Research On Microstructured Optical Fiber Sensors And OAM Devices Integrated With Functional Materials

Microstructured optical fibers are distinguished for their unique features such as flexible structure,high birefringence,and high nonlinearity.Compared with conventional optical fibers,MOFs have versatile refractive index distributions and arrangements of air holes,which greatly expands their applications areas.The presence of cross-sectional air holes provides the possibility to develop highly integrated MOF functional devices based on intergration of MOFs with functional materials.Addtionally,with the uprising of OAM-based optical communication technology and the breakingthrough progress of MOF fabrication technique,OAM devices based on MOFs integrated with functional materials provides ideal solutions to the design and applications of tunable OAM functional devices.In this thesis,through combination of MOFs with functional materials,optical sensing devices based on the meachinsms of Mach-Zehnder interference and resonance coupling are proposed and fabricated.In addition,an OAM light generator based on air-clad MOFs integrated with liquid crystals is designed,and mechanically induced fiber gratings are fabricated for the generation of OAM light with tunable operation wavelength and bandwidth.And finally,an OAM dual-parameter sensing device is designed based on the combination of Mach-Zehnder interferometer with functional materials.Main contents of this study includes the following aspects:1.A Mach-Zehnder interferometric sensor based on hollow core fiber capillary is proposed for refractive index measurement.The influences of capillary length on sensor sensitivity have been studied,and the length of the silica capillary has been optimized.Due to the presence of azo functional group,azobenzene molecules would experience photo-induced isomerization and photo-induced orientation effects.By experimentally monitoring transmission spectral responses of EO-integrated RI sensor to the polarization state and power density of 473 nm laser,refractive index change of azobenzene materials induced by photo-isomerization effect has been measured.As the laser polarization angle is 0 degree,maximum sensitivity of EO solution is up to-1.753×10^-5/（m W/cm²）.As laser power density increases from 100 m W/cm² to 500m W/cm²,by varying polarization state of 473 nm laser,birefringence of EO solution increases from 0.0001 to 0.0012 accordingly.2.A high-sensitivity temperature sensor based on side-hole microstructured optical fibers integrated with refractive index liquids has been proposed and fabricated.By infiltrating high refractive liquids into the air holes of side-hole microtructured optical fibers,coupling between the core mode and liquid rod modes would occur,results in the emergence of multiple resonance dips in the transmission spectrum.Within a temperature range of 80℃ to 100℃,a temperature sensitivity of-13.1 nm/℃ has been experimentally achieved.In addition,by infiltrating magnetic-field-sensitive magnetic ion liquids into side-hole microstructured optical fibers,simultaneous measurement of temperature and magnetic field could be realized.Experimental results show that for the temperature range of 25℃ to 100℃ and the magnetic field intensity range of 20 Oe to 200 Oe,temperature and magnetic field sensitivities reach-3.466nm/℃ and-0.0303 nm/Oe,respectively.3.An OAM generator based on liquid-crystal-integrated air-clad microstructured optical fibers have been proposed.A ring-like air hole clad layer is located close to the outer surface of the microstructured optical fiber,and by infiltrating high refractive index liquid crystals into the air holes,periodic angular refractive index distribution could be introduced inside the WGM microresonator.When the phase matching condition is satisfied,coupling between the WGM at specific frequency and its corresponding OAM would occur.In this work,the influences of variations in geometric parameters of the air holes on frequency tuning range as well as central frequency of OAMs have been evaluated.Further simulations results indicate that by tuning of OAM frequency can be realized by controlling refractive index of liquid crystals.4.An OAM light generation scheme has been proposed by employing mechanically induced long-period grating in few-mode fibers fabricated based on 3D printing technique.Experimental results show that coupling efficiency between the core mode and LP₁₁ mode can be adjusted by applying different lateral forces on few-mode fibers,and thus to achieve tuning of resonance wavelength of the fiber grating.On the basis of the fiber grating with even refractive index perturbations,transmission spectral broadening of cascaded few-mode fiber grating has been further studied,and a 10-d B bandwidth up to 114 nm has been experimentally acquired.5.A dual-parameter sensing system based on silica-capillary-assisted Mach-Zehnder interferometer（SCAMZI）in combination with interrogation of OAM interferograms has been proposed.The SCAMZI integrated with temperature-sensitive liquids and refractive index liquids is introduced into the interference path of the Gaussian beam.Due to the variations in intensity and phase of the Gaussian beam caused by the change of refractive index and temperature,the intensity and rotation angle of the interferogram resulting from the interference between output light of SCAMZI and OAM light would change accordingly.And by performing PCA to the image matrix of the OAM interferogram,the information about variations in refractive index and temperature could be retrieved.