An optical component in the form of a right angled triangular prism having a first side, a second side orthogonal to the first side, and a third side generally inclined to the first and second sides to reflect optical radiation incoming from the first side towards the second side. The first and second sides have semi-reflecting surfaces acting as etalon surfaces providing an interferometric pattern. The optical transmittance between the first and the second sides is wavelength dependent and the radiation exiting the second side of the component is rotated 90 degrees to the radiation entering the first side.