Optical scanning device and image output apparatus

The present invention provides an optical scanning device that prevents a disadvantageous increase in device size. Transfer optical system 17 includes at least concave mirrors 19 and 20. Furthermore, transfer optical system 17 allows a light beam scanned by scan mirror 16 to enter the scan mirror again at least via concave mirrors 19 and 20. Then, scan mirror 16 scans and emits the laser light beam received via concave mirrors 19 and 20, to a plane of projection.

TECHNICAL FIELD

The present invention relates to an optical scanning device and an image input apparatus both of which allow a light beam to enter a scan mirror a plurality of times to increase a scan angle.

BACKGROUND ART

In connection with optical scanning devices used for image output apparatuses such as laser printers, copiers, or facsimile machines, techniques for increasing a scan angle have been proposed or put to practical use.

These techniques include an optical scanning device described in Patent Document 1.FIG. 1is a diagram showing the configuration of the optical scanning device.

InFIG. 1, a transfer optical system includes concave mirror671with a plane of reflection directed toward scan mirror651, and lens672located between concave mirror671and scan mirror651. A light beam scanned by scan mirror651is guided to concave mirror671via lens672. Furthermore, the light beam folded back by concave mirror671is guided to scan mirror651via lens672. Thus, the light beam is scanned by scan mirror651again, and the resultant light beam is emitted toward a scan target surface. As a result, the scan angle of the emitted light beam is increased.

DISCLOSURE OF THE INVENTION

Problems to Be Solved by the Invention

In the optical scanning device described in Patent Document 1, the light beam scanned by scan mirror651is folded back by concave mirror671via lens672. This increases the distance from scan mirror651to a folding plane on which the light beam is folded back. For example, the distance from scan mirror651to the folding plane is about four times as long as the focal distance of the lens.

Therefore, the size of the device disadvantageously increases.

Thus, an object of the present invention is to provide an optical scanning device and an image output apparatus both of which allow the above-described disadvantageous increase in device size to be prevented.

Means for Solving the Problems

An optical scanning device according to the present invention comprises a scan mirror configured to reflect and scan an incident light beam, and a transfer optical system configured to receive the light beam scanned by the scan mirror and to allow the light beam to enter the scan mirror again. Furthermore, the transfer optical system comprises at least a first concave mirror and a second concave mirror, and allows the light beam scanned by the scan mirror to enter the scan mirror at least via the first concave mirror and the second concave mirror. The scan mirror scans and emits the light beam received via the first concave mirror and the second concave mirror, to a plane of projection.

Furthermore, an image output apparatus according to the present invention comprises the above-described optical scanning device, and an image signal output device configured to allow a light beam to enter the optical scanning device in accordance with an image signal.

Advantage of the Invention

The present invention enables the device to be miniaturized.

BEST MODE FOR CARRYING OUT THE INVENTION

Exemplary embodiments of the present invention will be described below with reference to the drawings. In the description below, components with the same functions are denoted by the same reference numerals throughout the drawings. Description of these components may be omitted.

First Exemplary Embodiment

FIG. 2is a diagram showing the configuration of a display system according to a first exemplary embedment.

Image projection apparatus1projects an image on screen101. The image projection apparatus is an example of an image output apparatus.

Image projection apparatus1includes image signal output device2and optical scanning device3.

Image signal output device2allows a laser beam to enter optical scanning device3in accordance with an input image signal. Specifically, image signal output device2includes laser light sources4to6, collimators7to9, modulators10to12, reflection mirror13, and dichroic mirrors14and15.

Laser light sources4to6emit laser light beams having different wavelengths for, for example, red (R: 620 nm), green (G: 530 nm), and blue (B: 470 nm), in accordance with an input image signal.

Collimators7to9collimate laser light beams emitted by respective laser light sources4to6into parallel light beams with a desired diameter.

Modulators10to12modulate the intensities of the laser light beams collimated by respective collimators7to9in accordance with an input modulation signal.

Reflection mirror13totally reflects the laser light beam modulated by modulator10. Furthermore, dichroic mirror14transmits the laser light beam reflected by reflection mirror13, while totally reflecting the laser light beam modulated by modulator11. Moreover, dichroic mirror15transmits the laser light beam reflected by reflection mirror13and dichroic mirror14, while totally reflecting the laser light beam modulated by modulator12.

Here, laser light sources4to6, collimators7to9, modulators10to12, reflection mirror13, and dichroic mirrors14and15are arranged such that the laser light beams reflected by reflection mirror13and dichroic mirrors14and15are multiplexed together on the same axis and such that the resultant light beam enters optical scanning device3.

Optical scanning device3scans the laser light beam received from image signal output device2, and projects the scanned laser light beam on screen101. Specifically, optical scanning device3includes scan mirror16, transfer optical system17, and scan mirror18.

Scan mirror16rotates reciprocatingly around a preset first axis of rotation to reflect the entered light beam, thus scanning the light beam in a first scanning direction (main scanning direction). InFIG. 2, the first scanning direction is a Y direction.

For example, scan mirror16scans and emits the laser light beam received from image signal output device2, to transfer optical system17. Furthermore, scan mirror16scans and emits the light beam received from transfer optical system17, to scan mirror18.

The light beam scanned by scan mirror16enters transfer optical system17. Furthermore, transfer optical system17allows the incident light beam to enter scan mirror17again.

Scan mirror18rotates reciprocatingly around a second axis of rotation different from that of scan mirror16. Scan mirror18thus scans the laser light beam received from scan mirror16, in a second scanning direction (sub-scanning direction) different from the first scanning direction, to emit the resultant laser light beam to screen101. The second scanning direction is a Z direction. Furthermore, a plane of incidence on scan mirror18on which the laser light beam received from scan mirror16is incident is an example of a plane of projection.

Thus, the three laser light beams having different wavelengths and having the intensities that are thereof modulated are two-dimensionally projected on screen101to form an image.

FIG. 3is a schematic diagram showing the configuration of transfer optical system17.

InFIG. 3, transfer optical system17includes a plurality of mirrors with at least two concave mirrors.

Furthermore, transfer optical system17allows a light beam scanned by scan mirror16to enter scan mirror16again via the plurality of mirrors. Scan mirror16then scans and emits the light beam received via the plurality of mirrors, to scan mirror18.

Specifically, the plurality of mirrors of transfer optical system17include concave mirrors19and20and reflection mirror21. Concave mirror19is an example of a first concave mirror, and concave mirror20is an example of a second concave mirror.

Concave mirror19reflects the light beam scanned by scan mirror16so that the light beam enters concave mirror20. Concave mirror20reflects the light beam received from concave mirror19so that the light beam enters reflection mirror21. Subsequently, reflection mirror21reflects the light beam received from concave mirror20so that the light beam enters concave mirror20. Concave mirror20reflects the light beam received from reflection mirror21so that the light beam enters concave mirror19. Concave mirror19reflects the light beam received from concave mirror20so that the light beam enters scan mirror16. Scan mirror16scans and emits the light beam received from concave mirror19, to scan mirror18.

Thus, the scan angle of scan mirror16can be increased without the use of a lens.

Now, the configuration of a transfer optical system17will be described below in detail.

The position of incidence of a laser light beam on scan mirror16and the position of incidence of a laser light beam on reflection mirror21are conjugate with respect to an optical system having concave mirrors19and20.

If a light beam emitted from a point on an object (object point) is formed, via an optical system, into an image at a point on an image plane (image point) corresponding to the object point, the relationship between the object point and the image point is called conjugate. Here, the conjugate need not be precise but has only to meet a required accuracy.

To conjugate the position of incidence of a laser light beam on scan mirror16and the position of incidence of a laser light beam on reflection mirror21, transfer optical system17may be configured, for example, as follows. In the description below, the focal distance of concave mirror19is defined as f0. The focal distance of concave mirror20is defined as f1.

First, the optical path length between scan mirror16and concave mirror19is equal to focal distance f0 of concave mirror19. The optical path length between concave mirrors19and20is equal to the sum (f0+f1) of focal distance f0 of concave mirror19and focal distance f1 of concave mirror20. The optical path length between concave mirror20and reflection mirror21is equal to focal distance f1 of concave mirror20.

