Thin-film magnetless Faraday rotators for compact heterogeneous integrated optical isolators

This report describes the fabrication, characterization, and transfer of ultra-compact thin-film magnetless Faraday rotators to silicon photonic substrates. Thin films of magnetization latching bismuth-substituted rare-earth iron garnets were produced from commercially available materials by mechanical lapping, dice polishing, and crystal-ion-slicing. Eleven-μm-thick films were shown to retain the 45° Faraday rotation of the bulk material to within 2° at 1.55 μm wavelength without re-poling. Anti-reflection coated films evince 0.09 dB insertion loses and better than –20 dB extinction ratios. Lower extinction ratios than the bulk are ascribed to multimode propagation. Significantly larger extinction ratios are predicted for single-mode waveguides. Faraday rotation, extinction ratios, and insertion loss tests on He-ion implanted slab waveguides of the same material yielded similar results. The work culminated with bond alignment and transfer of 7 μm-thick crystal-ion-sliced 50 × 480 μm2 films onto silicon photonic substrates.