Patent Publication Number: US-2022229220-A1

Title: Optical device for augmented reality having improved light transmittance

Description:
TECHNICAL FIELD 
     The present invention relates to an optical device for augmented reality, and more particularly to an optical device for augmented reality that can increase light transmittance for image light from the real world. 
     BACKGROUND ART 
     Augmented Reality (AR) refers to technology that superimposes a virtual image, generated by a computer or the like, on a real image of the real world and then provides a resulting image, as is well known. 
     In order to provide augmented reality, there is required an optical system that allows a virtual image, generated by a device such as a computer, to be superimposed on an image of the real world and a resulting image to be provided. As such an optical system, there is known a technology using an optical means, such as a prism, that reflects or refracts a virtual image by using a head-mounted display (HMD) or a glasses-type device. 
     However, devices using the conventional optical system have problems in that it is inconvenient for users to wear them because the configurations thereof are complicated and thus the weights and volumes thereof are considerable and in that the manufacturing costs thereof are high because the manufacturing processes thereof are also complicated. 
     Furthermore, the conventional devices have a limitation in that a virtual image becomes out of focus when a user changes focal length when gazing at the real world. To overcome this problem, there have been proposed technologies such as a prism capable of adjusting focal length for a virtual image and technologies for electrically controlling a variable focal lens in response to a change in focal length. However, these technologies also have a problem in that a user needs to perform a separate operation in order to adjust focal length or hardware such as an additional processor and software for controlling focal length are required. 
     In order to overcome the problems of the conventional technologies, the present applicant has developed an optical device capable of implementing augmented reality by projecting a virtual image onto the retina through the pupil using a reflective unit having a smaller size than a human pupil, as described in patent document 1. 
       FIG. 1  is a diagram showing an optical device for augmented reality such as that disclosed in patent document 1 below. 
     Referring to  FIG. 1 , an image output unit  30  is a means for outputting image light corresponding to an image for augmented reality, and may be implemented as, e.g., a small-sized display device. A reflective unit  20  provides the image for augmented reality to a user by reflecting image light corresponding to an image for augmented reality, output from the image output unit  30 , to the pupil of the user. 
     An optical means  10  is a means for transmitting at least part of the image light output from a real object, therethrough, and may be, e.g., a lens of eyeglasses. The reflective unit  20  is embedded inside the optical means  10 . A frame unit  40  is a means for fixing and supporting both the image output unit  30  and the optical means  10 . 
     The reflective unit  20  of  FIG. 1  is formed to have a smaller size, i.e., 8 mm or less, than the human pupil. By forming the reflective unit  20  to be smaller than the pupil as described above, the depth of field for light entering the pupil through the reflective unit  20  can be made almost infinite, i.e., considerably deep. 
     Here, the depth of field refers to a range within which an image for augmented reality is recognized as being in focus. When the depth of field get increased, focal length for an image for augmented reality get increased accordingly. Thus, even if a user changes the focal length for the real world while gazing at the real world, an image for augmented reality is always recognized as being in focus regardless of such a change. This may be considered as a kind of pinhole effect. 
     Accordingly, the optical device for augmented reality can always provide a clear virtual image for an image for augmented reality even when a user changes the focal length while gazing at a real object in the real world. 
     Although this technology has the advantages of increasing the depth of field and obtaining a pinhole effect, it is problematic in that light transmittance may be lowered because image light transmitted through the reflective unit  20  in image light entering from the real world is reflected by the reflective unit  20  and, thus, cannot be transferred to the pupil and is also problematic in that it is difficult to increase the size of the reflective unit  20  due to the former problem. 
     PRIOR DOCUMENT 
     
         
         Korean Patent No. 10-1660519 (published on Sep. 29, 2016) 
       
    
     DISCLOSURE 
     Technical Problem 
     The present invention has been conceived to overcome the above-described limitations, and an object of the present invention is to provide an optical device for augmented reality that can increase light transmittance for image light from the real world. 
     Another object of the present invention is to provide an optical device for augmented reality that can improve optical uniformity by increasing the size of a reflective unit. 
