Fiber laser is both Q-switched and modelocked

Modelocked lasers produce ultrashort pulses at high frequencies, but generally with low pulse energies (or with ultralong cavity lengths to increase pulse energy).

Nov 1st, 2009

Modelocked lasers produce ultrashort pulses at high frequencies, but generally with low pulse energies (or with ultralong cavity lengths to increase pulse energy). Q-switched lasers typically have lower repetition rates, but higher energies and wider pulses. Although combining both effects produces high-energy, higher-repetition-rate, shorter pulses, this doubly active performance had not been demonstrated for a fiber laser—until now. Researchers at Universidad de Valencia are the first to demonstrate a Q-switched, modelocked (QML) fiber laser; their device even uses all-fiber in-line components.

For the QML fiber laser, Q-switching is achieved by using a magnetostrictive device to modulate the output from a fiber Bragg grating (FBG) at the output of the fiber laser, in turn modulating the Q factor of the Fabry-Perot cavity. Modelocking is achieved by using a second FBG at the input of the fiber laser in an acousto-optic modulator configuration. For a Q-switched repetition rate of 500 Hz and a pump power of 100 mW, the QML laser (with an emission wavelength of 1530.55 nm) generates trains of 12 to 14 modelocked pulses with a pulse duration of about 1 ns each within an envelope of 550 ns. The envelope energy is about 0.65 µJ, with a peak power higher than 250 W for the central pulses of the train. Contact Christian Cuadrado-Laborde at Christian.Cuadrado@uv.es.

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