Study on ion slicing of iron garnet magneto-optic materials for near and mid-infrared on-chip optical isolators

Achieving high-crystalline-quality, large-size iron garnet magneto-optic (MO) films on silicon substrates remains a critical challenge in the development of CMOS compatible on-chip non reciprocal devices, such as isolators, circulators, etc. In this study, we explored ion slicing on commercial yttrium iron garnet (YIG) crystals, bismuth-doped iron garnet (BIG), and newly developed YIG ceramics. After He+ ion implantation, wafer bonding and annealing, the silicon-based BIG film was successfully fabricated, but its thickness and crystalline phase deviated from expectations. The underlying causes of these discrepancies were systematically investigated. In contrast, the YIG single crystals and ceramics showed blistering during annealing, which validates the potential of ion slicing for both materials. For the development of on-chip isolators at 1.55 and 2.1 μm, the nonreciprocal phase shift (NRPS) of the silicon-based BIG films reached 1410.97 rad/m and 251.32 rad/m, respectively, which are approximately 400% and 26% higher than those of YIG films. Based on these findings, we designed a TM-mode on-chip isolator using silicon-on-insulator (SOI) with an asymmetric Mach-Zehnder interferometer (MZI) structure, anticipated to achieve maximum isolation bandwidths of 62 nm at 1.55 μm and 84 nm at 2.1 μm, offering a practical solution for near- and mid-infrared on-chip isolators.