Experimental demonstration of an on-chip polarization splitter in a submicron asymmetric dielectric-coated metal slit

A submicron asymmetric dielectric-coated metal slit with a Fabry–Perot (FP) nano-resonator is experimentally fabricated to realize an ultra-small on-chip polarization splitter. In the hybrid plasmonic structure, both of the transverse-electric (TE) and transverse-magnetic (TM) modes can be efficiently generated on the front metal surface. Based on the quite different resonant conditions and the different field confinements of the two orthogonal polarization modes in the FP resonator, the TM and TE modes are generated to propagate in the opposite directions along the metal surface. In this device, there are no coupling waveguide regions, and the excitation and the splitting of the TE and TM modes are integrated into the same asymmetric nano-slit. This considerably shrinks the device dimension to only about 850 nm (about one wavelength). In such a submicron asymmetric slit, the measured extinction ratios for the two opposite directions can reach up to (ηL/ηR)TM ≈ 1:14 and (ηL/ηR)TE ≈ 11:1 at λ = 820 nm. This on-chip submicron polarization splitter is of importance in highly integrated photonic circuits.