Athermal Operation of a Waveguide Optical Isolator Based on Canceling Phase Deviations in a Mach–Zehnder Interferometer

Optical isolators play unique roles in photonic circuits. We have developed an optical isolator with silicon waveguides, based on a Mach-Zehnder interferometer. The device characteristics were temperature dependent. We investigated the temperature dependence of the refractive index (dn/dT) and the magneto-optical coefficient (dθf/dT ) of a magneto-optical garnet Ce:YIG, and estimated these as 9.1 × 10-5K-1and 44° · cm-1· K-1, respectively. We discuss the design of an athermal silicon waveguide optical isolator, in which the temperature dependences of the magneto-optical effect and refractive indices are canceled in the backward direction. The high optical isolation, greater than 20 dB, is demonstrated for temperature in the 20-60 °C range.