Focus modulation optical system and holographic display device having the same

A holographic display device comprising:

• a light source configured to emit a plurality of color lights;
• a focus modulation optical system comprising at least one variable focus lens that is configured to change a focusing position of incident light by electrical control of the at least one variable focus lens based on a color of light incident on the at least one variable focus lens;
• a spatial light modulator configured to form a holographic image by diffracting light output from the focus modulation optical system;
• and
• a controller configured to control the light source to time-sequentially emit the plurality of color lights,
• wherein the at least one variable focus lens is configured to time-sequentially adjust a focusing position corresponding to the plurality of color lights, and
• wherein the at least one variable focus lens comprises:
• a first substrate;
• a first electrode layer disposed on the first substrate;
• a second substrate disposed opposite to the first substrate, a second electrode layer disposed on the second substrate;
• and
• a liquid crystal layer disposed between the first substrate and the second substrate.

A holographic display device comprising:

• a light source configured to emit a plurality of color lights;
• a beam deflector configured to deflect the plurality of color lights emitted from the light source;
• a light guide plate configured to guide the plurality of color lights deflected from the beam deflector;
• a focus modulation optical system comprising a fixed focus lens and a plurality of variable focus lenses that are configured to change a focusing position of the plurality of color lights output from the light guide plate by electrical control of the plurality of variable focus lenses based on a color of the plurality of color lights incident;
• and
• a spatial light modulator configured to form a holographic image by diffracting the plurality of color lights output from the focus modulation optical system,
• wherein each of the plurality of variable focus lenses comprises a first substrate, a first electrode layer provided on the first substrate, a second substrate disposed opposite to the first substrate, a second electrode layer provided on the second substrate, and a liquid crystal layer provided between the first substrate and the second substrate.