The effect of terbium on the optical dispersion and magneto-optical properties of YIG crystals grown by flux-Bridgman method

Abstract

R3Fe5O12 (RIG) crystals are the key elements for magneto-optical isolators in the near-infrared (NIR) to mid-infrared (MIR) region, with ever-growing demands for integrated photonics. However, the growth of high-quality single crystals is still a big obstacle. The effect of rare earths on the optical and magneto-optical properties of YIG crystals is not well understood. Herein, a series of high quality Tb3+ doped yttrium iron garnet (Y3-xTbxFe5O12, x = 0, 0.5, 1.0, 1.5, 3.0) crystals have been successfully obtained by the flux-Bridgman method, with sizes over 20 mm. Tb:YIG crystals reserve typical cubic garnet structure, with spatial group of Ia3d. The lattice constants increase from 12.377 Å (YIG) to 12.448 Å (TbIG). The refractive index decreases from 2.38 (500 nm) to 2.11 (2500 nm) for YIG crystal, and it reduces from 2.51 (500 nm) to 2.17 (2500 nm) for TbIG crystal. The optical dispersion of the refractive indices was well fitted by the Wemple and DiDomenico (WDD) and the Sellmeier models, respectively. Relatively lower values of the absorption coefficient of the Tb:YIG crystals confirm the high transparency in the NIR region. The characteristic absorption of Tb3+ was observed from 1700 nm to 2500 nm. The specific Faraday rotation angles (θF) of both YIG and TbIG decrease with increasing wavelength, reaching 235.4 and 366.5 °/cm at 1300 nm, respectively. Compared with that of YIG, θF of TbIG crystal shows stronger wavelength dependence. This work provides more insight into the role of rare earths on the optical and magneto-optical behavior of RIG crystals, which will accelerate the design of high-performance magneto-optical crystals for application in NIR-MIR wavelength.