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Abstract:We demonstrate theoretically and experimentally a high extinction ratio and compact size TE-pass polarizer made by a D-shaped fiber coated with a double graphene/PMMA stack. The light propagating in the core of the fiber can be efficiently coupled into the graphene sheet thanks to the giant enhancement of the modal evanescent field associated with the high refractive index graphene/PMMA cladding. The strong interaction between the light and graphene produces a large attenuation difference between modes with orthogonal polarizations, resulting in an improved extinction ratio and a reduced insertion loss due to the device compactness. A double graphene/PMMA stack coated polarizer with an extinction ratio of up to 36 dB and an insertion loss of 5 dB has been achieved when the device length is only 2.5 mm. The double graphene/PMMA stack has proved to be significantly better than single graphene/PMMA stack and bilayer graphene/PMMA structures, providing a polarizer with maximum extinction ratio of 44 dB for a length of 4 mm. The achieved results indicate that the proposed high extinction ratio polarizer is a promising candidate for novel in-fiber graphene-based devices.

Tunable ultra-wideband achromatic plasmonic Airy beams are demonstrated on graphene surfaces. Surface plasmonic polaritons are excited using diffractive gratings. The phase and amplitude of plasmonic waves on the graphene surface are determined by the relative position between the grating arrays and the duty ratio of the grating unit cell, respectively. The transverse acceleration and nondiffraction properties of plasmonic waves are observed. The achromatic Airy plasmons with identical acceleration trajectory at different excited frequencies can be achieved by tuning dynamically the Fermi energy of graphene without reoptimizing the grating structures. The proposed devices may find applications in photonics integrations and surface optical manipulation.

We investigated an all-optical phase shifter and switch based on a graphene decorated side-polished twin-core fiber (TCF) Michelson interferometer (MI). The MI was fabricated by tapering the splicing point between the TCF and single-mode fiber. The flat surface of exposed polished core in the TCF was coated with monolayer graphene. A 980 nm pump laser is used to produce a photothermal effect. The graphene’s ohmic heating changes the effective refractive index of the exposed core, resulting in the phase shift of the MI. The MI with a polished length of 5 mm has a significant modulation phase shift with a nearly linear slope of 0.0102 π / m W near the wavelength of 1550 nm and can obtain an extinction ratio of 7 dB for optical switching with a rise (fall) time of 55.8 ms (15.5 ms). The high-density integration and all-optical control enable the proposed device to have great potential in the miniaturization of optical devices and all-optical signal processing.

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