Hybrid graphene anti-resonant fiber with tunable light absorption.

Controlling the output light-intensity and realizing the light-switch function in hollow-core anti-resonant fibers (HC-ARFs) is crucial for their applications in polarizers, lasers, and sensor systems. Here, we theoretically propose a hybrid light-intensity-tunable HC-ARF deposited with the sandwiched graphene/hexagonal boron nitride/graphene based on the typical six-circular-tube and the nested structures. Changing the external drive voltage from 12.3 to 31.8 V, the hybrid HC-ARF experiences a high-low alterative attenuation coefficient with a modulation depth 3.87 and 1.91 dB/cm for the six-circular-tube and nested structures respectively, serving as a well-performance light-switch at the optical communication wavelength of 1.55 µm. This response is attributed to the variation of the Fermi level of graphene and is obviously influenced by the core size, fiber length, and the number of graphene and hBN layers. Moreover, one attenuation dip of the modulation depth was found because of the epsilon-near-zero effect in graphene. Our design provides a feasible paradigm for integrating graphene with anti-resonant fibers and high-performance electro-optic modulators.

Ultra-high sensitive refractive index sensor based on D-shaped photonic crystal fiber with graphene-coated Ag-grating.

In this paper, an ultra-high sensitive plasmonic sensor is theoretically proposed for refractive index based on D-shaped photonic crystal fiber (PCF) with graphene-coated Ag-grating in mid-infrared region. Surface plasmon polariton at the metal/dielectric interface can be effectively excited by the fundamental guiding mode, leading to the surrounding medium-dependent loss spectrum. This metallic-grating PCF sensor exhibits a maximum sensitivity of 18612 nm/RIU with a detection resolution of 4.16 × 10-6 RIU in the index range from 1.33 to 1.395. Dependences of loss spectrum on the PCF parameters (air hole diameter and lattice constant) and the grating structure (grating thickness, period and width) are systematically analyzed. Moreover, the influence of the material parameters on the sensor performance is also investigated in term of graphene-layer number and the thickness of Ag layer. The compact design not only has great potentials in the applications of liquid detection, but also offers a guidance in the engineering of the metallic-grating fiber sensor.

Bragg grating sensor for refractive index based on a D-shaped circular photonic crystal fiber.

In this paper, a silica-based D-shaped circular photonic crystal fiber Bragg grating sensor for refractive index sensing is proposed theoretically. D-shaped fiber construction can effectively enhance the coupling effect between the guiding mode and external liquid analyte, which then causes a distinct shift in the typical reflection spectrum as the refractive index of the analyte varies. This design exhibits highly improved sensitivity of 487 nm/RIU in a large refractive index range from 1.30 to 1.40 compared with the previous fiber grating sensors. Study of the dependence of sensing performance on the structure parameters suggests that the resonance peak shifts towards longer wavelengths with the increased air-hole diameter of fiber, while it is almost immobile as the hole spacing and the number of air-hole layers change in a certain range. For the influence of the Bragg grating structure, results show that the resonance peak is not sensitive to the grating length, but linearly increases as the grating period expands. The effects of polishing depth and fiber preparation error on the sensor are also discussed in detail. This high-sensitivity sensor based on a D-shaped photonic crystal fiber and Bragg grating has great potential in biochemical detection, environmental monitoring, and medical sensing.