Q-switching and mode locking pulse generation from an all-fiber ring laser by intermodal acousto-optic bandpass modulation

Q-switched and mode-locked (QML) pulse generation from an all-fiber ring laser based on intermodal acousto-optic bandpass modulation is reported. The modulator relies on full-acousto-optic mode re-coupling cycle induced by a standing flexural acoustic wave, with a transmission response that is controlled by amplitude modulation of the acoustic wave signal. The Q factor of the cavity is controlled by a rectangular pulse wave with variable frequency and duty cycle, whereas mode locking is achieved by amplitude modulation derived from a standing flexural acoustic wave. The best QML pulses were obtained at 0.5 kHz repetition rate, with a pump power of 549.2 mW, at the optical wavelength of 1568.2 nm. A maximum overall energy of 2.14 µJ at an average output power of 1.07 mW was achieved, corresponding to a burst of mode-locked sub-pulses of 100 ps pulse duration within a QML envelope of 3.5 µs. (paper)