus, a bright display can be realized with a limited spatial region of visible display, and a highly visible HUD can be realized with a controlled spatial region of visible display (for example, controlled so that the display is visible to only one eye).

In the following, experimental results for the embodiment of the invention and the comparative example are described in detail.

FIG. 3is a schematic view showing the optical system used in the experiment for the display device according to the embodiment of the invention and the display device of the comparative example.

As shown inFIG. 3, in the optical system used in the experiment, a light beam (laser beam)112emitted from a He—Ne laser light source352travels to a beam magnifying optical system356, an ND filter358, a first lens360, an optical plate140, a second lens364, a third mirror366, and a fourth mirror368, and reaches a CCD (charge coupled device) element370. The distance from the emission position of the He—Ne laser light source352to the first lens360was 210 mm, the distance from the first lens360to the optical plate140was 245 mm, and the distance from the optical plate140to the second lens364was 250 mm. The distance from the second lens364to the CCD element370was varied in the range of ±25 mm around 330 mm, the imaging distance. Furthermore, the focal distance of the first lens360and the second lens364was 100 mm and 150 mm, respectively. The optical plate140was a lenticular plate in which microlenses (cylindrical lenses) having a focal distance of 100 mm are arranged with a pitch p of 1.5 mm. The diameter φ of the light beam112was adjusted to 1.0 mm, which is smaller than the microlens pitch p, or to 4.5 mm, which is larger than the microlens pitch p. This adjustment of the diameter φ of the light beam112was performed by the beam magnifying optical system356.

FIG. 4shows photographs illustrating the experimental results for the display device according to the embodiment of the invention and the display device of the comparative example.

FIGS. 4A and 4Billustrate, respectively, the cases where the diameter φ of the light beam112is 1.0 mm, which is smaller than the microlens pitch p, and is 4.5 mm, which is larger than the microlens pitch p. These figures illustrate the results in which the distance from the second lens364to the CCD element370is 305 mm. That is, in these illustrated cases, the distance from the second lens364to the CCD element370is 25 mm shorter than the imaging distance, 330 mm.

As shown inFIG. 4B, in the case where the diameter φ of the light beam112is 4.5 mm, which is larger than the pitch p, a horizontal fringe pattern372is seen. This fringe pattern372indicates interference of the laser light beams, that is, occurrence of speckles.

In contrast, as shown inFIG. 4A, in the case where the diameter φ of the light beam112is 1.0 mm, which is smaller than the pitch p, no fringe pattern is seen. That is, no interference occurs between the laser light beams, and speckles can be avoided.

In the following, simulation results for this phenomenon are described.

FIG. 5schematically illustrates simulation results for the display device according to the embodiment of the invention and the display device of the comparative example.

In the experiment, the results of which are illustrated inFIGS. 4A and 4B, the optical plate140has a lens configuration in which a plurality of microlenses are arrayed in one dimension. However, in the simulation illustrated inFIGS. 5A and 5B, the optical plate140is a fly-eye lens in which microlenses are arrayed in two dimensions. The pitch p of this fly-eye lens was 1.5 mm, like the experiment inFIGS. 4A and 4B.

As shown inFIG. 5A, in the case where the diameter φ of the light beam112is 4.5 mm, which is larger than the pitch p, many bright spots374are observed. This bright spot374corresponds to interference of the laser light beams. That is, in the case where the diameter φ of the light beam112is 4.5 mm, which is larger than the pitch p, speckles are produced.

In contrast, as shown inFIG. 5A, in the case where the diameter φ of the light beam112is 1.0 mm, which is smaller than the pitch p, bright spots374substantially disappear. That is, in the case where the diameter φ of the light beam112is 1.0 mm, which is smaller than the pitch p, no interference occurs between the laser light beams, and no speckle is produced.

Thus, the simulation also confirms that speckles can be avoided by designing the diameter φ of the light beam112to be smaller than the pitch p.

