In this article, we report a low-cost method to fabricate plastic optical fiber (POF) liquid-level and refractive index (RI) sensors integrated with smartphones by molds and drilling microholes in side-growing POFs (SGPOFs) with high-temperature metal wire. These sensors can be used for real-time liquid-level and RI monitoring, especially under situations requiring portability and illumination. When the liquid level changes, the change of the RI around the microholes leads to a change in the light intensity transmitted in the fiber, enabling us to measure the liquid level and RI. Utilizing one sensor with six holes (0.45 mm radius and 15 mm spacing) in 2.0-mm SGPOF, the results of level and RI measuring are in good agreement with the theory. The liquid-level measurement of the sensor is carried out for water with an RI of 1.333, the level sensitivity is 0.29%/cm ± 0.02%/cm. In the RI measurement, the RI sensitivity of the sensor is −22.8%/RIU ± 0.6%/RIU in the measurement range from 1.333 to 1.475.
A Refractive index (RI) sensor was fabricated with a multimode micro plastic optical fiber (mPOF) with macro-bending structures, which RI sensing resolution can reach 10−5 order. The experiments results agree with the simulation.
The temperature dependence of a refractive index (RI) sensing probe based on a U-shape tapered plastic optical fiber (POF) was investigated experimentally. The changes in light propagation loss in the probe induced by temperature are of the same order of magnitude as those induced by measured RI changes. The temperature dependence loss and temperature dependence RI deviation of the sensing probe were measured (at the wavelength of 635 nm) in temperature of 10-60 °C. By extracting pure temperature dependence of the sensing probe alone, the influence of temperature to the sensor was characterized.
A Refractive index (RI) sensor was fabricated with a multimode micro plastic optical fiber (mPOF) with macro-bending structures, which RI sensing resolution can reach 10−5 order. The experiments results agree with the simulation.
Linear-to-circular polarization converters are widely used in optical and microwave systems, but the polarization devices of traditional materials are untunable, and devices made of graphene materials can overcome this disadvantage. A circular polarization converter based on graphene metasurface is designed, whose properties are tunable over a broad range at terahertz frequencies. With appropriate structural parameters, simulations show that the axial ratio of reflected electromagnetic wave of the proposed device is lower than 3 dB in the frequency band of 2.25 to 2.475 THz, which means the linearly incident polarization can be converted to the circular polarization wave. The proposed design can also work when the electromagnetic wave is oblique incidence up to 40 deg with a high polarization conversion ratio. Moreover, the operating frequency band can be arbitrarily adjusted by applying a bias voltage.
A high-sensitivity Mach–Zehnder interferometer (MZI) based on the cascaded core-offset and macrobending fiber structure is proposed for refractive index (RI) measurement. The core-offset structure makes the fiber core mode couple to the cladding modes, and some of them recouple back to the fiber core at the macrobending structure forming a model interference effect. The liquid RI can be measured by monitoring the spectral shift of the modal interference. The RI sensing performances for the interferometers with different macrobending radii and core offsets are investigated experimentally. Experimental results show that when the core offset is 2 μm and the macrobending radius is 5.5 mm, the sensitivity can reach 699.95 nm/RIU for the RI of 1.43. The temperature dependence for the proposed sensor is also tested, and a temperature sensitivity of 0.112 nm/°C is obtained.
This paper investigates a refractive index (RI) sensor based on a macrobending micro-plastic optical fiber (m-POF), which is used as a sensitive probe. The m-POFs are fabricated from commercial POFs using a heating and pulling method. The m-POFs have diameters of approximately 20-40 μm and act as multimode fibers at visible wavelengths. The macrobending structure of the m-POFs is simulated and optimized using the ray tracing method. The RI sensitivity and the range of RI measurements are affected by the structure parameter R/ρ, which is the ratio of the radius of curvature of the macrobending fiber to the radius of the fiber itself. A linear RI sensing response is obtained when R/ρ=20 and the sensitivity reaches 500%/RIU. The experimental results coincide well with the simulation results.
Recent studies have shown that quadratic-power-exponent-phase (QPEP) vortex and modified QPEP vortex have some novel properties and potential applications in optical manipulation, orbital angular momentum (OAM) communication, OAM multicasting and so on. In these applications, there may be potential need of processing these kinds of beams by using uniaxial crystals. In this paper, the analytical propagation equations of Gaussian QPEP vortex and modified QPEP vortex propagating in uniaxial crystals are derived and the evolution of the angular momentum via spin-orbital coupling during the propagation is investigated. This may be meaningful for guiding and promoting the applications of the QPEP vortex and modified QPEP vortex.
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