After the vortex beam is transmitted in the space laser communication scene for thousands or even tens of thousands of kilometers, the spot diameter will expand to several meters or even tens of meters, and the existing detection methods that require receiving the whole spot are no longer applicable. To address this problem, this paper proposes a distributed detection scheme to identify the topological charge of the vortex beam by analyzing and processing the data received from each detector. Matlab is used to simulate the proposed scheme. The vortex beam is a Laguerre-Gaussian beam with a transmission distance of 100 km, and the simulation analysis shows that the scheme can detect Laguerre-Gaussian beams with topological charge number -3 to +3.
A cost-efficient multimode interference-based sensor with corroded polarization-maintaining fiber (PMF) is proposed and experimentally demonstrated for the measurement of liquid refractive index (RI) and temperature. The sensor consists of a segment of corroded PMF and two segments of multimode fiber (MMF). Two segments of MMF, which are used as beam splitter and combiner are embedded on both ends of the PMF. The all-fiber sensor is put in the middle of the single-mode fiber. The RI and temperature characteristics of the sensor are investigated experimentally. The results show that two resonant peaks have different spectral responses of RI and temperature changes, which indicate that the sensor can realize simultaneous RI and temperature measurements. The experimental result shows that the high RI sensitivity is up to 318.279 nm / RIU in the RI range from 1.333 to 1.350 and the high temperature sensitivity is 0.188 nm / ° C in the range from 20°C to 40°C. This sensor exhibits the advantages of low cost and high sensitivity and may have potential application in RI and temperature measurements.
A hybrid optical fiber structure sensor for simultaneous measurement of temperature and low pressure based on Fabry–Perot (FP) interference and fiber Bragg grating (FBG) is proposed. The FP cavity is fabricated with a capillary pure silica tube, whose one end is surface processed to result in an open FP cavity. The measurement of refractive index change of different pressures has been achieved by monitoring the wavelength shift of the interference pattern in the reflection spectrum. The FP cavity is integrated with the FBG to obtain temperature measurement simultaneously.
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