In the imaging results of laser light by the CCD element370illustrated inFIGS. 4A and 4B, no fringe pattern occurred in the case where the distance from the second lens364to the CCD element370is not less than the imaging distance, 330 mm, irrespective of whether the diameter φ of the light beam112is larger or smaller than the pitch p. That is, in the case where the distance from the second lens364to the CCD element370is shorter than the imaging distance, 330 mm, a plurality of light beams split by the optical plate140interfere with each other at the imaging surface of the CCD element370and produce a fringe pattern.

Next, the results of a visual observation experiment for the display device according to the embodiment of the invention are described.

FIG. 6is a schematic view showing the optical system used in the visual observation experiment for the display device according to the embodiment of the invention and the display device of the comparative example.

As shown inFIG. 6, in the experiment of visually observing a display on the display device, a light beam (laser beam)112emitted from a He—Ne laser light source352travels to a beam magnifying optical system356, an ND filter358, an optical plate140, and a fifth mirror376, and reaches the viewer's eye378. The distance from the emission position of the He—Ne laser light source352to the ND filter358was 210 mm, the distance from the ND filter to the optical plate140was 245 mm, and the distance from the optical plate140to the viewer's eye378was 2000 mm. The optical plate140was a lenticular plate in which semi-cylindrical lenses having a focal distance of 100 mm are arranged with a pitch p of 1.5 mm, like the optical plate140illustrated inFIG. 3. The diameter φ of the light beam112was adjusted to 1.0 mm, which is smaller than the pitch of the microlens (cylindrical lens), or to 4.5 mm, which is larger than the pitch of the microlens. This adjustment of the diameter φ of the light beam112was performed by the beam magnifying optical system356.

In the optical system shown inFIG. 6, in the case where the diameter φ of the light beam112is 1.0 mm, which is smaller than the microlens pitch, no speckle was observed at any times when the eye was focused on the optical plate140and on a nearer and farther position. On the other hand, in the case where the diameter φ of the light beam112is 4.5 mm, which is larger than the microlens pitch, no speckle was observed when the eye was focused on a position nearer than the optical plate140and on the optical plate140, but speckles were observed when the eye was focused on a position farther than the optical plate140.

In the following, this phenomenon is described in detail.

FIG. 7schematically illustrates the state of the eye in viewing the display device according to the embodiment of the invention and the display device of the comparative example.

FIGS. 7A,7B, and7C illustrate the state of the viewer's eye in looking at a position nearer than the optical plate140, at the optical plate140, and at a position farther than the optical plate140, respectively, in the case where the diameter φ of the light beam112is 1.0 mm, which is smaller than the microlens pitch, 1.5 mm. On the other hand,FIGS. 7D,7E, and7F illustrate the state of the viewer's eye in looking at a position nearer than the optical plate140, at the optical plate140, and at a position farther than the optical plate140, respectively, in the case where the diameter φ of the light beam112is 4.5 mm, which is larger than the microlens pitch, 1.5 mm.

As shown inFIG. 7D, in the case where the diameter φ of the light beam112is 4.5 mm, which is larger than the microlens pitch, 1.5 mm (the diameter φ of the light beam112is three times the microlens pitch p), the light beam112incident on the optical plate140is split into three light beams112a-112c. When the viewer looks at a position nearer than the optical plate140(focuses the eye378on a position nearer than the optical plate140), the lens (crystalline lens)410of the viewer's eye378converges the light beams112a-112cbefore the retina420of the eye378. On the retina420, the light beams112a-112care separated from each other and do not interfere with each other.

Furthermore, as shown inFIG. 7E, when the viewer looks at the optical plate140(focuses on the optical plate140), the lens (crystalline lens)410converges the light beams112a-112con the retina420so that the light beams border on each other. Also in this case, the light beams112a-112cdo not interfere with each other.

In contrast, as shown inFIG. 7F, when the viewer looks at a position farther than the optical plate140(focuses on a position farther than the optical plate140), the lens (crystalline lens)410converges the light beams112a-112cbehind the retina420. In this case, the light beams112a-112coverlap each other on the retina420, and hence interfere with each other, producing speckles.

On the other hand, as shown inFIGS. 7A to 7C, in the case where the diameter φ of the light beam112is smaller than the microlens pitch, 1.5 mm, the light incident on the optical plate140is not split, but remains a single light beam112. Thus, no interference phenomenon occurs in the light beam112irrespective of whether the viewer looks at a position nearer or farther than the optical plate140or at the optical plate140, and hence no speckle is produced.

