BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects and features of the present invention will be apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a cross-sectional view showing an outline of the structure of a beam expanding optical element as one embodiment of the invention;
FIG. 2 is a diagram schematically illustrating part of an exposure optical system used when a holographic diffractive optical element for the above beam expanding optical element is fabricated;
FIG. 3 is a plot showing the relationship between exposure amount and diffraction efficiency as observed when the above holographic diffractive optical element is fabricated;
FIG. 4 is a cross-sectional view showing an outline of the structure of a beam expanding optical element as another embodiment of the invention;
FIG. 5 is a diagram schematically illustrating part of an exposure optical system used when a holographic diffractive optical element for the above beam expanding optical element is fabricated;
FIG. 6 is a perspective view showing an outline of the structure of a beam expanding optical element as yet another embodiment of the invention;
FIG. 7 is a cross-sectional view showing an outline of the structure of an image display apparatus as yet another embodiment of the invention;
FIG. 8 is a plot showing the spectral intensity characteristics of a light source for the above image display apparatus;
FIG. 9A is a plan view showing an outline of the structure of an HMD as yet another embodiment of the invention;
FIG. 9B is a front view of the above HMD;
FIG. 10 is a perspective view showing an outline of the structure of an HMD as yet another embodiment of the invention;
FIG. 11 is a diagram schematically illustrating part of an exposure optical system used when a holographic diffractive optical element for a beam expanding optical element for use in the above HMD is fabricated;
FIG. 12A is a plan view showing another example of the structure of the above HMD; and
FIG. 12B is a plan view of the above HMD.