Optical fiber sensors offer unprecedented features, the most unique of which is the ability of monitoring varia- tions of the observed physical field with spatial continuity along the fiber. These distributed optical fiber sensors are based on the scattering processes that originate from the interaction between light and matter. Among the three different scatter- ing processes that may take place in a fiber—namely Rayleigh, Raman and Brillouin scattering, this paper focuses on Rayleigh-based distributed optical fiber sensors. For a given optical frequency, Rayleigh-based sensors exploit the three main properties of light: intensity, phase and polarization. All these sensing mechanisms are reviewed, along with basic principles, main acquisition techniques and fields of application. Emphasis, however, will be put on polarization-based distributed optical fiber sensors. While they currently represent a niche, they offer promising unique features worth being considered in greater detail.

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Distributed Optical Fiber Sensing Based on Rayleigh Scattering

Joining of carbon fibre reinforced polymer (CFRP) composites and aluminium alloys – A review Part A Applied science and manufacturing

An improved fast plane wave expansion method for topology optimization of phononic crystals

New designs of a complete set of Photonic Crystals logic gates

Phononic crystals (PnCs) with band-gaps can confine the propagation of elastic waves. In many applications, it is desired to have a unit cell with favored band-gaps. Topological distribution of elastic materials within a unit cell has a significant effect on the band-gap properties, which are extremely difficult to determine without an optimization-based systematic synthesis procedure. In this paper, the two-stage design method, based on genetic algorithm conjunction with fast plane wave expansion method, is adopted to carry out the topology optimization of the two-dimensional (2D) PnCs in square lattices configuration with the maximized relative band-gap between two prescribed dispersion branches. Three numerical examples are given to the optimization of 2D steel-epoxy PnCs in one-eighth symmetry for coupled mode, acoustic mode, and mixed mode, respectively. The results show that the developed method provides an effective tool for the design of the 2D PnCs with favorable band-gaps’ properties.

Band-gap optimization of two-dimensional phononic crystals based on genetic algorithm and FPWE

A two-dimensional (2D) phononic crystal (PC), including a type of linear defect that is composed of third component materials, is proposed in this paper. The sonic guided characteristics of the structure are investigated by combining the plane-wave expansion method and a supercell technique. The results show that there are guided modes in the original band gap when third material-based linear defects are introduced in the two-component PC. The frequency of the guided modes changes with the rotational angle and filling fraction of the linear defect. The frequency distribution is symmetric to the (0, 1) direction. The sonic waveguide characteristics of the PC do not change with the orientation and the type of cross-section of the defect cylinders when the filling fraction is very small. This property has potential application in controlling the guided modes in a 2D PC.

Characteristics of the guided modes in a two-dimensional three-component phononic crystal with linear defects

We develop a pair of tapered-tip single fiber optical tweezers, and study its multi-trapping characteristic. The finite difference time domain method is employed to simulate the trapping force characteristic of this pair of single fiber optical tweezers, and the results show that the number of trapped particles depends on the refractive index and the size of the particles. The trapping force of this pair of tapered-tip single fiber optical tweezers is calibrated by the experimental method, and the experimental results are consistent with the theoretical calculation results. The multi-trapping capability realized by the tapered-tip single fiber optical tweezers will be practical and useful for applications in biomedical research fields.

http://iopscience.iop.org/article/10.1088/1674-1056/23/8/088702/pdf

A study of multi-trapping of tapered-tip single fiber optical tweezers

In this paper, we study the complete and directional bandgap properties of two-dimensional mercury/air phononic crystals (PnCs) with L-shape scatters based on the plane wave expansion method combined with a parallel shift scheme. As the symmetry of the scatters is lower than the symmetry of a square lattice, we scan the whole first Brillouin zone when performing the calculation. The relationships between the parameters (including geometry and filling fraction) of L-shape scatters and bandgaps are simulated in detail. The complete bandgap could be gained at a very low filling fraction (even below 0.076). The bandgap and directional bandgap width could be adjusted widely by changing its geometry and rotating the L-shape scatters, which could be useful for applications such as an acoustic directional filter or acoustic isolator.

Bandgap properties of phononic crystals with L-shape scatters

In this paper, two fiber reinforced polymer/plastic (FRP) encapsulated fiber Bragg grating (FBG) sensors were installed on the two sides of the angle steel beam, which was used to measure the displacement and direction of the diagonal steel beam, so as to realize the health inspection of the angle steel structure The sensors were re-spectively installed on the different positions of angle steel beam, and the relationship between displacement and strain transmission of angle steel beam was simulated by the finite element analysis The optimum design of sensors installation were discussed and the experimental verification was carried out The simulation and experimental results show that the sensor has the capacity to discriminate the direction and measure the size of one side of the angle steel beam displacement when installed in a reasonable position To realize the health monitoring by using optical fiber sensors on the structures composed by angle steel, such as bridges, electric towers and cranes, and so on, a basic research was provided

Study on fiber Bragg grating displacement sensor with angle steel structure

The polarization crosstalk of a fiber optic polarization component and device refers to the optical power coupling that occurs at a disturbance point between the two orthogonal polarized modes propagating in it. The distributed polarization crosstalk along with the light propagation direction is directly responsible for the optical polarization properties, for example, the polarization, elliptical polarization, and depolarization properties. It also indirectly reflects the manufacturing technique and the state of the ambient environment, for example, the stress and strain at the joint and fixed position, as well as the temperature. Thus, it is the comprehensive embodiment of the intrinsic performance of the fiber optic polarization component and device and the influence of environment. It is expected to be a general characteristic parameter for online testing, diagnosis, and evaluation of the performance of the fiber optic polarization component and device. The best measurement method for distributed polarization crosstalk till now is the optical coherence domain polarimetry (OCDP). It is based on the white light interferometry and accurately measures the position and amplitude of the distributed polarization crosstalk using a scanning white light interferometer to realize interference between different polarized modes. It has the merits of ultrahigh sensitivity, ultra-wide dynamic range, and ultra-long measurable length. This review paper takes the polarization maintaining fiber coil and multifunctional integrated optical modulator as examples of distributed polarization crosstalk measurement and application. Firstly, the measurement principle of distributed polarization crosstalk based on the OCDP is introduced. Secondly, the measurement error sources and corresponding suppression methods are reviewed. Thirdly, the accurate measurement results of the fiber optic polarization component and device at different temperature are demonstrated. In the end, it outlooks the development of distributed polarization crosstalk measurement considering the complicated and changeable operation environment of the fiber optic polarization component and device.

[Opto-Electron Eng, 2018, 45(9)] Recent progress of accurate measurement for distributed polarization crosstalk of fiber optic polarization component and device

Yuan Li-bo

Papers

Characteristics of the guided modes in a two-dimensional three-component phononic crystal with linear defects

A study of multi-trapping of tapered-tip single fiber optical tweezers

Bandgap properties of phononic crystals with L-shape scatters

Study on fiber Bragg grating displacement sensor with angle steel structure

[Opto-Electron Eng, 2018, 45(9)] Recent progress of accurate measurement for distributed polarization crosstalk of fiber optic polarization component and device