Thus, speckles can be avoided by designing the diameter φ of the light beam112to be smaller than the microlens pitch p.

Furthermore, a description is given of the results of analyzing the relation of the microlens pitch p and the light beam diameter φ to the interference phenomenon.

FIG. 8schematically illustrates the results of simulation analysis on the relation of the microlens pitch p and the light beam diameter φ to the interference phenomenon.

FIG. 8Ais a schematic view illustrating the optical system used in this simulation.

As shown inFIG. 8A, an optical plate140and a convex lens388were placed, and the distance between the optical plate140and the convex lens388was 200 mm. The optical plate140was a lenticular plate in which microlenses (cylindrical lenses) are arranged in parallel. The pitch p of the microlens was 0.5 mm, and its curvature radius R was 13 mm. The focal distance of the convex lens388was set to 100 mm. In this optical system, a light beam112having a wavelength of 1 μm is incident on the optical plate140, passes through the convex lens388, and reaches the imaging position390. The distance between the convex lens388and the imaging position390was 150 mm, which was 50 mm shorter than the imaging position of the convex lens, 200 mm. In this optical system, the diameter φ of the light beam112was varied for wave simulation.

FIGS. 8B to 8Dare schematic views showing the simulation results in the case where the diameter φ of the light beam112is 0.25 mm, 0.5 mm, and 3.0 mm, respectively.

As shown inFIG. 8D, when the diameter of the light beam112is 3.0 mm, which is larger than the pitch of the optical plate140, 0.5 mm, a horizontal fringe pattern corresponding to the microlenses of the optical plate140is observed. This is because the light beam112is incident on the optical plate140over a plurality of microlenses (cylindrical lenses) to produce a plurality of light beams, which interfere with each other. In this case, speckles are produced.

On the other hand, as shown inFIG. 8B, when the diameter of the light beam112is 0.25 mm, which is smaller than the pitch of the optical plate140, 0.5 mm, no fringe pattern is produced. This is because the light beam112fits into a single microlens, and hence causes no interference. Thus, no speckle is produced.

Furthermore, as shown inFIG. 8C, when the diameter of the light beam112is equal to the pitch of the optical plate140, 0.5 mm, a fringe pattern is slightly produced. This is because, when the diameter φ of the light beam112is equal to the pitch of the optical plate140, 0.5 mm, the light surrounding the light beam112does not fit into a single microlens, but protrudes therefrom. More specifically, the diameter φ of the light beam112is defined by the size at 1/e2of the maximum intensity of the light beam112. A slight light beam exists also outside the diameter φ of the light beam112, and produces a slight fringe pattern ofFIG. 8C. In this case, weak speckles are produced. However, this weak speckle is not very visibly conspicuous, and causes no practical problem.

Thus, there is no practical problem with speckles occurring when the diameter φ of the light beam112is equal to the microlens pitch of the optical plate140, 0.5 mm, and speckles cause a problem when the diameter φ of the light beam112is larger than the microlens pitch of the optical plate140, 0.5 mm. Hence, speckles can be substantially eliminated by designing the diameter φ of the light beam112to be smaller than the pitch of the optical plate140.

As described above, in this disclosure, the diameter φ of the light beam is defined as the diameter at 1/e2of the maximum intensity, that is, approximately 13.5% of the maximum intensity, assuming that the intensity of the light beam has a Gaussian distribution. Hence, the area outside the diameter φ of the light beam is also irradiated with laser light having an intensity lower than 13.5%. However, speckles produced thereby have low intensity, and hence it is often the case that they cause no practical problem. Thus, in the display device of the embodiment of the invention, speckles can be substantially eliminated if the diameter φ of the light beam as defined above is smaller than the microlens pitch.

As described above, in the display device of this embodiment, the diameter φ of the light beam112is designed to be smaller than the pitch p of the microlens145of the optical plate140. Hence, a display free from speckles can be realized with high display uniformity and a controlled divergence angle. Thus, a bright display can be realized with a limited spatial region of visible display, and a highly visible HUD can be realized with a controlled spatial region of visible display (for example, controlled so that the display is visible to only one eye).

