Patent ID: 7099539

Claim:
An optical system, comprising: a first branch aligned in a first direction and having a first end, a second end, and a first side edge extending between the first and second ends such that the first side edge is parallel to the first direction, the first branch being capable of allowing light to pass therethrough in a forward direction from the first end to the second end and a reverse direction from the second end to the first end, the first branch including a first medium with a first refractive index (n 1 ); a second branch aligned in a second direction and having a first end, a second end, and a second side edge extending between the first and second ends such that the second side edge is parallel to the second direction, the second branch being capable of allowing light to pass therethrough in a forward direction from the first end to the second end, the second branch including a second medium with a second refractive index (n 2 ), the second end of the second branch abutting the first side edge of the first branch to form an interface, wherein the second side edge of the second branch forms an angle (θ 2 ) with the first side edge of the first branch, and wherein the interface is aligned parallel to the first direction and forms an incident angle (θ 1 ) with the first side edge of the first branch; wherein n 2 <n 1 and θ 1 ≧sin −1 (n 2 /n 1 ), whereby light passing through the first branch in the reverse direction is prevented from passing into the second branch through the interface.