Research On Fabrications And Sensing Applications Of Fiber Based Devices With Integrated Parallel Multi-Channel

With the booming developments of Internet,intelligent terminals and the Internet of Things(IoTs),the space division multiplexing(SDM)technology based on multicore fiber(MCF),few-mode fiber(FMF)and few-mode multicore fiber(FM-MCF)has attracted considerable interests in the field of improving transmission capacity.Apart from the transmission research,MCF and FM-MCF based devices also create a new path in the field of optical fiber sensing.The current researches of fiber sensors face the chanllenges of integration and high precision,especially the simultaneous measurment of multiple external parameters in the actual environment and the cross-sensitive effects.Taking the MCF/FM-MCF as the sensor carrier,the specially-designed fiber devices with highly-integrated multiple channels/cores have potentials to detect multiple environmental parameters simultaneously.Therefore,it’s necessary to conduct research on the fiber-based devices with integrated parallell multi-channel.In this thesis,considering the developing trend and requriements of fiber sensors,we designed and fabricated a series of functional devices with integrated parallel channels based on MCF and FM-MCF.These specially-designed devices successfully achieved the simultaneous measurement of dual-parameter and lay a solid foundation for simultaneous multi-parameter sensing.The main contents of this thesis are listed as follows:(1)We firstly investigated the basic structures and the fabrication techniques of SDM devices based on MCF and FM-MCF.The fabrication techniques are mainly summarized into laser inscription technique,high-temperature manufacturing technique and core-offset splicing technique.The laser inscription technique is widely used to fabricate devices with parallel grating structures and the core-offset splicing technique is often used to fabricate fiber devices with parallel interferometric structures.The above structures can both be fabricated by the high-temperature manufacturing technique.After careful comparision and trade-off,we decided to adopt the core-offset splicing technique as our main fabrication method and developed a programmable core-offset splicing platform based on the specialty fiber fusion splicers.(2)Based on the few-mode sevencore fiber(FM-SCF),a one-dimensional programmable core-offset splicing technique(controlling the rotation angle θ of the fiber)has been proposed.We successfully fabricated parallel six-channel Mach–Zehnder interferometers(MZIs)and achieved the integration of multiple sensing structures in one single fiber.Through the analysis of spectra,FM-SCF based device provided two sensing structures that can be used for practical measurement.In this device,the temperature sensitivities are 105.8 pm/°C for the outer core 1 and 223.6 pm/°C for the outer core 2,and the strain sensitivities are 13.96 pm/με for the outer core 1 and 11.7 pm/με for the outer core 2,respectively.Making use of two channel responses and the dual-parameter demodulation principle,we successfully realized the discriminative measurement of temperature and strain.This FM-SCF based device has advantages of simple structure,high integration,high sensitivities and wide measuring range,which is promising in the discriminative dual-parameter measurement.(3)In order to make full use of all the channels in MCF,we proposed a three-dimensional programmable core-offset splicing technique with higher controllable range and precision.In addition to the angular displacement of the fiber,this three-dimensional technique also introduced the fiber displacements in the X-axis direction and Y-axis direction individually.By using this technique,we successfully fabricated seven paralleled MZIs in one seven-core fiber(SCF).By analyzing the transmission spectra,the SCF-based device provided four parallel sensing channels that can be used for practical measurement and we measured the temperature and strain sensitivities of MZIs in two of the channels.What’s more,this device can also be utilized for the simultaneous measurement of temperature and strain.If the other two channels can be fully utilized,the device is expected to achieve discriminative measurement of more environmental parameters.This has broad application prospects in the field of multi-parameter measurement.