The optical plate140in this embodiment can be implemented variously.FIG. 9shows schematic perspective views illustrating optical plates used in the display device according to the embodiment of the invention.

As shown inFIG. 9A, the optical plate140can be made of two lenticular plates146with a plurality of cylindrical lenses144arrayed therein, the lenticular plates146being placed so that the cylindrical lenses144have generally orthogonal extending directions and are opposed to each other. Alternatively, as shown inFIG. 9B, it is also possible to use a microlens array in which dome-shaped microlenses145are linearly arrayed on a flat plate. Furthermore, as shown inFIG. 9C, it is possible to use a microlens array in which dome-shaped microlenses145are arrayed on a flat plate in a hexagonal packing configuration. Moreover, as shown inFIG. 9D, it is also possible to use a microlens array in which graded-index microlenses147with a generally circular distribution of refractive index are placed on a flat plate. In these optical plates, the divergence angle of the light beam can be controlled by controlling the shape of the cylindrical lens144and the dome-shaped microlens145, the refractive index of the material thereof, and the refractive index distribution of the graded-index microlens147. Besides the foregoing, for example, the optical plate140can be based on any of various configurations, such as a prism sheet or various louvered sheets in which a plurality of peaks and grooves shaped like triangular prisms are arrayed in parallel, and a structure in which a plurality of waveguides shaped like truncated triangular pyramids are arrayed.

The light beam112can be incident on the optical plate140whether from the first major surface (flat surface) of the optical plate140or from the second major surface (the surface provided with microlenses). Furthermore, microlenses can be formed on both the major surfaces of the optical plate140.

In the display device10of the first embodiment of the invention illustrated inFIG. 1, the first mirror (scanning section)120illustratively serves to scan the light beam112. The light beam112can be scanned by varying the set angle using the driver (not shown) of the first mirror. Furthermore, although the first mirror120is shown inFIG. 1as a flat mirror, it can be a concave mirror. Alternatively, it can be configured as a concave mirror combined with a convex mirror for correcting image distortion.

When the projection position of the light beam112is varied, the second mirror150can vary the projection position by varying the set angle using a second mirror driver, not shown. For example, it can be used to vary the projection position to follow the movement of the eye of the viewer510. Here, the viewer's head can be imaged by a camera, not shown, and the imaged data can be subjected to image processing to recognize the viewer's head and eye. In accordance therewith, the projection position can be automatically controlled. However, the mechanism for automatically controlling the second mirror150by the driver and the imaging camera is not necessarily needed, but can be provided if necessary.

The operation of the driver for the first mirror and the driver for the second mirror can be controlled by a controller108.

Second Embodiment

Next, a second embodiment is described.

FIG. 10is a schematic view illustrating the configuration of a display device according to the second embodiment of the invention.

The display device according to the second embodiment is configured like the display device according to the first embodiment illustrated inFIG. 1except that the light beam112is scanned.FIG. 10schematically illustrates the relative positional relationship between the optical plate140and the light beam112in the second embodiment.

As shown inFIG. 10, the diameter φ of the light beam112is designed to be smaller than the pitch p of the microlens145of the optical plate140. The light beam112is scanned in the scan direction113. More specifically, at a given time, the light beam112d1passes through the optical plate140to produce a light beam112d2. At a later time, the light beam112e1passes through the optical plate140to produce a light beam112e2. Subsequently, the light beam112f1passes through the optical plate140to produce a light beam112f2. These light beams112d2,112e2,112f2are temporally independent, and hence do not overlap each other. Thus, they do not interfere with each other, and no speckle is produced.

Here, in scanning the light beam112, if the light beam112straddles the boundary of the microlens145, the light beam112does not travel in the desired direction and causes interference. To avoid this, it is possible to substantially prevent the light beam112from irradiating the boundary of the microlens145. This can be realized by generating the light beam112in a pulsed manner (intermittently) and synchronizing the pulse generation with the scan timing. This can be performed by the controller108for controlling the light source110and the first mirror120illustrated inFIG. 1.

