Research On The Key Technologys Of All-Fiber Current Transformer Based On Bi-GdYIG Thin Films

All-fiber current sensor is the ultimate development goal in the area of traditional current sense of optical application,and it gets widespread attention because it can make up for many shortcomings of the electromagnetic current transformers.However,there are some problems in all-fiber current sensors so that they are unable to use in practice.This dissertation focused on the key theory and techniques of all-fiber current sensor,and it aimed at the solutions of two major problems that restrict its functionization: research on the low sensitivity of all-fiber current sensor and the poor stability in long-term running.The sensitivity is improved by improving the property of magneto-optical media of the sensor.The stability of the sensor is improved by designing the architecture of film sensor which is able to sense the current with non-surround film sensor and fiber ring cavity optical structure.In this thesis,the research results on the theory and algorithms was described comprehensively,and the method to solve the problems was put forward.The innovations in the thesis include three aspects as follows.Firstly,we started to improve the magneto-optical media of the sensor by demonstrating a way that using Bi-GdYIG as magneto-optical sensing materials to improve the sensitivity of all-fiber current sensor.For YIG,the doped atomic percentage of Bi is 30% and Gd is 15% which are figured out by the first principle,the changes of optical properties of material have the same rule with YIG.Investigation on Bi-GaYIG has provided a theoretical basis for choice of doped percentage of Bi-GdYIG target and the thin films.Secondly,the experiment was verified by coating the magneto-optic material on the glass substrate when the doped percentage of Bi is 30% and Gd is 15%.Meanwhile a scheme of the magneto-optical film sensor based on micro-nano fiber structure was proposed.It can solve the problems that the stability of current sensor is poor in long-term running such as external factors like vibration.The scheme of improved sensor was put forward to come across the poor stability when the sensing current is surrounded by the sensing fiber for many times..The scheme follows the principle of total reflection.The light is in the form of passing through the magneto-optical film many times,the sensor is made to pass through the measured current only one time,so it can avoid the instability of the scheme caused by surrounding the measured current of the sensing fiber many times.In the experiment,the paper doped Bi-GdYIG on the micro-nano fiber,then doped metal particles.The light passes through the magneto-optical film sensor,it replaces the method of surrounding the measured current of the sensing fiber to achieve the goal of sensing the current by non-surrounded way.The stability of the scheme is improved.Meanwhile the method of passing through the sensing media of the light is able to make up the problem of reduced sensitivity of reduced thickness of magneto-optical media of the film sensor.Simultaneously,experiment discipline exploration is achieved by doping the BiGdYIG on the glass substrate,and the sensor which is doping the Bi-GdYIG on the micro-nano fiber is created by the discipline.The structure makes it possible to use all-fiber in the optical fiber current sensor,and it can obtain a higher stability in the system.Finally,annular ring-down all-fiber current sensor based on Bi-GdYIG film micro-nano fiber is demonstrated,the design not only provides the stability of the sensor but also obtains a higher sensitivity.For proposing scheme,we analyzed the optical path of straight-through ones and reflective ones by Jones matrix,the system models of all-fiber current sensors of the two structures were created by Optisystem,the sensitivity of the two structures is also analyzed and verified by experiment.The analysis shows the straight-through optical path has the advantage of good stability in long-term running,and the reflective one has the advantage of high sensitivity.Based upon,we proposed an improved scheme of annular ring-down all-fiber current sensor,the scheme introduced annular ringdown fiber based on straight-through optical path,so it has both the advantage of straight-through optical path and the same transmission rules of reflective ones.And the feasibility was verified by experiment.Through the theory and experiment,the all-fiber current transformer scheme of sensor based on Bi-GdYIG film micro-nano optical fiber and the annular ringdown all-fiber current sensor we proposed can solve the problems of low sensing accuracy and poor stability of long-term running such as external factors like vibration.A new solution is provided for the application of all-fiber current sensor in practice.