Yanhua Han

Excitation and separation of vortex modes in twisted air-core fiber

An air-core fiber imposed by torsion is investigated in this paper. We refer to this kind of fiber as twisted air-core fiber (TAF). It has been demonstrated that the eigenstates of the TAF consist of guided optical vortex waves with different propagation constants of a different effective index. With the increase of the twist rate, TAF could separate the OAM modes which are near degenerate or degenerate in the air-core fiber. The separation of OAM modes in TAF is conductive to ultralong distance propagation with low crosstalk. TAF could be considered as an ideal candidate fiber for OAM based optical communication. Moreover, we investigated the twisted air-core photonic crystal fiber (TAPCF) which can improve the relative energy distribution of the OAM modes. Compared with TAF, more energy is located in the ring shaped core, which is conductive to ultralong distance propagation. TAF and TAPCF are of potential interest for increasing channel capacity in optical telecommunications, and the result is also of interest to the photonic crystal community.

Formation of two-dimensional periodic microstructures by a single shot of three interfered femtosecond laser pulses on the surface of silica glass.

Two-dimensional periodic microstructures, including both microholes and micro-orbicular platforms, have been fabricated on the surface of silica glass by a single shot of three interfered femtosecond laser pulses. The three-dimensional structure of a fabricated hexagonal lattice can be revealed by atomic force microscopy. The formation of the microstructure and the dynamic process of the interaction between the femtosecond laser and the silica glass have been discussed.

Holographic Fabrication of Periodic Microstructures by Interfered Femtosecond Laser Pulses

In recent years, with the developments of the laser technology, femtosecond laser technology is becoming more and more consummate as a novel technology. Femtosecond laser pulse is also becoming into a powerful tool for microfabrication and micro-machining of various multi-functional structures in dielectric materials through multi-photon absorption because of its high-quality and damage-free processing. Up to now, many highquality material processing techniques have been achieved by using femtosecond laser pulses with the methods of directly writing [1-10] and holographic fabrication [11-22], such as waveguide [1], special diffractive optical elements (DOE) [4-10], micro-gratings [11-15], and photonic crystals [16-20]. Because multiphoton nonlinear effects play a major role in this process, the resulting change in refractive index or cavity formation can be highly localized only in the focal volume where the fluence is above a certain material dependent threshold, which makes it possible to micro-fabricate devices inside the bulk of transparent materials. These structures were usually fabricated with a focused beam and written dot by dot by translation of the sample with respect to the focal point.

Enhanced Forward Scattering of Ellipsoidal Dielectric Nanoparticles

Dielectric nanoparticles can demonstrate a strong forward scattering at visible and near-infrared wavelengths due to the interaction of optically induced electric and magnetic dipolar resonances. For a spherical nanoparticle, the first Kerker’s condition within dipole approximation can be realized, where backward scattering can reach zero. However, for this type of dielectric sphere, maximum forward scattering without backward scattering cannot be realized by modulating the refractive index and particle size of this nanoparticle. In this paper, we have demonstrated that a larger directional forward scattering than the traditional spherical nanoparticle can be obtained by using the ellipsoidal nanoparticle, due to the overlapping electric and magnetic dipolar modes. For the oblate ellipsoid with a determined refractive index, there is an optimum shape for generating the suppressed backward scattering along with the enhanced forward scattering at the resonant wavelength, where the electric and magnetic dipolar modes overlap with each other. For the prolate ellipsoid, there also exist the overlapping electric and magnetic dipolar modes at the resonant wavelength of total scattering, which have much higher forward scattering than those for both oblate ellipsoid and sphere, due to the existence of the higher multipolar modes. Furthermore, we have also demonstrated the realization of the dimensional tailoring in order to make the strong forward scattering shift to the desired wavelength.

High-sensitivity double-parameter sensor based on the fibre-tip Fabry–Pérot interferometer

Abstract We have proposed an ultra-compact double polymer-capped Fabry–Pérot interferometer (FPI), which could be used for simultaneously measuring refractive index (RI) and temperature with low cross sensitivity. The designed and fabricated FPIs have double polymer layers which were fabricated by step-curing ultraviolet photoresist (SU-8) and polydimethylsiloxane on the end face of a traditional single-mode fibre. Three samples were fabricated with different Fabry–Pérot cavity lengths. Experimental results show that the double polymer structure has higher temperature and RI sensitivities than single-layer structure. About 689.68 pm/°C (based on the wavelength shift) in the temperature range of 20–75 °C and −147.04 dB/RIU (based on peak intensity measurement) in the RI range of 1.335–1.355 were measured, respectively. Moreover, the compact structure, high temperature sensitivity and low cross-sensitivity of the FPI make it suitable for integration such as biomedical and microfluidic sensor probe.