| In the optical communication system, the magneto-optic crystal is the most important part of magneto-optical devices, such as magneto-optic modulator, magneto-optic isolator, magneto-optic circulator and so on. The optical characteristics of the magneto-optic crystal will influence the working performance of the devices. In order to improve the performance of magneto-optical devices, the most important method to obtain the ideal purpose is to research the optical characteristics of the crystals. In these latter years, many new magneto-optic materials have been produced. So the research on these new materials is becoming more and more important.We collected and analyzed the overseas and domestic sufficient date for the optical characteristics of magneto-optic crystal. Then we bring forward a research topic in varying magnetic field on some crystals optical characteristics such as the angle of rotation, the depolarization ratio and so on. As we know the theoretical basis of all magneto-optical devices are various kinds of magneto-optic effect, the changes of these optical characteristics will be influenced by the variation of the external magnetic field. So, our research will benefit the improvement of Faraday polarization rotation apparatus at all aspects such as selecting material, manufacture, optimizing their working performance and so on. The work is significant for the advance of all kinds of magneto-optical devices.The thesis includes four sections. The theory on magneto-optic effect and the course of the research onmagneto-optic crystals are discussed in the first chapter. Being based on these, the idea of measuring the optical characteristics in varying magnetic field is brought about.In the second chapter, we explain the basic knowledge on magneto-optic effect and the progress of the magneto-optic materials in detail. First, the theory of Faraday effect, magnetic circular dichroism, magnetic linear birefringence and Kerr effect are argued. Then the kinds of the magnetic materials and the magneto-optical devices are discussed.In order to measuring the changes of optical polarization in magneto-optic crystals, it is necessary to establish an optical system in which the changes can be measured. So the third chapter focuses on the measuring system. The operating principle (Light extinction method), the factors which influence the result and the resolvent to avoid them are explained. The experimental procedure is also introduced. To satisfy the experiment request, the equipment generating magnetic field and the angular instrument are improved. For light wave from semiconductor laser is infrared wave in the experiment, the calibrating measurement utilizing visible light from He-Ne laser is used. Firstly the light path is adjusted using visible light roughly. Then it is adjusted accurately when the semiconductor ( =1. 53 m) is used.The fourth chapter is the core of this thesis. In the magnetopolarization measuring system, we have measured three kinds of magneto-optic crystals. The three kinds of crystal are BiCaInVIG (coming from Institute of physics , Chinese Academy of Sciences), Bi-YIG and GdYBiIG (coming from Zhejiang University). The experiment has been finished at two parts.Firstly, in the magnetic field varying from 0mT to 1200mT, we have tested the Faraday rotation angle of the three kinds of crystals. At different aspects such as nonlinear aspects, the influence on rotation angle caused by coating the crystals and inclining them the experiment has been finished. And the experiment achieved the following results: 1. The nonlinear curves on the Faraday rotation; 2. The comparison curves of the rotation angles between uncoated and coated samples. 3. The comparison curves of the rotation angles between the just and inclined samples. And the theoretic explanation is also given, too. Secondly, depolarization ratio on these crystals has been measured. On BiCaInVIG crystal, we have achieved the depolarization ratio curves when they are just and inclined. And We only measured the depol... |
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