Volume holographic optical elements with expanded angular acceptance

A waveguide image combiner for combining light from real imagery with light from a light engine, said waveguide image combiner comprising:

• a. an optically transparent substrate having top and bottom surfaces;
• b. a pair of incoupling and outcoupling volume holographic optical elements (VHOEs) spaced apart and overlaid on the top surface of the optically transparent substrate;
• wherein the optically transparent substrate is configured to convey light from the overlaid incoupling VHOE to the overlaid outcoupling VHOE via total internal reflection (TIR), and
• wherein each of the VHOEs comprises multiple Bragg gratings with substantially identical diffraction geometries and Bragg conditions shifted with respect to each other.

A method of fabricating a VHOE with extended acceptance angular range, the method comprising:

• a. providing a holographic recording film, a first laser, and a second laser;
• b. recording a first Bragg grating in the film using two laser beams from the first laser, the laser beams having a first recording beam geometry;
• and
• c. simultaneously recording a second Bragg grating in the film using two laser beams from the second laser, the laser beams having a second recording beam geometry;
• wherein the first Bragg grating and the second Bragg grating have substantially identical diffraction geometry, and wherein a Bragg condition of the first Bragg grating is shifted by an offset angle with respect to a Bragg condition of the second grating.

A method of fabricating a VHOE with extended acceptance angular range, the method comprising:

• a. providing a first holographic recording film;
• b. recording a first Bragg grating in the first film using two laser beams having a first recording beam geometry;
• c. repositioning the two laser beams to a second recording beam geometry;
• d. providing a second holographic recording film;
• and
• e. recording a second Bragg grating in the second film using the two laser beams having the second recording beam geometry;
• wherein the first Bragg grating and the second Bragg grating have substantially identical diffraction geometry, and wherein a Bragg condition of the first Bragg grating is shifted by an offset angle with respect to a Bragg condition of the second grating.