Image projecting device

A wavefront curvature modulating device is provided with a beam generating system that emits a plurality of beams having different wavefront curvatures, and a beam selecting system that selects at least one of the beams generated by the beam generating system.

BACKGROUND OF THE INVENTION

The present invention relates to an image projecting device which emits a scanning light beam into an eye of an observer to form an image on retina.

Conventionally, a retinal scanning display device which directly projects image on a retina by scanning weak light beams has been developed. The assignee of the present invention has suggested such a display device in Japanese Patent Publication No. 2874208. Such a retinal scanning display is typically known as a head-mounting display, which is configured such that an observer wears the display device, like spectacles, on the head. The retinal scanning display device is implemented with a wavefront curvature modulator which dynamically varies the wavefront curvature of the beam in order to provide a depth of the image formed on the retina of the observer.

Light emitted by a light source propagates as a light wave in all directions at the same phase, i.e., as isophase spherical wave. Depending on a distance between the light source and an observer, the radius of curvature of the spherical wave at the observer is different. That is, if the light source is close to the observer, an image of the light source is projected on the retina of the observer as an image having a small radius of curvature, while if the light source is remote, the image of the light source is projected on the retina of the observer as an image having a relatively large radius of curvature of the wavefront. The observer recognizes the difference of the radius of curvature and recognizes a natural perspective, or three-dimensional feelings.

In the conventional wavefront curvature modulator for a retinal scanning display, an optical system thereof is provided with a piezoelectric plate formed with a reflection surface thereon. A control voltage is applied to the piezoelectric plate so that the piezoelectric plate, and therefore the reflection surface is deformed. The light beam emitted by the light source is directed to the reflection surface, and the reflected beam is used for the retinal scanning. In this conventional wavefront curvature modulator, due to the deformation of the reflection surface (i.e., the piezoelectric plate), the wavefront curvature of the reflected beam is different from that of the incident beam. By varying the control voltage, the degree of change of the wavefront curvature of the reflected beam can be controlled. Recently, there is a requirement for an improved wavefront curvature modulating device which is capable of modulating the wavefront curvature at a higher frequency than the conventional device.

SUMMARY OF THE INVENTION

The present invention is advantageous in that the wavefront curvature of a beam can be modulated at high frequency which has not been achieved in the conventional wavefront curvature modulator.

According to an aspect of the invention, there is provided a wavefront curvature modulating device, which is provided with a beam generating system that emits a plurality of beams having different wavefront curvatures, and a beam selecting system that selects at least one of the beams generated by the beam generating system.

Optionally, the beam selecting system may include a plurality of intensity modulators that modulates intensities of the plurality of beams generated by the beam generating system, respectively.

Further optionally, the beam selecting system may include a beam combining system capable of combining the plurality of beam into a single combined beam. Thus, the combined beam may includes a plurality of components having different wavefront curvatures.

Still optionally, the beam selecting system may include an optical switch system that selects at least one of the plurality of beams.

Furthermore, the beam generating system may include a wavefront curvature modulating system which is capable of modulating the wavefront curvatures of the plurality of beams individually.

In this case, the wavefront curvature modulating system may be configured to modulate a radius of wavefront curvature within a range of 10 cm through the infinity using the plurality of beams.

Further optionally, each of the plurality of beams having the different wavefront curvatures may include a plurality of components having different wavelengths. For example, each beam may include wavelength components of red, blue and green.

Further, the beam emitting system may include a beam divider that divides at least one beam emitted by a single light source into the plurality of beams, and a converting system that converts the plurality of beams divided by the beam divider into the beams having different wavefront curvatures, respectively.

According to anther aspect of the invention, there is provided a retinal display device having a wavefront curvature modulating device configured as above.

Optionally, the retinal display device may include a scanning system that scans the beam emitted by the wavefront curvature modulating device, and an optical system that directs the beam scanned by the scanning system into an eye of an observer.

Further optionally, the retinal display device may include a virtual image projection device that generate image data representative of a three-dimensional object by projecting the three-dimensional object on a plurality of virtual planes at different distances with respect to a virtual observing point representing an observing point of the observer.

