## 4 Experimental Results  
Transmission characteristics were measured at some wavelengths with a parameter of the aperture size or solid angle between the sample and the aperture. To avoid complexity, the results at 1.523 \(\upmu\)m are shown in Figure 3 only for the reference and SIR132 sample. For both samples, the transmission \begin{table}
\begin{tabular}{c c c} \hline
**Dopant** & **Dye category** & **Absorption peak wavelength (\(\upmu\)m)** \\ \hline SIR132 & Metal complex & 1.03 \\ SIR103 & Phtalocyanine derivative & 0.95 \\ M370 & Anthraquinone derivative & 0.52, 0.55 \\ M618 & Azo derivative & 0.53 \\ \hline \end{tabular}
\end{table} 
Table 1: Summary of the dichroic dyes. Figure 1: **(a)** Cross-sectional (polymer/liquid crystal) composite film (PLCF) with no voltage; **(b)** Cross-sectional PLCF with a voltage exceeding a threshold. Small bars are liquid crystal molecules. Figure 2: Measurement setup. LD: laser diode, PD: photodiode. A voltage source is not shown but is connected to the sample. becomes larger as the applied voltage increases. When the samples were observed visibly, they were opaque at the voltage of 0 V but they became transparent at the voltage of 30 V or higher. The extinction ratios are about 3 and 51 for the reference and the SIR132 sample, respectively, when the ratio is evaluated at the smallest solid angle. Not shown in Figure 3, the extinction ratios of SIR103 is 7.4 and that of other samples is about 3, which is close to the extinction ratio of the reference. It is experimentally shown that the extinction was improved by doping SIR132 and SIR103. Very little improvements were observed for M370 and M618. In Figure 3, several lines are plotted for the different solid angle and this shows that the transmission becomes higher as the solid angle becomes larger. Figure 4 shows the transmission dependence on the voltage for the SIR132 at some wavelengths. As described, the SIR132 sample exhibits a good extinction from red to infrared although the transmission curves are somewhat different. All the transmission increase as the voltage increases. The voltage threshold is only about 2 V for 1.523 \(\upmu\)m while it is about 10 V at 0.523 and 0.635 \(\upmu\)m. These tendencies are the same as other samples. During the transmission measurements, we have not observed significant hysteresis effects in any samples. Typical rise times were a few ms and fall times were a few to 10 ms; however, these were dependent on the applied voltages and on the dye dopants. To distinguish the extinction mechanism, transmission and extinction ratio dependence on the solid angles is shown in Figures 5 and 6, respectively. If the extinction mechanism is based only on the light absorption, the transmission and extinction ratio should be independent of the solid angle. If the extinction mechanism includes the light scattering, the transmission and extinction ratio should depend on the solid angle. In Figure 5, high and H are the transmissions at 50 V and low and L the transmissions at 0 V. The high values are relatively flat even when the solid angle changes approximately \(10^{3}\) times. In addition, the high transmission is not strongly dependent on the dopants. On the other hand, the low transmissions increase as the solid angle becomes wider. The smallest low transmission was observed  
Figure 3: Transmission dependence on the applied voltage \(V_{\mathrm{LC}}\). The curves are drawn for the solid angle of 0.025 (top), 0.018, 0.0063, 0.0031, 0.0020, 0.0016, 0.0008, and 0.0004 steradians (bottom). The wavelength was 1.523 \(\upmu\)m. Dye-doped: SIR-132 doped, Reference: undoped. from the SIR132 sample and the second smallest form SIR103. The low transmissions of the M370 and M618 samples were not drastically reduced, even if the dichroic dyes were doped. The ratio of high to low (extinction ratio) are calculated and shown in Figure 6. The extinction ratio was measured as 51 or 17.1 dB, the largest among the samples, for SIR132, and as 7.4 or 8.7 dB, the second largest, for SIR103.