Furthermore, when a light beam traveling from scan mirror16into concave mirror19along a line joining the position of incidence of incident light beam D1on scan mirror16with the center of concave mirror19is reflected from the center of concave mirror19, the light beam is reflected from the center of concave mirror20. Thereafter, the light beam is reflected by reflection mirror21, then reflected from the center of concave mirror20, then reflected from the center of concave mirror19, and returns to the position of incidence on scan mirror16.

Thus, the position of incidence of the laser light beam on scan mirror16is conjugate to the position of incidence of the laser light beam on reflection mirror21.

Specifically, transfer optical system17may be configured as shown inFIG. 4andFIG. 5. Here,FIG. 4is a diagram of transfer optical system17as viewed in the X direction. Furthermore,FIG. 5is a diagram of transfer optical system17as viewed in the Z direction.

First, the configuration of transfer optical system17as viewed in the X direction will be described with reference toFIG. 4. The angle between normal E1of scan mirror16and incident light beam D1entering scan mirror16is defined as θi. Moreover, the angle between normal E1of scan mirror16and exit light beam D8emitted to scan mirror18by scan mirror16is defined as θo.

The angle between normal E1of scan mirror16and line E2joining the center of scan mirror16with the center of concave mirror19is (θo−θi)/2. Furthermore, the distance between the center of scan mirror16and the center of concave mirror19is f0. Moreover, the angle between normal E3of concave mirror19and line E2joining the center of scan mirror16with the center of concave mirror19is (θo−θi)/2.

Furthermore, the angle between normal E3of concave mirror19and line E4joining the center of concave mirror19with the center of concave mirror20is (θo−θi)/2. Additionally, the distance between the center of concave mirror19and the center of concave mirror20is (f0+f1). Moreover, the angle between normal E5of concave mirror20and line E4joining the center of concave mirror19with the center of concave mirror20is (θo−θi)/2.

Furthermore, the angle between normal E5of concave mirror20and line E6joining the center of concave mirror20with the center of reflection mirror21is (θo−θi)/2. Additionally, the distance between the center of concave mirror20and the center of reflection mirror21is f1.

Moreover, the angle between normal E7of reflection mirror21and line E6joining the center of concave mirror20with the center of reflection mirror21is zero degree.

Now, the configuration of transfer optical system17as viewed in the Z direction will be described with reference toFIG. 5.

Light beams resulting from scanning of incident light beam D1at maximum scan angles ±φi by scan mirror16are defined as D2and D2′, respectively.

The angle between line E2joining the center of scan mirror16with the center of concave mirror19and the center line between light beams D2and D2′ is zero degree. Furthermore, the angle between normal E3of concave mirror19and the center line between light beams D2and D2′ is zero degree.

Furthermore, the angle between normal E3of concave mirror19and line E4joining the center of concave mirror19with the center of concave mirror20is zero degree.

Additionally, the angle between normal E5of concave mirror20and line E4joining the center of concave mirror19with the center of concave mirror20is zero degree.

Furthermore, the angle between normal E5of concave mirror20and line E6joining the center of concave mirror20with the center of reflection mirror21is zero degree.

The angle between normal E7of reflection mirror21and line E6joining the center of concave mirror20with the center of reflection mirror21is zero degree.

First, the operation of transfer optical system17as viewed in the X direction will be described with reference toFIG. 4.

Incident light beam D1enters scan mirror16at angle θi to normal E1of scan mirror16.

Subsequently, incident light beam D1is reflected by scan mirror16, and resultant light beam D2enters concave mirror19at angle θi to normal E3of concave mirror19.

Then, light beam D2is reflected by concave mirror19, and resultant light beam D3is focused on focal plane22so as to have the minimum diameter. Thereafter, light beam D3enters concave mirror20at angle (θo−θi)/2 to normal E5of concave mirror20. Focal plane22is positioned at distance f0 from concave mirror19along the optical path between concave mirrors19and20.

Thereafter, light beam D3is reflected by concave mirror20, and resultant light beam D4enters reflection mirror21. Then, light beam D4is collimated into parallel light by concave mirror20.

Furthermore, light beam D4is reflected by reflection mirror21, and resultant light beam D5enters concave mirror20.

Then, light beam D5is reflected by concave mirror20, and resultant light beam D6is focused on focal plane22so as to have the minimum diameter. Thereafter, light beam D6enters concave mirror19at angle (θo−θi)/2 to normal E3of concave mirror19. Focal plane22is positioned at distance f1 from concave mirror20along the optical path between concave mirrors20and19.

Subsequently, light beam D6is reflected by concave mirror19, and resultant light beam D7enters scan mirror16at angle θo to normal E1of scan mirror16. Then, light beam D7is collimated into parallel light having the same diameter as that of light beam D1by concave mirror19.

Then, light beam D7is reflected by scan mirror16, and resultant light beam D8is emitted to scan mirror18at angle θo to normal E1of scan mirror16.

Now, the operation of transfer optical system17as viewed in the Z direction will be described with reference toFIG. 5.

Normals resulting from the maximum deflection of scan mirror16are defined as E1and E1′, respectively. Furthermore, the angle between incident light beam D1and normal E1of scan mirror16is defined as φs. The angle between incident light beam D1and normal E1′ of scan mirror16is defined as φs′.

First, a case where scan mirror16has normal E1will be described.

In this case, incident light beam D1enters scan mirror16at angle φs to normal E1of scan mirror16.

Subsequently, incident light beam D1is reflected by scan mirror16, and resultant light beam D2enters concave mirror19at angle φi to normal E3of concave mirror19.

Then, light beam D2is reflected by concave mirror19, and resultant light beam D3is focused on focal plane22so as to have the minimum diameter. Thereafter, light beam D3enters concave mirror20at zero degree to normal E5of concave mirror20.

Thereafter, light beam D3is reflected by concave mirror20, and resultant light beam D4enters reflection mirror21. Then, light beam D4is collimated into parallel light by concave mirror20.

Furthermore, light beam D4is reflected by reflection mirror21, and resultant light beam D5enters concave mirror20.

Moreover, light beam D5is reflected by concave mirror20, and resultant light beam D6is focused on focal plane22so as to have the minimum diameter. Thereafter, light beam D6enters concave mirror19at zero degree to normal E3of concave mirror19.

Subsequently, light beam D6is reflected by concave mirror19, and resultant light beam D7enters scan mirror16at angle (φs−2φi) to normal E1of scan mirror16. Then, light beam D7is collimated into parallel light having the same diameter as that of light beam D1by concave mirror19.

Then, light beam D7is reflected by scan mirror16, and resultant light beam D8is emitted to scan mirror18at angle (φs−2φi) to normal E1of scan mirror16. Thus, light beam D8is emitted at angle 2φi to incident light beam D1.

Now, a case where scan mirror16has normal E1′ will be described.

In this case, incident light beam D1enters scan mirror16at angle φs′ to normal E1′ of scan mirror16.

Subsequently, incident light beam D1is reflected by scan mirror16, and resultant light beam D2′ enters concave mirror19at angle φi to normal E3of concave mirror19.

Then, light beam D2′ is reflected by concave mirror19, and resultant light beam D3′ is focused on focal plane22so as to have the minimum diameter. Thereafter, light beam D3′ enters concave mirror20at zero degree to normal E5of concave mirror20.

Thereafter, light beam D3′ is reflected by concave mirror20, and resultant light beam D4′ enters reflection mirror21. Then, light beam D4′ is collimated into parallel light by concave mirror20.

Furthermore, incident light beam D4′ is reflected by reflection mirror21, and resultant light beam D5′ enters concave mirror20.

Moreover, light beam D5′ is reflected by concave mirror20, and resultant light beam D6′ is focused on focal plane22so as to have the minimum diameter. Thereafter, light beam D6′ enters concave mirror19at zero degree to normal E3of concave mirror19.