In this case, when the observer focuses on one of the plurality of virtual planes, distances to two planes closer to and farther from the one of the plurality of virtual planes are determined such that blurs of the images formed on the two planes due to out-of-focus state thereof are substantially the same.

Alternatively, when the observer focuses on one of the plurality of virtual planes, distances between the plurality of virtual planes are determined such that a blur of the image formed on the virtual plane next to the one of the plurality of virtual planes substantially corresponds to the visual resolution of the observer.

Further, the virtual image projecting device may be configured to project, in addition to the two-dimensional images projected on the plurality of virtual planes, image data including depth data and/or image data of three-dimensional shape represented by polygons on the virtual planes.

Still optionally, the virtual image projecting device may be configured to project portions of a three-dimensional object viewed from the virtual observing point on one of the plurality of virtual planes corresponding to a distance between the observing point to the portion of the three-dimensional object.

Optionally, the beam generating system may include a plurality of laser sources that emit a plurality of laser beams, respectively and a plurality of wavefront curvature modulating systems that modulate the plurality of laser beams emitted by the plurality of laser sources so as to have different wavefront curvature, respectively.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, wavefront curvature modulating devices according to embodiments will be described with reference to the accompanying drawings.

FIG. 1shows a configuration of a wavefront curvature modulating device (hereinafter referred to as WCM)1to which embodiments of the invention can be applied.FIG. 2schematically shows a structure of a beam generating system10employed in the WCM1shown inFIG. 1.

As shown inFIG. 1, the WCM1includes the beam generating system10and a beam selecting system20. The beam generating system10is configured to emits four beams having different wavefront curvatures. The beam selecting system20receives all the beams generated by the beam generating system10, and select at least one of the received beams, and directs the same to outside.

Specifically, the beam generating system10includes a light source11that emits a beam having substantially parallel rays of light, and first through fourth beam generators2,3,4and5that generate beams A through D whose wavefront curvatures are a, b, c and d, respectively.

As the light source11, it is preferable that a laser diode is employed since the substantially parallel light should be incident on each of the beam generators2,3,4and5. However, the invention is not limited to such a structure, and any other light source such as an LED (light emitting diode) may be used in combination of appropriate optical systems.

As shown inFIG. 2, the first beam generator2includes a first semi-transparent mirror12and a first lens system13. The first semi-transparent mirror12reflects a part of the incident beam, and allows the remainder of the incident beam to pass therethrough. The part of the beam passed through the first semi-transparent mirror12is incident on the first lens system13. It should be noted that an axis of the beam emitted by the light source11and passed through the first semi-transparent mirror12coincides with the optical axis of the first lens system13.

Hereinafter, the direction parallel with the optical axis of the first lens system13will be referred to as an X-axis direction, and the light source side (i.e., the left-hand side inFIG. 2) along the X axis will be referred to as an −X direction, while the right-hand side along the X axis will be referred to as a +X direction. The first lens system13is configured such that the beam passed therethrough has the wavefront curvature of a.

Along the axis of the beam reflected by the first semi-transparent mirror12, second and third semi-transparent mirrors14and16, and a mirror (a total reflection mirror)18are arranged. A direction along the axis of the beam reflected by the first semi-transparent mirror12will be referred to as a Y-axis. According to the embodiments, the X-axis and the Y-axis are perpendicular to each other.

The second beam generator3includes the second semi-transparent mirror14and a second lens system15, which are arranged such that the beam reflected by the first semi-transparent mirror12is partially reflected, in the X-axis direction, by the second semi-transparent mirror14and enters the second lens system15along the optical axis thereof, which is parallel with the X-axis. The second lens system15is configured such that the beam passed therethrough has the wavefront curvature of b.

The third beam generator4includes the third semi-transparent mirror16and a third lens system17, which are arranged such that the beam reflected by the first semi-transparent mirror12and passed through the second semi-transparent mirror14is partially reflected, in the X-axis direction, by the third semi-transparent mirror16and enters the third lens system17along the optical axis thereof, which is parallel with the X-axis. The third lens system17is configured such that the beam passed therethrough has the wavefront curvature of c.

