Light-guide plate, manufacturing method for the same, light-guide plate module, and image display device

A light-guide plate comprising:

• a substrate;
• an incidence diffraction grating that diffracts incident light;
• and
• an emission diffraction grating that emits light from the substrate, the light being diffracted by the incidence diffraction grating, the emission diffraction grating having two wave vectors that form an angle of 120°,
• wherein
• the emission diffraction grating is formed of a recessed/projected pattern formed on a surface of the substrate,
• the recessed/projected pattern includes a first group of parallel straight lines and a second group of parallel straight lines intersecting the first group of parallel straight lines, and a pitch of the first group of parallel straight lines is equal to a pitch of the second group of parallel straight lines, and
• a relationship between the pitch P of the first group of parallel straight lines and the second group of parallel straight lines and a pattern width W of the recessed/projected pattern is defined as W/P that is 0.15 or more and 0.85 or less.