Subsequently, light beam D6′ is reflected by concave mirror19, and resultant light beam D7′ enters scan mirror16at angle (φs′+2φi) to normal E1of scan mirror16. Then, light beam D7′ is collimated into parallel light with the same diameter as that of light beam D1by concave mirror19.

Then, light beam D7′ is reflected by scan mirror16, and resultant light beam D8′ is emitted at angle (φs′+2φi) to normal E1of scan mirror16.

Thus, light beam D8′ is emitted at angle −2φi to incident light beam D1. Furthermore, as described above, light beam D8is emitted at angle 2φi to incident light beam D1. Hence, the angle between light beams D8and D8′ is 4 φi. Therefore, the scan angle of scan mirror16can be doubled by transfer optical system17.

Now, another example of the configuration of the display system according to the exemplary embodiment will be described.

Each of concave mirrors19and20has power in both the X and Z directions. However, the aspect in the example of the configuration described below wherein each of concave mirrors19and20has power only in the X direction will be described. The X direction extends along a scan line placed on concave mirrors19and20by scan mirror16.

FIG. 6is a diagram illustrating the concave mirror having power only in the X direction.

Here, concave mirror19will be described by way of example.FIG. 6shows scan lines501and502placed on concave mirror19by scan mirror16. Scan line501corresponds to a laser light beam received from scan mirror16. Scan line502corresponds to a laser light beam received from concave mirror20.

When having power in both the X and Z directions, concave mirror19can be shaped like a sphere. In this case, as viewed in the Y direction, concave mirror19forms a circle with a subtense corresponding to a scan line placed on concave mirror19by scan mirror16, as shown inFIG. 6(a).

On the other hand, when having power only in the X direction, concave mirror19can be shaped like a cylinder. In this case, as viewed in the Y direction, concave mirror19forms a rectangle with a side corresponding to a scan line placed on concave mirror19by scan mirror16, as shown inFIG. 6(b).

The rectangle is smaller than the circle with the subtense corresponding to the scan line. Thus, concave mirror19having power only in the X direction can be made smaller than concave mirror19having power in both the X and Z directions.

Moreover, as shown inFIG. 6(c), reducing the distance between scan lines501and502enables a reduction in the size of concave mirror19in the Z direction. Thus, the concave surface can further be miniaturized.

FIG. 7is a diagram showing the configuration of transfer optical system17including concave mirrors19and20having power only in the X direction. Specifically,FIG. 7is a diagram of the configuration of transfer optical system17as viewed in the X direction.

InFIG. 7, concave mirror19has an elevation angle in a YZ plane in order to allow light beam D2received from scan mirror16to enter concave mirror20and to allow light beam D6received from concave mirror20to enter scan mirror16.

Furthermore, concave mirror20has an elevation angle in the YZ plane in order to allow light beam D3received from concave mirror19to enter reflection mirror21and to allow light beam D5received from reflection mirror21to enter concave mirror19.

Furthermore, in the exemplary embodiment, image projection apparatus1has been illustrated as an image output apparatus. However, the image output apparatus is not limited to the image projection apparatus but may be appropriately varied. For example, the image output apparatus may be an image forming apparatus such as a printer, a copier, or a facsimile machine.

FIG. 8is a diagram showing the configuration of an image forming apparatus.

Scan mirror16scans and emits a laser light beam received from image signal output device2A, to transfer optical system17. Furthermore, scan mirror16scans and emits a light beam received from transfer optical system17, to photosensitive member24via fθ lens23. A plane of incidence on photosensitive member24on which a laser light beam received from scan mirror16is incident is an example of a plane of projection.

Effects of the Invention

According to the exemplary embodiment, transfer optical system17includes at least concave mirrors19and20. Furthermore, transfer optical system17allows a light beam scanned by scan mirror16to enter the scan mirror again at least via concave mirrors19and20. Then, scan mirror16scans and emits the laser light beam received via concave mirrors19and20, to the plane of projection.

In this case, the laser light beam scanned by scan mirror16enters scan mirror16at least via concave mirrors19and20. Furthermore, the laser light beam having entered scan mirror16at least via concave mirrors19and20is scanned and emitted by scan mirror16.

Thus, the light beam scanned by scan mirror16can be allowed to enter scan mirror16again without the need for a lens. This enables the laser light beam scanned at a first scan angle to be emitted at a second scan angle larger than the first scan angle, without the need for a lens. Hence, the device can be miniaturized.

Furthermore, because a lens is not necessity, this enables optical scanning device3to be easily produced using, for example, a MEMS (Micro Electro Mechanical Systems).

Moreover, because a lens is not necessity, this enables possible chromatic aberration to be inhibited. Thus, for example, when optical scanning device3is used for the image output apparatus, possible color deviation in images can be inhibited.

Furthermore, in the exemplary embodiment, concave mirror19reflects the laser light beam scanned by scan mirror16so that the laser light beam enters concave mirror20. Additionally, concave mirror19reflects the laser light beam received from concave mirror20so that the laser light beam enters scan mirror16. Moreover, concave mirror20reflects the laser light beam received from concave mirror19so that the laser light beam enters reflection mirror21. In addition, concave mirror20reflects the laser light beam received from reflection mirror21so that the laser light beam enters concave mirror19. Then, reflection mirror21reflects the laser light beam received from concave mirror20so that the laser light beam enters concave mirror20.

In this case, the laser light beam scanned by scan mirror16is reflected by concave mirror19, then by concave mirror20, and further by reflection mirror21. Then, the laser light beam reflected by reflection mirror21is reflected by concave mirror20and then concave mirror19and subsequently enters scan mirror16.

Thus, the size (the length in the Y direction) of the optical scanning device can be made smaller than the optical path length between concave mirrors19and20.

For example, in the related art, the size (the distance from scan mirror651to a folding plane) of the optical scanning device is about four times as large as the focal distance of lens672. In the exemplary embodiment, the size of the optical scanning device can be set equal to or smaller than the sum (f0+f1) of the focal distances of concave mirrors19and20.

Furthermore, in the exemplary embodiment, each of concave mirrors19and20has power only in the direction (X direction) along the scan line placed on the concave mirror by scan mirror16.

In this case, each of concave mirrors19and20can be shaped like a cylinder and thus miniaturized.

Furthermore, in the present embodiment, the position of incidence of the laser light beam on scan mirror16is conjugate to the position of incidence of the laser light beam on reflection mirror21.

In this case, the laser light beam scanned at a particular position on scan mirror16enters reflection mirror21at a particular position. Furthermore, the laser light beam scanned at a particular position on reflection mirror21enters scan mirror16at a particular position.

This enables a reduction in the sizes of reflection areas of scan mirror16and reflection mirror21, thus enabling the device to be further miniaturized.

Second Exemplary Embodiment

FIG. 9is a diagram showing the configuration of a display system according to a second exemplary embodiment of the present invention.

FIG. 10is a schematic diagram showing the configuration of transfer optical system17according to the exemplary embodiment. InFIG. 10, a plurality of mirrors of transfer optical system17include concave mirrors19and20and scan mirror31.

Each of concave mirrors19and20has power in both the X and Z directions.

Scan mirror31reflects and scans a laser light beam received from concave mirror20, in a second scanning direction. The laser light beam thus enters concave mirror20. Scan mirror31is an example of a first reflection mirror.

Furthermore, the position of incidence of a laser light beam on scan mirror16is conjugate to the position of incidence of a laser light beam on scan mirror31.

Now, the configuration of transfer optical system17will be described in further detail.

FIG. 11is a diagram of transfer optical system17as viewed in the X direction. Furthermore,FIG. 12is a diagram of transfer optical system17as viewed in the Z direction.

Scan mirror31is provided at the position of reflection mirror21shown inFIG. 4andFIG. 5. Thus, the position of incidence of a laser light beam on scan mirror16and the position of incidence of a laser light beam on scan mirror31are conjugate with respect to an optical system with concave mirrors19and20.

Furthermore, scan mirror31rotates reciprocatingly around a second axis of rotation to scan a laser light beam received from concave mirror20in a second scanning direction (Z direction). The laser light beam thus enters concave mirror20.