The fourth beam generator5includes the mirror18and a fourth lens system19, which are arranged such that the beam reflected by the first semi-transparent mirror12, passed through the second and third semi-transparent mirrors14and16is partially reflected, in the X-axis direction, by the mirror18and enters the fourth lens system19along the optical axis thereof, which is parallel with the X-axis. The fourth lens system19is configured such that the beam passed therethrough has the wavefront curvature of d.

Each of the lens systems13,15,17and19consists of two positive (convex) lenses, each of which has a focal length of f. Further, the first through fourth lens systems13,15,17and19are configured such that distances between principal points of the two lenses are fa+f, fb+f, fc+f and fd+f, respectively, where,
fa=f . . .  (1), and
fa>fb>fc>fd>0 . . .  (2).

As shown inFIG. 2, the beam emitted by the light source11is divided into four beams by the first through third semi-transparent mirrors12,14and16and the total reflection mirror18. The divide four beams are incident on the first through fourth lens systems13,15,17and19, respectively.

The lens system13is configured such that the two lenses, each of which has a focal length of f, are arranged such that a distance between the principal points thereof is fa+f, where fa is equal to f. Thus, the distance of the principal points of the two lenses of the first lens system18is twice the focal length f. Accordingly, the beam incident on the left-hand side lens (hereinafter referred to as a first lens13A) inFIG. 2converges at the central position between the two lenses, and then enters the right-hand side lens (hereinafter referred to as a second lens13B) as a diverging beam. Since the converging point of the beam is the focal point of the second lens13B, the beam A that emerges from the second lens13B is a collimated beam, which is the same as the beam incident on the first lens13A. Since the beam A is collimated, the wavefront curvature a is substantially zero (i.e., the radius of the wavefront curvature is infinity).

The beam reflected by the second semi-transparent mirror14is incident on the second lens system15. As aforementioned, a distance between the principal points of the first and second lenses of the second lens system15is fb+f, where fb is less than fa. Thus, the parallel light beam incident on a first lens15A of the lens system15is converged at a point which is closer to a second lens15B than the focal point of the second lens15B. The beam converged by the first lens15A of the lens system15is incident on the second lens15B as a diverging beam. Since the converging point is closer to the second lens15B than the focal point thereof, the beam B emerges from the second lens15B as a diverging beam. Accordingly, the wavefront curvature b of the beam B is greater than the wavefront curvature a of the beam A.

Similarly, the beam C emerging from a second lens17A of the lens system17, and the beam C emerging from the second lens17B of the lens system19are diverging beams. Since the condition (2) is satisfied, the degree of divergence of the beam C is greater than that of the beam B, and the degree of divergence of the beam D is greater than that of the beam C. Therefore, the wavefront curvature c of the beam C is greater than the wavefront curvature b of the beam B, and the wavefront curvature d of the beam D is greater than the wavefront curvature c of the beam C. That is, wavefront curvature a<wavefront curvature b<wavefront curvature c<wavefront curvature d. Accordingly, from the beam generating system10, four beams A–D having different wavefront curvatures a–d are emitted.

In view of the sensitivity of the retina regarding the wavefront curvatures, it is not necessary to continuously vary the wavefront curvature. By providing a limited number of (e.g., four steps of) different wavefront curvatures, for example, by providing logarithmically varying radii of the wavefront curvatures of 10 cm, 50 cm, 3 m and infinity, practically sufficient three-dimensional effect can be achieved.

Hereinafter, three embodiments of the beam selecting systems will be described. In the following description, the beam selecting systems are assigned with reference numerals20A,20B and20C, respectively, each of which can be employed as the beam selecting system20described above.

FIRST EMBODIMENT

FIG. 3shows a structure of a beam selecting system20A according to the first embodiment of the invention.

As shown inFIG. 3, the beam selecting system20A includes first through fourth intensity modulators21,22,23and24. Each of the intensity modulators21,22,23and24is configured to modulate the intensity of the incident beam in accordance with an electrical signal applied thereto. An example of such an intensity modulator is an AOM (Acousto-Optical Modulator), with which the intensity of the beam can be modulated at a frequency of hundreds of megahertz.

