Study On The Cerium Substituted Yttrium Iron Garnet Magneto-optical Thin Films And Its Application

The advantage of optical information transmission and processing are obvious. But one of the most important problems for optical communication systems in general and for photonic integrated circuits (PICs) in particular is the elimination of reflected signals in laser resonators, optical interconnections and links of various optical elements. Reflections lead to parasitic oscillations which cause frequency instabilities and limit the modulation bandwidth. Optical isolators are nonreciprocal magnetooptic devices that prevent these problems by transmission signals in one direction which blocking them in reverse direction. Compared with bulk devices, Integrated optical (IO) isolators have many advantage, such as well guided light, low magnetic field requirements, low cost and the compact integration. But IO isolators are still far away from practice. The recently research activities focused on two aspects: one is continued search for new effective isolator concepts; the other is to find the smart materials with improved nonreciprocal properties. The basis of nonreciprocal behavior is the Faraday effect, which can be controlled by varying composition and substitutions.Magnetic garnets, which have low optical absorption and high Faraday rotation in near infrared window of transparency of optical fibers, meet the requirement of IO isolators. The Faraday rotation, which is the basis for nonreciprocal effects, can be enhanced greatly by cerium (Ce) substituted yttrium iron garnets (YIG). Ce substituted YIG have largest Faraday effect, are becoming the most promising candidate materials for IO isolator applications. The origin of Faraday effect of Ce substituted YIG (Ce:YIG) is discussed with microscopic theory, the formula for Faraday rotation is obtained. It is found that the amount of magnetooptic active Ce ions, energy level splitting, oscillator strength of electric dipole transition, and so on can influence the Faraday effect, it is confirmed that Ce3+ ions greatly enhanced magnetooptic Faraday effect. Also it is found that the temperature dependence of Faraday effect.The theoretic study of optical absorption reveals, the intrinsic optical absorptionof pure YIG due to crystal field transitions is very low, Gaussian fitting method is used to estimate the Ce contribution to the optical absorption, the fitting requires that the absorption near IR region is ascribed to two electronic transitions, which centered at and , respectively. The observed absorption is mainly ascribed to Ce3+-Fe3+ (tet) charge transfer transitions. The Ce1YIG ceramic powders with precise composition are obtained by coprecipitation method in order to make sputtering target. The precipitation process can be well controlled by adjusting pH value and adding surfactant. Some technical obstacles, such as the dissolve of yttrium oxide, agglomeration and separated precipitation are overcome. The optimized synthesizing conditions are as follows: pH value fall in range of 8~9, the temperature is 50℃. It is proposed to characterize the phase structure of Ce1YIG with IR spectra for the first time. The Ce ions in Ce1YIG distort the structure of YIG and cause the multi-peaks splitting of IR spectra. The weak magnetism is observed before the formation of YIG phase, then after the formation of YIG, the strong magnetism is observed.Energy band theory model (EBT) for Ce1YIG system is proposed, some new electronic traps are introduced due to the doped Cerium in Ce1YIG crystal, so the charge transfer transitions are changed. With this EBT model, we successfully predicts how to optimize post annealing conditions and get the giant magnetooptic Ce-substituted YIG thin films for waveguide applications.The preparation of crystalline Ce1YIG on amorphous silica substrate by RF magnetron sputtering method includes two steps: the amorphous thin films are prepared by RF magnetron sputtering, and then the thin films are crystallized by post annealing process. For the sputtering process, RF power density is the key factor to influence quality of thin films. Duri...