Patent ID: 8908185

Claim:
A prism, comprising: a lower surface, used to receive light; an upper surface, opposite to the lower surface; a first side surface, a one-dimensional parabolic surface, used to reflect the light from the lower surface to the upper surface; and a second side surface, a one-dimensional parabolic surface, used to reflect the light from the upper surface to the lower surface; wherein, the first side surface and the second side surface are disposed between the upper surface and the lower surface, wherein the light is respectively reflected in the prism from the lower surface to the upper surface and vice versa by the first side surface and the second side surface, wherein the incident angle of the light impinging onto the first side surface and then reflected to the upper surface is larger than the critical angle of the total internal reflection, and wherein the incident angle of the light, from the upper surface, impinging onto the second side surface is larger than the critical angle of the total internal reflection.