Integrated optical isolators have been a longstanding challenge for photonic integrated circuits (PIC). An ideal integrated optical isolator for PIC should be made by a monolithic process, have a small footprint, exhibit broadband and polarization-diverse operation, and be compatible with multiple materials platforms. Despite significant progress, the optical isolators reported so far do not meet all these requirements. In this article we present monolithically integrated broadband magneto-optical isolators on silicon and silicon nitride (SiN) platforms operating for both TE and TM modes with record high performances, fulfilling all the essential characteristics for PIC applications. In particular, we demonstrate fully-TE broadband isolators by depositing high quality magneto-optical garnet thin films on the sidewalls of Si and SiN waveguides, a critical result for applications in TE-polarized on-chip lasers and amplifiers. This work demonstrates monolithic integration of high performance optical isolators on chip for polarization-diverse silicon photonic systems, enabling new pathways to impart nonreciprocal photonic functionality to a variety of integrated photonic devices.

We report the magnetic proximity effect (MPE) and valley non-degeneracy in monolayer MoS and magnetic semiconductor EuS thin film heterojunctions studied by density functional theory (DFT) with the vdW-DF2 correlations. Magnetic moments are observed in MoS due to the MPE when forming chemical or van der Waals (vdW) adsorption states with EuS. Spin-orbit coupling (SOC) leads to observable valley non-degeneracy of MoS at the K (K') points in the Brillouin zone. The valley Zeeman splitting energy E can reach 5.1 meV and 37.3 meV for the vdW and chemical adsorption states, corresponding to a magnetic exchange field (MEF) of 22 T and 160 T respectively. By applying a gate voltage across the MoS/EuS interface, it is found that E can be tuned from 1.8 meV to 8.2 meV and from 24.5 meV to 53.8 meV for vdW and chemical adsorption states respectively. The strong MPE, large and tunable valley degeneracy in 2D material and ferromagnetic semiconductor/insulator vdW heterojunctions demonstrate their promising potential for novel optoelectronic and valleytronic device applications.

On-chip optical isolators constitute an essential building block for photonic integrated circuits (PICs). Here, we experimentally demonstrated a magneto-optical isolator monolithically integrated on silicon featuring 3 dB insertion loss and 40 dB isolation ratio, both of which represent significant improvements over state-of-the-art. The isolator is also fully passive and operates under a simple unidirectional magnetization scheme. Such superior performance is enabled through a three-way combination of a strip-loaded waveguide design, a compositionally optimized chalcogenide glass as the light guiding medium, and low-loss taper structures created via gray -scale lithographic processing. The device represents an important step toward a practical solution for on-chip isolation in PICs.