Image displacement device

An image displacement device, comprising:

• a first grating switchable between a diffracting state and a non-diffracting state having a first surface and a second surface opposite the first surface, the first surface being capable of receiving an image beam, and the second surface being capable of outputting the image beam;
• a second grating switchable between the diffracting state and the non-diffracting state and being disposed downstream from the first grating in a light path, the second grating having a third surface and a fourth surface opposite the third surface, the third surface being capable of receiving the image beam, and the fourth surface being capable of outputting the image beam;
• a third grating switchable between the diffracting state and the non-diffracting state and being disposed downstream from the second grating in the light path, the third grating having a fifth surface and a sixth surface opposite the fifth surface, the fifth surface being capable of receiving the image beam, and the sixth surface being capable of outputting the image beam;
• and
• a fourth grating switchable between the diffracting state and the non-diffracting state and being disposed downstream from the third grating in the light path, the fourth grating having a seventh surface and a eighth surface opposite the seventh surface, the seventh surface being capable of receiving the image beam, and the eighth surface being capable of outputting the image beam, wherein the image beam outputted from the eighth surface is capable of being projected on four different positions, and a shortest distance between two of the four different positions is substantially equal to a shortest distance between the other two of the four different positions.