Waveguide-based 1.5 μm optical isolator based on magneto-optic effect in ferromagnetic MnAs

We developed a 1.5-mu m-band, transverse-magnetic-mode waveguide isolator based on the nonreciprocal-loss phenomenon. The device consists of an optical waveguide with an InGaAs/InGaAlAs multiple-quantum-well amplifier and a ferromagnetic MnAs layer attached to the waveguide. The combination of the optical waveguide and the magnetized MnAs layer produces a magneto-optic effect called the nonreciprocal loss-a phenomenon where the propagation loss of light is larger in backward than in forward propagation. We present the guiding principle of the design of the structure of the device. A prototype device with a MBE-grown epitaxial MnAs layer showed a nonreciprocity of 9.8 dB/mm, at a wavelength of 1.54 mu m. Our device can be monolithically integrated with waveguide-based optical devices on an InP substrate.