JPH11224061A - Video display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the video display device which has a very high scanning frequency and is compact. SOLUTION: The video display device is equipped with a light source 11 whose emitted light intensity can be modulated, an optical element 13 which is variable in focal length, and a screen 14 which diffuses incident light. Then the optical element 13 images the light from the light source 11 on the screen 14 and varies in focal length to move the image formation position on the screen 14, thereby forming linear or two-dimensional video on the screen 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning type image display device which forms a one-dimensional or two-dimensional image by scanning light with a scanning means and displays the image.

[0002]

2. Description of the Related Art A laser scanning type image display device which uses a laser as a light source to scan a beam thereof to display a two-dimensional image has a higher contrast and a higher color reproduction than a display device using a two-dimensional display element such as a liquid crystal display. Various advantages, such as excellent performance and low power consumption, can be obtained.

As a conventional example of a scanning type video display device, there is a head mounted video display device (HMD) shown in FIG. FIG. 9 is a schematic view of the optical system of the HMD viewed from above. 1
A main scanning unit 01 scans incident light in a horizontal direction. As shown in FIG. A viewed from the side, light emitted from a laser light source 102 modulated by a video signal is condensed by a condenser lens 103 and enters the main scanning unit 101.

A sub-scanning unit 104 scans light from the main scanning unit 101 in the vertical direction. Reference numeral 105 denotes a half mirror that reflects the light from the sub-scanning unit 104 and provides the light to the concave mirror, and transmits the light from the concave mirror and provides the light to the pupil of the observer. 106 is a concave mirror that projects a virtual image on the pupil of the observer. The main scanning means 101 is a concave mirror 106
Through the pupil position of the observer.

The scanning means of the scanning type video display device includes:
Conventionally, a polygon mirror and a galvanometer mirror are known. These scanning means change light reflection direction by rotating and oscillating a mirror to scan light.

[0006]

However, in order to display a high-definition image having a sufficient pupil diameter in an image display apparatus using the above-described conventional scanning means, it is necessary to vibrate a large mirror with a large amplitude. Therefore, it was difficult to reduce the size of the entire apparatus. Furthermore, in order to display a high-definition image, a very high scanning frequency is required, but in order to configure a mirror having strength that can withstand high-speed vibration, it is necessary to use an expensive material, Cost was high. In addition, there is a problem that high-speed vibration of a large mirror is difficult.

The present invention has been made in view of the above problems, and has as its object to provide a compact video display device having a very high scanning frequency.

[0008]

According to a first aspect of the present invention, there is provided an image display apparatus comprising: a light source capable of modulating the intensity of emitted light; an optical element having a variable focal length; A screen for diffusing light, wherein the optical element forms a one-dimensional or two-dimensional image by moving light from the light source onto the screen and moving a focus position on the screen by changing a focal length. An image is formed on the screen.

The optical element can move the image forming position of light by changing the focal length. That is, it is a scanning unit that scans light in one direction. In the optical element, when incident light is light of a point image, 1
A two-dimensional image is formed. When the incident light is light of a one-dimensional image, a two-dimensional image is formed by scanning.

[0010] The screen is arranged at a position where light is focused by the optical element. Therefore, one-dimensional or two-dimensional image light is imaged and diffused on the screen. The diffused light is provided to the observer or the observation device.

According to a second aspect of the present invention, in the video display device according to the first aspect, the optical element is configured to form a point-like image of light. In such a configuration, since the image forming light from the optical element is collected at one point, it is possible to project strong light on the screen.

According to a third aspect of the present invention, in the video display device according to the first aspect, the optical element forms a linear image of light. In such a configuration, since the image-forming light from the optical element is linear, the image-forming position spreads one-dimensionally, so that the arrangement position of the screen is not limited to one.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS <First Embodiment> FIG.
1 is a schematic configuration diagram of a video display device according to an embodiment. Reference numeral 11 denotes a laser diode (hereinafter, referred to as an LD) that emits a laser beam whose intensity is modulated according to a video signal, and 12 denotes an LD 11
A collimator for emitting light from the collimator 12 into parallel light, 13 is a variable focal length mirror that forms the light from the collimator 12 into a point image, and 14 is a one-dimensional shape that diffuses the image formed by the variable focal length mirror 13 It is a screen of.