Thus, in the display device of this embodiment, the diameter φ of the light beam112is designed to be smaller than the pitch p of the microlens145of the optical plate140, and the light beam112is scanned so as to substantially avoid irradiating the boundary of the microlens145. Hence, a display free from speckles can be realized with high display uniformity and a controlled divergence angle. Thus, a bright display can be realized with a limited spatial region of visible display, and a highly visible HUD can be realized with a controlled spatial region of visible display (for example, controlled so that the display is visible to only one eye).

Third Embodiment

Next, a display device of a third embodiment of the invention is described. In the display device of the third embodiment, a light shielding layer is provided in the boundary region of the microlens.

FIG. 11is a schematic view illustrating the configuration of a display device according to the third embodiment of the invention.

As shown inFIG. 11, the display device according to the third embodiment is configured like the display device of the first embodiment illustrated inFIG. 1except that a light shielding layer148is provided in the boundary region of the microlens145, and the remaining configuration is the same as that of the first embodiment. As described previously, in scanning the light beam112, if the light beam112straddles the boundary of the microlens145, the light beam112does not travel in the desired direction and causes interference. To avoid this, the light shielding layer148is provided in the boundary region of the microlens145to substantially prevent the light beam112from irradiating the boundary of the microlens145. This serves to eliminate speckles that may otherwise occur when the light beam112is incident on or emitted from the boundary of the microlens145. Thus, speckles can be substantially avoided even if the diameter φ of the light beam112is slightly larger than the microlens pitch p, or even if the control for scanning the light beam112is slightly misaligned with the position of the microlens145. Hence, the design margin of various components in the display device10is expanded, and stable performance can be realized cost-effectively.

Thus, in the display device of this embodiment, the light shielding layer148is provided in the boundary region of the microlens145to substantially prevent the light beam112from irradiating the boundary of the microlens145. Hence, a display free from speckles can be realized with high display uniformity and a controlled divergence angle. Thus, a bright display can be realized with a limited spatial region of visible display, and a highly visible HUD can be realized with a controlled spatial region of visible display (for example, controlled so that the display is visible to only one eye).

The light shielding layer148can be illustratively made of a light shielding resin in which carbon, various inorganic pigments, or various organic pigments are mixed with a resin. By known photolithography methods, a light shielding layer148having a prescribed shape can be formed at the boundary of the microlens145. Here, if the resin is made of a photosensitive resin such as a photosensitive acrylic resin, the number of process steps can be advantageously reduced. Furthermore, the light shielding layer148can be provided by the ink jet method and the like.

The shape and size of the light shielding layer148are suitably designed in accordance with the relative relationship between the diameter φ of the light beam112and the microlens145so that the light beam112incident on the boundary of the microlens145can be substantially shielded.FIG. 11shows an example in which the light shielding layer148is provided on the second major surface142of the optical plate140provided with the microlens145. Alternatively, the light shielding layer148can be provided in a region corresponding to the boundary of the microlens145on the other side, that is, the first major surface141.

Fourth Embodiment

Next, a display device of a fourth embodiment of the invention is described. In the display device of the fourth embodiment, three color light sources are used to realize a color display.

FIG. 12is a schematic view illustrating the configuration of a display device according to the fourth embodiment of the invention.

As shown inFIG. 12, the display device20according to the fourth embodiment is configured like the display device of the first embodiment illustrated inFIG. 1except that the light source110is made of three color light sources, that is, a red LD110r, a green LD110g, and a blue LD110b. The light generated by the red LD110r, the green LD110g, and the blue LD110bpasses through a red-reflecting mirror114r, a green-reflecting mirror114g, and a blue-reflecting mirror114b, respectively, and through a polarization beam splitter116and a quarter-wave plate117, and reaches a MEMS (microelectromechanical system) scanner118. The light of each color is modulated with an image signal by the MEMS scanner118and emitted therefrom, passes through the quarter-wave plate117and the polarization beam splitter116, and is incident on a projection lens130. Then, the light passes through an optical system like that of the display device10shown inFIG. 1and reaches the viewer510. Thus, the viewer510can obtain a color display.

