## 3 Optical Characteristics  
The insertion losses of the 12-channel connectorized waveguides under overfilled and underfilled launch conditions at a wavelength of 850 nm were measured with and without the use of a mode scrambler (MS, Newport's FM-1), respectively. A schematic of the measurement setup is shown in Figure 5.  
Figure 4: (a) 1 m long and (b) 1.7 m long polymer waveguide films under twisting conditions. Figure 3: Images of (a) 1 m long and (b) 1.7 m long polymer waveguide illuminated by a red identification light. Figure 2: (a) Microscope image of the fabricated polymer waveguides, (b) 12-core MT connector for polymer waveguides, and (c) 12-core MT connector for OM3 optical fibers. The averaged 12-channel insertion loss of the 1 m-long waveguides under overfilled and underfilled launch conditions is 4.3 dB (0.043 dB/cm) and 4.0 dB (0.040 dB/cm), respectively, as shown in Figure 6a. The averaged 12-channel insertion loss of the connectorized waveguides with a length of 1.7 m under overfilled and underfilled launch conditions is 7.0 dB (0.042 dB/cm) and 6.9 dB (0.040 dB/cm), respectively, as shown in Figure 6b. The additional loss due to the increased number of curves and adoption of a tighter bending radius for a 1.7 m long waveguide sheet is negligible. Moreover, the slightly higher loss of about 0.002 to 0.003 dB/cm under the overfilled launch condition implies that a larger portion of the light transmits in higher order modes, which have a higher bending loss in comparison with that of the underfilled launch condition. The inter-channel crosstalk of the fabricated 12-channel polymer waveguides was measured using the setup as shown in Figure 7. When laser light operating at 850 nm is input from the waveguide numbered n, its inter-channel crosstalk can be obtained by measuring the received optical power at the outputs of the adjacent waveguides numbered n - 1, n, and n + 1. The measurement results of inter-channel crosstalk are shown in Table 1. The maximum crosstalk under the strictest overfilled launch working condition is as low as \(-46.4\) dB for the 1.7 m long waveguide film. Figure 5: Experimental setup for the insertion loss measurement. Figure 6: (**a**) Insertion loss of 1 m long waveguide and (**b**) insertion loss of 1.7 m long waveguide. Figure 7: Schematic of the inter-channel crosstalk measurement. The experimental setup for measuring the bending loss of flexible waveguide film and MMF ribbon is shown in Figure 8a. The polymer waveguide film and MMF ribbon in the same link are bent into a full circle using fixing jigs with various radii, as shown in Figure 8b. The measured bending loss under both the overfilled and underfilled launch conditions is shown in Figure 9. The fabricated polymer waveguide films exhibit a much smaller bending loss than that of the MMF ribbon with an additional loss of less than 1 dB at a bending radius as small as 1 mm under the overfilled launch condition. In addition, the mechanical flexibility of the fabricated polymer waveguide films is superior to that of the MMF ribbon due to both their thinner film thickness and the nature of polynorborene materials over silica glass. Therefore, our polymer waveguide film presents significant advantages for applications with tight spatial constraints, such as interconnection of miniature on-board transceivers. The PDL of the flexible waveguide under both the underfilled and overfilled conditions was measured using the experimental setup shown in Figure 4:0 Table 2 shows that the measured PDL of both 1 m long and 1.7 m-long waveguides was not higher than 0.05 dB under both of the launch conditions. \begin{table}
\begin{tabular}{l l l} \hline
**Length** & **Underfilled** & **Overfilled** \\ \hline
1 m & \(\leq\)\(-\)50.8 dB & \(\leq\)\(-\)48.0 dB \\
1.7 m & \(\leq\)\(-\)48.5 dB & \(\leq\)\(-\)46.4 dB \\ \hline \end{tabular}
\end{table} 
Table 1: Measurement results of inter-channel crosstalk.