1. Field of the Invention
The present invention relates to a magnetic garnet single crystal and a method for producing the same as well as an optical element using the same.
2. Description of the Related Art
Faraday rotator is an optical element with a function to rotate the polarization plane of transmitting light and is used in optical devices such as optical isolator, optical attenuator, optical circulator and photo-magnetic field sensor for communication. Faraday rotator is generally prepared by using a plane-like bismuth (Bi)-substituted rare-earth iron garnet single crystal. The Bi-substituted rare-earth iron garnet single crystal is grown by the liquid phase epitaxial (LPE) process as one of flux processes. Single crystals are grown at atmospheric pressure by the flux processes.
In growing the Bi-substituted rare-earth iron garnet single crystal by the solution process (the LPE process) such as flux processes, generally, lead oxide (PbO), bismuth oxide (Bi2O3) and boron oxide (B2O3) are used as the solvents so as to stably grow such garnet single crystal while the solvents are maintained at their supersaturation states. During the growth of the magnetic garnet single crystal, therefore, a small amount of lead (Pb) contaminates in the resulting crystal. In Faraday rotators for use in optical devices for communication, magnetic garnet single crystals at a Pb content “y” of about 0.03 to 0.06 in the chemical formula Bi3-x-yM11xPbyFe5-z-wM12zM13wO12 have been used conventionally. See Patent Reference 1: JP-A-2001-044026; Patent Reference 2: JP-A-2001-044027; and Patent Reference 3: JP-B-6-046604.
Following the upsurge in the recent environmental protection movement, however, efforts are now directed toward the reduction of the content of Pb as an environmental load substance in any of industrial products. Therefore, a trace amount of contaminating Pb in magnetic garnet single crystals grown by the LPE process draws concerns as a factor of environmental pollution. Therefore, it is necessary to reduce or eliminate the amount of Pb contained in magnetic garnet single crystals as materials constituting Faraday rotators.