Patent ID: 7414237

Claim:
A sensor for detecting moisture on a pane, the sensor comprising: a transmitter for transmitting optical radiation towards a pane; a receiver for receiving optical radiation reflected from the pane; a coupler having a plurality of prisms arranged in coupling areas for coupling optical radiation from the transmitter into the pane at a given input angle and a plurality of prisms arranged in decoupling areas for decoupling the optical radiation reflected from the pane out to the receiver at a corresponding given output angle, wherein the prisms arranged in the coupling areas have prism surfaces arranged perpendicular to the given input angle and the prisms arranged in the decoupling areas have prism surfaces arranged perpendicular to the given output angle; wherein each prism includes a prism flank in addition to a prism surface, wherein the prism flanks of the prisms arranged in the decoupling areas are arranged parallel to the given output angle; wherein at least some of the prism flanks of the prisms arranged in the decoupling areas are opaque.