Research On Development And Application Of All-optical Phase Modulator Based On Optical Microfiber

One of the main demodulation methods of fiber optic hydrophone system is PGC demodulation technology,which requires a device that can generate phase carrier,so the phase modulator directly determines the system performance and has important research value.Aim at the practical application demand of PGC demodulation system of fiber optic hydrophone.In this paper,OM(Optical Microfiber)was selected as the study subject,a new all-optical phase modulator is designed according to the application requirements of practical engineering by combining theoretical analysis with experimental testing.And the relevant research is finished.The main research contents are as follows:(1)Contrast electro-optic,thermo-optic and elastic-optic modulators.The advantages and research necessity of all optical modulator in the application of fiber optic hydrophone are discussed.The advantages and disadvantages of silicon based all-optical modulator,two-dimensional material or other special materials combined with OM are compared and summarized.(2)Starting from the modulation mechanism analysis of modulator,the photo-induced thermal phase shift effect in optical fiber is discussed and extended to OM.It is concluded that this effect is related to the uniform waist area diameter and length of OM.The shape parameters of OM are analyzed by studying its forming process.The thermal diffusion model is established with FEM(Finite Element Method)software,and the optimization rule of the modulator phase response is theoretically obtained: the photo-induced thermal phase shift effect in OM is inversely proportional to the uniform waist area diameter in a range,and directly proportional to the waist area length.(3)The PGC(Phase Generated Carrier)demodulation algorithm is discussed.Firstly,the advantages and disadvantages of PGC-DCM method and PGC-Atan method are analyzed,and PGC-Atan method is selected as the demodulation algorithm used in this paper.Then two important parameters C value and time delay of the system are discussed.In addition,compared with achieving demodulation scheme by circuit design.In this paper,the data acquisition card driver and demodulation algorithm are realized by using related functions in Matlab,and the GUI(Graphical User Interfaces)function is used to build user operation interface.A digital demodulation algorithm is obtained which is easy to debug and operate,to prepare for subsequent experiments.(4)On the basis of the above research,the PGC demodulation system of fiber optic hydrophone is taken as the main idea to build an experimental system and carry out relevant experimental tests.I prepare OM firstly.OM with waist length of 10 mm,12 mm and 15 mm was prepared,the above three parameters corresponding to waist diameter of 1.4 μm,1.6 μm and 1.8 μm,respectively.These nine samples were tested in the experimental system.It can be concluded that a larger phase response can be obtained in a certain range by increasing the length of the uniform waist area of OM or decreasing the diameter.(5)The length and diameter of the uniform waist area of OM are 15 mm and1.4 μm respectively.The modulation amplitude of OMAOPM(Optical microfiber all-optical phase modulator)can reach 1 rad,which can be used in fiber optic hydrophone systems and meet basic requirements.The demodulation test of underwater acoustic simulative signal is carried out by using the system.Taking low frequency signals of 1 k Hz and 170 Hz as an example,the experimental results show that the designed OMAOPM system can demodulate underwater acoustic(vibration)signals below 1 k Hz well.(6)For the special shape of OM,quartz tube groove was designed and customized for packaging,and OM hydrophone probe was designed.The all-optical phase modulator designed in this paper has the characteristics of low cost,simple fabrication and convenient coupling with optical fiber system,which provides a new solution to the existing engineering problems.