Now, the operation of the transfer optical system will be described.

Light beam D3is reflected by concave mirror20, and resultant light beam D4enters scan mirror31. Light beam D4is scanned by scan mirror31and enters concave mirror20.

Laser light beams resulting from scanning of reflected light beam D4at maximum scan angles ±φv by scan mirror31are defined as D5and D5″, respectively.

Light beams D5and D5″ are reflected by concave mirror20, and resultant respective light beams D6and D6″ are focused on focal plane22so as to have the minimum diameter. Thereafter, light beams D6and D6″ enter concave mirror19.

Light beams D6and D6″ are reflected by concave mirror19, and resultant respective light beams D7and D7″ enter scan mirror16. Then, light beams D7and D7″ are collimated, by concave mirror19, into parallel light with the same diameter as that of light beam D1.

Then, light beams D7and D7″ are reflected by scan mirror16, and resultant respective light beams D8and D8″ are emitted to screen101.

In this case, the angle 2φv between light beams D8and D8″ corresponds to the scan angle in the second scanning direction.

In the related art, scanning in two different directions requires that a second scan mirror configured to scan a laser light beam scanned by scan mirror16, in the second scanning direction be longer, in the Y direction, at least than a scan line provided by scan mirror16. Thus, the second scan mirror is normally larger than scan mirror16.

In the exemplary embodiment, scan mirror31reflects the laser light beam received from concave mirror20, in the second scanning direction so that the laser light beam enters concave mirror19. Furthermore, the position of incidence of the laser light beam on scan mirror16is conjugate to the position of incidence of the laser light beam on scan mirror31.

In this case, scan mirror31can reflect the incident laser light beam at a particular position to scan the laser light beam in the second scanning direction. Thus, scan mirror31can be miniaturized. For example, the size of scan mirror31can be made the same as that of scan mirror16.

Third Exemplary Embodiment

FIG. 13is a diagram showing the configuration of a display system according to a third exemplary embodiment of the present invention.

FIG. 14is a schematic diagram showing the configuration of transfer optical system17according to the exemplary embodiment. InFIG. 14, a plurality of mirrors of transfer optical system17include concave mirrors19and20and reflection mirrors21and41.

Reflection mirror41is located on the optical path between concave mirrors19and20. Reflection mirror41is an example of a second reflection mirror.

Here, concave mirrors19and20have an equal focal distance. At this time, reflection mirror41is located at the focal distance of concave mirror19from concave mirror19along the optical path between concave mirrors19and20.

Concave mirror19allows a laser light beam scanned by scan mirror16to enter concave mirror20via reflection mirror41. Furthermore, concave mirror20allows a laser light beam received from reflection mirror21to enter concave mirror19via reflection mirror41.

Now, the configuration of transfer optical system17will be described in detail.

FIG. 15is a diagram of transfer optical system17as viewed in the X direction. Furthermore,FIG. 16is a diagram of transfer optical system17as viewed in the Z direction.

First, the configuration of transfer optical system17as viewed in the X direction will be described with reference toFIG. 15.

The angle between the normal E3of concave mirror19and line E4ajoining the center of concave mirror19with the center of reflection mirror41is (θo−θi)/2. Furthermore, the distance between the center of concave mirror19and the center of reflection mirror41is f0. Moreover, the angle between normal E8of reflection mirror41and line E4ajoining the center of concave mirror19with the center of reflection mirror41is (θo−θi)/2.

Furthermore, the angle between normal E5of concave mirror20and line E4bjoining the center of concave mirror20with the center of reflection mirror41is (θo−θi)/2. Additionally, the distance between the center of concave mirror20and the center of reflection mirror41is f0.

Now, the configuration of transfer optical system17as viewed in the Z direction will be described with reference toFIG. 16.FIG. 16shows concave mirror20and reflection mirrors21and41for convenience. However, in actuality, reflection mirrors21and41overlap scan mirror16. Concave mirror20overlaps concave mirror19.

The angle between normal E3of concave mirror19and line E4ajoining the center of concave mirror19with the center of reflection mirror41is zero degree. Furthermore, the angle between normal E8of reflection mirror41and line E4ajoining the center of concave mirror19with the center of reflection mirror41is zero degree. Moreover, the angle between normal E5of concave mirror20and line E4bjoining the center of concave mirror20with the center of reflection mirror41is zero degree.

In the exemplary embodiment, concave mirrors19and20have an equal focal distance and are thus lie in line in the Z direction. Thus, concave mirrors19and20can be integrated together.

Furthermore, inFIG. 16, reflection mirrors21and41are separated from each other but can in actuality be integrated together.FIG. 17is a diagram showing the configuration of transfer optical system17in which reflection mirrors21and41are integrated together.

InFIG. 17, reflection mirror21is integrated with reflection mirror41. Furthermore, reflection mirror21has an elevation angle in the YZ plane in order to reflect a laser light beam received from concave mirror20so that the laser light beam enters concave mirror20.

Now, the operation of transfer optical system17will be described.

First, the operation of transfer optical system17as viewed in the X direction will be described with reference toFIG. 15.

Light beam D2is reflected by concave mirror19, and resultant light beam D3enters reflection mirror41at angle (θo−θi)/2 to normal E8of reflection mirror41. Light beam D3is focused at the position of incidence on reflection mirror41so as to have the minimum diameter.

Light beam D3is reflected by reflection mirror41, and resultant light beam D3aenters concave mirror20at angle (θo−θi)/2 to normal E5of concave mirror20.

Furthermore, light beam D5is reflected by concave mirror20, and resultant light beam D6enters reflection mirror41at angle (θo−θi)/2 to normal E8of reflection mirror41. Light beam D5is focused at the position of incidence on reflection mirror41so as to have the minimum diameter.

Light beam D6is reflected by reflection mirror41, and resultant light beam D6aenters concave mirror19at angle (θo−θi)/2 to normal E3of concave mirror19.

Now, the operation of transfer optical system17as viewed in the Z direction will be described with reference toFIG. 16.

Light beam D2is reflected by concave mirror19, and resultant light beam D3enters concave mirror20at zero degree to normal E8of reflection mirror41. Light beam D3is focused at the position of incidence on the reflection mirror so as to have the minimum diameter.

Light beam D3is reflected by reflection mirror41, and resultant light beam D3aenters concave mirror20at zero degree to normal E5of concave mirror20.

Furthermore, light beam D5is reflected by concave mirror20, and resultant light beam D6enters reflection mirror41at zero degree to the normal of reflection mirror41. Light beam D6is focused at the position of incidence on the reflection mirror so as to have the minimum diameter.

Light beam D6is reflected by reflection mirror41, and resultant light beam D6aenters concave mirror19at zero degree to normal E3of concave mirror19.

In the exemplary embodiment, reflection mirror41is located on the optical path between concave mirrors19and20.

In this case, the laser light beam traveling between concave mirrors19and20can be folded back by reflection mirror41. This enables optical scanning device3to be further miniaturized.

For example, when reflection mirror41can be provided at the position of focal distance f0 along the optical path from concave mirror19, the length of the optical scanning device in the Y direction can be set equal to or smaller than one, that is the longer of focal distance f0 of concave mirror19and focal distance f1 of concave mirror20.

Furthermore, in the exemplary embodiment, concave mirrors19and20have equal focal distance.

In this case, concave mirrors19and20lie in line in the Z direction. Furthermore, reflection mirrors21and41lie in line in the Z direction. Hence, concave mirrors19and20can be integrated together. Furthermore, reflection mirrors21and41can be integrated together. This enables the device configuration to be simplified, allowing, for example, simple adjustment of optical scanning device3.

Fourth Exemplary Embodiment

FIG. 18is a diagram showing the configuration of a display system according to a fourth exemplary embodiment of the present invention.

FIG. 19is a schematic diagram showing the configuration of transfer optical system17according to the exemplary embodiment.

Concave mirror51is an example of a third concave mirror. Concave mirror52is an example of a fourth concave mirror. Concave mirror53is an example of a fifth concave mirror. Concave mirror54is an example of a sixth concave mirror.

