Novel techniques for examination of light optical elements

A method for measuring parallelism of facets of a lightguide optical element (LOE), the LOE including a light-transmitting substrate having first and second major surfaces parallel to each other such that light coupled into the light-transmitting substrate is trapped between the first and second major surfaces by total internal reflection and the facets configured to couple the light out of the substrate, the method comprising:

• placing a first slit between a projector configured to emit light corresponding to an image and the first major surface, the first slit placed such that light from the projector travels through the first slit to the first major surface and to a first facet of the facets;
• placing a second slit between a detector and the second major surface, the second slit placed to block light transmitted by the first facet and such that light reflected by the first facet and a second facet, from the facets, travels from the second facet to the second major surface and through the second slit to the detector;
• and
• deducing the parallelism between the first facet and the second facet based on a shift of the image as detected by the detector relative to light transmitted normal to the first and second major surfaces through a portion of the substrate not including a facet from the facets.

A method for measuring homogeneity of refractive index of facets of a lightguide optical element (LOE), the LOE including a light-transmitting substrate having first and second major surfaces parallel to each other such that light coupled into the light-transmitting substrate is trapped between the first and second major surfaces by total internal reflection and the facets configured to couple the light out of the substrate, the method comprising:

• placing a first slit between a projector configured to emit light corresponding to an image and the first major surface, the first slit placed such that light from the projector travels through the first slit to the first major surface and to a first facet of the facets;
• placing a second slit between the second major surface and a detector such that light from the projector travels through the first slit to the first major surface and to the first facet and light transmitted through the first facet travels from the first facet to the second major surface and through the second slit to the detector;
• and
• determining homogeneity or deviation in refractive index between surfaces of the first facet based on the light transmitted through the first facet, as detected by the detector, relative to light transmitted normal to the first and second major surfaces through a portion of the substrate not including a facet from the facets.