Studies On Characters And Applications Of Tapered Optical Fibers

As an important post-processing technique of optical fibers, tapering of opticalfibers can change the shape and optical characters of fibers and make kinds of fiberdevices which are very useful to expand application field of fibers. As a kind ofbrand-new optical fiber, photonic crystal fiber(PCF) possesses many unique charactersthat can not find in conventional fibers because of it's flexible structure. The idea oftapering photonic crystal fiber puts this kind of fiber in a larger application platform andenriches fiber tapering theories. In this thesis, we study on tapering of conventionalfibers and PCFs and air hole collapsing of PCFs in theoretical and experimental. Alsosome applications, such as supercontinuum(SC) generation and low loss splicing, areexplored using these tapering fibers.1 Processes and shapes of tapering conventional fibers are studied on. Varying ofmode-field diameter(MFD) and controlling of group-velocity dispersion(GVD) are bothsimulated by numerical methods. Meanwhile, necessary conditions of low loss taperingare studied in three aspects: environments of tapering, controlling of parameters, andshapes of tapering fibers. In experimental, we get low loss tapering optical fibers withdifferent outer diameters using a fusing tapering rig. Fiber microwires and nanowiresare also simulated and analyzed.2. SC generation in tapering conventional optical fibers is reported. By varying thewavelength of femtosecond pumping laser and diameters of tapering fibers, we study onthe relationship of SC with these parameters.3. Tapering and air hole collapsing techniques of photonic crystal fibers areproposed in theoretical. Using"fast and cold"method, we taper PCFs while keepingd/Λunchanged and collapse air holes using"slow and holt"method while keeping outerdiameters unchanged.4. SC is generated in tapered PCFs. We taper a PCF to adjust its dispersion curve,and then pump this tapered PCF at anomalous dispersion regime with dual-wavelengthgenerated by four-wave mixing effect. SC with more than 600~1700 nm spectrum broad(at 20 dB level) is generated in 1m length PCF.5. Low loss splicing of small core PCFs and conventional fibers is achieved byremoving their mismatch of MFDs with hole collapse method of PCFs. For slight MFD mismatch condition, we get low loss splicing with repeat arc method, while for seriousMFD mismatch condition, we use heating method to collapse air holes accurately with atapering rig and get low loss splicing too.