Development of optical grade polycrystalline YIG ceramics for faraday rotator

Abstract Fully dense and infrared transparent YIG (Y 3 Fe 5 O 12 ) ceramics was successfully produced by solid‐state reaction of Y 2 O 3 and Fe 2 O 3 powders. Its relative density reached 99.8% (5.16 g/cm 3 ) after sintered at 1400°C for 3 hours, and almost 100% relative density (5.17 g/cm 3 ) was obtained by additional HIP treatment. It was transparent at wavelength ranges longer than 1100 nm, and its in‐line transmittance (ca. 75%‐77%) was very comparable to that of commercial YIG single crystal especially over 1700 nm. Faraday rotation angle at 1300 and 1550 nm was 224 and 175 deg/cm, respectively, and extinction ratio was 35 dB and insertion loss polarized at 45° was 0.3 dB at 1550 nm. It was confirmed that the Faraday effect of polycrystalline material which has numerous grain boundaries and randomized crystal orientations is analogous to that of the single crystal. To the best of our knowledge, this is the first report to achieve highly transparent polycrystalline iron garnet ceramics successfully, and it is expected to use as an optical isolator in optical communication and medical field.