Optical isolators and circulators are indispensable for photonic integrated circuits (PICs). Despite of significant progress in silicon-on-insulator (SOI) platforms, integrated optical isolators and circulators have been rarely reported on silicon nitride (SiN) platforms. In this paper, we report monolithic integration of magneto-optical (MO) isolators on SiN platforms with record high performances based on standard silicon photonics foundry process and magneto-optical thin film deposition. We successfully grow high quality MO garnet thin films on SiN with large Faraday rotation up to -5900 deg/cm. We show a superior magnetooptical figure of merit (FoM) of MO/SiN waveguides compared to that of MO/SOI in an optimized device design. We demonstrate TM/TE mode broadband and narrow band optical isolators and circulators on SiN with high isolation ratio, low cross talk and low insertion loss.In particular, we observe 1 dB insertion loss and 28 dB isolation ratio in a SiN racetrack resonator-based isolator at 1570.2 nm wavelength. The low thermo-optic coefficient of SiN also ensures excellent temperature stability of the device. Our work paves the way for integration of high performance nonreciprocal photonic devices on SiN platforms.

Integrated nonlinear metasurfaces leading to high-efficiency optical second harmonic generation (SHG) are highly desirable for optical sensing, imaging, and quantum photonic systems. Compared to traditional metal-only metasurfaces, their hybrid counterparts, where a noncentrosymmetric nonlinear photonic material is incorporated in the near-field of a metasurface, can significantly boost SHG efficiency. However, it is difficult to integrate such devices on-chip due to material incompatibilities, thickness scaling challenges, and the narrow band gaps of nonlinear optical materials. Here, we demonstrate significantly enhanced SHG in on-chip integrated metasurfaces by using nanometer thin films of ferroelectric Y:HfO2. This material has the merit of CMOS compatibility, ultraviolet transparency up to 250 nm, and significant scalability down to sub-10 nm when deposited on silicon. We observe a 20-fold magnitude enhancement of the SHG intensity from the hybrid metasurface compared to a bare ferroelectric HfO2 thin film. Moreover, a 3-fold SHG enhancement is observed from the hybrid metasurface compared to a control structure using nonferroelectric HfO2, demonstrating a major contribution to the SHG signal from ferroelectric Y:HfO2. The effective second-order nonlinear optical coefficient χ(2) of Y:HfO2 is determined to be 6.0 ± 0.5 pm/V, which is comparable to other complex nonlinear photonic oxide materials. Our work provides a general pathway to build an efficient on-chip nanophotonic nonlinear light source for SHG using ferroelectric HfO2 thin films.

Chiral nanophotonic devices are promising candidates for chiral molecules sensing, polarization diverse nanophotonics and display technologies. Active chiral nanophotonic devices, where the optical chirality can be controlled by an external stimulus has triggered great research interest.However, efficient modulation of the optical chirality has been challenging. Here, we demonstrate switching of the extrinsic chirality by applied magnetic fields in a magneto-plasmonic metasurface device based on a magneto-optical oxide material, Ce1Y2Fe5O12 (Ce:YIG). Thanks to the low optical loss and strong magneto-optical effect of Ce:YIG, we experimentally demonstrated a giant and continuous far-field circular dichroism (CD) modulation by applied magnetic fields from -0.65° to +1.9° at 950 nm wavelength under glancing incident conditions. The far field CD modulation is due to both magneto-optical circular dichroism and near-field modulation of the superchiral fields by applied magnetic fields. Finally, we demonstrate magnetic field tunable chiral imaging in millimeter-scale magneto-plasmonic metasurfaces fabricated using self-assembly. Our results 2 provide a new way for achieving planar integrated, large-scale and active chiral metasurfaces for polarization diverse nanophotonics. KEYWORDS: Magnetoplasmonic, Metasurface, Optical Chirality, Magneto-optical effectChirality describes the symmetry property of a structure, that its mirror image cannot be superimposed with itself through translation and rotation operations, like our two hands. The chirality of biomolecules is universal in our living body, such as amino acid and proteins, which has significance in biomolecules recognition. 1,2 However, the chiroptical signal of chiral biomolecules is very weak. Recently, chiral plasmonic 3,4 and all dielectric structures 5,6 with large chiroptical response have attracted great research interest. Benefitted from advanced nano-fabrication technologies, 3D or planar chiroptical nanostructures, such as helices, 7,8 shurikens, 9 gammadions, 6,10 and twisted split-rings 11 have been fabricated. On the other hand, extrinsic chirality can also be observed in achiral photonic nanostructures under obliquely incidence conditions. The extrinsic chirality is originated from asymmetric distributions of electromagnetic fields, i.e. the electromagnetic near field distribution is chiral. 12 Nanophotonic structures such as nanoholes, 12 squares 13 and split ring resonators 14,15 showed large extrinsic chirality. For instance, Ben et al.demonstrated a ~4 times stronger optical chirality in achiral periodic nanoholes compared to the gammadion structure. 12 Recently, Abraham et. al. experimentally demonstrated that the achiral nanohole structures can also show superchiral near-fields even at perpendicular incidence conditions. 16 In that case, the far-field circular dichroism (CD) background signals from the plasmonic structures is eliminated, improving the sensitivity for chiral molecule sensing applications. These reports demonstrate a promising potent...