Compared with conventional lenses, metalenses can offer smaller form factor, light weight and new functionality, and have become the focus of the recent investigations of metasurface. To date, quite a lot of studies have been reported for chromatic aberration correction of metalenses. Noting most work was carried out to satisfy the required group delay or dispersion by introducing sophisticated and integrated nanopillars, which are obtained using computationally intensive global search algorithms. Generally, the design is time-consuming. Here, we propose an alternative scheme, where metalens that corrects the chromatic aberration can be designed by optimizing the spectral degree of freedom C(ω), rather than relying on time-consuming algorithms. The proposed metalens is compatible with the complementary metal oxide semiconductor (CMOS) fabrication process. The numerically demonstrated metalens with a diameter of 200 μm and a numerical aperture (NA) of 0.24 has a small focal length fractional change (FLFC) of 4.1% over the wavelength of 9∼12 μm with an average efficiency of 51.7% in transmission mode. Moreover, the effect of fabrication deviations on the performance of the metalens is analyzed, showing critical dimension (CD) bias, sidewall angle and pillar height all have different levels of influence on the performance of the metalens.

ScAlN has been applied in piezoelectric micro-electro-mechanical systems, while application in photonics remains unexplored. Here, ScAlN photonic circuits on silicon are presented, demonstrating waveguide propagation loss of 9±2 dB/cm and microring quality factor of 1.4×10⁴.

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.

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.