Research On Optical Mode Converter And Optical Fiber Multiparameter Sensor

The MDM(Mode Division Multiplexing)is one of the most promising methods for increasing the single-fiber optical communication capacity.Mode converters are key technologies in MDM systems and OAM(Orbital Angular Momentum).Mode converters in MDM is applied to mode multiplexer and mode demultiplexer.In OAM,the mode converters are used to motivate mutual orthogonal modes that do not interfere with each other and can be used as independent channels.The communication structure that supports wavelength division multiplexing and mixed multiplexing is the key to achieving high-capacity all-optical transmission networks.The existing mode converter works in a single band.In the field of mode control,mode converters,mode filters,and mode filters supporting multi-wavelength and wide-band wavelength tunable modes are technical difficulties.In order to enhance the combination of the MDM and the current WDM(Wavelength Division Multiplexing)and compensate the high insertion loss of the space mode converter,this paper starts from the all-fiber mode converter to build multi-wavelength,wide-band wavelength and wavelength tunable mode converters.All-fiber mode converters based on few-mode fibers were developed by laboratory-owned MCVD(Modified Chemical Vapor Deposition)equipment.The production process of the acousto-optic device is optimized with experimentally studied,and an acousto-optic wavelength tunable mode converter based on few mode fiber is fabricated.Based on the wideband mode coupling and mode filtering characteristics of tilted long period fiber gratings,a simple multi-wavelength mode filter and wideband mode converter were designed.A multi-parameter fiber-optic sensor based on mode converter is designed and developed,and a self-product enhancement mode detection algorithm for fiber mode field is proposed to solve the difficulties in high-efficiency processing of recognition accuracy of optical mode field changes.The innovation results of this paper are as follows:1.In-depth analysis of the optical power loss caused by the coupling between different azimuth modes with different tilt angles in long-period dual-mode fiber gratings.The structural parameters of the tilted long period fiber gratings were optimized,and the optimal tilt angle range was 86o-87o.All-fiber mode converters with different functions in C-band and L-band were designed,including wideband mode converters,multi-wavelength band-stop mode converters,and high efficiency mode converters with 99.9%purity.2.Optimize the component selection and assembly process of piezoelectric generator-based sound wave generators.Optimized and analyzed a new process for preparing passive and active few-mode optical fibers using MCVD.It has been found that a new type of clad doping technique can be used to prepare a higher absorption erbium-doped fiber under the condition of a common doped germanium.The selection of piezoelectric ceramics in acoustic wave generators is discussed.The influence of the material selection of the tapered acoustic transducer on the output mode coupling efficiency caused by the acoustic impedance mismatch was analyzed.For the first time,discover and experimental verify that the main factors of transmission loss in acoustic waves is not the angle but the area of cone tip.In the experiment,a mode converters were built using self-made double-clad few-mode optical fibers and home-made sound wave generators which cover the C-band and L-band and the single-mode conversion operating wavelength region also exceed 20 nm.3.The mode excitation in IMI(insulator-metal-insulator)and MIM(metal-insulator-metal)composite waveguides is analyzed.Asymmetric plasma mode and asymmetric photon mode are simultaneously excited in the MIM mode.Image analysis is performed and the characteristics of the solution are obtained.For the first time,an algebraic solution method is used to solve the simultaneous excitation of the asymmetric plasma mode and the asymmetric photon mode in the MIM model,and an approximate analytical solution that is more suitable for computer programs is obtained.The forward and backward mode excitation and the normalized energy flow density distribution under different dielectric constants were analyzed.A forward and backward mode converter based on a silica-graphene MIM metamaterials structure was designed and simulated.4.For the first time,an ultra-wideband mode trapper based on a silica-graphene IMI type gradient trapezoidal metamaterial waveguide was proposed.The anisotropic effective dielectric constant distribution of gradient trapezoidal composite waveguides at different chemical potentials and wavelengths was analyzed.The phenomenon of mode trapping caused by the degeneracy of the forward and backward modes with negative refractive index was analyzed,and the distribution of the energy flow density in trapping was simulated.The mode tapping band reaches 400 nm wide at single voltage.For the first time,an ultra-wideband absorber based on a polyimide-graphene IMI gradient trapezoidal metamaterial structure was proposed.The absorption of the forward mode and reflection mode in a graded trapezoidal metamaterial waveguide are analyzed.The phenomenon of absorption induced by the mode trapping phenomenon was analyzed,and the distribution of energy flow density was simulated.The mode absorption band reaches 350 nm wide at single voltage.5.For the first time,a dual axial displacement and rotation detection sensor was proposed based on the identification of mode field profile changes.Using the asymmetric LP11 mode excited by the mode converter,the displacement and rotation of the environment are detected.For the experimental platform,multiple measurements were performed on each 50 ?m displacement on x-y axis,0°-180°angle range.The speed of the image processor was able to dynamically map the displacement pattern.The maximum angle sensor accuracy was 15 pixels/degree,and the displacement sensor accuracy was 5 Pixels/microns.Using the third-order enhanced self-integration algorithm can make the angular maximum measurement error range less than 11%.The stress error is less than the measurement error when applied parallel strain from 100 ?? to 1500 ??.6.For the first time,an image recognition algorithm based on the mode field enhancement is proposed for the detection of dual axis displacement and rotation.Specially based on the optical fiber mode field distribution to give the image processor feature learning process to enhance the processing efficiency.Solve the difficulty of high-efficiency processing of high-speed image data in optical model field recognition.In the backward mode field image test with 4 sensing amounts,the operation rate reached 60 frames/second The operation rate in the laser image test reached 12 frames/second.For the first time,a self-calibrating zeroing algorithm was proposed to reduce the angular maximum measurement error range from 11%to 3%.