Preparation Of Rare Earth Iron Garnet Film/bulk Crystal Composite Structure And Its Magneto-optical Properties In Optical Communication Band

The developments and present situation of magneto-optical materials, especially about rare earth (RE) iron garnets, were reviewed. The application of magneto-optical materials in optical communication devices was put on emphasis to introduce. Advances of high speed and mass scale optical communication systems required magneto-optical materials on higher performance of bandwidth and stable temperature properties. One solution was referred that combining two kinds of rare earth iron garnets with different signs of Faraday rotation wavelength coefficient (FWC) and Faraday rotation temperature coefficient (FTC) to prepare a bismuth-substituted compounded RE iron garnet bulk crystal TbYbBiIG with low FWC and FTC, a thin garnet single crystal film TbBiGaIG with compensation temperature was grown on the bulk crystal TbYbBilG substrate. The FTC of bulk crystal substrate may be improved by that TbBiGaIG film.This kind of composite structure materials was hoped to be a kind of magneto-optical materials with smaller FWC and FTC at the same time.A series of compound RE bismuth-substituted iron garnet (TbYbBi)₃Fe₅O₁₂ bulk crystal were grown by the modified flux method using Bi₂O₃ as main flux. The crystal structure and composition were characterized by XRD and EDS, respectively. The growing condition and raw materials mole-ratio were studied and then obtained. Afterwards, on the substrate of bulk crystal (TbYbBi)₃Fe₅O₁₂ directed in (110), bismuth-substituted RE iron garnet TbBiGaIG film was grown by the LPE method using PbO as flux. The film structure and growth condition were studied by XRD and SEM. A homemade apparatus was set up to test the Faraday rotation in the optical communication band of the wavelength range from 1500nm to 1620nm. The magneto-optical properties including FWC and FTC, specific Faraday rotation, optical absorption loss and saturation magnetization were investigated for both TbYbBilG bulk crystal and TbBiGaIG film/TbYbBiIG bulk crystal composite structure.It was found that the bismuth- substituted compounded RE iron garnet TbYbBilG bulk crystal prepared through combining two RE iron garnets (TbIG and YbIG) with opposite signs of FWC and FTC, were of low FWC and FTC, low saturationmagnetization, large specific Faraday rotation angles and small optical absorption loss. It was found that, as for TbBiGaIG film/ TbYbBilG bulk crystal composite structure, a thin TbBiGaIG film with compensation temperature located in the center of the operation temperature range reduced significantly FTC of the substrate. Meanwhile this TbBiGaIG film was so thin that it could not nearly affect other magneto optical properties. As a result, this kind of film/crystal composite structure materials could be applied to the broadband and temperature-stable devices in the optical communication.