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Actively mode-locked fiber laser with an acousto-optic in-fiber superlattice modulator

All-fiber lasers permit the development of efficient, robust and compact coherent light sources. However, all-fiber active mode-locking is a challenging objective and very few all-fiber techniques have been published [1–3]. The development of a low-insertion-loss acoustically-induced superlattice modulator that works in the MHz range has demonstrated its suitability to perform active mode-locking of an all-fiber laser. While travelling extensional acoustic waves launched along a fiber Bragg grating (FBG) produce stationary side bands and a frequency shift [4,5], we found that the excitation of a standing extensional acoustic wave should produce no frequency shift, but the amplitude modulation of the side-bands at twice the frequency of the acoustic wave.