Optical system and image display device

An optical system comprising:

• a projection optical system for projecting an image light ray which is output from a display element and forms an image;
• and
• a light guide for guiding the image light ray projected by the projection optical system toward a field of view region of a user as a virtual image,
• the light guide including:
• an in-coupling region for guiding the image light ray to an inside of the light guide and allowing the image light ray to travel in a direction of a first axis within the light guide, by diffraction or refraction;
• and
• a propagation region for allowing the image light ray from the in-coupling region to propagate in the direction of the first axis, and allowing part of the image light ray to travel in a predetermined direction including a directional component of a second axis perpendicular to the first axis,
• in an optical path of the image light ray projected by the projection optical system, a first distance from the projection optical system to an entrance pupil of the projection optical system relative to the display element in a first plane perpendicular to the first axis being longer than a distance from the projection optical system to the in-coupling region, and being longer than a second distance from the projection optical system to the entrance pupil of the projection optical system relative to the display element in a second plane perpendicular to the second axis in the optical path of the image light ray,
• the image light ray incident on the in-coupling region from the projection optical system including a main light beam corresponding to a center of the virtual image, a plurality of first auxiliary light beams which come close to the main light beam in a direction of the second axis as traveling from the projection optical system to the in-coupling region, and a plurality of second auxiliary light beams which come close to the main light beam in a direction of the first axis as traveling from the projection optical system to the in-coupling region,
• the plurality of first auxiliary light beams crossing the main light beam within the propagation region, and
• the plurality of second auxiliary light beams crossing the main light beam within the in-coupling region.