Manufacturing method of holographic optical element and display device including holographic optical device manufactured thereby

A method of manufacturing a holographic optical element, comprising:

• irradiating a first surface of a photosensitive substrate with a first laser, wherein light emitted by the first laser is spread in an irradiation direction;
• and
• irradiating a second surface of the photosensitive substrate with a second laser, wherein light emitted by the second laser is collected in the irradiation direction,
• wherein the first and second surfaces of the photosensitive substrate are irradiated with the first laser and the second laser to form a plurality of groups,
• wherein a plurality of overlapping angles are formed by a progress direction of the light emitted by the first laser and the progress direction of the light emitted by the second laser at a predetermined location of a photosensitive area of the photosensitive substrate at which the light emitted by the first laser and the light emitted by the second laser cross,
• wherein each of the plurality of the overlapping angles are different from each other,
• wherein in the irradiating of the first surface of the photosensitive substrate by the first laser, the photosensitive substrate is irradiated with a plurality of first lasers in which a plurality of irradiation directions are different from each other,
• wherein in the irradiating of the second surface of the photosensitive substrate with the second laser, the photosensitive substrate is irradiated with a plurality of second lasers in which the irradiation directions are different from each other, and
• wherein an overlapping angle formed by the irradiation direction of any one first laser among the plurality of first lasers and the irradiation direction of any one second laser among the plurality of second lasers is the same as the overlapping angle formed by the irradiation direction of any other first laser among the plurality of first lasers and the irradiation direction of any other second laser among the plurality of second lasers.