Systems and methods for measuring the speed andor direction of a target such as a vehicle in a field of view. The method and apparatus may also be used to control, for example, a robot or other spatially dependent machine. The result is an optically and mechanically stable composite birefringent crystal unit. The dual buffer structure provides better barrier to impurities diffusing from the substrate, and also acts as a black matrix to reduce unwanted reflections and is a source of hydrogen to passivate other layers. The flow portion has a seat orifice extending therethrough and an orifice disk coupled to the orifice disk retention surface so that the orifice plate is aligned in a fixed spatial axial orientation with respect to the flow portion.