Abstract

In the last few years, double-clad fibers have been more and more used to realize high power fiber lasers or amplifiers. These fibers consist in a single-mode core for the laser wavelength and a large inner cladding where high pumping levels can be injected. An intense effort is now carried out to generate short or ultra-short pulses with double-clad fiber lasers[1]. In the present paper, we report the mode-locking properties of a high power Yb-doped fiber laser which generates 24 nJ, 670 fs intracavity-compressed pulses at 1.05 μm with a repetition rate of 18 MHz. A diode-pumped Yb-doped double-clad fiber is used as the amplifying medium. The pumping laser diode is coupled in the fiber using the V-groove technique manufactured by Keopsys (Lannion, France). This technique allows to couple more than 90 % of the incident pump power into the inner cladding. The technique of nonlinear polarization rotation[2] is used to achieve passive mode-locking by inserting into the cavity a polarization-dependent optical isolator, and two polarization controllers before and after the doped fiber (figure 1). A dispersion delay line (DDL) with a grating pair (1200 lines/mm) ensures the pulse compression.

© 2001 EPS