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A novel refractive index (RI) sensor based on photonic crystal fiber Mach–Zehnder interferometer (PCF-MZI) was proposed. It was realized by cascading a section of PCF with half-taper collapse regions (HTCRs) between two single mode fibers (SMFs). The relationship between RI sensitivity and interference length of the PCF-MZI was firstly investigated. Both simulation and experimental results showed that RI sensitivity increased with the increase of interference length. Afterwards, influence of HTCR parameters on RI sensitivity was experimentally investigated to further improve the sensitivity. With intensification of arc discharge intensity in HTCR fabrication process, HTCR with larger maximum taper diameter and longer collapsed region length was obtained, which enhanced evanescent field of the PCF-MZI and then generated higher RI sensitivity. Consequently, a high RI sensitivity of 181.96 nm/refractive index unit (RIU) was achieved in the RI range of 1.3333–1.3574. Increasing arc discharge intensity in HTCR fabrication process has the capacity to improve RI sensitivity of PCF-MZI and meanwhile provides higher mechanical strength and longer sensor life compared to the traditional method of tapering the fiber, which improves the RI sensitivity at the cost of reducing mechanical strength of the sensor. This PCF-MZI was characterized by high RI sensitivity, ease of fabrication, high mechanical strength, and robustness. [ABSTRACT FROM AUTHOR]

A novel refractive index (RI) sensor based on an asymmetrical Mach–Zehnder interferometer (MZI) with two different step-like tapers is proposed. The step-like taper is fabricated by fusion splicing two half tapers with an appropriate offset. By further applying offset and discharging to the last fabricated step-like taper of MZI, influence of taper parameters on interference spectrum is investigated using only one device. This simple technique provides an on-line method to sweep parameters of step-like tapers and speeds up the optimization process of interference spectrum, meanwhile. In RI sensing experiment, the sensor has a high sensitivity of −185.79 nm/RIU (refractive index unit) in the RI range of 1.3333–1.3673. [ABSTRACT FROM AUTHOR]

Abstract Graphene as a promising material for terahertz-infrared region plays an important role in nanoplasmonic devices owing to its tunability. We propose a hybrid graphene nanoplasmonic waveguide and analyze its propagation properties by finite element method. The results show that the light in terahertz-infrared region can be confined at low-index material and the fundamental mode can be tuned flexibly by changing Fermi energy level of graphene. Then an application of the designed waveguide, an electrically controllable directional coupler is designed and its performance is numerically verified. This approach can be extended to novel designs of nanoscale integrated photonic devices. [ABSTRACT FROM AUTHOR]

An in-fiber rectangular air Fabry-Perot (FP) strain sensor based on a high-precision fiber cutting platform (HFCP) is proposed. The HFCP consisting of a CCD notation system, a micro-displacement platform, and an optical fiber cleaver can be used to precisely control the length of FP cavity. The microcavity of FP (even only tens of microns) with smooth reflective surface can be realized easily by using this system. The FP structures with different cavity lengths have been fabricated in this paper. Simulation and experimental results prove that the shorter length the cavity has, the higher strain sensitivity and the larger free spectral range (FSR) the sensor obtains. The strain sensitivity and FSR of in-fiber rectangular air FP sensor with a cavity length of 35 µm can be up to 2.23 pm/με and 28.5 nm respectively. Moreover, the proposed FP strain sensor has a negligible temperature sensitivity in the range of 25–75 °C. It is anticipated that such easy making, compact and low-cost fiber-optic strain sensors could find important applications in practice. [ABSTRACT FROM AUTHOR]

In this paper, composite nanoantenna arrays are simulative designed for energy harvesting in visible range. The composite nanoantenna on SiO 2 substrate consists of staircase bowtie and rectangular nanoaperture. Due to the interaction among rectangular nanoaperture, staircase bowtie and different layers of the staircase bowtie, the designed nanoantenna exhibits an ultrahigh localized intensity enhancement. Results show that the maximum intensity enhancement reaches higher than 9 × 104 ( E e 2 ∕ E 0 2 ), and the composite nanoantenna can confine electric field distribution uniformly around the bowtie in z direction. When the incident wavelength varies from 660 nm to 760 nm, the intensity enhancement reaches more than 2 × 104 ( E e 2 ∕ E 0 2 ). The excellent dual-resonance enhancement performance of the composite nanoantenna makes it especially suitable for surface enhanced Raman scattering (SERS), the maximum enhancement factor of SERS can reach 2.2 × 109. • Composite nanoantenna arrays produce huge dual-resonance intensity enhancement. • The resonance wavelength is described by an approximate model. • The nanoantenna is suitable for SERS and the maximum EF can reach 2.2 × 109. [ABSTRACT FROM AUTHOR]