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.

Metasurface holograms, with the capability to manipulate spatial light amplitudes and phases, are considered next-generation solutions for holographic imaging. However, conventional fabrication approaches for meta-atoms are heavily dependent on electron-beam lithography (EBL), a technique known for its expensive and time-consuming nature. In this paper, a polarization-insensitive metasurface hologram is proposed using a cost-effective and rapid nanoimprinting method with titanium dioxide (TiO₂) nanoparticle loaded polymer (NLP). Based on a simulation, it has been found that, despite a reduction in the aspect ratio of meta-atoms of nearly 20%, which is beneficial to silicon master etching, NLP filling, and the mold release processes, imaging efficiency can go up to 54% at wavelength of 532 nm. In addition, it demonstrates acceptable imaging quality at wavelengths of 473 and 671 nm. Moreover, the influence of fabrication errors and nanoimprinting material degradation in terms of residual layer thickness, meta-atom loss or fracture, thermal-induced dimensional variation, non-uniform distribution of TiO₂ particles, etc., on the performance is investigated. The simulation results indicate that the proposed device exhibits a high tolerance to these defects, proving its applicability and robustness in practice.

Filters with narrow bandwidth, high sidelobe suppression ratio (SLSR), and large free spectral range (FSR) play an important role in photonic circuits. In this work, we demonstrate a narrow-band silicon photonic filter using an adiabatic directional coupler (ADC)-assisted subwavelength multimode waveguide Bragg grating (SMWG). The complementary lateral misalignment modulation (CLMM) is applied to realize the apodization for suppressing sidelobes in the filtering spectrum. Two subwavelength corrugations with different widths are designed to achieve a narrow-band filtering spectrum and relieve the requirement of fabrication precision. Experiment results show that a 3-dB bandwidth of 0.51 nm and a SLSR of 16.6 dB are achieved on the CLMM apodized and ADC-assisted SMWG device. An unlimited FSR in the wavelength range of C band is demonstrated as well.

In the trend of spectrometer miniaturization, the design of combining computational imaging with the metasurfaces has been proved to be an efficient and feasible solution. Nevertheless, determining the optimal filter array design remains a compelling subject for ongoing research. A computational microspectrometer consisting of a planar array of broadband optical filters is proposed, which are formed by low-loss freeform dielectric metasurfaces. Diverse metasurface designs are obtained by using binary graph generation technology, and rich spectral responses are obtained. The final performance of microspectrometer depends on the trade-offs between reconstruction time, relative error, footprint, and resolution. To optimize these trade-offs, we have improved the existing freeform metasurface design scheme and optimized the filter array design. Simulation results show the proposed microspectrometer can successfully reconstruct the spectra over the 380 to 680 nm spectral range with a resolution of 1 nm. In summary, we propose an integrated design including meta-pixel design, filter combinations and simulation test flow, which leads to an impressive performance microspectrometer.

Benefiting from the progress of the germanium (Ge) epitaxy process on silicon (Si) substrates, waveguide-integrated Ge-on-Si photodetectors (PDs) have demonstrated decent performances in short-wave infrared (SWIR) detection. By lowering the operating temperature, theses PDs can meet the stringent signal-to-noise requirements for high-sensitivity detection. We systematically investigated the dark current characteristics and optical response in the 1500–1600 nm wavelength range of the waveguide-integrated Ge-on-Si PDs operated at low temperatures (200 K to 300 K). Under a −3 V bias, the PD exhibits a room-temperature dark current of 4.62 nA and a responsivity of 0.87 A/W at 1550 nm. When the temperature was reduced to 200 K, the dark current decreased to 93.69 pA, and the responsivity dropped to 0.34 A/W. Using finite-difference time-domain (FDTD) and technology computer-aided design (TCAD) simulations, we extracted the absorption coefficients of epitaxial Ge on Si at low temperatures. At room temperature, the absorption coefficient at the wavelength of 1550 nm was approximately 1100 cm⁻¹, while at 200 K, the absorption coefficient decreased to 248 cm⁻¹. The outcomes of this work pave the way for the high-performance low-temperature Si photonic systems in the future.