Interaction between light and magnetism in magneto‐optical (MO) nanophotonic devices has been actively studied in the past few years. The recent development of MO all‐dielectric resonators and metasurfaces has led to the emergence of various novel MO phenomena that were not observed in their bulk counterparts. For example, a large s‐polarized transverse MO Kerr effect can be observed at magnetic resonance wavelength, which cannot exist in the bare MO films. We review recent developments in nanophotonic devices based on MO materials and focus on different modes and related MO effects in nanophotonic structures with emphasis on recently discovered new MO phenomena in magnetoplasmonics and all‐dielectric nanostructures, such as dark mode, all‐dielectric Mie resonance and waveguide mode. Further, we discuss the potential applications of these nanostructures for biological/chemical sensing, magnetic field sensing, and magnetic field‐controlled active and nonreciprocal metasurfaces.

Active metasurfaces, in which the optical property of a metasurface device can be controlled by external stimuli, have attracted great research interest recently. For optical switching and modulation applications, high‐performance active metasurfaces need to show high transparency, high power efficiency, as well as ultrafast switching and large‐scale fabrication capability. This paper reports Au/VO ₂ ‐based active metasurfaces meeting the requirements above. Centimeter‐scale Au/VO ₂ metasurfaces are fabricated by polystyrene sphere colloidal crystal self‐assembly. The devices show optical modulation on‐off ratio up to 12.7 dB and insertion loss down to 3.3 dB at 2200 nm wavelength in the static heating experiment, and Δ T / T of 10% in ultrafast pump‐probe experiments. In particular, by judiciously aligning the surface plasmon resonance wavelength to the pump wavelength of the femtosecond laser, the enhanced electric field at 800 nm is capable to switch off the extraordinary optical transmission effect at 2200 nm in 100 fs time scale. Compared to VO ₂ thin‐film samples, the devices also show 50% power reduction for all‐optical modulation. Our work provides a practical way to fabricate large‐scale and power‐efficient active metasurfaces for ultrafast optical modulation.

Magneto-optical isolators are key components in photonic systems. Despite the progress of silicon-integrated optical isolators, the Faraday rotation of silicon-integrated magneto-optical materials, such as cerium-doped yttrium iron garnet (Ce:YIG), show a strong temperature dependence, limiting the temperature range for integrated nonreciprocal photonic device applications. In this work, we report dysprosium substituted Ce:YIG thin films (Dy₂Ce₁Fe₅O₁₂, Dy:CeIG) showing a low temperature coefficient of Faraday rotation. A temperature insensitive range of the Faraday rotation is observed in between 25 °C to 70 °C for this material, compared to 20% variation of the Faraday rotation in Ce:YIG thin films. A Dy:CeIG based temperature insensitive silicon-integrated optical isolator operating in the temperature range of 23 °C to 70 °C is experimentally demonstrated.

A low loss optical interconnection between optical fibers and photonic integrated circuits is critical for high performance photonic systems. In the past decade, spot size converters, subwavelength waveguide grating (SWG) structures, and different refractive index materials have been applied to allow efficient coupling between the fiber and the photonic chips. However, it is still challenging to achieve low-loss coupling when interfacing high index contrast waveguides such as SiN with SMF-28 fibers. In this work, we report a multilayer edge-coupler using SiO_xN materials with different indices to allow for efficient edge coupling between SMF-28 fiber and SiN single mode waveguides. A coupling loss of 0.068 dB for the TM mode was achieved theoretically at a 1550 nm wavelength, with a 1 dB alignment tolerance offset of 2.4 μm.