Research On The All-fiber Devices Based On Photonic Crystal Fiber

The fifth-generation mobile communication technology(5G)will be fully commercialized in 2020.The MIIT points out that all-optical network is the best choice for 5G.Since 2016,the“13th Five-Year Plan”proposed the“Network power strategy”and vigorously promoting the construction of all-optical network.However,the development of all-optical network is greatly restricted by the serious mode mismatch and high access coupling loss in the use of the non-all-fiber devices.Therefore,the construction of the all-fiber-based devices is imminent.Photonic crystal fiber(PCF)has unique air hole arrangement structure and excellent light guiding characteristics,which can effectively reduce mode mismatch and improve communication quality.Specially,two core photonic crystal fiber(TCPCF),which combines the advantages of two core fiber(TCF)and PCF,is widely used in the field of all-optical processing.In this paper,with the aim of all-fiber devices,we studied four kinds of PCF-based devices with all-fiber structure theoretically and experimentally,including electro-optic modulator,sensor,polarization filter and polarization splitter.The main work and innovation achievements are as follows:1.Based on the coupled mode theory,the modulation model for TCF is established,and an all-fiber electro-optic modulator based on a D-shaped two-core fiber(DTCF)is proposed.Firstly,the transmission spectrum of TCF is measured at different stress.The sensitivity of TCF is 1.36 pm/??,which indicates that TCF can be controlled by external parameters.Furthermore,according to the different sensitivity of the two cores in DTCF,the intensity modulation of light is realized by adjusting the voltage.The results show that the 3 d B modulation voltage is 1.26 V.At the voltage of 2.7 V,the modulator has a high extinction ratio.The all-fiber modulator can reduce the mode mismatch of the optical fiber system.Thus,it improves the modulation rate and bandwidth of the modulator.2.A PCF-based surface plasmon resonace(SPR)sensor for low refractive index detection is proposed.The core of PCF is composed of two-layer sector rings with nagative curvature.The structure of the sensor is simple and the performance is independent of the polarization.The results show that the sensitivity of the PCF-SPR sensor is up to-15900 nm/RIU in the range of 1.20?1.34.It is promising to apply in low refractive index solution accurate monitoring,water impurity detection and environmental measurement.3.Two kinds of SPS sensors based on photonic crystal fiber cascaded with single-mode fiber are proposed.The PCF is spliced with two pieces of single-mode fiber at both sides.Based on the manufactured sensor,the external temperature and stress are measured.The first structure is based on a hollow core PCF with six negative curvature ring.The results show that the sensitivity of the sensor is 20 pm/~oC and 0.67 pm/??,respectively.In the second structure,the sensor is based on a silica-core PCF.In the case of filling glycerol in the air hole,the sensitivity is 74 pm/~oC and 0.43 pm/??.Results show that both the sensors with hollow core and silica-core PCF have good resistance to stress-cross sensitivity,which is conducive to the accurate measurement of temperature.4.A tunable all-fiber polarization filter based on D-shaped PCF(DPCF)is studied.The upper surface of DPCF is coated with graphene and gold in turn.The single wavelength,double wavelength and three wavelength polarization filtering can be realized by combining the SPR effect and the tunability of graphene.By tuning the chemical potential,the wavelength position is flexible and adjustable.The results show that when the device length is 100?m,in the wavelength range of 1.0?1.4?m,the polarization extinction ratio is higher than25 d B.Based on the proposed DPCF-based filter,the fabrication process of DPCF is studied.The hydrofluoric acid etching method is used to provide a DPCF with smooth surface for the final realization of polarization filter.5.Two kinds of all-fiber tunable polarization beam splitters based on TCPCF are proposed,which are filled with magnetic fluid in the air hole.By adjusting the external magnetic field,the birefringence of TCPCF is changed,and the polarization state can be tuned and converted at the output.The finite element method is used to analyze the performance of the device.When the fiber is a circular hole structure,at the device size of 8.13 mm and the magnetic field strength of 25 m T,the polarization state can be completely converted.Based on this,the optimized TCPCF with elliptical and circular hybrid hole is proposed.The research shows that the device can realize polarization splitting at the length of 78?m when the central air hole is filled with glycerine solution of 37%concerntration.When the central air hole is filled with magnetic fluid,at the length of 1007?m and the magnetic field strength of 40.5 m T,the polarization conversion can be realized.The all-fiber tunable polarization beam splitter can realize the separation,tuning and conversion at the same time.The proposed devices are compact and easy for intergration.