The focal length variable mirror 13 changes the focal length by changing the shape of the reflecting surface, and moves the position of a point image on the screen 14. Therefore, it becomes a scanning means for scanning light in one direction. The light emitted by the LD 11 travels, for example, as indicated by arrows in the figure.

The reflecting surface of the variable focal length mirror 13 is 13a.
In this state, the light is imaged on the screen 14 at the position 14a. On the other hand, when the reflecting surface of the variable focal length mirror 13 is in the state of 13b, the light is imaged at the position of 14b on the screen. The observer observes the one-dimensional image by giving the light diffused by the one-dimensional screen 14 to the pupil.

In this embodiment, the variable focal length optical element is constituted by a mirror. The mirror can achieve a large change in focal length with a slight change in shape as compared with, for example, a lens, so that high-speed scanning can be easily performed.

<Second Embodiment> FIG. 2 shows a schematic configuration diagram of a video display apparatus according to a second embodiment. Reference numeral 21 denotes an LD that emits a laser beam whose intensity is modulated according to a video signal;
Is a collimator that emits light from the LD 21 as parallel light, 23 is an anamorphic variable focal length mirror that linearly images the light from the collimator 22, and 24 is a diffuser that forms an image formed by the anamorphic variable focal length mirror 23. 1 to do
It is a dimensional screen.

Anamorphic variable focal length mirror 23
Moves the position of line imaging by changing the focal length.
Therefore, it becomes a scanning means for scanning light in one direction. LD2
The light emitted in 1 travels, for example, as indicated by the arrow in the figure. The anamorphic variable focal length mirror 23 is
Depending on the focal length, for example, light is linearly imaged at positions 27a and 27b. Light (for example, 27a ′ and 27b ′) incident on the screen 24 in the line image is diffused by the screen 24. The observer observes the one-dimensional image when the diffused light is given to the pupil.

In this embodiment, the scanning means is constituted by an anamorphic focal length variable mirror 23 which has a variable magnification in only one direction to linearly image light. Since the image formed by the mirror is linear, the position of the one-dimensional screen 24 can be easily adjusted and the manufacturing cost can be reduced as compared with the case where the image is formed in a point.

<Third Embodiment> FIG. 3 shows a schematic configuration diagram of a video display device according to a third embodiment. Reference numeral 31 denotes an LD that emits a laser beam whose intensity is modulated according to a video signal;
Is a variable focal length lens that forms a point-like image of the light from the LD 31; 34 is a one-dimensional screen that diffuses the image forming light from the variable focal length lens 33; 35 is unnecessary light 36 that is not diffused by the screen 34; It is an absorbing plate that absorbs.

The variable focal length lens 33 changes the focal length by changing the refractive index and moves the position of the line image. Therefore, it becomes a scanning means for scanning light in one direction. The light emitted by the LD 31 travels, for example, as indicated by the arrow in the figure. The variable focal length lens 33 forms an image of light at, for example, positions 34a and 34b on the screen 34 by the refractive index. The observer observes the one-dimensional image by giving the light diffused by the one-dimensional screen 34 to the pupil.

Since the image display device of this embodiment is configured to apply the light emitted from the LD 31 to the variable focal length lens 33, which is a direct scanning means, the light emitted from the light source is once converted into parallel light by a collimator or the like. As compared with the configuration provided to the scanning means, the number of components is reduced, and compactness and cost reduction can be achieved.

<Fourth Embodiment> FIG. 4 shows a schematic configuration diagram of a video display device according to a fourth embodiment. Reference numeral 41 denotes a one-dimensional display element for displaying an image modulated according to an image signal;
Is a collimator for emitting light from the one-dimensional display element 41 as parallel light, 43 is a variable focal length mirror for imaging the one-dimensional image light from the collimator 42, and 44 is a collimator for focusing from the variable focal length mirror 43. This is a two-dimensional screen that diffuses image light. Note that the collimator 42 has a light-shielding band 42a that cuts off light passing through the screen 44.

