Based on the surface plasmon resonance of metal and anti-resonant principles of hole-core microstructure optical fiber (MSF), in this Letter, we demonstrate a MSF microfluidic sensor that combines silver film and hole-core MSF to achieve the sensitive real-time monitoring of refractive indices and components. The large hole core is a common channel for guiding light and flowing measured liquid. Because of the interaction between light and continuous flow measured liquid, the component and refractive indices can be simultaneously monitored by the characteristic absorption wavelength and the surface plasmon resonant peak position, respectively. These results indicate that the MSF microfluidic sensor is an ideal multi-parameter measurement optical sensor.

In this paper, a dual hollow-core negative curvature fiber is proposed for the polarization beam splitter. The effects of the structure parameters of the dual hollow-core negative curvature fiber on the coupling length and coupling length ratio of the x -polarized and y -polarized core modes and the higher-order mode extinction ratio are analyzed by the finite element method. Moreover, the normalized output powers of the x -polarized and y -polarized modes in the cores A and B and the corresponding extinction ratio are also investigated by the mode coupling theory. The simulation results show that a dual hollow-core negative curvature fiber polarization beam splitter with the length of 6.45 cm can achieve a broad bandwidth of 400 nm (1.23–1.63 µm), covering the O + E + S + C + L communication band. In addition, the higher-order mode extinction ratio is greater than 100 in the considered wavelength range, which means that it has good single-mode characteristics. It is believed that the proposed dual hollow-core negative curvature fiber polarization beam splitter will have significant applications in the optical communication system.

A helical Yb³⁺-doped three-core microstructure fiber (YTMF) amplifier is proposed in this paper, so as to solve the problem of generation and transmission of the orbital angular momentum (OAM) beams. The fiber is composed of three Yb³⁺-doped cores with a regular triangle shape and a longitudinal helical structure. The experimental results show that the 1064nm laser can be amplified due to the fluorescence amplification characteristics of the doped material Yb³⁺. Furthermore, theoretical analysis indicates the modes in YTMF at 1064nm, which is located in the amplified wavelength, can support nine modes carrying OAM. Therefore, the related experiments were performed and verified that the transmission modes can respectively carry 1, 2, and 3-order OAM at 1064nm in different coupling cases. These excellent properties indicate that the combination of doped materials and helical fiber provide favorable conditions for the generation and amplification of OAM, which provides a basis for the further development of OAM beams in the field of quantum communication and dense space division multiplexing.

In this Letter, we demonstrated an $\infty$-type multi-functional sensor through splicing double rare-earth-doped balls (REDBs) with a hollow-core microstructure fiber. Utilizing the different thermal expansion and thermo-optic coefficients of silica and rare earth, the interference of REDBs will be more sensitive to temperature. On both ends of the dual-ball, we spliced the anti-resonance fiber (ARF) to satisfy the broad waveband transmission. In addition, the special anti-resonance loss peak of the ARF can make the amplitude change of the signal more obvious. The experiments prove that a multi-functional sensor is capable of detecting versatile parameters, such as the illumination response, liquid concentration, and ambient temperature. In addition, the temperature sensitivity can reach 1 nm/°C, and the illumination response is obvious. We also analyze the concentration of P-Methylthiophenol, a substance harmful to human beings in the environment. Its resolution can reach 3.125E-5 mol/L. These results indicate that the sensor can be used in underground mine detection, environmental monitoring, and so on.