PURPOSE:To produce crystal for optical isolator having good temp. characteristic in a high yield, by epitaxially growing a specified rare earth garnet crystal on a substrate by using garnet crystal having fixed thermal expansion coefft. as intermediate layer. CONSTITUTION:When the rare earth garnet crystal contg. Bi, of formula I (where, R is rare earth element and M is Al, Ga, Sc, In, Lu, etc.) is epitaxially grown on the garnet substrate, at least one or more layers are grown as follows: at least one or more layers are grown by using garnet crystal existing between the rare earth garnet contg. Bi above-mentioned and the garnet substrate, as intermediate layer. Further, when the compd. of formula II (where, 0.7=x=1.3 and 0=y=1.7) is used as intermediate layer, the crystal for optical isolator having very good temp. characteristic can be obtd., because the temp. change in Faraday rotation angle is the reverse of one of usual Bi-substitution garnet.
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