The variable focal length mirror 43 changes the focal length to move the image forming position of the one-dimensional image light on the two-dimensional screen 44. Therefore, it becomes a scanning means for scanning light in one direction. The image light displayed on the one-dimensional display element 41 travels, for example, as indicated by arrows in the figure. The variable focal length mirror 43 focuses the one-dimensional image light on, for example, positions 44a and 44b on the screen 44 according to the focal length. The observer observes the two-dimensional image by giving the light diffused by the two-dimensional screen 44 to the pupil.

The video display device of the present embodiment can display a two-dimensional video with a compact configuration.

The arrangement, contents, and the like of the components of the video display device of each embodiment are not limited to those shown in the drawings. In the apparatuses of all the embodiments, it is desirable that the variable focal length optical system is eccentrically arranged like the apparatus shown in FIG. With this configuration, the degree of freedom of arrangement is increased, and the entire apparatus can be made compact. In addition, since the screen can be configured so that only the light beam involved in the image formation after passing through the variable focal length optical system is incident, the sharpness of the image can be improved. Hereinafter, the difference between the luminous flux incident on the screen at the time of non-eccentric arrangement and the eccentric arrangement of the variable focal length optical system will be described with a specific example.

FIG. 5 shows (a) non-eccentric arrangement of the variable focal length mirror 13 of the video display device of the first embodiment,
(B) shows how light travels during eccentric arrangement. (A) In the non-eccentric arrangement, unnecessary light 15 that travels straight without being scattered by the screen 14 enters the LD 11. This means
The output of the LD 11 becomes unstable and the contrast of the image is reduced due to stray light. On the other hand, in the case of (b) the eccentric arrangement, the configuration can be such that the unnecessary light 15 does not enter the LD 11.

In all the embodiments, it is desirable to configure an absorbing member that absorbs unnecessary light rays that travel straight without being scattered after forming an image on a screen as in the apparatus shown in FIG. As a result, L due to the incidence of unnecessary light on the LD
It is possible to prevent phenomena such as unstable output of D11 and a decrease in contrast of an image due to stray light (there is a difference in how these phenomena occur depending on the arrangement of components).

Further, in the case of a configuration in which there is light that passes directly through the collimator and is incident on the screen, it is desirable to arrange a light blocking member between the collimator and the screen (for example, as in the apparatus shown in FIG. 4). This prevents light that is not related to image formation from being incident on the screen, thereby preventing a decrease in image contrast.

Specific examples of the variable focal length optical system used in each of the above embodiments will be described below. 1) A mirror material made of a piezoelectric material such as PLZT ((Pb, La) (Zr, Ti) O ₃ ) is made into a mirror shape, and a voltage is applied by an electrode to deform the piezoelectric material to change the focal length. 2) Titanate A material having an electro-optical effect such as barium is formed into a lens shape, a transparent electrode is arranged on the surface thereof, and a voltage is applied to change the refractive index by the electro-optical effect to change the focal length. Focal length variable lens that changes the focal length by changing the refractive index of the liquid crystal by applying a voltage by placing a transparent electrode on the substrate and orienting it and enclosing it in a transparent substrate such as lens-shaped glass. A variable focal length lens or variable focal length mirror that changes the focal length by moving the holding member for a fixed focal length lens or mirror and moving the position with a piezoelectric material, etc.

For example, it is assumed that the variable focal length lens 3) is used in the video display device of the third embodiment. FIG. 10 is a simple block diagram showing a control circuit of the variable focal length lens in this case. A variable focal length lens 33a has a configuration in which liquid crystal is sealed in a lens-shaped transparent substrate.
Incident surface 33b and exit surface 33 of variable focal length lens 33a
Each of c is provided with a transparent electrode.

Reference numeral 37 denotes voltage applying means for applying a voltage to the transparent electrodes on both surfaces. The voltage application unit 37 can control the focal length of the focal length variable lens 33a by controlling the applied voltage. It is assumed that the focal length variable lens 33a is configured to obtain a focal length proportional to an applied voltage in consideration of characteristics of a liquid crystal and a transparent substrate. In this case, the voltage applying means 37 applies a sawtooth voltage. By doing so, the scanning can be repeatedly performed while the focal length is continuously changed.

