## 4 Results
### Critical Technology Network Analysis  
This study used level-4 CPC as a basis for the critical SOA technology network analysis. The network model results are displayed in Figure 1, and the key CPC results are presented in Table 3. Every patent can belong to multiple CPCs (nodes), and the value of 1 between different CPCs means that the number of appearances in the same patent is 1. The larger the value between two CPCs is, the stronger the technology correlation between the CPCs is. Consequently, the relations between CPCs (nodes) and patent numbers (sides) can be used to construct a technology network, as presented  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Ranking** & **CPC Classification Number** & **Appearing Number and Frequency** & **Percentage** \\ \hline
1 & H01S3 & 352 & 22.21\% \\
2 & H01S5 & 296 & 18.68\% \\
3 & H04B10 & 190 & 11.99\% \\
4 & G02B6 & 174 & 10.98\% \\
5 & H04J14 & 99 & 6.25\% \\
6 & G02F1 & 98 & 6.18\% \\
7 & G01B9 & 27 & 1.70\% \\
8 & H01L21 & 27 & 1.70\% \\
9 & H01L29 & 22 & 1.39\% \\
10 & G02F2 & 17 & 1.07\% \\ \hline \hline \end{tabular} Source: compiled in this study.  
\end{table}
Table 1: Distribution numbers of the top 10 level-4 CPC classification in Figure 1. The participants in the center of the technology network can be considered key nodes, that is, nodes with high attention.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Ranking** & **Patentee** & **Number of Patents** & **Percentage** & **Average Age of Patents** \\ \hline
1 & Fujitsu Limited, Kawasaki, JP & 76 & 7.62\% & 8 \\
2 & Electronics and Telecommunications Research Institute, & 40 & 4.01\% & 9 \\
3 & Samsung Electronics Co., Ltd., Suwon Si, KR & 34 & 3.41\% & 12 \\
4 & Finisar Corporation, Sunnyvale, US & 33 & 3.31\% & 13 \\
5 & Alcatel-Lucent Enterprise, Boulogne-Billancourt, FR & 33 & 3.31\% & 13 \\
6 & NEC Corporation, Tokyo, JP & 29 & 2.91\% & 12 \\
7 & Sumitomo Electric Industries, Ltd, Osaka, JP & 28 & 2.81\% & 11 \\
8 & The Furukawa Electric Co., Ltd., Tokyo, JP & 27 & 2.71\% & 12 \\
9 & Lucent Technologies Inc., Murray Hill, US & 20 & 2.01\% & 16 \\
10 & Sumitomo Electric Device Innovations, Inc., & 20 & 2.01\% & 3 \\ Yokohama-shi, JP & & & & \\ \hline \hline \end{tabular} Source: compiled in this study.  
\end{table}
Table 2: Number of approved patents for the top 10 patentees  
Figure 1: level-4 CPC network for SOA technologies. Note: The node size indicates the number of connected nodes, and the arc thickness indicates the connection strength. Only nodes with more than five connected nodes were retained.  
Table 3 indicates that H01S5, H01S3, G02B6, H04B10, and G02F1 are top five technology fields in both KPP-positive and KPP-negative. Thus, in addition to lasers and semiconductor lasers (H01S3 and H01S5), critical SOA technologies also include light guides (G02B6), electromagnetic wave transmission communication other than radio-wave communication (H04B10), and devices controlling light sources (G02F1). The aforementioned information suggests that the most important SOA technologies mainly include basic electric elements, optical elements, and communication techniques. These technologies and elements are the products of interdisciplinary studies and are indispensable.