Abstract: An optical device includes a light guide plate; a first diffraction element that is a transmission type diffraction element provided on a first face of the light guide plate and that diffracts and ejects at least a portion of light which is guided along inside the light guide plate; a second diffraction element that is a transmission type diffraction element provided on the first face of the light guide plate and that diffracts at least a portion of light proceeding to the light guide plate; and a third diffraction element that is a reflection type diffraction element provided on a face which is an opposite face of the light guide plate from the first face, and that diffracts at least a portion of light which enters an inside of the light guide plate via the second diffraction element.

Abstract: A first diffraction optical element is disposed on a light incident surface of a light guide, a second diffraction optical element is disposed on a light emitting surface of the light guide, and a reflection layer is disposed on an end surface of the light guide. A diffraction grating of the first diffraction optical element and a diffraction grating of the second diffraction optical element has an inclined portion respectively. The inclined portion of the first diffraction optical element and the inclined portion of the second diffraction optical element are inclined in same direction.

Abstract: In a display apparatus, image light emitted from an image forming device is incident on an image light incidence portion of a light guide member after being diffracted by a second diffractive optical element, and emitted from an image light emission portion after moving forward in the light guide member. The image light emitted from the image light emission portion is diffracted by a first diffractive optical element and reaches the eyes of an observer. On a position where unnecessary external light is made incident on the light guide member, an external light noise reduction element which has a polarizing member and the like is provided. For this reason, even when the unnecessary external light is made incident on the light guide member, it is possible to inhibit the unnecessary external light from reaching the eye of the observer.

Abstract: An optical device includes a light-conducting member, having a first panel surface disposed facing an image forming unit, that conducts image light incident on a light entry plane formed at an end of the first panel surface to a light exit plane formed in front of the viewer's eye; a first diffractive optics element, provided on the light entry plane, that diffracts the image light incident on the light entry plane in a predetermined direction and transmits that light into the light-conducting member; a second diffractive optics element, provided on the light exit plane, that diffracts the image light exiting from the light exit plane in a predetermined direction and transmits that light to the front of the viewer's eye; and one or more reflective planes disposed within a waveguide for the image light diffracted by the first diffractive optics element.

Abstract: The present invention discloses a new .alpha.-keto amide derivative or a salt thereof represented by the formula (1): ##STR1## wherein X represents (1) a peptide residue or amino acid residue in which the functional group may be protected, (2) a hydrogen atom or (3) an amino-protective group, Y represents a peptide residue or amino acid residue in which the functional group may be protected, E represents a substituent on the alkylene (C.sub.n H.sub.2n-1) and is a halogen, lower alkoxy or hydrogen, A represents a carbonyl group or mono- or di-substituted methylene (the substituent being a hydroxy, lower alkoxy, phenylimino or benzylimino), and n represents an integer of 2 to 6.The compound of the present invention is effective in inhibiting prolyl endopeptidase activity and useful as an active ingredient of an enzyme inhibitor.