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

Abstract

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-acoustooptic 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 J 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 s.

All-fiber broadband spectral acousto-optic modulation of a tubular-lattice hollow-core optical fiber

“…All-fiber acousto-optic modulators (AOMs) have been successfully employed in reconfigurable spectral filters (rejection band, passband, and add-drop), heterodyne sensors, Q-switched and mode-locked fiber lasers [1][2][3][4][5][6][7][8][9]. In particular, flexural acoustic waves induce dynamic longperiod gratings (LPGs) along an optical fiber, coupling power between the propagating optical modes.…”

“…The resulting modulated notch depth and resonant wavelength are tuned by the acoustic amplitude and frequency, respectively. Thus, standing acoustic waves inducing amplitude-modulated spectral bands are suitable for mode-lock pulsed fiber lasers, controlling the laser gain threshold by adding losses in the laser cavity [7][8][9]. However, in standard optical fibers, the acoustic waves are mostly distributed over the fiber cladding reducing the overlap with the optical modes in the core.…”

“…AOMs using long fibers and high voltages have increased the acousto-optic interaction [1][2][3][5][6][7]9] while providing wide spectral tuning ranges employing distinct fiber designs: hollow-core photonic bandgap optical fibers (18 -60 nm) [10,11], dispersion compensating fibers (36 -80 nm) [1,2,6], few-mode fibers (100 nm) [5], singlemode standard fibers (500 nm) [3] and, solid-core photonic crystal fibers (1000 nm) [12]. The modulated full width at half maximum (FWHM) bands usually range from 1 to 7 nm [2,5,11,12].…”