Light guide apparatus and fabrication method thereof

A light guide apparatus comprising:

• a first layer comprising a first optical medium having a first index of refraction and an inclusion structure in the first optical medium, said inclusion structure having a second index of refraction;
• the inclusion structure comprising a first periodic array;
• each repeating unit in the first periodic array comprising two truncated triangles, a height of a first truncated triangle being smaller than a height of a second truncated triangle;
• the first layer configured to receive light impinging in a predetermined range of angles;
• a second layer comprising a second optical medium having a third index of refraction and a second inclusion structure in the second optical medium, said second inclusion structure having a fourth index of refraction;
• the second inclusion structure comprising a second periodic array;
• each repeating unit in the second periodic array comprising two truncated triangles, a height of a first truncated triangle being smaller than a height of a second truncated triangle;
• a height of the second layer being about twice a height of the first layer;
• the second layer configured to receive light from the first layer;
• and
• a third layer comprising a third optical medium having a fifth index of refraction and a third inclusion structure in the third optical medium, said third inclusion structure having a sixth index of refraction;
• the third inclusion structure comprising a third periodic array;
• each repeating unit in the third periodic array comprising two truncated triangles, a height of a first truncated triangle being smaller than a height of the second truncated triangle;
• a height of this third layer being about twice a height of the second layer;
• the third layer configured to receive light from the second layer;
• said each repeating unit in the second periodic array being offset from said each repeating unit in the first periodic array;
• and, said each repeating unit in the third periodic array being offset from said each repeating unit in the second periodic array;
• a shape of said two truncated triangles in the first periodic array, a shape of said two truncated triangles in the second periodic array and a shape of said two truncated triangles in the third periodic array, said first, second, third, fourth, fifth and sixth index of refraction, and a relative alignment between repeating units in the first, second and third periodic arrays being configured such that light incident on the first layer in a predetermined angular range is deflected, deflection comprising refraction, when light strikes triangular faces of truncated triangles in the first, second and third layers, the deflection steering light toward a direction normal to the third layer.