Acousto-optic (AO) modulation technology holds significant promise for applications in microwave and optical signal processing. Thin-film scandium-doped aluminum nitride (AlScN), with excellent piezoelectric properties and a wide transparency window, is a promising candidate for achieving on-chip AO modulation with a fabrication process compatible with complementary metal-oxide-semiconductor (CMOS) technology. This study presents, to the best of our knowledge, the first demonstration of AO modulators with surface acoustic wave generation and photonic waveguides monolithically integrated on a 400-nm-thick film of AlScN on an insulator. The intramodal AO modulation is realized based on an AlScN straight waveguide, and the modulation efficiency is significantly enhanced by 12.3 dB through the extension of the AO interaction length and the utilization of bidirectional acoustic energy. The intermodal AO modulation and non-reciprocity are further demonstrated based on a multi-mode spiral waveguide, achieving a high non-reciprocal contrast (>10 dB) across an optical bandwidth of 0.48 nm. This research marks a significant stride forward, representing an advancement in the realization of microwave photonic filters, magnet-free isolators, and circulators based on the thin-film AlScN photonic platform.

In combination with higher piezoelectric effect and larger optical second-order susceptibility (χ ⁽²⁾ ) compared with aluminum nitride (AlN), scandium-doped aluminum nitride (AlScN) platform is considered as a new platform for future integrated photonics. Hence, further studies are necessary to unlock the potential of the AlScN photonic platform and achieve integrated photonic devices with better performance. In this work, we fabricated the highly c-axis-orientated and low-surface-roughness AlScN thin films by reactive magnetron sputtering with 9.6% and 20% Sc concentrations. Then, we fabricated essential photonic devices including directional coupler (DC), Mach-Zehnder interferometer (MZI), and micro-ring resonator (MRR) based on the AlScN photonic platform. The measured extinction ratios (ERs) of MZIs are 22 dB for A _l0.904 Sc _0.096 N and 24 dB for A _l0.8 Sc _0.2 N. The maximum quality (Q) factors of MRRs are 3.2×104 for A _l0.904 Sc _0.096 N and 2.2×10 ⁴ for Al0.8Sc0.2N, while the waveguide bending losses are about 6.1 dB/cm for A _l0.904 Sc _0.096 N and 10.1 dB/cm for A _l0.8 Sc _0.2 N, respectively. These results pave the way towards low-loss integrated AlScN photonic applications such as acousto-optic modulation, nonlinear optical generation.

Despite the increasing interest in metalenses for imaging applications, there is a scarcity of research on metalenses designed to deliver broadband achromatic performance while preserving a wide field of view (FOV). In this work, we present a single-layer broadband achromatic metalens (BAM) designed for a specified FOV within a longwave infrared (LWIR) regime. Utilizing an advanced genetic algorithm coupled with diffraction theory, we optimize the BAM to minimize the coefficient of variation (CV) of focal lengths. The proposed BAM operates across wavelengths from 8 to 12 μm, facilitating an FOV of 40°. Our methodology is validated through the initial design of a BAM with a 200 μm aperture. Simulation outcomes reveal a low CV of 2.56% and an average focusing efficiency of over 40%. Furthermore, a 5 mm-diameter metalens prototype was fabricated and characterized by our custom measurement setup, which is both precise and less prone to subjective error than traditional testing methodologies. The prototype demonstrates an average focal length of 5.478 mm with minimal distortion at 2.18%. The Modulation Transfer Function (MTF) analysis confirms alignment with design specifications. Last, the imaging characterization of the metalens is carried out through experiments, demonstrating that the metalens can clearly resolve the measured object.

Lithium niobate (LN) photonics has gained significant interest for their distinct material properties. However, achieving monolithically integrated photodetectors on lithium niobate on an insulator (LNOI) platform for communication wavelengths remains a challenge due to the large bandgap and extremely low electrical conductivity of LN material. A two-dimensional (2D) material photodetector is an ideal solution for LNOI photonics with a strong light–matter interaction and simple integration technique. In this work, a van der Waals heterostructure photodiode composed of a p-type black phosphorus layer and an n-type MoS₂ layer is successfully demonstrated for photodetection at communication wavelengths on a LNOI platform. The LNOI waveguide-integrated BP-MoS₂ photodetector exhibits a dark current as low as 0.21 nA and an on/off ratio exceeding 200 under zero voltage bias with an incident power of 13.93 µW. A responsivity as high as 1.46 A/W is achieved at −1 V bias with a reasonable dark current around 2.33 µA. With the advantages of high responsivity, low dark current, and simple fabrication process, it is promising for the monolithically integrated photodetector application for LNOI photonic platforms at communication wavelengths.

Scandium-doped aluminum nitride (AlScN) with an asymmetric hexagonal wurtzite structure exhibits enhanced second-order nonlinear and piezoelectric properties compared to aluminum nitride (AlN), while maintaining a relatively large bandgap. It provides a promising platform for photonic circuits and facilitates the seamless integration of passive and active functional devices. Here, we present the design, fabrication, and characterization of Al_0.904Sc_0.096N electro-optic (EO) micro-ring modulators, introducing active functionalities to the chip-scale AlScN platform. These waveguide-integrated EO modulators utilize sputtered Al_0.904Sc_0.096N thin films as the light-guiding medium, with the entire fabrication process being compatible with complementary metal-oxide-semiconductor (CMOS) technology. We extract the in-device effective EO coefficient of 2.86 pm/V at 12 GHz. The devices show a minimum half-wave voltage-length product of 3.12 V·cm at a modulation frequency of 14 GHz, and achieve a 3-dB modulation bandwidth of approximately 22 GHz. Our work provides a promising modulation scheme for cost-effective silicon-integrated photonics systems.

The anisotropic optical properties of aluminum scandium nitride (Al_1−xSc _x N) thin films for both ordinary and extraordinary light are investigated. A quantitative analysis of the band structures of the wurtzite Al_1−xSc _x N is carried out. In addition, Al_1−xSc _x N photonic waveguides and bends are fabricated on 8-inch Si substrates. With x = 0.087 and 0.181, the light propagation losses are 5.98 ± 0.11 dB/cm and 8.23 ± 0.39 dB/cm, and the 90° bending losses are 0.05 dB/turn and 0.08 dB/turn at 1550 nm wavelength, respectively.