In the display device20of this embodiment, the diameter φ of the three-color light beam112is designed to be smaller than the pitch p of the microlens145of the optical plate140. Furthermore, the light beam112generated in a pulsed manner is scanned so as to substantially avoid irradiating the boundary of the microlens145. Hence, a color display free from speckles can be realized with high display uniformity and a controlled divergence angle. Thus, a bright color display can be realized with a limited spatial region of visible display, and a highly visible color HUD can be realized with a controlled spatial region of visible display (for example, controlled so that the display is visible to only one eye).

In this embodiment, a light shielding layer148can be provided on the optical plate140so that the light beam112can substantially avoid irradiating the boundary of the microlens145. Alternatively, a light shielding layer148can be provided at the boundary of the microlens145of the optical plate140, and a continuously generated light beam112can be used.

With regard to the light source,FIG. 12illustrates three color light sources. However, it is also possible to use two colors, or four or more colors.

In this embodiment, the MEMS scanner118serves as a scanning section.

Fifth Embodiment

Next, a display device of a fifth embodiment of the invention is described. The display device of the fifth embodiment is an example of the rear projection display device.

FIG. 13is a schematic view illustrating the configuration of a display device according to the fifth embodiment of the invention.

As shown inFIG. 13, the display device30according to the fifth embodiment includes a projection plate312in addition to the display device20illustrated inFIG. 12. The projection plate312is illustratively made of a diffusive optical sheet and forms an image351in response to the light beam112incident on its rear surface. The image351is visible to the viewer510. That is, the display device30of this embodiment is a rear projection display device including a projection plate312. In the display device30of this embodiment, the diameter φ of the light beam112is designed to be smaller than the pitch p of the microlens145. Hence, even if a laser light source with low power and high brightness is used, a display free from speckles can be realized with high display uniformity. In the example shown inFIG. 13, three color LDs are used as light sources. However, this embodiment is not limited thereto, but it is also possible to use one light source, two color light sources, or four or more color light sources. Furthermore, the light beam112can be generated in a pulsed manner and scanned in synchronization with the pulse so as to avoid irradiating the boundary of the microlens145. Moreover, a light shielding layer can be provided at the boundary of the microlens145.

Sixth Embodiment

InFIGS. 1 and 12, the projection plate310can illustratively be a car windshield. Thus, simultaneously the background field outside the car windshield, various traffic information can be displayed and viewed through the windshield.

FIG. 14is a schematic view illustrating a vehicle based on the display device of the embodiments of the invention.

As shown inFIG. 14, the window, for example, in various vehicles of the sixth embodiment of the invention, such as a car, train, ship, helicopter, and aircraft, is provided with a projection plate310capable of forming a virtual image by projection of a light beam112. A light beam is projected on this projection plate by the display device of the embodiments of the invention to form a virtual image on the projection plate310. Thus, a display free from speckles can be produced with high display uniformity and a controlled divergence angle. This enables safe and efficient travel of the vehicle. The projection plate310can be formed from a glass or resin plate of various types shaped like a flat or curved plate, which illustratively serves as a window of the vehicle, and can be designed to have suitable reflection and transmission performance.

In this disclosure, it is assumed that the terms “parallel” and “orthogonal” include displacement from the exact parallelism and orthogonality due to variation in the manufacturing process and the like.

The embodiments of the invention have been described with reference to examples. However, the invention is not limited to these examples. For instance, any specific configurations of the components constituting the display device and the vehicle based thereon are encompassed within the scope of the invention as long as those skilled in the art can similarly practice the invention and achieve similar effects by suitably selecting such configurations from conventionally known ones.

Furthermore, any two or more components of the examples can be combined with each other as long as technically feasible, and such combinations are also encompassed within the scope of the invention as long as they fall within the spirit of the invention.

Furthermore, those skilled in the art can suitably modify and implement the display device and the vehicle based thereon described above in the embodiments of the invention, and any display devices and vehicles based thereon thus modified are also encompassed within the scope of the invention as long as they fall within the spirit of the invention.

Furthermore, those skilled in the art can conceive various modifications and variations within the spirit of the invention, and it is understood that such modifications and variations are also encompassed within the scope of the invention.