Concave mirror51reflects a laser light beam scanned by scan mirror16so that the laser light beam enters concave mirror53. Concave mirror52reflects a laser light beam received from concave mirror54so that the laser light beam enters scan mirror16.

Concave mirror53reflects a laser light beam received from concave mirror51so that the laser light beam enters reflection mirror21. Concave mirror54reflects a laser light beam received from reflection mirror21so that the laser light beam enters concave mirror52.

Reflection mirror21allows a laser light beam received from concave mirror53to enter concave mirror54.

Now, the configuration of transfer optical system17will be described in detail.

FIG. 20is a diagram of transfer optical system17as viewed in the X direction. Furthermore,FIG. 21is a diagram of transfer optical system17as viewed in the Z direction.

First, the configuration of transfer optical system17as viewed in the X direction will be described with reference toFIG. 20.

Here, the focal distance of concave mirror51is defined as f0. The focal distance of concave mirror52is defined as f3. The focal distance of concave mirror53is defined as f1. The focal distance of concave mirror54is defined as f2.

As is the case of the first exemplary embodiment, the angle between normal E1of scan mirror16and incident light beam D1on scan mirror16is defined as θi. Furthermore, the angle between normal E1of scan mirror16and exit light beam D8from scan mirror16is defined as θo.

Additionally, the angle between normal E1of scan mirror16and line E2joining the center of scan mirror16with the center of concave mirror51is defined as θ2. Moreover, the angle between normal E1of scan mirror16and line E12joining the center of scan mirror16with the center of concave mirror52is defined as θ12.

The angle between normal E3of concave mirror51and line E2joining the center of scan mirror16with the center of concave mirror51is defined as θ2. The angle between normal E9of concave mirror54and line E10joining the center of concave mirror54with the center of concave mirror52is defined as θ12.

The distance between the center of scan mirror16and the center of concave mirror51is f0.

Furthermore, the angle between normal E3of concave mirror51and line E4joining the center of concave mirror51with the center of concave mirror53is defined as θ2. Additionally, the distance between the center of concave mirror51and the center of concave mirror53is (f0+f1). In addition, the angle between normal E5of concave mirror53and line E4joining the center of concave mirror51with the center of concave mirror53is defined as θ2.

The angle between normal E5of concave mirror53and line E6joining the center of concave mirror53with the center of reflection mirror21is defined as θ2. Additionally, the distance between the center of concave mirror53and the center of reflection mirror21is f1.

Normal E7of reflection mirror21is the bisector of the angle between line E6joining the center of concave mirror53with the center of reflection mirror21and line E8joining the center of reflection mirror21with the center of concave mirror54. Furthermore, the distance between the center of reflection mirror21and the center of concave mirror54is f2.

The distance between the center of concave mirror52and the center of concave mirror54is (f2+f3).

The angle between normal E11of concave mirror52and line E12joining the center of concave mirror52with the center of scan mirror16is θ12. Additionally, the distance between the center of concave mirror52and the center of scan mirror16is f3.

Now, the configuration of transfer optical system17as viewed in the Z direction will be described with reference toFIG. 21.

The angle between the center line between light beams D2and D2′ and line E2joining the center of scan mirror16with the center of concave mirror51is zero degree.

Normal E3of concave mirror51is the bisector of the angle between line E2joining the center of scan mirror16with the center of concave mirror51and line E4joining the center of concave mirror51with the center of concave mirror53.

Normal E5of concave mirror53is the bisector of the angle between line E4joining the center of concave mirror51with the center of concave mirror53and line E6joining the center of concave mirror53with the center of reflection mirror21.

Normal E7of reflection mirror21is the bisector of the angle between line E6joining the center of concave mirror53with the center of reflection mirror21and line E8joining the center of reflection mirror21with the center of concave mirror54.

Normal E9of concave mirror54is the bisector of the angle between line E8joining the center of reflection mirror21with the center of concave mirror54and line E10joining the center of concave mirror54with the center of concave mirror52.

Normal E11of concave mirror52is the bisector of the angle between line E10joining the center of concave mirror54with the center of concave mirror52and line E12joining the center of concave mirror52with the center of scan mirror16.

Now, the operation of transfer optical system17will be described.

First, the operation of transfer optical system17as viewed in the X direction will be described.

Incident light beam D1enters scan mirror16at angle θi to normal E1of scan mirror16.

Subsequently, incident light beam D1is reflected by scan mirror16, and resultant light beam D2enters concave mirror51at angle θi to normal E3of concave mirror51.

Then, light beam D2is reflected by concave mirror51, and resultant light beam D3is focused on focal plane55so as to have the minimum diameter. Thereafter, light beam D enters concave mirror53at angle θ2to normal E5of concave mirror53. Focal plane55is positioned at distance f0 from concave mirror51along the optical path between concave mirrors51and53.

Thereafter, light beam D3is reflected by concave mirror20, and resultant light beam D4enters reflection mirror21. Then, light beam D4is collimated into parallel light by concave mirror53.

Furthermore, light beam D4is reflected by reflection mirror21, and resultant light beam D5enters concave mirror54.

Moreover, light beam D5is reflected by concave mirror54, and resultant light beam D6is focused on focal plane55so as to have the minimum diameter. Thereafter, light beam D6enters concave mirror52at angle θ12to normal E3of concave mirror52. Focal plane55is positioned at distance f2 from concave mirror54along the optical path between concave mirrors54and52.

Subsequently, light beam D6is reflected by concave mirror52, and resultant light beam D7enters scan mirror16at angle θo to normal E1of scan mirror16. Then, light beam D7is collimated, by concave mirror52, into parallel light with a diameter equal to f3/f0 of that of light beam D1.

Then, light beam D7is reflected by scan mirror16, and resultant light beam D8is emitted to scan mirror18at angle θo to normal E1of scan mirror16.

Now, the operation of transfer optical system17as viewed in the Z direction will be described.

Here, as is the case with the first embodiment, normals of scan mirror16resulting from the maximum deflection of scan mirror16are defined as E1and E1′, respectively. Furthermore, the angle between incident light beam D1and normal E1of scan mirror16is defined as φs. The angle between incident light beam D1and normal E1′ of scan mirror16is defined as φs′.

Furthermore, the angle between line E2joining the center of scan mirror16with the center of concave mirror51and line E12joining the center of concave mirror52with the center of scan mirror16is defined as φ12. Furthermore, the angle between line E12joining the center of concave mirror52with the center of scan mirror16and light beam D7reflected by concave mirror52is defined as φi′. Moreover, the angle between line E12joining the center of concave mirror52with the center of scan mirror16and light beam D7′ reflected by concave mirror52is defined as φi′.

First, the case where scan mirror16has normal E1will be described.

In this case, incident light beam D1enters scan mirror16at angle φs to normal E1of scan mirror16.

Subsequently, incident light beam D1is reflected by scan mirror16, and resultant light beam D2enters concave mirror51at angle φi to line E2joining the center of scan mirror16with the center of concave mirror51.

Then, light beam D2is reflected by concave mirror51, and resultant light beam D3is focused on focal plane55so as to have the minimum diameter. Thereafter, light beam D3enters concave mirror53. Focal plane55is positioned at distance f0 from concave mirror51along the optical path.

Thereafter, light beam D3is reflected by concave mirror53, and resultant light beam D4enters reflection mirror21. Then, light beam D4is collimated into parallel light by concave mirror53.

Furthermore, light beam D4is reflected by reflection mirror21, and resultant light beam D5enters concave mirror54.

Moreover, light beam D5is reflected by concave mirror54, and resultant light beam D6is focused on focal plane55so as to have the minimum diameter. Thereafter, light beam D6enters concave mirror52. Focal plane55is positioned at distance f3 from concave mirror52along the optical path.

Subsequently, light beam D6is reflected by concave mirror52, and resultant light beam D7enters scan mirror16at angle (φ−φi−φ12−φi′) to normal E1of scan mirror16. Then, light beam D7is collimated, by concave mirror52, into parallel light with a diameter equal to f3/f0 of that of light beam D1.

