We report an actively mode-locked fiber ring laser. A simple and low-insertion-loss acousto-optic modulator driven by standing flexural waves, which couples core-to-cladding modes in a standard single-mode optical fiber, is used as an active mechanism for mode locking. Among the remarkable features of the modulator, we mention its high modulation depth (72%), broad bandwidth ( $187\mathrm{GHz}$ ), easy tunability in the optical wavelength, and low insertion losses ( $0.7\mathrm{dB}$ ). The narrowest optical pulses obtained were of $95\mathrm{ps}$ time width, $21\mathrm{mW}$ peak power, repetition rate of $4.758\mathrm{MHz}$ , and $110\mathrm{mW}$ of pump power.