Experimental revealing of acousto–optic polarization-governed LP-mode switching in optical fibers

We experimentally study a recently predicted vectorial acousto–optic effect in circular few-mode optical fibers in which a linearly polarized fundamental flexural acoustic wave is externally excited. We reveal that when a condition of acousto–optic resonance is met at some specific fiber length, incident LP 0 y and LP 1 y modes, in which the polarization direction is perpendicular to the acoustic one, experience a total transformation to the modes LP 1 y and LP 0 y , respectively, with azimuthal numbers upshifted or downshifted by unity. Simultaneously, orthogonally polarized modes LP 0 x and LP 1 x emerge from the fiber in their initial states. This finding strongly validates a revised theoretical approach to an acousto–optic coupling in optical fibers proposed in Opt. Lett. 44 , 598 ( 2019 ) 10.1364/OL.44.000598 . We also show that the demonstrated mode swap mimics the logic of a controlled—NOT gate for the LP ℓ modes.