Then, light beam D7is reflected by scan mirror16, and resultant light beam D8is emitted to scan mirror18at angle (φs−φi−φ12−φi′) to normal E1of scan mirror16. Thus, light beam D8is emitted at angle (φi+φ12+φi′) to incident light beam D1.

Now, the case where scan mirror16has normal E1′ will be described.

In this case, incident light beam D1enters scan mirror16at angle φs′ to normal E1′ of scan mirror16.

Subsequently, incident light beam D1is reflected by scan mirror16, and resultant light beam D2′ enters concave mirror51at angle φi to line E2joining the center of scan mirror16with the center of concave mirror51.

Then, light beam D2′ is reflected by concave mirror51, and resultant light beam D3′ is focused on focal plane55so as to have the minimum diameter. Thereafter, light beam D3′ enters concave mirror53.

Thereafter, light beam D3′ is reflected by concave mirror53, and resultant light beam D4′ enters reflection mirror21. Then, light beam D4′ is collimated into parallel light by concave mirror53.

Furthermore, light beam D4′ is reflected by reflection mirror21, and resultant light beam D5′ enters concave mirror54.

Moreover, light beam D5′ is reflected by concave mirror53, and resultant light beam D6′ is focused on focal plane55so as to have the minimum diameter. Thereafter, light beam D6′ enters concave mirror52at zero degree to normal E3of concave mirror52.

Subsequently, light beam D6′ is reflected by concave mirror52, and resultant light beam D7′ enters scan mirror16at angle (φs′+φi−φ12+φi′) to normal E1′ of scan mirror16. Then, light beam D7′ is collimated, by concave mirror52, into parallel light with a diameter equal to f3/f0 of that of light beam D1.

Then, light beam D7′ is reflected by scan mirror16, and resultant light beam D8is emitted to scan mirror18at angle (φs′+φi−φ12+φi′) to normal E1of scan mirror16.

Thus, light beam D8′ is emitted at angle (−φi+φ12−φi′) to incident light beam D1. Furthermore, as described above, light beam D8is emitted at angle (φi+φ22+φi′) to incident light beam D1. Hence, the angle between light beams D8and D8′ is 2(φi+φi′).

In this case, provided that φi′ is larger than φi, the scan angle of scan mirror16can be increased at least to double by transfer optical system17. Thus, the scan angle of scan mirror16can be increased.

For example, if the angles φi and φi′ are small, φi′ is almost equal to φi×f0/f3. Thus, F0>f3 enables an increase in the scan angle of scan mirror16.

In the present embodiment, reflection mirror41may be provided on the optical path between concave mirrors19and20. In this case, reflection mirror41may be placed either on the optical path between concave mirrors51and53or on the optical path between concave mirrors54and52.

Furthermore, reflection mirror21may be replaced with scan mirror31. In this case, the laser light beam can be scanned in the second scanning direction by scan mirror31. Furthermore, provided that the position of incidence of the laser light beam on scan mirror16is conjugate to the position of incidence of the laser light beam on scan mirror31, scan mirror31can reflect and scan the incident laser light beam at a particular position. This enables scan mirror31to be miniaturized.

According to the exemplary embodiment, concave mirror51reflects the laser light beam scanned by scan mirror16so that the laser light beam enters concave mirror53. Concave mirror52reflects the laser light beam received from concave mirror54so that the laser light beam enters scan mirror16. Concave mirror53reflects the laser light beam received from concave mirror51so that the laser light beam enters reflection mirror21. Concave mirror54reflects the laser light beam received from reflection mirror21so that the laser light beam enters concave mirror52. Reflection mirror21reflects the laser light beam received from concave mirror53so that the laser light beam enters concave mirror54.

In this case, the scan angle of scan mirror16can further be increased by configuring concave mirrors51to54and reflection mirror21as follows: angle φ′, to line E12joining the center of concave mirror52with the center of scan mirror16, of light beam D7′ traveling from concave mirror52into the scan mirror is larger than angle φi, to the normal of concave mirror51, of light beam D2traveling from scan mirror16into concave mirror51.

Fifth Exemplary Embodiment

FIG. 22is a diagram showing the configuration of a display system according to a fifth exemplary embodiment of the present invention.

FIG. 23is a schematic diagram showing the configuration of transfer optical system17according to the exemplary embodiment.

InFIG. 23, a plurality of mirrors of transfer optical system17include concave mirrors19and20.

Concave mirrors19and20allow a laser light beam scanned by scan mirror16to enter scan mirror16via concave mirrors19and20. Furthermore, scan mirror16scans and emits the laser light beam received via concave mirrors19and20, to scan mirror18.

Specifically, concave mirror19reflects the laser light beam scanned by scan mirror16so that the laser light beam enters concave mirror20. Furthermore, concave mirror19reflects the laser light beam received from concave mirror20so that the laser light beam enters scan mirror16.

Concave mirror20reflects the laser light beam received from concave mirror19so that the laser light beam enters concave mirror19.

Furthermore, the position of incidence of the laser light beam on scan mirror16and the position of incidence of the laser light beam on concave mirror20are conjugate with respect to concave mirror19.

Now, the configuration of transfer optical system17will be described in detail.

FIG. 24is a diagram of transfer optical system17as viewed in the X direction. Furthermore,FIG. 25is a diagram of transfer optical system17as viewed in the Z direction.

First, the configuration of transfer optical system17as viewed in the X direction will be described with reference toFIG. 24.

As is the case with the first exemplary embodiment, the angle between normal E1of scan mirror16and incident light beam D1entering scan mirror16is defined as θi. Furthermore, the angle between normal E1of scan mirror16and exit light beam D8leaving scan mirror16is defined as θo.

Furthermore, the distance between the center of scan mirror16and the center of concave mirror19is defined as s0. s0 is the double of focal distance f0 of concave mirror19.

The angle between normal E1of scan mirror16and line E2joining the center of scan mirror16and the center of concave mirror19is (θo−θi)/2. Moreover, the angle between normal E3of concave mirror19and line E2joining the center of scan mirror16and the center of concave mirror19is (θo−θi)/2.

The angle between normal E5of concave mirror20and line E4joining the center of concave mirror19and the center of concave mirror20is zero degree. Furthermore, the distance between the center of concave mirror19and the center of concave mirror20is (f0+S1). Distance s1 is the distance between concave mirror20and focal plane61and is the double of focal distance f1 of concave mirror20.

Now, the configuration of transfer optical system17as viewed in the Z direction will be described with reference toFIG. 25.

As is the case with the first exemplary embodiment, reflected light beams resulting from scanning of incident light beam D1at maximum scan angle ±φi by scan mirror16are defined as D2and D2′, respectively.

The angle between line E2joining the center of scan mirror16with the center of concave mirror19and the center line between light beams D2and D2′ is zero degree. Furthermore, the angle between the center line, that is between light beams D2and D2′, and concave mirror19and normal E3is zero degree.

Furthermore, the angle between normal E3of concave mirror19and line E4joining the center of concave mirror19with the center of concave mirror20is zero degree.

Moreover, the angle between normal E5of concave mirror20and line E4joining the center of concave mirror19with the center of concave mirror20is zero degree.

Description of Operation

Now, the operation of transfer optical system17will be described.

First, the operation of transfer optical system17as viewed in the X direction will be described with reference toFIG. 24.

Subsequently, incident light beam D1is reflected by scan mirror16, and resultant light beam D2enters concave mirror19at angle θi to normal E3of concave mirror19.

Moreover, light beam D2is reflected by concave mirror19, and resultant light beam D3is focused on focal plane61so as to have the minimum diameter. Thereafter, light beam D3enters the center of concave mirror20. Focal plane61is positioned at distance f0 from concave mirror19along the optical path between concave mirrors19and20. Positioned at distance f0.

Subsequently, light beam D3is reflected by concave mirror20, and resultant light beam D6is focused on focal plane61so as to have the minimum diameter. Thereafter, light beam D6enters concave mirror19. Focal plane61is positioned at distance s1 along the optical path from concave mirror20.