The beam A emitted by the first beam generator2enters the first intensity modulator21, and is modulated thereby. Then, the beam A modulated by the first intensity modulator21emerges therefrom and is incident on a total reflection mirror25. It should be noted that the first intensity modulator21and the total reflection mirror25are arranged along the axis of the beam A, which is parallel with the X-axis.

The beam B emitted by the second beam generator3enters the second intensity modulator22, and is modulated thereby. Then, the beam B modulated by the second intensity modulator22emerges therefrom and is incident on a first beam combining mirror26. It should be noted that the second intensity modulator22and the first beam combining mirror26are arranged along the axis of the beam B, which is parallel with the X-axis.

Similarly, the beam C emitted by the third beam generator4enters the third intensity modulator23, and is incident on a second beam combining mirror27, the third intensity modulator23and the second beam combining mirror27being arranged along the axis of the beam C, which is parallel with the X-axis.

The beam D emitted by the fourth beam generator5enters the fourth intensity modulator24, and is incident on a third beam combining mirror28, the fourth intensity modulator24and the third beam combining mirror28being arranged along the axis of the beam D, which is parallel with the X-axis.

The mirrors25through28are arranged along the Y-axis. Each of the beam combining mirrors26,27and28is configured to reflects part of incident light and transmits the remaining part of the incident light. Further, the first through fourth intensity modulators21,22,23and24and the mirrors25,26,27and28are arranged such that the axes of the beams A, B and C reflected by the third beam combining mirror28coincide with the axis of the beam D passed through the third combining mirror28.

Each of the intensity modulators21through24is controlled by a beam selecting system driving circuit63(seeFIG. 7, which will be described later) to change its transparency so that the intensity of the beam passed therethrough is changed.

The beams A through D respectively passed through the intensity modulators21through24are combined by the mirrors25through28, and a combined beam emerges from the beam selecting system20A.

Specifically, the first through fourth intensity modulators21through24are driven such that only one modulator transmits the beam and the other three modulators shield the beams incident thereon. With this configuration, only one of the beams A through D can be selected, which emerges from the beam selecting system20A.FIG. 3shows a case where the beams A, C and D are shielded and the beam B emerges from the beam selecting system20A via the second intensity modulator22.

Alternatively, the intensities of the beams A through D can be adjusted separately so that a beam including a plurality components having different wavefront curvatures emerges from the beam selecting system20A.

For example, it is possible that the beams B and C may be combined with the intensity ratio is one to one, and emitted from the beam selecting system20A. In such a case, an observer may recognize that an image is formed on a virtual plane which is located between virtual planes respectively corresponding to the wavefront curvatures b and c. Further, by setting the ratios of the intensities of the beams to be combined appropriately, the virtual plane of an image can be located at a desired position. Therefore, with the configuration of the beam selecting system20A, the same effect as a case where the wavefront curvature is continuously changed can be achieved.

Some types of the intensity modulators affect the wavefront curvature. An example of such a modulator is the AOM, which disturbs the wavefront of a beam passed therethrough. If such intensity modulators are employed, it may be effective to arrange the intensity modulators between the lens systems13,15,17and19, and the mirrors12,14,16and18, respectively. With this configuration, the function of intensity modulation can be achieved.

Alternative to the above configuration, as shown inFIG. 9, four laser diodes11A–11D may be arranged on the upstream side of the lens systems13,15,17and19, respectively, as light sources. By controlling the intensities of the beams emitted by the four laser diodes11A–11D, the intensity modulators21through24can be omitted, and the same effects as the beam selecting system20A can be achieved.

