Nanocomposite Garnet-Enabled Monolithically Integrated Magneto-Optical Isolator Using an Asymmetric Mach–Zehnder Interferometer

High Resolution Image Download MS PowerPoint Slide Monolithically integrated magneto-optical (MO) isolators are crucial for photonic integrated circuits. We demonstrate an isolator based on an asymmetric Mach–Zehnder interferometer with 4.4 dB MO-loading insertion loss and an 18.7 dB isolation ratio at wavelengths between 1550 and 1570 nm, using a nanocomposite garnet film that achieves both large Faraday rotation and compatibility with silicon substrates. The garnet composite consists of ∼10 nm cerium-rich segregations in a single-crystalline cerium-substituted yttrium iron garnet (Ce:YIG) matrix with 1–5 μm-scale grains on silicon substrates. These results demonstrate the effectiveness of nanocomposite garnet films prepared by gradual annealing for realizing integrated magneto-optical isolators. The nanocomposite garnet film exhibited a Faraday rotation of −0.25°/μm, an optical absorption of −4.9 dB/cm, and an MO figure of merit of 510°/dB, four times greater than that of our previously reported polycrystalline Ce:YIG film.