# Extended L-Band InAs/InP Quantum-Dash Laser in Millimeter-Wave Applications
## 4 Conclusions  
A \(\sim\)1610 nm extended L-band SIL QD-DWL was proposed and demonstrated for the optical generation of MMW beat tones. The potential deployment of this QD-DWL as an MMW source was strengthened by demonstrating the successful transmission of a 2-Gbits/s QPSK signal in a WL (0-6 m) and a hybrid-WL (20-km SMF-6-m WL) channels. The respective exhibited receiver sensitivities of \(\sim\)\(-\)2.8 and \(\sim\)3.3 dBm were noted. Furthermore, the QD-DWL showed a slight power penalty of \(\sim\)1.6 dB in receiver sensitivity compared to the CL-DWL. However, the potential merits offered by QD-DWL highlight and affirms this source's potential as an L-band MMW light source for next-generation optical networks integrating MMW technology and hybrid channels. Besides, the niche feature of QD-LDs, from an SIL-based DWL to a mode-locked-based multiwavelength laser source, could also be exploited in future extended L-band RoF-WDM systems, thus serving as a single source for several MMW carriers (channels).  
**Author Contributions:** Conceptualization, A.M.R. and M.Z.M.K.; methodology, M.A.E. and E.A.; experiment, A.M.R., Q.T., E.A. and M.A.E.; validation, A.M.R., M.A.E., Q.T. and M.Z.M.K.; investigation, A.M.R., Q.T., S.A. and M.Z.M.K.; writing--original draft preparation, Q.T. and M.Z.M.K.; writing--review and editing, A.M.R., Q.T., E.A., M.A.E., S.A. and M.Z.M.K.; supervision, S.A. and M.Z.M.K.; funding acquisition, A.M.R. and M.Z.M.K. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by King Fahd University of Petroleum and Minerals, grant number SB191036, and National Plan for Science, Technology, and Innovation (MAARIFAH), King Abdulaziz City for Science and Technology, grant number 2-17-02-001-0009.  
**Institutional Review Board Statement:** Not applicable.  
Figure 6: (**a**) BER versus received optical power of the QD-DWL source at 30 GHz for the hybrid-FSO channel with 0- and 2-m WL link lengths. (**b**) The corresponding received QPSK constellation (top) and eye diagram (bottom) at a \(\sim\)\(-\)1.0 dBm received power for 0-m (left column) and 2-m (right column) WL link lengths.  
**Informed Consent Statement:** Not applicable.  
**Acknowledgments:** Q.T. and M.Z.M.K. acknowledge the support from King Fahd University of Petroleum and Minerals through grant SB191036. A.M.R. and S.A. thank the National Plan for Science, Technology, and Innovation (MAARIFAH), King Abdulaziz City for Science and Technology, Kingdom of Saudi Arabia (award number: 2-17-02-001-0009). M.A.E. acknowledges the support from Prince Sultan University.  
**Conflicts of Interest:** The authors declare no conflict of interest.  
**Glossary**  
5G fifth generation AWG arbitrary waveguide BER bit error rate BtB back-to-back c speed of light CL commercial laser CP optical coupler CW continuous wave D fiber dispersion parameter DFB distributed feedback DSB double sideband modulation DWG dual-wavelength generator ESA electrical spectrum analyzer EVM error-vector magnitude FEC forward-error correction FP Fabry-Perot FSO free-space optics FSR free spectral range FITX fiber-to-the-X LD laser diode LNA low-noise amplifier MLL mode-locked laser MMW,illimeter-wave MZM Mach-Zehnder modulator NRZ non-return-zero OC optical circulator OFC optical frequency comb OOK on-off-keying OSA optical spectrum analyzer OSNR optical signal-to-noise ratio PAM pulse amplitude modulation PBRS pseudo-random bit sequence PC polarization controller PD photodiode PM phase modulator POR optical received power PPP public private partnership QD quantum dash QD-DWL quantum-dash dual-wavelength laser QPSK quadrature phase-shift keying RBW resolution bandwidth RIN relative intensity noise ROF radio-over-fiber SIL self-injection locking SMF Single-mode fiber SMSR side-mode suppression ratio SNR signal-to-noise ratio