SECOND EMBODIMENT

FIG. 4shows a structure of a beam selecting system20B according to a second embodiment of the invention;

As shown inFIG. 4, the beam selecting system20B includes first through fourth optical switches31,32,33and34, which are arranged on the axes or the beams A, B, C and D, respectively. The optical switches31,32,33and34are configured to reflect the beams A, B, C and D, and the reflection directions are changeable, respectively. The beam selecting system20B further includes a total reflection mirror35, first through third beam combining mirrors36,37and39. The beams A, B, C and D reflected by the first through fourth optical switches31,32,33and34are directed to the mirrors35,36,37and38, respectively. The beam selecting system20B is also provided with a slit member39formed with a slit39S. The mirrors35,36,37and38, and the slit39S are arranged along the X-axis.

As the optical switches35,37,37and38, a silicon micro-mirror array can be used. In this case, the optical switches can be fabricated in accordance with a semiconductor fabricating process such as a silicon micro-fabrication process. With such a configuration, the beam selecting system20B can be downsized, thereby the entire device (i.e., the wavefront curvature modulating device1) can also be downsized.

When the first optical switch31is positioned such that the beam A reflected thereby is reflected by the total reflection mirror35and proceeds in the X-axis direction, a part of the beam A reflected by the total reflection mirror35passes through the first through third beam combining mirrors36,37and38, and emerges from the slit39S. If the first optical switch31is positioned such that the beam A is reflected in another direction (i.e., is inclined with respect to the X-axis), the beam A reflected by the total reflection mirror35does not pass through the slit39S and shielded by the slit member39, which is formed to be a light shielding member.

When the second optical switch32is positioned such that the beam B reflected thereby is reflected by the first beam combining mirror36and proceeds in the X-axis direction, a part of the beam B reflected by the first beam combining mirror36passes through the second and third beam combining mirrors37and38, and emerges from the slit39S. If the second optical switch32is positioned such that the beam B is reflected in another direction, the beam B reflected by the first beam combining mirror36does not pass through the slit39S.

Similarly, when the third optical switch33is positioned such that the beam C reflected thereby is reflected by the second beam combining mirror37and proceeds in the X-axis direction, a part of the beam C reflected by the second beam combining mirror37passes through the third beam combining mirror38, and emerges from the slit39S. If the third optical switch33is positioned such that the beam C is reflected in another direction, the beam C reflected by the second beam combining mirror37does not pass through the slit39S.

When the fourth optical switch34is positioned such that the beam D reflected thereby is reflected by the third beam combining mirror38and proceeds in the X-axis direction, a part of the beam D reflected by the third beam combining mirror38emerges from the slit39S. If the fourth optical switch34is positioned such that the beam D is reflected in another direction, the beam D reflected by the third beam combining mirror38does not pass through the slit39S.

By adjusting the reflection direction of each of the optical switches31through34, each of the beams A through D can be directed to the slit39S or not. Therefore, it is possible to let only one of the beams A through D pass through the slit39S. Further, since the optical switches31through34are controlled individually, it is also possible to allow two or more beams to pass through the slit39S as a combined beam. In the latter case, as in the first embodiment, the wavefront curvature corresponding to the combined beams can be provided.

Since the slit39S is formed such that the beam passes therethrough only when the beam proceeds along the X-axis, and if the axis of the beam inclined with respect to the X-axis, the beam does not pass through the slit39S, each of the optical switches31through34is only required to change the reflection direction within a relatively small range. It should be noted that the optical switches31through34may be controlled by the driving circuit63shown inFIG. 7.

THIRD EMBODIMENT

FIG. 5shows a structure of a beam selecting system20C according to a third embodiment of the invention.

As shown inFIG. 5, the beam selecting system20C includes first through fourth fixed mirrors44,45,46and47, which are aligned along the Y-axis, and respectively located on the axes of the beams A, B, C and D. The first mirror44reflects the beam A in the −Y direction, while the second mirror45reflects the beam B in the +Y direction. The axes of the beams A and B respectively reflected by the first and second mirrors44and45coincide with each other.

Similarly, the third mirror46reflects the beam C in the −Y direction, while the fourth mirror47reflects the beam D in the +Y direction. The axes of the beams C and D respectively reflected by the third and fourth mirrors46and47coincide with each other.

