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

Abstract

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 ( ${\rm d}n/{\rm d}T$ ) and the magneto-optical coefficient ( ${\rm d}\theta _f /{\rm d}T$ ) of a magneto-optical garnet Ce:YIG, and estimated these as $9.1 \times 10^{-5}$ K−1 and 44 ${\rm }^\circ \cdot {\rm cm}^{- 1} \cdot {\rm 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.