Single-mode operation and spectral depuration by W-type Yb-doped fibers in Q-switched fiber lasers.

• W-type fiber design to improve Q-switched Yb-doped fiber lasers (YDFLs) is proposed. • A fiber was fabricated by employing modified chemical vapor deposition. • The Yb-doped W-type fiber exhibited enhanced beam quality and output spectra. We report a W-type fiber design for improving the beam quality and spectral purity of the Q-switched Yb-doped fiber lasers (YDFLs). Our W-type fiber exhibited higher losses in the high order modes (>100 dB/m) and lower losses in the fundamental modes (<0.1 dB/m). A 20/130 μm Yb-doped W-type fiber was fabricated by employing a modified chemical vapor deposition (MCVD) process and a solution-doping technique. The Yb-doped W-type fiber was examined in an acousto-optic Q-switched YDFL. A robust single-mode operation with a 1.19 M2 factor was obtained by optimizing the bending radii. The suppression of mixed mode four-wave mixing (FWM) and amplified spontaneous emission (ASE) was observed in the output spectral with an 18 dB signal to noise ratio (SNR) enhancement at 1064 nm and a 5.3 dB ASE inhibition ratio at 1030 nm. The Yb-doped W-type fiber exhibited enhanced beam quality and output spectra than the conventional Yb-doped step-type refractive index fiber. Therefore the W-type fiber suits the Q-switched fiber laser applications. [ABSTRACT FROM AUTHOR]