Provided is an optical fiber including: a core at a center thereof; a first cladding adjacent to the core to cover a circumference of the core; and a second cladding adjacent to the first cladding to cover a circumference of the first cladding, where 0. The sliding element includes an upper sliding surface and a lower sliding surface, wherein the lower sliding surface is arranged below the upper sliding surface so as to be slideable in at least two directions. Therefore, the illumination range of the headlamps can timely provides a desirable driver’s view point. With the characteristics of power-control device, the voltage sent to motor is increased from low to full range. Thus, the magnet forms an effective remover of magnetorheological fluid from the carrier surface without any mechanical contact with the surface.