Systems and methods for testing gratings

A system for testing a primary grating, comprising:

• a substrate including a primary grating in the primary grating area;
• a laser configured to project light at a test wavelength to a test area within the primary grating area, the test wavelength not diffracted by the primary grating;
• a camera configured to capture a grating image of the light after the light passes through the test area;
• and
• a processor configured by software instructions to:
• detect diffracted orders in the grating image, the diffracted orders corresponding to diffraction from a secondary grating having a secondary grating period that is larger than a primary grating period, the secondary grating resulting from a defect in the primary grating;
• and
• analyze the diffracted orders to determine a characteristic of the secondary grating to characterize the defect of the primary grating.

A method for testing a waveguide display, comprising:

• sequentially directing a light from a laser to multiple different test areas on a primary grating of the waveguide display, the light at a test wavelength that is larger than a primary grating period of the primary grating so that the light is not diffracted by the primary grating;
• sequentially capturing grating images of the light after the light passes through each of the multiple different test areas;
• detecting diffracted orders in one or more of the grating images, the diffracted orders corresponding to a secondary grating, the secondary grating resulting from a deflect in the primary grating;
• and
• analyzing the diffracted orders to determine a characteristic of the secondary grating in each test area corresponding to each of the one or more grating images that include diffracted orders to characterize the defect of the primary grating.