Between the first and second mirrors44and45, along the Y-axis, a first optical switch41is arranged. The first optical switch41is configured to selectively reflects the beam A or beam B to a fixed mirror48. The optical switch41and the fixed mirror48are arranged along the X-axis.

Between the third and fourth mirrors46and47, along the Y-axis, a second optical switch42is arranged. The second optical switch42is configured to selectively reflects the beam C or beam D to a fixed mirror49. The optical switch42and the fixed mirror49are arranged along the X-axis.

The fixed mirrors48and49are arranged along the Y-axis, and the axis of the beam A or B reflected by the fixed mirror48and the axis of the beam C or D reflected by the fixed mirror49coincide with each other.

Between the fixed mirrors48and49, along the Y-axis, a third optical switch43is arranged. The beam A or the beam B incident on the fixed mirror48is reflected thereby to the third optical switch43. Similarly, the beam C or the beam D incident on the fixed mirror49is reflected thereby to the third optical switch43.

The third optical switch43is configured to selectively reflects the beam A or B reflected by the fixed mirror48, or the beam C or D reflected by the fixed mirror49to emerge from the beam selecting system20C along the X-axis.

It should be noted that each of the optical switches41,42and43is composed of, for example, the silicon micro-mirror array, which is capable of performing switching operation at a high speed. By controlling the switching operations of the first through third optical switches41,42and43, a desired one of the beams A through D can be selected to emerge from the beam selecting system20C.

In the beam selecting system20C shown inFIG. 5, the optical switch41is controlled by the beam selecting system driving circuit63(seeFIG. 7) such that one of the beams A and B is selectively directed to the mirror48. Similarly, the optical switch42is controlled by the driving circuit63(seeFIG. 7) such that one of the beams C and D is selectively directed to the mirror49. Further, the optical switch43is controlled by the driving circuit63(seeFIG. 7) such that one of the beams reflected by the mirrors48and49is selected and emitted from the beam selecting system20C. In this embodiment, only one beam is selected among the beams A through D, and emitted from the beam selecting system20C.

FIG. 5shows a condition where the optical switch41reflects the beam B toward the mirror48, the optical switch42reflects the beam C toward the mirror49, and the optical switch43reflects the beam reflected by the mirror48(i.e., the beam B) so that it is emitted from the beam selecting system20C.

In the second and third embodiments, the beam emitted by the light source is firstly divided into a plurality of beams, and then, the beams are modulated to have different wavefront curvatures. Then, at least one of the beams having different wavefront curvatures is selected using the optical switches. However, the invention need not be limited to this configuration. For example, the optical switches may be arranged on the upstream side of the system for modulating the wavefront curvature of the beams. In particular, if an optical switch coupled to an optical fiber is used, it is difficult to switch the beams with maintaining the wavefront curvatures of the incident beams. In such a case, it is necessary that the optical switches are arranged on the upstream side of the system modulating the wavefront curvature of the beams.

The invention is not limited to the first through third embodiments described above, and various modification can be made without departing from the scope of the invention. For example, the number of beams divided by the light beam generator10is not necessarily be four, and the number of the divided beams can be less or more than four.

The light source11may be omitted and the beam generator10may be configured to receive a light beam from an external device, and generates a plurality of beams having different wavefront curvatures.

MODIFICATION OF LENS SYSTEM

Next, an example of a modified configuration of the lens systems13,15,17and19will be described with reference toFIG. 6.

FIG. 6shows a modified lens system50which may replace each of the lens systems13,15,17and19. The lens system50includes two convex lenses51and53, each having a focal length off. The lenses51and53are arranged in the X-axis direction. The lens51is provided with an actuator52, and is configured to be movable in the X-axis direction. That is, by driving the actuator52, the lens51moves with respect to the lens53so that a distance between the lenses51and53varies. If a distance between the principal point of the lens51and the focal point of the lens53is represented by fe, the lens51is moved such that 0<fe≦f is satisfied. When fe is equal to f, the beam incident on the lens51is converged on the focal point of the lens53. In this case, the beam incident on the lens53is collimated thereby, and accordingly, the wavefront curvature is substantially zero. When the fe is smaller (i.e., if the lens51approaches the lens53), the focal point of the lens51is closer to the lens53than its focal point. Accordingly, the beam emerges from the lens53as a diverging beam. Thus, the wavefront curvature is larger as the lens51approaches the lens53. With this configuration, by moving the lens51, the wavefront curvature can be varied, or adjusted.

