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In this paper, we experimentally demonstrate a low-power, broadband, and narrow linewidth SBS-FWM OFC with tunable line spacing of 50 to 600 GHz. The SBS-FWM OFC spans a bandwidth of <inline-formula><tex-math notation="LaTeX">$\approx$</tex-math></inline-formula>100 nm over the C<inline-formula><tex-math notation="LaTeX">$+$</tex-math></inline-formula>L-band region using <inline-formula><tex-math notation="LaTeX">$\approx$</tex-math></inline-formula>15 dBm pump power. The OFC is obtained by cascaded FWM process in highly nonlinear fiber (HNLF), seeded by SBS pumps in an all-fiber ring cavity setup. The linewidth of the SBS-FWM comb lines is measured to be <inline-formula><tex-math notation="LaTeX">$\approx$</tex-math></inline-formula>20 MHz which is largely determined by the SBS pump properties. By using the optical Vernier effect, the linewidth of comb lines is reduced by a factor of more than 2000 to below 20 kHz. We utilize the SBS-FWM OFC to study the performance of binary and 4-PAM transmission at 1 and 10 Gbps in a back-to-back (B2B) setup. The side-modes caused by the FP-cavity, formed by the HNLF modules in the ring cavity in our setup, affects the performance of the B2B transmission of PAM system.