     Technical Solution 
     In order to accomplish the above objects, the present invention provides an optical device for augmented reality having improved light transmittance, the optical device including: an image output unit configured to output augmented reality image light corresponding to an image for augmented reality; a reflective unit configured to transfer the augmented reality image light, output from the image output unit, to the pupil of an eye of a user by reflecting the augmented reality image light toward the pupil, thereby providing the image for augmented reality to the user; and an optical means adapted such that the reflective unit is disposed therein, and configured to transmit at least a portion of real object image light, output from a real object, therethrough toward the pupil of the eye of the user; wherein the reflective unit is formed to have a size of 4 mm or less, and is composed of an optical filter that reflects only image light belonging to the wavelength band of a specific color and transmits image light having a wavelength other than the wavelength band of the specific color therethrough. 
     In this case, the reflective unit may transfer only augmented reality image light belonging to the wavelength band of the specific color, in the augmented reality image light output from the image output unit, to the pupil of the eye of the user by reflecting the former augmented reality image light toward the pupil, and may transfer the image light having a wavelength other than the wavelength band of the specific color, in the real object image light output from the real object and entering the reflective unit, to the pupil of the eye of the user by transmitting the image light toward the pupil. 
     Furthermore, the optical filter may be composed of any one of a red reflective filter configured to reflect image light belonging to a red wavelength band and transmit image light belonging to another wavelength band therethrough, a green reflective filter configured to reflect image light belonging to a green wavelength band and transmit image light belonging to another wavelength band, and a blue reflective filter configured to reflect image light belonging to a blue wavelength band and transmit image light belonging to another wavelength band, or a combination of two or more thereof. 
     Furthermore, the augmented reality image light output from the image output unit may be composed of only image light belonging to the wavelength band of the color reflected by the optical filter constituting the reflective unit. 
     Furthermore, the reflective unit may include a plurality of reflective units. 
     Furthermore, at least some of the reflective units may be disposed to partially overlap each other along the optical axis of the image light output from the image output unit. 
     Moreover, each of the plurality of reflective units may be composed of an optical filter that reflects image light belonging to at least any one of a plurality of wavelength bands obtained by dividing the wavelength band of the specific color and transmits rays of image light belonging to wavelength bands other than the at least any one of the plurality of wavelength bands. 
     Advantageous Effects 
     According to the present invention, there can be provided the optical device for augmented reality that can increase light transmittance for image light from the real world. 
     Furthermore, according to the present invention, there can be provided the optical device for augmented reality that can improve optical uniformity by increasing the size of the reflective unit. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram showing an optical device for augmented reality such as that disclosed in prior art document 1; 
         FIG. 2  is a diagram showing the configuration of an embodiment of an optical device ( 100 ) for augmented reality having improved light transmittance according to the present invention; 
         FIG. 3  is a graph showing the reflectance/transmittance of a blue reflective filter according to wavelength; 
         FIG. 4  is a view illustrating the operation of a reflective unit ( 20 ) composed of an optical filter according to the present invention; and 
         FIG. 5  is a diagram showing an optical device ( 200 ) according to another embodiment of the present invention. 
     
    
    
     BEST MODE 
     Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. 
       FIG. 2  is a diagram showing the configuration of an embodiment of an optical device  100  for augmented reality having improved light transmittance according to the present invention. 
     Referring to  FIG. 2 , the optical device  100  for augmented reality having improved light transmittance (hereinafter simply referred to as the “optical device  100 ”) according to the present embodiment includes an image output unit  10 , a reflective unit  20 , and an optical means  30 . 
     The image output unit  10  is a means that outputs augmented reality image light corresponding to an image for augmented reality. For example, the image output unit  10  may be a display device such as a small-sized LCD, or may be a reflective, refractive, or diffractive means that outputs image light output from a display device by reflecting, refracting, or diffracting the image light. 
     In other words, the image output unit  10  refers to a display device itself that displays an image for augmented reality, or refers to other various means such as a reflective, refractive or diffractive means that outputs augmented reality image light output from a display device. 
     Since the image output unit  10  itself is not a direct target of the present invention and is known in the prior art, a detailed description thereof will be omitted here. 
     Meanwhile, the image for augmented reality refers to a virtual image that is displayed on a display device and transferred to the pupil  40  of a user through the reflective unit  20  when the display device is the image output unit  10 , or refers to a virtual image that is displayed on a display device and transferred to the pupil  40  of a user through the image output unit  10  and the reflective unit  20  when the display device is not the image output unit  10 . 
