Abstract
We experimentally demonstrated a high-order optical vortex pulsed laser based on a mode selective all-fiber fused coupler composed of a single-mode fiber (SMF) and a few-mode fiber (FMF). The fused SMF-FMF coupler inserted in the cavity acts as a mode converter from LP
$_{01}$
mode to LP
$_{11}$
(LP
$_{21}$
) mode with a broadband width. Linearly polarized OAM modes can be obtained by combining different vector modes HE
$_{2,m}^{\rm {even}}$
(HE
$_{2,m}^{\rm {odd}}$
) and TE
$_{0,m}$
(TM
$_{0,m}$
) when l = 1 or combining HE
$_{l+1,m}^{\rm {even}}$
(HE
$_{l+1,m}^{\rm {odd}}$
) and EH
$_{l-1,m}^{\rm {odd}}$
(EH
$_{l-1,m}^{\rm {even}}$
) when
$l$
> 1 with a
$\pi /2$
phase shift. To the best of our knowledge, this is the first report on the generation of high-order pulse vortex beams in a mode-locked fiber laser. The measured time duration of OVB pulses is 273 fs, 140 fs of OAM
$_{\pm 1}$
and OAM
$_{\pm 2}$
.
© 2017 IEEE
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