# Tunable 60 GHz Multiwavelength Brillouin Erbium Fiber Laser
## 4 Conclusions  
The experimental results of a tunable 60 GHz multiwavelength Brillouin erbium fiber laser are successfully demonstrated in this paper. Four sextuple Stokes channels are presented and tuned over 30 nm from 1560 to 1590 nm. Three important parameters were incorporated to achieve such a wide tuning range: a high Bp power, a pre-amplification technique, and extraction of the self-lasing cavity modes outside the cavity using an open \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Ref. No.** & **No. of Stokes** & **Tuning Range (nm)** & **Channel Spacing GHz** & & **Description** \\ \hline
[24] & 2 & 22 & 30 & \(\bullet\) & Three cascade-long single-mode fiber \\  & & & & \(\bullet\) & Manual change in cavity \\  & & & & \(\bullet\) & Low output Stokes power of \(-3.5\) dBm \\ \hline
[25] & 10 & 35 & 30 & \(\bullet\) & Long SMF length of 50 km \\  & & & & \(\bullet\) & High pump power of 600 mW \\  & & & & \(\bullet\) & Low Stokes power of \(-4\) dBm \\ \hline
[26] & 4 & not covered & 30 & \(\bullet\) & 70 km SMF length \\  & & & & \(\bullet\) & 1.2 W pump power \\ \hline
[28] & 9 &
\begin{tabular}{c} only at the center \\ wavelength \\ \end{tabular} & 30 & \(\bullet\) & Two sections of erbium-ytterbium-doped fiber amplifier (EXDFA) \\  & & & & \(\bullet\) & Long SMF good with length of 45 km \\ \hline
[29] & 3 & 40 & 30 & \(\bullet\) & Long DCF good with length of 12 km \\  & & & & & added an additional loss inside the cavity \\ \hline
[26] & 3 & not covered & 40 & \(\bullet\) & Four cascade SMFs for long length of 112 km \\  & & & & \(\bullet\) & High EDF pump power of 1.1 W \\ \hline
[31] & 1 & not covered & 40 & \(\bullet\) & High-finesse ring filter \\  & & & & \(\bullet\) & Two cascaded double Brillouin \\  & & & & & frequency-spacing cavities \\ \hline
[32] & 4 & 60 & 40 & \(\bullet\) & Two ring cavities \\  & & & & \(\bullet\) & Two DCF (6 km) for each one \\  & & & & \(\bullet\) & Two EDF (5 m) \\ \hline
[33] & 4 & 40 & 50 & \(\bullet\) & Two ring cavities \\  & & & & & \(\bullet\) & One open-end cavity by DCF \\  & & & & & \(\bullet\) & Three DCF (6, 6, and 3 km) \\  & & & & & \(\bullet\) & Pre-amplification \\ \hline our work & 4 & 30 & 60 & \(\bullet\) & Two ring cavities \\  & & & & & \(\bullet\) & Two open-end cavities with DCF and SMF \\  & & & & & \(\bullet\) & Three DCF (6, 6, and 3 km) \\  & & & & & \(\bullet\) & Three EDF (10 m) \\ \hline \end{tabular}
\end{table} 
Table 1: Summary of different Brillouin frequency shifts in multiwavelength fiber laser with our work. Figure 8: (a,b) Stability within two periods for the Bp, S6, S12, and S18 Brillouin Stokes signals at a pump power of 450 mW and a Bp wavelength of 1570 nm with a power of 25 mW. end cavity for DCF3 and SMF loops. Extracting these modes can effectively reduce the competition between the Brillouin Stokes and the free-running modes and subsequently enhance the laser tunability. The advantage of the proposed design is a wide tuning range, high Stokes signal powers, a high OSNR, an excellent output spectrum at different wavelengths within the tuning range bandwidth, and a rigid Brillouin frequency shift of 60 GHz, which shows an opportunity for use in a DWDM communication system. Up to 62 sextuple channels can be used within the achieved tuning range and high data bit rate of about 300 Gb/s per individual sextuple Stokes signal. In addition, a large part of the tuning lies in the long band (L-band) optical communication region (1570-1590); therefore, most of the useful channel is out of the C-band region, which is fully utilized in an optical communication system. Conceptualization, M.K.A., T.F.A.-M., and N.A. ; methodology, M.K.A. and M.K.S.A.-M.; software, R.N.H. and A.y.A. ; validation, M.K.A., T.F.A.-M., and N.A. ; formal analysis, M.K.A., M.S.D.Z., and A.y.A. ; investigation, M.K.A., M.K.S.A.-M., and R.N.H. ; resources, M.K.S.A.-M. and M.S.D.Z. ; data curation, M.K.A., T.F.A.-M., and N.A. ; writing--original draft preparation, M.K.A. and M.K.S.A.-M.; writing--review and editing, T.F.A.-M. and N.A.