If each of the lens systems13,15,17and19is replaced with the lens system50, the wavefront curvatures of the four beams generated by the beam generators10can be adjusted depending on the images to be observed. For example, if images at a relatively distant location are to be observed, the radii of the wavefront curvatures of the four beams may be set to 10 cm,30cm, 50 cm and 1 m, while if image at a relative close location are to be observed, the radii of the wavefront curvature of the four beams may be set to 1 m, 3 m, 5 m and the infinity. With such a control, the natural perspective can be provided.

Next, with reference toFIG. 7, the entire system of a retinal displaying device80, to which the WCM1according to each of the embodiments is applicable, will be described.

As shown inFIG. 7, the retinal displaying device80includes a video signal supplying unit71, which receives video signals78from a virtual image projection device77. The virtual image projection device77analyses a three-dimensional object image, and generates two-dimensional images in accordance with the depth of the three-dimensional image. The virtual image projection device77outputs a video signal78, which is input to the video signal supplying unit71.

The video signal supplying unit71generates, based on the received video signal78, a video signal68, a depth signal67, a horizontal synchronizing signal69and a vertical horizontal signal70, which are input to the beam selecting system drive circuit63, a beam generating system drive circuit64, a horizontal scanning system drive circuit65, and a vertical scanning system drive circuit66, respectively.

The beam selecting system drive circuit63and the beam generating system drive circuit64drive the WCM1. Specifically, when the beam generating system drive circuit64receives the video signal68from the video signal supplying unit71, the beam generating system drive circuit64generates a driving voltage to drive the beam generating system10(seeFIG. 2), and applies the same to the beam generating system10. Then, as described above, the light source11of the beam generating system10emits the light beam, which is divide into four beams having different wavefront curvatures.

The beam selecting system drive circuit63generates, when it receives the depth signal67, a driving voltage to drive the beam selection system20(seeFIG. 3), and applies the same to the beam selection system20(20A,20B or20C). Then, at least one of the beams output by the beam generating system10is selected, which is emitted by the WCM1and directed to the horizontal scanning system60.

The horizontal scanning system drive circuit65drives the horizontal scanning system60. Similarly, the vertical scanning system66drives a vertical scanning system61.

The horizontal scanning system60is provided with a polygonal mirror (not shown) which deflects the incident beam to scan in the main scanning direction. The polygonal mirror is driven to rotate as a driving voltage generated by the horizontal scanning system drive circuit65is applied. The horizontal scanning system drive circuit65generates the driving voltage so that the polygonal mirror rotates synchronously with the horizontal synchronizing signal69.

The beam scanned by the horizontal scanning system60is incident on a vertical scanning system61through a first relaying optical system75.

The vertical scanning system61is provided with a galvano mirror (not shown) which deflects the beam scanned by the polygonal mirror to further scan in the auxiliary scanning direction. The galvano mirror is driven to rotate as a driving voltage generated by the vertical scanning system drive circuit66is applied. The vertical scanning system drive circuit66generates the driving voltage so that the galvano mirror swings synchronously with the vertical synchronizing signal70.

The beam two-dimensionally scanned by the horizontal scanning system60and the vertical scanning system61is directed to an eye62of the observer through a second relaying optical system76, and the image is formed on the retina of the observer.

FIG. 8shows processing of the three-dimensional image by the virtual image projection device77.

According to the embodiments, the virtual image projection device77generates a group of two-dimensional image data at different image planes by projecting a three-dimensional image on virtual image planes. InFIG. 8, the up-and-down direction of the drawing is referred to as a Z-axis direction, right-and-left direction is referred to as the X-axis direction, and a direction perpendicular to the plane ofFIG. 8is referred to as the Y-axis direction.

