# A Study of High-Efficiency Laser Headlight Design Using Gradient-Index Lens and Liquid Lens
## 2 Concept Design of Laser Car Headlight System
laser can be effectively used as the headlight source [18; 19]. However, the disadvantage of the diode laser is that its small size makes it difficult to dissipate heat, and heat dissipation is a crucial technical consideration [20]. No. 2 is the optical fiber that this study uses to transfer laser light. Optical fibers are flexible and can be bent to direct light to a desired location. The laser light source is small in size, which makes it difficult to dissipate heat; therefore, the laser light source is eliminated from the headlight system and an optical fiber is used to direct the light to the system. A suitable laser source heat dissipation system can, therefore, be effectively established, allowing for the maintenance of the laser light source. This study uses \(\mathcal{O}\) 1 mm single-mode fiber as the optical transmission component. No. 3 is a ROD. A ROD is an all-around surface-polished optical device, with an appearance similar to that of a cylindrical lens. It comprises a highly reflective mirror, and its function is to integrate a light source and produce a uniform light beam with a specific shape created by a ROD [21]. Its purpose is to focus laser gaussian beam then after multiple reflection, finally form a homogenized laser light distribution. Therefore, the laser beam will become more uniform in square shape after entering a light shaper ROD, which is commonly seen in pico-laser projectors. No. 4 is a light shaper. Its main function is to adjust the light type. To produce a clear cut-off line that satisfies the regulations, the exit light should be a square type to produce a cut-off line effect. No. 5 is a GRIN lens. The GRIN lens is a cylindrical lens, which has different refractive indices when viewed along the lens axis, and can be used to focus or diffuse light beams. The use of GRIN lens can reduce the number of lenses required to achieve the effect of light diffusion [22]. No. 6 is a liquid lens. Liquid lenses represent a new technology in optical devices, in which the shape of interface between the two liquids in the lens is changed by controlling the electricity. Therefore, the direction of light projection can be controlled, and the focus can be varied. The use of liquid lenses made from certain special liquids, such as disulfide, enables precise control of the focal length, where the liquid must eliminate the stray light to enable the lens to produce accurate and reliable light. In this study, a liquid lens was used as a change switch, which was capable of switching between the high and low beams by adjusting the liquid lens curvature and optical axis. This pioneering study can effectively satisfy the simplified requirements of the headlight components. No. 7 is a freeform lens. The laser beam processed using the six optical devices described above was diffused in this study. However, the output light pattern failed to satisfy regulatory requirements. Therefore, we adjusted the output light pattern using a freeform lens, which has an aspheric surface with asymmetrical and multi-symmetric axes, and was designed using Equation (1). By controlling the curvature parameters of the X- and Y-axes of the lens, a lens with an asymmetrical pattern can be manufactured, and the projected light pattern can be changed. The shape of the freeform lens is depicted in Figure 3.  
\[\mathrm{z}=\frac{\mathrm{cr}^{2}}{1+\sqrt{1-(1+k)c^{2}r^{2}}}+\sum_{j=2}^{66} Cj\cdot x^{m}y^{n} \tag{1}\]  
where \(j=\frac{(m+n)^{2}+m+3n}{2}+1\), \(\mathrm{z}\) denotes the depth from the surface to the mirror, \(c\) denotes the central curvature of the mirror, \(r\) denotes the perpendicular distance from any point on the mirror to the optical axis, \(k\) denotes the conic constant (quadratic curve), \(Cj\) denotes the monomial coefficient and \(m\) and \(n\) denote the powers of \(x\) and \(y\) terms in the polynomial series. Figures 4 and 5 denote the European regulations associated with the high- and low-beam distribution range and intensity. The test configurations of the high and low beams are the same.