Abstract
We have demonstrated an ultra-broadband fiber mode converter based on ${{\rm CO}_2}$-laser inscribed length apodized phase-shifted long-period gratings (LPGs) with a three-section linear length apodization profile, where a $\pi $-phase shift was introduced between two adjacent grating sections. The grating parameters were optimized theoretically to achieve the broadband mode conversion between the ${{\rm LP}_{01}}$ mode and ${{\rm LP}_{11}}$ mode. The demonstrated device provides mode conversion efficiency higher than 90% over an ultra- broad bandwidth of $ {\sim} {182}\;{\rm nm}$. The insertion loss of the LPGs is negligible. Orbital angular momentum modes with left- and right-handed circular polarization can be generated from the demonstrated ultra-broadband mode converter successfully.
© 2019 Optical Society of America
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