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Multimode Metallic Double‐Strip Waveguides for Polarization Manipulation

The plasmonic waveguide is a key element in the nanophotonic devices and highly integrated photonic circuits. The single‐mode waveguide greatly limits the degrees of freedom in the filed manipulating and information encoding. Here, a multimode metallic double‐strip waveguide, comprising two metallic strips placed on the metal substrate, is proposed to realize field manipulating and polarization splitting. This waveguide design is quite different from that of the previous waveguides. As a result, both of the symmetric and the antisymmetric surface‐plasmon‐polariton (SPP) modes supported by the proposed waveguide have long propagation lengths (ten times greater than the plasmon wavelengths). Moreover, the field distributions of the two SPP modes are located in different areas in the metallic double‐strip waveguide. Hence, these two SPP modes can be easily manipulated independently. The metallic double‐strip waveguide is fabricated on the metal film and is then measured. As an example, the polarization manipulation is demonstrated in the experiment with a structure size as small as 0.7 × 4.5 µm2. The multimode metallic double‐strip waveguide with long propagation lengths and different field distributions provides more degrees of freedom to manipulate fields and encode information, and thus it has important applications in multifunctional nanophotonic devices and integrated photonic circuits.