# Enhancement of ECE SuperPin Curved Reflex Reflector by the Use of Double Pins with Corner Cubes
## 3 Experimental Setups and Analysis  
In order to investigate the property of a curved reflex reflector, a commercialized CCCR (curved corner cube retroreflector) for a car was used for testing, as shown in Figure 6. The \(146\times 34\) mm sample is made of PMMA (poly methyl methacrylate) and composed of 2.75-mm sized corner-cube arrays. The product is provided by OWL LIGHT AUTOMOTIVE MFG. CORP (Lukang, Chunghua, Taiwan) and it has been in mass production for automotives in the EU. The experimental setup for CCCR testing is shown in Figure 7. In the optical setup, a 532 nm diode-pumped solid state (DPSS) laser operated with a 5 mW output acted as the light source. The distance between the laser and the curved reflex reflector was set to be 30.5 meters to measure the reflected light spot. Based on the laser spectrum specification, its coherence length is calculated to be about 0.5 mm, which is less than the corner-cube dimension of 2.75 mm in the experiments. Therefore, the retro-reflected output spots were spatially incoherent, and the laser can be considered as an incoherent light source for the following retro-reflector testing experiments. The laser light had an incident angle of \(0^{\circ}\) with respect to the car driving direction, as it shone on the commercialized CCCR with a spot area of 520 mm\({}^{2}\). As a result, several retro-reflected light spots can be found on the black screen located 30.5 meters away from the test sample. A Minolta  
Figure 5: (a) Set-up for optical simulations of corner-cube retro-reflectors (CCRs); (b) the orientation of the corner cube; and (c) the retro-reflected beams intensity distribution.  
T10 illuminance meter was used to measure the illuminance of the sample and of the retro-reflected light spot in order to get the incident light illuminance (in lux) and the retro-reflected light intensity (in candela). The coefficient of luminous intensity \(\mathbf{R_{I}}\) and retro-reflection efficiency \(\mathbf{R_{A}}\) of the test sample can be obtained. During experiments, the anterior, central and posterior regions of the CCCR were investigated. Their locations and the car's driving direction are presented in Figure 8.  
Initially, the laser light was adjusted to be parallel with the driving direction and focus on the central part of each region. The reflected outputs are shown in Figure 9a-c, respectively. It can be found that the reflected light spots become gloomy as the test region shifted from the front part to the end part of the CCCR. The curved shape of the CCCR seems to have caused interferences regarding its functions.  
Figure 8: The test regions of CCCR; each testing area is 520 mm\({}^{2}\).  
Figure 6: The commercial SuperPin curved reflex reflector.  
Figure 7: Experimental setup for curved corner-cube retro-reflector (CCCR) testing.  
In order to enhance the performance of the.SuperPin CCCR, a single beam parallel with driving direction was used to probe the reflecting surfaces of the posterior region by optical simulations. As shown in Figure 9, the anterior and the central regions areas have a higher performance than the rest. In contrast, at the upper position (0.33\({}^{\circ}\)) of the posterior area of CCCR, there is almost no reflected light. Therefore, it can be concluded that the posterior area cannot meet ECE regulation requirements.  
In order to rescue the posterior region, the relationship between the incident light location of CCR and its retro-reflected light direction is investigated. The simulation experiments of rays shining on face #1, face #2, and face #3 are conducted, respectively. Their resulted reflected light intensity distribution are shown in Figures 10-12. Comparing Figure 9 with Figures 10-12, it can be understood that the #1 and #3 reflecting surfaces in the posterior region do not function normally, so that three light spots are missed in the output screen. If the pin group structures could be reconstructed, the coefficient of luminous intensity R