Initially, the virtual image projection device77analyzes a three-dimensional model90in order to realize a three-dimensional image on the retina of the observer.

In this example, the virtual image projection device77defines three virtual planes P1, P2and P3in the depth direction (i.e., the Z-axis direction) of the three-dimensional object model90. Each of the virtual planes P1, P2and P3is a plane perpendicular to the Z-axis (i.e., an X-Y plane). A dividing plane DP1is defined as a plane at an intermediate position between the virtual planes P1and P2, and another dividing plane DP2is defined as a plane at an intermediate position between the virtual planes P2and P3.

The three-dimensional object model90is divided into three pieces in the Z-axis direction with the dividing planes DP1and DP2. Then, the virtual image projection device77projects the three-dimensional object model90onto the virtual planes P1, P2and P3based on a positional relationship between the three-dimensional object model90and a virtual observing point82. The virtual observing point82is a point from which the observer observes the three-dimensional object model90when the image of the three-dimensional object model90is projected on the retina of the observer. By projecting the images representing the positional relationship between the virtual observing point82and the three-dimensional object model90, it is possible to make the observer feel as if the three-dimensional object model90is observed at the virtual observing point82.

The virtual image projecting device77projects a portion of the three-dimensional object model90located on the virtual observing point side with respect to the dividing plane DP2when viewed from the virtual observing point82on the virtual plane P3, i.e., a projected image81cis generated.

Similarly, the virtual image projecting device77projects a portion of the three-dimensional object model90located between the dividing planes DP1and DP2when viewed from the virtual observing point82on the virtual plane P2, i.e., a projected image81bis generated.

Further, the virtual image projecting device77projects a portion of the three-dimensional object model90located on a side opposite to the virtual observing point82with respect to the dividing plane DP1(i.e., the +Z side) when viewed from the virtual observing point82on the virtual plane P1, i.e., a projected image81ais generated.

Then, the virtual image projection device77processes the three projected images81a,81band81cas a single image having three different depths, and generates the video signal78representing such an image, which is transmitted to the video signal supplying unit71. As described above, the thus generated and transmitted video signal78is processed and the image representing the three-dimensional object model90is formed on the retina of the observer.

It should be noted that the number of the virtual planes is not limited to three, and two or more than three planes may be employed.

Further, the positions of the virtual planes P1-P3are determined based on the size of the three-dimensional object model90. This can be modified such that distances between the virtual planes may be determined based on the depth of the three-dimensional object model90so that when an image combining the three projected images is projected on the retina of the observer, the degree of blur of the images on the virtual planes P1and P3due to the out-of-focus state thereof becomes substantially the same. For example, the distances between the virtual planes P1-P3are determined such that, assuming that the eye of the observer focuses on an image on the virtual plane P2, the degrees of the blurs, at the retina of the observer, of the images on the virtual planes P1and P2are substantially the same.

Alternatively, distances between the virtual planes may be determined so that the degrees of blurs of the images on the virtual planes P1and P3with respect to the image on the virtual plane P2become substantially the same in terms of a visual resolution of the observer.

The configuration of the retinal display device80shown inFIG. 8can be modified such that the video signal supplying unit71merges the video signal78output by the virtual image projection device77and another video signal output by a not shown external device, and image corresponding to the merged signals may be formed on the retinal of the observer. In this case, the signal transmitted from the external device is not limited to a signal which does not include the depth signal, but the image data including the depth signal or data representative of a three-dimensional shape expressed by polygons.

Optionally, the retinal display device80may configured to include a plurality of WCMs for generating, for example, Red, Green and Blue component beams whose wavefront curvatures are modulated. With such a configuration, a color image can be formed on the retina of the observer.

It should be noted that, for each image pixel, the wavefront curvatures of the R, G and B beams are generally considered to be substantially the same. Therefore, instead of employing three WCMs for respective color components, only one WCM may be employed and arranged such that the R, G and B beams are combined and then enter the single WCM.

The present disclosure relates to the subject matter contained in Japanese Patent Application No. 2002-029037, filed on Feb. 6, 2002, which is expressly incorporated herein by reference in its entirety.