CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Korean Patent Application No. 10-2019-0133262, filed on Oct. 24, 2019 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

1. Field

Example embodiments of the present disclosure relate to a display apparatus such as an augmented reality system, and more particularly, to a display apparatus providing a wide viewing window while being miniaturized.

2. Description of Related Art

Recently, along with the development of electronic apparatuses and display apparatuses capable of implementing virtual reality (VR), interest in such apparatuses has increased. As a next step of VR, technology for implementing augmented reality (AR) and mixed reality (MR) has been researched.

Unlike VR that is based on a complete virtual world, AR is a display technique that shows the real world with virtual objects or information superimposed thereon, thereby further increasing the effect of reality. While VR is limitedly applied only to fields such as games or virtual experience, AR is advantageous in that it may be applied to various real environments. For example, AR attracts attention as next-generation display technology suitable for a ubiquitous environment or an Internet of things (IoT) environment. AR may be an example of MR in that it shows a mixture of the real world and additional information.

In order to manufacture a display apparatus capable of realizing such AR, for example, in the form of a head mounted type, glasses type, or goggles type, research is being conducted to miniaturize an optical system combining the real world with a virtual image. In addition, in a general AR display apparatus, it is necessary to place the eye at a very small focal size so that the correct image may be viewed, and even if the eye position is slightly out of the focus position, the image may not be properly viewed. Therefore, research is being conducted to enlarge a viewing window to observe an image.

SUMMARY

Example embodiments provide display apparatuses having a wide viewing window while being miniaturized.

Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the example embodiments of the disclosure.

According to an aspect of an example embodiment, there is provided a display apparatus including an image forming apparatus configured to form an image, a projection optical system configured to project the image formed by the image forming apparatus, and a combining optical system configured to provide the image projected from the projection optical system combined with light emitted from an external landscape, wherein the combining optical system is configured to divide the image projected from the projection optical system into same images and focus the same images on different positions.

The combining optical system may include a plurality of holographic optical elements sequentially provided along an optical path of the image projected from the projection optical system.

Each of the plurality of holographic optical elements may include a first surface configured to diffract a portion of incident light and transmit the remaining portion of the incident light, and a second surface provided opposite the first surface and configured to transmit incident light.

Each of the plurality of holographic optical elements may include a reflective holographic optical element configured to diffract incident light that is incident on the first surface and to focus the incident light that is diffracted in a space facing the first surface.

Each of the plurality of holographic optical elements may be configured to diffract incident light that is incident obliquely on the first surface and to converge the incident light that is diffracted in a direction perpendicular to the first surface.

The plurality of holographic optical elements may include a first holographic optical element and a second holographic optical element sequentially provided along the optical path of the image projected from the projection optical system, wherein the first holographic optical element is configured to focus the image projected from the projection optical system to a first position and to form a first image on the first position, and wherein the second holographic optical element is configured to focus the image projected from the projection optical system and transmitted by the first holographic optical element to a second position different from the first position and to form a second image on the second position.

The first holographic optical element may be configured to transmit an image that is diffracted by the second holographic optical element.

The first image and the second image may be identical to each other, and wherein the first position and the second position may be spaced apart from each other in a direction parallel to a first surface of the first holographic optical element.

The first position and the second position may be provided on a single plane parallel to the first surface of the first holographic optical element.

The first holographic optical element and the second holographic optical element may be identical to each other.

A focal length of the first holographic optical element may be different from a focal length of the second holographic optical element.

The first holographic optical element and the second holographic optical element may be provided to be shifted from each other in a direction parallel to a first surface of the first holographic optical element.

A diffraction efficiency of the second holographic optical element may be greater than a diffraction efficiency of the first holographic optical element.

The first holographic optical element and the second holographic optical element may be spaced apart from each other in a direction perpendicular to a first surface of the first holographic optical element.

A second surface of the first holographic optical element and a first surface of the second holographic optical element may be in contact with each other.

The combining optical system may include a holographic optical element and a plurality of translucent mirrors sequentially provided along an optical path of the image projected from the projection optical system.

The holographic optical element may include a first surface configured to diffract incident light, and a second surface provided opposite the first surface and configured to transmit incident light.

The holographic optical element may include a transmissive holographic optical element configured to diffract incident light that is incident on a first surface and to focus the incident light that is diffracted to a space facing a second surface.

The holographic optical element may be configured to diffract incident light that is divergent and incident obliquely on the first surface and to converge the incident light that is diffracted in a direction perpendicular to the second surface.

Each of the plurality of translucent mirrors may be configured to transmit a portion of incident light and reflect the remaining portion of the incident light, and the plurality of translucent mirrors may include a first translucent mirror and a second translucent mirror sequentially provided along the optical path of the image projected from the projection optical system.

The first translucent mirror may be configured to reflect an image diffracted by the holographic optical element and to form a first image a first position in a space facing the first surface of the holographic optical element, and the second translucent mirror may be configured to form a second image a second position that is different from the first position by reflecting an image diffracted by the holographic optical element and transmitted by the first translucent mirror.

The first image and the second image may be identical to each other, and the first position and the second position may be spaced apart from each other in a direction perpendicular to a first surface of a first holographic optical element.

An image reflected by the first translucent mirror and an image reflected by the second translucent mirror may converge and cross each other at a third position and a fourth position that is different from the third position in the space facing the first surface of the holographic optical element to form a third image and a fourth image, respectively.

The third image and the fourth image may be identical to each other, and the third position and the fourth position may be spaced apart from each other in a direction parallel to a first surface of a first holographic optical element.

A reflectance of the second translucent mirror may be greater than a reflectance of the first translucent mirror.

The display apparatus may include a virtual reality (VR) display apparatus, an augmented reality (AR) display apparatus, or a mixed reality (MR) display apparatus implemented in a form of a head mounted type apparatus, glasses type apparatus, or goggles type apparatus.

According to another aspect of an example embodiment, there is provided a display apparatus including an image forming apparatus configured to form an image, a projection optical system configured to project the image formed by the image forming apparatus, and a combining optical system configured to provide the image projected from the projection optical system combined with light emitted from an external landscape, the combining optical system including a plurality of holographic optical elements sequentially provided along an optical path of the image projected from the projection optical system, wherein the plurality of holographic optical elements are configured to respectively focus a same image on different positions

