Surface Plasmon Polaritons (SPP) are electromagnetic excitations that propagate at the interface between a dielectric and conductor, confined in the perpendicular direction. Their polarization selectivity makes them ideal for polarization controllers. In this study by Y. Yang et al., simulations demonstrated that coupling optical fiber modes with graphene and gold nanostructures enabled the evanescent field to interact with graphene's SPP, inducing polarization dependent loss in the x-direction by up to 38 dB/mm. The approach involved incorporating graphene layers beneath a series of periodic gold nano-pillars within a CYTOP medium on a polished D-shaped optical fiber. This arrangement allowed the evanescent field of the fiber within the cladding to couple directly with the SPP modes of the graphene layer. The gold pillars and CYTOP adjusted the effective index of SPP modes, altering the phase matching point between fiber core modes and those of the graphene layer. In a specific 1.3 μm wavelength configuration, an extinction ratio of up to 38 dB/mm between polarization directions was achieved, operating within a 136 nm bandwidth (with an effective extinction ratio of 20 dB). This design suggests potential as a broadband filter. Moreover, by adjusting the chemical potential of graphene or altering the gold nano-pillars' periodicity, the resonant wavelength could be fine-tuned or shifted into the C-band while maintaining 20 dB/mm extinction ratio. This implementation in standard fiber optics demonstrates promise as an effective, miniaturized polarization control with broad applications in optical communication and sensing.
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