Research On Characteristics And Applications Of Novel Optical Fiber Filter Based On Spun Fiber And No-core Fiber

Optical fiber filters are indispensable optical elements with wide application and penetrating into every link of optical communication system.Due to the rapid development of the filtering technology,the research of fiber-optic sensing and fiber-optic laser based on optical fiber filters have attracted more and more attention.With the advantages of easy fabrication,low cost,compact size and insensitivity to electromagnetic interference,they have a significant meaning and application prospect in the field of communication system and internet of things.In this dissertation,the investigation of both theory and experimental measurement on birefringent filter based on spun fiber and model interference filter based on no-core fiber(NCF)have been performed.The proposed filters also applied for the different kinds of fiber sensors and fiber lasers sensing system.By utilizing special optical properties of spun fiber and NCF combined with fiber grating,the compound filters can be fabricated and applied for fiber laser and multi-parameters simultaneous sensing measurement.The highlights of this work are summarized as follow:1.A novel Solc-like tunable birefringent fiber filter based on elliptical-core spun fiber(ECSF)is presented and applied to fabricate an all-fiber high sensitivity twist sensor.It is the first time to build a discrete model of spun fiber by using Jones matrix analysis.The transmission characteristics of proposed all-fiber birefringent filter are studied and discussed in detail.By utilizing appropriate length and parameters of the ECSF and adjusting the polarization controller(PC),a tunable narrowband and high extinction ratio periodic optical filter transmission spectra is realized.All-fiber high sensitivity twist sensor based on Solc-like structure filter has been reported.The transmission and sensing characteristics of proposed sensing system has been theoretically and experimentally studied.The results show that this twist sensor has a very low temperature and strain sensitivity,which can avoid the cross-sensitivity problem existing in most twist sensors.2.By optimizing Solc-like structure fiber filter,an all-fiber,tunable,polarization-independent comb filter based on a birefringent spun fiber in a Sagnac loop has been modeled and experimentally demonstrated.We generalize the birefringent spun fiber in our model to include birefringent fibers.Also,we present modeling of the filter'^optical spectra characteristics based on Jones matr:ix analysis,and show theoretically that dynamic wavelength tunability can be achieved by adjusting the PC parameters.We also demonstrate experimentally full wavelength tunability over the entire free-spectral range while maintaining highest possible peak transmission,high extinction ratio(>25dB),and polarization independence of input light of the proposed filter.3.Fiber ring laser sensor for curvature and temperature measurement based on single-mode-no-core-single-mode fiber(SNS)structure is proposed and experimentally demonstrated.The detection of liquid level and temperature based on a dual-wavelength fiber ring cavity laser sensing configuration using SNS and fiber Bragg grating(FBG)is also presented.Compared with the conventional fiber sensing system,the proposed laser sensor system has a higher optical signal-to-noise ratio and a narrower 3 dB bandwidth.The main element of proposed dual-wavelength fiber laser sensing system is a compound fiber filter,which contains a FBG and a SNS structure multimode interferometer in parallel.This filter can function as both sensor head and wavelength-selective components.In the experiment,the corresponding sensitivities of the liquid level with four different refractive indices and temperature characteristic are obtained,and maximum liquid level sensitivity of propsed sensor is 106.3 pm/mm.4.Two kinds of compound fiber filter based on the combination of NCF,spun fiber and phase shifted FBG is presented and applied on simultaneous measurement of magnetic field and temperature and tunable switchable fiber laser.One compound filter is realized by concatenating NCF with ECSF in a fiber loop mirror,which could cause both multimode interference and Sagnac interference effect resulting in a configuration capable of magnetic field and temperature discrimination.The proposed sensor can achieve both a high magnetic field sensitivity with 713.07 pm/mT and temperature sensitivity with-304.55 pm/?.The other filter is consisted of quasi-Solc-Sagnac filter and phase shifted FBG When we introduce this compound filter into erbium-doped fiber ring laser system and change the state of polarization in the laser cavity,the tunable and switchable single or dual-wavlength stable laser output can be realized.