Holographic display apparatus having steerable viewing window

A holographic display apparatus comprising:

• a light source configured to output light;
• a first lens configured to collimate light incident thereon from the light source;
• a second lens configured to focus collimated light, incident thereon from the first lens, to an intermediate image plane;
• a third lens configured to collimate light incident thereon from the intermediate image plane;
• a fourth lens configured to focus the collimated light, incident thereon from the third lens, to a focal plane;
• a spatial light modulator configured to modulate incident light and thereby reproduce a holographic image;
• a spatial filter configured to transmit only the holographic image;
• an eye tracker configured to track a pupil location of an observer;
• a stage on which the light source and the spatial filter are mounted;
• and
• a controller configured to move the stage to adjust locations of the light source and the spatial filter in response to information identifying a change in the pupil location of the observer received from the eye tracker,
• wherein the fourth lens is further configured to focus the holographic image on a viewing window and a location of the viewing window coincides with the location of the spatial filter.