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A refractive index sensor based on the thinned and microstructure fiber Bragg grating (ThMs-FBG) was proposed and realized as a chemical sensing. The numerical simulation for the reflectance spectrum of the ThMs-FBG was calculated and the phase shift down-peak could be observed from the reflectance spectrum. Many factors influencing the reflectance spectrum were considered in detail for simulation, including the etched depth, length, and position. The sandwich-solution etching method was utilized to realize the microstructure of the ThMs-FBG, and the photographs of the microstructure were obtained. Experimental results demonstrated that the reflectance spectrum, phase shift down-peak wavelength, and reflected optical intensity of the ThMs-FBG all depended on the surrounding refractive index. However, only the down-peak wavelength of the ThMs-FBG changed with the surrounding temperature. Under the condition that the length and cladding diameter of the ThMs-FBG microstructure were 800 and 14 mum, respectively, and the position of the microstructure of the ThMs-FBG is in the middle of grating region, the refractive index sensitivity of the ThMs-FBG was 0.79 nm/refractive index unit with the wide range of 1.33-1.457 and a high resolution of 1.2 x 10(-3). The temperature sensitivity was 0.0103 nm/ degrees C, which was approximately equal to that of common FBG.

Traditional spherical lenses are bulky and often the limiting factor for the miniaturization of modern smart devices. Metalenses can break the limitations of traditional spherical lenses, allowing for the development of ultra-thin planar lenses. Here, we experimentally demonstrated metalenses in the mid-infrared spectral range by patterning a germanium wafer using standard nanofabrication processes. Three 6 mm × 6 mm planar lenses operating at 3μm, 5μm and 8μm were fabricated and characterized. The results show that the focusing efficiency of the metalenses reaches 80% and the numerical aperture is as high as ∼ 0.8, close to the designed theoretical value. The metalenses are also used to image a lighter fire with a quality comparable to traditional spherical lenses.

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We present a novel optical fiber dynamic light scattering measurement system for nanometer particle size. A multimode fiber probe is used to highly efficiently couple and deliver laser light, while a single-mode fiber probe is used to only receive single scattering light. This design not only improves the measuring ability of the system but also provides flexibility in choosing scattering angle for measurement. By using this system, four kinds of polystyrene nanoparticles are evaluated. Experimentation shows the measured sizes of the nanoparticles are well consistent with the nominal ones, verifying the feasibility of the system.