     The image for augmented reality may be a still image or moving image. 
     The image for augmented reality is output from the image output unit  10  and transferred to the pupil  40  of the user through the reflective unit  20 , so that a virtual image is provided to the user. At the same time, image light output from a real object present in the real world is transferred to the user through the optical means  30 . As a result, the virtual image is provided while being superimposed on the real object, so that the user is provided with an augmented reality service. 
     Meanwhile, although the image output unit  10  is disposed in a direction perpendicular to the pupil  40  with respect to the reflective unit  20  and shown as being disposed on a side when the user gazes at the front, this is exemplary. When the user gazes at the front, the image output unit  10  may be disposed on an upper side, a lower side, or the like, or may be disposed at a different angle. 
     The reflective unit  20  is a means that transfers augmented reality image light corresponding to an image for augmented reality, output from the image output unit  10 , to the pupil  40  of an eye of the user by reflecting the augmented reality image light toward the pupil  40 , thereby providing the image for augmented reality to the user. 
     It is preferable that the reflective unit  20  is spaced apart from the surface of the optical means  30  and completely embedded and disposed inside the optical means  30 . However, in some cases, the reflective unit  20  may be disposed on the surface (the surface facing the pupil  40  of the user) of the optical means  30 . 
     The reflective unit  20  is disposed at an appropriate angle between the image output unit  10  and the pupil  40  in order to reflect augmented reality image light toward the pupil  40 . For example, when the image output unit  10  is disposed on the right side of the optical means  30  as shown in  FIG. 2 , the reflective unit  20  may be disposed such that the center of the optical axis of augmented reality image light output from the image output unit  10  has an angle of 45 degrees with respect to a forward direction from the pupil  40 . 
     Meanwhile, it is preferable that the reflective unit  20  is formed to have a size smaller than the size of the human pupil, i.e., 8 mm or less, more preferably 4 mm or less, in order to obtain a pinhole effect by increasing the depth of field, as described in the background art section. 
     In other words, the reflective unit  20  is formed to have a size smaller than the size of the common human pupil, so that the depth of field for light entering the pupil  40  through the reflective unit  20  can be made almost infinite, i.e., considerably deep. Accordingly, there can be generated a pinhole effect that allows an image for augmented reality to be always recognized as being in focus regardless of a change in focal length even when the user changes the focal length for the real world while gazing at the real world. 
     Meanwhile, when the size of the reflective unit  20  is excessively small, a diffraction phenomenon may occur, so that it is preferable to allow the size of the reflective unit  20  to be larger than about 700 μm. 
     Meanwhile, the present invention is characterized in that the reflective unit  20  is composed of an optical filter that reflects only image light belonging to the wavelength band of a specific color and transmits image light having a wavelength other than the wavelength band of the specific color. 
     In other words, the reflective unit  20  of the present invention transfers only the image light belonging to the wavelength band of the specific color in the augmented reality image light output from the image output unit  10  by reflecting the image light toward the pupil  40  of the eye of the user, and transmits image light having a wavelength other than the wavelength band of the specific color, in the augmented reality image light output from the image output unit  10 , therethrough. 
     Furthermore, the reflective unit  20  transfers image light having a wavelength other than the wavelength band of the specific color, in real object image light output from a real object and entering the reflective unit  20 , to the pupil  40  of the eye of the user by transmitting the image light therethrough toward the pupil  40 , and reflects image light belonging to the wavelength band of the specific color in the real object image light output from the real object and entering the reflective unit  20 . 
     In other words, the reflective unit  20  is composed of an optical filter that transfers image light belonging to the wavelength band of the specific color, in the augmented reality image light output from the image output unit  10 , to the pupil  40  of the eye of the user by reflecting the image light toward the pupil  40  and transfers image light having a wavelength other than the wavelength band of the specific color, in the real object image light output from the real object and entering the reflective unit  20 , to the pupil  40  of the eye of the user by transmitting the latter image light therethrough. 
     In this case, the optical filter may be an optical filter that reflects only image light belonging to at least one of red, green, and blue wavelength bands. 
