Research On The Broadband SBS Slow Light Based On Phase Modulation Of Pump In Optical Fibers

During the past two decades, the state of the art of fiber-optic communication systems has advanced dramatically. The highest capacity of fiber-optic links available in the laboratory has reached Tb/s scale and thus the development of all-optical communication has become necessary. All-optical buffer functions as a key element in the all-optical router. All-optical buffer based on tunable all-optical delay in fiber attracts much attention because it offers the advantage of easy integration with existing optical communication systems as well as room temperature operation. However, slow-light based on stimulated Brillouin scattering (SBS) is limited to useful data rates of less than a few tens Mb/s due to the narrow Brillouin gain bandwidth (some 30 ~ 45 MHz). In this regard, broadening the spectrum of pump is essential to support a higher data rate. In this paper, we present an extensive study on the broadband SBS slow-light based on phase modulation of pump in fiber both in theory and in experiment.The theoretical research indicates that by virtue of phase modulation of pump, a broadband and flat-top gain spectrum can be achieved, which can lessen the amplitude distortion and phase distortion significantly; three equal-amplitude lines can be achieved by single-frequency modulation while 2n+1 equal-amplitude lines can be achieved by multi-frequency modulation by considering a signal possessing a fundamental frequency until nth harmonic wave. In addition, we have calculated the signal parameters for modulation to attain three, five, seven, nine and even eleven equal-amplitude spectrum lines as examples.In experiment, two different modulation signals are applied, generating three and five equal-amplitude lines and achieving Brillouin gain bandwidth of ~150 MHz and ~330 MHz, which correspond to a broadening factor of ~3.5 and ~7.8, respectively. As to the pulse less than 10ns (6.0ns and 4.2ns), a delay up to 4.7ns in three equal-amplitude lines and 2.2ns in five equal-amplitude lines are observed, thereby supporting a data rate of over 100Mb/s. We compare the broadening factor and fractional delay of pulse longer than 10ns (45.4ns) in the absence of pump modulation with those of pulse less than 10ns (6.0ns) in three equal-amplitude lines. They have almost the same broadening factor; however, the fractional delay for the former is less than that for the latter, indicating that larger fractional delay can be attained via pump phase modulation in a certain distortion limit.