Induced circular dichroism (ICD) is found between plasmonic nanostructures and chiral molecules, where at least one of them is chiral. However, it is a great challenge to generate ICD only through achiral structures with the simple coupling model. Here, we demonstrate that ICD is approximately contributed by the cross-electromagnetic coupling between equivalent electric dipole moments and magnetic dipole moments for two achiral plasmon nanostructures. To prove electromagnetic couplings between different wavebands, graphene belts are introduced into plasmon nanostructures composing achiral metal-nanorods with graphene-nanobelt arrays (AMGAs). Results showed that ICD signals are achieved in a near-infrared band of metal resonance and a micron band of graphene resonance. Near-field charge distributions of AMGAs reveal the coupling effect between metal-nanorods and graphene-nanobelts. The handedness of AMGAs can be actively controlled by adjusting the Fermi levels of graphenenanobelts; the strength and resonant wavelength of ICD can be tuned by adjusting the geometric parameters of AMGAs. Besides, AMGAs can enhance the CD signal of chiral molecules with different handedness. The maximum enhancement factor of chiral molecules could reach up to 800 times in a near-infrared band and 600 times in a micron band. These results are helpful to design dynamically tunable chiral sensors in biological monitoring and analytical chemistry.

A promising technology for fabricating chiral long-period gratings (CLPGs) is demonstrated using a commercial fusion splicer. The key aspect of this technology is the incorporation of a fully automatic program we designed for the fusion splicer. High-quality CLPGs are successfully fabricated from single-mode fibers, which have very flat surfaces and low insertion loss. We also investigate the tuning characteristics of the transmission spectrum with the mechanical twist rate in CLPGs for torsion sensing application. The torsion sensitivity is improved and the shift in resonance wavelength versus the mechanical twist rate shows an almost perfect linear relationship. In addition, by choosing appropriate fabrication parameters, the fabricated CLPGs can be used as tunable single-band-rejection filters in a broad wavelength range.

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We present a novel online fabrication scheme of helical long-period fiber gratings (H-LPFGs) by directly twisting a standard single-mode fiber (SMF) in a microheater. This is done by taking advantage of the inherent core-cladding eccentricity in SMF. We adopt a fiber optic rotary joint to eliminate the accompanying twisting spiral for real-time spectral monitoring and a stepping mechanical system to accurately control the twisting length in fabrication. As a consequence, low-cost and high-quality H-LPFGs can be readily fabricated. Meanwhile, by using this kind of H-LPFG, we design a simple and low-cost wavelength-interrogated liquid-level sensor with a high sensitivity of 0.1 nm/mm.

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