Next, specific examples of the screen used in each of the above embodiments will be described below. 1) Screen having a structure in which a number of microprisms are arranged in a transparent substrate 60 to form a microprism array 61 as shown in FIG. 6. In this screen, light is emitted in a direction (emission direction) different from the incident direction (incident direction of incident light 63). It is desirable that the light is reflected in the direction of emission of the diffused light 64) and strongly reflected in a desired direction. 2) As shown in FIG. 7, a screen having a structure in which a member such as a diffraction grating 62 or a hologram optical element (HOE) that diffuses light due to a minute shape change or refractive index change in the order of the wavelength of light is arranged in a transparent substrate 60. In this screen, similar to the screen of FIG.
The light is reflected in a direction different from the incident direction (the incident direction of the incident light 63) (for example, the primary light 65, the secondary light 66, the emission direction of the tertiary light 67), and in a desired direction (for example, the secondary light 66). (Emission direction of light) is desirably strongly reflected.

The configurations of the variable focal length optical system and the screen are not limited to the above specific examples.

<Fifth Embodiment> FIG. 8 is a schematic diagram showing a head-mounted image (virtual image) display device according to a fifth embodiment. The LD 11, the collimator 12, the variable focal length mirror 13, and the one-dimensional screen 14 of the video display device of the present embodiment have the same configuration as that of the first embodiment. Hereinafter, other components will be described.

Reference numeral 50 denotes a relay optical system that relays a one-dimensional image formed on the screen 14, and 51 denotes a scanning mirror that scans the one-dimensional image in a direction perpendicular to the one-dimensional direction of the one-dimensional image to form a two-dimensional image. Reference numeral 52 denotes an eyepiece optical system for projecting a two-dimensional image from the scanning mirror onto a pupil 53 of the observer as a virtual image.

In the image display apparatus of the present embodiment, since the variable focal length mirror 13 serving as the horizontal scanning means is not of a configuration that rotates and vibrates, the entire apparatus can be made compact. In addition, when displaying a high-definition image, high-frequency scanning is necessary especially in horizontal scanning. However, in this apparatus, for example, since scanning can be performed by electrically changing the focal length of a mirror, high-speed scanning can be performed. Can be easily achieved.

[0038]

According to the video display apparatus of the present invention, a high scanning frequency and a compact configuration can be achieved. Therefore, high-definition video display is possible. In addition, since it can be configured compactly, for example, in a head-mounted image display device, the load on the observer due to the weight and size of the device itself is reduced. Then, it is possible to present a high-definition image, that is, an image with a high sense of reality to the observer.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a video display device according to a first embodiment.

FIG. 2 is a schematic configuration diagram of a video display device according to a second embodiment.

FIG. 3 is a schematic configuration diagram of a video display device according to a third embodiment.

FIG. 4 is a schematic configuration diagram of a video display device according to a fourth embodiment.

FIGS. 5A and 5B are diagrams showing how light travels when the variable focal length mirror is (a) non-eccentrically arranged and (b) eccentrically arranged in the video display device of FIG.

FIG. 6 is a diagram showing an example of a screen.

FIG. 7 is a view showing an example of a screen different from that of FIG. 7;

FIG. 8 is a schematic configuration diagram of a video display device according to a fifth embodiment.

FIG. 9 is a schematic configuration diagram of a conventional head-mounted image display device.

FIG. 10 is a block diagram of a control circuit of a variable focal length lens according to a third embodiment.

[Explanation of symbols]

11, 21, 31 LD 12, 22, 42 Collimator 13, 43 Variable focal length mirror 14, 24, 34 One-dimensional screen 23 Anamorphic variable focal length mirror 33 Variable focal length lens 35 Unnecessary light absorbing plate 41 One-dimensional display element 44 Two-dimensional screen 50 relay optical system 51 scanning mirror 52 eyepiece optical system

Claims (3)

[Claims] 1. A light source capable of modulating the intensity of emitted light, an optical element having a variable focal length, and a screen for diffusing incident light, wherein the optical element transmits light from the light source onto the screen. An image display device, wherein a one-dimensional or two-dimensional image is formed on the screen by moving an image forming position on the screen by forming an image and changing a focal length. 2. The image display device according to claim 1, wherein the optical element focuses light into a point. 3. The image display device according to claim 1, wherein the optical element forms a linear image of the light.