Terahertz (THz) lenses have numerous applications in imaging and communication systems. Currently, the common THz lenses are still based on the traditional design of a circular convex lens. In this work, we present a method for the design of a 3D-printed multilevel THz lens, taking advantage of the benefits offered by 3D printing technology, including compact size, lightweight construction, and cost-effectiveness. The approach utilizes an inverse design methodology, employing optimization methods to promise accurate performance. To reduce simulation time, we employ the finite-difference time-domain method in cylindrical coordinates for near-field computation and couple it with the Rayleigh–Sommerfeld diffraction theory to address far-field calculations. This technology holds great potential for various applications in the field of THz imaging, sensing, and communications, offering a novel approach to the design and development of functional devices operating in the THz frequency range.

On-chip focusing of plasmons in graded-index lenses is important for imaging, lithography, signal processing, and optical interconnects at the deep subwavelength nanoscale. However, owing to the inherent strong wavelength dispersion of plasmonic materials, the on-chip focusing of plasmons suffers from severe chromatic aberrations. With the well-established planar dielectric grating, a graded-index waveguide array lens (GIWAL) is proposed to support the excitation and propagation of acoustic graphene plasmon polaritons (AGPPs) and to achieve the achromatic on-chip focusing of the AGPPs with a focus as small as about 2% of the operating wavelength in the frequency band from 10 to 20 THz, benefiting from the wavelength-independent index profile of the GIWAL. An analytical theory is provided to understand the on-chip focusing of the AGPPs and other beam evolution behaviors, such as self-focusing, self-collimation, and pendulum effects of Gaussian beams as well as spatial inversions of digital optical signals. Furthermore, the possibility of the GIWAL to invert spatially broadband digital optical signals is demonstrated, indicating the potential value of the GIWAL in broadband digital communication and signal processing.

为了实现基于双棱镜的光电跟踪平台，需要根据光束指向精确求解两棱镜转角。基于非近轴光线追迹法与二步法，利用神经网络拟合了消色差旋转双棱镜角度差值与偏转角之间的关系，并在求解方位角与消色差旋转双棱镜两组棱镜转角的时候，将其中的非线性关系与线性关系分开，利用神经网络对其中的非线性关系进行了拟合，最终得到了消色差旋转双棱镜转角与出射光束指向的数值关系。实验表明，在仅用3层神经网络共20个神经元的条件下，得到了两棱镜旋转角度反向解算值达到了 0.000 1°量级。

Metasurfaces have emerged as a flexible platform for shaping the electromagnetic field via the tailoring phase, amplitude, and polarization at will. However, the chromatic aberration inherited from building blocks’ diffractive nature plagues them when used in many practical applications. Current solutions for eliminating chromatic aberration usually rely on searching through many meta-atoms to seek designs that satisfy both phase and phase dispersion preconditions, inevitably leading to intensive design efforts. Moreover, most schemes are commonly valid for incidence with a specific spin state. Here, inspired by the Rayleigh criterion for spot resolution, we present a design principle for broadband achromatic and polarization-insensitive metalenses using two sets of anisotropic nanofins based on phase change material Ge₂Sb₂Se₄Te₁. By limiting the rotation angles of all nanofins to either 0 deg or 90 deg, the metalens with a suitable numerical aperture constructed by this fashion allows for achromatic and polarization-insensitive performance across the wavelength range of 4–5 μm, while maintaining high focusing efficiency and diffraction-limited performance. We also demonstrate the versatility of our approach by successfully implementing the generation of broadband achromatic and polarization-insensitive focusing optical vortex. This work represents a major advance in achromatic metalenses and may find more applications in compact and chip-scale devices.