Investigation On The Design,fabrication And Application Of Multicore And Few Mode Fibers

Since the optical fiber has been regarded as the communication medium,the limitations of attenuation,dispersion,nonlinearity and other factors on the transmission distance and bandwidth of the system have been gradually mitigated.Driven by the dramatic growth of the digital media,cloud computing and 5G communication service,the Internet traffic is explosively increasing.So far,the capacity provided by standard single-mode fiber(SMF)is approaching Shannon's limit.In order to further extend the transmission capacity,the space division multiplexing(SDM)technology has attracted extensive attention in the past decade.The few mode fiber(FMF)and multicore fiber(MCF)are considered to be promising candidates in the next generation of large-capacity optical fiber communication system.In the field of optical fiber sensing,SMF with low nonlinear threshold results in a limited system signal noise ratio(SNR),and can only provide single dimension for measurement.The MCF and FMF with multiple spatial channels and optimizable mode property have been regarded as desirable sensing medium for distributed fiber-optic sensing techniques.In this thesis,we designed and fabricated two kinds of ultra-wideband MCF and FMF which can support both multimode and quasi-single mode operation for high speed optical interconnect application.On the other hand,we proposed a novel FMF with optimized structure to relief the compromise between the temperature and spatial resolution in Raman distributed temperature sensor(RDTS)system.The detailed work is as follows:(1)We designed and fabricated a graded-index MCF which is compatible with both standard multimode fiber(MMF)and SMF for high-speed optical interconnect application in large-scale data centers.We investigated its characteristics such as bandwidth,dispersion,inter-crosstalk and misalignment tolerance.The results show that the MCF has a high bandwidth at 850 nm while remaining a comparable performance with standard SMF at 1310 and 1550 nm.The largest differential mode delay(DMD)of 0.112 ps/m and the minimum effective modal bandwidth(EMB)of 8.44 GHz·km are achieved with the MCF for multimode operation,while the chromatic dispersion of the MCF at 1550 nm only increases by 1.23 ps/(km·nm)compared with that of standard SMF.The worst inter-core crosstalk is less than-43 d B over a 10 kmlong MCF.Moreover,within a misalignment of 2 ?m,the quasi-single mode operation can be guaranteed and the additional power penalty induced by insertion loss and the modal noise are negligible.In experiment,we successfully performed the 7×25 Gb/s error free multimode transmission over a 300 meter-long MCF at 850 mm and quasi-single mode transmission over a 12.4 and 10 km-long fiber at 1310 and 1550 nm,respectively.No obvious degradation was observed when all cores operated simultaneously.(2)We analyzed the wavelength dependency of EMB of FMF with different dopants based on Wentzel-Kramers-Brillouin(WKB)theory.According to the simulation results,employing fluorine-doped silica as cladding could be an effective solution to minimize the bandwidth dependency on wavelength in the SWDM operation window(850-940 nm).The EMBs of the fabricated FMF are measured to be 6.5,6.9,4.9 and 4.0 GHz·km at 850,880,910 and 940 nm respectively.The results indicate that the fabricated fiber with fluorine-doped cladding well satisfies the minimal bandwidth requirement suggested by the specification of OM5 fiber.Besides,in order to simultaneously support high-performance SWDM and coarse wavelength division multiplexing(CWDM)transmission,the core size and relative refractive index difference between the core and cladding the of the fiber were optimized to be 30 ?m and 1.2%,respectively.In experiment,we successfully demonstrated the error free 100 Gb/s(4×25.78Gb/s)transmission by employing commercially available SWDM and CWDM transceivers over250 meter-long and 10 km-long proposed fiber,respectively.(3)We designed and fabricated a novel FMF with a core diameter of 24 ?m for RDTS system.In order to relief the tradeoff between the temperature and spatial resolution in RDTS using traditional MMF or SMF,the refractive index profile and core size of the FMF were optimized to simultaneously achieve a large effective mode area and a low intermodal dispersion.By using the FMF under the overfilled launch condition,the temperature and spatial resolution and of 1?C and 1.13 m at the distance of 25 km were achieved.For comparison,the spatial resolution using the OM2 MMF degraded to 2.58 m with only a 0.3?C improvement on temperature resolution.Moreover,the RDTS using the FMF under quasi-single mode launch condition can achieve a temperature resolution of 4.7?C at the distance of 25 km with a 2.2?C improvement and no spatial resolution degradation compared with that of the standard SMF.This thesis focuses on the research of the novel MCF and FMF for optical communication and sensing applications.High speed and ultra-wideband MCF and FMF are proposed to improve the capacity and efficiency of optical interconnection systems.Besides,the performance of RDTS system is improved by taking the advantages of FMF with large mode field area and low modal dispersion.