Search

A real-time interrogation technology for a large-scale fiber laser sensor array is proposed and experimentally investigated by employing a hybrid topological structure based on the wavelength- and frequency-division multiplexing techniques. In this system, a 2-D n × m sensor array is established by using a 1 × n coupler and n 1 × m couplers. All sensors are divided into n units by the 1 × n coupler. In each unit, there are m fiber-ring laser sensors with approximately the same wavelength and different beat frequencies due to different laser cavity lengths. Meanwhile, different units are characteristic of different operating wavelengths by splicing different fiber Bragg grating (FBG) as a reflector. Therefore, each sensor has a unique wavelength- and frequency-encoded information. All sensors can be interrogated by the combination of wavelength and frequency multiplexing technology. In the paper, a 4 × 4 sensor array is set up experimentally to verify the interrogation ability, and the sensing information of the strain and temperature has been successfully extracted. The experimental results show that the proposed interrogation system has the ability of real-time monitoring for a large-scale fiber laser sensor array.

A series of novel heterocycles 1-aryl- or alkyl-substituted-4-arylazamethylene-6-arylpyrazolo[5,4-d]-1,3-oxazines were synthesized from the acylation of (5-amino-1-substituted-pyrazol-4-yl)-N-carboxamide in 63-89% isolated yields at room temperature within 12 hours. The structure was confirmed by X-ray crystal analysis.

This paper reports the design of a microcoupler in the near-infrared region. The proposed structure consists of two alternately arranged complementary media. The complementary media, which consist of double-positive material and double-negative material, also can be made of a pair of single-negative materials. Simulation results show that the proposed structure has an excellent coupling efficiency compared to direct coupling. It has a maximum coupling efficiency closing to 1 at 1550 nm. As the total size of the coupling structure decreases, the passband exhibits a property of gradual blue shift. Therefore, we can design couplers operating in different frequency bands with high coupling efficiency. The influence of the permittivity and the thickness of each material layer on the coupling efficiency are also studied in detail. The proposed microcoupler has potential guidance in the design and development of high-performance coupling structures.

We theoretically and experimentally demonstrate the unidirectional negative refraction in an acoustic metafluid prism. The acoustic metafluid is designed to be uniaxial and highly anisotropic in inertia. Since the directions of phase and group velocities do not coincide in the anisotropic medium, it is possible to realize the unidirectional negative refraction by the broken symmetry of phase velocity vectors with respect to the acoustic axis. Being a distinct case of the asymmetric sound propagation, the unidirectional negative refracting effect could be potentially significant in various areas such as underwater sensing, and medical ultrasonics.