Slow light in multi-line Brillouin gain spectrum.

We present a method to achieve flat-top gain spectrum through overlapping multiple gain lines, which can be used to increase slow light bandwidth and relative pulse delay. A tunable gain bandwidth can be realized by changing the number of spectral lines and frequency separation between adjacent spectral lines. We demonstrate the method in a SBS-based slow light system. A phase modulator is used to modulate the phase of the pump wave, generating a pump wave with multi-line spectrum and achieving a Brillouin gain bandwidth of ~ 330 MHz.