     In other words, the optical filter may be composed of any one of a red reflective filter configured to reflect image light belonging to a red wavelength band and transmit image light belonging to another wavelength band therethrough, a green reflective filter configured to reflect image light belonging to a green wavelength band and transmit image light belonging to another wavelength band, and a blue reflective filter configured to reflect image light belonging to a blue wavelength band and transmit image light belonging to another wavelength band, or may be composed of a combination of two or more thereof. 
     An optical filter known in the prior art may be used as the optical filter. Since the optical filter is not a direct target of the present invention, a detailed description thereof will be omitted here. 
       FIG. 3  is a graph showing the reflectance/transmittance of a blue reflective filter according to wavelength. 
     In  FIG. 3 , the horizontal axis represents wavelength λ (nm), and the vertical axis represents transmittance according to wavelength. 
     As shown in  FIG. 3 , it can be seen that the blue reflective filter reflects image light having a wavelength of about 350 nm to about 370 nm belonging to a blue wavelength band and transmits image light belonging to another wavelength band therethrough. 
     As described above, the reflective unit  20  may be composed of an optical filter that reflects image light belonging to the wavelength band of a specific color and transmits image light belonging to the wavelength band of another color therethrough. 
     Referring back to  FIG. 2 , the optical means  30  is a means in which the reflective unit  20  is embedded and which transmits at least a portion of the real object image light, output from the real object, therethrough toward the pupil  40  of the eye of the user. 
     Although the reflective unit  20  is embedded and disposed in the inner surface of the optical means  30 , it may also be disposed on the surface of the optical means  30 . 
     The optical means  30  may be made of a material such as glass or transparent plastic. The optical means  30  is disposed in front of the pupil  40  of the user during use and transmits real object image light, output from a real object present in the real world, therethrough to the pupil  40 . The optical means  30  may be implemented using a translucent material, in which case the optical means  30  transmits a portion of image light, output from a real object, therethrough toward the pupil  40 . 
     The optical means  30  may be coupled to the surface of the lens of a glasses-type augmented reality provision device (not shown), composed of lenses and a frame, in a modular form. Alternatively, the lens itself of the augmented reality provision device may be configured as the optical means  30 . 
     Meanwhile, although image light corresponding to an image for augmented reality output from the image output unit  10  may be transferred directly to the reflective unit  20 , it may be transferred after being reflected at least once from the inner surface of the optical means  30 . 
       FIG. 4  is a view illustrating the operation of the reflective unit  20  composed of an optical filter according to the present invention. 
     In  FIG. 4 , as described above, the reflective unit  20  is composed of a red, green and blue reflective filter that is a combination of a red reflective filter, a green reflective filter, and a blue reflective filter and has the property of reflecting image light belonging to red, green, and blue wavelength bands and transmitting light having a wavelength other than the red, green, and blue wavelength bands therethrough. 
     Referring to the left drawing of  FIG. 4 , it can be seen that image light A 1  belonging to red, green, and blue wavelength bands in real object image light A output from a real object and entering the reflective unit  20  is reflected downward by the reflective unit  20  composed of the red, green and blue reflective filter and real object image light A 2  belonging to the wavelength bands of colors other than red, green, and blue is transmitted through the reflective unit  20  and transferred to the pupil  40 . 
     In other words, only the image light A 2  belonging to the remaining wavelength bands excluding the image light A 1  belonging to the red, green, and blue wavelength bands in the real object image light A output from the real object and entering the reflective unit  20  is transferred to the pupil  40 . 
     Furthermore, referring to the intermediate drawing of  FIG. 4 , it can be seen that image light B 1  belonging to the red, green, and blue wavelength bands in augmented reality image light B output from the image output unit  10  and entering the reflective unit  20  is reflected by the reflective unit  20  composed of the red, green and blue reflective filter and is then transferred to the pupil  40  and image light B 2  belonging to the wavelength bands of colors other than red, green, and blue is transmitted through the reflective unit  20  and is then moved in a downward direction. In other words, in the augmented reality image light B output from the image output unit  10  and transferred to the reflective unit  20 , only the image light B 1  belonging to the red, green, and blue wavelength bands is transferred to the pupil  40 . 
       FIG. 4  shows the real object image light A output from the real object and entering the reflective unit  20 , the augmented reality image light B output from the image output unit  10 , and image light A 2 +B 1  entering the pupil  40  in combination. As shown in this drawing, it can be seen that the augmented reality image light B 1  belonging to the red, green, and blue wavelength bands output from the image output unit  10  and the real object image light A 2  belonging to wavelength bands other than the red, green, and blue wavelength bands output from the real object and transmitted through the reflective unit  20  reach the pupil  40 . 
