UV Detection Technology Based On Microfiber Coated With Nano-ZnO

Partial discharge(PD)is a common phenomenon in high voltage equipment,which will radiate light signals outward in the process of discharge,by detecting this optical signal,we can evaluate whether the high voltage equipment has PDs or not.The conventional detection methods under impulse voltage are very complex due to the interference of electromagnetic waves,but the optical method does not have this problem.The optical signal detection method based on optical fiber sensing technology is especially suitable for sensing physical quantities inside high-voltage power equipment in high temperatures,high electric fields,and harsh electromagnetic environments.In this paper,optical fiber sensing technology for UV light detection applied to PD detection is researched.A high-speed optical fiber UV sensing system with high sensitivity,high selectivity,and high stability was designed and fabricated by combining the nano-material technology,micro-nano fiber sensing technology,and microwave photonics signal processing technology using a microfiber sensor coated with nano-ZnO.To improve the UV selection characteristics,nano ZnO is proposed to be used as sensitive material.The selectivity of the optical fiber UV sensor is improved by using ZnO’s wide band gap characteristics and high exciton binding energy,and the sensitivity of the sensor to UV light radiated by PD is further improved through the graphene modification method.The UV spectrum selection characteristics of ZnO nanoparticles and the modification effect of graphene on the UV sensitivity of ZnO were investigated theoretically by first-principles calculation.Based on theoretical research,nano-ZnO and graphene composite nano-ZnO were prepared by hydrothermal method and applied to an optical fiber UV sensing system.The experimental results of UV detection show that the UV sensing characteristics of the sensors are significantly improved after graphene modification.To improve the detection sensitivity,a fiber UV sensing system based on Mach-Zehnder Interferometer(MZI)utilizing a microfiber coupler(MFC)is proposed in this paper.Nano ZnO-coated MFC was used as a UV sensing unit.The sensitivity of UV detection can be improved by the high evanescent field characteristics of microfiber.The free spectrum range of the output spectrum can be changed by adjusting the optical path difference of MZI arms,then the UV detection sensitivity of the system can be optimized.In addition,graphene composite nano ZnO with different surface morphology was prepared by hydrothermal method,and UV detection experiments were carried out.The experimental results show that graphene composite flaky nano ZnO has higher UV detection sensitivity of 2443.71 pm/m W·cm-2.To improve the system stability,an in-line microfiber MZI structure is further designed in this paper.Single mode-tapered multiple mode-single mode(STMS)microfiber MZI structure was fabricated through the method of heating with hydrogen and oxygen flame.Microfiber UV sensor was achieved by coating nano ZnO on the surface of cone region in multiple mode fiber.Compared with the MFC-MZI UV detection system,the STMS sensor has a smaller volume and higher integration.The experimental results of UV detection show that the STMS microfiber UV sensor coated with nano-ZnO is more stable.In order to solve the problem that the scanning speed of the spectrum is too slow to meet the real-time detection of PD signal,microwave photonics fiber signal processing technology is introduced in this paper.A wavelength interrogation system based on wavelength-to-time(WTT)mapping is proposed.In addition,considering that the system is susceptible to the random time delay in the environment,which leads to a decrease in the accuracy of signal demodulation,a high-speed and stable optical fiber wavelength signal demodulation system based on chirp frequency encoding is proposed.The parameters of the system are optimized by theoretical simulation and verified by experiments.The experimental results show that the signal acquisition speed of the system can reach 50 MHz,which is significantly improved compared with that of spectral scanning technology.In this paper,an all-fiber UV detection scheme for PD detection is proposed based on microfiber coated with nano ZnO.Theoretical simulation and experimental research were used in this paper.An all-fiber UV detection system with high speed,high sensitivity,and high stability is realized,which uses ZnO nanomaterial coated microfiber as a sensing unit and microwave photonic technology based on the chirp frequency encoding method as a demodulation scheme.It provides an all-fiber scheme for PD detection of power equipment.