Mid-air image display device and method of operating the same

A method of operating a mid-air image display device comprising a projection system, a positive lens, and a light multiplication module comprising a first transmission grating, a second transmission grating, a waveguide, and a reflection grating, the positive lens being disposed on the light multiplication module, the method comprising:

• transmitting a beam forming an image from the projection system to the first transmission grating, the beam, as a result of diffraction at the first transmission grating, being split into a 1st order diffraction beam and a 0th order diffraction beam of the first transmission grating;
• transmitting the 0th order diffraction beam of the first transmission grating to the second transmission grating, the 0th order diffraction beam of the first transmission grating, as a result of diffraction at the second transmission grating, being split into a 1st order diffraction beam and a 0th order diffraction beam of the second transmission grating;
• transmitting the 1st order diffraction beams of the first and second transmission gratings and the 0th order diffraction beam of the second transmission grating to the waveguide;
• allowing the 1st order diffraction beams of the first and second transmission gratings transmitted to the waveguide at an angle corresponding to a total internal reflection angle range to be reflected at an interface between air and the first transmission grating and an interface between the waveguide and the reflection grating, thereby to propagate along the waveguide to form another 1st order diffraction beam at the second transmission grating as a result of diffraction of the 1st order diffraction beam of the first transmission grating at the waveguide, and to form another 1st order diffraction beam at the first transmission grating as a result of diffraction of the 1st order diffraction beam of the second transmission grating at the waveguide;
• diffracting, by the reflection grating, the other 1st order diffraction beam of the second transmission grating and the other 1st order diffraction beam of the first transmission grating to be out-coupled to the positive lens through the waveguide, the second transmission grating, and the first transmission grating;
• and
• refracting the out-coupled beams and focusing a mid-air image on a focal plane, by the positive lens.

A mid-air image display device comprising:

• a projection system configured to output a light beam for an image;
• a second positive lens disposed below the projection system;
• a light multiplication module configured to receive the light beam output from the projection system;
• a first positive lens and a second positive lens disposed below and above the light multiplication module, respectively, and configured to receive the light beam transmitted through the light multiplication module to form a mid-air image,
• wherein the light multiplication module comprises:
• a reflection grating disposed above the first positive lens;
• a waveguide disposed above the reflection grating;
• a second transmission grating disposed above the waveguide;
• a first transmission grating disposed above the second transmission grating and below the second positive lens.