# Extended L-Band InAs/InP Quantum-Dash Laser in Millimeter-Wave Applications
## 3 Results and Discussion
### WL and SMF Transmission Performance Analysis  
First, the WL transmission performances of the 28-GHz modulated MMW carrier signal generated by the CL-DWL and the QD-DWL were investigated for 0 m (BtB) and 4-m WL lengths, and the results are plotted in Figure 4a,b, respectively. The measured minimum optical received power (\(P_{OR}\)) for FEC BER are summarized in Table 1. While the WL BtB channel exhibited a receiver sensitivity of \(-\)\(-\)9.4 dBm, the 4-m WL channel showed a \(-\)1.6 dBm receiver sensitivity for the CL-DWL source. On the other hand, the QD-DWL-based 28 GHz MMW carrier displayed a corresponding \(P_{OR}\) of \(-\)\(-\)7.9 dBm and \(-\)\(-\)0.2 dBm under the BtB and the 4-m WL distance, respectively. This indicated an average \(P_{OR}\) penalty of \(\sim\)1.4 dB exhibited by the QD-DWL compared to that by the CL-DWL counterpart, considering the WL channel. Furthermore, a similar trend was also observed for the hybrid-WL channel (20 km SMF and 0-4 m WL), of which the results for both the sources are plotted in Figure 5a,b. In this case, the CL-DWL exhibited \(P_{OR}\) values of \(-\)\(-\)7.5 and \(-\)\(-\)0.5 dBm to reach the FEC limit for the BtB and the 4-m WL sub-linklength, respectively. On the other hand, the corresponding performance of the QD-DWL MMW source at the aforementioned WL sub-link lengths are \(--\)5.1 and \(-\)0.7 dBm. Hence, in the hybrid-WL channel configuration, a minor average \(P_{OR}\) penalty of \(-\)1.8 dB was observed from the QD-DWL compared to that from the CL-DWL. Thus, an overall minor \(P_{OR}\) penalty of \(-\)1.6 dB has been demonstrated by the QD-DWL considering both the WL and hybrid-WL channels. This disparity of performance between the QD-DWL and the CL-DWL could be explained by the following qualitative model. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Source**} & \multicolumn{8}{c}{**Receiver Sensitivity \(P_{OR}\) (dBm)**} \\ \cline{2-10}  & \multicolumn{4}{c}{**WL**} & \multicolumn{4}{c}{**Hybrid-WL**} & \multicolumn{4}{c}{**Hybrid-FSO**} \\ \cline{2-10}  & **0 m** & 2 m & 4 m & 6 m & 0 m & 2 m & 4 m & 6 m & 0 m & 2 m \\ \hline CL-DWL (28 GHz) & \(\sim\)\(-9.4\) & - & \(\sim\)\(-1.6\) & - & \(\sim\)\(-7.5\) & - & \(\sim\)\(-0.5\) & - & - & - \\ QD-DWL (28 GHz) & \(\sim\)\(-7.9\) & \(\sim\)\(-2.9\) & \(\sim\)\(-0.2\) & \(\sim\)\(2.8\) & \(\sim\)\(-5.1\) & \(\sim\)\(-1.3\) & \(\sim\)\(0.7\) & \(\sim\)\(3.3\) & - & - \\ QD-DWL (30 GHz) & - & - & - & - & - & - & - & - & \(\sim\)\(-7.3\) & \(\sim\)\(-3\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Measured optical received power levels required for error-free transmissions in various channels for 28- and 30-GHz MMW systems. Figure 4: Bit error rate (BER) versus optical received power of the commercial laser and dual-wavelength laser (CL-DWL) source at 28 GHz (**a**) and the QD-DWL source at 28 GHz (**b**) for the WL channel with various link lengths. The respective insets show the received QPSK constellation at a \(\sim\)0 dBm received optical power for the 0-m (top) and 4-m (bottom) WL link lengths. Figure 5: BER versus optical received power of the CL-DWL at 28 GHz (**a**) and QD-DWL at 28 GHz (**b**) for the hybrid-WL channel with various WL sub-link lengths. The respective insets show the received QPSK constellation at a \(\sim\)0 dBm received optical power for the 0-m (top) and 4-m (bottom) WL link lengths and the eye diagram at a \(\sim\)0 dBm received power for the 0-m WL link length.