Wepropose and experimentally demonstrate the ultra-compact mode (de)multiplexers and polarization beam splitter (PBS) based on tapered bent asymmetric directional couplers. The strong coupling strength introduced by tapered bent waveguides significantly shortens the coupling length. As a result, high coupling and conversion efficiencies over a broad bandwidth can be obtained with small footprint. The coupling length of the fabricated PBS and mode (de)multiplexers are less than 4.9 μm and 8.7 μm, respectively. From 1534-1600 nm, the measured insertion loss (IL) is less than 1.4 and 1.55 dB for the TE ₁ -TE ₀ and TE ₂ -TE ₀ mode (de)multiplexers, respectively, and the crosstalk (CT) is less than −10 dB. The fabricated PBS shows low insertion loss of 0.55 dB and decent crosstalk of < −14 dB for both polarizations over an 85 nm wavelength range from 1505-1590 nm. Meanwhile, the larger fabrication tolerance ensures that the proposed devices can be readily fabricated with the standard complementary metal-oxide-semiconductor (CMOS) process.

We experimentally demonstrate a low-loss and low-crosstalk 16-channel 200 GHz-channel-spacing arrayed waveguide grating router (AWGR) with a size of 0.67 × 0.37 mm ² , targeting for C-band wavelength division multiplexing (WDM) interconnect routing applications. As a result, the AWGR features a channel spacing of 200±10 GHz, a free spectral range of 25.62 nm and a 3 dB channel bandwidth of 0.9 nm. Based on comprehensive optimal design, the measured characterization revealed 5.55 dB maximum channel loss non-uniformity with 1.13 dB best-case channel insertion loss. Besides, the fabricated device exhibits good cyclic-frequency operation for all 16 × 16 port combinations with channel crosstalk of –15.11 dB.

Technological advancements have enabled the active control of electromagnetic waves. Metalenses, known for their precision in wavefront shaping and functional versatility, represent a breakthrough in optical modulation. This study addresses the challenge of achieving dual-wavelength multifunctionality in metalens design. We developed and experimentally validated metalenses with polarization dual-function multiplexing at discrete mid-wave infrared wavelengths, demonstrating high phase fidelity and functional versatility. In addition, the proposed design method was extended to long-wave infrared wavelengths, showcasing its adaptability to different application scenarios. The application of spatial multiplexing significantly enhanced the performance of the metalenses, providing a promising solution for efficient and compact optoelectronic devices.

Compared with traditional phase-shifting metasurface design methods, computer-aided optimization has attracted significant interest due to its advantages of high efficiency and a wide modulation range, resulting in the ability to generate various random-shaped meta-atoms to maximize their phase modulation capabilities. However, these meta-atoms often have sharp boundaries, chamfers, microscopic particles, and small holes, which are unsuitable for micro-/nano-fabrication. We propose a method to generate 2D meta-balls, which can generate random-shaped meta-atoms with smooth boundaries free of small particles or holes and suitable for micro-/nano-fabrication. This method can easily control the characteristics of generated shapes, such as boundary continuity and symmetry. It is simple, straightforward, and time-saving, and it helps in computer-aided optimization phase-shifting metasurfaces design.

Metalenses have excellent modulation capabilities in terms of phase, amplitude, and polarization of light, significantly reducing the size and complexity of imaging systems, and showing great application prospects. However, like traditional optical meta-atoms, ordinary metalenses suffer from a significant chromatic aberration problem because it is difficult to design the phase distribution for different wavelengths on a single-layer metalens. To address this, various methods for correcting chromatic aberration in metalenses have been proposed and demonstrated, such as spatial multiplexing, material hybridization, and increasing the cross-sectional diversity of metalens meta-atoms. In this paper, a novel design method is used, which expands the parameter space by increasing the cross-sectional diversity of the metalens meta-atoms to provide the phase required for focusing different wavelengths, combined with particle swarm optimization for phase compensation. The multi-level metalens designed by this method achieves a constant and approximate focal length in the visible wavelength range of λ = 450–650 nm, with a polarization-independent absolute focusing efficiency of about 17%, and a numerical aperture (NA) of 0.31 for a lens diameter of 100 μm. This improves the imaging quality.

This article used far-field light source to investigate the focal length of the short focal length, multifocal metalens. The feasibility of the scheme was analyzed by using imaging simulation. In addition, the relative error between far-field imaging method and collimated laser measurement was analyzed. The data results show that the relative error is 0.49%, as the point light source located 2000mm away, for ideal test lens with focal length of 10mm. An optical system composed of double lenses was constructed to measure the focal length of a metasurface with four focal points. The experimental results show that the system can determine the focal position within a step of 0.1mm.