Characterization of normal dispersion mode-locked Yb-doped fiber laser with birefringent spectral filter

Abstract

We present an investigation into the characteristics of a normal dispersion mode-locked Yb-doped fiber laser using a birefringent plate as a spectral filter. Before implementing mode locking using a birefringent plate, the transmission characteristics of the birefringent plate were analyzed. It was observed that the center wavelength and the full width at half maximum (FWHM) of the transmitted light varied according to the azimuthal angle and optical axis of the birefringent plate. The total dispersion value of the laser cavity was 0.04673 ps2 at a center wavelength of 1.03 μm. The mode locking was therefore achieved in the normal-dispersion region. The total cavity length of the Yb-doped fiber laser was about 1.9 m including free space, and the repetition rate of the mode-locked pulse was ∼104.2 MHz. The FWHM of the optical spectrum was ∼18.09 nm, and the pulse width measured by an autocorrelator was ∼1.71 ps assuming a Gaussian pulse shape. To obtain the transform limited pulse, a pulse was compressed using a pair of diffraction gratings outside the cavity. We achieved a compressed pulse of ∼148 fs assuming a Gaussian pulse shape. The output characteristics of the mode-locked Yb-doped fiber laser were observed while rotating the optical axis of the birefringent plate in the laser cavity. It was found that the center wavelength and FWHM of the optical spectrum could be varied by rotating the optical axis of the birefringent plate. The center wavelength changed by about 18.7 nm from 1026.9 to 1045.6 nm during rotation of the optical axis of the birefringent plate.