In this paper, we use the experimental data to verify the technology of Optical Time Domain Reflectometry (OTDR) to realize multi-branch fault monitoring in PON access network. Then the monitoring effects of the two optical splitter structures are analyzed in detail, and the dynamic monitoring of different fault degrees is realized. We prepared single-mode optical fibers, with the length of 10.282 km, 10.768 km, 14.45 km, 25.2 km and 50.38 km respectively. Optical attenuators with different optical attenuation values, like 5 dB and 2 dB, respectively corresponding to different fault degrees of optical fiber link. The fault monitoring of branches with similar distance is analyzed, and the influencing factors such as pulse width are analyzed in detail. In experiments, it can be found that the selection of scanning pulse width has little impact on the identification of event position, but when two adjacent events fold each other due to the increase of attenuation dead zone, the identification of event position cannot be realized. It is believed that these research data can provide valuable reference for the management and maintenance of optical fiber in the actual PON network, and provide valuable data for the promotion of this new technology.
A novel optical fiber sensor based on weak coupling twin-core fiber (TCF) is proposed and experimentally demonstrated. The sensing structure consists of two single mode fibers (SMF) and fabricated by program controlled tapering the spliced region between the first SMF and a segment of TCF. During this period the light power was gradually transferred from the SMF into the cladding mode near the waist zone, after the waist zone, the optical power was gradually concentrated from the cladding mode into the cores mode, which could affect the extinction ratio of the interference peaks in the transmission spectrum. In order to obtain better interference spectrum, we adjusted the fusion structure of the tail fiber and the TCF, and the cross sections of the optical fibers are dislocated to a certain extent, so that the interference process of the beam changes. In the process of adjusting the structure, we observed the spectral changes in the spectrometer at the same time until the best interference spectrum appeared, and then we completed the fusion. The interference between different modes can be affected by changes in the external environment, like refractive index (RI) and strain, which also dictates the wavelength shift of the transmission spectrum. In the experiment, we have studied the sensing response of the optical fiber sensor to the RI and strain, and the sensing sensitivity is 131.1nm/RIU and 1.26x10-3 dB/με respectively. All sensors fabricated in this paper show good linearity in terms of the spectral wavelength shift.
In this paper, we develop a novel optical fiber temperature sensor based on Fabry-Perot interferometer (FPI). The structure of the sensor includes a spliced seven-core fiber (SCF) and a piece of quartz glass capillary. During fabrication, we use the fusion splicer to move two SCFs into glass capillaries gradually. The length of the SCF is about 4 cm. In the cavity structure, the end faces of two SCFs are parallel to each other. The light transmitted in the optical fibers will be reflected twice at the two end faces. We can use the relationship between the length of the cavity and the power change of the reflected light to realize the sensing measurement of temperature parameters. We have gradually tested seven groups of reflective spectra as the temperature increases from 20°C to 50°C. The free spectral range (FSR) of the sensor has changed, also the beam propagation in the air cavity will cause loss, and the power of the reflection spectrum will change with the cavity length. The values of FSR and extinction ratio (ER) vary nonlinearly with temperature, and through data analysis, the equation describing the sensor was obtained, like the sensitivity function of FSR is y=107.7exp(-x/12.36)+5.35, the sensitivity function of ER is y=39.6exp(- x/15.75)+3.02, and the correlation coefficients of the two non-linear fitting are 0.991 and 0.998, respectively.
In this paper, a novel optical fiber pressure sensor based on duralumin grooved plate was experimentally demonstrated. The sensing structure consists of two duralumin plates, and uniform grooves were carved on the plates. The fiber was vertically placed between the plate grooves. Under different pressure conditions, there will be different micro-bending of the optical fiber, which will result in the modes conversion of the fiber. Some fiber modes become radiative modes, which will lead to the loss of transmission power in the fiber. We can make use of this special effect to fabricate optical fiber pressure sensor. We first tested the single mode fiber (SMF). By repeat applied cyclic pressure on the sensing structure, we recorded the changes of light power and obtained the sensitivity of 1.11 mW/kgf and 1.4 mW/kgf at 1550 nm and 1310 nm, respectively. In addition, we analyzed the spectral changes in the fiber and experimentally analyzed the temperature characteristics of the sensing structure, found that the sensor has good temperature stability. Moreover, because of its simple fabrication and highly adjustable property, this sensor is suitable for engineering application. We also use this duralumin grooved plate to test the few mode fiber (FMF), and found that due to a variety of core modes coupling in the fiber, the pressure sensing characteristics are not good. However, by analyzing its spectrum, we found that this device can achieve some special mode conversion and has a good application prospect.
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