     Meanwhile, the wavelength band of augmented reality image light output from the image output unit  10  may be adjusted in accordance with the property of the optical filter constituting the reflective unit  20 . In other words, a configuration may be made such that only augmented reality image light belonging to the wavelength band of a color reflected by the optical filter constituting the reflective unit  20  may be output from the image output unit  10 . 
     For example, when the optical filter is a red, green and blue reflective filter as shown in  FIG. 4 , rays of augmented reality image light output from the image output unit  10  may be composed of only rays of image light belonging to red, green, and blue wavelength bands. 
       FIG. 5  is a diagram showing an optical device  200  according to another embodiment of the present invention. 
     The embodiment of  FIG. 5  is basically the same as the embodiment of  FIGS. 2 to 4  except that a reflective unit is implemented as a plurality of reflective units  20 . 
     Referring to  FIG. 5 , the plurality of reflective units  20  may be disposed to partially overlap each other when viewed in the optical axis direction of augmented reality image light output from the image output unit  10  so that at least a portion of the augmented reality image light output from the image output unit  10  can be blocked. 
     For example, in  FIG. 5 , the reflective units  20  is disposed alongside each other in the optical axis direction of image light output from the image output unit  10 , and the reflective units  20  disposed alongside each other overlap each other when viewed from the optical axis direction of the image light output from the image output unit  10 . Accordingly, in  FIG. 5 , for the left reflective unit  20 , at least a portion of image light output from the image output unit  10  is blocked by the right reflective unit  20 . 
     In this case, each of the reflective units  20  disposed alongside each other may be composed of an optical filter that reflects image light belonging to at least any one of a plurality of wavelength bands obtained by dividing the wavelength band of a specific color and transmits rays of image light belonging to wavelength bands other than the at least any one of the plurality of wavelength bands therethrough. 
     For example, each of the reflective units  20  may be composed of an optical filter that, when a blue wavelength band ranges from 350 nm to 370 nm and is divided into a wavelength band from 350 nm to 360 nm and a wavelength band from 360 nm to 370 nm, reflects only image light belonging to each of the plurality of divided wavelength bands. 
     In other words, in  FIG. 5 , the right reflective unit  20  may be composed of an optical filter that reflects image light having a wavelength of 350 nm to 360 nm and transmits image light belonging to other wavelength bands therethrough, and the left reflective unit  20  may be composed of an optical filter that reflects image light having a wavelength of 360 nm to 370 nm and transmits image light belonging to other wavelength bands therethrough 
     According to this disposition structure, the image light having a wavelength of 360 nm to 370 nm may be transmitted through the right reflective unit  20 , may reach the left reflective unit  20 , and may be transferred to the pupil  40  by the left reflective unit  20 . Furthermore, the image light having a wavelength of 350 nm to 360 nm may be reflected by the right reflective unit  20 , and may be transferred to the pupil  40 . Accordingly, a specific color recognized by a human as the same color may be divided into a plurality of wavelength bands, and then each of the reflective units  20  may independently reflect image light belonging to a corresponding one of the divided wavelength bands. 
     Meanwhile, although the reflective units  20  are disposed alongside each other in the optical axis direction of image light output from the image output unit  10  and are shown as completely overlapping each other in the embodiment of  FIG. 5 , this is an example. It is obvious that the reflective units  20  may be disposed to partially overlap each other in the optical axis direction. 
     Meanwhile, the plurality of reflective units  20  may be disposed not to overlap each other when viewed in the optical axis direction of augmented reality image light output from the image output unit  10  so that the image light output from the image output unit  10  is not blocked. 
     While the present invention has been described with reference to the preferred embodiments of the present invention, it is obvious that the present invention is not limited to the embodiments and it should be noted that other various modifications and alterations may be possible within the scope of the present invention. 
     For example, although the optical filter that reflects image light having a wavelength in the wavelength bands of red, green, and blue has been chiefly described in the above embodiment, it is obvious that an optical filter that reflects image light having a wavelength in wavelength bands other than the wavelength bands of these colors may be used as the reflective unit  20 .