Implementations And Applications Of Micro-structures In Multi-core Fibers

With the network popularizing and developing,the conventional single mode optical fibers have been unable to meet current increasingly requirements of transmission capacity and speed.Under this background,the multiplexing multicore fiber,which has the characteristic of space division multiplexing(SDM),can overcome the characteristic problem effectually.Thus the multicore fiber has become a trend in the development of optical fiber communication.Furthermore,the optical devices based on fiber micro-structures have been widely used in various areas of industry,such as optical fiber communications,optical integration and optical fiber sensing.Although multicore fiber has been extensively studied as transmission medium,the applications in fiber sensing still need more attention.The multicore fiber sensors based on the space multiplexing structure and micro-structures have vast application foreground.In this thesis,some optical fiber devices utilizing the microstructure processing based on weak coupling seven core fiber were designed and fabricated,including a multipath Michelson interferometer(MI)on account of the taper and spherical end face,and the paralleled Mach-Zehnder Interferometers(MZI)based on controllable core-offset splicing.Theoretical analysis,simulations and experiments have been implemented for these structures.The MCF-MI was used to realize a high sensitivity measurement for high temperature.And the paralleled device integrated several MZIs in one single fiber,which can support multiple channels.The main content of the thesis includes:(1)Set out the typical microstructures and micromachining technologies which can be applied to optical fiber sensor.Then discuss the promising applications in multicore fiber device.Splicing is the simplest microstructure for not changing the basic structure of the fiber,including core-align and core-offset.In addition,taper,micro-cavity and micro-channel are also common types of micro-structures.These structures are fabricated by micromachining technologies,for instance,femtosecond laser micromachining,fused taper,chemical etching,grinding,polishing and so on.All these microstructures and technologies can be combined with the multicore fiber,and explore the applications.(2)Design and fabricate the multicore fiber microstructures utilizing fused taper.The taper process based on arc discharge is controllable and stable,and the tapered structure can realize the coupling of optical field between center core,surrounding cores and claddings.Several structures were designed and fabricated,which proved that the taper can be used in multicore fiber based devices.(3)Propose a multipath Michelson interferometer,which is constructed of a taper area and spherical end face in multicore fiber.The tapering process was conducted at the splice point between the lead-in SMF and MCF in order to enhance the coupling between cores of MCF,thus facilitating the generation of multipath propagation.Moreover,even distribution of optical power among cores has been achieved with the help of spherical structure fabricated at the MCF end face.Theoretical analysis assisted by experiments have been carried out to figure out the principle of this specific multipath MI structure;simulation and corresponding experiments were performed to investigate the effect of taper and spherical end face on system’s performance.(4)Measurement of high temperature for multipath Michelson interferometer.Enhanced inter-core interference spectrum has been obtained,with an extinction ratio of 25 dB,large FSR(166.34 nm with a MCF length of 10 mm)and steep dips.The large FSR helps to increase the measurement accuracy especially and,in the meantime,keeps large measurement temperature range without overlapping reading problem.Between 250 °C and 900 °C,a sensitivity of 165 pm/°C has been achieved.This type of sensor has a promising use in the future due to its high sensitivity,high extinction ratio,wide detection range and simple fabrication process.(5)Propose a paralleled Mach-Zehnder interferometers with seven-core fiber based on core-offset splicing.In this device,rotation and translation processes were introduced when the MCF was spliced with the fan-in/fan-out device.Thanks to the symmetrical structure of seven-core fiber,off-center launching can be achieved in every core.Experiments have been carried out to figure out the principle of this structure.This compact device integrates several MZIs in one single fiber,which can support multiple channels.