An optical depolarizer for depolarizing a beam having a direction of propagation along a first direction relative to the depolarizer, the beam entering through a front surface (36a,b, 44) of the optical depolarizer and leaving through a back surface (39a,b, 46) of the optical depolarizer, the optical depolarizer comprising - a first and second body (30, 32, 40a,b 42a,b) of transparent material, adjoining the front and back surface (36a,b, 44, 46) respectively, the first and second body (30, 32, 40a,b 42a,b) each having a thickness in the first direction that varies as a function of a position for entry of the beam at the front surface, a sum of the thicknesses of the first and second body being substantially independent of said position; - the transparent material in the first and second body (30, 32, 40a,b 42a,b) having speeds of light of first and second polarization components that are mutually different, the speed of light of the first polarization component in the first body (30, 40a,b) equalling the speed of light of the second polarization component in the second body (32, 42a,b) and vice versa; - the front surface (36a, 44) having a first and second planar surface part (36a,b) extending on first and second, mutually opposite sides from a virtual plane through the depolarizer respectively, the virtual plane being parallel to the first direction, the first and second planar surface part (36a,b) forming a concave angle in the front surface (36a,b, 44), - the back surface (39a,b, 46) having a third and fourth surface part (39a,b) substantially parallel to the first and second surface parts (36a,b), on the first and second side of the virtual plane respectively when the transparent material of the first and second body (30, 32, 40a,b 42a,b) is the same but, when different materials are used, with the third and fourth surface part (39a,b) oriented along different directions at a non-zero angle relative to the first and second surface parts (36a,b), so that a same beam direction of the incoming and outgoing beam is provided for. - a first and second body (30, 32, 40a,b 42a,b) of transparent material, adjoining the front and back surface (36a,b, 44, 46) respectively, the first and second body (30, 32, 40a,b 42a,b) each having a thickness in the first direction that varies as a function of a position for entry of the beam at the front surface, a sum of the thicknesses of the first and second body being substantially independent of said position; - the transparent material in the first and second body (30, 32, 40a,b 42a,b) having speeds of light of first and second polarization components that are mutually different, the speed of light of the first polarization component in the first body (30, 40a,b) equalling the speed of light of the second polarization component in the second body (32, 42a,b) and vice versa; - the front surface (36a, 44) having a first and second planar surface part (36a,b) extending on first and second, mutually opposite sides from a virtual plane through the depolarizer respectively, the virtual plane being parallel to the first direction, the first and second planar surface part (36a,b) forming a concave angle in the front surface (36a,b, 44), - the back surface (39a,b, 46) having a third and fourth surface part (39a,b) substantially parallel to the first and second surface parts (36a,b), on the first and second side of the virtual plane respectively when the transparent material of the first and second body (30, 32, 40a,b 42a,b) is the same but, when different materials are used, with the third and fourth surface part (39a,b) oriented along different directions at a non-zero angle relative to the first and second surface parts (36a,b), so that a same beam direction of the incoming and outgoing beam is provided for.