In recent years, an image display device which is used in a state of being worn on a head portion of a viewer such as a head mounted display is provided as a wearable information device. For example, PTL 1 which is described below discloses a video display device which is provided with a light source, a display element which modulates light from the light source and displays a video, and a viewing optical system which guides the video light from the display element to a pupil of the viewer. In the video display device, a holographic optical element is disposed in front of the eyes of the viewer, and the holographic optical element transmits light from the outdoor scenes. Accordingly, the viewer is capable of visually recognizing an image of the outdoor scenes in addition to a video from the display element. An image display device with which it is possible to visually recognize both a video from a display element and an image of the outdoor scenes may also be referred to as a see-through type image display device hereinafter. In the video display device, since only the holographic optical element has an optical power, it is difficult to correct aberration and distortion which are caused by the holographic optical element. Therefore, it is difficult to display an image with a wide angle of view at a high resolution, that is, an image of a large size.
In PTL 1, a liquid crystal display element is given as an example of the display element; however, in a case in which a device which has a two-dimensional external shape such as a liquid crystal display element is used, there is a problem in that the size of the display element becomes great. In order to reduce the size of the display element, PTLs 2 and 3 which are described below disclose an image display device which is provided with scanning means for driving a mirror to two-dimensionally scan light. However, in the device of PTL 2, in a case in which the diameter of the laser beam to be scanned is narrow, there is a problem in that the laser beam shifts from the position of the pupil when the eye is moved, and the image becomes invisible. Additionally, since the interval between the right eye and the left eye, the so-called interpupillary distance differs depending on the person, there is a problem in that when the user changes, the image becomes invisible.
On the other hand, PTL 3 discloses an image display device in which light deflecting means is provided in a light emission region of a light guide plate which guides scanned light to the front of an eye, and an image is visible even if the eye moves due to spreading the image light over the entirety of the light emission region and emitting the image light. Hereinafter, a function of magnifying the exit pupil by spreading the image light in this manner will be referred to as a pupil magnifying function. However, in the device of PTL 3, since the light guiding plate also stretches outside of the region in front of the eyes of the viewer which is necessary for the image display and the light guiding plate overhangs the side of the face, the device increases in size, and this is not preferable from the standpoint of external appearance.
PTL 4 discloses a video display device which includes a pupil magnifying function in a case in which an ocular optical system is formed of a mirror which is disposed in front of the eye. Specifically, in the video display device, a diffraction grating is disposed between a concave mirror and the eye, and the pupil magnifying function is exhibited by dividing the light which is reflected by the concave mirror into plurality of pencils of rays. However, in this configuration, since the diffraction grating is displaced in front of the eyes of the viewer, the see-through property is impaired.
USPTO Backgrounds
USPTO Backgrounds