We demonstrate an ultra-narrow-band mode-selection method based on a hybrid-microsphere-cavity which consists of a coated silica microsphere. Optical field distribution and narrow-band transmission spectrum of the whispering gallery modes (WGM) are investigated by finite-difference time-domain method. WGM transmission spectra are measured for microsphere and tapered fibers with different diameters. A high refractive index layer coated on the microsphere-cavity make the Q factor increased, the transmission spectrum bandwidth compressed and the side-mode suppression ratio increased. Parameters of the hybrid-microsphere-cavity, namely, the coated shell thickness and its refractive index are optimized under different excitation light source as to investigate the whispering-gallery-modes’ transmission spectrum. The 3dB bandwidth of the proposed filter can be less than MHz which will have great potential for applications in all-optical sensing and communication systems.
A fiber-wireless sensor system based on a power-over-fiber technique is developed to offer a flexible, distributed sensing ability over a middle distance, especially under environments that are sensitive to electromagnetic interference. In this system, the optical energy of a high-power laser in the base station is transmitted via a fiber and then converted into electrical energy by a photovoltaic power converter (PPC) in the remote unit. This optically power-supplied remote unit operates as the coordinator in the wireless sensor network (WSN) and exchanges the sensing information with the base station via another fiber. In our demonstration system, the sensing information can be collected by a WSN 2 km away and be transmitted back. In order to improve the power supply ability of PPC, a maximum power point tracking technique is applied. More than 80% of PPC’s maximum output power can be obtained. Moreover, to reduce the power consumption of the remote unit and the sensor nodes, a simple and stable low-power communication protocol is designed.
The fine manipulations of cylindrical vector beams (CVBs) based on metallic microstructures, such as sub-wavelength
focusing, have entered many interdisciplinary areas, and the important applications have been found in many fields
including optical micromanipulation, super-resolution imaging, micro-machining and so on. But so far, the
sub-wavelength focusing of azimuthally polarized beams is encountered, since the manipulation mechanisms rely
heavily on the excitation of surface plasmon polaritons, which brings the polarization limitation. We theoretically
investigated the focusing behavior of CVBs in 1D metallic photonic crystals (MPCs). The simulation results show that a
1D MPC plano-concave lens can focus cylindrical vector beams into scale of sub-wavelength. The negative refraction at
the interface between the air and the 1D MPC is analyzed at the frequencies corresponding to the second photonic band,
which makes the 1D MPC has the ability to focus higher Fourier components of light beams. The cylindrical
plano-concave structure is constructed to focus the radially and azimuthally polarized beams simultaneously. The
behavior is demonstrated by Finite Element Method (FEM). The shape of focusing field can be tailored, by changing the
polarization ratio of the incident beams. In addition, the effective sub-wavelength focusing phenomenon can also be
realized in variety of wave ranges, by choosing the proper materials and adjusting the parameters. We believe that it’s the
first time to realize the simultaneous sub-wavelength focusing of radially and azimuthally polarized beams, the
application of which is quite promising in broad prospects.
The finite-difference time-domain (FDTD) method, which solves time-dependent Maxwell’s curl equations numerically,
has been proved to be a highly efficient technique for numerous applications in electromagnetic. Despite the simplicity
of the FDTD method, this technique suffers from serious limitations in case that substantial computer resource is
required to solve electromagnetic problems with medium or large computational dimensions, for example in high-index
optical devices. In our work, an efficient wavelet-based FDTD model has been implemented and extended in a parallel
computation environment, to analyze high-index optical devices. This model is based on Daubechies compactly
supported orthogonal wavelets and Deslauriers-Dubuc interpolating functions as biorthogonal wavelet bases, and thus is
a very efficient algorithm to solve differential equations numerically. This wavelet-based FDTD model is a
high-spatial-order FDTD indeed. Because of the highly linear numerical dispersion properties of this high-spatial-order
FDTD, the required discretization can be coarser than that required in the standard FDTD method. In our work, this
wavelet-based FDTD model achieved significant reduction in the number of cells, i.e. used memory. Also, as different
segments of the optical device can be computed simultaneously, there was a significant gain in computation time.
Substantially, we achieved speed-up factors higher than 30 in comparisons to using a single processor. Furthermore, the
efficiency of the parallelized computation such as the influence of the discretization and the load sharing between
different processors were analyzed. As a conclusion, this parallel-computing model is promising to analyze more
complicated optical devices with large dimensions.