Many applications, from micromachining to biomedicine, among others, demand few megahertz frequency, sub-nanosecond pulse width fiber laser systems. These pulses could be later amplified to higher energy levels. These requirements preclude the use of standard laser sources like Q-switched lasers.
 In this work we demonstrate that a mode-locked laser can emit light pulses (time width 330 picoseconds) at a frequency of 1.5 MHz, while simultaneously preserving the advantages of an all-fiber configuration. This was possible with the design of a new in-fiber acousto-optic modulator, which is shown schematically in the figure.

“Long-cavity all-fiber ring laser actively mode locked with an in-fiber bandpass acousto-optic modulator”
C. Cuadrado-Laborde, M. Bello-Jiménez, A. Díez, J. L. Cruz, and M. V. Andrés,  Optics Letters 39 (2014) 68−71.
doi: 10.1364/OL.39.000068