Fine control of optical pulse width via doublet gain lines

We demonstrate a general technique for realizing fine control of optical pulse width via doublet gain or loss lines. The optimized doublet gain or loss lines for fine control of optical pulse width can be designed by using an inverse design method. The preliminary experimental demonstration of fine control of optical pulse width is performed by using doublet Brillouin gain lines in an optical fiber. Tunable pulse compression or stretching ratio of 1.47-0.43 accompanying a time delay is achieved by controlling the separation between two gain lines, for an input pulse train with a 40 ns pulse width and a repetition rate of 5 MHz, in a 4 km silica fiber with a fixed pump power of 88.1 mW.