OPTICAL SYSTEM, VIRTUAL IMAGE DISPLAY DEVICE, AND HEAD-MOUNTED DISPLAY

An optical system includes: a light guide to guide image light; a partial reflector; and a reflector. The partial reflector transmits a first image light guided in a first direction from a first side of the partial reflector in a light guide; and reflects second image light to exit outside from a light emission surface of the light guide, the second image light being guided in the light guide in a second direction opposite to the first direction from a second side of the partial reflector. The reflector at the second side of the partial reflector reflects the first image light back to the partial reflector as the second image light in the second direction. A dimension of the light guide in a thickness direction is longer than a beam diameter of the image light guided in the light guide. The light emission surface has a negative power.