Wearable Display Using a Holographic Optical Element
Holographic Optical Element
A hologram has various features. By utilizing a hologram as an optical element, an optical element having specific characteristics can be realized. An optical element that utilizes a hologram is called a holographic optical element (HOE). It is widely used in the industry as an optical element for optical disk units.
By utilizing the wavefront reconstruction function--a feature of the hologram--as a lens, and by further utilizing the wavelength selection function as a combiner that superimposes two fluxes of light, a compact see-through information display device can be achieved by superimposing an external image and an information image from the display element.
Wavefront Reconstruction Function
A hologram is created by irradiating two fluxes of light with high coherence, such as laser, onto a photosensitive material, and by recoding that coherent state. If one of the fluxes of light used when creating the hologram is given to the hologram created, the other flux of light used when creating the hologram is reconstructed. This is called the wavefront reconstruction function of holograms. Because this function converts light, it can be used as a lens function.
Wavelength Selection Function
A hologram has a characteristic to react to only the wavelength of the light used when it was created using the reflection type. This is called the wavelength selection function of holograms. For example, a reflection type hologram created using a red laser beam at a wavelength of 633nm only reflects red light beams near 633nm, and transmits light beams at other wavelengths. By effectively utilizing this feature, a combiner function that effectively superimposes two fluxes of light can be realized.
Conventionally, a half mirror or polarization beam splitter was used as a combiner that superimposes a display image and an external image. However, it had a large optical loss ratio and a good see-through function could not be achieved. With efficient optical superimposition using an HOE, the high see-through characteristic that seldom loses external light and bright image display can be achieved together. Furthermore, by providing the HOE itself with a lens function, the structure can be simplified by combining functions. By using the HOE having these features as an ocular eyepiece that projects enlarged display images and by further combining it with an image flux folding function using the internal reflection of a prism, a super lightweight wearable display with high see-through characteristic can be realized.
This is a display that the observer wears on the head, just like a pair of eyeglasses, and is generally called the head mounted display (HMD). This product can be used as a personal display in mobile and ubiquitous applications that will become generally available in the near future.