Patent ID: 8064134

Claim:
An optical element comprising: first and second entrance surfaces through each of which light enters the optical element; one emergence surface from which light emerges; three transmissive surfaces each of which faces a reflective image-forming element; and a first optical structure formed along a first plane and a second optical structure formed along a second plane, the first and second planes intersecting each other inside the optical element; wherein all normals to the first and second entrance surfaces, the one emergence surface, the three transmissive surfaces and the first and second planes are parallel to a same plane, wherein the following condition is satisfied: 45°<θ0<75° where θ0 is a smaller one of angles made by the first and second planes, wherein an angle made by normals to the first entrance surface and the first plane is θ1, wherein an angle made by normals to the first entrance surface and the second plane is θ2, wherein an angle made by normals to the second entrance surface and the first plane is θ3, wherein an angle made by normals to the second entrance surface and the second plane is θ4, and wherein θ1 is equal to θ4 and θ2 is equal to θ3.