Thereafter, light beam D6is reflected by concave mirror19, and resultant light beam D7enters scan mirror16at angle θo to normal E1of scan mirror16. Then, light beam D7is collimated, by concave mirror19, into parallel light with the same diameter as that of light beam D1.

Then, light beam D7is reflected by scan mirror16, and resultant light beam D8is emitted at angle θo to normal of scan mirror16.

Now, the operation of transfer optical system17as viewed in the Z direction will be described with reference toFIG. 25.

As is the case with the first exemplary embodiment, normals of scan mirror16resulting from the maximum deflection of scan mirror16are defined as E1and E1′. Normals of scan mirror16resulting from the maximum deflection of scan mirror16are defined as E1and E1′, respectively. Furthermore, the angle between incident light beam D1and normal E1of scan mirror16is defined as φs. The angle between incident light beam D1and normal E1′ of scan mirror16is defined as φs′.

First, the case where scan mirror16has normal E1will be described.

Subsequently, incident light beam D1is reflected by scan mirror16, and resultant light beam D2enters concave mirror19at angle φi to normal E3of concave mirror19.

Moreover, light beam D2is reflected by concave mirror19, and resultant light beam D3is focused on focal plane61so as to have the minimum diameter. Thereafter, light beam D3enters the center of concave mirror20.

Thereafter, light beam D3is reflected by concave mirror20, and resultant light beam D6is focused on focal plane61so as to have the minimum diameter. Thereafter, light beam D6enters concave mirror19.

Subsequently, light beam D6is reflected by concave mirror19, and resultant light beam D7enters scan mirror16at angle (φs−2φi) to normal E1of scan mirror16. Then, light beam D7is collimated, by concave mirror19, into parallel light with the same diameter as that of light beam D1.

Moreover, light beam D7is reflected by scan mirror16, and resultant light beam D8is emitted at angle (φs−2φi) to normal E1of scan mirror16. Thus, light beam D8is emitted at angle 2φi to incident light beam D1.

Now, the case where scan mirror16has normal E1′ will be described.

First, incident light beam D1′ enters scan mirror16at angle φs′ to normal E1′ of scan mirror16.

Subsequently, incident light beam D1is reflected by scan mirror16, and resultant light beam D2′ enters concave mirror19at angle φi to normal E3of concave mirror19.

Moreover, light beam D2′ is reflected by concave mirror19, and resultant light beam D3′ is focused on focal plane61so as to have the minimum diameter. Thereafter, light beam D3′ enters the center of concave mirror20.

Thereafter, light beam D3′ is reflected by concave mirror20, and resultant light beam D6′ is focused on focal plane61so as to have the minimum diameter. Thereafter, light beam D6′ enters concave mirror19.

Subsequently, light beam D6′ is reflected by concave mirror19, and resultant light beam D7′ enters scan mirror16at angle (φs′+2φi) to normal E1of scan mirror16. Then, light beam D7is collimated, by concave mirror19, into parallel light with the same diameter as that of light beam D1.

Then, light beam D7′ is reflected by scan mirror16, and resultant light beam D8′ is emitted at angle (φs′+2φi) to normal E1of scan mirror16. Thus, light beam D8′ is emitted at angle 2φi to incident light beam D1. Furthermore, as described above, light beam D8′ is emitted at angle 2φi to incident light beam D1. Hence, the angle between light beams D8and D8′ is 4φi. Thus, the scan angle of scan mirror16can be increased to double by transfer optical system17.

Description of Effects

According to the exemplary embodiment, concave mirror19reflects the laser light beam scanned by scan mirror16so that the laser light beam enters concave mirror20. Concave mirror19reflects the laser light beam received from concave mirror20so that the laser light beam enters scan mirror16. Concave mirror20reflects the laser light beam received from concave mirror19so that the laser light beam enters concave mirror19.

In this case, the laser light beam scanned by scan mirror16is reflected by concave mirror19and further by concave mirror20. The laser light beam reflected by concave mirror20enters scan mirror16reflected by concave mirror19.

Thus, the size (the length in the Y direction) of the optical scanning device can be made smaller than the optical path length between concave mirrors19and20. For example, in the exemplary embodiment, the size of the optical scanning device can be set equal to or smaller than (f0+2f1).

Furthermore, the exemplary embodiment eliminates the need for reflection mirror21, thus enabling the device configuration to be simplified. This enables, for example, simple adjustment of optical scanning device3.

Sixth Exemplary Embodiment

FIG. 26is a diagram showing the configuration of a display system according to a sixth exemplary embodiment.

FIG. 27is a schematic diagram showing the configuration of transfer optical system17according to the exemplary embodiment.

InFIG. 27, a plurality of mirrors of transfer optical system17include concave mirrors19and20and reflection mirrors42and43.

Reflection mirror42is located on the optical path between concave mirrors19and20. Furthermore, reflection mirror43is located on the optical path between scan mirror16and concave mirror19. Reflection mirror42is an example of a third reflection mirror. Reflection mirror43is an example of a fourth reflection mirror.

Specifically, reflection mirror42is located at focal distance f0 of concave mirror19along the optical path from concave mirror19. Furthermore, reflection mirror43is located at focal distance f0(s0/2) of concave mirror19along the optical path from scan mirror16.

Reflection mirror43reflects a laser light beam scanned by scan mirror16so that the laser light beam enters concave mirror19. Furthermore, reflection mirrors43reflects a laser light beam received from concave mirror19so that the laser light beam enters scan mirror16.

Concave mirror19allows a laser light beam scanned by reflection mirror43to enter concave mirror20via reflection mirror42. Furthermore, concave mirror20allows a laser light beam received from reflection mirror42to enter concave mirror19via reflection mirror42.

The position of incidence of the laser light beam on scan mirror16and the position of incidence of the laser light beam on concave mirror20are conjugate with respect to concave mirror19.

Now, the configuration of transfer optical system17will be described in detail.

FIG. 28is a diagram of transfer optical system17as viewed in the X direction. Furthermore,FIG. 29is a diagram of transfer optical system17as viewed in the Z direction.

First, the configuration of transfer optical system17as viewed in the X direction will be described with reference toFIG. 28.

As is the case with the first exemplary embodiment, the angle between normal E1of scan mirror16and incident light beam D1entering scan mirror16is defined as θi. Furthermore, the angle between normal E1of scan mirror16and exit light beam D8leaving scan mirror16is defined as θo.

Furthermore, the distance between the center of scan mirror16and the center of reflection mirror43is defined as f0(s0/2). The distance between the center of reflection mirror43and the center of concave mirror19is defined as f0.

The angle between normal E1of scan mirror16and line E2joining the center of scan mirror16with the center of reflection mirror43is (θo−θi)/2. Moreover, the angle between normal E8of reflection mirror43and line E2joining the center of scan mirror16with the center of reflection mirror43is (θo−θi)/2.

The angle between normal E3of concave mirror19and line E4ajoining the center of reflection mirror43with the center of concave mirror19is (θo−θi)/2.

The angle between normal E7of reflection mirror42and line E4bjoining the center of concave mirror19with the center of reflection mirror42is (θo−θi)/2. Furthermore, the distance between the center of concave mirror19and the center of reflection mirror42is f0.

The angle between normal E5of concave mirror20and line E4cjoining the center of reflection mirror42with the center of concave mirror20is zero degree. Furthermore, the distance between the center of reflection mirror42and the center of concave mirror20is s1(2f1)

Now, the configuration of transfer optical system17as viewed in the Z direction will be described with reference toFIG. 28.

As is the case with the first embodiment, reflected light beams resulting from scanning of incident light beam D1at maximum scan angle ±φi by scan mirror16are defined as D2and D2′, respectively.

The angle between line E2joining the center of scan mirror16with the center of reflection mirror42and the center line between light beams D2and D2′ is zero degree. Furthermore, the angle between normal E8of reflection mirror43and the center line between light beams D2and D2′is zero degree.

Furthermore, the angle between normal E8of reflection mirror43and line E4ajoining the center of reflection mirror43with the center of concave mirror19is zero degree.

