An optical isolator includes first and second optical splitter-combiners disposed within a semiconductor die. The optical splitter-combiners are coupled together into an interferometer configuration by first and second waveguide sections also disposed in the semiconductor die. A non-reciprocal optical phase shift element is disposed within the semiconductor die and includes the first waveguide section passing through the non-reciprocal optical phase shift element. The optical isolator is configured such that forward propagating waves are constructively recombined by the second optical splitter-combiner while reverse propagating wave are destructively recombined by the first optical splitter-combiner.