Additionally, the angle between normal E3of concave mirror19and line E4bjoining the center of concave mirror19with the center of reflection mirror42is zero degree.

In addition, the angle between normal E7of reflection mirror42and line E4cjoining the center of reflection mirror42with the center of concave mirror20is zero degree.

Moreover, the angle between normal E5of concave mirror20and line E4cjoining the center of reflection mirror42with the center of concave mirror20is zero degree.

Description of Operation

Now, the operation of transfer optical system17will be described with reference toFIG. 28.

First, the operation of transfer optical system17as viewed in the X direction will be described.

Subsequently, incident light beam D1is reflected by scan mirror16, and resultant light beam D2enters reflection mirror43at angle θi to normal E8of reflection mirror43.

Moreover, light beam D2is reflected by reflection mirror43, and resultant light beam D3enters concave mirror19at angle θi to normal E3of concave mirror19.

Then, light beam D3is reflected by concave mirror19, and resultant light beam D4enters reflection mirror42. Light beam D4is focused at the position of incidence on reflection mirror42so as to have the minimum diameter.

Then, light beam D4is reflected by reflection mirror42, and resultant light beam D5enters the center of concave mirror20.

Subsequently, light beam D5is reflected by concave mirror20, and resultant light beam D6enters reflection mirror42. Light beam D6is focused at the position of incidence on reflection mirror42so as to have the minimum diameter.

Moreover, light beam D6is reflected by reflection mirror42, and resultant light beam D7enters concave mirror19at angle θo to normal E3of concave mirror19.

Moreover, light beam D7is reflected by concave mirror19, and resultant light beam D8enters reflection mirror43at angle θo to normal E8of reflection mirror43. Then, light beam D8is collimated, by concave mirror19, into parallel light with the same diameter as that of light beam D1.

Thereafter, light beam D8is reflected by reflection mirror43, and resultant light beam D9enters scan mirror16at angle θo to normal E1of scan mirror16.

Then, light beam D9is reflected by scan mirror16, and resultant light beam D10is emitted at angle θo to normal E1of scan mirror16.

Now, the operation of transfer optical system17as viewed in the Z direction will be described with reference toFIG. 29.

As is the case with the first embodiment, normals of scan mirror16resulting from the maximum deflection of scan mirror16are defined as E1and E1′. Normals of scan mirror16resulting from the maximum deflection of scan mirror16are defined as E1and E1′, respectively. Furthermore, the angle between incident light beam D1and normal E1of scan mirror16is defined as φs. The angle between incident light beam D1and normal E1′ of scan mirror16is defined as φs′.

First, the case where scan mirror16has normal E1will be described.

Subsequently, incident light beam D1is reflected by scan mirror16, and resultant light beam D2enters reflection mirror43at angle φi to normal E8of reflection mirror43.

Moreover, light beam D2is reflected by reflection mirror43, and resultant light beam D3enters concave mirror19at angle φi to normal E3of concave mirror19.

Then, light beam D3is reflected by concave mirror19, and resultant light beam D4enters reflection mirror42. Light beam D4is focused at the position of incidence of reflection mirror42so as to have the minimum diameter.

Moreover, light beam D4is reflected by reflection mirror42, and resultant light beam D5enters the center of concave mirror20.

Thereafter, light beam D5is reflected by concave mirror20, and resultant light beam D6enters reflection mirror42. Light beam D6is focused at the position of incidence of reflection mirror42so as to have the minimum diameter.

Subsequently, light beam D6is reflected by reflection mirror42, and resultant light beam D7enters concave mirror19at angle φi to normal E3of concave mirror19.

Moreover, light beam D7is reflected by concave mirror19, and resultant light beam D8enters reflection mirror43at angle φi to normal E8of reflection mirror43. Then, light beam D8is collimated, by concave mirror19, into parallel light with the same diameter as that of light beam D1.

Moreover, light beam D8is reflected by reflection mirror43, and resultant light beam D9enters scan mirror16at angle φi to normal E1of scan mirror16.

Thereafter, light beam D9is reflected by scan mirror16, and resultant light beam D10is emitted at angle (φs−2φi) to normal E1of scan mirror16. Thus, light beam D10is emitted at angle 2φi to incident light beam D1.

Now, the case where scan mirror16has normal E1′ will be described.

First, incident light beam D1′ enters scan mirror16at angle φs′ to normal E1′ of scan mirror16.

Subsequently, incident light beam D1is reflected by scan mirror16, and resultant light beam D2′ enters reflection mirror43at angle φi to normal E8of reflection mirror43.

Moreover, light beam D2′ is reflected by reflection mirror43, and resultant light beam D3′ enters concave mirror19at angle φi to normal E3of concave mirror19.

Moreover, light beam D3′ is reflected by concave mirror19, and resultant light beam D4′ enters reflection mirror42. Light beam D4is focused at the position of incidence of reflection mirror42so as to have the minimum diameter.

Moreover, light beam D4′ is reflected by reflection mirror42, and resultant light beam D5′ enters the center of concave mirror20.

Thereafter, light beam D5′ is reflected by concave mirror20, and resultant light beam D6′ enters reflection mirror42. Light beam D4is focused at the position of incidence of reflection mirror42so as to have the minimum diameter.

Subsequently, light beam D6′ is reflected by reflection mirror42, and resultant light beam D7′ enters concave mirror19at angle φi to normal E3of concave mirror19.

Moreover, light beam D7′ is reflected by concave mirror19, and resultant light beam D8′ enters reflection mirror43at angle φi to normal E8of reflection mirror43. Then, light beam D8′ is collimated, by concave mirror19, into parallel light having the same diameter as that of light beam D1′.

Moreover, light beam D8′ is reflected by reflection mirror43, and resultant light beam D9′ enters scan mirror16at angle φi to normal E1of scan mirror16.

Thereafter, light beam D9′ is reflected by scan mirror16, and resultant light beam D10′ is emitted at angle (φs′−2φi) to normal E1of scan mirror16. Thus, light beam D10′ is emitted at angle 2φi to incident light beam D1′.

Furthermore, as described above, light beam D10is emitted at angle 2φi to incident light beam D1. Hence, the angle between light beams D10and D10′ is 4φi. Thus, the scan angle of scan mirror16can be increased to double by transfer optical system17.

Description of Effects

In the exemplary embodiment, reflection mirror42is located on the optical path between concave mirrors19and20. Furthermore, reflection mirror43is located on the optical path between scan mirror16and concave mirror19.

In this case, the laser light beam traveling between concave mirrors19and20can be folded back by reflection mirror42. Furthermore, the laser light beam traveling between concave mirrors19and20can be folded back by reflection mirror43. This enables optical scanning device3to be further miniaturized.

For example, it is assumed that reflection mirror42is provided at the position of focal distance f0 along the optical path from concave mirror19and that reflection mirror43is provided at the position of focal distance f0(S0/2) along the optical path from concave mirror19. In this case, the length of the optical scanning device in the Y direction can be set equal to or smaller than the longer of focal distance f0 of concave mirror19and the double (s1) of focal distance f1 of concave mirror20.

Furthermore, in the present exemplary embodiment, reflection mirrors42and43are both located at the position of focal distance f0 of concave mirror19. In this case, reflection mirrors42and43lie in line in the Z direction. Hence, reflection mirrors42and43can be integrated together. Therefore, the device configuration can be simplified, enabling, for example, simple adjustment of optical scanning device3.

Furthermore, in the exemplary embodiment, if focal distance f0 of concave mirror19is equal to the double of focal distance f1 of concave mirror20, concave mirrors19and20lie in line in the Z direction. In this case, concave mirrors19and20can be integrated together. Therefore, the device configuration can be simplified, enabling, for example, simple adjustment of optical scanning device3.

The present invention has been described above with reference to the exemplary embodiments. However, the present invention is not limited to the above-described exemplary embodiments. Various changes understandable to those skilled in the art may be made to the components and details of the present invention without departing from the scope of the present invention.

The present application claims priority based on JP2007-307511A filed on Nov. 28, 2007 and incorporates the entirety of the disclosure thereof.